Platelet-derived growth factor-BB stimulates hypertrophy of peritubular smooth muscle cells from rat testis in primary cultures

The tunica propria of seminiferous tubules contains a particular type of sm ooth muscle cell (myoid cells) arranged in a contractile epithelioid layer that is responsible for sperm and tubular fluid flow. Unlike other types of smooth muscle (SM) cells, highly purified populations of peritubular smoot h muscle cells (PSMC) survive and maintain their contractile phenotype in p rimary cultures in controlled conditions. We used this culture model to inv estigate the response of the SM contractile phenotype to prolonged exposure to platelet-derived growth factor (PDGF), one of the main factors involved in vascular SM pathologies. We observed that 4-day continuous exposure of PSMC to PDGF-BB at nanomolar concentrations in plain medium enhances contra ctile phenotype traits and induces cell hypertrophy without inducing prolif eration. In Northern and Western blotting experiments, SM-alpha-actin trans cript and protein were found to be markedly increased in the PDGF-BB-treate d samples, which is in line with the formation of conspicuous SM-ol-actin-c ontaining stress fibers. Moreover, binding sites for endothelin-l were incr eased, and the calcium response to the contractile agonist, determined in s ingle fura-a-loaded cells, was enhanced. In response to PDGF-BB, the cells underwent immediate, transient contraction, as seen in a scanning electron microscope, followed by a gradual increase in size, as evaluated by cytoflu orometry, and enhancement of protein synthesis. The observed pattern of res ponse to PDGF-BB was not accompanied by cell proliferation, as assessed by [H-3]thymidine incorporation and direct cell counts. Unlike other SM cell t ypes, in which proliferation and loss of contractile traits are induced by PDGF, chronic treatment of PSMC with this growth factor results in hypertro phy rather than hyperplasia.