Sirt3 Depletion Research Articles

Melatonin modulates the Notch1 signaling pathway and Sirt3 in the hippocampus of hypoxic-ischemic neonatal rats

The Notch1 signaling pathway plays a crucial role in the development of the central nervous system, governing pivotal functional activities in the brain, such as neurogenesis. Sirt3 is instrumental in managing mitochondrial homeostasis and is essential to cell survival. Dysregulation of these signaling pathways is implicated in the pathogenesis of a wide range of diseases, including neurodegenerative disorders such as stroke. We have previously shown that melatonin significantly improved the perinatal brain damage caused by hypoxia-ischemia (HI) through the activation of several protective mechanisms such as restoring mitochondria status and increasing the hippocampal cell proliferation. This study assessed whether melatonin affects the Notch1 signaling pathway and Sirt3 after neonatal HI. Results show that HI significantly increased Notch1 expression both in hippocampal neurons and glial cells as well as the expression of the key proteins of the pathway NICD, HES1, and c-Myc. Melatonin significantly prevented the Notch1 signaling pathway activation induced by HI, maintaining NICD and HES1 expression to control levels. In the same neurons, melatonin also prevents the Sirt3 depletion caused by HI. In summary, this study provides new insights into the effects of melatonin on the Notch1 signaling pathway and Sirt3 in in vivo neonatal brain ischemia. We suggest that the rapid modulation of the Notch1 signaling pathway and Sirt3 induced by melatonin may support neuronal survival during ischemia.

Abstract P354: Endothelial Sirt3 deficiency and SOD2 acetylation voids female protection from hypertension

The prevalence of hypertension in early adulthood among women is 3-times lower than in men; but with aging hypertension rate increases in women much steeper, and hypertensive vascular and kidney damage is significantly higher in women. Gender-specific aspects of hypertension are poorly understood and clinical studies did not show protection by estrogen hormone therapy. We found that human hypertension is linked to hyperacetylation of critical antioxidant and metabolic mitochondrial enzymes superoxide dismutase (SOD2) and long-chain acyl dehydrogenase (LCAD) due to vascular deficiency of mitochondrial deacetylase Sirt3. We hypothesized that endothelial Sirt3 depletion leads to the loss of female protective cardiovascular phenotype and exacerbates hypertension in female compared with male mice due to hyperacetylation of mitochondrial proteins. Indeed, infusion of angiotensin II in wild-type female mice showed protection of vascular metabolism, endothelial nitric oxide and lower blood pressure compared with male littermates which was coupled with reduced acetylation of mitochondrial LCAD and SOD2 in female mice. Endothelial specific Sirt3 knockout female mice showed increased mitochondrial acetylation, exacerbated angiotensin II-induced hypertension and higher blood pressure compared with male mice which models human hypertension. Hypertension is linked to SOD2 acetylation (Circ Res. 2020;126(4):439-452) which leads to SOD2 inactivation and vascular oxidative stress. We found that endothelial specific acetylation mimetic SOD2-K68Q knock-in female mice lost antihypertensive phenotype and had higher blood pressure compared with angiotensin II-infused male mice. These studies demonstrate critical role of mitochondrial acetylation in endothelial dysfunction and hypertension suggesting that female antihypertensive phenotype can be associated with reduced mitochondrial acetylation protecting mitochondrial and endothelial functions. It is conceivable that pharmacological targeting of mitochondrial metabolism and acetylation can rescue female cardiovascular protection and improve treatment of endothelial dysfunction and hypertension.

The lncRNA HOTAIR attenuates pyroptosis of diabetic cardiomyocytes by recruiting FUS to regulate SIRT3 expression.

Diabetic cardiomyopathy (DCM) is a serious cardiovascular complication of diabetes that severely affects the quality of life of diabetic patients. Long noncoding RNAs (lncRNAs) play important roles in the pathogenesis of DCM. However, the role of the lncRNA homeobox transcript antisense RNA (HOTAIR) in the progression of DCM remains unclear. The present study aimed to investigate the role of HOTAIR in high glucose (HG)-induced pyroptosis in cardiomyocytes. The expression of the lncRNA HOTAIR, FUS, and SIRT3 in H9C2 cardiomyocytes was detected by RT-qPCR. Western blotting was used to evaluate the expression of FUS and SIRT3 as well as that of pyroptosis- and inflammation-related proteins. RT-qPCR and ELISA were used to determine the expression and secretion of IL-1β and IL-18. RNA pulldown and RIP experiments were used to validate the binding relationship among HOTAIR, FUS, and SIRT3. Flow cytometry was performed to detect pyroptosis. HG induced pyroptosis and elevated the expression of proteins associated with pyroptosis and inflammation (NLRP3, GSDMD-N, cleaved caspase-1, IL-1β, and IL-18) in cardiomyocytes. HOTAIR and SIRT3 levels were decreased in HG-exposed H9C2 cells. Additionally, overexpression of HOTAIR inhibited the HG-induced pyroptosis and inflammatory response in cardiomyocytes. HOTAIR upregulated SIRT3 expression in H9C2 cells by targeting FUS. Moreover, SIRT3 upregulation suppressed HG-mediated pyroptosis of cardiomyocytes. Notably, SIRT3 depletion reversed the inhibitory effect of HOTAIR on HG-triggered pyroptosis in cardiomyocytes. Our research indicates that HOTAIR alleviates pyroptosis in diabetic cardiomyocytes through the FUS/SIRT3 axis, providing a potential marker for the diagnosis and treatment of DCM.

