Mitochondrial OPA1, apoptosis, and heart failure.
OBJECTIVE
Mitochondrial fusion and fission are essential processes for preservation of normal mitochondrial function. We hypothesized that fusion proteins would be decreased in heart failure (HF), as the mitochondria in HF have been reported to be small and dysfunctional.


RESULTS
Expression of optic atrophy 1 (OPA1), a mitochondrial fusion protein, was decreased in both human and rat HF, as observed by western blotting. OPA1 is important for maintaining normal cristae structure and function, for preserving the inner membrane structure and for protecting cells from apoptosis. Confocal and electron microscopy studies demonstrated that the mitochondria in the failing hearts were small and fragmented, consistent with decreased fusion. OPA1 mRNA levels did not differ between failing and normal hearts, suggesting post-transcriptional control. Simulated ischaemia in the cardiac myogenic cell line H9c2 cells reduced OPA protein levels. Reduction of OPA1 expression with shRNA resulted in increased apoptosis and fragmentation of the mitochondria. Overexpression of OPA1 increased mitochondrial tubularity, but did not protect against simulated ischaemia-induced apoptosis. Cytochrome c release from the mitochondria was increased both with reduction in OPA1 and with overexpression of OPA1.


CONCLUSIONS
This is the first report, to our knowledge, of changes in mitochondrial fusion/fission proteins in cardiovascular disease. These changes have implications for mitochondrial function and apoptosis, contributing to the cell loss which is part of the downward progression of the failing heart.
Chen
Le
L
Molecular and Cellular Cardiology, Department of Medicine, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
Gong
Qizhi
Q
Stice
James P
JP
Knowlton
Anne A
AA
D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D016572:Cyclosporine / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D006333:Heart Failure / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D008565:Membrane Proteins / Q000032:analysis; D026901:Membrane Transport Proteins / Q000032:analysis; D008928:Mitochondria / Q000502:physiology*; D033681:Mitochondrial Membrane Transport Proteins; D024101:Mitochondrial Proteins / Q000032:analysis; D017202:Myocardial Ischemia / Q000378:metabolism / Q000473:pathology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats
D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D024101:Mitochondrial Proteins; D012333:RNA, Messenger; D016572:Cyclosporine; D045304:Cytochromes c; D020558:GTP Phosphohydrolases; C470018:MFN2 protein, human; C415198:OPA1 protein, human; C498811:Opa1 protein, rat; C470017:Mfn1 protein, human