Cardiac Specific Overexpression of N-RAP in Transgenic Mice

The muscle specific protein NRAP plays a role in myofibril assembly and is upregulated in mouse models of dilated cardiomyopathy. We sought to determine if increased N-RAP expression would directly lead to a cardiomyopathy phenotype. Novel transgenic lines were developed using the tet-off system with transgenic N-RAP expression requiring the tetracycline transactivator (tTA). tTA was introduced by mating the N-RAP transgenic animals with well-characterized animals carrying the tTA transgene controlled by the cardiac specific alpha-myosin heavy chain promoter. Multiple founder lines were examined and lines showing the most significant increase in NRAP expression were used for further investigation. N-RAP expression in theses animals was up to 2.5 times greater than control littermates as determined by western blot analysis. Histological examination of hearts from ∼12 week old transgenic mice showed no structural defects compared to control littermates. Additionally, examination of these hearts by immunofluorescence microscopy revealed normal myofibrillar structure and localization of the transgenic protein to intercalated disks, as normally seen with the endogenous protein. Protein markers for cardiomyopathy were examined by qPCR and revealed no difference between non-transgenic and transgenic animals. Echocardiography and magnetic resonance imaging of the N-RAP transgenic animals revealed no significant structural or functional differences when compared to control littermates at 12 weeks of age. Based on these data, it does not appear that overexpression of N-RAP directly leads to an observable cardiac phenotype. The alternative hypothesis that upregulation of N-RAP in dilated cardiomyopathy is compensatory remains to explored.