Unresolved issues regarding the role of apoptosis in the pathogenesis of ischemic injury and heart failure

Abstract

Apoptosis is "suicidal" programmed cell death followed by necrosis, i.e. cellular degradation. This review presents a critical evaluation of the methods used for detection of apoptosis and on data regarding the role of apoptosis in ischemia and heart failure.

Methods: DNA laddering by electrophoresis and the TUNEL method in histology for the final stage of apoptosis, Annexin V labeling, evidence of caspase activation, cleavage of substrates, measurements of mitochondrial pro-apoptotic and anti-apoptotic factors (Bcl-2, Bax and others) and determination of the mitochondrial transitional pore potential. Much work has been carried out regarding the mechanism and the importance of apoptosis in ischemia and heart failure but many issues still remain unsolved: (1)Time needed for completion of apoptosis from stimulus to DNA fragmentation? (2)Importance of mitochondrial pathway considering the fact that cardiomyocytes contain the highest volume density of mitochondria of all mammalian cells (25% in humans, 37% in mice)? (3)Means of removal of dead cells, disconnection at the intercalated disc from neighbouring myocytes, time frame of this process? (4)Reversibility of apoptosis? (5)Differences between physiological (postnatal differentiation of the conduction system) v pathological apoptotic cell death? (6)Why do cells, under ischemic conditions, die by either apoptosis or oncosis? (7)Is apoptosis an epiphenomenon or a true cause of heart failure? (8)Quantification of the rate of apoptosis in different pathophysiological situations? Clarification of these unresolved issues will then allow an estimation of the importance of apoptosis in cardiac pathophysiology and, if necessary because the role of apoptosis has been established, the development of new therapeutic concepts.