Serine synthesis sustains macrophage IL-1ß production via NAD+-dependent protein acetylation.

Serine metabolism is involved in the fate decisions of immune cells; however, whether and how de novo serine synthesis shapes innate immune cell function remain unknown. Here, we first demonstrated that inflammatory macrophages have high expression of phosphoglycerate dehydrogenase (PHGDH, the rate-limiting enzyme of de novo serine synthesis) via nuclear factor κB signaling. Notably, the pharmacological inhibition or genetic modulation of PHGDH limits macrophage interleukin (IL)-1ß production through NAD+ accumulation and subsequent NAD+-dependent SIRT1 and SIRT3 expression and activity. Mechanistically, PHGDH not only sustains IL-1ß expression through H3K9/27 acetylation-mediated transcriptional activation of Toll-like receptor 4 but also supports IL-1ß maturation via NLRP3-K21/22/24/ASC-K21/22/24 acetylation-mediated activation of the NLRP3 inflammasome. Moreover, mice with myeloid-specific depletion of Phgdh show alleviated inflammatory responses in lipopolysaccharide-induced systemic inflammation. This study reveals a network by which a metabolic enzyme, involved in de novo serine synthesis, mediates post-translational modifications and epigenetic regulation to orchestrate IL-1ß production, providing a potential inflammatory disease target.

Lysine acetylation restricts mutant IDH2 activity to optimize transformation in AML cells.

Mutant isocitrate dehydrogenase (IDH) 1 and 2 play a pathogenic role in cancers, including acute myeloid leukemia (AML), by producing oncometabolite 2-hydroxyglutarate (2-HG). We recently reported that tyrosine phosphorylation activates IDH1 R132H mutant in AML cells. Here, we show that mutant IDH2 (mIDH2) R140Q commonly has K413 acetylation, which negatively regulates mIDH2 activity in human AML cells by attenuating dimerization and blocking binding of substrate (α-ketoglutarate) and cofactor (NADPH). Mechanistically, K413 acetylation of mitochondrial mIDH2 is achieved through a series of hierarchical phosphorylation events mediated by tyrosine kinase FLT3, which phosphorylates mIDH2 to recruit upstream mitochondrial acetyltransferase ACAT1 and simultaneously activates ACAT1 and inhibits upstream mitochondrial deacetylase SIRT3 through tyrosine phosphorylation. Moreover, we found that the intrinsic enzyme activity of mIDH2 is much higher than mIDH1, thus the inhibitory K413 acetylation optimizes leukemogenic ability of mIDH2 in AML cells by both producing sufficient 2-HG for transformation and avoiding cytotoxic accumulation of intracellular 2-HG.

SENP1-Sirt3 Signaling Controls Mitochondrial Protein Acetylation and Metabolism.

Sirt3, as a major mitochondrial nicotinamide adenine dinucleotide (NAD)-dependent deacetylase, is required for mitochondrial metabolic adaption to various stresses. However, how to regulate Sirt3 activity responding to metabolic stress remains largely unknown. Here, we report Sirt3 as a SUMOylated protein in mitochondria. SUMOylation suppresses Sirt3 catalytic activity. SUMOylation-deficient Sirt3 shows elevated deacetylation on mitochondrial proteins and increased fatty acid oxidation. During fasting, SUMO-specific protease SENP1 is accumulated in mitochondria and quickly de-SUMOylates and activates Sirt3. SENP1 deficiency results in hyper-SUMOylation of Sirt3 and hyper-acetylation of mitochondrial proteins, which reduces mitochondrial metabolic adaption responding to fasting. Furthermore, we find that fasting induces SENP1 translocation into mitochondria to activate Sirt3. The studies on mice show that Sirt3 SUMOylation mutation reduces fat mass and antagonizes high-fat diet (HFD)-induced obesity via increasing oxidative phosphorylation and energy expenditure. Our results reveal that SENP1-Sirt3 signaling modulates Sirt3 activation and mitochondrial metabolism during metabolic stress.

