BACKGROUNDUrotensin II (UII) is a new vasoconstrictive peptide that may activate the adventitial fibroblasts. Transforming growth factor-β1 (TGF-β1) is an important factor that could induce the phenotypical transdifferentiation of adventitial fibroblasts. This study aimed to explore whether TGF-β1 is involved in UII-induced phenotypic differentiation of adventitial fibroblasts from rat aorta.

METHODSAdventitial fibroblasts were prepared by the explant culture method. TGF-β1 protein secretion from the cells was determined by enzyme-linked immunosorbent assay (ELISA). The mRNA and protein expression of α-smooth nuscle actin (α-SM-actin), the marker of phenotypic differentiation from fibroblasts to myofibroblasts, were determined using real-time quantitative RT-PCR (real-time RT-PCR) and Western blotting, respectively.

RESULTSUII stimulated the secretion of TGF-β1 in cultured adventitial fibroblasts in a time-dependent manner. The secretion reached a peak at 24 hours, was higher by 69.8% (P < 0.01), than the control group. This effect was also concentration dependent. Maximal stimulation was reached at 10(-8) mol/L of UII (P < 0.01), which was increased by 59.9%, compared with in the control group (P < 0.01). The secretion of TGF-β1 induced by UII was significantly blocked by SB-710411 (10(-7) mol/L), a specific antagonist of UII receptor. In addition, both UII (10(-8) mol/L) and TGF-β1 significantly stimulated α-SM-actin mRNA and protein expression. Moreover, the α-SM-actin induced by UII was inhibited by the specific neutralizing antibody (20 µg/ml) of TGF-β1, while the α-SM-actin expression stimulated by TGF-β1 (20 ng/ml) was inhibited by SB-710411 (10(-7) mol/L), the UII receptor antagonist.

CONCLUSIONThis study suggests that UII could induce TGF-β1 secretion in adventitial fibroblasts via UT activation, and TGF-β1 might be involved in phenotypic differentiation from adventitial fibroblasts into myofibroblasts induced by UII, and TGF-β1 signaling might be one of the important pathways by which UII is involved in vascular fibrosis.

Actins ; analysis ; genetics ; Animals ; Aorta ; cytology ; Cell Transdifferentiation ; drug effects ; Cells, Cultured ; Dose-Response Relationship, Drug ; Fibroblasts ; cytology ; drug effects ; Male ; Myofibroblasts ; cytology ; Phenotype ; RNA, Messenger ; analysis ; Rats ; Rats, Wistar ; Signal Transduction ; Transforming Growth Factor beta1 ; physiology ; Urotensins ; antagonists & inhibitors ; pharmacology