The Wilf Family Cardiovascular Research Institute, Department of Medicine (Cardiology), Albert Einstein College of Medicine, Bronx, NY, United States of America.
Department of Pediatrics, Indiana University, Indianapolis, IN, United States of America.
J Mol Cell Cardiol. 2019 Jul;132:84-97. doi: 10.1016/j.yjmcc.2019.05.006. Epub 2019 May 11.
TGF-βs regulate fibroblast responses, by activating Smad2 or Smad3 signaling, or via Smad-independent pathways. We have previously demonstrated that myofibroblast-specific Smad3 is critically implicated in repair of the infarcted heart. However, the role of fibroblast Smad2 in myocardial infarction remains unknown. This study investigates the role of myofibroblast-specific Smad2 signaling in myocardial infarction, and explores the mechanisms responsible for the distinct effects of Smad2 and Smad3. In a mouse model of non-reperfused myocardial infarction, Smad2 activation in infarct myofibroblasts peaked 7 days after coronary occlusion. In vitro, TGF-β1, -β2 and -β3, but not angiotensin 2 and bone morphogenetic proteins-2, -4 and -7, activated fibroblast Smad2. Myofibroblast-specific Smad2 and Smad3 knockout mice (FS2KO, FS3KO) and corresponding control littermates underwent non-reperfused infarction. In contrast to the increase in rupture rates and adverse remodeling in FS3KO mice, FS2KO animals had mortality comparable to Smad2 fl/fl controls, and exhibited a modest but transient improvement in dysfunction after 7 days of coronary occlusion. At the 28 day timepoint, FS2KO and Smad2 fl/fl mice had comparable adverse remodeling. Although both FS3KO and FS2KO animals had increased myofibroblast density in the infarct, only FS3KO mice exhibited impaired scar organization, associated with perturbed alignment of infarct myofibroblasts. In vitro, Smad3 but not Smad2 knockdown downmodulated fibroblast α2 and α5 integrin expression. Moreover, Smad3 knockdown reduced expression of the GTPase RhoA, whereas Smad2 knockdown markedly increased fibroblast RhoA levels. Smad3-dependent integrin expression may be important for fibroblast activation, whereas RhoA may transduce planar cell polarity pathway signals, essential for fibroblast alignment. Myofibroblast-specific Smad3, but not Smad2 is required for formation of aligned myofibroblast arrays in the infarct. The distinct in vivo effects of myofibroblast Smad2 and Smad3 may involve Smad3-dependent integrin synthesis, and contrasting effects of Smad2 and Smad3 on RhoA expression.
TGF-βs 通过激活 Smad2 或 Smad3 信号通路，或通过 Smad 非依赖性途径来调节成纤维细胞的反应。我们之前已经证明，肌成纤维细胞特异性 Smad3 在梗死心脏的修复中起着至关重要的作用。然而，成纤维细胞 Smad2 在心肌梗死中的作用尚不清楚。本研究探讨了肌成纤维细胞特异性 Smad2 信号在心肌梗死中的作用，并探讨了导致 Smad2 和 Smad3 不同作用的机制。在非再灌注心肌梗死的小鼠模型中，冠状动脉闭塞后 7 天梗死区肌成纤维细胞中的 Smad2 激活达到峰值。在体外，TGF-β1、-β2 和 -β3，但不是血管紧张素 2 和骨形态发生蛋白-2、-4 和 -7，可激活成纤维细胞 Smad2。肌成纤维细胞特异性 Smad2 和 Smad3 敲除小鼠（FS2KO、FS3KO）及其相应的对照同窝仔鼠经历了非再灌注性梗死。与 FS3KO 小鼠破裂率增加和不良重塑相反，FS2KO 动物的死亡率与 Smad2 fl/fl 对照相似，并且在冠状动脉闭塞 7 天后，心功能障碍有适度但短暂的改善。在 28 天时间点，FS2KO 和 Smad2 fl/fl 小鼠的不良重塑相当。尽管 FS3KO 和 FS2KO 动物的梗死区肌成纤维细胞密度均增加，但只有 FS3KO 小鼠表现出瘢痕组织受损，与梗死区肌成纤维细胞排列紊乱有关。在体外，Smad3 但不是 Smad2 的敲低下调了成纤维细胞 α2 和 α5 整联蛋白的表达。此外，Smad3 敲低降低了 GTPase RhoA 的表达，而 Smad2 敲低则显著增加了成纤维细胞 RhoA 的水平。Smad3 依赖性整合素表达可能对成纤维细胞的激活很重要，而 RhoA 可能转导平面细胞极性途径信号，这对于成纤维细胞的排列至关重要。肌成纤维细胞特异性 Smad3，但不是 Smad2，是梗死区排列整齐的肌成纤维细胞形成所必需的。肌成纤维细胞 Smad2 和 Smad3 的不同体内作用可能涉及 Smad3 依赖性整合素合成，以及 Smad2 和 Smad3 对 RhoA 表达的相反作用。