Dual modifying of MAVS at lysine 7 by SIRT3-catalyzed deacetylation and SIRT5-catalyzed desuccinylation orchestrates antiviral innate immunity.

To effectively protect the host from viral infection while avoiding excessive immunopathology, the innate immune response must be tightly controlled. However, the precise regulation of antiviral innate immunity and the underlying mechanisms remain unclear. Here, we find that sirtuin3 (SIRT3) interacts with mitochondrial antiviral signaling protein (MAVS) to catalyze MAVS deacetylation at lysine residue 7 (K7), which promotes MAVS aggregation, as well as TANK-binding kinase I and IRF3 phosphorylation, resulting in increased MAVS activation and enhanced type I interferon signaling. Consistent with these findings, loss of Sirt3 in mice and zebrafish renders them more susceptible to viral infection compared to their wild-type (WT) siblings. However, Sirt3 and Sirt5 double-deficient mice exhibit the same viral susceptibility as their WT littermates, suggesting that loss of Sirt5 in Sirt3-deficient mice may counteract the increased viral susceptibility displayed in Sirt3-deficient mice. Thus, we not only demonstrate that SIRT3 positively regulates antiviral immunity in vitro and in vivo, likely via MAVS, but also uncover a previously unrecognized mechanism by which SIRT3 acts as an accelerator and SIRT5 as a brake to orchestrate antiviral innate immunity.

Decrotonylation of cGAS K254 prompts homologous recombination repair by blocking its DNA binding and releasing PARP1.

Cyclic GMP-AMP synthase (cGAS), a cytosolic DNA sensor, also exhibits nuclear genomic localization and is involved in DNA damage signaling. In this study, we investigated the impact of cGAS crotonylation on the regulation of the DNA damage response, particularly homologous recombination repair, following exposure to ionizing radiation (IR). Lysine 254 of cGAS is constitutively crotonylated by the CREB-binding protein; however, IR-induced DNA damage triggers sirtuin 3 (SIRT3)-mediated decrotonylation. Lysine 254 decrotonylation decreased the DNA-binding affinity of cGAS and inhibited its interaction with PARP1, promoting homologous recombination repair. Moreover, SIRT3 suppression led to homologous recombination repair inhibition and markedly sensitized cancer cells to IR and DNA-damaging chemicals, highlighting SIRT3 as a potential target for cancer therapy. Overall, this study revealed the crucial role of cGAS crotonylation in the DNA damage response. Furthermore, we propose that modulating cGAS and SIRT3 activities could be potential strategies for cancer therapy.

SIRT3-dependent delactylation of cyclin E2 prevents hepatocellular carcinoma growth.

Lysine lactylation (Kla) is a recently discovered histone mark derived from metabolic lactate. The NAD+ -dependent deacetylase SIRT3, which can also catalyze removal of the lactyl moiety from lysine, is expressed at low levels in hepatocellular carcinoma (HCC) and has been suggested to be an HCC tumor suppressor. Here we report that SIRT3 can delactylate non-histone proteins and suppress HCC development. Using SILAC-based quantitative proteomics, we identify cyclin E2 (CCNE2) as one of the lactylated substrates of SIRT3 in HCC cells. Furthermore, our crystallographic study elucidates the mechanism of CCNE2 K348la delactylation by SIRT3. Our results further suggest that lactylated CCNE2 promotes HCC cell growth, while SIRT3 activation by Honokiol induces HCC cell apoptosis and prevents HCC outgrowth in vivo by regulating Kla levels of CCNE2. Together, our results establish a physiological function of SIRT3 as a delactylase that is important for suppressing HCC, and our structural data could be useful for the future design of activators.

Uncovering SIRT3 and SHMT2-dependent pathways as novel targets for apigenin in modulating colorectal cancer: In vitro and in vivo studies.

