Publications - 2018

Lipid accumulation facilitates mitotic slippage-induced adaptation to anti-mitotic drug treatment

Alex Wong, Sixun Chen, Lay Kien Yang, Yoganathan Kanagasundaram & Karen Crasta

Cell Death Discovery volume 4, Article number: 109 (2018). DOI: 10.1038/s41420-018-0127-5

Abstract

Aberrant lipid accumulation is a hallmark of cancer known to contribute to its aggressiveness and malignancy. Emerging studies have demonstrated context-dependent changes in lipid metabolism during chemotherapy. However, there is little known regarding the mechanisms linking lipid metabolism to chemotherapy-induced cell fates. Here, we describe lipid accumulation in cells following antimitotic drug treatment. Cells arrested in mitosis, as well as cells that escaped mitotic arrest and underwent mitotic slippage, showed elevated cytoplasmic lipid droplets. Interestingly, we found that TOFA, a lipid biosynthesis inhibitor that targets acetyl-CoA carboxylase (ACC) and blocks lipid accumulation, promoted early slippage, reduced cellular stress and enhanced survival of antimitotic-treated cells. Our work previously revealed that cells that survive after mitotic slippage can become senescent and confer pro-tumourigenic effects through paracrine signalling. Modulating lipid biosynthesis in cells post slippage by TOFA amplified their inflammatory secretion profiles and accelerated the development of tumourigenic behaviour, particularly cell migration and invasion, in a paracrine-dependent manner. In contrast to TOFA, inhibition of lipid accumulation by C75, a drug targeting fatty acid synthase (FASN), significantly reduced the production of pro-tumourigenic factors and associated phenotypic effects. This suggests that discrete lipid biosynthesis pathways could contribute differentially to the regulation of pro-tumourigenic inflammation. The divergent effects of TOFA and C75 may be attributed to the opposing regulation of Malonyl-CoA, an intermediate in fatty acid synthesis that serves as a mediator of fatty acid oxidation. Taken together, our data reveal a previously unappreciated role for lipid accumulation in the cellular adaptation to antimitotic drug treatment. Targeting lipid biosynthesis in cells post slippage may reprogramme its secretory profile such that it not only negates tumour-promoting effects, but may also promote anti-tumour inflammation for clearance of post-slippage senescent cells.

Dropping in on lipid droplets: insights into cellular stress and cancer

Peter Shyu Jr, Xing Fah Alex Wong, Karen Crasta, Guillaume Thibault

Biosci Rep. 2018 Sep 19;38(5):BSR20180764. DOI: 10.1042/BSR20180764.

Abstract

Lipid droplets (LD) have increasingly become a major topic of research in recent years following its establishment as a highly dynamic organelle. Contrary to the initial view of LDs being passive cytoplasmic structures for lipid storage, studies have provided support on how they act in concert with different organelles to exert functions in various cellular processes. Although lipid dysregulation resulting from aberrant LD homeostasis has been well characterised, how this translates and contributes to cancer progression is poorly understood. This review summarises the different paradigms on how LDs function in the regulation of cellular stress as a contributing factor to cancer progression. Mechanisms employed by a broad range of cancer cell types in differentially utilising LDs for tumourigenesis will also be highlighted. Finally, we discuss the potential of targeting LDs in the context of cancer therapeutics.

Chromosomal instability-induced senescence potentiates cell non-autonomous tumourigenic effects

Qianqian He, Bijin Au, Madhura Kulkarni, Yang Shen, Kah. J. Lim, Jiamila Maimaiti, Cheng. Kit. Wong, Monique. N. H. Luijten, Han C. Chong, Elaine H. Lim, Giulia Rancati, Indrajit Sinha, Zhiyan Fu, Xiaomeng Wang, John. E. Connolly & Karen C. Crasta

Oncogenesis volume 7, Article number: 62 (2018). DOI: 10.1038/s41389-018-0072-4.

Abstract

Chromosomal instability (CIN), a high rate of chromosome loss or gain, is often associated with poor prognosis and drug resistance in cancers. Aneuploid, including near-polyploid, cells contain an abnormal number of chromosomes and exhibit CIN. The post-mitotic cell fates following generation of different degrees of chromosome mis-segregation and aneuploidy are unclear. Here we used aneuploidy inducers, nocodazole and reversine, to create different levels of aneuploidy. A higher extent of aneuploid and near-polyploid cells in a given population led to senescence. This was in contrast to cells with relatively lower levels of abnormal ploidy that continued to proliferate. Our findings revealed that senescence was accompanied by DNA damage and robust p53 activation. These senescent cells acquired the senescence-associated secretory phenotype (SASP). Depletion of p53 reduced the number of senescent cells with concomitant increase in cells undergoing DNA replication. Characterisation of these SASP factors demonstrated that they conferred paracrine pro-tumourigenic effects such as invasion, migration and angiogenesis both in vitro and in vivo. Finally, a correlation between increased aneuploidy and senescence was observed at the invasive front in breast carcinomas. Our findings demonstrate functional non-equivalence of discernable aneuploidies on tumourigenesis and suggest a cell non-autonomous mechanism by which aneuploidy-induced senescent cells and SASP can affect the tumour microenvironment to promote tumour progression.

Autophagy Governs Protumorigenic Effects of Mitotic Slippage-induced Senescence

Rekha Jakhar, Monique N H Luijten, Alex X F Wong, Bing Cheng, Ke Guo, Suat P Neo, Bijin Au, Madhura Kulkarni, Kah J Lim, Jiamila Maimaiti, Han C Chong, Elaine H Lim, Tee B K Tan, Kong W Ong, Yirong Sim, Jill S L Wong, James B K Khoo, Juliana T S Ho, Boon T Chua, Indrajit Sinha, Xiaomeng Wang, John E Connolly, Jayantha Gunaratne, Karen C Crasta

Mol Cancer Res. 2018 Nov;16(11):1625-1640. DOI: 10.1158/1541-7786.MCR-18-0024.

Abstract

The most commonly utilized class of chemotherapeutic agents administered as a first-line therapy are antimitotic drugs; however, their clinical success is often impeded by chemoresistance and disease relapse. Hence, a better understanding of the cellular pathways underlying escape from cell death is critical. Mitotic slippage describes the cellular process where cells exit antimitotic drug-enforced mitotic arrest and "slip" into interphase without proper chromosome segregation and cytokinesis. The current report explores the cell fate consequence following mitotic slippage and assesses a major outcome following treatment with many chemotherapies, therapy-induced senescence. It was found that cells postslippage entered senescence and could impart the senescence-associated secretory phenotype (SASP). SASP factor production elicited paracrine protumorigenic effects, such as migration, invasion, and vascularization. Both senescence and SASP factor development were found to be dependent on autophagy. Autophagy induction during mitotic slippage involved the autophagy activator AMPK and endoplasmic reticulum stress response protein PERK. Pharmacologic inhibition of autophagy or silencing of autophagy-related ATG5 led to a bypass of G1 arrest senescence, reduced SASP-associated paracrine tumorigenic effects, and increased DNA damage after S-phase entry with a concomitant increase in apoptosis. Consistent with this, the autophagy inhibitor chloroquine and microtubule-stabilizing drug paclitaxel synergistically inhibited tumor growth in mice. Sensitivity to this combinatorial treatment was dependent on p53 status, an important factor to consider before treatment.Implications: Clinical regimens targeting senescence and SASP could provide a potential effective combinatorial strategy with antimitotic drugs. Mol Cancer Res; 16(11); 1625-40. ©2018 AACR.

