Novel association of <i>NAV3</i> with dilated cardiomyopathy and its role in cardiac fibrosis

A genome-wide association study (GWAS) identified neuron navigator 3 (<i>NAV3</i>) as a potential genetic determinant of myocardial recovery in dilated cardiomyopathy (DCM). This study aimed to understand its functional role in cardiac pathophysiology by leveraging omics approaches. Single-cell RNA-seq transcriptomic data from previously published adult human hearts indicate that <i>NAV3</i> expression is highest in cardiac fibroblasts, suggesting its functional role in these cells. In vitro, stimulation of primary human ventricular cardiac fibroblasts with transforming growth factor β1 (TGF-β1) induced <i>NAV3</i> expression in a dose and time-dependent manner. Small-interfering-RNA-mediated knockdown of <i>NAV3</i> significantly attenuated TGF-β1-induced fibroblast activation, reducing the expression of α-smooth muscle actin (α-SMA), collagens, and fibronectin. RNA sequencing of <i>NAV3</i>-silenced fibroblasts, confirmed by Western blot, revealed upregulation of cell cycle regulators and downregulation of profibrotic markers, suggesting that NAV3 facilitates TGF-β1-induced cell cycle arrest and fibroblast-to-myofibroblast transition. Notably, <i>NAV3</i> silencing did not alter canonical SMAD2/3 phosphorylation, implying a role for NAV3 in modulating fibrotic signaling through other pathways. Our findings provide functional and mechanistic insights into <i>NAV3</i>'s novel role in cardiac fibrosis, showing that reduced <i>NAV3</i> expression attenuates TGF-β1-mediated fibroblast activation by regulating cell cycle signaling. These results support further investigation of NAV3 as a potential modulator of cardiac fibrosis and myocardial recovery in DCM.<b>NEW & NOTEWORTHY</b> This study uncovers a previously unrecognized role for <i>NAV3</i> in TGF-β1-driven cardiac fibroblast activation. We show that <i>NAV3</i> facilitates profibrotic remodeling through noncanonical signaling and cell cycle arrest, independently of SMAD2/3. These findings position <i>NAV3</i> as a novel regulator of fibroblast phenotype and a potential modulator of cardiac fibrosis.