Role of sirtuins in stem cell differentiation

Sirtuins Affect Cancer Stem Cells via Epigenetic Regulation of Autophagy

Sirtuins (SIRTs) are stress-responsive proteins that regulate several post-translational modifications, partly by acetylation, deacetylation, and affecting DNA methylation. As a result, they significantly regulate several cellular processes. In essence, they prolong lifespan and control the occurrence of spontaneous tumor growth. Members of the SIRT family have the ability to govern embryonic, hematopoietic, and other adult stem cells in certain tissues and cell types in distinct ways. Likewise, they can have both pro-tumor and anti-tumor effects on cancer stem cells, contingent upon the specific tissue from which they originate. The impact of autophagy on cancer stem cells, which varies depending on the specific circumstances, is a very intricate phenomenon that has significant significance for clinical and therapeutic purposes. SIRTs exert an impact on the autophagy process, whereas autophagy reciprocally affects the activity of certain SIRTs. The mechanism behind this connection in cancer stem cells remains poorly understood. This review presents the latest findings that position SIRTs at the point where cancer cells and autophagy interact. Our objective is to highlight the various roles of distinct SIRTs in cancer stem cell-related functions through autophagy. This would demonstrate their significance in the genesis and recurrence of cancer and offer a more precise understanding of their treatment possibilities in relation to autophagy.

A state-of-the-art review on the MicroRNAs roles in hematopoietic stem cell aging and longevity

Aging is a biological process determined through time-related cellular and functional impairments, leading to a decreased standard of living for the organism. Recently, there has been an unprecedented advance in the aging investigation, especially the detection that the rate of senescence is at least somewhat regulated via evolutionarily preserved genetic pathways and biological processes. Hematopoietic stem cells (HSCs) maintain blood generation over the whole lifetime of an organism. The senescence process influences many of the natural features of HSC, leading to a decline in their capabilities, independently of their microenvironment. New studies show that HSCs are sensitive to age-dependent stress and gradually lose their self-renewal and regeneration potential with senescence. MicroRNAs (miRNAs) are short, non-coding RNAs that post-transcriptionally inhibit translation or stimulate target mRNA cleavage of target transcripts via the sequence-particular connection. MiRNAs control various biological pathways and processes, such as senescence. Several miRNAs are differentially expressed in senescence, producing concern about their use as moderators of the senescence process. MiRNAs play an important role in the control of HSCs and can also modulate processes associated with tissue senescence in specific cell types. In this review, we display the contribution of age-dependent alterations, including DNA damage, epigenetic landscape, metabolism, and extrinsic factors, which affect HSCs function during aging. In addition, we investigate the particular miRNAs regulating HSCs senescence and age-associated diseases. Video Abstract.

Mitochondrial respiratory quiescence: A new model for examining the role of mitochondrial metabolism in development

Mitochondria are vital organelles with a central role in all aspects of cellular metabolism. As a means to support the ever-changing demands of the cell, mitochondria produce energy, drive biosynthetic processes, maintain redox homeostasis, and function as a hub for cell signaling. While mitochondria have been widely studied for their role in disease and metabolic dysfunction, this organelle has a continually evolving role in the regulation of development, wound repair, and regeneration. Mitochondrial metabolism dynamically changes as tissues transition through distinct phases of development. These organelles support the energetic and biosynthetic demands of developing cells and function as key structures that coordinate the nutrient status of the organism with developmental progression. This review will examine the mechanisms that link mitochondria to developmental processes. We will also examine the process of mitochondrial respiratory quiescence (MRQ), a novel mechanism for regulating cellular metabolism through the biochemical and physiological remodeling of mitochondria. Lastly, we will examine MRQ as a system to discover the mechanisms that drive mitochondrial remodeling during development.

