Angiotensin II type 1 receptors stimulate protein synthesis in human cardiac fibroblasts via a Ca2+-sensitive PKC-dependent tyrosine kinase pathway

The aim of the present study was to investigate the proliferative effects o f Ang II in human cardiac fibroblasts. The effects of Ang II in human cardi ac fibroblasts on the H-3-thymidine incorporation, the cell number, the H-3 -leucine incorporation and the total protein content were measured. The exp ression of receptor mRNA was performed by reverse transcription-polymerase chain reaction (RT-PCR). Ang II increased H-3-leucine incorporation in a co ncentration-dependent manner but not H-3-thymidine incorporation in primary cultures of human cardiac fibroblasts. The maximum effect (24 +/- 3% over control) was obtained at a concentration of 10 nM. There were no significan t alterations of cell number or total protein content, suggesting that Ang II stimulated protein synthesis but did not induce hypertrophy. The accumul ation of 3H-leucine was blocked by the AT(1) receptor antagonist candesarta n but not by the AT(2) receptor antagonist PD123319. By using RT-PCR, both AT(1) and AT(2) receptors mRNA were found to be expressed in human cardiac fibroblasts. The selective MAPKK inhibitor PD098059, the protein kinase C i nhibitor K252a or the phospholipase C inhibitor U73122 did nor significantl y inhibit Ang ii augmented 3H-leucine incorporation. However, this was sign ificantly blocked by the Ca2+-dependent protein kinase C inhibitor GO6976, the non-selective protein kinase inhibitor staurosporine and the tyrosine k inase inhibitor tyrphostin 25. The effects of Ang ii were unaffected by the G(i)-protein blocker pertussis toxin, indicating a G(i)-protein-independen t pathway. Ang II was synergistic with insulin but showed no significant in crease on H-3-leucine incorporation when combined with PDGF or EGF. In summ ary, Ang II stimulates protein synthesis through AT(1) receptors in human c ardiac fibroblasts, but has no hypertrophic or hyperplastic effect. The res ponse is mediated by a MAPKK-independent and Ca2+-sensitive PKC-dependent p athway.