Stimulating cardiomyocyte proliferation in the adult heart has emerged as a promising strategy for cardiac regeneration following myocardial infarction (MI). The NRG1-ERBB4 signaling pathway has been implicated in the regulation of cardiomyocyte proliferation. However, the therapeutic potential of recombinant human NRG1 (rhNRG1) has been limited due to the low expression of ERBB4 in adult cardiomyocytes. Here, we investigated whether a fusion protein of rhNRG1 and an ERBB3 inhibitor (rhNRG1-HER3i) could enhance the affinity of NRG1 for ERBB4 and promote adult cardiomyocyte proliferation. In vitro and in vivo experiments were conducted using postnatal day 1 (P1), P7, and adult cardiomyocytes. Western blot analysis was performed to assess the expression and activity of ERBB4. Cardiomyocyte proliferation was evaluated using Ki67 and pH 3 immunostaining, while fibrosis was assessed using Masson staining. Our results indicate that rhNRG1-HER3i, but not rhNRG1, promoted P7 and adult cardiomyocyte proliferation. Furthermore, rhNRG1-HER3i improved cardiac function and reduced cardiac fibrosis in post-MI hearts. Administration of rhNRG1-HER3i inhibited ERBB3 phosphorylation while increasing ERBB4 phosphorylation in adult mouse hearts. Additionally, rhNRG1-HER3i enhanced angiogenesis following MI compared to rhNRG1. In conclusion, our findings suggest that rhNRG1-HER3i is a viable therapeutic approach for promoting adult cardiomyocyte proliferation and treating MI by enhancing NRG1-ERBB4 signaling pathway.

刺激成人心脏中的心肌细胞增殖已成为心肌梗死（MI）后心脏再生的一种有前景的策略。NRG1-ERBB4 信号通路参与心肌细胞增殖的调节。然而，由于成人心肌细胞中ERBB4的低表达，重组人 NRG1 (rhNRG1) 的治疗潜力受到限制。在这里，我们研究了rhNRG1和ERBB3抑制剂的融合蛋白（rhNRG1-HER3i）是否可以增强NRG1对ERBB4的亲和力并促进成体心肌细胞增殖。使用出生后第 1 天 (P1)、P7 和成年心肌细胞进行体外和体内实验。进行蛋白质印迹分析以评估 ERBB4 的表达和活性。使用 Ki67 和 pH 3免疫染色评估心肌细胞增殖，同时使用 Masson 染色评估纤维化。我们的结果表明，rhNRG1-HER3i（而非 rhNRG1）促进 P7 和成体心肌细胞增殖。此外，rhNRG1-HER3i 可改善 MI 后心脏的心脏功能并减少心脏纤维化。在成年小鼠心脏中，给予 rhNRG1-HER3i 可以抑制 ERBB3 磷酸化，同时增加 ERBB4 磷酸化。此外，与 rhNRG1 相比，rhNRG1-HER3i 增强了MI 后的血管生成。总之，我们的研究结果表明，rhNRG1-HER3i 是一种通过增强 NRG1-ERBB4 信号通路促进成人心肌细胞增殖和治疗 MI 的可行治疗方法。