Activation Of Silent Information Regulator 1 Research Articles

SIRT1 antagonizes liver fibrosis by blocking hepatic stellate cell activation in mice.

Hepatic stellate cells (HSCs) are a major source of fibrogenesis in the liver, contributing to cirrhosis. When activated, HSCs transdifferentiate into myofibroblasts and undergo profound functional alterations paralleling an overhaul of the transcriptome, the mechanism of which remains largely undefined. We investigated the involvement of the class III deacetylase sirtuin [silent information regulator 1 (SIRT1)] in HSC activation and liver fibrosis. SIRT1 levels were down-regulated in the livers in mouse models of liver fibrosis, in patients with cirrhosis, and in activated HSCs as opposed to quiescent HSCs. SIRT1 activation halted, whereas SIRT1 inhibition promoted, HSC transdifferentiation into myofibroblasts. Liver fibrosis was exacerbated in mice with HSC-specific deletion of SIRT1 [conditional knockout (cKO)], receiving CCl4 (1 mg/kg) injection or subjected to bile duct ligation, compared to wild-type littermates. SIRT1 regulated peroxisome proliferator activated receptor γ (PPARγ) transcription by deacetylating enhancer of zeste homolog 2 (EZH2) in quiescent HSCs. Finally, EZH2 inhibition or PPARγ activation ameliorated fibrogenesis in cKO mice. In summary, our data suggest that SIRT1 plays an essential role guiding the transition of HSC phenotypes.-Li, M., Hong, W., Hao, C., Li, L., Wu, D., Shen, A., Lu, J., Zheng, Y., Li, P., Xu, Y. SIRT1 antagonizes liver fibrosis by blocking hepatic stellate cell activation in mice.

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) 24hours 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 (1hour) modulation of SIRT1 and its downstream targets, and the consequences on necrosis, apoptosis, autophagy, and glial cell activation. We found that melatonin administered 5minutes after the ischemic insult significantly reduced necrotic cell death assessed 1hour 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.

Effects of activating silent information regulator 1 on early kidney damage in rats with severe burn

Objective: To investigate the effects of activating silent information regulator 1 (SIRT1) on the early kidney damage in rats with severe burn. Methods: Thirty healthy male SD rats were divided into sham injury group (SI), pure burn group (PB), and SIRT1 activator group (SA) according to the random number table, with 10 rats in each group. Rats in groups PB and SA were inflicted with 30% total body surface area full-thickness scald (hereinafter referred to as burn) on the back. Immediately after injury, rats in group PB were intraperitoneally injected with normal saline in the dosage of 50 mL/kg, and those in group SA with 1 mg/mL (final mass concentration) resveratrol in the dosage of 50 mL/kg. Rats in group SI were sham injured and intraperitoneally injected with normal saline in the dosage of 50 mL/kg immediately after injury. Kidney tissue and abdominal aorta blood of rats in the three groups were collected at 24 hours after injury. The morphology of kidney tissue was observed after HE staining. The serum content of creatinine and urea nitrogen was determined with enzyme-linked immunosorbent assay. Protein expressions of SIRT1, Bax, and Bcl-2 in kidney tissue were determined with Western blotting. mRNA expressions of tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and IL-10 in kidney tissue were determined with real-time fluorescent quantitative reverse transcription polymerase chain reaction. Data were processed with one-way analysis of variance and LSD-t test. Results: (1) In rats of group SI, structures of kidney tubules and glomeruli were intact. In rats of group PB, structures of kidney tubules were not clear with casts in them, and glomeruli showed pyknosis. In rats of group SA, structures of kidney tubules were relatively intact, and the pyknosis of glomeruli were slighter as compared with that of group PB with fewer glomeruli showing pyknosis. (2) The serum content of creatinine and urea nitrogen in rats of group PB was (67±14) μmol/L and (22.0±4.4) mmol/L, respectively, which was significantly higher than that of group SI [(28±7) μmol/L and (5.5±1.2) mmol/L respectively, with t values respectively 6.07 and 11.53, P values below 0.01]. The serum content of creatinine and urea nitrogen in rats of group SA was (39±9) μmol/L and (14.1±1.7) mmol/L, respectively, significantly lower than that of group PB (with t values respectively 4.09 and 4.17, P values below 0.01). (3) Compared with those of group SI, protein expressions of SIRT1 and Bcl-2 in kidney tissue of rats in group PB were significantly decreased (with t values respectively 16.32 and 19.58, P values below 0.01), while the protein expression of Bax was significantly increased (t=5.98, P<0.01). Compared with those of group PB, protein expressions of SIRT1 and Bcl-2 in kidney tissue of rats in group SA were significantly increased (with t values respectively 6.94 and 5.37, P values below 0.01), while the protein expression of Bax was significantly decreased (t=3.44, P<0.01). (4) mRNA expressions of TNF-α, IL-1β, and IL-10 in kidney tissue of rats in group PB were 17.0±4.0, 2.27±0.59, and 2.5±0.9, respectively, significantly higher than those of group SI (1.0, 1.00, and 1.0, respectively, with t values from 3.27 to 8.93, P<0.05 or P<0.01). mRNA expressions of TNF-α and IL-1β in kidney tissue of rats in group SA were 6.8±1.2 and 1.18±0.26, respectively, significantly lower than those of group PB (with t values respectively 4.59 and 4.32, P values below 0.01). mRNA expression of IL-10 in kidney tissue of rats in group SA was 5.0±1.0, significantly higher than that of group PB (t=5.51, P<0.01). Conclusions: Activating SIRT1 on early stage of severe burn in rats can decrease levels of creatinine and urea nitrogen, thus improving the kidney function. It can down-regulate the protein expression of Bax and up-regulate the protein expression of Bcl-2, thus reducing the apoptosis in kidney tissue. Meanwhile, it can inhibit expressions of TNF-α and IL-1β and promote the expression of IL-10, thus alleviating the inflammatory response in kidney.

