Tumor necrosis factor-α in mechanic trauma plasma mediates cardiomyocyte apoptosis

Abstract

Mechanical traumatic injury causes cardiomyocyte apoptosis and cardiac dysfunction. However, the signaling mechanisms leading to posttraumatic cardiomyocyte apoptosis remains unclear. The present study attempted to identify the molecular mechanisms responsible for cardiomyocyte apoptosis induced by trauma. Normal cardiomyocytes (NC) or traumatic cardiomyocytes (TC; isolated immediately after trauma) were cultured with normal plasma (NP) or traumatic plasma (TP; isolated 1.5 h after trauma) for 12 h, and apoptosis was determined by caspase-3 activation. Exposure of TC to NP failed to induce significant cardiomyocyte apoptosis. In contrast, exposure of NC to TP resulted in a greater than twofold increase in caspase-3 activation ( P < 0.01). Incubation of cardiomyocytes with cytomix (a mixture of TNF-α, IL-1β, and IFN-γ) or TNF-α alone, but not with IL-1β or IFN-γ alone, caused significant caspase-3 activation ( P < 0.01). TP-induced caspase-3 activation was virtually abolished by an anti-TNF-α antibody, and TP isolated from TNF-α^−/− mice failed to induce caspase-3 activation. Moreover, incubation of cardiomyocytes with TP upregulated inducible nitric oxide (NO) synthase (iNOS)/NADPH oxidase expression, increased NO/superoxide production, and increased cardiomyocyte protein nitration (measured by nitrotyrosine content). These oxidative/nitrative stresses and the resultant cardiomyocyte caspase-3 activation can be blocked by neutralization of TNF-α (anti-TNF-α antibody), inhibition of iNOS (1400W), or NADPH oxidase (apocynin) and scavenging of peroxynitrite (FP15) ( P < 0.01). Taken together, our study demonstrated that there exists a TNF-α-initiated, cardiomyocyte iNOS/NADPH oxidase-dependent, peroxynitrite-mediated signaling pathway that contributes to posttraumatic myocardial apoptosis. Therapeutic interventions that block this signaling cascade may attenuate posttraumatic cardiac injury and reduce the incidence of secondary organ dysfunction after trauma.