Abstract
Rapamycin can inhibit fibroblast proliferation, collagen accumulation, and urethral stricture in rabbits. Transforming growth factor-beta-1 (TGF-β1) signaling, with downstream recruitment of Smad2, is known to promote fibrosis. This in vitro study examined the effects of rapamycin on fibroblasts derived from human urethral scar tissue (FHUS) and investigated the possible mechanism with respect to regulation of TGF-β1 signaling. FHUS were cultured from urethral scar tissues collected from four patients with urethral stricture. The cells were exposed to different concentrations of rapamycin (0, 10, 20, 40, 80, or 160 ng/ml) for 24 or 48 hours. Cell growth was assessed by the MTT assay. Collagen content was measured based on hydroxyproline levels. The mRNA expressions of Smad2, eIF-4E, and alpha-1 chains of collagen types I and III (Col1α1 and Col3α1) were determined by semiquantitative reverse-transcription PCR. The protein expressions of Smad2, phospho-Smad2, and eIF-4E were evaluated by western blot. Rapamycin caused a concentration-dependent inhibition of FHUS growth at 24 and 48 hours (P < 0.01). Rapamycin decreased total collagen content (P < 0.01), collagen content per 105 cells (P < 0.05), and mRNA expressions of Col1α1 and Col3α1 (P < 0.05) in a concentration-dependent manner. Rapamycin elicited concentration-dependent reductions in the mRNA (P < 0.05) and protein (P < 0.01) expressions of Smad2 and eIF-4E. The two highest concentrations of rapamycin also enhanced phospho-Smad2 levels (P < 0.01). In conclusion, the present study confirmed that rapamycin may reduce the growth and collagen production of FHUS, possibly through inhibition of TGF-β1 signaling.