AMPK activator acadesine fails to alleviate isoniazid-caused mitochondrial instability in HepG2 cells.

Isoniazid (INH) is a first-line antituberculosis drug that is adversely associated with hepatotoxicity. Recently, impairment of mitochondrial homeostasis involved in this side effect has been noticed. Mitochondrial homeostasis is achieved by the balance between the generation of functional mitochondria by biogenesis and elimination of dysfunctional mitochondria by autophagy. AMP-activated protein kinase (AMPK) can maintain mitochondrial stability through positive control of these two processes. In this study, we showed that AMPK activator acadesine (AICAR) alleviated INH-caused impairment of mitochondrial biogenesis by activation of silent information regulator two ortholog 1 (SIRT1)-peroxisome proliferator-activated receptor γ coactivator 1α (PGC1 α) pathway in HepG2 cells. However, mitochondrial instability and apoptosis were caused by AICAR along with an unexpected decrease in INH-induced cytoprotective autophagy. Therefore, AICAR failed to alleviate INH-caused mitochondrial instability in HepG2 cells due to its inhibitory effect on autophagy induced by INH. Copyright © 2017 John Wiley & Sons, Ltd.

Diallyl trisulfide ameliorates myocardial ischemia-reperfusion injury by reducing oxidative stress and endoplasmic reticulum stress-mediated apoptosis in type 1 diabetic rats: role of SIRT1 activation.