Mutational game changer: Chromothripsis and its emerging relevance to cancer

Monique Nicole Helena Luijten, Jeannie Xue Ting Lee, Karen CarmelinaCrasta

Mutation Research/Reviews in Mutation Research. Volume 777, July–September 2018, Pages 29-51. DOI: 10.1016/j.mrrev.2018.06.004.

Abstract

In recent years, the paradigm that genomic abnormalities in cancer cells arise through progressive accumulation of mutational events has been challenged by the discovery of single catastrophic events. One such phenomenon termed chromothripsis, involving massive chromosomal rearrangements arising all at once, has emerged as a major mutational game changer. The strong interest in this process stems from its widespread association with a range of cancer types and its potential as a mutational driver.
In this review, we first describe chromothripsis detection and incidence in cancers. We then explore recently proposed underlying mechanistic origins, which explain the curious observations of the highly localised nature of the rearrangements on chromothriptic chromosomes. Detection of chromothriptic patterns following incorporation of single chromosomes into micronuclei or following telomere attrition have greatly contributed to our understanding of the reasons behind this chromosomal restriction. These underlying cellular events have been found to be participants in the tumourigenic process, strongly suggesting a potential role for chromothripsis in cancer development. Thus, we discuss potential implications of chromothripsis for cancer progression and therapy.

Mitochondrial Dysfunction in Age-Related Metabolic Disorders

Venkateswaran Natarajan Ritu Chawla, Tania Mah, Rajesh Vivekanandan, Shu Yi Tan, Priscila Y Sato, Karthik Mallilankaraman

Proteomics. 2020 Mar;20(5-6):e1800404. doi: 10.1002/pmic.201800404. Epub 2020 Mar 17.

Abstract

Aging is a natural biological process in living organisms characterized by receding bioenergetics. Mitochondria are crucial for cellular bioenergetics and thus an important contributor to age-related energetics deterioration. In addition, mitochondria play a major role in calcium signaling, redox homeostasis, and thermogenesis making this organelle a major cellular component that dictates the fate of a cell. To maintain its quantity and quality, mitochondria undergo multiple processes such as fission, fusion, and mitophagy to eliminate or replace damaged mitochondria. While this bioenergetics machinery is properly protected, the functional decline associated with age and age-related metabolic diseases is mostly a result of failure in such protective mechanisms. In addition, metabolic by-products like reactive oxygen species also aid in this destructive pathway. Mitochondrial dysfunction has always been thought to be associated with diseases. Moreover, studies in recent years have pointed out that aging contributes to the decay of mitochondrial health by promoting imbalances in key mitochondrial-regulated pathways. Hence, it is crucial to understand the nexus of mitochondrial dysfunction in age-related diseases. This review focuses on various aspects of basic mitochondrial biology and its status in aging and age-related metabolic diseases.

The physiological strain index modified for trained heat acclimatized individuals in outdoor heat.

Byrne C, Lee JKW.

International Journal Sports Physiology and Performance, 14 (6): 805-813. doi: 10.1123/ijspp.2018-0506

Abstract

Purpose: To determine if the Physiological Strain Index (PSI), in original or modified form, can evaluate heat strain on a 0-10 scale, in trained and heat-acclimatized men undertaking a competitive half-marathon run in outdoor heat. Methods: Core (intestinal) temperature (TC) and heart rate (HR) were recorded continuously in 24 men (mean [SD] age = 26 [3] y, VO2peak = 59 [5] mL·kg·min-1). A total of 4 versions of the PSI were computed: original PSI with upper constraints of TC 39.5°C and HR 180 beats·min-1 (PSI39.5/180) and 3 modified versions of PSI with each having an age-predicted maximal HR constraint and graded TC constraints of 40.0°C (PSI40.0/PHRmax), 40.5°C (PSI40.5/PHRmax), and 41.0°C (PSI41.0/PHRmax). Results: In a warm (26.1-27.3°C) and humid (79-82%) environment, all runners finished the race asymptomatic in 107 (10) (91-137) min. Peak TC and HR were 39.7°C (0.5°C) (38.5-40.7°C) and 186 (6) (175-196) beats·min-1, respectively. In total, 63% exceeded TC 39.5°C, 71% exceeded HR 180 beats·min-1, and 50% exceeded both of the original PSI upper TC and HR constraints. The computed heat strain was significantly greater with PSI39.5/180 than all other methods (P < .003). PSI >10 was observed in 63% of runners with PSI39.5/180, 25% for PSI40.0/PHRmax, 8% for PSI40.5/PHRmax, and 0% for PSI41.0/PHRmax. Conclusions: The PSI was able to quantify heat strain on a 0-10 scale in trained and heat-acclimatized men undertaking a half-marathon race in outdoor heat, but only when the upper TC and HR constraints were modified to 41.0°C and age-predicted maximal HR, respectively.

Sarcopenia: Tilting the Balance of Protein Homeostasis.

Tan KT, Ang SJ, Tsai SY.

Proteomics. 2019 Nov 13:e1800411. doi: 10.1002/pmic.201800411. [Epub ahead of print]

Abstract

Sarcopenia, defined as age-associated decline of muscle mass and function, is a risk factor for mortality and disability, and comorbid with several chronic diseases such as type II diabetes and cardiovascular diseases. Clinical trials showed that nutritional supplements had positive effects on muscle mass, but not on muscle function and strength, demonstrating our limited understanding of the molecular events involved in the ageing muscle. Protein homeostasis, the equilibrium between protein synthesis and degradation, is proposed as the major mechanism underlying the development of sarcopenia. As the key central regulator of protein homeostasis, the mammalian target of rapamycin (mTOR) is proposed to be essential for muscle hypertrophy. Paradoxically, sustained activation of mTOR complex 1 (mTORC1) is associated with a loss of sensitivity to extracellular signaling in the elderly. It is not understood why sustained mTORC1 activity, which should induce muscle hypertrophy, instead results in muscle atrophy. Here, recent findings on the implications of disrupting protein homeostasis on muscle physiology and sarcopenia development in the context of mTOR/protein kinase B (AKT) signaling are reviewed. Understanding the role of these molecular mechanisms during the ageing process will contribute towards the development of targeted therapies that will improve protein metabolism and reduce sarcopenia.

Thermoregulation in the Aging Population and Practical Strategies to Overcome a Warmer Tomorrow.

Tan CCS, Chin LKK, Low ICC.

Proteomics. 2019 Oct 25:e1800468. doi: 10.1002/pmic.201800468. [Epub ahead of print]

Abstract

As global temperatures continue to rise, improving thermal tolerance in the aged population is crucial to counteract age-associated impairments in thermoregulatory function. Impairments in reflex cutaneous vasodilation and sweating response can augment the vulnerability of older adults to heat-related injuries following exposure to heat stress. Mechanisms underlying a compromised cutaneous vasodilation are suggested to include reduced sympathetic neural drive, diminished cholinergic co-transmitter contribution, and altered second messenger signaling events. On the other hand, impairments in sweating response are ascribed to reduced sweat gland cholinergic sensitivity and altered cyclooxygenase and nitric oxide signaling. Several practical mitigation strategies such as exercise, passive heating, and behavioral adaptations are proposed as means to overcome heat stress and improve thermal tolerance in the aged. Aerobic exercise training is shown to be amongst the most effective ways to enhance thermoregulatory function. However, in elderly with limited exercise capability due to chronic diseases and mobility issues, passive heating can serve as a functional alternative as it has been shown to confer similar benefits to that of exercise training. Supplementary to exercise training and passive heating, behavioral adaptations can be applied to further enhance the heat-preparedness of the aged.

