Sirt3 Protects Retinal Pigment Epithelial Cells From High Glucose-Induced Injury by Promoting Mitophagy Through the AMPK/mTOR/ULK1 Pathway

Purpose

The regulation of mitophagy by Sirt3 has rarely been studied in ocular diseases. In the present study, we determined the effects of Sirt3 on AMPK/mTOR/ULK1 signaling pathway-mediated mitophagy in retinal pigment epithelial (RPE) cells in a high glucose environment.

Methods

The mRNA expression levels of Sirt3, AMPK, mTOR, ULK1, and LC3B in RPE cells under varying glucose conditions were measured by real-time polymerase chain reaction (RT-PCR). The expressions of Sirt3, mitophagy protein, and AMPK/mTOR/ULK1 signaling pathway-related proteins were detected by Western blotting. Lentivirus (LV) transfection mediated the stable overexpression of Sirt3 in cell lines. The experimental groups were NG (5.5 mM glucose), hypertonic, HG (30 mM glucose), HG + LV-GFP, and HG + LV-Sirt3. Western blotting was performed to detect the expressions of mitophagy proteins and AMPK/mTOR/ULK1-related proteins in a high glucose environment during the overexpression of Sirt3. Reactive oxygen species (ROS) production in a high glucose environment was measured by DCFH-DA staining. Mitophagy was detected by labeling mitochondria and lysosomes with MitoTracker and LysoTracker probes, respectively. Apoptosis was detected by flow cytometry.

Results

Sirt3 expression was reduced in the high glucose group, inhibiting the AMPK/mTOR/ULK1 pathway, with diminished mitophagy and increased intracellular ROS production. The overexpression of Sirt3, increased expression of p-AMPK/AMPK and p-ULK1/ULK1, and decreased expression of p-mTOR/mTOR inhibited cell apoptosis and enhanced mitophagy.

Conclusions

Sirt3 protected RPE cells from high glucose-induced injury by activating the AMPK/mTOR/ULK1 signaling pathway.

Translational Relevance

By identifying new targets of action, we aimed to establish effective therapeutic targets for diabetic retinopathy treatment.

The Therapeutic Potential of Targeting Ferroptosis in the Treatment of Mitochondrial Cardiomyopathies and Heart Failure

ABSTRACT

Ferroptosis is a form of iron-regulated cell death implicated in a wide array of diseases, including heart failure, hypertension, and numerous cardiomyopathies. In addition, mitochondrial dysfunction has been associated with several of these same disease states. However, the role of the mitochondrion in ferroptotic cell death remains debated. As a major regulator of cellular iron levels, the mitochondria may very well play a crucial role in the mechanisms behind ferroptosis, but at this point, this has not been adequately defined. Emerging evidence from our laboratory and others indicates a critical role of mitochondrial Sirtuin 3, a deacetylase linked with longevity and protection against numerous conditions, in the prevention of cardiovascular diseases. Here, we provide a brief overview of the potential roles of Sirtuin 3 in mitochondrial iron homeostasis and its contribution to the mitochondrial cardiomyopathy of Friedreich's ataxia and diabetic cardiomyopathy. We also discuss the current knowledge of the involvement of ferroptosis and the mitochondria in these and other cardiovascular disease states, including doxorubicin-induced cardiomyopathy, and provide insight into areas requiring further investigation.

Liquid chromatography-tandem mass spectrometry analysis of a ratio-optimized drug pair of Sophora flavescens Aiton and Coptis chinensis Franch and study on the mechanism of anti-colorectal cancer effect of two alkaloids thereof

The drug pair consisting of Sophora flavescens Aiton (Sophorae flavescentis radix, Kushen) and Coptis chinensis Franch. (Coptidis rhizoma, Huanglian), as described in Prescriptions for Universal Relief (Pujifang), is widely used to treat laxation. Matrine and berberine are the major active components of Kushen and Huanglian, respectively. These agents have shown remarkable anti-cancer and anti-inflammatory effects. A mouse model of colorectal cancer was used to determine the most effective combination of Kushen and Huanglian against anti-colorectal cancer. The results showed that the combination of Kushen and Huanglian at a 1:1 ratio exerted the best anti-colorectal cancer effect versus other ratios. Moreover, the anti-colorectal cancer effect and potential mechanism underlying the effects of matrine and berberine were evaluated by the analysis of combination treatment or monotherapy. In addition, the chemical constituents of Kushen and Huanglian were identified and quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 67 chemical components were identified from the Kushen-Huanglian drug pair (water extraction), and the levels of matrine and berberine were 129 and 232 µg/g, respectively. Matrine and berberine reduced the growth of colorectal cancer and relieved the pathological conditions in mice. In addition, the combination of matrine and berberine displayed better anti-colorectal cancer efficacy than monotherapy. Moreover, matrine and berberine reduced the relative abundance of Bacteroidota and Campilobacterota at phylum level and that of Helicobacter, Lachnospiraceae_NK4A136_group, Candidatus_Arthromitus, norank_f_Lachnospiraceae, Rikenella, Odoribacter, Streptococcus, norank_f_Ruminococcaceae, and Anaerotruncus at the genus level. Western blotting results demonstrated that treatment with matrine and berberine decreased the protein expressions of c-MYC and RAS, whereas it increased that of sirtuin 3 (Sirt3). The findings indicated that the combination of matrine and berberine was more effective in inhibiting colorectal cancer than monotherapy. This beneficial effect might depend on the improvement of intestinal microbiota structure and regulation of the RAS/MEK/ERK-c-MYC-Sirt3 signaling axis.