Diallyl trisulfide (DATS) protects against apoptosis during myocardial ischemia-reperfusion (MI/R) injury in diabetic state, although the underlying mechanisms remain poorly defined. Previously, we and others demonstrated that silent information regulator 1 (SIRT1) activation inhibited oxidative stress and endoplasmic reticulum (ER) stress during MI/R injury. We hypothesize that DATS reduces diabetic MI/R injury by activating SIRT1 signaling. Streptozotocin (STZ)-induced type 1 diabetic rats were subjected to MI/R surgery with or without perioperative administration of DATS (40mg/kg). We found that DATS treatment markedly improved left ventricular systolic pressure and the first derivative of left ventricular pressure, reduced myocardial infarct size as well as serum creatine kinase and lactate dehydrogenase activities. Furthermore, the myocardial apoptosis was also suppressed by DATS as evidenced by reduced apoptotic index and cleaved caspase-3 expression. However, these effects were abolished by EX527 (the inhibitor of SIRT1 signaling, 5mg/kg). We further found that DATS effectively upregulated SIRT1 expression and its nuclear distribution. Additionally, PERK/eIF2α/ATF4/CHOP-mediated ER stress-induced apoptosis was suppressed by DATS treatment. Moreover, DATS significantly activated Nrf-2/HO-1 antioxidant signaling pathway, thus reducing Nox-2/4 expressions. However, the ameliorative effects of DATS on oxidative stress and ER stress-mediated myocardial apoptosis were inhibited by EX527 administration. Taken together, these data suggest that perioperative DATS treatment effectively ameliorates MI/R injury in type 1 diabetic setting by enhancing cardiac SIRT1 signaling. SIRT1 activation not only upregulated Nrf-2/HO-1-mediated antioxidant signaling pathway but also suppressed PERK/eIF2α/ATF4/CHOP-mediated ER stress level, thus reducing myocardial apoptosis and eventually preserving cardiac function.

Magnolol attenuates the inflammation and apoptosis through the activation of SIRT1 in experimental stroke rats.

Silent information regulator 1 (SIRT1), a histone deacetylase, plays a protective role in ischemic brain injury. Previous studies have shown that magnolol has a beneficial effect on ischemic stroke; however, the role of SIRT1 in the protective effect of magnolol against cerebral ischemia has not been investigated. We used a middle cerebral artery occlusion model of stroke in rats. Before stroke induction, the rats received intraperitoneal injections of magnolol with or without the SIRT1 inhibitor, EX527. Brain water content, neurological score, and infarct volume were measured. Moreover, the levels of the proinflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were measured. Western blot analysis was performed to detect Ac-FOXO1, SIRT1, bax, and Bcl-2 expression. Magnolol exerted a beneficial effect on cerebral ischemia, as indicated by reduced brain edema, decreased infarct volume, and improved neurological score. Magnolol had an anti-inflammatory effect mediated by a decrease in the expression of IL-1β and TNF-α in the brain tissue. Additionally, magnolol down-regulated bax and Ac-FOXO1 expression and up-regulated Bcl-2 and SIRT1 expression. This effect of magnolol was abolished by EX527 treatment. In conclusion, our data clearly indicate that magnolol modulates brain injury caused by ischemic stroke by inhibiting inflammatory cytokines and apoptosis through SIRT1 activation.

SIRT1 Activation by Resveratrol Alleviates Cardiac Dysfunction via Mitochondrial Regulation in Diabetic Cardiomyopathy Mice.

Background Diabetic cardiomyopathy (DCM) is a major threat for diabetic patients. Silent information regulator 1 (SIRT1) has a regulatory effect on mitochondrial dynamics, which is associated with DCM pathological changes. Our study aims to investigate whether resveratrol, a SRIT1 activator, could exert a protective effect against DCM. Methods and Results Cardiac-specific SIRT1 knockout (SIRT1KO) mice were generated using Cre-loxP system. SIRT1KO mice displayed symptoms of DCM, including cardiac hypertrophy and dysfunction, insulin resistance, and abnormal glucose metabolism. DCM and SIRT1KO hearts showed impaired mitochondrial biogenesis and function, while SIRT1 activation by resveratrol reversed this in DCM mice. High glucose caused increased apoptosis, impaired mitochondrial biogenesis, and function in cardiomyocytes, which was alleviated by resveratrol. SIRT1 deletion by both SIRT1KO and shRNA abolished the beneficial effects of resveratrol. Furthermore, the function of SIRT1 is mediated via the deacetylation effect on peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), thus inducing increased expression of nuclear respiratory factor 1 (NRF-1), NRF-2, estrogen-related receptor-α (ERR-α), and mitochondrial transcription factor A (TFAM). Conclusions Cardiac deletion of SIRT1 caused phenotypes resembling DCM. Activation of SIRT1 by resveratrol ameliorated cardiac injuries in DCM through PGC-1α-mediated mitochondrial regulation. Collectively, SIRT1 may serve as a potential therapeutic target for DCM.

The Neuroprotective Effects of SIRT1 on NMDA-Induced Excitotoxicity.