Zika virus alters DNA methylation status of genes involved in Hippo signaling pathway in human neural progenitor cells.

Kandilya D, Maskomani S, Shyamasundar S, Tambyah PA, Shiao Yng C, Lee RCH, Hande MP, Mallilankaraman K, Chu JJH, Dheen ST.

Epigenomics. 2019 Aug;11(10):1143-1161. doi: 10.2217/epi-2018-0180. Epub 2019 Jun 25.

Abstract

Aim: This study was aimed to understand if Zika virus (ZIKV) alters the DNA methylome of human neural progenitor cells (hNPCs). Materials & methods: Whole genome DNA methylation profiling was performed using human methylationEPIC array in control and ZIKV infected hNPCs. Results & conclusion: ZIKV infection altered the DNA methylation of several genes such as WWTR1 (TAZ) and RASSF1 of Hippo signaling pathway which regulates organ size during brain development, and decreased the expression of several centrosomal-related microcephaly genes, and genes involved in stemness and differentiation in human neural progenitor cells. Overall, ZIKV downregulated the Hippo signaling pathway genes which perturb the stemness and differentiation process in hNPCs, which could form the basis for ZIKV-induced microcephaly.

Bhlhe40 and Bhlhe41 transcription factors regulate alveolar macrophage self-renewal and identity.

Rauschmeier R, Gustafsson C, Reinhardt A, A-Gonzalez N, Tortola L, Cansever D, Subramanian S, Taneja R, Rossner MJ, Sieweke MH, Greter M, Månsson R, Busslinger M, Kreslavsky T.

EMBO Journal. 2019 Aug 15:e101233. doi: 10.15252/embj.2018101233. [Epub ahead of print]

Abstract

Tissues in multicellular organisms are populated by resident macrophages, which perform both generic and tissue-specific functions. The latter are induced by signals from the microenvironment and rely on unique tissue-specific molecular programs requiring the combinatorial action of tissue-specific and broadly expressed transcriptional regulators. Here, we identify the transcription factors Bhlhe40 and Bhlhe41 as novel regulators of alveolar macrophages (AMs)-a population that provides the first line of immune defense and executes homeostatic functions in lung alveoli. In the absence of these factors, AMs exhibited decreased proliferation that resulted in a severe disadvantage of knockout AMs in a competitive setting. Gene expression analyses revealed a broad cell-intrinsic footprint of Bhlhe40/Bhlhe41 deficiency manifested by a downregulation of AM signature genes and induction of signature genes of other macrophage lineages. Genome-wide characterization of Bhlhe40 DNA binding suggested that these transcription factors directly repress the expression of lineage-inappropriate genes in AMs. Taken together, these results identify Bhlhe40 and Bhlhe41 as key regulators of AM self-renewal and guardians of their identity.

Metabolic reprogramming of oncogene-addicted cancer cells to OXPHOS as a mechanism of drug resistance

Hirpara J, Eu JQ, Tan JKM, Wong AL, Clement MV, Kong LR, Ohi N, Tsunoda T, Qu J, Goh BC, Pervaiz S.

Redox Biol. 2018 Dec 17:101076. DOI: 10.1016/j.redox.2018.101076.

Abstract

The ability to selectively eradicate oncogene-addicted tumors while reducing systemic toxicity has endeared targeted therapies as a treatment strategy. Nevertheless, development of acquired resistance limits the benefits and durability of such a regime. Here we report evidence of enhanced reliance on mitochondrial oxidative phosphorylation (OXPHOS) in oncogene-addicted cancers manifesting acquired resistance to targeted therapies. To that effect, we describe a novel OXPHOS targeting activity of the small molecule compound, OPB-51602 (OPB). Of note, a priori treatment with OPB restored sensitivity to targeted therapies. Furthermore, cancer cells exhibiting stemness markers also showed selective reliance on OXPHOS and enhanced sensitivity to OPB. Importantly, in a subset of patients who developed secondary resistance to EGFR tyrosine kinase inhibitor (TKI), OPB treatment resulted in decrease in metabolic activity and reduction in tumor size. Collectively, we show here a switch to mitochondrial OXPHOS as a key driver of targeted drug resistance in oncogene-addicted cancers. This metabolic vulnerability is exploited by a novel OXPHOS inhibitor, which also shows promise in the clinical setting.

Gene expression analysis of heat-shock proteins and redox regulators reveals combinatorial prognostic markers in carcinomas of the gastrointestinal tract.

Pohl SÖ, Pervaiz S, Dharmarajan A, Agostino M.

Redox Biol. 2018 Nov 29. pii: S2213-2317(18)30928-5. DOI: 10.1016/j.redox.2018.11.018.

Abstract

Heat shock proteins (HSPs) are a large family of ubiquitously expressed proteins with diverse functions, including protein assembly and folding/unfolding. These proteins have been associated with the progression of various gastrointestinal tumours. Dysregulation of cellular redox has also been associated with gastrointestinal carcinogenesis, however, a link between HSPs and dysregulation of cellular redox in carcinogenesis remains unclear. In this study, we analysed mRNA co-expression and methylation patterns, as well as performed survival analysis and gene set enrichment analysis, on gastrointestinal cancer data sets (oesophageal, stomach and colorectal carcinomas) to determine whether HSP activity and cellular redox dysregulation are linked. A widespread relationship between HSPs and cellular redox was identified, with specific combinatorial co-expression patterns demonstrated to significantly alter patient survival outcomes. This comprehensive analysis provides the foundation for future studies aimed at deciphering the mechanisms of cooperativity between HSPs and redox regulatory enzymes, which may be a target for future therapeutic intervention for gastrointestinal tumours.

MnSOD is implicated in accelerated wound healing upon Negative Pressure Wound Therapy (NPWT): A case in point for MnSOD mimetics as adjuvants for wound management

Bellot GL, Dong X, Lahiri A, Sebastin SJ, Batinic-Haberle I, Pervaiz S, Puhaindran ME.

Redox Biol. 2019 Jan;20:307-320. DOI: 10.1016/j.redox.2018.10.014.

Abstract

Negative Pressure Wound Therapy (NPWT), a widely used modality in the management of surgical and trauma wounds, offers clear benefits over conventional wound healing strategies. Despite the wide-ranging effects ascribed to NPWT, the precise molecular mechanisms underlying the accelerated healing supported by NPWT remains poorly understood. Notably, cellular redox status-a product of the balance between cellular reactive oxygen species (ROS) production and anti-oxidant defense systems-plays an important role in wound healing and dysregulation of redox homeostasis has a profound effect on wound healing. Here we investigated potential links between the use of NPWT and the regulation of antioxidant mechanisms. Using patient samples and a rodent model of acute injury, we observed a significant accumulation of MnSOD protein as well as higher enzymatic activity in tissues upon NPWT. As a proof of concept and to outline the important role of SOD activity in wound healing, we replaced NPWT by the topical application of a MnSOD mimetic, Mn(III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP5+, MnE, BMX-010, AEOl10113) in the rodent model. We observed that MnE is a potent wound healing enhancer as it appears to facilitate the formation of new tissue within the wound bed and consequently advances wound closure by two days, compared to the non-treated animals. Taken together, these results show for the first time a link between NPWT and regulation of antioxidant mechanism through the maintenance of MnSOD activity. Additionally this discovery outlined the potential role of MnSOD mimetics as topical agents enhancing wound healing.

