Myofibroblast Involvement in Glycosaminoglycan Synthesis and Lipid Retention during Coronary Repair

Abstract

Myofibroblasts of adventitial origin have been linked to neointimal formation and remodeling after coronary injury. Accordingly, the goal of this study was to examine whether myofibroblasts contribute to focal accumulation of glycosaminoglycans (GAGs) and lipids during coronary repair. GAG synthesis was assessed by ex vivo labeling of balloon-injured porcine coronary arteries with ¹⁴C-glucosamine. The synthesis of total GAGs transiently increased at 8 days in the normolipemic model (a 2.2-fold increase over baseline, p < 0.05). The majority of newly synthesized GAGs were sensitive to chondroitin ABC lyase (chondroitin/dermatan sulfate GAGs). Versican was localized to myofibroblast-rich regions in the adventitia and neointima [positive for α-smooth muscle (SM) actin, negative for h-caldesmon and SM myosin heavy chain]. In contrast, the adjacent SM-rich media showed no increase in versican expression. The association between injury-induced GAG accumulation and lipid retention was examined at 2 weeks after coronary injury in the hyperlipemic model. Lipid (Oil Red O) accumulated in the neointima and adventitia, but not in the adjacent media. Coronary repair under hyperlipemic conditions was associated with macrophage infiltration (19 ± 5 vs. 3 ± 2% of neointimal cells in normolipemic animals, p < 0.001) and increased neointimal formation (1.8 ± 0.5 vs. 1.0 ± 0.3 mm² in normolipemic animals, p < 0.01). In conclusion, this study demonstrated a transient increase in GAG synthesis following coronary injury. Chondroitin sulfate proteoglycans (e.g., versican) were rapidly synthesized by activated adventitial and neointimal cells which could contribute to early lipid retention in injured vessels.