高盐介导的SIRT3抑制促发肝脏持续性炎症的机制

The inflammatory response evoked by high salt intake plays a critical role in the development of cardiovascular and metabolic diseases. In addition to be a crucial metabolic organ, liver also acts as the main source of inflammatory cytokines. We have observed that the hepatic inflammation and mitochondrial dysfunction induced by high salt diet persist even after changing to normal diet, accompanied by increase of the acetylation level of histone 3 (H3K27ac) on the promoter of mitochondrial protein SIRT3 gene and lowered its expression. Treatment with metformin significantly suppressed high salt-induced hepatic continuous inflammation, inhibited the increase of H3K27ac on the promoter of SIRT3 and promoted NRF2 binding on it. However, the possible regulatory factors involved in the high salt-increased H3K27ac level and the mechanism of NRF2-dependent SIRT3 transcription remain unclear. Therefore, we hypothesized that high salt intake would reduce the binding of NRF2 on SIRT3 promoter to decrease its expression by augmenting the H3K27ac level, whereas the expression of those inflammatory factors without NRF2 binding continuously increase. Metformin might enhance the binding of NRF2 on SIRT3 promoter to increase its expression and inhibit the continuous inflammation through AMPK-mediated decrease of H3K27ac level. We plan to use three specific gene-knockout mice, accompanied with cellular experiments, to elucidate the molecular mechanism of high salt-induced hepatic continuous inflammation. This project would provide new theoretical knowledge and intervention targets to prevention and cure of the cardiovascular and metabolic diseases caused by high salt intake.

高盐摄入引起的炎症反应在心血管及代谢性疾病发生中有重要作用。肝脏不仅是重要代谢器官，也是炎症因子产生的主要场所。我们前期工作发现高盐介导的肝脏炎症反应和线粒体功能异常在撤盐后持续存在，并伴随线粒体蛋白SIRT3基因启动子组蛋白3乙酰化H3K27ac异常；二甲双胍能抑制高盐介导的肝脏持续性炎症，阻碍SIRT3启动子H3K27ac增加并促进NRF2结合, 但高盐导致H3K27ac增加的调控因素及NRF2依赖的促SIRT3转录机制不甚清楚。为此，我们提出假设：高盐通过增加SIRT3启动子的H3K27ac水平减少NRF2的结合抑制SIRT3，而无NRF2结合的炎症因子则表达增加；激活AMPK抑制H3K27ac，增加NRF2的结合，促进SIRT3表达并抑制持续性炎症。本研究拟采用三种基因敲除小鼠，结合细胞实验阐明高盐导致肝脏持续性炎症的分子机制，为拮抗高盐所致心血管代谢性疾病提供新的干预靶点。

高盐摄入是心血管疾病的主要饮食危险因素。尽管临床证据表明高盐摄入与非酒精性脂肪肝相关，而非酒精性脂肪肝是心血管疾病的独立危险因素，但盐诱导的肝损伤是否会导致心血管疾病的发展仍不清楚。我们饲喂了C57小鼠高盐饮食8周以确定盐负荷对肝脏组织学变化和血压的影响，并对一些高盐饮食喂养的小鼠进行了撤盐和二甲双胍治疗。我们在实验中使用腺相关病毒、整体敲除或组织特异性敲除小鼠来操纵体内一些靶基因的表达，包括 SIRT3 (sirtuin 3)、NRF2 (NF-E2-related factor 2) 和 AMPK (AMP活化蛋白激酶）。结果显示：高盐饮食小鼠表现出明显的肝脏脂肪变性和炎症，并伴有高血压和心功能不全。所有这些病理变化在停盐后持续存在，表现出记忆现象。基因表达分析显示，SIRT3表达减少是导致肝脏持续炎症的主要原因。我们用腺相关病毒在肝脏中特异性过表达SIRT3能够有效抑制持续肝脏炎症和心血管损伤，并且肝脏特异性敲除SIRT3加重了高盐饮食造成的肝脏炎症和心血管损伤。机制研究表明，高盐能够增加肝细胞中 SIRT3 启动子上的乙酰化组蛋白 3 赖氨酸 27 (H3K27ac)，从而抑制 NRF2 的结合，并导致 SIRT3 表达的持续抑制。用二甲双胍激活 AMPK进行治疗能够通过降低 SIRT3 启动子上的 H3K27ac 水平增加 NRF2 结合能力来激活 SIRT3 表达，从而抑制盐诱导的肝脏炎症记忆和心血管损伤。本研究表明，组蛋白修饰引起的 SIRT3 抑制是在高盐负荷下导致心血管损伤的持续性肝脏脂肪变性和炎症的关键因素。避免过量盐摄入和积极干预表观遗传修饰可能有助于避免临床实践中高盐诱导的心血管损害的持续炎症状态。