Redox Dichotomy in Cell Fate Decision: Evasive Mechanism or Achilles Heel?

Pervaiz S.

Antioxid Redox Signal. 2018 Nov 1;29(13):1191-1195. DOI: 10.1089/ars.2018.7586.

Abstract

Cellular redox state is a consequence of the balance between the rates of reactive oxygen species and/or reactive nitrogen species, and their dissipation via enzymatic and nonenzymatic redox buffering systems. While low levels of oscillation are associated with normal cellular metabolism, stimuli that favor a significant shift in the redox microenvironment, through either the increased production and/or compromise of the antioxidant defenses, induce overt oxidative stress. This change in the redox set point triggers a host of cellular responses ranging from modifications in cellular macromolecules, organelle morphology and physiology, amplified cell-to-cell and intracellular signaling, and changes in genome, epigenome, and proteome. The consequence of this dysregulated cellular homeostasis is therefore manifested in the form of a plethora of pathological states such as inflammation, diabetes mellitus, neurodegenerative disorders, atherosclerosis, and cancer. On the backdrop of these observations, this Forum attempts at reviewing the current understanding of how a prooxidant intracellular milieu favors cell survival while overt oxidative stress results in death execution, and the translation of these biological effects in human disease states, in particular cancer. The far-reaching biochemical, biological, and clinical ramifications of an altered redox environment are also discussed from the standpoint of strategic therapeutic design against refractory and aggressive cancers. It is tempting to conjecture if the inherent or acquired redox heterogeneity, at least in the case of cancer, has evolved as an “evasive mechanism,” or presents itself as the “Achilles heel” for therapeutic exploitation.

Redox regulation of cell state and fate.

Lee BWL, Ghode P, Ong DST.

Redox Biology. 2018 Nov 23; pii: S2213-2317(18)30899-1. doi: 10.1016/j.redox.2018.11.014.

Abstract

The failure in effective cancer treatment is thought to be attributed to a subpopulation of tumor cells with stem cell-like properties. These cancer stem cells (CSCs) are intimately linked to tumor initiation, heterogeneity, maintenance, recurrence and metastasis. Increasing evidence supports the view that a tight redox regulation is crucial for CSC proliferation, tumorigenicity, therapy resistance and metastasis in many cancer types. Since the distinct metabolic and epigenetic states of CSCs may influence ROS levels, and hence their malignancy, ROS modulating agents hold promise in their utility as anti-CSC agents that may improve the durability of current cancer treatments. This review will focus on (i) how ROS levels are regulated for CSCs to elicit their hallmark features; (ii) the link between ROS and metabolic plasticity of CSCs; and (iii) how ROS may interface with epigenetics that would enable CSCs to thrive in a stressful tumor microenvironment and survive therapeutic insults.

Abnormal TDP-43 function impairs activity-dependent BDNF secretion, synaptic plasticity, and cognitive behavior through altered Sortilin splicing.

Tann JY, Wong LW, Sajikumar S, Ibáñez CF.

EMBO Journal. 2019 Mar 1;38(5). pii: e100989. doi: 10.15252/embj.2018100989.

Abstract

Aberrant function of the RNA-binding protein TDP-43 has been causally linked to multiple neurodegenerative diseases. Due to its large number of targets, the mechanisms through which TDP-43 malfunction cause disease are unclear. Here, we report that knockdown, aggregation, or disease-associated mutation of TDP-43 all impair intracellular sorting and activity-dependent secretion of the neurotrophin brain-derived neurotrophic factor (BDNF) through altered splicing of the trafficking receptor Sortilin. Adult mice lacking TDP-43 specifically in hippocampal CA1 show memory impairment and synaptic plasticity defects that can be rescued by restoring Sortilin splicing or extracellular BDNF. Human neurons derived from patient iPSCs carrying mutated TDP-43 also show altered Sortilin splicing and reduced levels of activity-dependent BDNF secretion, which can be restored by correcting the mutation. We propose that major disease phenotypes caused by aberrant TDP-43 activity may be explained by the abnormal function of a handful of critical proteins, such as BDNF.

Generation of mature kupffer cells from human induced pluripotent stem cells.

Tasnim F, Xing J, Huang X, Mo S, Wei X, Tan MH, Yu H.

Biomaterials. 2019 Feb; 192:377-391. doi: 10.1016/j.biomaterials.2018.11.016.

Abstract

Liver macrophages, Kupffer cells (KCs), play a critical role in drug-induced liver injury (DILI) and liver diseases including cholestasis, liver fibrosis and viral hepatitis. Application of KCs in in vitro models of DILI and liver diseases is hindered due to limited source of human KCs. In vivo, KCs originate from MYB-independent macrophage progenitors, which differentiate into liver-specific macrophages in response to hepatic cues in the liver. Here, we recapitulated KCs ontogeny by differentiation of MYB-independent iPSCs to macrophage-precursors and exposing them to hepatic cues to generate iPSC-derived KCs (iKCs). iKCs expressed macrophage markers (CD11/CD14/CD68/CD163/CD32) at 0.3-5 folds of primary adult human KCs (pKCs) and KC-specific CLEC-4F, ID1 and ID3. iKCs phagocytosed and secreted IL-6 and TNFα upon stimulation at levels similar to pKCs but different from non-liver macrophages. Hepatocyte-iKCs co-culture model was more sensitive in detecting hepatotoxicity induced by inflammation-associated drugs, Acetaminophen and Trovafloxacin, and Chlorpromazine-induced cholestasis when compared to hepatocytes alone. Overall, iKCs were mature, liver-specific and functional. Furthermore, donor-matched iKCs and iPSC-hepatocyte co-culture exhibited minimal non-specific background response compared to donor-mismatched counterpart. iKCs offer a mature renewable human cell source for liver-specific macrophages, useful in developing in vitro model to study DILI and liver diseases such as cholestasis.

Stressing the (Epi)genome: dealing with Reactive Oxygen Species in Cancer

Bhat AV, Hora S, Pal A, Jha S, Taneja R.

Antioxid Redox Signal. 2018 Nov 1;29(13):1273-1292. doi: 10.1089/ars.2017.7158.

Abstract

SIGNIFICANCE:
Growing evidence indicates cross-talk between reactive oxygen species (ROS) and several key epigenetic processes such as DNA methylation, histone modifications, and miRNAs in normal physiology and human pathologies including cancer. This review focuses on how ROS-induced oxidative stress, metabolic intermediates, and epigenetic processes influence each other in various cancers. Recent Advances: ROS alter chromatin structure and metabolism that impact the epigenetic landscape in cancer cells. Several site-specific DNA methylation changes have been identified in different cancers and are discussed in the review. We also discuss the interplay of epigenetic enzymes and miRNAs in influencing malignant transformation in an ROS-dependent manner.
CRITICAL ISSUES:
Loss of ROS-mediated signaling mostly by epigenetic regulation may promote tumorigenesis. In contrast, augmented oxidative stress because of high ROS levels may precipitate epigenetic alterations to effect various phases of carcinogenesis. We address both aspects in the review.
FUTURE DIRECTIONS:
Several drugs targeting ROS are under various stages of clinical development. Recent analysis of human cancers has revealed pervasive deregulation of the epigenetic machinery. Thus, a better understanding of the cross-talk between ROS and epigenetic alterations in cancer could lead to the identification of new drug targets and more effective treatment modalities.