Nesting and fate of transplanted stem cells in hypoxic/ischemic injured tissues: The role of HIF1α/sirtuins and downstream molecular interactions

The nesting mechanisms and programming for the fate of implanted stem cells in the damaged tissue have been critical issues in designing and achieving cell therapies. The fracture site can induce senescence or apoptosis based on the surrounding harsh conditions, hypoxia, and oxidative stress (OS). Respiration deficiency, disruption in energy metabolism, and consequently OS induction change the biophysical, biochemical, and cellular components of the native tissue. Additionally, the homeostatic molecular players and cell signaling might be changed. Despite all aforementioned issues, in the native stem cell niche, physiological hypoxia is not toxic; rather, it is vitally required for homing, self-renewal, and differentiation. Hence, the key macromolecular players involved in the support of stem cell survival and re-adaptation to a new dysfunctional niche must be understood for managing the cell therapy outcome. Hypoxia-inducible factor 1-alpha is the master transcriptional regulator, involved in the cell response to hypoxia and the adaptation of stem cells to a new niche. This protein is regulated by interaction with sirtuins. Sirtuins are highly conserved NAD+-dependent enzymes that monitor the cellular energy status and modulate gene transcription, genome stability, and energy metabolism in response to environmental signals to modulate the homing and fate of stem cells. Herein, new insights into the nesting of stem cells in hypoxic-ischemic injured tissues were provided and their programming in a new dysfunctional niche along with the involved complex macromolecular players were critically discussed.

NRF2: An emerging role in neural stem cell regulation and neurogenesis

The birth of new neurons from neural stem cells (NSC)s during developmental and adult neurogenesis arises from a myriad of highly complex signalling cascades. Emerging as one of these is the nuclear factor erythroid 2-related factor (NRF2)-signaling pathway. Regulation by NRF2 is reported to span the neurogenic process from early neural lineage specification and NSC regulation to neuronal fate commitment and differentiation. Here, we review these reports selecting only those where NRF2 signaling was directly manipulated to provide a clearer case for a direct role of NRF2 in embryonic and adult neurogenesis. With few studies providing mechanistic insight into this relationship, we lastly discuss key pathways linking NRF2 and stem cell regulation outside the neural lineage to shed light on mechanisms that may also be relevant to NSCs and neurogenesis.

Sirt2 promotes white matter oligodendrogenesis during development and in models of neonatal hypoxia

Delayed oligodendrocyte (OL) maturation caused by hypoxia (Hx)-induced neonatal brain injury results in hypomyelination and leads to neurological disabilities. Previously, we characterized Sirt1 as a crucial regulator of OL progenitor cell (OPC) proliferation in response to Hx. We now identify Sirt2 as a critical promoter of OL differentiation during both normal white matter development and in a mouse model of Hx. Importantly, we find that Hx reduces Sirt2 expression in mature OLs and that Sirt2 overexpression in OPCs restores mature OL populations. Reduced numbers of Sirt2+ OLs were also observed in the white matter of preterm human infants. We show that Sirt2 interacts with p27Kip1/FoxO1, p21Cip1/Cdk4, and Cdk5 pathways, and that these interactions are altered by Hx. Furthermore, Hx induces nuclear translocation of Sirt2 in OPCs where it binds several genomic targets. Overall, these results indicate that a balance of Sirt1 and Sirt2 activity is required for developmental oligodendrogenesis, and that these proteins represent potential targets for promoting repair following white matter injury.

A Potential Strategy for Treatment of Neurodegenerative Disorders by Regulation of Adult Hippocampal Neurogenesis in Human Brain

Abstract:

Adult hippocampal neurogenesis is a multistage mechanism that continues throughout the lifespan of human and non-human mammals. These adult-born neurons in the central nervous system (CNS) play a significant role in various hippocampus-dependent processes, including learning, mood regulation, pattern recognition, etc. Reduction of adult hippocampal neurogenesis, caused by multiple factors such as neurological disorders and aging, would impair neuronal proliferation and differentiation and result in memory loss. Accumulating studies have indicated that functional neuron impairment could be restored by promoting adult hippocampal neurogenesis. In this review, we summarized the small molecules that could efficiently promote the process of adult neurogenesis, particularly the agents that have the capacity of crossing the blood-brain barrier (BBB), and showed in vivo efficacy in mammalian brains. This may pave the way for the rational design of drugs to treat humnan neurodegenerative disorders in the future.

