The major underpinning of massive cell death associated with
myocardial infarction involves opening of the
mitochondrial permeability transition pore (mPTP), resulting in disruption of mitochondria membrane integrity and programmed
necrosis. Studies in human lymphocytes suggested that the hematopoietic-substrate-1 associated
protein X-1 (HAX-1) is linked to regulation of mitochondrial membrane function, but its role in controlling
mPTP activity remains obscure. Herein we used models with altered HAX-1 expression levels in the heart and uncovered an unexpected role of HAX-1 in regulation of
mPTP and cardiomyocyte survival. Cardiac-specific HAX-1 overexpression was associated with resistance against loss of mitochondrial membrane potential, induced by oxidative stress, whereas HAX-1 heterozygous deficiency exacerbated vulnerability. The protective effects of HAX-1 were attributed to specific down-regulation of
cyclophilin-D levels leading to reduction in
mPTP activation. Accordingly,
cyclophilin-D and
mPTP were increased in heterozygous hearts, but genetic ablation of
cyclophilin-D in these hearts significantly alleviated their susceptibility to
ischemia/reperfusion injury. Mechanistically, alterations in
cyclophilin-D levels by HAX-1 were contributed by the
ubiquitin-proteosomal degradation pathway. HAX-1 overexpression enhanced
cyclophilin-D ubiquitination, whereas proteosomal inhibition restored
cyclophilin-D levels. The regulatory effects of HAX-1 were mediated through interference of
cyclophilin-D binding to heat shock protein-90 (Hsp90) in mitochondria, rendering it susceptible to degradation. Accordingly, enhanced Hsp90 expression in HAX-1 overexpressing cardiomyocytes increased
cyclophilin-D levels, as well as
mPTP activation upon oxidative stress. Taken together, our findings reveal the role of HAX-1 in regulating
cyclophilin-D levels via an Hsp90-dependent mechanism, resulting in protection against activation of
mPTP and subsequent cell death responses.