Sirt6 opposes glycochenodeoxycholate-induced apoptosis of biliary epithelial cells through the AMPK/PGC-1α pathway

Mitochondrial regulation of diabetic endothelial dysfunction: Pathophysiological links

Micro- and macrovascular complications frequently occur in patients with diabetes, with endothelial dysfunction playing a key role in the development and progression of the complications. For the early diagnosis and optimal treatment of vascular complications associated with diabetes, it is imperative to comprehend the cellular and molecular mechanisms governing the function of diabetic endothelial cells. Mitochondria function as crucial sensors of environmental and cellular stress regulating endothelial cell viability, structural integrity and function. Impaired mitochondrial quality control mechanisms and mitochondrial dysfunction are the main features of endothelial damage. Hence, targeted mitochondrial therapy is considered promising novel therapeutic options in vascular complications of diabetes. In this review, we focus on the mitochondrial functions in the vascular endothelial cells and the pathophysiological role of mitochondria in diabetic endothelial dysfunction, aiming to provide a reference for related drug development and clinical diagnosis and treatment.

USP18 Stabilized FTO Protein to Activate Mitophagy in Ischemic Stroke Through Repressing m6A Modification of SIRT6

Ischemic stroke (IS) is a dangerous cerebrovascular disorder with a significant incidence and death rate. Ubiquitin-specific peptidase 18 (USP18) has been proven to mitigate ischemic brain damage; however, its potential regulatory mechanisms remain unclear. In vivo and in vitro models of IS were established by middle cerebral artery occlusion (MCAO) and oxygen-glucose deprivation/reoxygenation (OGD/R). Neurocyte injury was detected by MTT, LDH, ROS level, mitochondrial membrane potential (Δψm), and flow cytometry. Molecular expression was evaluated by qPCR, Western blotting, and immunofluorescence staining. Molecular mechanisms were determined by Co-IP, RIP, and MeRIP. IS injury was determined by neurological behavior score and TTC staining. Mitophagy was observed by TEM. USP18 and fat mass and obesity-associated protein (FTO) expression declined after OGD/R. Dysfunctional mitochondrial and apoptosis in OGD/R-stimulated neurocytes were eliminated by USP18/FTO overexpression via mitophagy activation. USP18-mediated de-ubiquitination was responsible for increasing FTO protein stability. Up-regulation of FTO protein restrained m6A modification of sirtuin6 (SIRT6) in a YTHDF2-dependent manner to enhance SIRT6 expression and subsequent activation of AMPK/PGC-1α/AKT signaling. FTO induced mitophagy to ameliorate nerve cell damage through SIRT6/AMPK/PGC-1α/AKT pathway. Finally, USP18/FTO overexpression relieved IS in rats via triggering SIRT6/AMPK/PGC-1α/AKT axis-mediated mitophagy. USP18 increased FTO protein stability to trigger SIRT6-induced mitophagy, thus mitigating IS. Our data unravel the novel neuroprotective mechanism of USP18 and suggest its potential as a promising treatment target for IS.

Oridonin ameliorates doxorubicin induced-cardiotoxicity via the E2F1/Sirt6/PGC1α pathway in mice

Doxorubicin induced cardiotoxicity (DIC) arises from mitochondrial dysfunction and oxidative stress. Oridonin (Ori), a natural tetracycline diterpenoid, has shown cardiac protective effect; however, its role in DIC remains unclear. This study investigates the protective effect of Ori against DIC and elucidates its underlying molecular mechanisms. The results demonstrate that Ori significantly alleviated DIC by improving myocardial structure, reducing the proportion of apoptotic cells, and alleviating the myocardial oxidative damage and mitochondrial dysfunction both in vivo and in vitro. Doxorubicin significantly decreased Sirt6 and PGC1α levels in cardiac tissues, which was reversed by Ori. Furthermore, Sirt6 overexpression significantly improved myocardial structure and reduced the proportion of apoptotic cells by reducing oxidative stress and improving mitochondrial function. The protective effect of Ori is neutralized by the Sirt6 inhibitor OSS_128167, evidenced by downregulated mRNA and protein expression of PGC1α. The transcription factor E2F1 was upregulated by doxorubicin, leading to decreased Sirt6 expression-an effect mitigated by Ori. Molecular docking simulations indicate direct binding between Ori and specific amino acid residues on E2F1 through hydroxyl bonds. These findings uncover a novel mechanism whereby Ori attenuates DIC by modulating the E2F1/Sirt6/PGC1α pathway.

