Human smooth muscle cell subpopulations differentially accumulate cholesteryl ester when exposed to native and oxidized lipoproteins

Background - Vascular smooth muscle cells (SMCs) manifest diverse phenotypes and emerging evidence suggests this is caused by inherently distinct SMC subtypes. Recently, Li et al (Circ Res 2001; 89: 517 - 525) successfully cloned 2 uniquely responsive SMC subpopulations from a single human artery and we used this unique resource to test the hypothesis that distinct SMC subtypes are differential precursors of foam cell formation. Methods and Results - When challenged with human atherogenic native or oxidized hypertriglyceridemic very-low-density lipoprotein (HTG-VLDL), the larger, slower-growing, spindle-shaped HITB5 SMC clone accumulated significantly more cholesteryl ester (CE) and triglyceride (TG) than the smaller, faster-growing epithelioid-shaped HITA2 SMC clone (10 versus 2 mug CE/mg cell protein [PN] and 60 versus 7 mug TG/mg PN, P < 0.05). Lipoprotein lipase (LPL), a key enzyme involved in lipoprotein uptake, was identified as one differentially expressed protein that altered the predisposition of HITA2 SMCs for lipid accumulation. Although HITB5 SMCs secreted significantly more LPL than did HITA2 SMCs (0.7 versus 0.2 U/mL media, P < 0.05), the addition of bovine milk LPL to HITA2 SMCs, significantly increased native and oxidized HTG-VLDL - induced lipid accumulation. Conclusions - Inherently distinct SMC subsets are differentially predisposed to lipoprotein-induced lipid accumulation. Moreover, the environment can influence the response of SMC subsets to atherogenic lipoproteins.