HIMF在心肌肥大发生中的作用与机制研究

Cardiac hypertrophy is a detrimental pathological remodeling of the heart. The presence of left ventricular hypertrophy is the main risk factor for subsequent development of heart failure and thus prevention of hypertrophy is important for decreasing morbidity and mortality of cardiovascular diseases. However, the mechanisms underlying the pathogenesis of hypertrophy are still largely unknown. Hypoxia-Induced Mitogenic Factor (HIMF) is a kind of secretory protein, which can be expressed only in a minority of organs, including lung and cardiac muscle. Previous work demonstrated the important role of HIMF in pulmonary diseases. No study investigated the role of HIMF in heart disease. Our pioneering work revealed for the first time that the expression and secretion of HIMF were increased in phenylephrine (PE)-induced cardiomyocyte hypertrophy and pressure overload-induced cardiac hypertrophy. Furthermore, we found that overexpression of HIMF in cultured neonatal cardiomyocytes induced hypertrophy directly, and increased the proliferation and migration of cultured cardiac fibroblasts through paracrine action. The preliminary data implicate the important role of HIMF in the development of cardiac hypertrophy. In this project, we would address the following important questions. First, what are the molecular mechanisms underlying the development of cardiac hypertrophy, including cardiomyocyte hypertrophy and fibrosis, induced by HIMF? Second, why is HIMF increased in hypertrophy? Third, whether anti-HIMF antibody has a therapeutic effect on the treatment of cardiac hypertrophy. Through these efforts, we hope to enrich our understanding of the mechanisms for the development of cardiac hypertrophy and try to find new therapeutic strategies for the treatment of cardiac hypertrophy.

心肌肥大是一种有害的心脏病理性重构，对其发病机制的研究以及寻找新的治疗靶点一直是心血管研究领域的热点。缺氧诱导的有丝分裂因子（HIMF）是一种在肺脏和心肌等少数组织特异表达的可分泌蛋白，但其在心脏中的生理和病理作用尚无人研究。我们前期工作首次发现，心肌肥大时HIMF表达和分泌明显增加；心肌细胞过表达HIMF会引起心肌肥大，同时通过旁分泌作用引起心脏成纤维细胞增殖和迁移，提示HIMF在心肌肥大发生中起重要作用。本项目拟采用蛋白定量分析、基因表达调控、染色质免疫沉淀（ChIP）、心脏特异性敲除HIMF基因的小鼠、压力负荷性心肌肥大（TAC）模型等多项技术，从分子、细胞和整体水平开展以下研究：1.HIMF引起心肌肥大和纤维化的机制；2.肥大刺激引起HIMF表达上调的机制；3. 探索HIMF抗体对心肌肥大的治疗作用。旨在阐明心肌肥大发生的新机制，为临床治疗提供新思路。

缺氧诱导有丝分裂因子（HIMF）是一种分泌性细胞因子样蛋白，是缺氧性肺动脉高压的重要刺激因子。本项目的研究发现并阐明了HIMF促进心肌肥大和心脏纤维化的机制。（1）我们发现，在苯肾上腺素（PE）刺激的心肌细胞肥大、小鼠横主动脉缩窄（TAC）诱导的心肌肥大模型，以及扩张型心肌病患者心脏中，HIMF mRNA和蛋白质水平上调。HIMF过度表达可诱导心肌细胞肥大，而HIMF基因敲除可阻止PE诱导的心肌细胞肥大，HIMF基因敲除可显著减轻TAC诱导的心肌肥厚重塑和心功能不全。HIMF过表达增加了细胞内Ca2+浓度，激活了活化T细胞核因子（NFAT）和MAPK途径；这种效应可以通过用L型钙通道阻滞剂硝苯地平降低细胞内Ca2+浓度或用calhex-231抑制Ca2+敏感受体（CaSR）来抑制。（2）此外，我们还发现了HIMF和IL6在心脏纤维化中的重要作用。TAC小鼠心脏组织白细胞介素6（IL-6）的产生增加；敲除 HIMF基因可抑制IL-6的增高。培养的心肌细胞过度表达HIMF时IL-6的产生也增加，用IL-6抗体可抑制HIMF诱导的心肌细胞肥大。过表达HIMF的心肌细胞的培养基和外源性重组HIMF（rHIMF）可以增加IL-6的产生，并促进成纤维细胞（CFs）的增殖、迁移和分化。在这个过程中我们发现MAPK、CaMKII信号转导和转录激活因子3（STAT3）途径被激活。这些数据支持HIMF通过心肌细胞到成纤维细胞旁分泌效应诱导心肌纤维化。IL-6是HIMF的下游信号，通过激活MAPK和CaMKII–STAT3途径在心肌细胞肥大和心肌纤维化中发挥中心作用。总之，HIMF在心肌肥大和心脏纤维化的发生发展中起着关键作用，靶向HIMF可能是一种潜在的治疗策略。