Spatiotemporal Coordination of RPE Cell Quality by Extracellular Vesicle miR-494-3p Via Competitive Interplays With SIRT3 or PTEN

Purpose

To reveal the molecular mechanism underlying degeneration in human retinal pigment epithelial (hRPE) cells with dysfunctional mitochondrial homeostasis.

Methods

The expression of recently identified miR-494-3p in extracellular vesicles (EV) released from induced-pluripotential-stem-cell-derived human RPE (iPS-hRPE), during coculture with macrophages (Mps) was investigated in iPS-hRPE and ARPE cells differentiated in the presence of nicotinamide (Nic-ARPE). The expression of phosphatase and tensin homolog (PTEN), sirtuin3 (SIRT3), and mitochondrial marker proteins before and after the transfection of miR-494-3p inhibitor and mimic, and the changes in mitochondrial metabolism, membrane potential, and oxidative phosphorylation (OXPHOS) were monitored.

Results

Compared with senescent dedifferentiated ARPE19 cells, iPS-hRPE and Nic-ARPE cells expressed elevated levels of mitochondrial marker proteins but a repressed cellular miR-494-3p level. The expression of target proteins of miR-494-3p, PTEN, and SIRT3 was upregulated along with the differentiation disposition of these RPE cells. The ratio of PTEN/SIRT3 in de-differentiated ARPE19 cells was surprisingly elevated by around 20 times compared with that in iPS-hRPE and Nic-ARPE cells. The novel molecular interplay of EV miR-494-3p either with mitochondria selective SIRT3 or organelle nonselective PTEN was found to participate in the degeneration of hRPE cells by inducing mitochondrial dysfunctions and repressed OXPHOS, mitochondrial membrane potential, and ATP and NAD+ production.

Conclusions

Our results demonstrate a clear causal link between miR-494-3p and hRPE cell degeneration via the regulation of mitochondrial integrity. EV miR-494-3p may play a pivotal role in pathogenic spreading of degenerated hRPE cells from the local perifovea throughout the macula.

Effect of electroacupuncture treatment combined with rehabilitation care on serum sirt3 level and motor function in elderly patients with stroke hemiparesis

OBJECTIVE

Acupuncture treatment helps to improve neurological and motor function in elderly patients with stroke hemiplegia. However, the exact mechanism by which electroacupuncture improves stroke hemiparesis is uncertain. The aim of this study was to determine the effect of electroacupuncture care on sirt3 levels in elderly patients with stroke hemiparesis.

METHODS

One hundred and ten elderly patients with hemiplegia after first stroke were divided into an experimental group and a control group (n = 55 in each group). The control group was given conventional rehabilitation care by a rehabilitation therapist. In the experimental group, on the basis of conventional rehabilitation care, electroacupuncture was performed once a day for 28 days.

RESULTS

Fugl-Meyer assessment (FMA) and barthel index (BI) scores were significantly higher, while neurologic deficit scale (NDS) and physiological state scores were significantly lower in both groups after 14 and 28 days of intervention compared to preintervention. The Generalized estimating equation (GEE) model also showed that the experimental group showed more favorable improvements in all outcomes at postintervention time points compared to the control group. After the intervention, serum sirt3 levels increased significantly in both groups compared to preintervention, and the increase was more pronounced in the experimental group. Consistently, the GEE model showed that serum sirt3 levels were significantly higher in the experimental group compared to the control group at postintervention time points. Correlation analysis revealed that serum sirt3 levels in the experimental group were negatively correlated with FMA and BI pre- and postintervention, while showing a significant positive correlation with NDS and physiological state scores.

CONCLUSION

Electroacupuncture intervention led to significant improvements in motor function, activities of daily living and neurological function in elderly patients with stroke hemiplegia, which may be associate with increased serum sirt3 levels.

