Calcineurin Splicing Variant Calcineurin Aβ1 Improves Cardiac Function After Myocardial Infarction Without Inducing Hypertrophy

Background-Calcineurin is a calcium-regulated phosphatase that plays a major role in cardiac hypertrophy. We previously described that alternative splicing of the calcineurin A beta (CnA beta) gene generates the CnA beta 1 isoform, with a unique C-terminal region that is different from the autoinhibitory domain present in all other CnA isoforms. In skeletal muscle, CnA beta 1 is necessary for myoblast proliferation and stimulates regeneration, reducing fibrosis and accelerating the resolution of inflammation. Its role in the heart is currently unknown. Methods and Results-We generated transgenic mice overexpressing CnA beta 1 in postnatal cardiomyocytes under the control of the alpha-myosin heavy chain promoter. In contrast to previous studies using an artificially truncated calcineurin, CnA beta 1 overexpression did not induce cardiac hypertrophy. Moreover, transgenic mice showed improved cardiac function and reduced scar formation after myocardial infarction, with reduced neutrophil and macrophage infiltration and decreased expression of proinflammatory cytokines. Immunoprecipitation and Western blot analysis showed interaction of CnA beta 1 with the mTOR complex 2 and activation of the Akt/SGK cardioprotective pathway in a PI3K-independent manner. In addition, gene expression profiling revealed that CnA beta 1 activated the transcription factor ATF4 downstream of the Akt/mTOR pathway to promote the amino acid biosynthesis program, to reduce protein catabolism, and to induce the antifibrotic and antiinflammatory factor growth differentiation factor 15, which protects the heart through Akt activation. Conclusions-Calcineurin A beta 1 shows a unique mode of action that improves cardiac function after myocardial infarction, activating different cardioprotective pathways without inducing maladaptive hypertrophy. These features make CnA beta 1 an attractive candidate for the development of future therapeutic approaches. (Circulation. 2011; 123: 2838-2847.)