Abstract 250: Haploinsufficiency of Muscle-Enriched A-Type Lamin Interacting Protein (MLIP) Manifests as Enlarged Dilated Hearts
Approximately 116 unique mutations in the lamin A/C gene have been described to date that are associated with dilated cardiomyopathy. We recently reported the discovery of MLIP through its interaction with lamin A/C. MLIP is expressed ubiquitously and most abundantly in heart, skeletal and smooth muscle of amniotes (mammals, reptiles and birds) and has no paralogous homologue suggesting no functional redundancy. The MLIP gene encodes at least seven, alternatively spliced, LMNA-interacting factors that possess several structural motifs not found in any other protein. The MLIP isoforms pattern of expression differs between each of the tissues with heart being the most heterogeneous. Down-regulation of lamin A/C expression by shRNA results in the up-regulation and mis-localization of MLIP. In addition to interacting and co-localizing with lamin A/C we also demonstrated that MLIP localizes to micro-domains in the nucleus with promyelocytic leukemia protein (PML) in close proximity to chromatin. MLIP's biological function still remains elusive.
Eight week old hemizygous MLIP null mice develop enlarged hearts with a significant increase in heart to body weights (MLIP+/+ 5.62mg/g vs MLIP+/- 10.73mg/g, p<0.0001 n=7) with an overall 30% increase in the anterior-posterior ventricle length of MLIP hearts while maintaining a normal body weight (Figure). Echocardiographic analysis of MLIP+/- mice revealed that their hearts as having a significant (p3.93mm with a significant (p=0.011, n=12) reduction of left ventricular fractional shorting (LVFS) 31% when compare to littermate controls. Histological analysis of the hearts showed no overt phenotype other than an overall increase in the size of the MLIP+/- hearts. The cellular source for the increase in heart size and mass remains to be determined if it is the product of an increase in the number of cardiomyocytes due to aberrant hyperplasia or an increase in cardiomyocyte size through cellular hypertrophy.
In conclusion, MLIP is a newly discovered lamin interacting protein that may serve as a transcriptional regulator that impact genes involved in heart development, growth and function and provides a new signaling paradigm.
- © 2012 by American Heart Association, Inc.