Sirt3 regulates NLRP3 and participates in the effects of plantainoside D on acute lung injury sepsis

Sepsis, a common critical disease, has high morbidity and mortality. Acute lung injury (ALI) is one of the important complications of sepsis, its effective treatment measures remain scarce. The purpose of the present study was to search for the biomarker and effective treatment measures. Lipopolysaccharide (LPS) was used to establish sepsis induced ALI model in vivo and in vitro. Proteomics, immunoprecipitation, molecular docking techniques, and Sirt3 knockout (KO) mice and silence MLE-12 cells were used to search for biomarker and treatment measures for sepsis ALI. 38 differentially expressed proteins were found in the lung tissues of sepsis ALI mice, among which Sirt3 changed most. Further study found that Sirt3 could inhibit NLRP3 activation. Sirt3 KO or silence significantly aggravated sepsis induced ALI and MLE-12 cell injury. Plantainoside D (PD), an effective component of Plantago asiatica L., significantly improved sepsis induced ALI by regulation of Sirt3/NLRP3 pathway. In conclusion, Sirt3 may be the important molecular targets for sepsis ALI. PD could protect sepsis ALI via Sirt3/NLRP3 signal pathway. The findings provide a new treatment target for sepsis ALI and a potential treatment measure.

Honokiol attenuates mitochondrial fission and cell apoptosis by activating Sirt3 in intracerebral hemorrhage

BACKGROUND

Sirtuin-3 (Sirt3) has been documented to protect against mitochondrial dysfunction and apoptosis. Honokiol (HKL) is a Sirt3 pharmacological activator with reported neuroprotective effects in multiple neurological disorders. The present study aimed to explore the neuroprotective effects of HKL and the role of Sirt3 following intracerebral hemorrhage (ICH).

METHODS

An in vivo ICH model in rats was established by injecting autologous blood into the right basal ganglia. PC12 cells were stimulated with hemin. For the in vivo investigation, the modified Neurological Severity Scores and the Morris water maze test were performed to assess neurological deficits. Hematoxylin-Eosin and Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining were employed to evaluate the histopathology and apoptosis. Immunohistochemical staining was used to investigate the expression of Sirt3. Adenosine triphosphate (ATP) levels were quantified to assess mitochondrial dysfunction. Cell counting kit-8, lactate dehydrogenase assay, and flow cytometry were used to analyze cell vitality and apoptosis in vitro. Immunofluorescence staining was performed to observe mitochondrial morphology and dynamin-related protein 1 (Drp1) localization to mitochondria. Western blot was applied to quantify the expression of Sirt3, Bax, Bcl-2, cleaved-caspase-3, Drp1, phosphorylation of Drp1 at serine-616, and phosphorylation of Drp1 at serine-637 in vivo and in vitro.

RESULTS

HKL treatment alleviated neurological deficits, attenuated the histopathological damage and cell apoptosis, and restored the decreased ATP levels in ICH rats. HKL improved cell survival rate, reduced cell apoptosis, and inhibited mitochondrial fission in PC12 cells. Moreover, both in vivo and in vitro models showed increased phosphorylation of Drp1 at Ser616, and reduced phosphorylation of Drp1 at Ser637. Meanwhile, immunofluorescence co-localization analysis revealed that hemin increased the overlap of Drp1 and mitochondria in PC12 cells. The phosphorylation and mitochondrial translocation of Drp1 were effectively reversed by HKL treatment. Importantly, the selective Sirt3 inhibitor 3-(1H-1,2,3-triazol-4-yl) pyridine suppressed these effects.

CONCLUSION

Our findings demonstrated that HKL ameliorated ICH-induced apoptosis and mitochondrial fission by Sirt3, suggesting that HKL has immense prospects for the treatment of ICH.

Salidroside reduces neuropathology in Alzheimer’s disease models by targeting NRF2/SIRT3 pathway

Background

Neurite dystrophy is a pathologic hallmark of Alzheimer’s disease (AD). However, drug discovery targeting neurite protection in AD remains largely unexplored.

Methods

Aβ-induced neurite and mitochondrial damage assays were used to evaluate Aβ toxicity and the neuroprotective efficacy of a natural compound salidroside (SAL). The 5×FAD transgenic mouse model of AD was used to study the neuroprotective function of SAL. To verify the direct target of SAL, we used surface plasmon resonance and cellular thermal shift assays to analyze the drug-protein interaction.

Results

SAL ameliorates Aβ-mediated neurite damage in cell culture. We further reveal that SAL represses mitochondrial damage in neurites by promoting mitophagy and maintaining mitochondrial homeostasis, dependent on an NAD-dependent deacetylase SIRT3. In AD mice, SAL protects neurite morphology, mitigates Aβ pathology, and improves cognitive function, which are all SIRT3-dependent. Notably, SAL directly binds to transcription factor NRF2, inhibits its degradation by blocking its interaction with KEAP1 ubiquitin ligase, and then advances NRF2-mediated SIRT3 transcription.

Conclusions

Overall, we demonstrate that SAL, a potential anti-aging drug candidate, attenuates AD pathology by targeting NRF2/SIRT3 pathway for mitochondrial and neurite protection. Drug discovery strategies focusing on SAL may thus provide promising therapeutics for AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00918-z.

Mitochondrial deacetylase Sirt3 in vascular dysfunction and hypertension

PURPOSE OF REVIEW

Hypertension 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 FINDINGS

In 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.

SUMMARY

Sirt3 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.