Heat-induced SIRT1-mediated H4K16ac deacetylation impairs resection and SMARCAD1 recruitment to double strand breaks

Hyperthermia inhibits DNA double-strand break (DSB) repair that utilizes homologous recombination (HR) pathway by a poorly defined mechanism(s); however, the mechanisms for this inhibition remain unclear. Here we report that hyperthermia decreases H4K16 acetylation (H4K16ac), an epigenetic modification essential for genome stability and transcription. Heat-induced reduction in H4K16ac was detected in humans, Drosophila, and yeast, indicating that this is a highly conserved response. The examination of histone deacetylase recruitment to chromatin after heat-shock identified SIRT1 as the major deacetylase subsequently enriched at gene-rich regions. Heat-induced SIRT1 recruitment was antagonized by chromatin remodeler SMARCAD1 depletion and, like hyperthermia, the depletion of the SMARCAD1 or combination of the two impaired DNA end resection and increased replication stress. Altered repair protein recruitment was associated with heat-shock-induced γ-H2AX chromatin changes and DSB repair processing. These results support a novel mechanism whereby hyperthermia impacts chromatin organization owing to H4K16ac deacetylation, negatively affecting the HR-dependent DSB repair.

Adipose-Derived Stem Cell Features and MCF-7

Human adipose tissue-derived stem cells (hADSCs) are highly suitable for regeneration therapies being easily collected and propagated in vitro. The effects of different external factors and culturing conditions are able to affect hADSC proliferation, senescence, differentiation, and migration, even at the molecular level. In the present paper, we exposed hADSCs to an exhausted medium from the breast cancer cell line (MCF-7) to evaluate whether the soluble factors released by these cells may be able to induce changes in stem cell behavior. In particular, we investigated the expression of stemness-related genes (OCT4; Sox 2; Nanog), the cell-cycle regulators p21 (WAF1/CIP1) p53, epigenetic markers (DNMT1 and Sirt1), and autophagy-related proteins. From our results, we can infer that the exhausted medium from MCF-7 is able to influence the hADSCs behavior increasing the expression of stemness-related genes, cell proliferation, and autophagy. Polyamines detectable in MCF-7 exhausted medium could be related to the higher proliferation capability observed in hADSCs, suggesting direct crosstalk between these molecules and the observed changes in stem cell potency.

Effect of vitrification on global gene expression dynamics of bovine elongating embryos

Embryo vitrification involves exposure to high concentrations of cryoprotectants and osmotic stress during cooling and warming in the cryopreservation process. Many of these factors can potentially affect gene expression. In this study, invitro-produced bovine embryos at the blastocyst stage were subjected to vitrification. Four recipients each were used for transferring non-vitrified (n=80) and vitrified (n=80) embryos. A total of 12 non-vitrified and 9 vitrified viable day-14 (D14) embryos were recovered by uterine flushing. RNA-seq analysis of the whole embryo or isolated trophectoderm (TE) from vitrified and fresh recovered D14 embryos revealed a total of 927 and 4376 genes with changed expression in embryos and TE isolates, respectively, as a result of vitrification. In addition, we found 671 and 61 genes commonly up- or downregulated in both vitrified whole embryos and TE. Commonly upregulated pathways by vitrification included epithelial adherens junctions, sirtuin signalling, germ cell-sertoli cell junction, ATM signalling, NER and protein ubiquitination pathways. The commonly downregulated pathways included EIF2 signalling, oxidative phosphorylation, mitochondrial dysfunction, regulation of eIF4 and p70S6K signalling and mTOR signalling pathways. Our analysis identified specific pathways and implicated specific gene expression patterns affecting embryo developmental competence that are important to cryopreservation.

Combined Ischemic Preconditioning and Resveratrol Improved Bloodbrain Barrier Breakdown via Hippo/YAP/TAZ Signaling Pathway

BACKGROUND

Transient Ischemia/Reperfusion (I/R) is the main reason for brain injury and results in disruption of the Blood-Brain Barrier (BBB). It had been reported that BBB injury is one of the main risk factors for early death in patients with cerebral ischemia. Numerous investigations focus on the study of BBB injury which have been carried out.

OBJECTIVE

The objective of this study was to investigate the treatment function of the activation of the Hippo/Yes-Associated Protein (YAP) signaling pathway by combined Ischemic Preconditioning (IPC) and resveratrol (RES) before brain Ischemia/Reperfusion (BI/R) improves Blood-Brain Barrier (BBB) disruption in rats.

METHODS

Sprague-Dawley (SD) rats were pretreated with 20 mg/kg RES and IPC and then subjected to 2 h of ischemia and 22 h of reperfusion. The cerebral tissues were collected; the cerebral infarct volume was determined; the Evans Blue (EB) level, the brain Water Content (BWC), and apoptosis were assessed; and the expressions of YAP and TAZ were investigated in cerebral tissues.