Silent information regulator 1 (SIRT1), an NAD+-dependent deacetylase, is involved in the regulation of gene transcription, energy metabolism, and cellular aging and has become an important therapeutic target across a range of diseases. Recent research has demonstrated that SIRT1 possesses neuroprotective effects; however, it is unknown whether it protects neurons from NMDA-mediated neurotoxicity. In the present study, by activation of SIRT1 using resveratrol (RSV) in cultured cortical neurons or by overexpression of SIRT1 in SH-SY5Y cell, we aimed to evaluate the roles of SIRT1 in NMDA-induced excitotoxicity. Our results showed that RSV or overexpression of SIRT1 elicited inhibitory effects on NMDA-induced excitotoxicity including a decrease in cell viability, an increase in lactate dehydrogenase (LDH) release, and a decrease in the number of living cells as measured by CCK-8 assay, LDH test, and Calcein-AM and PI double staining. RSV or overexpression of SIRT1 significantly improved SIRT1 deacetylase activity in the excitotoxicity model. Further study suggests that overexpression of SIRT1 partly suppressed an NMDA-induced increase in p53 acetylation. These results indicate that SIRT1 activation by either RSV or overexpression of SIRT1 can exert neuroprotective effects partly by inhibiting p53 acetylation in NMDA-induced neurotoxicity.

Resveratrol Protects Against Pulmonary Arterial Hypertension in Rats via Activation of Silent Information Regulator 1

Background/Objectives: The polyphenol resveratrol (Rev) has been found to exhibit various beneficial effects including prevention of pulmonary arterial hypertension (PAH). The present study was designed to investigate the action and potential mechanism of Rev on PAH, focusing on the role of SIRT1 (Silent Information Regulator 1) in apoptosis of pulmonary artery smooth muscle cells (PASMCs). Methods: PAH rats were established by exposure to hypoxia for 21 days. Rev and SRT1720 (a selective SIRT1 activator) were used to reverse PAH by gavaging rats. PASMCs were confronted with hypoxia for 24 h or 48 h and were then treated with Rev or SRT1720 in vitro. Western blot was performed to detect the protein expression of SIRT1. CCK-8 and scratch wound experiments were carried out to verify cell proliferation. In addition, the TUNEL positive assay and flow cytometry assay were used to measure PASMC apoptosis. Mitochondrial permeability transition (mPT) was identified by confocal microscopy. Right ventricular systolic pressure (RVSP) was determined with a Gould pressure transducer, and right ventricular hypertrophy (RVH) was determined by weighing the cardiac muscle. Results: We demonstrated that Rev could reverse the remodelling of the pulmonary vasculature, thus contributing to alleviating the severity of PAH. Down-regulation of SIRT1 was observed in PAH, but administration of Rev had no obvious effect on the protein expression of SIRT1. In addition, Rev could induce mitochondrial swelling and nuclear pyknosis, leading to small, dense, and dysmorphic mitochondria in rats exposed to hypoxia alone. Rev treatment inhibited PASMC proliferation in a dose-dependent manner in vitro. Incubation with SRT1720, a specific activator of SIRT1, significantly retarded PASMC proliferation and promoted PASMC apoptosis in vitro. The mechanism could be associated with inducing mPT damage in PASMCs. Rev and SRT1720 treatment mitigated RVSP and reduced RVH. Conclusion: Rev produced a beneficial effect partially by enhancing the activation of SIRT1, thus improving RVSP and reducing RVH. SIRT1 activation increased PASMC apoptosis by inducing mPT dysfunction, which might be a novel future strategy for the treatment of PAH.