Serum levels of SIRT3 and other inflammatory factors are associated with clinical outcomes and prognosis in severe community-acquired pneumonia in adults: A prospective study

The aim of this study was to investigate clinical significance of SIRT3 in severe community-acquired pneumonia (CAP) patients.This prospective observational research enrolled a total of 114 severe CAP patients who went to our hospital during January 2018 to December 2019. Serum SIRT3 and IL-1β, IL-6, and tumor necrosis factor (TNF)-α levels were determined using the enzyme-linked immunosorbent assay (ELISA) method. Demographic data, including age, sex, and body mass index (BMI), as well as clinical symptoms, SOFA and SMART-COP scores were collected. The routine blood test was conducted for all patients and white blood cell (WBC) amount, as well as serum levels of C-reactive protein (CRP), D-Dimer, and procalcitonin (PCT).Among all patients, 55 cases died during the study period. The serum levels of CRP, PCT, IL-1β, and IL-6, as well as SOFA and SMART-COP scores were markedly higher in deceased patients than in the survival patients. The expression of SIRT3 was significantly decreased in severe CAP patients compared with the healthy, especially in the deceased patients. SIRT3 levels were negatively correlated with levels of CRP, PCT, IL-1β, and IL-6. Patients with SIRT3 low expression showed remarkably higher expression of CRP, PCT, IL-1β, and IL-6, as well as high SMART-COP scores, higher 1-month mortality rate, and shorter survival. Only SIRT3 and IL-1β were independent risk factors for 1-month mortality in severe CAP patients.Lower serum SIRT3 level predicts poor clinical outcomes and prognosis in severe CAP patients.

Effects of Lipotoxicity in Brain Microvascular Endothelial Cells During Sirt3 Deficiency-Potential Role in Comorbid Alzheimer's Disease

Silence information regulator 3 (SIRT3) is an NAD⁺ dependent deacetylase enzyme that enhances the function of key mitochondrial proteins. We have earlier demonstrated that deletion of Sirt3 gene leads to downregulation of metabolic enzymes, mitochondrial dysfunction and neuroinflammation in the brain, the major causes of Alzheimer’s disease (AD). We also reported recently that Sirt3 gene deletion in Alzheimer’s transgenic mice leads to exacerbation of neuroinflammation, amyloid plaque deposition and microglial activation. AD often coexists with other brain lesions caused by comorbidities which can exert their deleterious effects through the neurovascular unit. This unit consists of brain microvascular endothelial cells (BMECs), end feet of astrocytes, and pericytes. BMECs are uniquely different from other vascular endothelial cells because they are glued together by tight-junction proteins. BMECs are in constant contact with circulating factors as they line the luminal side. Therefore, we hypothesized that vascular endothelial injury caused by comorbidities plays a significant role in neuroinflammation. Herein, we investigated the effects of lipotoxicity in BMECs and how Sirt3 deficiency facilitate the deleterious effects of lipotoxicity on them using in vivo and in vitro models. We observed decreases in the levels of SIRT3 and tight junction proteins in the brain samples of western diet-fed APP/PS1 mice. Similar observations were obtained with Alzheimer’s post-mortem samples. Exposure of BEND3 cells, mouse brain-derived Endothelial cells3, to a combination of high glucose and palmitic acid resulted in significant (P < 0.01-P < 0.001) decreases in the levels of SIRT3, claudin-5 and ZO-1. Induction of inflammatory mediators, including Cox-2, CXCL1, RANTES, and GADD45β was also observed in these treated cells. Interestingly, the induction was more with Sirt3-silenced BEND3 cells, suggesting that Sirt3 deficiency exacerbates inflammatory response. Palmitic acid was more potent in inducing the inflammatory mediators. Significant cytotoxicity and changes in microglial morphology were observed when cocultures of Sirt3-silenced BEND3 and Sirt3-silenced BV2 cells were exposed to palmitic acid. Transendothelial electrical resistance measurement with these cocultures suggested decreased barrier integrity. The findings of this study suggest that hyperlipidemia in comorbidities can compromise blood brain barrier integrity by inducing inflammatory mediators and decreasing tight junction proteins in the vascular endothelial cells of the AD brain, leading to activation of microglia.

Sirt3 Protects Against Thoracic Aortic Dissection Formation by Reducing Reactive Oxygen Species, Vascular Inflammation, and Apoptosis of Smooth Muscle Cells

Sirtuin3 (Sirt3) is a histone deacetylase involved in the regulation of many cellular processes. Sirt3 deficiency is known to increase oxidative stress. Reactive oxygen species (ROS) promote degradation of the extracellular matrix and vascular smooth muscle cell (VSMC) apoptosis. Reducing oxidative stress by Sirt3 overexpression could have therapeutic potential for limiting thoracic aortic dissection (TAD) development. We hypothesized that Sirt3 deficiency could increase the risk for TAD by decreasing ROS elimination and that Sirt3 overexpression (Sirt3^OE) could provide an alternative option for TAD treatment. Mice with TAD had significantly lower Sirt3 expression than normal subjects. Sirt3 KO mice exhibit significantly increased TAD incidence rate and increased aortic diameters. Moreover, Sirt3 overexpression reduced Ang II-induced ROS production, NF-kB activation, and apoptosis in human aortic smooth muscle cells (HASMCs). Sirt3 overexpression attenuated aneurysm formation and decreased aortic expansion. In conclusion, our data showed that Sirt3 deficiency increases susceptibility to TAD formation by attenuating anti-ROS effects and increasing VSMC apoptosis and vascular inflammation.