Sirtuin 3 Plays a Critical Role in the Antidepressant- and Anxiolytic-like Effects of Kaempferol.

An estimated 20% of women experience depression at some point during menopause. Hormone replacement therapy (HRT), as the main therapy for depression and other menopausal syndromes, comes with a few undesirable side effects and a potential increase in cancer and cardiovascular risk. Consequently, there is a dire need for the development of new therapies to treat menopausal depression. Oxidative stress combined with the decline in sex hormones might explain the occurrence of psychological symptoms characteristic of menopause. Therefore, antioxidants have been suggested as a promising therapy for aging-associated diseases, such as menopausal depression. As a flavonoid antioxidant, kaempferol might have a potential neuroprotective action. Hence, the study was conducted to assess the potential antidepressant action of kaempferol and clarify the underlying mechanism. The results show that kaempferol has potential beneficial effects on VCD-induced rodent model of menopausal depression and produces antioxidant effects as well as increases the deacetylation of superoxide dismutase 2 (SOD2) and the protein level of Sirtuin3 (Sirt3) in the hippocampus. On the contrary, Sirt3 depletion abrogated the antidepressant- and anxiolytic-like effects as well as antioxidant effects of kaempferol. In conclusion, kaempferol might produce antidepressant effects via upregulating the expression of Sirt3, the major deacetylase in mitochondria, and subsequently activate the mitochondrial antioxidases. These findings shed some light on the use of kaempferol or vegetables and herbs that contain kaempferol as a complementary therapy for menopausal depression.

Oxidative Stress-induced Autophagy Compromises Stem Cell Viability.

Stem cell therapies have emerged as a promising treatment strategy for various diseases characterized by ischemic injury such as ischemic stroke. Cell survival after transplantation remains a critical issue. We investigated the impact of oxidative stress, being typically present in ischemically challenged tissue, on human dental pulp stem cells (hDPSC) and human mesenchymal stem cells (hMSC). We used oxygen-glucose deprivation (OGD) to induce oxidative stress in hDPSC and hMSC. OGD-induced generation of O2•- or H2O2 enhanced autophagy by inducing the expression of activating molecule in BECN1-regulated autophagy protein 1 (Ambra1) and Beclin1 in both cell types. However, hDPSC and hMSC pre-conditioning using reactive oxygen species (ROS) scavengers significantly repressed the expression of Ambra1 and Beclin1 and inactivated autophagy. O2•- or H2O2 acted upstream of autophagy, and the mechanism was unidirectional. Furthermore, our findings revealed ROS-p38-Erk1/2 involvement. Pre-treatment with selective inhibitors of p38 and Erk1/2 pathways (SB202190 and PD98059) reversed OGD effects on the expression of Ambra1 and Beclin1, suggesting that these pathways induced oxidative stress-mediated autophagy. SIRT3 depletion was found to be associated with increased oxidative stress and activation of p38 and Erk1/2 MAPKs pathways. Global ROS inhibition by NAC or a combination of polyethylene glycol-superoxide dismutase (PEG-SOD) and polyethylene glycol-catalase (PEG-catalase) further confirmed that O2•- or H2O2 or a combination of both impacts stems cell viability by inducing autophagy. Furthermore, autophagy inhibition by 3-methyladenine (3-MA) significantly improved hDPSC viability. These findings contribute to a better understanding of post-transplantation hDPSC and hMSC death and may deduce strategies to minimize therapeutic cell loss under oxidative stress.

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See article, p. 16.B-precursor acute lymphoblastic leukemia (B-ALL) relapse often involves the central nervous system (CNS). In this article, Vanner, Dobson, et al. characterize B-ALL subclones with differential CNS involvement in patient-derived xenografts. By comparing transcriptional profiles, the authors identify complement component C3 and stem cell, metabolic, and mRNA translation pathways enriched in subclones with preferential CNS residence regardless of mutational composition. These findings are validated by proteomics and by genetic or pharmacologic targeting of the candidate pathways. The protein translation inhibitor omacetaxine mepesuccinate strongly reduces CNS infiltration.See article, p. 32.In this study, Petti et al. evaluated mechanisms that contribute to the relapse of patients with acute myeloid leukemia (AML) after therapy. Bone marrow samples from presentation and relapse from six patients with normal karyotype AML were subjected to enhanced whole-genome sequencing to identify all somatic mutations and their evolution. Single-cell RNA sequencing defined transcriptional and cellular changes at relapse. Each case had a unique set of genetic and transcriptional adaptations associated with relapse, but most acquired a conserved relapse-enriched leukemia cell (RELC) signature that had features of stemness, quiescence, and adhesion.See article, p. 50.Diffuse large B-cell lymphomas (DLBCL) are dependent on anaplerotic glutaminolysis driven by SIRT3. Li et al. show that the metabolic collapse induced by SIRT3 depletion leads to marked repression of ATF4 target genes that are highly expressed in DLBCL. ATF4 is required for DLBCL cell proliferation and is translationally activated when sensing depletion of nonessential amino acids (NEAA). Reciprocally, loss of SIRT3 induces accumulation of NEAAs due to induction of autophagy, which in turn suppresses ATF4 translation, further aggravates nutrient starvation, and ultimately leads to cell death, which is further enhanced by exposure to GCN2 inhibitors.See article, p. 66.Although 80% to 90% of patients treated with CD19 CAR T-cell therapy for ALL achieve remission, half will relapse. Biomarkers predicting relapse have so far been unknown. In this study, Pulsipher et al. hypothesize that the presence of minimal residual disease detected by next-generation sequencing (NGS-MRD) after tisagenlecleucel therapy would predict relapse of both CD19+ and CD19− blasts. They demonstrate that any level of NGS-MRD positivity was highly associated with relapse risk. A combination of early loss of B-cell aplasia with NGS-MRD >0 predicted relapse with sufficient time to intervene with various approaches aimed at preventing relapse.