Unravelling the role of Aurora A beyond centrosomes and spindle assembly: implications in muscle differentiation

Dhanasekaran K, Bose A, Rao VJ, Boopathi R, Shankar SR, Rao VK, Swaminathan A, Vasudevan M, Taneja R, Kundu TK.

FASEB Journal. 2019 Jan; 33(1):219-230. doi: 10.1096/fj.201800997.

Abstract

Aurora kinases are critical mitotic serine/threonine kinases and are often implicated in tumorigenesis. Recent studies of the interphase functions for aurora kinase (Aurk)A have considerably expanded our understanding of its role beyond mitosis. To identify the unknown targets of AurkA, we used peptide array-based screening and found E2F4 to be a novel substrate. Phosphorylation of E2F4 by AurkA at Ser75 regulates its DNA binding and subcellular localization. Because E2F4 plays an important role in skeletal muscle differentiation, we attempted to gain insight into E2F4 phosphorylation in this context. We observed that a block in E2F4 phosphorylation retained it better within the nucleus and inhibited muscle differentiation. RNA sequencing analysis revealed a perturbation of the gene network involved in the process of muscle differentiation and mitochondrial biogenesis. Collectively, our findings establish a novel role of AurkA in the process of skeletal muscle differentiation.

SIRT2 Inhibition Confers Neuroprotection by Downregulation of FOXO3a and MAPK Signaling Pathways in Ischemic Stroke.

She DT, Wong LJ, Baik SH, Arumugam TV.

Molecular Neurobiology. 2018 Dec;55(12):9188-9203. doi: 10.1007/s12035-018-1058-0. Epub 2018 Apr 14.

Abstract

Sirtuin 2 (SIRT2) is a family member of nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases which appears to have detrimental roles in an array of neurological disorders such as Parkinson's disease (PD) and Huntington's disease (HD). In light of the recently emerging roles of sirtuins in normal physiology and pathological conditions such as ischemic stroke, we investigated the role of SIRT2 in ischemic stroke-induced neuronal cell death. Primary cortical neurons were subjected to oxygen-glucose deprivation (OGD) under in vitro ischemic conditions, and subsequently tested for the efficacy of SIRT2 inhibitors AK1 and AGK2 in attenuating apoptotic cell death caused by OGD. We have also evaluated the effect of SIRT2 inhibition in C57BL/6 mice subjected to 1 h middle cerebral artery occlusion (MCAO) followed by 24 h reperfusion, which is a model for ischemic reperfusion injury in vivo. Significant reductions in apoptotic cell death were noted in neurons treated with AK1 or AGK2, as evidenced by reduced cleaved caspase-3 and other apoptotic markers such as Bim and Bad. In addition, downregulation of phosphorylated-AKT and FOXO3a proteins of the AKT/FOXO3a pathway, as well as a marked reduction of JNK activity and its downstream target c-Jun, were also observed. When tested in animals subjected to MCAO, the neuroprotective effects of AGK2 in vivo were evidenced by a substantial reduction in ipsilateral infarct area and a significant improvement in neurological outcomes. A similar reduction in the levels of pro-apoptotic proteins in the infarct tissue, as well as downregulation of AKT/FOXO3a and JNK pathway, were also noted. In summary, the current study demonstrated the neuroprotective effects of SIRT2 inhibition in ischemic stroke, and identified the downregulation of AKT/FOXO3a and MAPK pathways as intermediary mechanisms which may contribute to the reduction in apoptotic cell death by SIRT2 inhibition.

Metabolic Remodeling during Liver Regeneration.

Caldez MJ, Van Hul N, Koh HWL, Teo XQ, Fan JJ, Tan PY, Dewhurst MR, Too PG, Talib SZA, Chiang BE, Stünkel W, Yu H, Lee P, Fuhrer T, Choi H, Björklund M, Kaldis P.

Developmental Cell. 2018 Nov 19;47(4):425-438.e5. doi: 10.1016/j.devcel.2018.09.020. Epub 2018 Oct 18.

Abstract

Liver disease is linked to a decreased capacity of hepatocytes to divide. In addition, cellular metabolism is important for tissue homeostasis and regeneration. Since metabolic changes are a hallmark of liver disease, we investigated the connections between metabolism and cell division. We determined global metabolic changes at different stages of liver regeneration using a combination of integrated transcriptomic and metabolomic analyses with advanced functional redox in vivo imaging. Our data indicate that blocking hepatocyte division during regeneration leads to mitochondrial dysfunction and downregulation of oxidative pathways. This resulted in an increased redox ratio and hyperactivity of alanine transaminase allowing the production of alanine and α-ketoglutarate from pyruvate when mitochondrial functions are impaired. Our data suggests that during liver regeneration, cell division leads to hepatic metabolic remodeling. Moreover, we demonstrate that hepatocytes are equipped with a flexible metabolic machinery able to adapt dynamically to changes during tissue regeneration.

Generation of mature kupffer cells from human induced pluripotent stem cells.

Tasnim F, Xing J, Huang X, Mo S, Wei X, Tan MH, Yu H.

Biomaterials. 2019 Feb;192:377-391. doi: 10.1016/j.biomaterials.2018.11.016. Epub 2018 Nov 16.

Abstract

KDM4B-regulated unfolded protein response as a therapeutic vulnerability in PTEN-deficient breast cancer

Wang W, Oguz G, Lee PL, Bao Y, Wang P, Terp MG, Ditzel HJ, Yu Q

J Exp Med. 2018 Sep 28. pii: jem.20180439. doi: 10.1084/jem.20180439. [Epub ahead of print]

Abstract

PTEN deficiency in breast cancer leads to resistance to PI3K-AKT inhibitor treatment despite aberrant activation of this signaling pathway. Here, we report that genetic depletion or small molecule inhibition of KDM4B histone demethylase activates the unfolded protein response (UPR) pathway and results in preferential apoptosis in PTEN-deficient triple-negative breast cancers (TNBCs). Intriguingly, this function of KDM4B on UPR requires its demethylase activity but is independent of its canonical role in histone modification, and acts through its cytoplasmic interaction with eIF2α, a crucial component of UPR signaling, resulting in reduced phosphorylation of this component. Targeting KDM4B in combination with PI3K inhibition induces further activation of UPR, leading to robust synergy in apoptosis. These findings identify KDM4B as a therapeutic vulnerability in PTEN-deficient TNBC that otherwise would be resistant to PI3K inhibition.

Localisation of Formyl-Peptide Receptor 2 in the Rat Central Nervous System and Its Role in Axonal and Dendritic Outgrowth.

Ho CF, Ismail NB, Koh JK, Gunaseelan S, Low YH, Ng YK, Chua JJ, Ong WY.

Neurochem Res. 2018 Aug;43(8):1587-1598. doi: 10.1007/s11064-018-2573-0. Epub 2018 Jun 13.

