活化素受体IIB在心梗后心肌纤维化中的作用和机制研究

Fibrotic repair after myocardial infarction (MI) maintains the structural integrity of heart and prevents from cardiac rupture. However, excessive fibrosis deteriorates cardiac function and subsequently results in inevitable resultant heart failure. So far the underlying mechanism of cardiac fibrosis post MI remains unclear and also lacks of effective therapeutic approaches in clinical practice. In our pilot studies, we found that the protein levels of Activin receptor type-IIB (ActRIIB) were gradually increased in the border zone rather than the remote zone throughout 4 weeks post MI, meanwhile hypoxia induced upregulation of ActRIIB in primary cardiac fibroblasts. These results strongly indicated that ActRIIB’s expression was closely related to MI induced cardiac fibrosis. In addition, cardiac fibroblasts were infected with Lentiviral vector carrying ActRIIB-shRNA, and we observed that downregulation of ActRIIB contributed to apoptosis of cardiac fibroblasts in hypoxia, inhibited proliferation, reduced the expression of α-SMA, along with suppressed autophagic activity. However, increased autophagic activity by rapamycin could significantly reverse the effect of ActRIIB deficiency. We therefore hypothesize that upregulation of ActRIIB promotes the proliferation, migration, phenotypic changes and secretion of cardiac fibroblasts, and also inhibits apoptosis which eventually results in cardiac fibrosis after MI. Thus, next in this study, we first plan to determine the spatiotemporal expression of ActRIIB in the setting of MI. Secondly, we need to investigate whether blocking ActRIIB's expression could alleviate cardiac fibrosis and improve ventricular function after MI. Thirdly, we will elucidate the role of ActRIIB in regulating the phenotypic changes, migration, secretion, as well as proliferation and apoptosis of cardiac fibroblasts. Finally, well will explore the relationship of autophagy and ActRIIB in modulating the physiological and pathological changes of cardiac fibroblasts and the underlying signaling pathway between ActRIIB and autophagy. Our study will expand the understanding of the molecular mechanisms of the cardiac fibrosis after MI and provide potential therapeutic targets.

心梗后心肌组织过度纤维性修复导致心功能恶化而发生心力衰竭，但目前其具体分子机制不明。我们的前期研究发现心梗后梗死边缘区活化素受体IIB（ActRIIB）上调，同时低氧刺激下心脏成纤维细胞ActRIIB明显上调，提示其表达与心梗后心肌纤维化密切相关。慢病毒感染下调ActRIIB后促进低氧下心脏成纤维细胞凋亡，抑制增殖和分化，同时减弱自噬活动，增强自噬水平可逆转ActRIIB下调对心脏成纤维细胞的影响。故提出假设：ActRIIB上调通过增强自噬调控心脏成纤维细胞表型、功能和生存状态，导致心梗后心肌纤维化。下一步，本项目旨在深入研究ActRIIB表达变化对心梗后心肌纤维化和心功能的影响；揭示ActRIIB对心脏成纤维细胞表型转变、迁移、分泌和增殖、凋亡的调控作用；解明自噬在ActRIIB调控心脏成纤维细胞病理生理功能和状态中的作用及ActRIIB与自噬之间的信号转导通路。

尽管当前冠脉急诊手术的广泛开展和应用，极大的提高了心肌梗死患者的生存率。然而部分心肌梗死患者即便在最优化的药物治疗下仍不可避免的出现心力衰竭，导致患者生活质量、经济上的巨大负担。因此迫切需要阐明心肌梗死后心肌纤维性重构的关键细胞和分子靶点。该课题以TGF-β家族成员之一，活化素受体IIB（ActRIIB），为切入点进一步探索其在心肌梗死后心肌纤维化中的作用和机制。研究发现小鼠心肌梗死后其梗死边缘区心肌组织中的ActRIIB表达量显著升高，于心梗后14天达到峰值，至心梗后28天其表达量较前虽然有所下降，但仍然保持于高表达水平。通过免疫组化分析，心梗后心肌组织中的ActRIIB在其空间上主要表达于梗死边缘区的心肌间质组织，而梗死远隔区则无明显变化。结合预实验结果，考虑其主要来源于梗死边缘区的心脏成纤维细胞。随后通过小鼠尾静脉注射腺相关病毒下调或上调ActRIIB表达量发现敲减ActRIIB可改善心梗后小鼠生存率，提高心脏收缩功能，减少水钠潴留以及减轻心肌纤维性重构。然而过表达ActRIIB则扩大心梗后梗死疤痕面积，增加梗死边缘区心肌纤维化及胶原蛋白沉积，恶化心功能。细胞实验中通过慢病毒敲减或过表达心脏成纤维细胞中ActRIIB可以调控增殖、分化、分泌功能，进而参与组织纤维性重构。通过对ActRIIB在心梗后心肌纤维化中的研究，证实其可能是参与疾病状态下病理性纤维化中的关键分子。对其细胞和分子机制的深入解明，可以为临床治疗提供一个新的、有效的分子靶点，提高心梗后心衰患者的生存率。