Mitochondrial deacetylase Sirt3 in vascular dysfunction and hypertension.

Purpose of reviewHypertension is a multifactorial disorder involving perturbations of the vasculature, the kidney, and the central nervous system. Hypertension represents a major risk factor for stroke, myocardial infarction, and heart failure. Despite treatment with multiple drugs, 37% of hypertensive patients remain hypertensive, likely due to the mechanisms contributing to blood pressure elevation that are not affected by current treatments. This review focuses on recently described novel role of mitochondrial deacetylase Sirt3 in vascular dysfunction and hypertension.Recent findingsIn the past several years, we have shown that the mitochondria are dysfunctional in hypertension; however, the role of mitochondria in the pathogenesis of hypertension remains elusive. We recently showed that patients with essential hypertension have decreased levels of the mitochondrial deacetylase Sirt3 leading to hyperacetylation of mitochondrial proteins. There is likely a causative role. Indeed, genetic deletion of Sirt3 in mice promotes vascular dysfunction and hypertension. Sirt3 depletion promotes endothelial dysfunction, increases smooth muscle cell hypertrophy, instigates vascular inflammation, and induces age-dependent hypertension.SummarySirt3 is critical for vascular cell homeostasis, however, multiple risk factors impair Sirt3 leading to mitochondrial dysfunction and vascular dysregulation which contribute to hypertension and end-organ injury. Targeting Sirt3 may represent novel therapeutic approach to improve treatment of vascular dysfunction and reduce hypertension.

Hesperetin derivative-16 attenuates CCl4-induced inflammation and liver fibrosis by activating AMPK/SIRT3 pathway

Liver fibrosis, a chronic inflammatory healing reaction, progresses to hepatocirrhosis without effective intervention. Hesperetin derivative (HD-16), a monomer compound derived from hesperitin, exerts anti-inflammatory and hepatoprotective effects against a spectrum of liver diseases. However, the anti-fibrotic potential of HD-16 in liver fibrosis and its underlying mechanism have not yet been elucidated. In this study, we investigated the anti-fibrotic effect of HD-16 on mouse liver fibrosis induced by CCl4 and on LX-2 cells (human immortalized HSCs) stimulated by TGF-β1, in vivo and in vitro. HD-16 exerted an anti-fibrotic effect via regulation of the AMPK/SIRT3 pathway. Pharmacodynamic results showed that HD-16 alleviated the degree of injury and inflammation in CCl4-induced mouse liver fibrosis. Consistently, HD-16 also effectively inhibited the expression of α-SMA, Col1α1, Col3α1, and TIMP-1 in TGF-β1-activated LX-2 cells. Mechanistically, HD-16 promoted SIRT3 expression and activity in fibrotic liver and activated LX-2 cells. Furthermore, SIRT3 depletion attenuated the anti-fibrotic effects of HD-16. Intriguingly, HD-16 increased AMPK phosphorylation, whereas inhibition of SIRT3 expression did not affect AMPK phosphorylation. In contrast, AMPK silencing suppressed SIRT3 expression, suggesting that SIRT3 is a downstream target of AMPK in liver fibrosis. Overall, HD-16 attenuated CCl4-induced liver inflammation and fibrosis by activating the AMPK/SIRT3 pathway, and HD-16 may be a potential anti-fibrotic compound in the treatment of liver fibrosis.

Translational Activation of ATF4 through Mitochondrial Anaplerotic Metabolic Pathways Is Required for DLBCL Growth and Survival.