Abstract

Arachidonic acid and docosahexaenoic acid (DHA) released by the action of phospholipases A2 (PLA2) on membrane phospholipids may be metabolized by lipoxygenases to the anti-inflammatory mediators lipoxin A4 (LXA4) and resolvin D1 (RvD1), and these can bind to a common receptor, formyl-peptide receptor 2 (FPR2). The contribution of this receptor to axonal or dendritic outgrowth is unknown. The present study was carried out to elucidate the distribution of FPR2 in the rat CNS and its role in outgrowth of neuronal processes. FPR2 mRNA expression was greatest in the brainstem, followed by the spinal cord, thalamus/hypothalamus, cerebral neocortex, hippocampus, cerebellum and striatum. The brainstem and spinal cord also contained high levels of FPR2 protein. The cerebral neocortex was moderately immunolabelled for FPR2, with staining mostly present as puncta in the neuropil. Dentate granule neurons and their axons (mossy fibres) in the hippocampus were very densely labelled. The cerebellar cortex was lightly stained, but the deep cerebellar nuclei, inferior olivary nucleus, vestibular nuclei, spinal trigeminal nucleus and dorsal horn of the spinal cord were densely labelled. Electron microscopy of the prefrontal cortex showed FPR2 immunolabel mostly in immature axon terminals or 'pre-terminals', that did not form synapses with dendrites. Treatment of primary hippocampal neurons with the FPR2 inhibitors, PBP10 or WRW4, resulted in reduced lengths of axons and dendrites. The CNS distribution of FPR2 suggests important functions in learning and memory, balance and nociception. This might be due to an effect of FPR2 in mediating arachidonic acid/LXA4 or DHA/RvD1-induced axonal or dendritic outgrowth.

Forebrain medial septum sustains experimental neuropathic pain.

Ariffin MZ, Ibrahim KM, Lee AT, Lee RZ, Poon SY, Thong HK, Liu EHC, Low CM, Khanna S.

Sci Rep. 2018 Aug 8;8(1):11892. doi: 10.1038/s41598-018-30177-3.

Abstract

The present study explored the role of the medial septal region (MS) in experimental neuropathic pain. For the first time, we found that the MS sustains nociceptive behaviors in rodent models of neuropathic pain, especially in the chronic constriction injury (CCI) model and the paclitaxel model of chemotherapy-induced neuropathic pain. For example, inactivation of the MS with intraseptal muscimol (2 μg/μl, 0.5 μl), a GABA mimetic, reversed peripheral hypersensitivity (PH) in the CCI model and induced place preference in a conditioned place preference task, a surrogate measure of spontaneous nociception. The effect of intraseptal muscimol on PH was comparable to that seen with microinjection of the local anesthetic, lidocaine, into rostral ventromedial medulla which is implicated in facilitating experimental chronic nociception. Cellular analysis in the CCI model showed that the MS region sustains nociceptive gain with CCI by facilitating basal nociceptive processing and the amplification of stimulus-evoked neural processing. Indeed, consistent with the idea that excitatory transmission through MS facilitates chronic experimental pain, intraseptal microinjection of antagonists acting at AMPA and NMDA glutamate receptors attenuated CCI-induced PH. We propose that the MS is a central monitor of bodily nociception which sustains molecular plasticity triggered by persistent noxious insult.

Type 2 Diabetes Promotes Cell Centrosome Amplification via AKT-ROS-Dependent Signalling of ROCK1 and 14-3-3σ.

Wang P, Lu YC, Wang J, Wang L, Yu H, Li YF, Kong A, Chan J, Lee S.

Cell Physiol Biochem. 2018;47(1):356-367. doi: 10.1159/000489812. Epub 2018 May 11.

Abstract

BACKGROUND/AIMS:
Type 2 diabetes is associated with oxidative stress and DNA damage which can cause centrosome amplification. Thus, the study investigated centrosome amplification in type 2 diabetes and the underlying mechanisms.
METHODS:
Centrosome numbers in human peripheral blood mononuclear blood cells (PBMC) from healthy subjects and patients with type 2 diabetes were compared to access the association between type 2 diabetes and centrosome amplification. Colon cancer cells were used to investigate the molecular mechanisms underlying the centrosome amplification triggered by high glucose, insulin and palmitic acid. Western blot analysis was used to quantify the level of protein and protein phosphorylation. Immunofluorescent staining was performed to detect centrosomes. ROS was quantified using flow cytometry technique. Transcriptpmic profiling was performed using Illumina HiSeqTM500 platform.
RESULTS:
We found that centrosome amplification was increased PBMC from the type 2 diabetic patients, which correlated with the levels of fasting blood glucose and HbA1c. High glucose, insulin and palmitic acid, alone or in combinations, induced ROS production and centrosome amplification. Together, they increased AKT activation as well as the expression, binding and centrosome translation of ROCK1 and 14-3-3σ. Results from further analyses showed that AKT-ROS-dependent upregulations of expression, binding and centrosome translocation of ROCK1 and 14-3-3σ was the molecular pathway underlying the centrosome amplification in vitro triggered by high glucose, insulin and palmitic acid. Moreover, the key in vitro molecular signalling events activated by high glucose, insulin and palmitic acid were verified in PBMC from the patients with type 2 diabetes.
CONCLUSION:
Our results show that type 2 diabetes promotes cell centrosome amplification, and suggest that the diabetic pathophysiological factors-activated AKT-ROS-dependent signalling of ROCK1 and 14-3-3σ is the underlying molecular mechanism.

TGFβ1-mediated suppression of cytochrome P450(CYP) induction responses in rat hepatocyte-fibroblast co-cultures.

Yu Y, Ananthanarayanan A, Singh NH, Hong X, Sakban RB, Mittal N, Xiaobei L, Robens J, Xia L, McMillian M, Yu H.

Toxicol In Vitro. 2018 Aug;50:47-53. doi: 10.1016/j.tiv.2018.01.015. Epub 2018 Jan 31.

Abstract

Co-culture of hepatocyte and fibroblasts has shown distinct advantages in enhancing certain liver specific functions and maintaining hepatic polarity. However, the utility of hepatocyte co-culture models for studies, such as drug-drug interaction studies, has not been completely elucidated. In this study the induction of Cyp1a2, Cyp2b1/2, and Cyp3a2, the three major cytochrome P450 (CYP) isoforms in the rat liver, was evaluated in randomly mixed co-cultures and micropatterned co-cultures. We found that in both co-culture configurations, the drug-induced Cyp1a2, Cyp2b1/2, Cyp3a2 mRNA and activity were suppressed relative to those in monocultured hepatocytes. Further, we observed a significant increase in TGFβ1 production in the co-cultures. Addition of 100 pg/ml TGFβ1 to hepatocyte monocultures resulted in the suppression of Cyp1a2, Cyp2b1/2, and Cyp3a2 induction. These findings implicate TGFβ1 as one of the important factors impairing drug induced CYP induction in co-cultures and suggests that caution needs to be exercised in the use of hepatocyte-fibroblast co-cultures for CYP induction studies.

Cross Talk Between Cellular Redox State and the Antiapoptotic Protein Bcl-2.

Pohl SÖ, Agostino M, Dharmarajan A, Pervaiz S.

Antioxid Redox Signal. 2018 Feb 15. doi: 10.1089/ars.2017.7414.

