uPAR deficiency triggers TGFβ1-mediated fibrotic remodeling in a cardiac perivascular-like microenvironment

This study investigated how loss of urokinase plasminogen activator receptor (uPAR/Plaur) promotes fibrotic remodeling within the cardiac perivascular microenvironment. Public single-cell RNA-seq analysis and mouse-heart immunofluorescence showed Plaur expression is low but detectable in a subset of endothelial cells and fibroblasts in healthy hearts. The authors modeled the perivascular niche in vitro using 3D cardiospheres (CSs) generated from mouse cardiac explant-derived non-myocyte cells, which contain stromal and vascular components and deposit ECM. Compared with wild-type CSs, uPAR-/- CSs formed in greater numbers but were smaller, had reduced viability, higher stiffness, increased deposition of collagen I/IV and fibronectin, elevated vimentin and smooth muscle-like markers (alphaSMA/SM22alpha), and reduced endothelial-cell content—consistent with fibrotic remodeling and endothelial dysfunction. Mechanistically, uPAR loss increased the active form of TGFbeta1 without increasing Tgfb1 transcript levels, suggesting enhanced TGFbeta1 activation. In Plaur-knockout 3T3 fibroblasts, uPAR deficiency increased baseline ECM protein synthesis and active TGFbeta1 and amplified TGFbeta1-driven noncanonical signaling (notably Akt phosphorylation), leading to exaggerated collagen/fibronectin deposition. Secretome profiling of cardiosphere-derived cells (mCDCs) showed an anti-angiogenic/pro-fibrotic shift in uPAR-/- conditioned media that impaired endothelial tube formation on Matrigel and promoted myofibroblast-like transformation. Overall, the work demonstrates that uPAR loss drives a TGFbeta1-centered feedback loop involving altered integrin function, excessive ECM deposition, niche stiffening, and endothelial depletion, identifying uPAR as a potential therapeutic lever for limiting perivascular fibrosis.