No Contribution of IP3-R(2) to Disease Phenotype in Models of Dilated Cardiomyopathy or Pressure Overload Hypertrophy.

We investigated the contribution of inositol(1,4,5)-trisphosphate (Ins(1,4,5)P₃ [IP₃]) receptors (IP₃-R) to disease progression in mouse models of dilated cardiomyopathy (DCM) and pressure overload hypertrophy. Mice expressing mammalian sterile 20-like kinase and dominant-negative phosphatidylinositol-3-kinase in heart (Mst1×dn-PI3K-2Tg; DCM-2Tg) develop severe DCM and conduction block, associated with increased expression of type 2 IP₃-R (IP₃-R(2)) and heightened generation of Ins(1,4,5)P₃. Similar increases in Ins(1,4,5)P₃ and IP₃-R(2) are caused by transverse aortic constriction.To evaluate the contribution of IP₃-R(2) to disease progression, the DCM-2Tg mice were further crossed with mice in which the type 2 IP₃-R (IP₃-R(2)-/-) had been deleted (DCM-2Tg×IP₃-R(2)-/-) and transverse aortic constriction was performed on IP₃-R(2)-/- mice. Hearts from DCM-2Tg mice and DCM-2Tg×IP₃-R(2)-/- were similar in terms of chamber dilatation, atrial enlargement, and ventricular wall thinning. Electrophysiological changes were also similar in the DCM-2Tg mice, with and without IP₃-R(2). Deletion of IP₃-R(2) did not alter the progression of heart failure, because DCM-2Tg mice with and without IP₃-R(2) had similarly reduced contractility, increased lung congestion, and atrial thrombus, and both strains died between 10 and 12 weeks of age. Loss of IP₃-R(2) did not alter the progression of hypertrophy after transverse aortic constriction.We conclude that IP₃-R(2) do not contribute to the progression of DCM or pressure overload hypertrophy, despite increased expression and heightened generation of the ligand, Ins(1,4,5)P₃. [ABSTRACT FROM AUTHOR]