Abstract

SIGNIFICANCE:B cell lymphoma-2 (Bcl-2) was discovered over three decades ago and is the prototype antiapoptotic member of the Bcl-2 family that comprises proteins with contrasting effects on cell fate. First identified as a consequence of chromosomal translocation (t 14:18) in human lymphoma, subsequent studies have revealed mutations and/or gene copy number alterations as well as posttranslational modifications of Bcl-2 in a variety of human cancers. The canonical function of Bcl-2 is linked to its ability to inhibit mitochondrial membrane permeabilization, thereby regulating apoptosome assembly and activation by blocking the cytosolic translocation of death amplification factors. Of note, the identification of specific domains within the Bcl-2 family of proteins (Bcl-2 homology domains; BH domains) has not only provided a mechanistic insight into the various interactions between the member proteins but has also been the impetus behind the design and development of small molecule inhibitors and BH3 mimetics for clinical use. Recent Advances: Aside from its role in maintaining mitochondrial integrity, recent evidence provides testimony to a novel facet in the biology of Bcl-2 that involves an intricate cross talk with cellular redox state. Bcl-2 overexpression modulates mitochondrial redox metabolism to create a "pro-oxidant" milieu, conducive for cell survival. However, under states of oxidative stress, overexpression of Bcl-2 functions as a redox sink to prevent excessive buildup of reactive oxygen species, thereby inhibiting execution signals. Emerging evidence indicates various redox-dependent transcriptional changes and posttranslational modifications with different functional outcomes.
CRITICAL ISSUES:Understanding the complex interplay between Bcl-2 and the cellular redox milieu from the standpoint of cell fate signaling remains vital for a better understanding of pathological states associated with altered redox metabolism and/or aberrant Bcl-2 expression.
FUTURE DIRECTIONS:Based on its canonical functions, Bcl-2 has emerged as a potential druggable target. Small molecule inhibitors of Bcl-2 and/or other family members with similar function, as well as BH3 mimetics, are showing promise in the clinic. The emerging evidence for the noncanonical activity linked to cellular redox metabolism provides a novel avenue for the design and development of diagnostic and therapeutic strategies against cancers refractory to conventional chemotherapy by the overexpression of this prosurvival protein.

Reactive Oxygen Species and Oncoprotein Signaling-A Dangerous Liaison.

Chong SJF, Lai JXH, Eu JQ, Bellot GL, Pervaiz S.

Antioxid Redox Signal. 2018 Jan 9. doi: 10.1089/ars.2017.7441.

Abstract

SIGNIFICANCE: here is evidence to implicate reactive oxygen species (ROS) in tumorigenesis and its progression. This has been associated with the interplay between ROS and oncoproteins, resulting in enhanced cellular proliferation and survival. Recent Advances: To date, studies have investigated specific contributions of the crosstalk between ROS and signaling networks in cancer initiation and progression. These investigations have challenged the established dogma of ROS as agents of cell death by demonstrating a secondary function that fuels cell proliferation and survival. Studies have thus identified (onco)proteins (Bcl-2, STAT3/5, RAS, Rac1, and Myc) in manipulating ROS level as well as exploiting an altered redox environment to create a milieu conducive for cancer formation and progression.
CRITICAL ISSUES: Despite these advances, drug resistance and its association with an altered redox metabolism continue to pose a challenge at the mechanistic and clinical levels. Therefore, identifying specific signatures, altered protein expressions, and modifications as well as protein-protein interplay/function could not only enhance our understanding of the redox networks during cancer initiation and progression but will also provide novel targets for designing specific therapeutic strategies.
FUTURE DIRECTIONS: Not only a heightened realization is required to unravel various gene/protein networks associated with cancer formation and progression, particularly from the redox standpoint, but there is also a need for developing more sensitive tools for assessing cancer redox metabolism in clinical settings. This review attempts to summarize our current knowledge of the crosstalk between oncoproteins and ROS in promoting cancer cell survival and proliferation and treatment strategies employed against these oncoproteins.

PTEN-L is a novel protein phosphatase for ubiquitin dephosphorylation to inhibit PINK1-Parkin-mediated mitophagy

Wang L, Cho YL, Tang Y, Wang J, Park JE, Wu Y, Wang C, Tong Y, Chawla R, Zhang J, Shi Y, Deng S, Lu G, Wu Y, Tan HW, Pawijit P, Lim GG, Chan HY, Zhang J, Fang L, Yu H, Liou YC, Karthik M, Bay BH, Lim KL, Sze SK, Yap CT, Shen HM.

Cell Res. 2018 Aug;28(8):787-802. doi: 10.1038/s41422-018-0056-0. Epub 2018 Jun 22.

Abstract

Mitophagy is an important type of selective autophagy for specific elimination of damaged mitochondria. PTEN-induced putative kinase protein 1 (PINK1)-catalyzed phosphorylation of ubiquitin (Ub) plays a critical role in the onset of PINK1-Parkin-mediated mitophagy. Phosphatase and tensin homolog (PTEN)-long (PTEN-L) is a newly identified isoform of PTEN, with addition of 173 amino acids to its N-terminus. Here we report that PTEN-L is a novel negative regulator of mitophagy via its protein phosphatase activity against phosphorylated ubiquitin. We found that PTEN-L localizes at the outer mitochondrial membrane (OMM) and overexpression of PTEN-L inhibits, whereas deletion of PTEN-L promotes, mitophagy induced by various mitochondria-damaging agents. Mechanistically, PTEN-L is capable of effectively preventing Parkin mitochondrial translocation, reducing Parkin phosphorylation, maintaining its closed inactive conformation, and inhibiting its E3 ligase activity. More importantly, PTEN-L reduces the level of phosphorylated ubiquitin (pSer65-Ub) in vivo, and in vitro phosphatase assay confirms that PTEN-L dephosphorylates pSer65-Ub via its protein phosphatase activity, independently of its lipid phosphatase function. Taken together, our findings demonstrate a novel function of PTEN-L as a protein phosphatase for ubiquitin, which counteracts PINK1-mediated ubiquitin phosphorylation leading to blockage of the feedforward mechanisms in mitophagy induction and eventual suppression of mitophagy. Thus, understanding this novel function of PTEN-L provides a key missing piece in the molecular puzzle controlling mitophagy, a critical process in many important human diseases including neurodegenerative disorders such as Parkinson's disease.

G9a/GLP Complex Acts as a Bidirectional Switch to Regulate Metabotropic Glutamate Receptor-Dependent Plasticity in Hippocampal CA1 Pyramidal Neurons.

Sharma M, Sajikumar S.

Cereb Cortex. 2018 Jul 6. doi: 10.1093/cercor/bhy161.

Abstract

Metabotropic glutamate receptor-dependent long-term depression (mGluR-LTD) is conventionally considered to be solely dependent on local protein synthesis. Given the impact of epigenetics on memory, the intriguing question is whether epigenetic regulation influences mGluR-LTD as well. G9a/GLP histone lysine methyltransferase complex is crucial for brain development and goal-directed learning as well as for drug-addiction. In this study, we analyzed whether the epigenetic regulation by G9a/GLP complex affects mGluR-LTD in CA1 hippocampal pyramidal neurons of 5-7 weeks old male Wistar rats. In hippocampal slices with intact CA1 dendritic regions, inhibition of G9a/GLP activity abolished mGluR-LTD. The inhibition of this complex upregulated the expression of plasticity proteins like PKMζ, which mediated the prevention of mGluR-LTD expression by regulating the NSF-GluA2-mediated trafficking of AMPA receptors towards the postsynaptic site. G9a/GLP inhibition during the induction of mGluR-LTD also downregulated the protein levels of phosphorylated-GluA2 and Arc. Interestingly, G9a/GLP inhibition could not impede the mGluR-LTD when the cell-body was severed. Our study highlights the role of G9a/GLP complex in intact neuronal network as a bidirectional switch; when turned on, it facilitates the expression of mGluR-LTD, and when turned off, it promotes the expression of long-term potentiation.

Regulation of feeding by somatostatin neurons in the tuberal nucleus.

Luo SX, Huang J, Li Q, Mohammad H, Lee CY, Krishna K, Kok AM, Tan YL, Lim JY, Li H, Yeow LY, Sun J, He M, Grandjean J, Sajikumar S, Han W, Fu Y.