RESULTS

Both IPC and RES preconditioning reduced the cerebral infarct size, improved BBB permeability, lessened apoptosis, and upregulated expressions of YAP and transcriptional co-activator with PDZ-binding motif (TAZ) compared to the Ischemia/Reperfusion (I/R) group, while combined IPC and RES significantly enhanced this action.

CONCLUSION

combined ischemic preconditioning and resveratrol improved blood-brain barrier breakdown via Hippo/YAP/TAZ signaling pathway.

Per2 Upregulation in Circulating Hematopoietic Progenitor Cells During Chronic HIV Infection

Chronic HIV infection accelerates immune aging and is associated with abnormal hemato-lymphopoiesis, but the relationship between HIV-induced aging and Hematopoietic Progenitor Cells (HPC) function is not well-defined. In the context of aging, it has been demonstrated using a murine model that Per2 (Period circadian clock 2) is a negative regulator of HPC survival and lineage potential. A possible involvement of Per2 modulation on hematopoietic failure during HIV infection has not yet been investigated. The aim of this study was to analyze whether Per2 is differently expressed and regulated on HPC during HIV infection, possibly providing a therapeutic target to restore lymphoid potential in the HPC compartment. To this purpose, Per2 expression in circulating HPC was compared in 69 chronic HIV infected patients under successful ART and in matched 30 uninfected healthy donors (HD). HPC aging was assessed by measuring relative telomere length (RTL), and HPC functionality was evaluated by Colony Forming Cell (CFC) assay from both ex vivo HIV+ patients and in vitro Per2 overexpressing donors. Our results showed a lower RTL in HPC and a decrease of white progenitor colonies from HIV+ patients with lower CD4 respect to those with higher CD4 T cell count (<500 respect to >500 CD4 T cell/mmc). Interestingly, we found that the frequency of Per2-expressing HPC is higher in HIV+ patients than in HD and correlated to RTL of CFC derived cells, highlighting a relationship between low proliferative rate and Per2 expression. Indeed, the in vitro overexpression of Per2 resulted in a significant decrease of white progenitor colonies respect to control cells. Finally, we showed that the deacetylase Sirtuin 1, a negative regulator of Per2, was downregulated in HPC from HIV+ patients, and the peripheral blood treatment with resveratrol (Sirtuin 1 inducer) determined a decrease of Per2 expressing HPC. Altogether, these results suggest that during HIV infection, Per2 is involved in the regulation of HPC expansion and differentiation and its overexpression may impair the immune reconstitution. These data support the rationale to explore the role of this regulatory mechanism during aged-associated hemato-lymphopoiesis impairment in HIV infection.

SIRT1 in forebrain excitatory neurons produces sexually dimorphic effects on depression-related behaviors and modulates neuronal excitability and synaptic transmission in the medial prefrontal cortex

Sirtuin 1 (SIRT1), an NAD+-dependent deacetylase, is a key regulator of cellular metabolism. Recent genome-wide association studies identified genetic variants of SIRT1 linked to major depressive disorders. SIRT1 is widely expressed in the brain; however, neuronal substrates that mediate SIRT1 action on depressive behaviors remain largely unknown. Here we show that selective deletion of SIRT1 in forebrain excitatory neurons causes depression-like phenotypes in male but not female mice. AAV-Cre-mediated SIRT1 knockdown in the medial prefrontal cortex (mPFC) of adult male mice induces depressive-like behaviors. Whole-cell patch-clamp recordings demonstrate that loss of SIRT1 decreases intrinsic excitability and spontaneous excitatory synaptic transmission in layer V pyramidal neurons in the prelimbic mPFC. Consistent with neuronal hypoexcitability, SIRT1 knockout reduces mitochondrial density and expression levels of genes involved in mitochondrial biogenesis and dynamics in the prelimbic mPFC. When a SIRT1 activator (SRT2104) is injected into the mPFC or lateral ventricle of wild-type mice, it reverses chronic unpredictable stress-induced anhedonia and behavioral despair, indicating an antidepressant-like effect. These results suggest that SIRT1 in mPFC excitatory neurons is required for normal neuronal excitability and synaptic transmission and regulates depression-related behaviors in a sex-specific manner.

