Abstract 17978: Mlp Interacting Protein 1 (MIP1) Plays a Role for Cardiomyopathy

Abstract

Mutations in genes involved in cardiac mechanosensation (mec), such as the muscle LIM protein (MLP) have been shown to cause heart failure. Identification of novel mec genes may provide new insights into underlying mechanisms. A yeast 2 hybrid screen identified a novel MIP, located at a chromosomal region recently implicated by GWASs in the pathogenesis of dilated cardiomyopathy (DCM), an interaction confirmed by various assays. We found that MIP1 is a stress inducible transcription factor, binds to the calcineurin promoter and activates NFAT, a known mediator of hypertrophy. Also overexpression of MIP1 in vitro promotes autophagy and activates expression of anti-apoptotic genes in cardiac myocytes. Mip1 conventional knockout animals die during gastrulation whereas Mip1 conditional knockout (cKO) animals failed to adapt to transverse aortic constriction. Four weeks after intervention, fractional shortening was significantly decreased, whereas LVEDD and LVESD were significantly increased in cKO mice compared to control littermates. TUNEL assays combined with activated caspase, whole gene expression arrays and qRT-PCR provide strong evidence that Mip1 cKO hearts are unable to undergo autophagy and as a result activate apoptotic processes which are responsible for the observed heart failure phenotype. However, overexpression of MIP1 in vivo resulted in marked cardiac hypertrophy at the organ and single cell levels, pointing to a link between autophagy and hypertrophy. As MIP1 contains the peak association signal (rs10927875) at the replicated 1p36 cardiomyopathy locus, we sequenced this gene in 575 unrelated individuals affected by DCM and identified 4 MIP1 missense mutations (T106M, G179S, A188V, Q531R) of which 2 co-segregate in two families with DCM and arrhythmia. All 4 variants show abnormalities with regards to their ability to interact with MLP, localization, structure, stability and potential to drive the calcineurin promoter. WT-MIP1 is able to efficiently protect cells from apoptosis, a property missing in all mutants. At least G179S and Q531R cause heart failure in the zebrafish. MIP1 is important for the initiation of survival pathways and autophagy upon biomechanical stress and represents a novel cardiomyopathy candidate gene.