TNF-alpha-induced impairment of mitochondrial integrity and apoptosis mediated by caspase-8 in adult ventricular myocytes.
Tumor necrosis factor (TNF)-alpha has been shown to induce apoptosis in a variety of cell types including cardiac myocytes. Sphingosine/ceramide and nitric oxide have been associated with apoptosis induced by TNF-alpha; however, signaling mechanisms of TNF-alpha-induced apoptosis in cardiac myocytes are not well defined. This study examined whether alterations in mitochondrial integrity are involved in TNF-alpha-induced apoptosis in adult ventricular myocytes (ARVM) and determined the roles of caspase-8 (an upstream mediator of TNF-alpha receptor-associated signaling) in this process. After incubation for 24-48 h in serum-free culture medium, ARVM underwent spontaneous apoptosis, which remained stable and was not affected by Z-IETD-FMK, a selective caspase-8 inhibitor. Meanwhile, exposure to TNF-alpha resulted in an increase in apoptosis that was detectable at 6 h and became significant after 12 h, when compared to time-controls. After 24-h exposure, TNF-alpha increased caspase-8 activities, mitochondrial cytochrome C (Cyt C) release to the cytosol, accompanied by loss of mitochondrial transmembrane potential (delta psi(m)). Inhibition of caspase-8 activation in the presence of Z-IETD-FMK abolished the TNF-alpha-induced increases in mitochondrial Cyt C release, loss of delta psi(m) and apoptosis. Therefore, these results suggest that TNF-alpha-induced increase in apoptosis in ARVM results from caspase-8-dependent impairment of mitochondrial integrity.
Zhu
JiaXuan
J
Department of Pharmaceutical Sciences, University of Arkansas for Medical Sciences, 4301 West Markham St., Little Rock, AR 72205, USA.
Liu
MeeiYueh
M
Kennedy
Richard H
RH
Liu
Shi J
SJ
D000818:Animals; D017209:Apoptosis; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D002518:Ceramides / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006352:Heart Ventricles / Q000473:pathology; D008297:Male; D008564:Membrane Potentials; D008928:Mitochondria / Q000473:pathology*; D032342:Muscle Cells / Q000166:cytology* / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013110:Sphingosine / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
D002518:Ceramides; D004791:Enzyme Inhibitors; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; C505528:Casp8 protein, rat; D053181:Caspase 8; D020169:Caspases; D013110:Sphingosine