Sarcoplasmic Reticulum Proteins as Potential Targets for Gene Therapy of Heart Failure

Abstract

A decrease in the rate of active Ca2+ uptake into the SR is a central feature in human and animal heart failure. Several studies indicated that the mRNA- as well as the protein levels of the sarcoplasmic reticulum (SR) Ca2+ ATPase (encoded by SERCA2 gene) are reduced in hypertrophied and failing myocardium. On the other hand, investigations on phospholamban (PLB) knock-out and phospholamban transgenic mice have proven that the expression ratio of PLB- to SERCA2a- protein is an important determinant of SR function. More recently, it was shown via complementation of the genetically based mouse model of dilated cardiomyopathy (muscle-specific LIM-domain cytoskeletal protein (MLP) knock-outs) that development of heart failure is dependent on a Ca2+ cycling defect in the cardiac SR. Remarkably, double MLP/PLB knockout mice display a rescue of the entire spectrum of MLP deficient heart failure phenotype at the structural, functional and molecular level. The state of knowledge on the molecular aspects and physiological functions of SERCA2a by PLB is briefly reviewed. Alltogether, these observations on PLB function have led us to explore novel strategies of interference by genetic manipulation of PLB-SERCA2a interaction to provide a basis for future development of gene therapy for improving function of the failing myocardium. With this aim we explored the antisense RNA strategy directed against de novo synthesis of PLB. Because the option of in vitro and in vitro gene transfer into the heart by replication-deficient adenovirus had already been proven, recombinant adenoviral vectors expressing PLB-antisense were prepared under control of cytomegalovirus (CMV) as well as an atrial natriuretic factor (ANF) promoter. Although at present the principle has still not been tested in vivo, our in vitro results obtained with isolated beating rat cardiomyocytes strongly suggest that vector-mediated PLB-antisense-RNA expression may become a feasible approach to improve function of the failing heart. Furthermore, the endothelin-1 inducible ANF promoter offers the perspective for “induction-by disease” gene therapy by selective expression of therapeutic genes in the hypertrophied and failing myocytes.