Tanshinone IIA inhibits myocardial remodeling induced by pressure overload via suppressing oxidative stress and inflammation: Possible role of silent information regulator 1

Tanshinone IIA (Tan) exerts potential protective effects against cardiovascular diseases. Oxidative stress and inflammation are involved in cardiac hypertrophy. Activation of silent information regulator 1 (SIRT1) signaling has been suggested to attenuate cardiac hypertrophy. This study aims to evaluate the antioxidative and anti-inflammatory effects of Tan treatment in pressure overload-induced myocardial remodeling and elucidated its potential mechanisms. Sprague-Dawley rats were treated with Tan in the absence or presence of the SIRT1 inhibitor sirtinol (Snl) and then subjected to transverse aortic constriction (TAC). Tan conferred cardioprotective effects by improving cardiac function, reducing apoptosis and myocardial remodeling, upregulating SIRT1, Bcl-2 expressions, and downregulating Bax and caspase-3 expressions. Snl attenuated these effects by inhibiting SIRT1 signaling. Tan treatment also reduced myocardium malondialdehyde (MDA) content, and cardiac inflammatory cytokines (TNF-α and IL-6) and increased myocardium superoxide dismutase (SOD) level. However, these effects were also abolished by Snl. In conclusion, these results indicate that Tan significantly attenuates TAC-induced myocardial remodeling possibly due to its strong anti-oxidative and anti-inflammatory activity. Importantly, SIRT1 signaling activation is involved in this process.

SIRT1 activation by pterostilbene attenuates the skeletal muscle oxidative stress injury and mitochondrial dysfunction induced by ischemia reperfusion injury.

Ischemia reperfusion (IR) injury is harmful to skeletal muscles and causes mitochondrial oxidative stress. Pterostilbene (PTE), an analogue of resveratrol, has organic protective effects against oxidative stress. However, no studies have investigated whether PTE can protect against IR-related skeletal muscular injury. In this study, we sought to evaluate the protective effect of PTE against IR-related skeletal muscle injury and to determine the mechanisms in this process. Male Sprague-Dawley rats were pretreated with PTE for a week and then underwent limb IR surgery. The IR injury induced segmental necrosis and apoptosis, myofilament disintegration, thicker interstitial spaces, and inflammatory cell infiltration. Furthermore, mitochondrial respiratory chain activity in the muscular tissue was inhibited, methane dicarboxylic aldehyde concentration and myeloperoxidase activity were up-regulated, and superoxide dismutase was down-regulated after IR. However, these effects were significantly inhibited by PTE in a dose-dependent manner. The mechanism underlying IR injury is attributed to the down-regulation of silent information regulator 1 (SIRT1)-FOXO1/p53 pathway and the increase of the Bax/Bcl2 ratio, Cleaved poly ADP-ribose polymerase 1, Cleaved Caspase 3, which can be reversed with PTE. Furthermore, EX527, an SIRT1 inhibitor, counteracted the protective effects of PTE on IR-related muscle injury. In conclusion, PTE has protective properties against IR injury of the skeletal muscles. The mechanism of this protective effect depends on the activation of the SIRT1-FOXO1/p53 signaling pathway and the decrease of the apoptotic ratio in skeletal muscle cells.

Rutin protects rat articular chondrocytes against oxidative stress induced by hydrogen peroxide through SIRT1 activation

The progressive degeneration and ossification of articular chondrocytes are main symptoms in the pathogenesis of osteoarthritis (OA). Several flavonoids may provide an adjunctive alternative for the management of moderate OA in humans. Rutin, a natural flavone derivative (quercetin-3-rhamnosylglucoside), is well known for its potent anti-inflammatory and anti-oxidant properties against oxidative stress. However, the protective function of rutin related to OA, which is characterized by deterioration of articular cartilage, remains unclear. The present study investigated the protective effects of rutin, an activator of silent information regulator 1 (SIRT1), involved in the inhibition of NF-κB/MAPK signaling pathway in hydrogen peroxide (H2O2)-induced oxidative stress in rat chondrocytes. SIRT1 activation by rutin attenuated levels of inflammatory cytokines and NF-κB/MAPK signaling, whereas the inhibition of SIRT1 by sirtinol counteracted the beneficial effects of rutin in H2O2-treated chondrocytes. The findings of these studies suggested the potential involvement of SIRT1 in the pathogenesis of OA, and indicated that rutin is a possible therapeutic option for OA.