Diffuse large B-cell lymphomas (DLBCL) are broadly dependent on anaplerotic metabolism regulated by mitochondrial SIRT3. Herein we find that translational upregulation of ATF4 is coupled with anaplerotic metabolism in DLBCLs due to nutrient deprivation caused by SIRT3 driving rapid flux of glutamine into the tricarboxylic acid (TCA) cycle. SIRT3 depletion led to ATF4 downregulation and cell death, which was rescued by ectopic ATF4 expression. Mechanistically, ATF4 translation is inhibited in SIRT3-deficient cells due to the increased pools of amino acids derived from compensatory autophagy and decreased glutamine consumption by the TCA cycle. Absence of ATF4 further aggravates this state through downregulation of its target genes, including genes for amino acid biosynthesis and import. Collectively, we identify a SIRT3-ATF4 axis required to maintain survival of DLBCL cells by enabling them to optimize amino acid uptake and utilization. Targeting ATF4 translation can potentiate the cytotoxic effect of SIRT3 inhibitor to DLBCL cells. SIGNIFICANCE: We discovered the link between SIRT3 and ATF4 in DLBCL cells, which connected lymphoma amino acid metabolism with ATF4 translation via metabolic stress signals. SIRT3-ATF4 axis is required in DLBCL cells regardless of subtype, which indicates a common metabolic vulnerability in DLBCLs and can serve as a therapeutic target.This article is highlighted in the In This Issue feature, p. 1.

Abstract LB014: Translational activation of ATF4 through mitochondrial anaplerotic metabolic pathways is required for DLBCL growth and survival

Abstract Diffuse large B-cell lymphomas (DLBCLs) tolerate various forms of cellular stress associated with their rapid proliferation and depletion of nutrients in their microenvironment. Our previous finding discovered that DLBCLs are broadly dependent mitochondrial SIRT3 as a critical source of non-oncogene addiction in DLBCL. SIRT3 promotes tumorigenesis in DLBCL, where it is required for glutamine fueled anaplerosis, and its loss of function leads to tumor suppressive autophagy. However, it is not known why SIRT3 deficient DLBCL cells are so vulnerable to such metabolic changes and autophagy, which points to potentially novel and critical nutrient regulatory circuits occurring in this disease. We set out to identify downstream signals induced by SIRT3 deficiency in DLBCL cells in order to gain insight into how SIRT3 could interface with nutrient flux stress response pathways to support tumorigenesis of DLBCLs. First, we carried out RNA sequencing study in three DLBCL cell lines representing different subtypes of DLBCLs. The data showed that all SIRT3 deficient DLBCL cells experienced transcriptional inhibitions of ATF4 target genes. We further observed that ATF4 protein was decreased due to the translational inhibition in SIRT3 deficient DLBCL cells, which indicates that ATF4 may play a role downstream of SIRT3 contributing to DLBCL cell proliferation. Secondly, we proved that ATF4 is indeed required to DLBCL cells' proliferation. ATF4 target genes are more expressed in DLBCL tumor cells than normal germinal center B cells. Loss of ATF4 induced proliferation arrest as SIRT3 depletion and over-expression of ATF4 can partially rescue the proliferation and viability inhibited by SIRT3 deficiency. Consistently, we observed that loss of SIRT3 led to ATF4 reduction in the vavP-Bcl2 mouse lymphoma model. Mechanistically, we identified that ATF4 functions downstream of SIRT3 through the metabolic cascade of GDH-TCA cycle-autophagy. GDH and DMKG can rescue the ATF4 protein decreased by SIRT3 depletion. Blockage of autophagy with chloroquine or knocking down ATG5 can also neutralize SIRT3's inhibition on ATF4. Furthermore, we discovered that ATF4's translation is highly sensitive to nutrient/amino acid levels in DLBCL cells as a stress signal for cell survival. However, ATF4 translation failed to respond to glutamine starvation in SIRT3 depleted DLBCL cells. SIRT3 deficiency underwent drastic changes of amino acid levels because of the TCA cycle inhibition and autophagy activation, which interfered the ATF4's translation and can lead to deleterious metabolic stresses. Collectively, we identify a novel SIRT3-ATF4 axis required to maintain survival of DLBCL cells by enabling them to optimize amino acid utilization. Lack of this coordination is lethal to DLBCL cells, exposing a critical and exploitable metabolic vulnerability. Citation Format: Meng Li, Matthew R. Teater, Jun Young Hong, Cihangir Duy, Hao Shen, Ling Wang, Zhengming Chen, Leandro Cerchietti, Hening Lin, Ari Melnick. Translational activation of ATF4 through mitochondrial anaplerotic metabolic pathways is required for DLBCL growth and survival [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB014.

Chronic High Fat Diet Intake Impairs Hepatic Metabolic Parameters in Ovariectomized Sirt3 KO Mice.

