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

Abstract

The aim of the present study was to investigate the proliferative effects of Ang II in human cardiac fibroblasts. The effects of Ang II in human cardiac fibroblasts on the 3H-thymidine incorporation, the cell number, the 3H-leucine incorporation and the total protein content were measured. The expression of receptor mRNA was performed by reverse transcription-polymerase chain reaction (RT-PCR). Ang II increased 3H-leucine incorporation in a concentration-dependent manner but not 3H-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 significant alterations of cell number or total protein content, suggesting that Ang II stimulated protein synthesis but did not induce hypertrophy. The accumulation of 3H-leucine was blocked by the AT1 receptor antagonist candesartan but not by the AT2 receptor antagonist PD123319. By using RT-PCR, both AT1 and AT2 receptors mRNA were found to be expressed in human cardiac fibroblasts. The selective MAPKK inhibitor PD098059, the protein kinase C inhibitor K252a or the phospholipase C inhibitor U73122 did not significantly inhibit Ang II augmented 3H-leucine incorporation. However, this was significantly blocked by the Ca2+-dependent protein kinase C inhibitor GO6976, the non-selective protein kinase inhibitor staurosporine and the tyrosine kinase inhibitor tyrphostin 25. The effects of Ang II were unaffected by the Gi-protein blocker pertussis toxin, indicating a Gi-protein-independent pathway. Ang II was synergistic with insulin but showed no significant increase on 3H-leucine incorporation when combined with PDGF or EGF. In summary, Ang II stimulates protein synthesis through AT1 receptors in human cardiac fibroblasts, but has no hypertrophic or hyperplastic effect. The response is mediated by a MAPKK-independent and Ca2+-sensitive PKC-dependent pathway.

Candesartan Cilexetil Improves Left Ventricular Function, Left Ventricular Hypertrophy, and Endothelial Function in Patients With Hypertensive Heart Disease.

“…There is clinical evidence of significant efficacy of treatment with ARBs in reversing the LV hypertrophy of hypertensive patients. [5][6][7][9][10][11][12][13][14][15][16][17] Candesartan has been shown to induce regression of LV hypertrophy within 8-12 weeks of starting treatment, 9,13,16 but in the present study, that was not significant until after 6 months of treatment.…”

“…[23][24][25] Candesartan cilexetil, a new angiotensin II type 1 (AT1) receptor blocker, shows strong and long-lasting binding to the AT1 receptor and thus provides 24-h control of blood pressure (BP) while blocking the major negative cardiovascular effects of angiotensin II. 10 The beneficial effects of candesartan have been reported, [5][6][7][9][10][11][12][13][14][15][16][17]21,22 but there has not been a study that followed both cardiac status Circulation Journal Vol.66, November 2002 and endothelial function in hypertensive patients for up to 12 months. Accordingly, we instigated the present study of the effects of candesartan on LV function, LV hypertrophy, and endothelial function in patients with hypertensive heart disease (HHD) during a 1-year period.…”

Phospholipase Cγ-Erk Axis in Vascular Endothelial Growth Factor-induced Eukaryotic Initiation Factor 4E Phosphorylation and Protein Synthesis in Renal Epithelial Cells

“…Its role in the regulation of protein translation has not been studied in depth. U73122, an inhibitor of PLC, has been shown to abolish cardiac myocyte hypertrophy induced by norepineph- rine (24), although it appears to be not required in angiotensin II induction of protein synthesis in cardiac fibroblasts (25). Thus, the involvement of PLC␥ in protein synthesis appears to be cell-and agonist-specific.…”

Angiotensin II Enhances Adenylyl Cyclase Signaling via Ca2+/Calmodulin

“…The striking potentiation of ␤AR signaling in the presence of ANG II might occur via several different mechanisms. ANG II activates AT 1 receptors in cardiac fibroblasts, thereby activating both G q -coupled and tyrosine kinase signaling pathways (28,29). Several pieces of evidence indicate that this cross-talk is mediated by activation of G q : 1) at least 2 other G q -coupled receptors (P2Y and bradykinin) are capable of inducing similar potentiation (Fig.…”

“…However, cross-talk was not inhibited in cells treated with ing, an important distinction given that ANG II activates both G protein and tyrosine kinase pathways in cardiac fibroblasts (28,29).…”