Abstract P126: Calpain Protects the Heart from Hemodynamic Stress
Although calpains are well-known Ca2+-dependent intracellular cysteine proteases, the pathophysiological function of calpains in the heart remains to be elucidated. Previous reports have suggested that calpains play detrimental roles to induce apoptotic or necrotic cell death in pathological Ca2+-overloaded conditions such as ischemia-reperfusion injury or myocardial infarction. Recent loss of function studies have suggested that calpains play important physiological roles in development, cell migration, organization of actin cytoskeleton, and plasma membrane repair. In the present study, we generated and analyzed cardiac-specific calpain 4-deficient mice (CKO) to answer unresolved questions as to in vivo function of calpains in the heart. Ubiquitous calpain is consisted of a common regulatory subunit (calpain 4) and a large catalytic subunit (calpain 1 for μ-calpain and calpain 2 for m-calpain). In agreement with previous reports, cardiac-specific deletion of calpain 4 markedly resulted in a simultaneous decrease in protein levels of calpain 1 and 2, indicating that calpain activity was almost absent in CKO hearts. CKO showed no cardiac phenotypes under basal conditions. Then, we subjected CKO and control mice (CTL) to pressure overload by means of transverse aortic constriction (TAC). One week after TAC, CKO showed left ventricle dilatation (LVDd, CKO 3.64 ± 0.2 mm versus CTL 2.66 ± 0.05 mm), and contractile dysfunction (FS, CKO 33.2 ± 3.9% versus CTL 47 ± 0.7%). CKO hearts took up Evans blue, a membrane-impermeant dye, within cardiomyocytes after TAC, whereas CTL hearts or sham-operated CKO hearts did not. This indicates plasma membrane was disrupted in CKO hearts in response to pressure overload. We performed membrane repair assays on isolated cardiomyocytes from CKO hearts using a two-photon laser-scanning microscope. CKO cardiomyocytes continued to take up FM1-43FX dye for at least 480 sec after disruption of a plasma membrane by laser irradiation, although CTL cardiomyocytes resealed within 250 sec. These data indicate that plasma membrane of cardiomyocytes disrupted by pressure overload failed to be resealed in CKO hearts. Thus, we conclude that calpains protect the heart from hemodynamic stresses by promoting membrane repair.
- © 2011 by American Heart Association, Inc.