Loss of Sirt3 accelerates arterial thrombosis by increasing formation of neutrophil extracellular traps and plasma tissue factor activity

Aims

Sirtuin 3 (Sirt3) is a mitochondrial, nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase that reduces oxidative stress by activation of superoxide dismutase 2 (SOD2). Oxidative stress enhances arterial thrombosis. This study investigated the effects of genetic Sirt3 deletion on arterial thrombosis in mice in an inflammatory setting and assessed the clinical relevance of these findings in patients with ST-elevation myocardial infarction (STEMI).

Methods and results

Using a laser-induced carotid thrombosis model with lipopolysaccharide (LPS) challenge, in vivo time to thrombotic occlusion in Sirt3-/- mice (n = 6) was reduced by half compared to Sirt3+/+ wild-type (n = 8, P < 0.01) controls. Ex vivo analyses of whole blood using rotational thromboelastometry revealed accelerated clot formation and increased clot stability in Sirt3-/- compared to wild-type blood. rotational thromboelastometry of cell-depleted plasma showed accelerated clotting initiation in Sirt3-/- mice, whereas overall clot formation and firmness remained unaffected. Ex vivo LPS-induced neutrophil extracellular trap formation was increased in Sirt3-/- bone marrow-derived neutrophils. Plasma tissue factor (TF) levels and activity were elevated in Sirt3-/- mice, whereas plasma levels of other coagulation factors and TF expression in arterial walls remained unchanged. SOD2 expression in bone marrow -derived Sirt3-/- neutrophils was reduced. In STEMI patients, transcriptional levels of Sirt3 and its target SOD2 were lower in CD14+ leukocytes compared with healthy donors (n = 10 each, P < 0.01).

Conclusions

Sirt3 loss-of-function enhances experimental thrombosis in vivo via an increase of neutrophil extracellular traps and elevation of TF suggesting thrombo-protective effects of endogenous Sirt3. Acute coronary thrombosis in STEMI patients is associated with lower expression levels of SIRT3 and SOD2 in CD14+ leukocytes. Therefore, enhancing SIRT3 activity by pan-sirtuin activating NAD+-boosters may provide a novel therapeutic target to prevent or treat thrombotic arterial occlusion in myocardial infarction or stroke.

Sirt3 Ameliorates Oxidative Stress and Mitochondrial Dysfunction After Intracerebral Hemorrhage in Diabetic Rats

Aim: Sirtuin3 (sirt3) plays a pivotal role in improving oxidative stress and mitochondrial dysfunction which directly induced neuronal apoptosis after intracerebral hemorrhage (ICH). Reactive oxygen species (ROS) is also a critical activator in triggering NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasomes activation which can regulate inflammatory responses in brain. Moreover, hyperglycemia can aggravate the ICH-induced damage. Hence, this study was designed to investigate the mechanisms of neuroprotection of sirt3 in hyperglycemic ICH.

Methods: ICH model was established by autologous blood injection. Hyperglycemia was induced by intraperitoneal injection with streptozotocin. Honokiol (HKL, a pharmacological agonist of sirt3) was injected intraperitoneally at doses of 2.5, 5, or 10 mg/kg. Sirt3 small interfering RNA transfection was implemented through intracerebroventricular injection. The expression of sirt3 and its downstream signaling molecules were detected using Western blotting or immunofluorescence staining. Morphological changes of mitochondria were detected by electron microscopy. SH-SY5Y cells were incubated with 10 μM oxyhemoglobin for 48 h to establish an in vitro ICH model, and then JC-1 staining was used to determine mitochondrial membrane potential (Δψm).

Results: Hyperglycemia could suppress sirt3 expression after ICH when compared with non-diabetic rats. Sirt3 protein expression was decreased to the minimum at 24 h in perihematoma tissues. Electron microscope analysis indicated that hyperglycemic ICH induced extensive mitochondrial vacuolization. HKL attenuated ROS accumulation, adenosine triphosphate reduction, and Δψm through Sirt3–superoxide dismutase 2 (SOD2) and Sirt3–NRF1–TFAM pathway. Sirt3 knockdown could exacerbate the neuronal apoptosis and reverse the positive effects of HKL. Sirt3 activation could decrease NLRP3 and interleukin-1β levels through deacetylating SOD2 and scavenging ROS.

Conclusion: HKL protects against hyperglycemic ICH-induced neuronal injury via a sirt3-dependent manner.

