Deficiency of the Bax gene attenuates denervation-induced apoptosis

Apoptosis has been implicated in mediating denervation-induced muscle wasting. In this study we determined the effect of interference of apoptosis on muscle wasting during denervation by using mice genetically deficient in pro-apoptotic Bax. After denervation, muscle wasting was evident in both wild-type and Bax(-/-) muscles but reduction of muscle weight was attenuated in Bax(-/-) mice. Apoptotic DNA fragmentation increased in wild-type denervated muscles whereas there was no statistical increase in DNA fragmentation in denervated muscles from Bax(-/-) mice. Mitochondrial AIF and Smac/DIABLO releases and Bcl-2, p53 and HSP27 increased whereas XIAP and MnSOD decreased to a similar extent in muscles from wild-type and Bax(-/-) mice following denervation. Mitochondrial cytochrome c release was elevated in denervated muscles from wild-type mice but the increase was suppressed in muscles from Bax(-/-) mice. Increases in caspase-3 and -9 activities and oxidative stress markers H2O2, MDA/4-HAE and nitrotyrosine were all evident in denervated muscles from wild-type mice but these changes were absent in muscles from Bax(-/-) mice. Moreover, ARC increased exclusively in denervated Bax(-/-) muscle. Our data indicate that under conditions of denervation, pro-apoptotic signalling is suppressed and muscle wasting is attenuated when the Bax gene is lacking. These findings suggest that interventions targeting apoptosis may be valuable in ameliorating denervation-associated pathologic muscle wasting in certain neuromuscular disorders that involve partial or full denervation.