A new SIRT1 inhibitor, MHY2245, induces autophagy and inhibits energy metabolism via PKM2/mTOR pathway in human ovarian cancer cells

Ovarian cancer is a common gynecological cancer that is found worldwide. Class III histone deacetylase (HDAC) inhibitors, a new class of anticancer agents, induce autophagy in various human cancer cells. The aim of the present study was to investigate the antitumor activity of MHY2245, a new synthetic SIRT inhibitor, on human ovarian cancer cells. We found that MHY2245 exhibited potent cytotoxicity to SKOV3 cells in a time- and concentration-dependent manner. The cytotoxicity of MHY2245 (IC50=0.32 µM) was higher than that of doxorubicin (DOX, IC50=1.38µM) against SKOV3 cells. MHY2245 significantly inhibited SIRT1 enzyme activity, reduced the expression of SIRT1, increased cell cycle arrest at G2/M phase, and induced apoptotic cell death in SKOV3 cells via expression of cytochrome c, cleaved-PARP, cleaved caspase-3, and Bax. This might be associated with blocking of the pyruvate kinase M2 (PKM2)/mTOR pathway. MHY2245 also inhibited tumor growth and reduced tumor size when SKOV3 cells were transplanted into nude mice. Our results indicate that MHY2245 exerts antitumor activity against ovarian cancer cells by blocking the PKM2/mTOR pathway. We suggest that MHY2245 is a promising anticancer agent that disrupts ovarian cancer cell metabolism.

SIRT1 Activation Promotes β-Cell Regeneration by Activating Endocrine Progenitor Cells via AMPK Signaling-Mediated Fatty Acid Oxidation

Induction of β-cell regeneration from endogenous cells represents a highly promising strategy in stem cell-based treatment for patients with diabetes. Recently, calorie restriction has been shown to affect the regulation of tissue and cell regeneration, including β cells, via metabolic related mechanisms. Here, we examined the potential utility of sirtuin 1 (SIRT1), a calorie restriction mimetic, for stimulating β-cell regeneration and the underlying mechanisms of such stimulation. The present results showed that SIRT1 activation with SRT1720 promoted β-cell regeneration in streptozotocin (STZ)-induced β-cell-deficient neonatal rats. This beneficial effect involved enhanced activation of neurogenin3 (NGN3)-positive endocrine progenitors from pancreatic ductal cells, rather than an expansion of residual β cells. A dynamic expression profile of SIRT1 was observed in endocrine progenitors both during β-cell regeneration in neonatal rats and in the second transition phase of mouse pancreas development. Consistently, SRT1720 treatment upregulated endocrine progenitor differentiation in cultured pancreatic rudiments. Upregulation of NGN3 by SIRT1 activation was through stimulating AMP-activated protein kinase (AMPK) signaling-mediated fatty acid oxidation (FAO) in human pancreatic progenitor cells; AMPK inhibition abolished these effects. The present findings demonstrate a promotional effect of SIRT1 activation on β-cell restoration and endocrine progenitor differentiation that involves regulation of AMPK signaling-mediated FAO. Stem Cells 2019;37:1416-1428.

Novel Lysine-Based Thioureas as Mechanism-Based Inhibitors of Sirtuin 2 (SIRT2) with Anticancer Activity in a Colorectal Cancer Murine Model

Sirtuin 2 (SIRT2) is a protein lysine deacylase that has been indicated as a therapeutic target for cancer. To further establish the role of SIRT2 in cancers, it is necessary to develop selective and potent inhibitors. Here, we report the facile synthesis of novel lysine-derived thioureas as mechanism-based SIRT2 inhibitors with anticancer activity. Compounds AF8, AF10, and AF12 selectively inhibited SIRT2 with IC₅₀ values of 0.06, 0.15, and 0.08 μM, respectively. Compounds AF8 and AF10 demonstrated broad cytotoxicity amongst cancer cell lines, but minimal toxicity in noncancerous cells. AF8 and AF10 inhibited the anchorage-independent growth of human colorectal cancer cell line HCT116 with GI₅₀ values of ∼7 μM. Furthermore, AF8 potently inhibited tumor growth in a HCT116 xenograft murine model, supporting that SIRT2 is a viable therapeutic target for colorectal cancer.

