Cardiac Myofibroblast‐Derived Small Extracellular Vesicles Moderate Fibrotic Responses via piRNA‐62788/PIWIL2‐Mediated SRF Silencing

During fibrogenesis, certain negative feedback loops are elicited to restrain persistent and hyperactive fibrotic responses. Activated fibroblasts have been found to acquire anti-fibrotic phenotypes. However, the specific inhibitory modulators remain largely enigmatic. Thus, the present study aimed to examine the intrinsic autoregulatory mechanisms of fibroblasts. Here, we demonstrated that angiotensin II (AngII)-primed cardiac myofibroblast moderated subsequent profibrotic activation. More importantly, this suppressive action was dependent on small extracellular vesicles (sEVs). Strikingly, small RNA sequencing identified an abundant presence of Piwi-interacting RNAs (piRNAs) in sEVs. In cultured primary cardiac fibroblasts, piRNA-62788 was induced by AngII receptor type 2 (AT₂R) stimulation and encapsulated into sEVs. Furthermore, fibrogenic responses were attenuated by piRNA-62788 overexpression, whereas aggravated by piRNA-62788 knockdown. In a mouse model of transverse aortic constriction, either piRNA-62788 agomir or circulating sEVs of patients with heart failure (HF) mitigated adverse cardiac remodelling, while piRNA-62788 inhibitor-containing sEVs accentuated myocardial fibrosis. Mechanistically, piRNA-62788 formed a functional complex with PIWI-like protein 2 (PIWIL2) and bound to the 3' untranslated region (UTR) region of serum response factor (Srf) mRNA transcripts, leading to inhibition of the SRF signalling. Additionally, plasma sEV-derived piRNA-62788 was significantly upregulated in HF patients and negatively correlated with left ventricular ejection fraction. Collectively, we uncovered a protective negative feedback circuit controlled by AngII/AT₂R/sEVs axis. Understanding this endogenous anti-fibrotic pathway may hold therapeutic promise in HF.