Protective role of silent information regulator 1 against hepatic ischemia: effects on oxidative stress injury, inflammatory response, and MAPKs

ABSTRACTObjective: Previous studies have verified that silent information regulator 1 (SIRT1), a class III histone deacetylase, protects against ischemia reperfusion (IR) injury (IRI) in some organs. In this study, we examined whether SIRT1 could protect against hepatic IRI and explored the potential mechanisms.Research design and methods: We examined whether SIRT1 could protect against hepatic IRI in vivo and in vitro using hepatic-specific SIRT1−/- mice, SIRT1 siRNA-transfected hepatocytes and SIRT1+/+ hepatocytes.Results: The expression and activity of SIRT1 were significantly reduced during reperfusion compared with that observed in the control group. Hepatic-specific SIRT1−/- mice exhibited significant increase of hepatic damage markers and augment of oxidative stress and inflammatory response compared with control mice. In vitro studies demonstrated similar results. Furthermore, SIRT1 upregulation protects against hepatic IRI, through the overexpression of p-JNK, p-p38MAPK, and p-ERK. The protection of SIRT1 can be effectively reversed by the inhibitors of p38MAPK, JNK, and ERK.Conclusion: The activation of SIRT1 significantly inhibits the oxidative stress and inflammatory response during hepatic IRI, which can be developed as a novel method to protect against hepatic IRI.

Melatonin Attenuates Early Brain Injury via the Melatonin Receptor/Sirt1/NF-κB Signaling Pathway Following Subarachnoid Hemorrhage in Mice.

Melatonin (Mel) has been reported to alleviate early brain injury (EBI) following subarachnoid hemorrhage (SAH). The activation of silent information regulator 1 (Sirt1), a histone deacetylase, has been suggested to be beneficial in SAH. However, the precise role of Sirt1 in Mel-mediated protection against EBI following SAH has not been elucidated. The present study aims to evaluate the role of melatonin receptor/Sirt1/nuclear factor-kappa B (NF-κB) in this process. The endovascular perforation SAH model was used in male C57BL/6J mice, and melatonin was administrated intraperitoneally (150mg/kg). The mortality, SAH grade, neurological score, brain water content, and neuronal apoptosis were evaluated. The expression of Sirt1, acetylated-NF-κB (Ac-NF-κB), Bcl-2, and Bax were detected by western blot. To study the underlying mechanisms, melatonin receptor (MR) antagonist luzindole and Sirt1 small interfering RNA (siRNA) were administrated to different groups. The results suggest that Mel improved the neurological deficits and reduced the brain water content and neuronal apoptosis. In addition, Mel enhanced the expression of Sirt1 and Bcl-2 and decreased the expression of Ac-NF-κB and Bax. However, the protective effects of Mel were abolished by luzindole or Sirt1 siRNA. In conclusion, our results demonstrate that Mel attenuates EBI following SAH via the MR/Sirt1/NF-κB signaling pathway.

Berberine Attenuates Myocardial Ischemia/Reperfusion Injury by Reducing Oxidative Stress and Inflammation Response: Role of Silent Information Regulator 1.

Berberine (BBR) exerts potential protective effect against myocardial ischemia/reperfusion (MI/R) injury. Activation of silent information regulator 1 (SIRT1) signaling attenuates MI/R injury by reducing oxidative damage and inflammation response. This study investigated the antioxidative and anti-inflammatory effects of BBR treatment in MI/R condition and elucidated its potential mechanisms. Sprague-Dawley rats were treated with BBR in the absence or presence of the SIRT1 inhibitor sirtinol (Stnl) and then subjected to MI/R injury. BBR conferred cardioprotective effects by improving postischemic cardiac function, decreasing infarct size, reducing apoptotic index, diminishing serum creatine kinase and lactate dehydrogenase levels, upregulating SIRT1, Bcl-2 expressions, and downregulating Bax and caspase-3 expressions. Stnl attenuated these effects by inhibiting SIRT1 signaling. BBR treatment also reduced myocardium superoxide generation, gp91phox expression, malondialdehyde (MDA) level, and cardiac inflammatory markers and increased myocardium superoxide dismutase (SOD) level. However, these effects were also inhibited by Stnl. Consistently, BBR conferred similar antioxidative and anti-inflammatory effects against simulated ischemia reperfusion injury in cultured H9C2 cardiomyocytes. SIRT1 siRNA administration also abolished these effects. In summary, our results demonstrate that BBR significantly improves post-MI/R cardiac function recovery and reduces infarct size against MI/R injury possibly due to its strong antioxidative and anti-inflammatory activity. Additionally, SIRT1 signaling plays a key role in this process.

