Endothelial PARP1 orchestrates endothelial-to-mesenchymal transition via the PARylation of FHL2 in ischaemic heart failure.

Endothelial-to-mesenchymal transition (EndoMT), a process in which endothelial cells progressively differentiate into a mesenchymal phenotype, is a pivotal contributor to cardiac fibrotic remodelling and heart failure (HF) pathogenesis following ischaemic injury. In this study, poly(ADP-ribose) polymerase 1 (PARP1) was identified as a critical driver of EndoMT in ischaemic HF. Single-cell sequencing data indicated that compared with other cardiac cell types, cardiac endothelial cells highly express PARP1. PARP1 was upregulated in patients with dilated or ischaemic cardiomyopathy, as well as in patients with myocardial infarction who developed HF. Similarly, PARP1 upregulation was observed in vitro in EndoMT models induced by hypoxia or TGF-β1(Transforming Growth Factor Beta 1)/IL-1β (Interleukin-1β) and in vivo in cardiac endothelial cells from mice with ischaemic HF induced by permanent left anterior descending (LAD) artery ligation. Pharmacological inhibition and knockdown of PARP1 expression significantly inhibited EndoMT. Moreover, treatment with PARP1 inhibitors or endothelial-specific AAV-mediated delivery of PARP1 shRNA prevented ischaemia-induced EndoMT, fibrosis and cardiac dysfunction in mice. Mechanistically, PARP1 catalysed the poly(ADP-ribosyl)ation (PARylation) modification of four-and-a-half LIM domains protein 2 (FHL2), a key regulator of EndoMT. PARylation of FHL2 at residues Asp50, Glu63 and Asp77 promoted its nuclear retention, enhanced its interaction with β-catenin, and potentiated β-catenin transcriptional activity. Abrogating FHL2 PARylation via site-directed mutagenesis abolished the pro-EndoMT effects of PARP1. These findings establish endothelial PARP1 as a promising therapeutic target for EndoMT in ischaemic HF.