Modulation of human longevity by SIRT3 single nucleotide polymorphisms in the prospective study "Treviso Longeva (TRELONG)"

Human sirtuins are seven proteins with deacetylase activity that are emerging as key modulators of basic physiological functions. Some evidence links SIRT3 to longevity in mammals. This study aimed to investigate whether variants within SIRT3 gene were associated to human longevity. We analyzed 549 genomic DNA collected during the prospective study "Treviso Longeva," including elderly over 70 years of age from the municipality of Treviso, a small city in the northeast of Italy. We genotyped SIRT3 rs3825075, rs4980329, and rs11555236 single nucleotide polymorphisms (SNPs) by real-time polymerase chain reaction allelic discrimination assay. A cross-sectional analysis performed by comparing people over and under 85 years of age did not evidence association among the SIRT3 SNPs and longevity. However, when we performed a longitudinal analysis considering mortality as a dependent variable, we observed an association of SIRT3 rs11555236 and rs4980329 with longevity in the whole population (p values corrected for potential confounders = 0.04 and 0.03, respectively). After stratification according to gender, the same SNPs were associated to female longevity only (p values corrected for potential confounders = 0.03 and 0.02, respectively). Finally, as rs11555236 was reported to be in linkage disequilibrium with a putative functional enhancer within the SIRT3 gene, we assessed whether rs11555236 genotypes correlated with a different level of SIRT3 protein in peripheral blood mononuclear cells. We found an increased level of SIRT3 in subjects homozygous for the (T) allele. We suggest that SIRT3 genetic variability might be relevant for the modulation of human longevity in the Italian population.

SIRT3 overexpression antagonizes high glucose accelerated cellular senescence in human diploid fibroblasts via the SIRT3-FOXO1 signaling pathway

Sirtuin 3 (SIRT3) is one of the seven mammalian sirtuins, which are homologs of the yeast Sir2 gene. SIRT3 is the only sirtuin reported to be associated with human life span. Many recent studies have indicated that SIRT3 levels are elevated by exercise and caloric restriction, but whether SIRT3 influences cell senescence under stressed conditions in human diploid fibroblasts has not been established. Our data showed that expression of SIRT3 is elevated in human diploid fibroblasts under low glucose (3.3 mM glucose) growth conditions and decreased under high glucose (25 mM glucose) growth conditions. We have demonstrated that SIRT3 interacts with forkhead box protein O1 (FOXO1). High glucose levels also increased aging phenotypes and FOXO1 acetylation level. We have demonstrated that overexpression of SIRT3 under high glucose conditions reduces FOXO1 acetylation, suggesting that deacetylation of FOXO1 by SIRT3 elevates the expression of the FOXO1 target genes, catalase, and manganese superoxide dismutase (MnSOD) while decreasing senescence phenotypes. We studied the effects of SIRT3 protein knockdown by shRNA under low glucose conditions. The data showed that shRNA-SIRT3 accelerated senescence phenotypes and acetylation of FOXO1; the expression level of catalase and MnSOD decreased compared with the control group. As a consequence, SIRT3 antagonized cellular senescence with the characteristic features of delayed SA-β-gal staining, senescence-associated heterochromatin foci (SAHF) formation, and p16(INK4A) expression. These results demonstrate for the first time that SIRT3 overexpression antagonizes high glucose-induced cellular senescence in human diploid fibroblasts via the SIRT3-FOXO1 signaling pathway.

Sirtuins: from metabolic regulation to brain aging

Brain aging is characterized by progressive loss of neurophysiological functions that is often accompanied by age-associated neurodegeneration. Calorie restriction has been linked to extension of lifespan and reduction of the risk of neurodegenerative diseases in experimental model systems. Several signaling pathways have been indicated to underlie the beneficial effects of calorie restriction, among which the sirtuin family has been suggested to play a central role. In mammals, it has been established that sirtuins regulate physiological responses to metabolism and stress, two key factors that affect the process of aging. Sirtuins represent a promising new class of conserved deacetylases that play an important role in regulating metabolism and aging. This review focuses on current understanding of the relation between metabolic pathways involving sirtuins and the brain aging process, with focus on SIRT1 and SIRT3. Identification of therapeutic agents capable of modulating the expression and/or activity of sirtuins is expected to provide promising strategies for ameliorating neurodegeneration. Future investigations regarding the concerted interplay of the different sirtuins will help us understand more about the aging process, and potentially lead to the development of therapeutic approaches for the treatment of age-related neurodegenerative diseases and promotion of successful aging.