Suppression of silent information regulator 1 activity in noncancerous tissues of hepatocellular carcinoma: Possible association with non-B non-C hepatitis pathogenesis.

Silent information regulator 1 (SIRT1) is a nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylase. In mice, mSirt1 deficiency causes the onset of fatty liver via regulation of the hepatic nutrient metabolism pathway. In this study, we demonstrate SIRT1 expression, activity and NAD+ regulation using noncancerous liver tissue specimens from hepatocellular carcinoma patients with non-B non-C (NBNC) hepatitis. SIRT1 expression levels were higher in NBNC patients than in healthy donors, while SIRT1 histone H3K9 deacetylation activity was suppressed in NBNC patients. In the liver of hepatitis patients, decreased NAD+ amounts and its regulatory enzyme nicotinamide phosphoribosyltransferase expression levels were observed, and this led to inhibition of SIRT1 activity. SIRT1 expression was associated with HIF1 protein accumulation in both the NBNC liver and liver cancer cell lines. These results may indicate that the NBNC hepatitis liver is exposed to hypoxic conditions. In HepG2 cells, hypoxia induced inflammatory chemokines, such as CXCL10 and MCP-1. These inductions were suppressed in rich NAD+ condition, and by SIRT1 activator treatment. In conclusion, hepatic SIRT1 activity was repressed in NBNC patients, and normalization of NAD+ amounts and activation of SIRT1 could improve the inflammatory condition in the liver of NBNC hepatitis patients.

SIRT1/PGC-1α signaling protects hepatocytes against mitochondrial oxidative stress induced by bile acids

Oxidative stress and mitochondrial dysfunction are hypothesized to contribute to the pathogenesis of chronic cholestatic liver diseases. Silent information regulator 1 (SIRT1) attenuates oxidative stress and improves mitochondrial biogenesis in numerous mitochondrial-related diseases; however, a functional role for SIRT1 in chronic liver cholestasis, characterized by increased levels of toxic bile acids, remains unknown. We show decrease in SIRT1 levels and its activity and impairment of mitochondrial biogenesis in the liver of patients with extrahepatic cholestasis. Moreover, we found that glycochenodeoxycholic acid (GCDCA) stimulated cytotoxicity, disrupted the mitochondrial membrane potential, increased reactive oxygen species production, and decreased mitochondrial mass and mitochondrial DNA content in L02 cells. Consistent with this finding, GCDCA was found to decrease SIRT1 protein expression and activity, thus promoting the deacetylation of peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (PGC-1α), a key enzyme involved in mitochondrial biogenesis and function. Conversely, GCDCA-induced mitochondrial injury was efficiently attenuated by SIRT1 overexpression. In summary, these findings indicate that the loss of SIRT1 may play a crucial role in the pathogenesis of liver damage observed in patients with extrahepatic cholestasis. The findings also indicate that genetic supplementation of SIRT1 can ameliorate GCDCA-induced hepatotoxicity through the activation of PGC-1α-dependent mitochondrial biogenesis.

Accelerated onset of senescence of endothelial progenitor cells in patients with type 2 diabetes mellitus: Role of dimethylarginine dimethylaminohydrolase 2 and asymmetric dimethylarginine

The risk of cardiovascular complications in diabetic patients is mainly associated with endothelial dysfunction. Reduced number of EPCs and impaired function of EPCs in diabetes result in imbalance of endothelial homeostasis and dysfunction of vessels. In patients with diabetes mellitus, plasma levels of asymmetric dimethylarginine (ADMA) were elevated, while the expression and activity of dimethylarginine dimethylaminohydrolase (DDAH) were reduced. In the present study, we investigated the role of the DDAH2/ADMA pathway in the senescence of EPCs in type 2 diabetic patients and cultured EPCs treated with high glucose. The results showed that the percentage of senescent EPCs increased while the expression of DDAH2 decreased concomitantly with an increase in the plasma levels of ADMA in patients with type 2 diabetes mellitus (T2DM). Similar results were seen in cultured EPCs treated with high glucose. Exogenous application of ADMA accelerated the senescence of EPCs in a dose-dependent manner, and overexpression of DDAH2 inhibited high glucose-induced EPCs senescence. In addition, it has also been reported that DDAH/ADMA pathway is regulated by silent information regulator 1 (SIRT1) in endothelial cell. In the present study, we found decreased expression of SIRT1 both in T2DM patients and EPCs pretreated with high glucose. And resveratrol (activating SIRT1) inhibited high glucose-induced EPCs senescence by upregulating the expression of DDAH2 and decreasing the levels of ADMA. Taken together, we concluded that DDAH2/ADMA is involved in the accelerated senescence of EPCs in diabetes, which is associated with the activation of SIRT1.

