Rationale: Cardiac fibrosis is a common feature in left ventricular remodeling that leads to heart failure, regardless of the cause. EphrinB2 (erythropoietin-producing hepatoma interactor B2), a pivotal bidirectional signaling molecule ubiquitously expressed in mammals, is crucial in angiogenesis during development and disease progression. Recently, EphrinB2 was reported to protect kidneys from injury-induced fibrogenesis. However, its role in cardiac fibrosis remains to be clarified.

Objective: We sought to determine the role of EphrinB2 in cardiac fibrosis and the underlying mechanisms during the pathological remodeling process.

Methods and Results: EphrinB2 was highly expressed in the myocardium of patients with advanced heart failure, as well as in mouse models of myocardial infarction and cardiac hypertrophy induced by angiotensin II infusion, which was accompanied by myofibroblast activation and collagen fiber deposition. In contrast, intramyocardial injection of lentiviruses carrying EphrinB2-shRNA ameliorated cardiac fibrosis and improved cardiac function in mouse model of myocardial infarction. Furthermore, in vitro studies in cultured cardiac fibroblasts demonstrated that EphrinB2 promoted the differentiation of cardiac fibroblasts into myofibroblasts in normoxic and hypoxic conditions. Mechanistically, the profibrotic effect of EphrinB2 on cardiac fibroblast was determined via activating the Stat3 (signal transducer and activator of transcription 3) and TGF-β (transforming growth factor-β)/Smad3 (mothers against decapentaplegic homolog 3) signaling. We further determined that EphrinB2 modulated the interaction between Stat3 and Smad3 and identified that the MAD homology 2 domain of Smad3 and the coil–coil domain and DNA-binding domain of Stat3 mediated the interaction.

Conclusions: This study uncovered a previously unrecognized profibrotic role of EphrinB2 in cardiac fibrosis, which is achieved through the interaction of Stat3 with TGF-β/Smad3 signaling, implying a promising therapeutic target in fibrotic diseases and heart failure.

原理：心脏纤维化是左心室重塑的常见特征，无论原因如何，都会导致心力衰竭。EphrinB2（产生促红细胞生成素的肝癌相互作用因子B2）是在哺乳动物中普遍表达的关键双向信号分子，在发育和疾病进展过程中对血管生成至关重要。最近，据报道EphrinB2保护肾脏免受损伤诱导的纤维生成。但是，其在心脏纤维化中的作用尚待阐明。

目的：我们试图确定EphrinB2在心脏纤维化中的作用及其在病理重塑过程中的潜在机制。

方法和结果：EphrinB2在晚期心力衰竭患者的心肌中以及在血管紧张素II输注诱导的心肌梗塞和心脏肥大的小鼠模型中高表达，并伴有成肌纤维细胞活化和胶原纤维沉积。相反，在心肌梗塞的小鼠模型中，心肌内注射携带EphrinB2-shRNA的慢病毒可改善心脏纤维化并改善心脏功能。此外，在培养的心脏成纤维细胞中进行的体外研究表明，在常氧和低氧条件下，EphrinB2促进了心脏成纤维细胞向肌成纤维细胞的分化。机械上，EphrinB2对心脏成纤维细胞的促纤维化作用是通过激活Stat3（信号转导子和转录激活子3）和TGF-β（转化生长因子-β）/ Smad3（针对去能力障碍同系物3的母亲）信号转导来确定的。我们进一步确定EphrinB2调节Stat3和Smad3之间的相互作用，并确定Smad3的MAD同源2结构域和Stat3的线圈-螺旋结构域和DNA结合结构域介导了相互作用。

结论：这项研究发现了EphrinB2在心脏纤维化中先前未被认识的纤维化作用，这是通过Stat3与TGF-β/ Smad3信号传导的相互作用来实现的，这意味着在纤维化疾病和心力衰竭中有希望的治疗靶点。