Astragaloside IV Inhibited Podocyte Pyroptosis in Diabetic Kidney Disease by Regulating SIRT6/HIF-1α Axis

To investigate the effect of astragaloside IV (AS) on podocytes pyroptosis in diabetic kidney disease (DKD). Forty male Sprague-Dawley rats were randomly divided into normal group (n = 10) and model group (n = 30). Rats in model group were intraperitoneally injected streptozotocin (60 mg/kg) for 3 days to induce DKD. Then rats were divided into DKD group, AS group, and UBCS group. The AS group was given 40 mg/kg/d of AS by gavage, and UBCS group was given 50 mg/kg/d of UBCS039 by gavage, and normal group and DKD group were given the same amount saline for 8 weeks, once a day. Hematoxylin-eosin and masson staining were used to observe pathology of kidney. Rat podocytes were divided into normal group, mannitol hypertonic group, high-glucose group, UBCS group, OSS group, and AS group. Western blotting, quantitative real-time polymerase chain reaction, immunofluorescence, and flow cytometry were used to analyze pyroptosis-related markers and reactive oxygen species (ROS) levels. Results showed that AS inhibited ROS and alleviated podocytes pyroptosis in rats by increasing expression of sirtuin 6 (SIRT6) and decreasing expression of hypoxia inducible factor 1 subunit alpha (HIF-1α). UBCS039 and AS enhanced SIRT6 level, decreased HIF-1α level, and finally improved pyroptosis of podocytes in vitro, whereas OSS-128167 showed the opposite effect for podocytes pyroptosis. AS improved podocytes pyroptosis in DKD by regulating SIRT6/HIF-1α pathway, thereby alleviating injury of DKD.

KLF6 alleviates hepatic ischemia-reperfusion injury by inhibiting autophagy

Hepatic ischemia-reperfusion (I/R) injury, a common clinical complication of liver transplantation, gravely affects patient prognosis. Krüppel-like factors (KLFs) constitute a family of C2/H2 zinc finger DNA-binding proteins. KLF6, a member of the KLF protein family, plays crucial roles in proliferation, metabolism, inflammation, and injury responses; however, its role in HIR is largely remains unknown. After I/R injury, we found that KLF6 expression in mice and hepatocytes was significantly upregulated. Mice were then subjected to I/R following injection of shKLF6- and KLF6-overexpressing adenovirus through the tail vein. KLF6 deficiency markedly exacerbated liver damage, cell apoptosis, and activation of hepatic inflammatory responses, whereas hepatic overexpression of KLF6 in mice produced the opposite results. In addition, we knocked out or overexpressed KLF6 in AML12 cells before exposing them to a hypoxia-reoxygenation challenge. KLF6 knockout decreased cell viability and increased hepatocyte inflammation, apoptosis, and ROS, whereas KLF6 overexpression had the opposite effects. Mechanistically, KLF6 inhibited the overactivation of autophagy at the initial stage, and the regulatory effect of KLF6 on I/R injury was autophagy-dependent. CHIP-qPCR and luciferase reporter gene assays confirmed that KLF6 bound to the promoter region of Beclin1 and inhibited its transcription. Additionally, KLF6 activated the mTOR/ULK1 pathway. Finally, we performed a retrospective analysis of the clinical data of liver transplantation patients and identified significant associations between KLF6 expression and liver function following liver transplantation. In conclusion, KLF6 inhibited the overactivation of autophagy via transcriptional regulation of Beclin1 and activation of the mTOR/ULK1 pathway, thereby protecting the liver from I/R injury. KLF6 is expected to serve as a biomarker for estimating the severity of I/R injury following liver transplantation.

