Characterization of angiotensin receptors on human skin fibroblasts

Abstract

 Angiotensin II is involved in blood pressure regulation, cell growth and angioneogenesis. The angiotensin receptors which mediate the intracellular effects of angiotensin II are expressed in numerous tissues and cell types. We studied the expression of angiotensin II receptors in cultured human skin fibroblasts derived from a skin biopsy. Angiotensin II binding characteristics were analyzed by radioligand binding assays. The DNA synthesis was assessed by [H]thymidine incorporation assays. Intracellular calcium concentrations were measured by fura-2 spectrofluorometry, and mRNA expression levels were analyzed by northern blot technology. Two distinct angiotensin receptors were detectable on human skin fibroblasts: the AT1 receptor with K _d=1.0± 0.7 nmol/l and B _max=17.9±0.9 fmol/mg protein, and an angiotensin_(1–7) binding site with K _d=26±6.6 nmol/l and B _max=80.4±3.5 fmol/mg protein, as shown by competition binding assays using selective angiotensin II receptor antagonists and the heptapeptide angiotensin_(1–7). The angiotensin AT1 receptor mRNA was substantially expressed in human skin fibroblasts and was subjected to homologous downregulation. In human skin fibroblasts angiotensin II caused a profound increase in intracellular calcium which was blocked by angiotensin AT1 receptor antagonists such as Exp-3174. Furthermore, both angiotensin II and angiotensin_(1–7) led to increased DNA synthesis in human skin fibroblasts. In conclusion, cultured human skin fibroblasts express angiotensin AT1 receptors and a putatively new angiotensin receptor activated by angiotensin_(1–7), both coupled to signaling pathways involved in DNA synthesis.