Oroxylin A induces dissociation of hexokinase II from the mitochondria and inhibits glycolysis by SIRT3-mediated deacetylation of cyclophilin D in breast carcinoma

Oroxylin A is a major active component of the Chinese traditional medicinal plant Scutellaria baicalensis Georgi, which has been reported as a potential anticancer drug. We demonstrated that, Oroxylin A inhibited the glycolysis and the binding of hexokinase II (HK II) with mitochondria in human breast carcinoma cell lines, which was dependent on sirtuin-3 (SIRT3). The level of SIRT3 in mitochondria was increased by Oroxylin A. Then SIRT3 deacetylated cyclophilin D, diminished its peptidyl-prolyl cis-trans isomerase activity and induced its dissociation from the adenine nucleotide translocator. Finally, SIRT3-induced inactivation of cyclophilin D resulted in the detachment of mitochondrial HK II and the inhibition of glycolysis. These results have important implications for the metabolism reprogramming effect and the susceptibility to Oroxylin A-induced mitochondrial cytotoxicity through the regulation of SIRT3 in breast carcinoma.

Single-wall carbon nanohorns inhibited activation of microglia induced by lipopolysaccharide through blocking of Sirt3

Single-wall carbon nanohorns (SWNHs) have been demonstrated to accumulate in cytotoxic levels within organs of various animal models and cell types, which emerge as a wide range of promising biomedical imaging. Septic encephalopathy (SE) is an early sign of sepsis and associated with an increased rate of morbidity and mortality. Microglia activation plays an important role in neuroinflammation, which contributes to neuronal damage. Inhibition of microglia activation may have therapeutic benefits, which can alleviate the progression of neurodegeneration. Therefore, we investigated the functional changes of mice microglia cell lines pre-treated with or without lipopolysaccharide (LPS) induced by SWNHs. To address this question, the research about direct role of SWNHs on the growth, proliferation, and apoptosis of microglia cell lines in mice (N9 and BV2) pre-treated with or without LPS had been performed. Our results indicate that the particle diameter of SWNHs in water is between 342 to 712 nm. The images in scanning electron microscope showed that SWNHs on polystyrene surface are individual particles. LPS induced activation of mice microglia, promoted its growth and proliferation, and inhibited its apoptosis. SWNHs inhibited proliferation, delayed mitotic entry, and promoted apoptosis of mice microglia cells. The effects followed gradually increasing cultured time and concentrations of SWNHs, especially in cells pre-treated with LPS. SWNHs induced a significantly increase in G1 phase and inhibition of S phase of mice microglia cells in a dose-manner dependent of SWNHs, especially in cells pre-treated with LPS. The transmission electron microscope images showed that individual spherical SWNH particles smaller than 100 nm in diameters were localized inside lysosomes of mice microglia cells. SWNHs inhibited mitotic entry, growth and proliferation of mice microglia cells, and promoted its apoptosis, especially in cells pre-treated with LPS. SWNHs inhibited expression of Sirt3 and energy metabolism related with Sirt3 in mice microglia cells in a dose-dependent manner, especially in cells pre-treated with LPS. The role of SWNHs on mice microglia was implicating Sirt3 and energy metabolism associated with it.

Exploring the electrostatic repulsion model in the role of Sirt3 in directing MnSOD acetylation status and enzymatic activity

Mitochondrial oxidative metabolism is the major site of ATP production as well as a significant source of reactive oxygen species (ROS) that can cause damage to critical biomolecules. It is well known that mitochondrial enzymes that scavenge ROS are targeted by stress responsive proteins to maintain the fidelity of mitochondrial function. Manganese superoxide dismutase (MnSOD) is a primary mitochondrial ROS scavenging enzyme, and in 1983 Irwin Fridovich proposed an elegant chemical mechanism/model whereby acetylation directs MnSOD enzymatic activity. He christened it the "electrostatic repulsion model." However, the biochemical and genetic mechanism(s) determining how acetylation directs activity and the reasons behind the evolutionarily conserved need for several layers of transcriptional and posttranslational MnSOD regulation remain unknown. In this regard, we and others have shown that MnSOD is regulated, at least in part, by the deacetylation of specific conserved lysines in a reaction catalyzed by the mitochondrial sirtuin, Sirt3. We speculate that the regulation of MnSOD activity by lysine acetylation via an electrostatic repulsion mechanism is a conserved and critical aspect of MnSOD regulation necessary to maintain mitochondrial homeostasis.

The role of sirtuins in modulating redox stressors

For much of the time since their discovery, the sirtuin family of deacetylase enzymes has been associated with extension of life span. This longevity-promoting capacity in numerous model systems has enabled the sirtuins to gain "celebrity status" in the field of aging research. However, the mechanisms underpinning these changes remain incompletely defined. A general phenotype long associated with aging is the dysregulation of biological systems, which partly occurs via the accumulation of damage over time. One of the major sources of this damage is oxidative stress, which can harm both biological structures and the mechanisms with which they are repaired. It is now becoming clear that the beneficial life-span effects of sirtuins, along with many of their other functions, are closely linked to their ability to regulate systems that control the redox environment. Here we investigate the links between sirtuins and their oxidative/redox environment and review the control mechanisms that are regulated by the activity of sirtuin deacetylase proteins.

