Suppression of canonical TGF-β signaling enables GATA4 to interact with H3K27me3 demethylase JMJD3 to promote cardiomyogenesis

Direct reprogramming of fibroblasts into cardiomyocytes (CMs) represents a promising strategy to regenerate CMs lost after ischemic heart injury. Overexpression of GATA4, HAND2, MEF2C, TBX5, miR-1, and miR-133 (GHMT2m) along with transforming growth factor beta (TGFbeta) inhibition efficiently promotes reprogramming. However, the mechanisms by which TGFbeta; blockade promotes cardiac reprogramming remain unknown. Here, we identify interactions between the histone H3 lysine 27 trimethylation (H3K27me3), demethylase JMJD3, the SWI/SNF remodeling complex subunit BRG1, and cardiac transcription factors. Furthermore, canonical TGFbeta; signaling regulates the interaction between GATA4 and JMJD3. TGF-beta; activation impairs the ability of GATA4 to bind target genes and prevents demethylation of H3K27 at cardiac gene promoters during cardiac reprogramming. Finally, a mutation in GATA4 (V267M) exhibits reduced binding to JMJD3 and impaired cardiomyogenesis. Thus, we have identified an epigenetic mechanism wherein canonical TGFbeta; pathway activation impairs cardiac gene programming by interfering with GATA4-JMJD3 interactions. Examination of H3K27me3 in mouse embryonic fibroblasts following induction of cardiomyocyte differentiation

将成纤维细胞直接重编程为心肌细胞（cardiomyocytes, CMs），是缺血性心脏损伤后丢失的心肌细胞再生的极具前景的策略。过表达GATA4、HAND2、MEF2C、TBX5、miR-1及miR-133（GHMT2m）并联合转化生长因子β（transforming growth factor beta, TGFβ）抑制，可有效促进该重编程过程。然而，转化生长因子β阻断促进心脏重编程的具体机制仍未明确。本研究鉴定出组蛋白H3赖氨酸27三甲基化（histone H3 lysine 27 trimethylation, H3K27me3）、去甲基化酶JMJD3、SWI/SNF染色质重塑复合物亚基BRG1与心脏转录因子之间的相互作用。此外，经典转化生长因子β信号通路可调控GATA4与JMJD3之间的相互作用。在心脏重编程过程中，转化生长因子β激活会削弱GATA4结合靶基因的能力，并阻止心脏基因启动子区域H3K27me3的去甲基化。最后，GATA4的V267M突变体与JMJD3的结合能力降低，且心肌生成功能受损。综上，本研究鉴定出一种表观遗传机制：经典转化生长因子β通路通过干扰GATA4-JMJD3相互作用，损害心脏基因重编程程序。本研究还对心肌细胞分化诱导后的小鼠胚胎成纤维细胞中的H3K27me3水平进行了检测。