Plasticity of Adipose Tissue-Derived Stem Cells and Regulation of Angiogenesis

Adipose tissue is recognized as an important organ with metabolic, regulatory, and plastic roles. Adipose tissue-derived stem cells (ASCs) with self-renewal properties localize in the stromal vascular fraction (SVF) being present in a vascular niche, thereby, contributing to local regulation of angiogenesis and vessel remodeling. In the past decades, ASCs have attracted much attention from biologists and bioengineers, particularly, because of their multilineage differentiation potential, strong proliferation, and migration abilities in vitro and high resistance to oxidative stress and senescence. Current data suggest that the SVF serves as an important source of endothelial progenitors, endothelial cells, and pericytes, thereby, contributing to vessel remodeling and growth. In addition, ASCs demonstrate intriguing metabolic and interlineage plasticity, which makes them good candidates for creating regenerative therapeutic protocols, in vitro tissue models and microphysiological systems, and tissue-on-chip devices for diagnostic and regeneration-supporting purposes. This review covers recent achievements in understanding the metabolic activity within the SVF niches (lactate and NAD+ metabolism), which is critical for maintaining the pool of ASCs, and discloses their pro-angiogenic potential, particularly, in the complex therapy of cardiovascular and cerebrovascular diseases.

SIRT3 Protects Against Acute Kidney Injury via AMPK/mTOR-Regulated Autophagy

Acute kidney injury (AKI), which involves the loss of kidney function caused by damage to renal tubular cells, is an important public health concern. We previously showed that sirtuin (SIRT)3 protects the kidneys against mitochondrial damage by inhibiting the nucleotide-binding domain (NOD)-like receptor protein 3 (NLRP3) inflammasome, attenuating oxidative stress, and downregulating proinflammatory cytokines. In this article, we investigated the role of autophagy, mediated by a mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK), in the protective effect of SIRT3, against sepsis-induced AKI, in a mouse model of cecal ligation and puncture (CLP). The AKI in CLP mice was associated with the upregulation of autophagy markers; this effect was abolished in SIRT3^- mice in parallel with the downregulation of phospho (p)-AMPK and the upregulation of p-mTOR. Pretreatment with the autophagy inhibitor 3-methyladenine (3-MA) or AMPK inhibitor compound isotonic saline (C), exacerbated AKI. SIRT3 overexpression promoted autophagy, upregulated p-AMPK and downregulated p-mTOR in CLP mice, attenuating sepsis-induced AKI, tubular cell apoptosis, and inflammatory cytokine accumulation in the kidneys. The blockage of autophagy induction largely abolished the protective effect of SIRT3 in sepsis-induced AKI. These findings indicate that SIRT3 protects against CLP-induced AKI by inducing autophagy through regulation of the AMPK/mTOR pathway.

Rapamycin ameliorates chitosan nanoparticle-induced developmental defects of preimplantation embryos in mice

Chitosan nanoparticles (CSNPs) are used as drug or gene delivery vehicles. However, a detailed understanding of the effects of CSNPs on embryonic development remains obscure. Here, we show that CSNPs can be internalized into mouse blastocysts, such as the zona pellucida, the perivitelline space, and the cytoplasm. Consequently, CSNPs-induced endoplasmic reticulum (ER) stress increases both of Bip/Grp78, Chop, Atf4, Perk, and Ire1a mRNAs expression levels, and reactive oxygen species. Moreover, CSNPs show double- and multi-membraned autophagic vesicles, and lead to cell death of blastocoels. Conversely, treatment with rapamycin, which plays an important role as a central regulator of cellular proliferation and stress responses, decreased CSNPs-induced mitochondrial Ca⁺² overloading, apoptosis, oxidative stress, ER stress, and autophagy. In vivo studies demonstrated that CSNPs injection has significant toxic effect on primordial and developing follicles. Notably, rapamycin rescued oxidative stress-induced embryonic defects via modulating gene expression of sirtuin and mammalian target of rapamycin. Interestingly, CSNPs treatment alters epigenetic reprogramming in mouse embryos. Overall, these observations suggest that rapamycin treatment could ameliorate CSNPs-induced developmental defects in preimplantation embryos. The data from this study would facilitate to understand the toxicity of these CSNPs, and enable the engineering of safer nanomaterials for therapeutic applications.