High fat diet (HFD) is an important factor in the development of metabolic diseases, with liver as metabolic center being highly exposed to its influence. However, the effect of HFD-induced metabolic stress with respect to ovary hormone depletion and sirtuin 3 (Sirt3) is not clear. Here we investigated the effect of Sirt3 in liver of ovariectomized and sham female mice upon 10 weeks of feeding with standard-fat diet (SFD) or HFD. Liver was examined by Folch, gas chromatography and lipid hydroperoxide analysis, histology and oil red staining, RT-PCR, Western blot, antioxidative enzyme and oxygen consumption analyses. In SFD-fed WT mice, ovariectomy increased Sirt3 and fatty acids synthesis, maintained mitochondrial function, and decreased levels of lipid hydroperoxides. Combination of ovariectomy and Sirt3 depletion reduced pparα, Scd-1 ratio, MUFA proportions, CII-driven respiration, and increased lipid damage. HFD compromised CII-driven respiration and activated peroxisomal ROS scavenging enzyme catalase in sham mice, whereas in combination with ovariectomy and Sirt3 depletion, increased body weight gain, expression of NAFLD- and oxidative stress-inducing genes, and impaired response of antioxidative system. Overall, this study provides evidence that protection against harmful effects of HFD in female mice is attributed to the combined effect of female sex hormones and Sirt3, thus contributing to preclinical research on possible sex-related therapeutic agents for metabolic syndrome and associated diseases.

Human SIRT2 and SIRT3 deacetylases function in DNA homologous recombinational repair.

SIRT2 and SIRT3 protein deacetylases maintain genome integrity and stability. However, their mechanisms for maintaining the genome remain unclear. To examine the roles of SIRT2 and SIRT3 in DSB repair, I-SceI-based GFP reporter assays for HR, single-strand annealing (SSA) and nonhomologous end joining (NHEJ) repair were performed under SIRT2- or SIRT3-depleted conditions. SIRT2 or SIRT3 depletion inhibited HR repair equally to RAD52 depletion, but did not affect SSA and NHEJ repairs. SIRT2 or SIRT3 depletion disturbed the recruitment of RAD51 to DSB sites, an essential step for RAD51-dependent HR repair, but not directly through RAD52 deacetylation. SIRT2 or SIRT3 depletion decreased the colocalization of γH2AX foci with RPA1, and thus, they might be involved in initiating DSB end resection for the recruitment of RAD51 to DSB sites at an early step in HR repair. These results show the novel underlying mechanism of the SIRT2 and SIRT3 functions in HR for genome stability.

SIRT3 consolidates heterochromatin and counteracts senescence.

Sirtuin 3 (SIRT3) is an NAD+-dependent deacetylase linked to a broad range of physiological and pathological processes, including aging and aging-related diseases. However, the role of SIRT3 in regulating human stem cell homeostasis remains unclear. Here we found that SIRT3 expression was downregulated in senescent human mesenchymal stem cells (hMSCs). CRISPR/Cas9-mediated depletion of SIRT3 led to compromised nuclear integrity, loss of heterochromatin and accelerated senescence in hMSCs. Further analysis indicated that SIRT3 interacted with nuclear envelope proteins and heterochromatin-associated proteins. SIRT3 deficiency resulted in the detachment of genomic lamina-associated domains (LADs) from the nuclear lamina, increased chromatin accessibility and aberrant repetitive sequence transcription. The re-introduction of SIRT3 rescued the disorganized heterochromatin and the senescence phenotypes. Taken together, our study reveals a novel role for SIRT3 in stabilizing heterochromatin and counteracting hMSC senescence, providing new potential therapeutic targets to ameliorate aging-related diseases.

Role of Sirt3 in Differential Sex-Related Responses to a High-Fat Diet in Mice.

Metabolic homeostasis is differently regulated in males and females. Little is known about the mitochondrial Sirtuin 3 (Sirt3) protein in the context of sex-related differences in the development of metabolic dysregulation. To test our hypothesis that the role of Sirt3 in response to a high-fat diet (HFD) is sex-related, we measured metabolic, antioxidative, and mitochondrial parameters in the liver of Sirt3 wild-type (WT) and knockout (KO) mice of both sexes fed with a standard or HFD for ten weeks. We found that the combined effect of Sirt3 and an HFD was evident in more parameters in males (lipid content, glucose uptake, pparγ, cyp2e1, cyp4a14, Nrf2, MnSOD activity) than in females (protein damage and mitochondrial respiration), pointing towards a higher reliance of males on the effect of Sirt3 against HFD-induced metabolic dysregulation. The male-specific effects of an HFD also include reduced Sirt3 expression in WT and alleviated lipid accumulation and reduced glucose uptake in KO mice. In females, with a generally higher expression of genes involved in lipid homeostasis, either the HFD or Sirt3 depletion compromised mitochondrial respiration and increased protein oxidative damage. This work presents new insights into sex-related differences in the various physiological parameters with respect to nutritive excess and Sirt3.