Despite significant advances in the treatment of colorectal cancer (CRC), identification of novel targets and treatment options are imperative for improving its prognosis and survival rates. The mitochondrial SIRT3 and SHMT2 have key roles in metabolic reprogramming and cell proliferation. This study investigated the potential use of the natural product apigenin in CRC treatment employing both in vivo and in vitro models and explored the role of SIRT3 and SHMT2 in apigenin-induced CRC apoptosis. The role of SHMT2 in CRC patients' survival was verified using TCGA database. In vivo, apigenin treatment restored the normal colon appearance. On the molecular level, apigenin augmented the immunohistochemical expression of cleaved caspase-3 and attenuated SIRT3 and SHMT2 mRNA expression CRC patients with decreased SHMT2 expression had improved overall and disease-free survival rates. In vitro, apigenin reduced the cell viability in a time-dependent manner, induced G0/G1 cell cycle arrest, and increased the apoptotic cell population compared to the untreated control. Mechanistically, apigenin treatment mitigated the expression of SHMT2, SIRT3, and its upstream long intergenic noncoding RNA LINC01234 in CRC cells. Conclusively, apigenin induces caspase-3-dependent apoptosis in CRC through modulation of SIRT3-triggered mitochondrial pathway suggesting it as a promising therapeutic agent to improve patient outcomes.

SIRT3/6: an amazing challenge and opportunity in the fight against fibrosis and aging.

Fibrosis is a typical aging-related pathological process involving almost all organs, including the heart, kidney, liver, lung, and skin. Fibrogenesis is a highly orchestrated process defined by sequences of cellular response and molecular signals mechanisms underlying the disease. In pathophysiologic conditions associated with organ fibrosis, a variety of injurious stimuli such as metabolic disorders, epigenetic changes, and aging may induce the progression of fibrosis. Sirtuins protein is a kind of deacetylase which can regulate cell metabolism and participate in a variety of cell physiological functions. In this review, we outline our current understanding of common principles of fibrogenic mechanisms and the functional role of SIRT3/6 in aging-related fibrosis. In addition, sequences of novel protective strategies have been identified directly or indirectly according to these mechanisms. Here, we highlight the role and biological function of SIRT3/6 focus on aging fibrosis, as well as their inhibitors and activators as novel preventative or therapeutic interventions for aging-related tissue fibrosis.

Staphylococcus aureus Conquers Host by Hijacking Mitochondria via PFKFB3 in Epithelial Cells.

Staphylococcus aureus (S. aureus) persists within mammary epithelial cells for an extended duration, exploiting the host metabolic resources to facilitate replication. This study revealed a mechanism by which intracellular S. aureus reprograms host metabolism, with PFKFB3 playing a crucial role in this process. Mechanistically, S. aureus induced mitochondrial damage, leading to increased levels of mitochondrial reactive oxygen species (mROS) and dysfunction in electron transport chain (ETC). Moreover, S. aureus shifted the balance of mitochondrial dynamics from fusion to fission, subsequently activating PINK1-PRKN-dependent mitophagy, causing loss of the sirtuin 3 (SIRT3) to stabilize hypoxic inducible factor 1α (HIF1α), and shifting the host metabolism toward enhanced glycolysis. The inhibition of PFKFB3 reversed the mitochondrial damage and degradation of SIRT3 induced by S. aureus. Overall, our findings elucidate the mechanism by which S. aureus reprograms host metabolism and offer insights into the treatment of S. aureus infection.

Ferrostatin-1 specifically targets mitochondrial iron-sulfur clusters and aconitase to improve cardiac function in Sirtuin 3 cardiomyocyte knockout mice.