Oridonin ameliorates acetaminophen-induced acute liver injury through ATF4/PGC-1α pathway

Acetaminophen (APAP) overdose-induced acute liver injury (ALI) causes hepatocyte cell death, oxidative stress, and inflammation. Oridonin (Ori), a covalent NLRP3-inflammasome inhibitor, ameliorates APAP-induced ALI through an unclear molecular mechanism. This study found that Ori decreased hepatic cytochrome P450 2E1 level and increased glutathione content to prevent APAP metabolism, and then reduced the necrotic area, improved liver function, and inhibited APAP-induced proinflammatory cytokines and oxidative stress. Ori also decreased activating transcription factor 4 (ATF4) protein levels and increased peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) to reduce APAP-induced endoplasmic reticulum stress activation and mitochondrial dysfunction. Furthermore, western blot and luciferase assay found that ATF4 inhibited transcription in the PGC-1α promoter -507 to -495 region to reduce PGC-1α levels, while ATF4 knockdown neutralized the hepatoprotective effect of Ori. Molecular docking showed that Ori bound to ATF4's amino acid residue glutamate 302 through 6, 7, and 18 hydroxyl bands. Our findings demonstrated that Ori prevented metabolic activation of APAP and further inhibited the ATF4/PGC-1α pathway to alleviate APAP overdose-induced hepatic toxicity, which illuminated its potential therapeutic effects on ALI.

Rhaponticum carthamoides improved energy metabolism and oxidative stress through the SIRT6/Nrf2 pathway to ameliorate myocardial injury

BACKGROUND

Rhaponticum carthamoides (Willd.) Iljin (Rha) is a member of the family Compositae that is widely used in folk medicine as a dietary supplement to treat cardiovascular diseases (CVDs), such as senile cardiac insufficiency, and to restore myocardial function after surgery. Sirtuin 6 (SIRT6), an NAD⁺-dependent class III histone deacetylase, plays a considerable role in the administration of CVDs. However, the specific effects and mechanism of Rha on myocardial injury remain unknown.

PURPOSE

This study aimed to explore the therapeutic potential of Rha against myocardial injury as well as its underlying mechanisms in vivo and in vitro.

METHODS

A myocardial ischaemia model was established in male SD rats by subcutaneously injecting ISO. The rats were gavaged with Rha (40, 80, 160 mg/kg) or Rho (6 ml/kg) for 14 successive days and then injected subcutaneously with ISO or saline solution on the 13th and 14th days. The positive effects of Rha against myocardial injury in rats were evaluated by ECG assessment, BP measurements, H&E staining, and myocardial enzyme detection. Biochemical indicators of energy metabolism and oxidative stress, such as NAD⁺/NADH, ATP, and MDA, were analysed by assay kits to assess the effects of Rha. The protein and mRNA expression levels of SIRT6 and Nrf2 in the myocardium were determined by western blotting and real-time PCR.

RESULTS

Our results showed that Rha ameliorated myocardial ischaemia and inhibited energy metabolism disorders (NAD⁺/NADH ratio, ATP, and LD) and oxidative stress (SOD, ROS, etc.) in rat myocardial tissue and H9c2 cells. In addition, Rha upregulated SIRT6 and Nrf2 expression in myocardial injury. Mechanistic studies then found that SIRT6 knockdown reduced the expression of Nrf2 as well as the effects of Rha on the levels of ATP, LD, and ROS, whereas activation of Nrf2 improved the effects of Rha in cells. In summary, Rha might exert its cardioprotective effects via the SIRT6-mediated Nrf2 signaling pathway.

CONCLUSION

The results suggest that Rha regulates energy metabolism and oxidative stress through the SIRT6/Nrf2 signaling pathway to play a protective role in myocardial injury.