Rapid modulation of the silent information regulator 1 by melatonin after hypoxia-ischemia in the neonatal rat brain

Increasing evidence indicates that melatonin possesses protective effects toward different kinds of damage in various organs, including the brain. In a neonatal model of hypoxia-ischemia (HI), melatonin was neuroprotective and preserved the expression of the silent information regulator 1 (SIRT1) 24 hours after the insult. This study aimed to gain more insight into the role of SIRT1 in the protective effect of melatonin after HI by studying the early (1 hour) modulation of SIRT1 and its downstream targets, and the consequences on necrosis, apoptosis, autophagy, and glial cell activation. We found that melatonin administered 5 minutes after the ischemic insult significantly reduced necrotic cell death assessed 1 hour after its administration. In parallel, we found a reduced activation of the early phases of intrinsic apoptosis, detected by reduced BAX translocation to the mitochondria and preservation of the mitochondrial expression of cytochrome C, indicating a reduced outer mitochondrial membrane permeabilization in the melatonin-treated ischemic animals. These effects were concomitant to increased expression and activity of SIRT1, reduced expression and acetylation of p53, and increased autophagy activation. Melatonin also reduced HI-induced glial cells activation. SIRT1 was expressed in neurons after HI and melatonin but not in reactive glial cells expressing GFAP. Colocalization between SIRT1 and GFAP was found in some cells in control conditions. In summary, our results provide more insight into the connection between SIRT1 and melatonin in neuroprotection. The possibility that melatonin-induced SIRT1 activity might contribute to differentiate neuronal progenitor cells during the neurodegenerative process needs to be further investigated.

Upregulation of mitochondrial NAD+ levels impairs the clonogenicity of SSEA1+ glioblastoma tumor-initiating cells

Emerging evidence has emphasized the importance of cancer therapies targeting an abnormal metabolic state of tumor-initiating cells (TICs) in which they retain stem cell-like phenotypes and nicotinamide adenine dinucleotide (NAD+) metabolism. However, the functional role of NAD+ metabolism in regulating the characteristics of TICs is not known. In this study, we provide evidence that the mitochondrial NAD+ levels affect the characteristics of glioma-driven SSEA1+ TICs, including clonogenic growth potential. An increase in the mitochondrial NAD+ levels by the overexpression of the mitochondrial enzyme nicotinamide nucleotide transhydrogenase (NNT) significantly suppressed the sphere-forming ability and induced differentiation of TICs, suggesting a loss of the characteristics of TICs. In addition, increased SIRT3 activity and reduced lactate production, which are mainly observed in healthy and young cells, appeared following NNT-overexpressed TICs. Moreover, in vivo tumorigenic potential was substantially abolished by NNT overexpression. Conversely, the short interfering RNA-mediated knockdown of NNT facilitated the maintenance of TIC characteristics, as evidenced by the increased numbers of large tumor spheres and in vivo tumorigenic potential. Our results demonstrated that targeting the maintenance of healthy mitochondria with increased mitochondrial NAD+ levels and SIRT3 activity could be a promising strategy for abolishing the development of TICs as a new therapeutic approach to treating aging-associated tumors.

Sirt1 regulates glial progenitor proliferation and regeneration in white matter after neonatal brain injury

Regenerative processes in brain pathologies require the production of distinct neural cell populations from endogenous progenitor cells. We have previously demonstrated that oligodendrocyte progenitor cell (OPC) proliferation is crucial for oligodendrocyte (OL) regeneration in a mouse model of neonatal hypoxia (HX) that reproduces diffuse white matter injury (DWMI) of premature infants. Here we identify the histone deacetylase Sirt1 as a Cdk2 regulator in OPC proliferation and response to HX. HX enhances Sirt1 and Sirt1/Cdk2 complex formation through HIF1α activation. Sirt1 deacetylates retinoblastoma (Rb) in the Rb/E2F1 complex, leading to dissociation of E2F1 and enhanced OPC proliferation. Sirt1 knockdown in culture and its targeted ablation in vivo suppresses basal and HX-induced OPC proliferation. Inhibition of Sirt1 also promotes OPC differentiation after HX. Our results indicate that Sirt1 is an essential regulator of OPC proliferation and OL regeneration after neonatal brain injury. Therefore, enhancing Sirt1 activity may promote OL recovery after DWMI.

Oligodendrocyte progenitor cell (OPC) proliferation is crucial for regeneration after hypoxic lesions in mice, a model of diffuse white matter injury of premature infants. Here, the authors show that the histone deacetylase Sirt1 is a Cdk2-dependent mediator of OPC proliferation and OPC response to hypoxia.