AIMS: Ferroptosis is a form of iron-regulated cell death implicated in ischemic heart disease. Our previous study revealed that Sirtuin 3 (SIRT3) is associated with ferroptosis and cardiac fibrosis. In this study, we tested whether the knockout of SIRT3 in cardiomyocytes (SIRT3cKO) promotes mitochondrial ferroptosis and whether the blockade of ferroptosis would ameliorate mitochondrial dysfunction. METHODS AND RESULTS: Mitochondrial and cytosolic fractions were isolated from the ventricles of mice. Cytosolic and mitochondrial ferroptosis were analyzed by comparison to SIRT3loxp mice. An echocardiography study showed that SIRT3cKO mice developed heart failure as evidenced by a reduction of EF% and FS% compared to SIRT3loxp mice. Comparison of mitochondrial and cytosolic fractions of SIRT3cKO and SIRT3loxp mice revealed that, upon loss of SIRT3, mitochondrial, but not cytosolic, total lysine acetylation was significantly increased. Similarly, acetylated p53 was significantly upregulated only in the mitochondria. These data demonstrate that SIRT3 is the primary mitochondrial deacetylase. Most importantly, loss of SIRT3 resulted in significant reductions of frataxin, aconitase, and glutathione peroxidase 4 (GPX4) in the mitochondria. This was accompanied by a significant increase in levels of mitochondrial 4-hydroxynonenal. Treatment of SIRT3cKO mice with the ferroptosis inhibitor ferrostatin-1 (Fer-1) for 14 days significantly improved preexisting heart failure. Mechanistically, Fer-1 treatment significantly increased GPX4 and aconitase expression/activity, increased mitochondrial iron­sulfur clusters, and improved mitochondrial membrane potential and Complex IV activity. CONCLUSIONS: Inhibition of ferroptosis ameliorated cardiac dysfunction by specifically targeting mitochondrial aconitase and iron­sulfur clusters. Blockade of mitochondrial ferroptosis may be a novel therapeutic target for mitochondrial cardiomyopathies.

Anticancer actions of carnosine in cellular models of prostate cancer.

Treatments for organ-confined prostate cancer include external beam radiation therapy, radical prostatectomy, radiotherapy/brachytherapy, cryoablation and high-intensity focused ultrasound. None of these are cancer-specific and are commonly accompanied by side effects, including urinary incontinence and erectile dysfunction. Moreover, subsequent surgical treatments following biochemical recurrence after these interventions are either limited or affected by the scarring present in the surrounding tissue. Carnosine (ß-alanyl-L-histidine) is a histidine-containing naturally occurring dipeptide which has been shown to have an anti-tumorigenic role without any detrimental effect on healthy cells; however, its effect on prostate cancer cells has never been investigated. In this study, we investigated the effect of carnosine on cell proliferation and metabolism in both a primary cultured androgen-resistant human prostate cancer cell line, PC346Flu1 and murine TRAMP-C1 cells. Our results show that carnosine has a significant dose-dependent inhibitory effect in vitro on the proliferation of both human (PC346Flu1) and murine (TRAMP-C1) prostate cancer cells, which was confirmed in 3D-models of the same cells. Carnosine was also shown to decrease adenosine triphosphate content and reactive species which might have been caused in part by the increase in SIRT3 also shown after carnosine treatment. These encouraging results support the need for further human in vivo work to determine the potential use of carnosine, either alone or, most likely, as an adjunct therapy to surgical or other conventional treatments.

Acetylation of aldehyde dehydrogenase ALDH1L2 regulates cellular redox balance and the chemosensitivity of colorectal cancer to 5-fluorouracil.