Science. 2018 Jul 6;361(6397):76-81. doi: 10.1126/science.aar4983.

Abstract

The tuberal nucleus (TN) is a surprisingly understudied brain region. We found that somatostatin (SST) neurons in the TN, which is known to exhibit pathological or cytological changes in human neurodegenerative diseases, play a crucial role in regulating feeding in mice. GABAergic tuberal SST (TNSST) neurons were activated by hunger and by the hunger hormone, ghrelin. Activation of TNSST neurons promoted feeding, whereas inhibition reduced it via projections to the paraventricular nucleus and bed nucleus of the stria terminalis. Ablation of TNSST neurons reduced body weight gain and food intake. These findings reveal a previously unknown mechanism of feeding regulation that operates through orexigenic TNSST neurons, providing a new perspective for understanding appetite changes.

Enriched Expression of Neutral Sphingomyelinase 2 in the Striatum is Essential for Regulation of Lipid Raft Content and Motor Coordination.

Tan LH, Tan AJ, Ng YY, Chua JJ, Chew WS, Muralidharan S, Torta F, Dutta B, Sze SK, Herr DR, Ong WY.

Molecular Neurobiology. 2018 Jul;55(7):5741-5756. doi: 10.1007/s12035-017-0784-z. Epub 2017 Oct 17.

Abstract

Sphingomyelinases are a family of enzymes that hydrolyze sphingomyelin to generate phosphocholine and ceramide. The brain distribution and function of neutral sphingomyelinase 2 (nSMase2) were elucidated in this study. nSMase2 mRNA expression was greatest in the striatum, followed by the prefrontal cortex, hippocampus, cerebellum, thalamus, brainstem, and olfactory bulb. The striatum had the highest level of nSMase2 protein expression, followed by the prefrontal cortex, thalamus, hippocampus, brainstem, and cerebellum. Dense immunolabeling was observed in the striatum, including the caudate-putamen, while moderately dense staining was found in the olfactory bulb and cerebral neocortex. Electron microscopy of the caudate-putamen showed nSMase2 immunoreaction product was present in small diameter dendrites or dendritic spines, that formed asymmetrical synapses with unlabeled axon terminals containing small round vesicles; and characteristics of glutamatergic axons. Lipidomic analysis of the striatum showed increase in long chain sphingomyelins, SM36:1 and SM38:1 after inhibition of nSMase activity. Quantitative proteomic analysis of striatal lipid raft fraction showed many proteins were downregulated by more than 2-fold after inhibition or antisense knockdown of nSMase; consistent with the notion that nSMase2 activity is important for aggregation or clustering of proteins in lipid rafts. Inhibition or antisense knockdown of nSMase2 in the caudate-putamen resulted in motor deficits in the rotarod and narrow beam tests; as well as decreased acoustic startle and improved prepulse inhibition of the startle reflex. Together, results indicate an important function of nSMase2 in the striatum.

Hallmarks of Brain Aging: Adaptive and Pathological Modification by Metabolic States.

Mattson MP, Arumugam TV.

Cell Metabolism. 2018 Jun 5;27(6):1176-1199. doi: 10.1016/j.cmet.2018.05.011.

Abstract

During aging, the cellular milieu of the brain exhibits tell-tale signs of compromised bioenergetics, impaired adaptive neuroplasticity and resilience, aberrant neuronal network activity, dysregulation of neuronal Ca2+ homeostasis, the accrual of oxidatively modified molecules and organelles, and inflammation. These alterations render the aging brain vulnerable to Alzheimer's and Parkinson's diseases and stroke. Emerging findings are revealing mechanisms by which sedentary overindulgent lifestyles accelerate brain aging, whereas lifestyles that include intermittent bioenergetic challenges (exercise, fasting, and intellectual challenges) foster healthy brain aging. Here we provide an overview of the cellular and molecular biology of brain aging, how those processes interface with disease-specific neurodegenerative pathways, and how metabolic states influence brain health.

A 3D Microfluidic Model to Recapitulate Cancer Cell Migration and Invasion.

Toh YC, Raja A, Yu H, van Noort D.

Bioengineering. 2018 Apr 8;5(2). pii: E29. doi: 10.3390/bioengineering5020029.

Abstract

We have developed a microfluidic-based culture chip to simulate cancer cell migration and invasion across the basement membrane. In this microfluidic chip, a 3D microenvironment is engineered to culture metastatic breast cancer cells (MX1) in a 3D tumor model. A chemo-attractant was incorporated to stimulate motility across the membrane. We validated the usefulness of the chip by tracking the motilities of the cancer cells in the system, showing them to be migrating or invading (akin to metastasis). It is shown that our system can monitor cell migration in real time, as compare to Boyden chambers, for example. Thus, the chip will be of interest to the drug-screening community as it can potentially be used to monitor the behavior of cancer cell motility, and, therefore, metastasis, in the presence of anti-cancer drugs.

Epigenetic regulation of inflammation in stroke.

Ng GY, Lim YA, Sobey CG, Dheen T, Fann DY, Arumugam TV.

Ther Adv Neurol Disord. 2018 Apr 26;11:1756286418771815. doi: 10.1177/1756286418771815. eCollection 2018.

Abstract

Despite extensive research, treatments for clinical stroke are still limited only to the administration of tissue plasminogen activator and the recent introduction of mechanical thrombectomy, which can be used in only a limited proportion of patients due to time constraints. A plethora of inflammatory events occur during stroke, arising in part due to the body's immune response to brain injury. Neuroinflammation contributes significantly to neuronal cell death and the development of functional impairment and death in stroke patients. Therefore, elucidating the molecular and cellular mechanisms underlying inflammatory damage following stroke injury will be essential for the development of useful therapies. Research findings increasingly point to the likelihood that epigenetic mechanisms play a role in the pathophysiology of stroke. Epigenetics involves the differential regulation of gene expression, including those involved in brain inflammation and remodelling after stroke. Hence, it is conceivable that epigenetic mechanisms may contribute to differential interindividual vulnerability and injury responses to cerebral ischaemia. In this review, we summarize recent findings on the emerging role of epigenetics in the regulation of neuroinflammation in stroke. We also discuss potential epigenetic targets that may be assessed for the development of stroke therapies.

Triple negative breast cancer in Asia: An insider's view

Wang C, Kar S, Lai X, Cai W, Arfuso F, Sethi G, Lobie PE, Goh BC, Lim LHK, Hartman M, Chan CW, Lee SC, Tan SH, Kumar AP.

Cancer Treatment Reviews. 2018 Jan. 62: 29-38. doi: 10.1016/j.ctrv.2017.10.014. [Epub ahead of print]

Abstract

While tremendous improvement has been made for the treatment of breast cancers, the treatment of triple negative breast cancer (TNBC) still remains a challenge due to its aggressive characteristics and limited treatment options. Most of the studies on TNBC were conducted in Western population and TNBC is reported to be more frequent in the African women. This review encapsulates the studies conducted on TNBC patients in Asian population and elucidates the similarities and differences between these two regions. The current treatment of TNBC includes surgery, radiotherapy and chemotherapy. In addition to the current chemotherapies, which mainly include cytotoxic agents, such as taxanes and anthracyclines, many clinical trials are investigating the potential use of other chemotherapy drugs, targeted therapeutics and combinational therapies to treat TNBC. Moreover, this review also integrates the studies involving novel markers, which will help us to dissect the pathologic process of TNBC and in turn facilitate the development of better treatment strategies to combat TNBC.