Transgenic overexpression of HSP56 does not result in cardiac hypertrophy nor protect from ischaemia/reperfusion injury

Heat shock proteins are known to be induced during and following different forms of cardiac stress. It has previously been shown that their expression is beneficial for the heart following trauma such as ischaemia–reperfusion (I/R) injury. Heat shock protein 56 (HSP56) belongs to the family of FK506-binding immunophilin proteins and is found in steroid receptor complexes, notably the glucocorticoid receptor. We have previously shown that HSP56 and other HSPs are induced in cardiac myocytes treated with cardiotrophin-1, a cytokine with potent hypertrophic and protective properties on cardiac cells. The hypertrophic action of cardiotrophin-1 on cardiac cells is dependent on HSP56 induction and overexpression of HSP56 is sufficient for inducing hypertrophy in cardiac cells. To investigate this phenomenon in vivo, we have generated transgenic mice overexpressing HSP56 and assessed them for the development cardiac hypertrophy and resistance of their hearts to I/R-injury by Langendorff perfusion. Mice generated demonstrated stable, yet varying expression levels of HSP56. Initial characterisation identified a sex-specific phenotype where male overexpressing mice exhibited a moderate, but significant, reduced body weight compared to wild-type controls. In ex vivo stress analyses we found, unexpectedly, that significant overexpression of HSP56 does not induce myocardial hypertrophy and nor does it protect the intact heart from I/R-injury. These observations now suggest a more intricate HSP56-Sp. Cardiophenotype that requires further studies to determine if HSP56 is necessary in mediating hypertrophy induced by other myocardial stimuli.