Folate-mediated one-carbon metabolism (FOCM) is crucial in sustaining rapid proliferation and survival of cancer cells. The folate cycle depends on a series of key cellular enzymes, including aldehyde dehydrogenase 1 family member L2 (ALDH1L2) that is usually overexpressed in cancer cells, but the regulatory mechanism of ALDH1L2 remains undefined. In this study, we observed the significant overexpression of ALDH1L2 in colorectal cancer (CRC) tissues, which is associated with poor prognosis. Mechanistically, we identified that the acetylation of ALDH1L2 at the K70 site is an important regulatory mechanism inhibiting the enzymatic activity of ALDH1L2 and disturbing cellular redox balance. Moreover, we revealed that sirtuins 3 (SIRT3) directly binds and deacetylates ALDH1L2 to increase its activity. Interestingly, the chemotherapeutic agent 5-fluorouracil (5-Fu) inhibits the expression of SIRT3 and increases the acetylation levels of ALDH1L2 in colorectal cancer cells. 5-Fu-induced ALDH1L2 acetylation sufficiently inhibits its enzymatic activity and the production of NADPH and GSH, thereby leading to oxidative stress-induced apoptosis and suppressing tumor growth in mice. Furthermore, the K70Q mutant of ALDH1L2 sensitizes cancer cells to 5-Fu both in vitro and in vivo through perturbing cellular redox and serine metabolism. Our findings reveal an unknown 5-Fu-SIRT3-ALDH1L2 axis regulating redox homeostasis, and suggest that targeting ALDH1L2 is a promising therapeutic strategy to sensitize tumor cells to chemotherapeutic agents.

Gastrodin regulates the expression of renin-angiotensin system-SIRT3 and proinflammatory mediators in reactive astrocytes via activated microglia.

Gastrodin, an anti-inflammatory herbal agent, is known to suppress microglia activation. Here, we investigated whether it would exert a similar effect in reactive astrocytes and whether it might act through the renin-angiotensin system (RAS) and sirtuin 3 (SIRT3). Angiotensinogen (ATO), angiotensin-converting enzyme (ACE), angiotensin II type 1 (AT1) and type 2 (AT2) receptor and SIRT3 expression was detected in TNC-1 astrocytes treated with BV-2 microglia conditioned medium (CM) with or without gastrodin and lipopolysaccharide (LPS) pre-treatment by RT-PCR, immunofluorescence and western blotting analysis. Expression of C3 (A1 astrocyte marker), S100A10 (A2 astrocyte marker), proinflammatory cytokines and neurotrophic factors was then evaluated. The results showed a significant increase of ATO, ACE, AT1, SIRT3, C3, proinflammatory cytokines and neurotrophic factors expression in TNC-1 astrocytes incubated in CM + LPS when compared with cells incubated in the CM, but AT2 and S100A10 expression was reduced. TNC-1 astrocytes responded vigorously to BV-2 CM treated with gastrodin + LPS as compared with the control. This was evident by the decreased expression of the abovementioned protein markers, except for AT2 and S100A10. Interestingly, SIRT3, IGF-1 and BDNF expression was enhanced, suggesting that gastrodin inhibited the expression of RAS and proinflammatory mediators but promoted the expression of neurotrophic factors. And gastrodin regulated the phenotypic changes of astrocytes through AT1. Additionally, azilsartan (a specific inhibitor of AT1) inhibited the expression of C3 and S100A10, which remained unaffected in gastrodin and azilsartan combination treatment. These findings provide evidence that gastrodin may have a therapeutic effect via regulating RAS-SIRT3.

Glutamine deprivation in glioblastoma stem cells triggers autophagic SIRT3 degradation to epigenetically restrict CD133 expression and stemness.

Glioblastoma multiforme (GBM) is a highly malignant brain tumor, and glioblastoma stem cells (GSCs) are the primary cause of GBM heterogeneity, invasiveness, and resistance to therapy. Sirtuin 3 (SIRT3) is mainly localized in the mitochondrial matrix and plays an important role in maintaining GSC stemness through cooperative interaction with the chaperone protein tumor necrosis factor receptor-associated protein 1 (TRAP1) to modulate mitochondrial respiration and oxidative stress. The present study aimed to further elucidate the specific mechanisms by which SIRT3 influences GSC stemness, including whether SIRT3 serves as an autophagy substrate and the mechanism of SIRT3 degradation. We first found that SIRT3 is enriched in CD133+ GSCs. Further experiments revealed that in addition to promoting mitochondrial respiration and reducing oxidative stress, SIRT3 maintains GSC stemness by epigenetically regulating CD133 expression via succinate. More importantly, we found that SIRT3 is degraded through the autophagy-lysosome pathway during GSC differentiation into GBM bulk tumor cells. GSCs are highly dependent on glutamine for survival, and in these cells, we found that glutamine deprivation triggers autophagic SIRT3 degradation to restrict CD133 expression, thereby disrupting the stemness of GSCs. Together our results reveal a novel mechanism by which SIRT3 regulates GSC stemness. We propose that glutamine restriction to trigger autophagic SIRT3 degradation offers a strategy to eliminate GSCs, which combined with other treatment methods may overcome GBM resistance to therapy as well as relapse.

