Mechanisms linking the Branched-Chain alpha-Keto Acid regulatory network to the pathogenesis of NASH

非酒精性脂肪性肝炎(NASH)是一个主要的全球健康问题，并以惊人的速度继续上升 在肥胖症流行浪潮的推动下。众所周知，纳什极大地增加了 发生肝细胞癌、肝硬变、急性肝功能衰竭以及2型糖尿病和 心血管疾病。然而，目前还没有批准的疗法来治疗或逆转 纳什。我们的基础性工作定义了支链氨基中连接干扰的分子路径 酸(BCAA)代谢到代谢性疾病的病因学最近发现了一个新的调节节点， 对肥胖和瘦肉动物的肝脏脂肪沉积有很大的影响。我们发现， 抑制支链α-酮酸的支链α-酮酸脱氢酶 (BCKA)氧化通过使造脂酶ATP磷酸化，有力地刺激从头脂肪生成(DNL) 柠檬酸裂解酶(ACLY)对其激活丝氨酸。同样，我们发现BCKDH磷酸酶，蛋白质 促进BCKA氧化的磷酸酶M1K(PPM1K)在其激活的丝氨酸上使ACLY去磷酸化。 因此，腺病毒介导的BDK在瘦健康Wistar大鼠肝脏中的过度表达被发现是 足以使肝脏DNL增加2.5倍。鉴于，治疗遗传性肥胖的Zucker Fatty大鼠 BDK抑制剂BT-2或表达重组PPM1K的腺病毒降低循环BCKA，减少 ACLY的磷酸化，并显著促进这些小鼠肝脏甘油三酯含量下降40% 在没有改变食物摄入量、体重、肥胖或体力活动的情况下，严重肥胖的动物。随后， 我们实验室的研究发现，BT2还有一个降低脂肪酸转运蛋白表达的作用， CD36，在肝脏中。因此，我们目前的工作模式是，调节肝脏BCKA调节网络施加 由于其对CD36介导的脂类摄取和ACLY介导的DNL的双重作用，因此对脂类含量的影响很强。 除了这些机制之外，目前还不清楚BCKA本身是否发挥了直接或协同作用 对肝脂代谢的影响。重要的是，我们最近的MedRxiv预印本表明，循环中的BCKA 在288名减肥手术患者中，肝脏BDK的表达与NASH状态密切相关 严重肥胖与NAFLD和NASH不协调。在目前的提案中，我们将利用我们的 新开发的小鼠模型，建立的分子/药理学武器库，以及对 通过以下途径解决BCKA调控网络与NASH发病相关的分子机制 完成三个特定目标：1)表征肝脏BDK、PPM1K和BCKA对 纳什进展。2)评价BDK小分子抑制剂逆转NASH的治疗潜力。 3)明确BCKA调节网络与肝脂含量之间的联系机制。成功者 完成具体目标1-3中概述的研究将把BCKA监管网络定义为一个重要的 具有很强翻译相关性的NASH进程调节剂用于人类NASH的治疗。

Non-alcoholic steatohepatitis (NASH) is a major global health concern that continues to rise at an alarming rate driven by the tide of the obesity pandemic. It is well appreciated that NASH significantly raises risk for development of hepatocellular carcinoma, cirrhosis, and acute liver failure as well as type 2 diabetes and cardiovascular disease. However, there are currently no approved therapies for the treatment or reversal of NASH. Our foundational work defining the molecular pathways linking disturbances in branched-chain amino acid (BCAA) metabolism to the etiology of metabolic disease recently identified a novel regulatory node that exerts a powerful influence on hepatic lipid deposition in obese and lean animals. We discovered that the branched-chain α-keto acid dehydrogenase (BCKDH) kinase, BDK that inhibits branched-chain α-keto acid (BCKA) oxidation robustly stimulates de novo lipogenesis (DNL), by phosphorylating the lipogenic enzyme ATP citrate lyase (ACLY) on its activating serine. Likewise, we found that the BCKDH phosphatase, protein phosphatase M1K (PPM1K), that promotes BCKA oxidation, dephosphorylates ACLY on its activating serine. Accordingly, adenoviral mediated overexpression of BDK in liver of lean healthy Wistar rats was found to be sufficient to raise hepatic DNL by 2.5 fold. Whereas, treatment of genetically obese Zucker Fatty rats with the BDK inhibitor, BT-2, or adenovirus expressing recombinant PPM1K lowered circulating BCKA, reduced phosphorylation of ACLY, and remarkably prompted a 40% reduction in liver triglyceride content in these severely obese animals without altering food intake, body weight, adiposity, or physical activity. Subsequent, studies in our lab have identified an additional effect of BT2 to lower expression of the fatty acid transporter, CD36, in liver. Thus, our current working model is that modulation of the hepatic BCKA regulatory network exerts robust effects on lipid content due to its dual effects on CD36-mediated lipid uptake and ACLY-mediated DNL. Beyond these mechanisms, it remains unclear whether the BCKA themselves exert any direct or synergistic effects on hepatic lipid metabolism. Importantly, our recent medRxiv preprint demonstrates that circulating BCKA and liver BDK expression are strongly associated with NASH status in a cohort of 288 bariatric surgery patients with severe obesity that are discordant for NAFLD and NASH. In the current proposal, we will leverage our newly developed mouse models, established molecular/pharmacologic armamentarium, and novel insight to resolve the molecular mechanisms connecting the BCKA regulatory network to the pathogenesis of NASH by completing three specific aims: 1) Characterize the relative contribution of hepatic BDK, PPM1K, and BCKA to NASH progression. 2) Evaluate the therapeutic potential of small molecule inhibitors of BDK for reversing NASH. 3) Define the mechanisms connecting the BCKA regulatory network to hepatic lipid content. The successful completion of the studies outlined in specific aims 1-3 will define the BCKA regulatory network as an important modulator of NASH progression with strong translation relevance for the treatment of NASH in humans.