Inhibition of human cardiac fibroblast mitogenesis by blockade of mitogen-activated protein kinase and phosphatidylinositol 3-kinase

1. Interstitial fibroblast proliferation is an elemental feature in the dev elopment of cardiac fibrosis. The effects of inhibitors of the intracellula r signalling proteins, MEK, a kinase involved in the mitogen-activated prot ein kinase (MAP) pathway and phosphatidylinositol 3-kinase (PI3-K), were te sted on growth of cultured human cardiac fibroblasts, 2. Cardiac fibroblasts were isolated from transplant recipient myocardium a nd made quiescent by serum deprivation for;48 h, Cells were incubated for 2 4 h with the inhibitors PD 098059 (0.3-30 mu mol/L) and LY294002 (1-25 mu m ol/L) in the presence and absence of platelet-derived growth factor-AB (PDG F-AB, 10 ng/mL), DNA synthesis was measured by [H-3]-thymidine incorporatio n assay (20-24 h), 3. Both compounds markedly inhibited both basal and PDGF-stimulated increas es in DNA synthesis in a concentration-dependent manner. Cardiac fibroblast DNA synthesis was reduced to near control levels by PD 098059, while it wa s inhibited completely by LY294002. 4. These results implicate the importance of MAPK and PI3-K activation in t he signal transduction pathways necessary for cardiac fibroblast replicatio n.