ACE2 deficiency inhibits thoracic aortic dissection by enhancing SIRT3 mediated inhibition of inflammation and VSCMs phenotypic switch.

BACKGROUND: Thoracic aortic dissection (TAD) is an irreversible cardiovascular disorder with high mortality and morbidity. However, the molecular mechanisms remain elusive. Thus, identifying an effective therapeutic target to prevent TAD is especially critical. The purpose of this study is to elucidate the potential mechanism of inflammation and vascular smooth muscle cell (VSMCs) phenotypic switch in ß-aminopropionitrile fumarate (BAPN)-induced TAD. METHODS: A mouse model of TAD induced by BAPN and IL-1ß -stimulated HVSMCs in vivo and in vitro models, respectively. ACE2 Knockdown mice treated with BAPN or without, and the TAD mouse model was treated with or without AAV-ACE2. Transthoracic ultrasound was conducted for assessment the maximum internal diameter of the thoracic aorta arch. RNA sequencing analysis was performed to recapitulate transcriptome profile changes. Western blot were used to detect the expression of MMP2, MMP9, ACE2, SIRT3, OPN, SM22α and other inflammatory markers. The circulating levels of ACE2 was measured by ELISA assay. Histological changes of thoracic aorta tissues were assessed by H&E, EVG and IHC analysis. RESULTS: We found that circulating levels of and the protein levels of ACE2 were increased in the TAD mouse model and in patients with TAD. For further evidence, ACE2 deficiency decelerated the formation of TAD. However, overexpression of ACE2 aggravated BAPN-induced aortic injury and VSMCs phenotypic switch via lowered SIRT3 expression and elevated inflammatory cytokine expression. CONCLUSION: ACE2 deficiency prevented the development of TAD by inhibiting inflammation and VSMCs phenotypic switch in a SIRT3-dependent manner, suggesting that the ACE2/SIRT3 signaling pathway played a pivotal role in the pathological process of TAD and might be a potential therapeutical target.

ML335 inhibits TWIK2 channel-mediated potassium efflux and attenuates mitochondrial damage in MSU crystal-induced inflammation.

BACKGROUND: Activation of the NLRP3 inflammasome is critical in the inflammatory response to gout. Potassium ion (K+) efflux mediated by the TWIK2 channel is an important upstream mechanism for NLRP3 inflammasome activation. Therefore, the TWIK2 channel may be a promising therapeutic target for MSU crystal-induced inflammation. In the present study, we investigated the effect of ML335, a known K2P channel modulator, on MSU crystal-induced inflammatory responses and its underlying molecular mechanisms. METHODS: By molecular docking, we calculated the binding energies and inhibition constants of five K2P channel modulators (Hydroxychloroquine, Fluoxetine, DCPIB, ML365 and ML335) with TWIK2. Intracellular potassium ion concentration and mitochondrial function were assessed by flow cytometry. The interaction between MARCH5 and SIRT3 was demonstrated by immunoprecipitation and Western blotting assay. MSU suspensions were injected into mouse paw and peritoneal cavity to induce acute gout model. RESULTS: ML335 has the highest binding energy and the lowest inhibition constant with TWIK2 in the five calculated K2P channel modulators. In comparison, among these five compounds, ML335 efficiently inhibited the release of IL-1ß from MSU crystal-treated BMDMs. ML335 decreased MSU crystal-induced K+ efflux mainly dependent on TWIK2 channel. More importantly, ML335 can effectively inhibit the expression of the mitochondrial E3 ubiquitin ligase MARCH5 induced by MSU crystals, and MARCH5 can interact with the SIRT3 protein. ML335 blocked MSU crystal-induced ubiquitination of SIRT3 protein by MARCH5. In addition, ML335 improved mitochondrial dynamics homeostasis and mitochondrial function by inhibiting MARCH5 protein expression. ML335 attenuated the inflammatory response induced by MSU crystals in vivo and in vitro. CONCLUSION: Inhibition of TWIK2-mediated K+ efflux by ML335 alleviated mitochondrial injury via suppressing March5 expression, suggesting that ML335 may be an effective candidate for the future treatment of gout.

