Down-regulation of Akt/PKB in senescent cardiac fibroblasts impairs PDGF-induced cell proliferation

Objective: Cardiovascular diseases are the leading cause of death in the Western World, especially in the elder population. One pathophysiological component of cardiovascular disease is myocardial fibrosis, primarily derived from cardiac fibroblasts. Here we investigated the regulation of proliferation of fibroblasts from hearts of adult rats by platelet derived growth factor AA (PDGF-AA). Methods: Cardiac fibroblasts were isolated from adult Wistar rats. PDGF-induced cell proliferation was analysed by FAGS. PDCF-receptor numbers were analysed by receptor binding assays. Using differential display, differentially expressed kinases were identified during ageing in vitro and confirmed by Northern and Western blotting. Transient overexpression of IRES-GFP constructs was used to analyse the role of the akt kinase on proliferation by FAGS. Results: During in vitro senescence/aging of primary fibroblasts, the growth response to PDGF-AA was greatly reduced without alterations in its receptor number or affinity and without changes in downstream signalling via the MAP-kinase pathway. By using a differential display strategy selective for protein kinases, we identified reduced expression of Akt-1 kinase (PKB-alpha) in senescent rat cardiac fibroblasts. These findings were supported by data showing reduced expression of Akt-1 in heart samples from old humans. Overexpression of activated Akt-1 almost completely reconstituted PDGF-AA dependent cell proliferation in aged fibroblasts. Conclusion: These results support an important role for Act in senescence and regulation of cardiac fibroblast cell proliferation. (C) 2001 Elsevier Science B.V. All rights reserved.