SIRT6 regulates SREBP1c-induced glucolipid metabolism in liver and pancreas via the AMPKα-mTORC1 pathway

The aim of this study was to determine the mechanism by which SIRT6 regulates glucolipid metabolism disorders. We detected histological and molecular changes in Sprague-Dawley rats as well as in BRL 3A and INS-1 cell lines subjected to overnutrition and starvation. SIRT6, SREBP1c, and glucolipid metabolism biomarkers were identified by fluorescence co-localization, real-time PCR, and western blotting. Gene silencing studies were performed. Recombinant SIRT6, AMPK agonist (AICAR), mTOR inhibitor (rapamycin), and liver X receptor (LXR) agonist (T0901317) were used to pre-treated in BRL 3A and INS-1 cells. Real-time PCR and western blotting were used to detect related proteins, and cell counting was utilized to detect proliferation. We obtained conflicting results; SIRT6 and SREBP1c appeared in both the liver and pancreas of high-fat and hungry rats. Recombinant SIRT6 alleviated the decrease in AMPKα and increase in mTORC1 (complex of mTOR, Raptor, and Rheb) caused by overnutrition. SIRT6 siRNA reversed the glucolipid metabolic disorders caused by the AMPK agonist and mTOR inhibitor but not by the LXR agonist. Taken together, our results demonstrate that SIRT6 regulates glycolipid metabolism through AMPKα-mTORC1 regulating SREBP1c in the liver and pancreas induced by overnutrition and starvation, independent of LXR.

Roles of SIRT6 in kidney disease: a novel therapeutic target

SIRT6 is an NAD+ dependent deacetylase that belongs to the mammalian sirtuin family. SIRT6 is mainly located in the nucleus and regulates chromatin remodeling, genome stability, and gene transcription. SIRT6 extensively participates in various physiological activities such as DNA repair, energy metabolism, oxidative stress, inflammation, and fibrosis. In recent years, the role of epigenetics such as acetylation modification in renal disease has gradually received widespread attention. SIRT6 reduces oxidative stress, inflammation, and renal fibrosis, which is of great importance in maintaining cellular homeostasis and delaying the chronic progression of kidney disease. Here, we review the structure and biological function of SIRT6 and summarize the regulatory mechanisms of SIRT6 in kidney disease. Moreover, the role of SIRT6 as a potential therapeutic target for the progression of kidney disease will be discussed. SIRT6 plays an important role in kidney disease. SIRT6 regulates mitochondrial dynamics and mitochondrial biogenesis, induces G2/M cycle arrest, and plays an antioxidant role in nephrotoxicity, IR, obstructive nephropathy, and sepsis-induced AKI. SIRT6 prevents and delays progressive CKD induced by hyperglycemia, kidney senescence, hypertension, and lipid accumulation by regulating mitochondrial biogenesis, and has antioxidant, anti-inflammatory, and antifibrosis effects. Additionally, hypoxia, inflammation, and fibrosis are the main mechanisms of the AKI-to-CKD transition. SIRT6 plays a critical role in the AKI-to-CKD transition and kidney repair through anti-inflammatory, antifibrotic, and mitochondrial quality control mechanisms. AKI Acute kidney injury, CKD Chronic kidney disease.

Vitexin ameliorates glycochenodeoxycholate-induced hepatocyte injury through SIRT6 and JAK2/STAT3 pathways

Objectives

Vitexin, a natural flavonoid, is commonly found in many foods and traditional herbal medicines and has clear health benefits. However, the role of vitexin in cholestasis is presently unclear. This study investigated whether vitexin mitigated glycochenodeoxycholate (GCDC)-induced hepatocyte injury and further elucidated the underlying mechanisms.

Materials and Methods

A cell counting kit-8 (CCK-8) assay was conducted to evaluate cell viability. The mitochondrial membrane potential (MMP, Δψm), reactive oxygen species (ROS) levels, and apoptosis rate of hepatocytes exposed to GCDC were detected by flow cytometry (FCM). We then measured the cytoprotective effects of vitexin against oxidative stress. The molecular signaling pathway was further investigated by using Western blotting and signaling pathway inhibitors.