Exosomes regulate SIRT3-related autophagy by delivering miR-421 to regulate macrophage polarization and participate in OSA-related NAFLD.

PURPOSE: To analyze the role of and mechanism underlying obstructive sleep apnea (OSA)-derived exosomes in inducing non-alcoholic fatty liver (NAFLD). METHODS: The role of OSA-derived exosomes was analyzed in inducing hepatocyte fat accumulation in mice models both in vivo and in vitro. RESULTS: OSA-derived exosomes caused fat accumulation and macrophage activation in the liver tissue. These exosomes promoted fat accumulation; steatosis was more noticeable in the presence of macrophages. Macrophages could internalize OSA-derived exosomes, which promoted macrophage polarization to the M1 type. Moreover, it inhibited sirtuin-3 (SIRT3)/AMP-activated protein kinase (AMPK) and autophagy and promoted the activation of nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 (NLRP3) inflammasomes. The use of 3-methyladenine (3-MA) to inhibit autophagy blocked NLRP3 inflammasome activation and inhibited the M1 polarization of macrophages. miR-421 targeting inhibited SIRT3 protein expression in the macrophages. miR-421 was significantly increased in OSA-derived exosomes. Additionally, miR-421 levels were increased in OSA + NAFLD mice- and patient-derived exosomes. In the liver tissues of OSA and OSA + NAFLD mice, miR-421 displayed similar co-localization with the macrophages. Intermittent hypoxia-induced hepatocytes deliver miR-421 to the macrophages via exosomes to inhibit SIRT3, thereby participating in macrophage M1 polarization. After OSA and NAFLD modeling in miR-421-/- mice, liver steatosis and M1 polarization were significantly reduced. Additionally, in the case of miR-421 knockout, the inhibitory effects of OSA-derived exosomes on SIRT3 and autophagy were significantly alleviated. Furthermore, their effects on liver steatosis and macrophage M1 polarization were significantly reduced. CONCLUSIONS: OSA promotes the delivery of miR-421 from the hepatocytes to macrophages. Additionally, it promotes M1 polarization by regulating the SIRT3/AMPK-autophagy pathway, thereby causing NAFLD.

Intrauterine hyperglycemia induces SIRT3-mediated mitochondrial dysfunction: the fetal origin pathogenesis of precocious osteoarthritis.

OBJECTIVE: Diabetes and other metabolic and inflammatory comorbidities are highly associated with osteoarthritis (OA). However, whether early-life hyperglycemia exposure affects susceptibility to long-term OA is still unknown. The purpose of this study was to explore the fetal origins of OA and provide insights into early-life safeguarding for individual health. METHOD: This study utilized streptozotocin to induce intrauterine hyperglycemia and performed destabilization of the medial meniscus surgery on the knee joints of the offspring mice to induce accelerated OA. Cartilage degeneration-related markers, as well as the expression levels of mitochondrial respiratory chain complexes and mitophagy genes in the adult offspring mice, were investigated. In vitro, mitochondrial function and mitophagy of chondrocyte C28/I2 cells stimulated under high glucose conditions were also evaluated. The methylation levels of the sirt3 gene promoter region in the articular cartilage of intrauterine hyperglycemia-exposed offspring mice were further analyzed. RESULTS: In this study, we found that the intrauterine hyperglycemic environment could lead to an increase in individual susceptibility to OA in late adulthood, mainly due to persistently low levels of Sirt3 expression. Downregulation of Sirt3 causes impaired mitophagy in chondrocytes and abnormal mitochondrial respiratory function due to a failure to clear aged and damaged mitochondria in a timely manner. Overexpressing Sirt3 at the cellular level or using Sirt3 agonists like Honokiol in mouse models can partially rescue mitophagy disorders caused by the hyperglycemic environment and thus alleviate the progression of OA. CONCLUSION: Our study revealed a significantly increased susceptibility to OA in the gestational diabetes mellitus offspring, which is partly attributed to exposure to adverse factors in utero and ultimately to the onset of disease via epigenetic modulation.

