Mutations in genes involved in cardiac mechanosensation (mec), such as the muscle LIM protein (MLP), have been shown to cause cardiomyopathy - as such identification of novel mec genes by searching for new MLP interacting proteins (MiP) may provide novel insights into underlying molecular mechanisms of human disease.Methods & Results
A yeast two hybrid screen resulted in the identification of novel MLP-interacting proteins (MiP) where MiP1 is a member of the POZ domain/zinc finger transcription factor family and MiP2 of the MYM domain protein family. Immunoprecipitation and co-localization studies confirmed the yeast two hybrid results for both proteins, however MiP2 is localized to the Z-disc whereas MiP1co-localizes with MLP in the nucleus.Methods & Results
Recent genome wide association and large case control studies point to a significant association of a genomic locus, where MiP1 is localized, to dilated cardiomyopathy (DCM). We sequenced genomic DNA of 116 unrelated DCM patients and identified two MiP1 missense mutations, both localized between the POZ and the zinc finger domains. These mutations co-segregate with the disease (i. e. DCM associated with arrhythmia) in these families and they are not present in 700 control or 800 DCM/heart failure chromosomes. In addition, both index patients carry no additional mutations in 12 well-known cardiomyopathy disease genes which supports a disease causing role of these mutations.Methods & Results
Moreover, MiP1 is downregulated in human ischemic cardiomyopathy and DCM (DCM, P=0.01), whereas MiP2 is transcriptionally induced in DCM (n=12, P=0.001). Conventional homozygous loss of MiP1 and MiP2 alleles results in embryonic lethality. MiP1 conditional knockout (cKO) animals failed to adapt to biomechanical stress in form of transverse aortic constriction (TAC). Four weeks after TAC, fractional shortening (FS) was significantly decreased (46.5 ± 6.3% vs 52.0 ± 3.7%, P < 0.04) and LVEDD (3.74 ± 0.19% vs 3.44 ± 0.16%, P < 0.003) as well as LVESD (2.00 ± 0.28% vs 1.65 ± 0.14%, P < 0.005) were significantly increased in cKO mice (n=10) compared to control WT littermates (n=8).Methods & Results
In addition, MiP2 heterozygous knockout mice develop age dependent sarcopenia, but no change in cardiac function which suggests that this protein is involved in the regulation of myocardial hypertrophy and/or atrophy.Conclusions
MiP1 and MiP2 are novel MLP interacting proteins with potentially important implications for myocardial function, hypertrophy and heart failure. In addition, MiP1 might be a novel candidate gene for DCM associated with arrhythmia.