MITOGENIC EFFECT OF ERYTHROPOIETIN ON NEONATAL RAT CARDIOMYOCYTES - SIGNAL-TRANSDUCTION PATHWAYS

The mitogenic effect of recombinant human erythropoietin (rHuEpo) on p rimary cultures of neonatal rat cardiac myocytes was observed. rHuEpo triggered a dose-dependent increase in myocyte proliferation. The horm one effect over optimally grown control culture 1 day after addition w as maximum with 0.5 U/ml and was inhibited with anti-rHuEpo. Inhibitor s of enzymatic pathways known to be involved in the cytokines intracel lular mechanism such as genistein (tyrosine kinase inhibitor), 2-nitro -4-carboxiphenyl-N,N-diphenylcarbamate (phospholipase C [PLC] inhibito r), and 1-(5-isoquinolinylsulfonyl)-2-methyl-pipeerazine (protein kina se C [PKC] inhibitor) prevented the mitogenic action of rHuEpo. Also t he inhibition of Na+-K+-ATPase activity by ouabain blunted the stimula tory action of rHuEpo on cell proliferation. The mitogenic action of t he hormone was correlated with cardiac membrane paranitrophenilphospha tase (pNPPase) and PKC activity, since concentrations of rHuEpo that s timulate DNA synthesis increased pNPPase and PKC activity. Moreover, t he enzymatic inhibition of tyrosine kinase, PLC, and PKC attenuated th e stimulatory action of rHuEpo upon cardiac pNPPase activity. In this paper we demonstrate a non-hematopoietic action of rHuEpo showing both mitogenic and enzymatic effect upon primary myocyte cell culture and on pNPPase activity of neonatal rat heart. These effects are related t o the capacity of rHuEpo to stimulate Na+-K+-ATPase activity and appea r to be secondary to the activation of tyrosine kinase and PKC, indica ting that in the rHuEpo mediated mitogenic action on cardiomyocytes in volves the activation of the same enzymatic pathways that have been de scribed by other cytokines in different tissues. (C) 1996 Wiley-Liss, Inc.