Curcumin Attenuates Hydrogen Peroxide-Induced Premature Senescence via the Activation of SIRT1 in Human Umbilical Vein Endothelial Cells.

Endothelial senescence has been proposed to be involved in endothelial dysfunction and atherogenesis. Curcumin, a natural phenol, possesses antioxidant and anti-inflammatory properties. However, the effect of curcumin on endothelial senescence is unclear. This study explores the effect of curcumin on hydrogen peroxide (H2O2)-induced endothelial premature senescence and the mechanisms involved. Human umbilical vein endothelial cells (HUVECs) were cultured, and premature senescence was induced with 100 µM H2O2. Results showed that pretreatment with curcumin significantly attenuated the H2O2-induced HUVECs' premature senescence, which was evidenced by a decreased percentage of senescence-associated β-galactosidase positive cells, improved cell division and decreased expression of senescence-associated protein p21 (all p<0.05). Pretreatment with curcumin decreased oxidative stress and apoptosis in H2O2-treated HUVECs. Treatment of HUVECs with H2O2 also down-regulated the phosphorylation of endothelial nitric oxide synthase (eNOS), decreased the level of nitric oxide in the culture medium, and inhibited the protein expression and enzymatic activity of silent information regulator 1 (SIRT1), while pretreatment with curcumin partly reversed these effects (all p<0.05). Treatment with curcumin alone enhanced the enzymatic activity of SIRT1, but didn't affect cellular senescence, cell growth or apoptosis compared to the Control. The inhibition of SIRT1 using SIRT1 short interfering RNA (siRNA) could decrease the expression and phosphorylation of eNOS and abrogate the protective effect of curcumin on H2O2-induced premature senescence. These findings suggest that curcumin could attenuate oxidative stress-induced HUVECs' premature senescence via the activation of SIRT1.

Class II transactivator (CIITA) mediates transcriptional repression of pdk4 gene by interacting with hypermethylated in cancer 1 (HIC1).

Increased accumulation and/or impaired utilization of fatty acid in extra-adipose tissues are implicated in the pathogenesis of insulin resistance and type 2 diabetes. Pyruvate dehydrogenase kinase 4 (Pdk4) is a key enzyme involved in fatty oxidation and energy expenditure, and its expression can be repressed by pro-inflammatory stimuli. Previously, we have shown that class II transactivator (CIITA) mediates the adverse effect of interferon gamma (IFN-γ) in skeletal muscle cells by cooperating with hypermethylated in cancer 1 (HIC1) to repress silent information regulator 1 (SIRT1) transcription. Building upon this finding, we report here that CIITA interacted with HIC1 via the GTP-binding domain (GBD) while HIC1 interacted with CIITA via the BTB/POZ domain. The GBD domain was required for CIITA to repress SIRT1 transcription probably acting as a bridge for CIITA to bind to HIC1 and consequently to bind to the SIRT1 promoter. IFN-γ stimulation, CIITA over-expression, or HIC1 over-expression repressed Pdk4 promoter activity while silencing either CIITA or HIC1 normalized Pdk4 expression in the presence of IFN-γ. An increase in SIRT1 expression or activity partially rescued Pdk4 expression in the presence of CIITA, but SIRT1 inhibition abrogated Pdk4 normalization even in the absence of CIITA. Taken together, our data have identified a HIC1-CIITA-SIRT1 axis that regulates Pdk4 transcription in response to IFN-γ stimulation.