title: Regulation of bcl-2 family proteins during development and in response to oxidative stress in cardiac myocytes: association with changes in mitochondrial membrane potential.
abstract: Cardiac myocyte apoptosis is potentially important in many cardiac disorders. In other cells, Bcl-2 family proteins and mitochondrial dysfunction are probably key regulators of the apoptotic response. In the present study, we characterized the regulation of antiapoptotic (Bcl-2, Bcl-xL) and proapoptotic (Bad, Bax) Bcl-2 family proteins in the rat heart during development and in oxidative stress-induced apoptosis. Bcl-2 and Bcl-xL were expressed at high levels in the neonate, and their expression was sustained during development. In contrast, although Bad and Bax were present at high levels in neonatal hearts, they were barely detectable in adult hearts. We confirmed that H(2)O(2) induced cardiac myocyte cell death, stimulating poly(ADP-ribose) polymerase proteolysis (from 2 hours), caspase-3 proteolysis (from 2 hours), and DNA fragmentation (from 8 hours). In unstimulated neonatal cardiac myocytes, Bcl-2 and Bcl-xL were associated with the mitochondria, but Bad and Bax were predominantly present in a crude cytosolic fraction. Exposure of myocytes to H(2)O(2) stimulated rapid translocation of Bad (<5 minutes) to the mitochondria. This was followed by the subsequent degradation of Bad and Bcl-2 (from approximately 30 minutes). The levels of the mitochondrial membrane marker cytochrome oxidase remained unchanged. H(2)O(2) also induced translocation of cytochrome c from the mitochondria to the cytosol within 15 to 30 minutes, which was indicative of mitochondrial dysfunction. Myocytes exposed to H(2)O(2) showed an early loss of mitochondrial membrane potential (assessed by fluorescence-activated cell sorter analysis) from 15 to 30 minutes, which was partially restored by approximately 1 hour. However, a subsequent irreversible loss of mitochondrial membrane potential occurred that correlated with cell death. These data suggest that the regulation of Bcl-2 and mitochondrial function are important factors in oxidative stress-induced cardiac myocyte apoptosis.
authors.affiliation: National Heart and Lung Institute, Cardiac Medicine Section (S.A.C., P.H.S.), and the Division of Biomedical Sciences, Molecular Pathology Section (A.C.), Imperial College School of Medicine, London, UK.
authors.forename: S A
authors.initials: SA
authors.lastname: Cook
authors.forename: P H
authors.initials: PH
authors.lastname: Sugden
authors.forename: A
authors.initials: A
authors.lastname: Clerk
mesh_terms: D000375:Aging / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D008929:Mitochondria, Heart / Q000502:physiology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D016877:Oxidants / Q000494:pharmacology; D018384:Oxidative Stress / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions / Q000378:metabolism; D014018:Tissue Distribution / Q000502:physiology; D051025:bcl-Associated Death Protein
chemical_list: C494821:Bad protein, rat; D002352:Carrier Proteins; D003574:Cytochrome c Group; D016877:Oxidants; D019253:Proto-Oncogene Proteins c-bcl-2; D051025:bcl-Associated Death Protein; D006861:Hydrogen Peroxide