CALD1 promotes cardiac fibroblast activation and fibrosis after myocardial infarction via lactylation-associated mechanisms

Background Myocardial infarction (MI) triggers pathological cardiac remodeling, during which fibroblasts differentiate into myofibroblasts and excessively produce extracellular matrix (ECM), leading to fibrosis and heart failure. Lactylation, a lactate-derived post-translational modification, regulates metabolism and gene expression, but its role and its relationship with CALD1 in post-MI cardiac fibroblasts remain unclear. Methods We integrated single-nucleus RNA sequencing, spatial transcriptomics, and bulk RNA-seq datasets to characterize the single-cell landscape of MI and identify lactylation-related molecular events in cardiac fibroblasts. Bioinformatic analyses were combined with in vitro experiments. Human cardiac fibroblasts were treated with TGF-β1 to induce myofibroblast differentiation, followed by CALD1 knockdown using siRNA. Fibrosis marker expression, Smad signaling, lactylation levels, cell viability, and migration were assessed. Results Our analysis revealed that CALD1 was significantly upregulated in lactylation-high fibroblast subpopulations (LacHighFib) following MI and showed a spatial expression pattern highly consistent with the distribution of LacHighFib. In vitro, TGF-β1 stimulation increased CALD1 and fibrosis marker expression, and induced time-dependent upregulation of Pan Kla, with spatial colocalization of CALD1 and Pan Kla confirmed by immunofluorescence. CALD1 knockdown attenuated TGF-β1-induced fibroblast activation and ECM production, accompanied by reduced Smad signaling and global lactylation, and suppressed cell viability and migration. Conclusion This study identifies CALD1 as a key regulator of post-MI cardiac fibroblast activation. CALD1 is upregulated in LacHighFib subpopulations and is required for TGF-β1-induced fibroblast activation, ECM production, Smad signaling, and lactylation in vitro. These findings provide novel insights into post-MI fibrosis and identify CALD1 as a potential therapeutic target.