Results

Here, we showed that vitexin increased cell viability and reduced cell apoptosis, necroptosis, and oxidative stress in a dose-dependent manner in GCDC-treated hepatocytes. In addition, by using selective inhibitors, we further confirmed that inhibition of the JAK2/STAT3 pathway by vitexin was mediated by prolonged activation of Sirtuin 6 (SIRT6).

Conclusion

Vitexin attenuated GCDC-induced hepatocyte injury via SIRT6 and the JAK2/STAT3 pathways.

PRMT1-mediated EZH2 methylation promotes breast cancer cell proliferation and tumorigenesis

Protein arginine methyltransferase 1 (PRMT1) is able to promote breast cancer cell proliferation. However, the detailed mechanisms of PRMT1-mediated breast cancer cell proliferation are largely unknown. In this study, we reveal that PRMT1-mediated methylation of EZH2 at the R342 site (meR342-EZH2) has a great effect on PRMT1-induced cell proliferation. We also demonstrate that meR342-EZH2 can accelerate breast cancer cell proliferation in vitro and in vivo. Further, we show that meR342-EZH2 promotes cell cycle progression by repressing P16 and P21 transcription expression. In terms of mechanism, we illustrate that meR342-EZH2 facilitates EZH2 binding with SUZ12 and PRC2 assembly by preventing AMPKα1-mediated phosphorylation of pT311-EZH2, which results in suppression of P16 and P21 transcription by enhancing EZH2 expression and H3K27me3 enrichment at P16 and P21 promoters. Finally, we validate that the expression of PRMT1 and meR342-EZH2 is negatively correlated with pT311-EZH2 expression. Our findings suggest that meR342-EZH2 may become a novel therapeutic target for the treatment of breast cancer.

Melatonin attenuates diabetic cardiomyopathy and reduces myocardial vulnerability to ischemia-reperfusion injury by improving mitochondrial quality control: Role of SIRT6

Targeting mitochondrial quality control with melatonin has been found promising for attenuating diabetic cardiomyopathy (DCM), although the underlying mechanisms remain largely undefined. Activation of SIRT6 and melatonin membrane receptors exerts cardioprotective effects while little is known about their roles during DCM. Using high-fat diet-streptozotocin-induced diabetic rat model, we found that prolonged diabetes significantly decreased nocturnal circulatory melatonin and heart melatonin levels, reduced the expressions of cardiac melatonin membrane receptors, and decreased myocardial SIRT6 and AMPK-PGC-1α-AKT signaling. 16 weeks of melatonin treatment inhibited the progression of DCM and the following myocardial ischemia-reperfusion (MI/R) injury by reducing mitochondrial fission, enhancing mitochondrial biogenesis and mitophagy via re-activating SIRT6 and AMPK-PGC-1α-AKT signaling. After the induction of diabetes, adeno-associated virus carrying SIRT6-specific small hairpin RNA or luzindole was delivered to the animals. We showed that SIRT6 knockdown or antagonizing melatonin receptors abolished the protective effects of melatonin against mitochondrial dysfunction as evidenced by aggravated mitochondrial fission and reduced mitochondrial biogenesis and mitophagy. Additionally, SIRT6 shRNA or luzindole inhibited melatonin-induced AMPK-PGC-1α-AKT activation as well as its cardioprotective actions. Collectively, we demonstrated that long-term melatonin treatment attenuated the progression of DCM and reduced myocardial vulnerability to MI/R injury through preserving mitochondrial quality control. Melatonin membrane receptor-mediated SIRT6-AMPK-PGC-1α-AKT axis played a key role in this process. Targeting SIRT6 with melatonin treatment may be a promising strategy for attenuating DCM and reducing myocardial vulnerability to ischemia-reperfusion injury in diabetic patients.