HNMT调控肝脏胰岛素抵抗和糖脂代谢的机制研究

Histamine N-methyl transferase (HNMT) is one of the key enzymes that catalyze histamine metabolism, which is most abundant in human liver tissue. However, the role of HNMT in regulating glucose and lipid metabolism in the liver has not been elucidated. The applicant's previous studies found that HNMT was significantly up-regulated in the liver of type 2 diabetic and obese mice, and was responsive to changes in nutritional status and insulin treatment. The overexpression of HNMT significantly increased the lipid deposition in primary hepatocytes and up-regulated the expression of lipid synthesis genes such as SREBP-1c, suggesting that HNMT may promote lipid deposition and insulin resistance in the liver by up-regulating the expression of genes related to lipid synthesis. On this basis, this study intends to investigate the effect of HNMT on insulin sensitivity and glucose and lipid metabolism in the liver by using adenovirus vectors to mediate HNMT overexpression or knockdown. HNMT downstream target molecules were identified by high-throughput screening, Co-IP mass spectrometry, chromatin immunoprecipitation and other methods, so as to elucidate the molecular mechanism by which HNMT regulates liver metabolism. This study helps to further understand the regulation mechanism of liver glucose and lipid metabolism, and provides a theoretical basis for the establishment of new therapeutic strategies for metabolic diseases such as type 2 diabetes and fatty liver.

组胺N-甲基转移酶（HNMT）是催化组胺代谢的关键酶之一，其在人体肝脏组织中的表达丰度最高。然而，有关HNMT是否可调控肝脏糖脂代谢，目前尚未阐明。申请人前期研究发现，HNMT在2型糖尿病和肥胖小鼠肝脏中表达显著上调，并且对营养状态改变和胰岛素处理的应答迅速；HNMT过表达显著增加原代肝细胞的脂质沉积、上调SREBP-1c等脂质合成基因表达，提示HNMT可能通过上调脂质合成相关基因的表达从而促进肝脏脂质沉积和胰岛素抵抗。在此基础上，本项目拟利用腺病毒载体介导HNMT过表达或敲减的方法，在动物实验和离体研究中明确HNMT对肝脏胰岛素敏感性和糖脂代谢的调控作用；通过高通量筛选、Co-IP质谱、染色质免疫共沉淀等方法，鉴定HNMT作用的下游靶分子，进而阐明HNMT调控肝脏代谢的分子机制。本研究有助于深入了解肝脏糖脂代谢的调控机制，为建立2型糖尿病、脂肪肝等代谢性疾病的治疗新策略提供理论基础。

肝脏糖脂代谢异常导致的肝脏脂质沉积和胰岛素抵抗，是糖尿病、脂肪肝等代谢性疾病关键的致病因素，探索其调控机制，有利于阐明代谢性疾病的发病机理。研究表明组胺N-甲基转移酶HNMT与代谢性疾病密切相关，但其如何调控肝脏糖脂代谢和胰岛素抵抗目前尚不清楚。本项目首先研究糖尿病、肥胖小鼠肝脏HNMT表达及其与肝脏胰岛素敏感性和糖脂代谢的相关性，随后明确HNMT对肝脏胰岛素敏感性和糖脂代谢的调控作用，其中包括构建过表达HNMT和short hairpin RNA（ShRNA）沉默HNMT的腺病毒来上调和下调HNMT的表达，从正反两个方向证实HNMT表达变化对肝脏胰岛素敏感性和肝脏糖脂代谢的影响，最后阐明HNMT调控肝脏胰岛素敏感性和糖脂代谢的作用机制，此外还进一步探索了新型降糖药物（GCGR单抗、达格列净等）对肝脏糖脂代谢的影响和对HNMT的调控，以及HNMT在降糖药物通过肝脏—胰岛轴促进胰岛再生中的作用。结果发现，在糖尿病和肥胖小鼠肝脏中HNMT均出现异常高表达，而且HNMT的表达与胰岛素水平有显著相关性；HNMT能升高小鼠空腹血糖，损害肝脏胰岛素敏感性，并促进肝脏脂质合成和脂肪沉积；此外我们还发现新型降糖药物（GCGR单抗、达格列净等）可改善肥胖糖尿病小鼠血糖和肝脏脂质沉积，并降低了肝脏HNMT水平，而HNMT在GCGR通过肝脏–胰岛轴促进胰岛再生中也发挥重要调控作用。本课题的研究不仅阐明了HNMT在肝脏胰岛素抵抗和糖脂代谢异常中的作用，为糖尿病、非酒精性脂肪肝病等代谢性疾病提供了新的理论依据；同时还揭示了HNMT在新型降糖药物改善机体糖脂代谢中发挥重要作用，为肝脏–胰腺间器官对话提供了新的视角。