PROJECT SUMMARY / ABSTRACT Ischemic heart disease is a major cause of death in the United States. At the cellular level, myocardial ischemia alters excitation-contraction coupling and promoted the development of heart failure. Junctophilin-2 (JPH2) is an inter-membrane linker protein that maintains the plasmalemma and sarcoplasmic reticulum (SR) at a fixed distance to facilitate excitation-contraction coupling. Ischemia/reperfusion injury and ischemic heart disease lead to a loss of JPH2 protein levels, which in part is caused by proteolysis by the Ca2+-sensitive enzyme calpain. Our long-term goal of this project is to elucidate the molecular and cellular mechanisms by which calpain causes JPH2 cleavage and how the ensuing JPH2 C-terminal peptide alters myocardial function. We will test the central hypothesis that calpain cleaves JPH2 to release a C-terminal peptide that traffics into the cardiomyocyte nucleus where it alters CaMKII-d splicing which affects myocardial remodeling.