Caffeine upregulates SIRT3 expression to ameliorate astrocytes-mediated HIV-1 Tat neurotoxicity via suppression of EGR1 signaling pathway.

Caffeine is one of the most popular consumed psychostimulants that mitigates several neurodegenerative diseases. Nevertheless, the roles and molecular mechanisms of caffeine in HIV-associated neurocognitive disorders (HAND) remain largely unclear. Transactivator of transcription (Tat) is a major contributor to the neuropathogenesis of HAND in the central nervous system. In the present study, we determined that caffeine (100 µM) treatment significantly ameliorated Tat-induced decreased astrocytic viability, oxidative stress, inflammatory response and excessive glutamate and ATP release, thereby protecting neurons from apoptosis. Subsequently, SIRT3 was demonstrated to display neuroprotective effects against Tat during caffeine treatment. In addition, Tat downregulated SIRT3 expression via activation of EGR1 signaling, which was reversed by caffeine treatment in astrocytes. Overexpression of EGR1 entirely abolished the neuroprotective effects of caffeine against Tat. Furthermore, counteracting Tat or caffeine-induced differential expression of SIRT3 abrogated the neuroprotection of caffeine against Tat-triggered astrocytic dysfunction and neuronal apoptosis. Taken together, our study establishes that caffeine ameliorates astrocytes-mediated Tat neurotoxicity by targeting EGR1/SIRT3 signaling pathway. Our findings highlight the beneficial effects of caffeine on Tat-induced astrocytic dysfunction and neuronal death and propose that caffeine might be a novel therapeutic drug for relief of HAND.

Nicotinamide riboside activates SIRT3 to prevent paclitaxel-induced peripheral neuropathy.

Paclitaxel (PTX) is a microtubule stabilizer that disrupts the normal cycle of microtubule depolymerization and repolymerization, leading to cell cycle arrest and cancer cell death. It is commonly used as a first-line chemotherapeutics for various malignancies, such as breast cancer, non-small cell lung cancer, and ovarian cancer. However, PTX chemotherapy is associated with common and serious side effects, including chemotherapy-induced peripheral neuropathy (CIPN). As cancer treatment advances and survival rates increase, the impact of CIPN on patients' quality of life has become more significant. To date, there is no effective treatment strategy for CIPN. Surtuin3 (SIRT3) is a nicotinamide adenine dinucleotide (NAD+) dependent protein deacetylase located on mitochondria. It transfers the acetyl group of the lysine side chain of acetylated substrate proteins to NAD+, producing deacetylated proteins to regulate mitochondrial energy metabolic processes. SIRT3 has been found to play an important role in various diseases, including aging, neurodegenerative diseases, cancer, heart disease, metabolic diseases, etc. However, the role of SIRT3 in CIPN is still unknown. This study found for the first time that activating SIRT3 helps to improve paclitaxel-induced CIPN. Nicotinamide riboside (NR) can protect dorsal root ganglion (DRG) mitochondria against oxidative damage caused by paclitaxel through activating SIRT3-MnSOD2 and SIRT3-Nrf2 pathway. Moreover, NR can enhance the anticancer activity of paclitaxel. Together, our research provides new strategy and candidate drug for the treatment of CIPN.