Quantitation of Platelet-Derived Growth Factor Receptors in Human Arterial Smooth Muscle Cells In Vitro

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Abstract
Abstract Platelet-derived growth factor (PDGF) is suggested to play an important role in the development of atherosclerosis as a migratory and mitogenic stimulus to arterial smooth muscle cells (ASMCs). Stimulated and unstimulated ASMCs were studied with respect to PDGF receptor (PDGF-R) mRNA and protein expression. Quantitative RT-PCR was developed for simultaneous evaluation of both PDGF-Rα and -Rβ mRNA expression and a quantitative ELISA for estimation of corresponding PDGF-R subunits. On the mRNA level, the overall PDGF-Rβ expression was approximately 100 times lower than that of PDGF-Rα. Furthermore, although PDGF-Rα mRNA levels were high irrespective of hASMC phenotype, PDGF-Rβ mRNA was influenced by serum stimulation with lower copy numbers in proliferating and confluent cells compared with quiescent cells. On the protein level, quiescent hASMCs expressed 10 times more PDGF-Rβ than PDGF-Rα. Serum stimulation decreased cell surface PDGF-Rs, with most prominent loss of PDGF-Rα (ELISA and immunohistochemistry). Our results suggest a differential regulatory pattern for PDGF-Rα and -Rβ and are compatible with the usage of alternative promoters for regulation of -Rα expression. Further, it seems that the number of available receptor subunits is not the only determinant of variations in cell stimulation with different PDGF isoforms.