TNF-α signal transduction in rat neonatal cardiac myocytes:: definition of pathways generating from the TNF-α receptor

Cardiomyocyte hypertrophy and apoptosis have been implicated in the loss of contractile function during heart failure (HF). Moreover, patients with HF have been shown to exhibit increased levels of tumor necrosis factor alpha (TNF-alpha) in the myocardium. However, the multiple signal transduction pathways generating from the TNF-alpha receptor in cardiomyocytes and leading preferentially to apoptosis or hypertrophy are still unknown. Here we demonstrate in neonatal rat cardiomyocytes that 1) TNF-alpha induces phosphorylation of AKT, activation of NF-kappaB, and the phosphorylation of JUN kinase; 2) blocking AKT activity prevents NF-kappaB activation, suggesting a role for AKT in regulating NF-kappaB function; 3) AKT and JUN are both critical for the hypertrophic effects of TNF-alpha, since dominant-negative mutants of these genes are capable of inhibiting TNF-alpha-induced ANF-promoter up-regulation and increase in cardiomyocyte cell size, and 4) blocking NF-kappaB, AKT, or JUN alone or in combination does not sensitize cardiomyocytes to the proapoptotic effects of TNF-alpha, in contrast to other cell types, suggesting a cardiac-specific pathway regulating the anti-apoptotic events induced by TNF-alpha. Altogether, the data presented evidence the role of AKT and JUN in TNF-alpha-induced cardiomyocyte hypertrophy and apoptosis.