Melanoidins, extracted from Chinese traditional vinegar powder, inhibit alcohol-induced inflammation and oxidative stress in macrophages via activation of SIRT1 and SIRT3.

Alcohol induces inflammation and oxidative stress with the dysregulation of proinflammatory cytokines, which are implicated in the pathogenesis of alcoholic liver injury. Melanoidins are known to exert an antioxidant effect, however, their function in inhibiting alcohol-induced inflammation is unclear. In this study, we examined the role of melanoidins from Chinese traditional vinegar powder in terms of their anti-inflammatory and antioxidant properties in RAW 264.7 macrophages and elucidated their mechanisms of function. In macrophages, melanoidins significantly suppress the mRNA expression of interleukin (Il)-6, Il-1ß and tumor necrosis factor α (Tnf-α) with a concomitant inhibitory effect on IL-1ß, IL-6 and TNFα secretion, which are increased by ethanol. In addition, ethanol significantly increases the cellular reactive oxygen species (ROS) levels and the expression of cytochrome ß-245 and beta polypeptide (Cybb), which are repressed by melanoidins to basal level. However, the expression of genes related to oxidative stress significantly decreases in response to ethanol, while it is significantly increased by melanoidins. Importantly, treatment with ethanol led to significant decreases in SIRT1 and SIRT3 transcription, translation, and activation, as well as the nicotinamide adenine dinucleotide (NAD+) levels. Interestingly, all the decreases were markedly attenuated by melanoidins. Ethanol promoted the expression of proinflammatory genes, whereas coincubation with resveratrol (a potent SIRT agonist) inhibited this effect. Conversely, the addition of sirtinol (a known SIRT inhibitor) augmented the proinflammatory gene expression. Taken together, our findings suggest that melanoidins exert anti-inflammatory and antioxidant functions via abolishing decreases in SIRT1 and SIRT3 expression and cellular NAD+ levels in ethanol-induced macrophages and may serve as a new therapeutic agent for the prevention of alcohol-induced cell damage.

Protective effects of metformin against osteoarthritis through upregulation of SIRT3-mediated PINK1/Parkin-dependent mitophagy in primary chondrocytes.

Mitochondrial damage is involved in the pathogenesis of osteoarthritis. Metformin, one of the most common prescriptions for patients with type 2 diabetes, can reportedly activate Sirtuin 3 (SIRT3) expression which protects mitochondria from oxidative stress. In this study, we investigated the inhibitory property of metformin on mitochondrial damage by focusing on the interleukin-1 beta (IL-1ß)-stimulated osteoarthritis model by using primary murine chondrocytes. Our results demonstrated that SIRT3 was downregulated in chondrocytes under IL-1ß stimulation, where its expression was positively correlated with mitochondrial damage and reactive oxygen species (ROS) production. Metformin treatment upregulated SIRT3 expression and mitigated loss of cell viability and decreased the generation of mitochondria-induced ROS in chondrocytes stimulated with IL-1ß. Metformin also attenuated IL-1ß-induced expressions of catabolic genes such as matrix metalloproteinase-3 (MMP3) and MMP13 and enhanced the anabolic indicator Collagen Ⅱ. These effects were mediated by phosphatase and tensin homolog (PTEN)-induced putative kinase protein 1 (PINK1)/Parkin-dependent mitophagy and the autophagic elimination of damaged mitochondria. Further, the SIRT3 inhibitor 3-TYP effectively inhibited the initiation of mitophagy, as decreased expression of PINK1 and Parkin, decreased the LC3II/LC3I, enhanced the expression of MMP3 and MMP13, and decreased the expression of Collagen Ⅱ. Overall, our findings provide evidence that metformin suppresses IL-1ß-induced oxidative and osteoarthritis-like inflammatory changes by enhancing the SIRT3/PINK1/Parkin signaling pathway, thereby indicating metformin's potential in prevention and treatment of osteoarthritic joint disease.

Polydatin alleviated radiation-induced lung injury through activation of Sirt3 and inhibition of epithelial-mesenchymal transition.

Radiation-induced lung injury (RILI) is one of the most common and fatal complications of thoracic radiotherapy. It is characterized with two main features including early radiation pneumonitis and fibrosis in later phase. This study was to investigate the potential radioprotective effects of polydatin (PD), which was shown to exert anti-inflammation and anti-oxidative capacities in other diseases. In this study, we demonstrated that PD-mitigated acute inflammation and late fibrosis caused by irradiation. PD treatment inhibited TGF-ß1-Smad3 signalling pathway and epithelial-mesenchymal transition. Moreover, radiation-induced imbalance of Th1/Th2 was also alleviated by PD treatment. Besides its free radical scavenging capacity, PD induced a huge increase of Sirt3 in culture cells and lung tissues. The level of Nrf2 and PGC1α in lung tissues was also elevated. In conclusion, our data showed that PD attenuated radiation-induced lung injury through inhibiting epithelial-mesenchymal transition and increased the expression of Sirt3, suggesting PD as a novel potential radioprotector for RILI.

Essential role of mitochondrial energy metabolism in Foxp3⁺ T-regulatory cell function and allograft survival.

Conventional T (Tcon) cells and Foxp3(+) T-regulatory (Treg) cells are thought to have differing metabolic requirements, but little is known of mitochondrial functions within these cell populations in vivo. In murine studies, we found that activation of both Tcon and Treg cells led to myocyte enhancer factor 2 (Mef2)-induced expression of genes important to oxidative phosphorylation (OXPHOS). Inhibition of OXPHOS impaired both Tcon and Treg cell function compared to wild-type cells but disproportionally affected Treg cells. Deletion of Pgc1α or Sirt3, which are key regulators of OXPHOS, abrogated Treg-dependent suppressive function and impaired allograft survival. Mef2 is inhibited by histone/protein deacetylase-9 (Hdac9), and Hdac9 deletion increased Treg suppressive function. Hdac9(-/-) Treg showed increased expression of Pgc1α and Sirt3, and improved mitochondrial respiration, compared to wild-type Treg cells. Our data show that key OXPHOS regulators are required for optimal Treg function and Treg-dependent allograft acceptance. These findings provide a novel approach to increase Treg function and give insights into the fundamental mechanisms by which mitochondrial energy metabolism regulates immune cell functions in vivo.