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HomeCirculation ResearchVol. 126, No. 4In This Issue Free AccessIn BriefPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessIn BriefPDF/EPUBIn This Issue Ruth Williams Ruth WilliamsRuth Williams Search for more papers by this author Originally published13 Feb 2020https://doi.org/10.1161/RES.0000000000000326Circulation Research. 2020;126:413is related toMitochondrial Deacetylase Sirt3 Reduces Vascular Dysfunction and Hypertension While Sirt3 Depletion in Essential Hypertension Is Linked to Vascular Inflammation and Oxidative StressIncreased Drp1 Acetylation by Lipid Overload Induces Cardiomyocyte Death and Heart Dysfunctionis related toBMX Represses Thrombin-PAR1–Mediated Endothelial Permeability and Vascular Leakage During Early SepsisSirt3 Reduces Hypertension and Vascular Dysfunction (p 439)Boosting Sirt3 could be a novel treatment strategy for hypertension, suggest Dikalova et al.Download figureDownload PowerPointHypertension, which affects approximately a third of the global adult population, is a risk factor for stroke, myocardial infarction, and heart failure. Although blood pressure-lowering treatments are widely available, in approximately one third of patients, the condition remains uncontrolled. A thorough understanding of the complex pathophysiology of the condition would facilitate the search for much needed alternative treatments. To that end, Dikalova and colleagues have investigated Sirt3, an enzyme that tends to be at lower-than-usual levels in patients with hypertension and that regulates metabolic and antioxidant functions—both of which, if disturbed, can contribute to vascular dysfunction. The team showed that mice genetically engineered to overexpress Sirt3 had healthier blood vessels and lower blood pressure than control animals when subjected to experimentally induced hypertension. By contrast, Sirt3 depletion was shown to cause vascular inflammation and increased signs of vascular aging in mice. The team also confirmed the link between low Sirt3 levels and hypertension in humans. It is not clear why Sirt3 levels are low in certain people, but nevertheless, the findings suggest that boosting this enzyme may be a potential therapy for hypertension, say the authors.Lipid Overload Acetylates Drp1 in the Heart (p 456)Hu et al discover a mechanism by which lipid overload drives heart cell dysfunction.Download figureDownload PowerPointThe main energy source of the heart is fatty acid metabolism, but excessive lipids—resulting from diet-induced dyslipidemia, for example—can cause cardiomyocyte dysfunction. It’s known that lipid overload in the heart can cause increased activity of Drp1 (dynamin-related protein 1)—an enzyme that directs mitochondrial fission. But exactly how Drp1 becomes activated is unclear. In mice fed a high-fat diet, Hu and colleagues confirm that Drp1 activity and mitochondrial fission are abnormally increased, and that there are signs of heart dysfunction. They also show similar effects of a high-fat diet in monkeys. While levels of Drp1 mRNA were not altered in the mouse hearts, Drp1 protein acetylation was increased. The team went on to perform experiments on cultured rat cardiomyocytes, showing that incubation with the saturated fatty acid palmitate led to acetylation of Drp1 and thus its activation—resulting in excess mitochondrial fission and reduced cell viability. Mutation of Drp1 to prevent its acetlyation, by contrast, protected the cells. Together, the results reveal how dyslipidemia can contribute to heart cell dysfunction and suggest that Drp1 activity or acetylation state could be novel targets for treating obesity-related heart disease.BMX Represses Thrombin-PAR1 and Sepsis (p 471)Li et al show that signaling kinase BMX represses vascular leakage during sepsis.Download figureDownload PowerPointDuring an infection or injury, blood vessels become leaky to allow white blood cells to reach the sites of invasion or damage. But in sepsis, this normal inflammatory response becomes excessive and can lead to organ failure and death. The blood factor thrombin is a driver of vessel endothelium permeability, acting through its receptor, PAR1 (protease-activated receptor 1), on endothelial cells. But downstream molecular details of thrombin-induced endothelial permeability are lacking. Now, Li and colleagues show that a protein called BMX (bone marrow kinase on the X chromosome), which is highly expressed in endothelial cells and was known to interact with PAR1, actively suppresses thrombin-induced permeability. Studying mice with and without BMX after experimentally induced sepsis, the team showed that a lack of BMX exacerbated the condition, increasing vessel leakage. They also showed in cultured cells that BMX repressed thrombin-PAR1 signaling by phosphorylating and internalizing the receptor causing its deactivation. Indeed, PAR1 inhibition could reduce endothelial permeability in the sepsis-stricken, BMX-lacking mice and improve their survival. These results suggest that boosting BMX could be a treatment strategy for excessive or uncontrolled vascular leakage. Previous Back to top Next FiguresReferencesRelatedDetailsRelated articlesMitochondrial Deacetylase Sirt3 Reduces Vascular Dysfunction and Hypertension While Sirt3 Depletion in Essential Hypertension Is Linked to Vascular Inflammation and Oxidative StressAnna E. Dikalova, et al. Circulation Research. 2020;126:439-452Increased Drp1 Acetylation by Lipid Overload Induces Cardiomyocyte Death and Heart DysfunctionQingxun Hu, et al. Circulation Research. 2020;126:456-470BMX Represses Thrombin-PAR1–Mediated Endothelial Permeability and Vascular Leakage During Early SepsisZhao Li, et al. Circulation Research. 2020;126:471-485 February 14, 2020Vol 126, Issue 4 Advertisement Article InformationMetrics © 2020 American Heart Association, Inc.https://doi.org/10.1161/RES.0000000000000326 Originally publishedFebruary 13, 2020 PDF download Advertisement

Mitochondrial Deacetylase Sirt3 Reduces Vascular Dysfunction and Hypertension While Sirt3 Depletion in Essential Hypertension Is Linked to Vascular Inflammation and Oxidative Stress.

