Discoidin Domain Receptor-1 Regulates Calcific Extracellular Vesicle Release in Vascular Smooth Muscle Cell Fibrocalcific Response via Transforming Growth Factor-β Signaling

Objective- Collagen accumulation and calcification are major determinants of atherosclerotic plaque stability. Extracellular vesicle (EV)-derived microcalcifications in the collagen-poor fibrous cap may promote plaque rupture. In this study, we hypothesize that the collagen receptor discoidin domain receptor-1 (DDR-1) regulates collagen deposition and release of calcifying EVs by vascular smooth muscle cells (SMCs) through the transforming growth factor-beta (TGF-beta) pathway. Approach and Results- SMCs from the carotid arteries of DDR-1(-/-) mice and wild-type littermates (n=5-10 per group) were cultured in normal or calcifying media. At days 14 and 21, SMCs were harvested and EVs isolated for analysis. Compared with wild-type, DDR-1(-/-) SMCs exhibited a 4-fold increase in EV release (P < 0.001) with concomitantly elevated alkaline phosphatase activity (P < 0.0001) as a hallmark of EV calcifying potential. The DDR-1(-/-) phenotype was characterized by increased mineralization (Alizarin Red S and Osteosense, P < 0.001 and P=0.002, respectively) and amorphous collagen deposition (P < 0.001). We further identified a novel link between DDR-1 and the TGF-beta pathway previously implicated in both fibrotic and calcific responses. An increase in TGF-beta 1 release by DDR-1(-/-) SMCs in calcifying media (P < 0.001) stimulated p38 phosphorylation (P=0.02) and suppressed activation of Smad3. Inhibition of either TGF-beta receptor-I or phospho-p38 reversed the fibrocalcific DDR-1(-/-) phenotype, corroborating a causal relationship between DDR-1 and TGF-beta in EV-mediated vascular calcification. Conclusions- DDR-1 interacts with the TGF-beta pathway to restrict calcifying EV-mediated mineralization and fibrosis by SMCs. We therefore establish a novel mechanism of cell-matrix homeostasis in atherosclerotic plaque formation.