Emerging characterization of the role of SIRT3-mediated mitochondrial protein deacetylation in the heart

Studies to quantify the protein acetylome show that lysine-residue acetylation rivals phosphorylation in prevalence as a posttranslational modification. Interesting, this posttranslational modification is modified by nutrient flux and by redox stress and targets the vast majority of metabolic pathway proteins in the mitochondria. Furthermore, the mitochondrial deacetylase enzyme SIRT3 appears to be regulated by exercise in skeletal muscle and in response to pressure overload in the heart. The alteration of protein lysine residues by acetylation and the enzymes controlling deacetylation are beginning to be explored as important regulatory events in the control of mitochondrial function and homeostasis. This review focuses on the mitochondrial targets of SIRT3 that are functionally implicated in heart biology and pathology and on the direct cardiac consequences of the genetic manipulation of SIRT3. As therapeutic modulators of other SIRT isoforms have been identified, the longer-term objective of our understanding of this biology would be to identify SIRT3 modulators as putative cardiac therapeutic agents.

Regulation of the mPTP by SIRT3-mediated deacetylation of CypD at lysine 166 suppresses age-related cardiac hypertrophy

Cardiac failure is a leading cause of age-related death, though its root cause remains unknown. Mounting evidence implicates a decline in mitochondrial function due to increased opening of the mitochondrial permeability transition pore (mPTP). Here we report that the NAD+-dependent deacetylase SIRT3 deacetylates the regulatory component of the mPTP, cyclophilin D (CypD) on lysine 166, adjacent to the binding site of cyclosporine A, a CypD inhibitor. Cardiac myocytes from mice lacking SIRT3 exhibit an age-dependent increase in mitochondrial swelling due to increased mPTP opening, a phenotype that is rescued by cyclosporine A. SIRT3 knockout mice show accelerated signs of aging in the heart including cardiac hypertrophy and fibrosis at 13 months of age. SIRT3 knockout mice are also hypersensitive to heart stress induced by transverse aortic constriction (TAC), as evidenced by cardiac hypertrophy, fibrosis, and increased mortality. Together, these data show for the first time that SIRT3 activity is necessary to prevent mitochondrial dysfunction and cardiac hypertrophy during aging and shed light on new pharmacological approaches to delaying aging and treating diseases in cardiac muscle and possibly other post-mitotic tissues.

SIRT3 is regulated by nutrient excess and modulates hepatic susceptibility to lipotoxicity

SIRT3 is the primary mitochondrial deacetylase that modulates mitochondrial metabolic and oxidative stress regulatory pathways. However, its role in response to nutrient excess remains unknown. Thus, we investigated SIRT3 regulation of the electron transfer chain and evaluated the role of SIRT3 in hepatic lipotoxic stress. SIRT3-depleted HepG2 cells show diffuse disruption in mitochondrial electron transfer chain functioning, a concurrent reduction in the mitochondrial membrane potential, and excess basal reactive oxygen species levels. As this phenotype may predispose to increased lipotoxic hepatic susceptibility we evaluated the expression of SIRT3 in murine liver after chronic high-fat feeding. In this nutrient-excess model SIRT3 transcript and protein levels are downregulated in parallel with increased hepatic fat storage and oxidative stress. Palmitate was used to investigate lipotoxic susceptibility in SIRT3 knockout mouse primary hepatocytes and SIRT3-siRNA-transfected HepG2 cells. Under SIRT3-deficient conditions palmitate enhances reactive oxygen species and increases hepatocyte death. Reconstitution of SIRT3 levels and/or treatment with N-acetylcysteine ameliorates these adverse effects. In conclusion SIRT3 functions to ameliorate hepatic lipotoxicity, although paradoxically, exposure to high fat downregulates this adaptive program in the liver. This SIRT3-dependent lipotoxic susceptibility is possibly modulated, in part, by SIRT3-mediated control of electron transfer chain flux.

NAD+-dependent deacetylase SIRT3 regulates mitochondrial protein synthesis by deacetylation of the ribosomal protein MRPL10

A member of the sirtuin family of NAD(+)-dependent deacetylases, SIRT3, is located in mammalian mitochondria and is important for regulation of mitochondrial metabolism, cell survival, and longevity. In this study, MRPL10 (mitochondrial ribosomal protein L10) was identified as the major acetylated protein in the mitochondrial ribosome. Ribosome-associated SIRT3 was found to be responsible for deacetylation of MRPL10 in an NAD(+)-dependent manner. We mapped the acetylated Lys residues by tandem mass spectrometry and determined the role of these residues in acetylation of MRPL10 by site-directed mutagenesis. Furthermore, we observed that the increased acetylation of MRPL10 led to an increase in translational activity of mitochondrial ribosomes in Sirt3(-/-) mice. In a similar manner, ectopic expression and knockdown of SIRT3 in C2C12 cells resulted in the suppression and enhancement of mitochondrial protein synthesis, respectively. Our findings constitute the first evidence for the regulation of mitochondrial protein synthesis by the reversible acetylation of the mitochondrial ribosome and characterize MRPL10 as a novel substrate of the NAD(+)-dependent deacetylase, SIRT3.