CARDIAC HYPERTROPHY AND SERCA2 GENE EXPRESSION

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Cardiac pump failure presents a major health problem and the molecular mechanisms which contribute to decreased cardiac contractility are activately investigated butt are currently largely unknown. In animals with pressure overload (PO) induced cardiac hypertrophy and in human beings in a majority of studies, a marked decrease in cardiac sarcoplasmic reticulum Ca2+ ATPase (SERCA2) mRNA, protein levels and enzyme activity occur resulting in delayed calcium transients which may contribute to slowed diastolic relaxation. The functional contribution which the lowering of SERCA2 activity makes to heart failure has not been fully explored and it is currently unclear if increased SERCA2 levels in PO failing hearts would improve contractile function. The molecular mechanisms leading to the decrease in the expression of the endogenous SERCA2 gene in PO hearts have also only been incompletely explored. We hypothesize that increasing SERCA2 enzyme levels in myocytes from PO failing hearts will improve contractile function and that alteration in specific nuclear factors and changes in signaling through specific pathways will contribute to decreased SERCA2 gene expression. To test this hypothesis, we will pursue three aims. In the first aim, we will determine if increasing SERCA2 levels by expressing a SERCA2 transgene in the heart of transgenic delivery of a replication deficient human adenovirus 5 vectors expressing the SERCA2 transgene (Adv5 SERCA2) in PO hearts leads to a significant increase in SERCA2 levels and improvement in contractile behavior towards the normal range. We have constructed such an adenovirus vector which expresses significant amounts of SERCA2 levels. The virally expressed SERCA2 protein is functional as indicated by infection of cardiac myocytes and obtaining an accelerated calcium transient in myocytes infected with this virus. PO hearts of rabbits and rats will be infected with ADV5 SERCA2 and SERCA2 activity and contractile function will be evaluated. In the third aim, we will determine which specific nuclear transcription factors and cellular signaling systems influence SERCA2 gene transcription and evaluate the participation of a limited number of such factors and signaling systems. A determination if increasing SERCA2 levels in PO hypertrophied hearts will improve cardiac function toward the normal range, and additional knowledge related to the molecular mechanisms which contribute to decreased cardiac function in PO hearts will result from this research effort.