Sirtuin 3 (SIRT3) is an NAD؉ -dependent protein deacetylase.Recent studies have shown that SIRT3 expression is decreased in nonalcoholic fatty liver disease (NAFLD). Moreover, SIRT3 is a key regulator of succinate dehydrogenase (SDH), which catalyzes the oxidation of succinate to fumarate. Increased succinate concentrations and the specific G protein-coupled receptor 91 (GPR91) are involved in the activation of hepatic stellate cells (HSCs). In this study, we aimed to establish whether SIRT3 regulated the SDH activity, succinate, and GPR91 expression in HSCs and an animal model of NAFLD. Our goal was also to determine whether succinate released from hepatocytes regulated HSC activation. Inhibiting SIRT3 using SIRT3 siRNA exacerbated HSC activation via the SDH-succinate-GPR91 pathway, and SIRT3 overexpression or honokiol treatment attenuated HSC activation in vitro. In isolated liver and HSCs from methionine-and choline-deficient (MCD) diet-induced NAFLD, the expression of SIRT3 and SDH activity was decreased, and the succinate concentrations and GPR91 expression were increased. Moreover, we found that GPR91 knockdown or resveratrol treatment improved the steatosis in MCD diet-fed mice. This investigation revealed a novel mechanism of the SIRT3-SDH-GPR91 cascade in MCD diet-induced HSC activation in NAFLD. These findings highlight the biological significance of novel strategies aimed at targeting SIRT3 and GPR91 in HSCs with the goal of improving NAFLD treatment.Nonalcoholic fatty liver disease (NAFLD) 2 is the most common chronic liver disease in many developed countries (1), and nonalcoholic steatohepatitis (NASH), the more severe histological form of NAFLD, is associated with an increased risk for the progression to cirrhosis in 20% of these patients (2). NAFLD also increases the cardiometabolic risk (3-5) and all-cause mortality (6, 7) in humans. It is presently regarded as the main cause of cryptogenic liver cirrhosis in the United States (8). During liver injury, quiescent hepatic stellate cells (HSCs) transdifferentiate into activated myofibroblasts, which produce ␣-smooth muscle actin (␣-SMA) and become a major cell type in hepatic fibrogenesis (9, 10).Sirtuin 3 (SIRT3) is an NAD ϩ -dependent protein deacetylase predominantly localized in the mitochondrial matrix (11-13). SIRT3 is up-regulated during prolonged fasting or a calorierestricted diet and is thus involved in the metabolic regulation of obesity and diabetes (14 -16). Based on several recent studies, SIRT3 is a primary regulator of the acetylation of mitochondrial proteins and their biological activity (16 -19) and is associated with NAFLD (20 -22).Two studies yielded findings showing that SIRT 3 is a major physiological regulator of succinate dehydrogenase (SDH) activity (23, 24). SDH catalyzes the oxidation of succinate to fumarate, thereby decreasing SDH activity, resulting in increased succinate levels (25,26). The succinate receptor (also known as GPR91) is a G protein-coupled receptor expressed in various tissues, including the retina, live...

Laurus nobilis Linn. (Lauraceae), commonly known as Bay, has been used as a traditional medicine in the Mediterranean and Europe to treat diverse immunological disorders. Although the effects of L. nobilis on immunosuppression have been reported, the detailed underlying mechanism remains unclear. In this study, to elucidate the anti‐inflammatory mechanism of L. nobilis, we examined the effect of L. nobilis leaf extract on inflammasome activation in mouse bone marrow‐derived macrophages. L. nobilis leaf extract inhibited NOD‐like receptor pyrin domain‐containing 3 (NLRP3) inflammasome activation, which was associated with caspase‐1 activation, interleukin‐1β secretion, and apoptosis‐associated speck‐like protein containing a CARD (ASC) pyroptosome complex formation. We also observed that 1,8‐cineole, the major component of L. nobilis extract, consistently suppressed NLRP3 inflammasome activation. Furthermore, L. nobilis leaf extract attenuated the in vivo expression of proinflammatory cytokines in an acute lung injury mouse model. Our results provide the first evidence that L. nobilis leaf extract modulates inflammatory signaling by suppressing inflammasome activation.

A natural phenolic acid compound, sinapic acid (SA), is a cinnamic acid derivative that contains 3,5-dimethoxyl and 4-hydroxyl substitutions in the phenyl ring of cinnamic acid. SA is present in various orally edible natural herbs and cereals and is reported to have antioxidant, antitumor, anti-inflammatory, antibacterial, and neuroprotective activities. Although the anti-inflammatory function of SA has been reported, the effect of SA on the NOD-like receptor pyrin domain-containing 3 (NLRP3) inflammasome has not been explored. In the present study, to elucidate the anti-inflammatory mechanism of SA, we examined whether SA modulates the NLRP3 inflammasome. We found that SA blocked caspase-1 activation and IL-1β secretion by inhibiting NLRP3 inflammasome activation in bone marrow-derived macrophages (BMDMs). Apoptosis-associated speck-like protein containing CARD (ASC) pyroptosome formation was consistently blocked by SA treatment. SA specifically inhibited NLRP3 activation but not the NLRC4 or AIM2 inflammasomes. In addition, SA had no significant effect on the priming phase of the NLRP3 inflammasome, such as pro-IL-1β and NLRP3 inflammasome expression levels. Moreover, we found that SA attenuated IL-1β secretion in LPS-induced systemic inflammation in mice and reduced lethality from endotoxic shock. Our findings suggest that the natural compound SA has potential therapeutic value for the suppression of NLRP3 inflammasome-associated inflammatory diseases.

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Acne is an inflammatory skin disorder in puberty with symptoms including papules, folliculitis, and nodules. Propionibacterium acnes (P. acnes) is the main anaerobic bacteria that cause acne. It is known to proliferate within sebum-blocked skin hair follicles. P. acnes activates monocytic cell immune responses to induce the expression of proinflammatory cytokines. Although the anti-inflammatory function of the Laurus nobilis (L. nobilis) extract (LNE) on several immunological disorders have been reported, the effect of LNE in P. acnes-mediated skin inflammation has not yet been explored. In the present study, we examined the ability of the LNE to modulate the P. acnes-induced inflammatory signaling pathway, and evaluated its mechanism. LNE significantly suppressed the expression of P. acnes-mediated proinflammatory cytokines, such as IL-1β, IL-6, and NLRP3. We also found that LNE inhibited the inflammatory transcription factor NF-κB in response to P. acnes. In addition, eucalyptol, which is the main constituent of LNE, consistently inhibited P. acnes-induced inflammatory signaling pathways. Moreover, LNE significantly ameliorated P. acnes-induced inflammation in a mouse model of acne. We suggest for the first time that LNE hold therapeutic value for the improvement of P. acnes-induced skin inflammation.