Transforming growth factor-beta and platelet-derived growth factor synergistically stimulate contraction by testicular peritubular cells in culture in serum-free medium

We report investigations on factors influencing contractility by testicular peritubular cells (PC) maintained in culture in a three-dimensional collagen gel system, and the behavior of PC in culture on a two-dimensional system. At low and moderate cell densities, PC embedded in collagen gels in serum-free Eagle's minimal essential medium (MEM) have a lesser degree of contractility than PC in culture in MEM containing calf serum. The contractility by PC, measured by determining changes in diameter of the collagen gel, was increased by addition of transforming growth factor-beta (TGF-beta) to serum-free MEM, and this was further enhanced by supplementing the medium with platelet-derived growth factor (PDGF). In the absence of TGF-beta, however, PDGF had no detectable effects on PC contractility. Other growth factors examined (epidermal growth factor, insulin, and fibroblast growth factor) did not influence the degree of contractility of PC in serum-free MEM in the presence or absence of TGF-beta. PC maintained in MEM supplemented with platelet-poor serum (PPS) have a lesser degree of contractility than their counterparts in MEM containing 2.5% calf serum. The addition of TGF-beta and PDGF to PPS-supplemented MEM restored contractility by PC to a level comparable to that observed by PC in MEM containing complete serum. The addition of nonpurified bovine serum albumin (BSA) to MEM greatly increased PC contractility. By contrast, highly purified BSA had no such effect, suggesting that one or more components adsorbed to the impure BSA was implicated. Polyclonal antibody against fibronectin did not influence the contractility of PC in collagen gels in the presence or absence of serum. Antiserum against TGF-beta partially blocked the enhancement of contractility of PC in MEM containing non-purified BSA. In PC plated on top of a collagen gel lattice, the attachment, spreading, and cell shape were greatly influenced by the presence of TGF-beta and PDGF, both singly and together. Data presented are interpreted to indicate that effects elicited by serum on the properties of PC in culture, and on the contractility of PC, can be attributed in part to the combined influences of TGF-beta and PDGF in serum.