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 FACS. PDGF-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 FACS.


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.


CONCLUSIONS
These results support an important role for Akt in senescence and regulation of cardiac fibroblast cell proliferation.
Diez
C
C
Institut für Klinische Biochemie and Pathobiochemie, Versbacher Str. 5, D-97078, Würzburg, Germany.
Nestler
M
M
Friedrich
U
U
Vieth
M
M
Stolte
M
M
Hu
K
K
Hoppe
J
J
Simm
A
A
D000818:Animals; D000077214:Becaplermin; D015152:Blotting, Northern; D015153:Blotting, Western; D002455:Cell Division / Q000187:drug effects; D016922:Cellular Senescence; D003864:Depression, Chemical; D005347:Fibroblasts / Q000378:metabolism*; D005355:Fibrosis; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D009206:Myocardium / Q000201:enzymology* / Q000473:pathology*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D020574:Proto-Oncogene Proteins c-sis; D051381:Rats; D017208:Rats, Wistar; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D010982:Platelet-Derived Growth Factor; D011518:Proto-Oncogene Proteins; D020574:Proto-Oncogene Proteins c-sis; C075278:platelet-derived growth factor A; D000077214:Becaplermin; D017479:Receptors, Platelet-Derived Growth Factor; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1