A potent and selective small molecule inhibitor of sirtuin 1 promotes differentiation of pluripotent P19 cells into functional neurons

Sirtuin 1 (SIRT1) is known to suppress differentiation of pluripotent/multipotent cells and neural progenitor cells into neurons by blocking activation of transcription factors critical for neurogenesis. EX-527 is a highly selective and potent inhibitor against SIRT1 and has been used as a chemical probe that modulates SIRT1-associated biological processes. However, the effect of EX-527 on neuronal differentiation in pluripotent cells has not been well elucidated. Here, we report an examination of EX-527 effects on neurogenesis of pluripotent P19 cells. The results showed that EX-527 greatly accelerated differentiation of P19 cells into neurons without generation of cardiac cells and astrocytes. Importantly, neurons derived from P19 cells treated with EX-527 generated voltage-dependent sodium currents and depolarization-induced action potentials. The findings indicate that the differentiated cells have electrophysiological properties. The present study suggests that the selective SIRT1 inhibitor could have the potential of being employed as a chemical inducer to generate functionally active neurons.

Whole blood transcriptional profiling reveals deregulation of oxidative and antioxidative defence genes in myelofibrosis and related neoplasms. Potential implications of downregulation of Nrf2 for genomic instability and disease progression

The Philadelphia-negative chronic myeloproliferative neoplasms - essential thrombocythemia (ET), polycythemia vera (PV), and myelofibrosis (MF) (MPNs) - have recently been shown to be associated with chronic inflammation, oxidative stress and accumulation of reactive oxygen species (ROS). Using whole blood transcriptional profiling, we report that several oxidative stress and anti-oxidative stress genes are significantly deregulated in MPNs. Among the twenty most up- and downregulated genes, ATOX1, DEFB122, GPX8, PRDX2, PRDX6, PTGS1, and SEPP1 were progressively upregulated from ET over PV to PMF, whereas AKR1B1, CYBA, SIRT2, TTN, and UCP2 were progressively downregulated in ET, PV and PMF (all FDR <0.05). The gene Nrf2, encoding the transcription factor nuclear factor erythroid 2-related factor 2 (NFE2L2 or Nrf2) was significantly downregulated in all MPNs. Nrf2 has a key role in the regulation of the oxidative stress response and modulates both migration and retention of hematopoietic stem cells (HSCs) in their niche. The patogenetic importance of Nrf2 depletion in the context of expansion of the hematopoietic progenitor pool in MPNs is discussed with particular focus upon the implications of concomitant downregulation of Nrf2 and CXCR4 for stem cell mobilization.

Bone cell senescence: mechanisms and perspectives

Age-related bone loss is in large part the consequence of senescence mechanisms that impact bone cell number and function. In recent years, progress has been made in the understanding of the molecular mechanisms underlying bone cell senescence that contributes to the alteration of skeletal integrity during aging. These mechanisms can be classified as intrinsic senescence processes, alterations in endogenous anabolic factors, and changes in local support. Intrinsic senescence mechanisms cause cellular dysfunctions that are not tissue specific and include telomere shortening, accumulation of oxidative damage, impaired DNA repair, and altered epigenetic mechanisms regulating gene transcription. Aging mechanisms that are more relevant to the bone microenvironment include alterations in the expression and signaling of local growth factors and altered intercellular communications. This review provides an integrated overview of the current concepts and interacting mechanisms underlying bone cell senescence during aging and how they could be targeted to reduce the negative impact of senescence in the aging skeleton.

Role of histone acetyltransferases and histone deacetylases in adipocyte differentiation and adipogenesis

Adipogenesis is a complex process strictly regulated by a well-established cascade that has been thoroughly studied in the last two decades. This process is governed by complex regulatory networks that involve the activation/inhibition of multiple functional genes, and is controlled by histone-modifying enzymes. Among such modification enzymes, histone acetyltransferases (HATs) and histone deacetylases (HDACs) play important roles in the transcriptional regulation and post-translational modification of protein acetylation. HATs and HDACs have been shown to respond to signals that regulate cell differentiation, participate in the regulation of protein acetylation, mediate transcription and post-translation modifications, and directly acetylate/deacetylate various transcription factors and regulatory proteins. In this paper, we review the role of HATs and HDACs in white and brown adipocyte differentiation and adipogenesis, to expand our knowledge on fat formation and adipose tissue biology.