Hypertension represents a major risk factor for stroke, myocardial infarction, and heart failure and affects 30% of the adult population. Mitochondrial dysfunction contributes to hypertension, but specific mechanisms are unclear. The mitochondrial deacetylase Sirt3 (Sirtuin 3) is critical in the regulation of metabolic and antioxidant functions which are associated with hypertension, and cardiovascular disease risk factors diminish Sirt3 level. We hypothesized that reduced Sirt3 expression contributes to vascular dysfunction in hypertension, but increased Sirt3 protects vascular function and decreases hypertension. To test the therapeutic potential of targeting Sirt3 expression, we developed new transgenic mice with global Sirt3OX (Sirt3 overexpression), which protects from endothelial dysfunction, vascular oxidative stress, and hypertrophy and attenuates Ang II (angiotensin II) and deoxycorticosterone acetate-salt induced hypertension. Global Sirt3 depletion in Sirt3-/- mice results in oxidative stress due to hyperacetylation of mitochondrial superoxide dismutase (SOD2), increases HIF1α (hypoxia-inducible factor-1), reduces endothelial cadherin, stimulates vascular hypertrophy, increases vascular permeability and vascular inflammation (p65, caspase 1, VCAM [vascular cell adhesion molecule-1], ICAM [intercellular adhesion molecule-1], and MCP1 [monocyte chemoattractant protein 1]), increases inflammatory cell infiltration in the kidney, reduces telomerase expression, and accelerates vascular senescence and age-dependent hypertension; conversely, increased Sirt3 expression in Sirt3OX mice prevents these deleterious effects. The clinical relevance of Sirt3 depletion was confirmed in arterioles from human mediastinal fat in patients with essential hypertension showing a 40% decrease in vascular Sirt3, coupled with Sirt3-dependent 3-fold increases in SOD2 acetylation, NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activity, VCAM, ICAM, and MCP1 levels in hypertensive subjects compared with normotensive subjects. We suggest that Sirt3 depletion in hypertension promotes endothelial dysfunction, vascular hypertrophy, vascular inflammation, and end-organ damage. Our data support a therapeutic potential of targeting Sirt3 expression in vascular dysfunction and hypertension.

A novel metadherinΔ7 splice variant enhances triple negative breast cancer aggressiveness by modulating mitochondrial function via NFĸB-SIRT3 axis.

Metadherin (MTDH) expression inversely correlates with prognosis of several cancers including mammary carcinomas. In this work, we identified a novel splice variant of MTDH with exon7 skipping (MTDHΔ7) and its levels were found significantly high in triple negative breast cancer (TNBC) cells and in patients diagnosed with TNBC. Selective overexpression of MTDHΔ7 in MDA-MB-231 and BT-549 cells enhanced proliferation, invasion, and epithelial-to-mesenchymal (EMT) transition markers in comparison to its wildtype counterpart. In contrast, knockdown of MTDHΔ7 induced antiproliferative/antiinvasive effects. Mechanistically, MTDH-NFĸB-p65 complex activated SIRT3 transcription by binding to its promoter that in turn enhanced MnSOD levels and promoted EMT in TNBC cells. Intriguingly, mitochondrial OCR through Complex-I and -IV, and glycolytic rate (ECAR) were significantly high in MDA-MB-231 cells stably expressing MTDHΔ7. While depletion of SIRT3 inhibited MTDH-Wt/Δ7-induced OCR and ECAR, knockdown of MnSOD inhibited only ECAR. In addition, MTDH-Wt/Δ7-mediated pro-proliferative/-invasive effects were greatly obviated with either siSIRT3 or siMnSOD in these cells. The functional relevance of MTDHΔ7 was further proved under in vivo conditions in an orthotopic mouse model of breast cancer. Mice bearing labeled MDA-MB-231 cells stably expressing MTDHΔ7 showed significantly more tumor growth and metastatic ability to various organs in comparison to MTDH-Wt bearing mice. Taken together, MTDHΔ7 promotes TNBC aggressiveness through enhanced mitochondrial biogenesis/function, which perhaps serves as a biomarker.

Abstract P3018: Sirt3 Depletion in Human Essential Hypertension is Linked to Vascular Inflammation and Oxidative Stress While Endothelial Specific Sirt3 Depletion in Mice Promotes Vascular Dysfunction and Increases Hypertension

