Myocardial 14-3-3η protein protects against mitochondria mediated apoptosis

There is a definite cardioprotective role for 14-3-3η protein against pressure overload induced cardiac hypertrophy and streptozotocin induced cardiac dysfunction in type 1 diabetes mellitus (DM). But it is not conclusive whether it has any influence on mitochondrial mediated cardiomyocyte apoptosis in type 2 DM. In order to test this hypothesis, we have used C57BL6/J (WT) mice with cardiac specific dominant negative mutation of 14-3-3η protein (DN 14-3-3η). Both WT and DN 14-3-3η mice were fed with high fat diet (HFD) for 12 weeks. Their body weight and blood glucose levels were measured weekly and compared with standard diet (SD) fed mice. By the end of 12 weeks, echocardiography was performed. Frozen myocardial sections were prepared to stain the apoptotic cardiomyocytes using TUNEL staining. DN 14-3-3η mice fed with HFD showed cardiac dysfunction as identified by the decreased fractional shortening and ejection fraction and increased cardiomyocyte apoptosis in TUNEL staining. Western blotting analysis using mitochondrial fraction of the ventricular tissue homogenates showed a significant reduction in the level of cytochrome c suggesting its translocation into cytoplasm, which may be crucial in inducing cardiomyocyte apoptosis. In addition, DN 14-3-3η mice depicted significantly increased levels of NADPH oxidase subunits suggesting oxidative stress, a significant reduction in phospho apoptosis signal-regulating kinase-1 (p-Ask-1) and increase in Ask-1 and phospho c-Jun N-terminal kinase (p-JNK) levels suggesting activation of Ask-1/JNK signaling. These results suggest that 14-3-3η has a protective role against mitochondria mediated cardiomyocyte apoptosis with the involvement of Ask-1/JNK signaling during HFD induced type 2 DM.