Abstract
Angiotensin II (Ang II) and transforming growth factor (TGF) beta1 play a role in vascular remodeling in hypertension. In this process they may interact on various levels, including that of receptor regulation. This consideration prompted the present study on transcriptional regulation of TGF-beta receptors by Ang II and TGF-beta in vascular smooth muscle cells. Transcriptional expression of the components of the TGF-beta system was demonstrated for TGF-beta and for TGF-beta receptors I, II, and III. As measured by quantitative reverse transcriptase polymerase chain reaction, TGF-beta mRNA increased about 2.4-fold in the presence of 40 pM exogenous TGF-beta. Ang II at 10(-6) M increased TGF-beta mRNA 2.5-fold compared to control cells (P<0.05). Ang II also significantly increased TGF-beta protein concentration in the supernatant of confluent vascular smooth muscle cells. Ang II caused the induction of TGF-beta, but short-term experiments showed TGF-beta receptor II mRNA to be differentially regulated by Ang II and TGF-beta; while TGF-beta caused a 40% decrease in TGF-beta receptor II mRNA after 4 h (P<0.05), Ang II caused an increase by about 70%. In contrast, both TGF-beta and Ang II increased TGF-beta receptor I mRNA to about 260% or 180% of controls (P<0.05). TGF-beta effects were abrogated by coincubation with a TGF-beta neutralizing antibody, and Ang II effects were abrogated by losartan, an AT-1 receptor antagonist. Coincubation of Ang II with the TGF-beta neutralizing antibody did not inhibit the effect of Ang II, indicating that the short-term effects of Ang II on the expression of the TGF-beta receptors are not mediated via TGF-beta. Furthermore, Ang II stimulated DNA synthesis even in the presence of the TGF-beta neutralizing antibody. In conclusion, this study indicates (a) that in vascular smooth muscle TGF-beta receptors are regulated on the RNA level by TGF-beta and Ang II, and (b) that Ang II dependent regulation of TGF-beta receptors is at least partially independent of endogenous TGF-beta. Stimulation of the transcriptional expression of TGF-beta receptors by Ang II may increase sensitivity of vascular smooth muscle cells to TGF-beta.