Hypertension represents a major risk factor for stroke, myocardial infarction, and heart failure and affects 30% of adult population. Vascular dysfunction is crucial in hypertension pathophysiology and exhibits bidirectional relationship. Metabolic disorders and oxidative stress contribute to vascular dysfunction, and mitochondrial deacetylase Sirt3 is critical in the regulation of metabolic and antioxidant functions. We hypothesized that reduced Sirt3 expression contributes to vascular dysfunction and essential hypertension. We studied Sirt3 in arterioles from human mediastinal fat in patients with essential hypertension compared with normotensive subjects. Pathophysiological role of vascular Sirt3 depletion was studied in mice with tamoxifen-inducible endothelial specific Sirt3 depletion (Ec Sirt3KO ). For the first time, we showed a 40% decrease in vascular Sirt3 level and 400% increase in SOD2 acetylation in hypertensive subjects which was linked to increased oxidative stress measured by superoxide overproduction and vascular inflammation due to elevated NfKB activity, VCAM, ICAM and MCP-1 levels. Interestingly, global Sirt3 depletion in mice increases blood pressure, inactivates key mitochondrial antioxidant SOD2 due to acetylation, increases vascular p65, VCAM, ICAM and MCP1, and increased T cell infiltration in kidney, induces cell-senescence and promotes vascular aging while global Sirt3 overexpression prevents these deleterious effects. We tested if Ec Sirt3KO mice have vascular dysfunction and hypertension. Both basal and angiotensin II-induced blood pressure was increased in Ec Sirt3KO mice accompanied by endothelial dysfunction and vascular O 2 • overproduction. Treatment of Ec Sirt3KO mice with SOD2-mimetic mitoTEMPO reduced vascular inflammation, markers of cell-senescence and vascular aging to the wild-type control levels while treatment of Ang II-infused Ec Sirt3KO mice partially rescues from vascular inflammation and attenuates accelerated vascular aging. We suggest that Sirt3 depletion in hypertension promotes both endothelial oxidative stress and metabolic dysfunction. Our data support a therapeutic potential of targeting Sirt3 expression in vascular dysfunction and hypertension.

Non-oncogene Addiction to SIRT3 Plays a Critical Role in Lymphomagenesis

Diffuse large B cell lymphomas (DLBCLs) are genetically heterogeneous and highly proliferative neoplasms derived from germinal center (GC) B cells. Here, we show that DLBCLs are dependent on mitochondrial lysine deacetylase SIRT3 for proliferation, survival, self-renewal, and tumor growth invivo regardless of disease subtype and genetics. SIRT3 knockout attenuated B cell lymphomagenesis in VavP-Bcl2 mice without affecting normal GC formation. Mechanistically, SIRT3 depletion impaired glutamine flux to the TCA cycle via glutamate dehydrogenase and reduction in acetyl-CoA pools, which in turn induce autophagy and cell death. We developed a mitochondrial-targeted class I sirtuin inhibitor, YC8-02, which phenocopied the effects of SIRT3 depletion and killed DLBCL cells. SIRT3 is thus a metabolic non-oncogene addiction and therapeutic target for DLBCLs.

Mitochondrial Deacetylase Sirt3 as a New Target in Cardiovascular Diseases

Multiple risk factors such as aging, vascular dysfunction, metabolic disorders and hypertension contribute to the pathogenesis of heart failure. The convergent mechanism that may underlie the interplay of these major risk factors is not clear but may provide novel strategies for treatment. Clinical studies show that Sirtuin 3 (Sirt3) expression declines by 40% by age 65 and sedentary lifestyle paralleling the increased incidence of cardiovascular diseases and heart failure while aerobic exercise increases Sirt3 expression and attenuates age‐dependent Sirt3 decline. Meanwhile, the pathophysiological role of Sirt3 depletion is not clear. Mitochondrial deacetylase Sirt3 is critical in regulation of mitochondrial metabolism and it activates a key antioxidant enzyme, superoxide dismutase 2 by deacetylation of specific lysine residues. We hypothesized that Sirt3 plays critical role in vascular dysfunction and hypertension. To test this hypothesis, we have developed new tamoxifen‐inducible endothelium specific Sirt3 knockout (EcSirt3KO), endothelial Sirt3 overexpressing (EcSirt3OX), smooth muscle Sirt3 knockout (SmcSirt3KO), smooth muscle Sirt3 overexpressing (SmcSirt3OX) and global Sirt3 overexpressing (Sirt3OX) mice on C57Bl/6J background, and examined the effect of Sirt3 expression on vascular dysfunction and angiotensin II‐induced hypertension. Sirt3 depletion in EcSirt3KO and SmcSirt3KO mice raises basal vascular permeability in the heart by 2‐fold, reduces endothelial NO, increases blood pressure and accelerates vascular aging compared with wild‐type mice. Angiotensin II infusion in EcSirt3KO and SmcSirt3KO mice caused vascular hyperpermeability, increased vascular hypertrophy, exacerbated endothelial dysfunction and hypertension. Meanwhile, Sirt3 overexpression attenuates vascular aging, normalizes vascular permeability, diminishes vascular inflammation, inhibits vascular oxidative stress, preserves endothelial‐dependent relaxation, reduces vascular hypertrophy and attenuates hypertension in Sham and angiotensin II‐infused EcSirt3OX and SmcSirt3OX mice compared with the wild‐type littermates. We suggest that Sirt3 is central in redox and metabolic regulations of smooth muscle and endothelial cells. As vascular permeability increases, the access of cytokines, inflammatory cells and LDL to tissue is greater contributing to cardiac inflammation, altered tissue remodeling, hypertrophy and dysfunction. Our data support a therapeutic potential of targeting Sirt3 in cardiovascular dysfunction and hypertension which can improve treatment of the heart failure.Support or Funding InformationThis work was supported by funding from National Institute of Health (NHLBI 1R01HL124116) and American Heart Association (16GRNT31230017).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.