Abstract 11816: Brca1-associated Protein 2 (BRAP) is Essential for Embryonic Heart Development and for Neonatal Cardiomyocyte Proliferation
BRAP was identified as a cytoplasmic protein that binds to the nuclear localisation sequences of BRCA1. We previously reported BRAP to be differentially regulated upon load induced cardiac hypertrophy in a proteomic study. The aim of this study was to examine the function of BRAP in the heart. We generated several Brap knockout (-/-) mice and cardiac restricted conditional Brap-/- and Brap transgenic (TG) mice. Brap-/- led to embryonic lethality at day 11.5 while heterozygous mice were born and survived without phenotypic abnormalities. Brap-/- embryos displayed growth retardation and early embryonic heart failure including enlargement of the cardinal veins, dilated sinus venosi and primitive atria as well as a thinning of the trabecular and compact layer of the ventricular myocardium. Likewise, conditional cardiomyocyte restricted Brap deletion using the early expressed Mlc2v-Cre recombinase resulted in embryonic lethality, whereas alphaMHC-Cre Brap-/- mice were born, but developed severe heart failure and died shortly after birth. Echocardiographic examination revealed ventricular dilatation and strong functional impairment 4 days after birth. While tunel staining displayed no signs of increased apoptosis, immunohistological staining of the cell cycle regulator CyclinD1 and proliferation marker PCNA demonstrated a marked attenuation of cardiomyocyte cell cycle progression (PCNA posive cells: Brap2flox/flox MHC-Cre/-: 94.2±0.5 %; n=6; Brap2flox/flox MHC-Cre/+ : 46.7±10.4 %; n=4; p<0.0005). Moreover, BrdU assay showed a significantly reduced rate of DNA synthesis in the BRAP deficient myocardium. Vice versa, cardiomyocyte-specific transgenic overexpression of BRAP lead to increased CyclinD1 expression and BrdU incorporation suggesting increased cell cycle activity in BRAP TG hearts. We demonstrate that BRAP is essential for cardiac development and myocardial function as BRAP knockout models exhibited cell cycle arrest, attenuated cardiomyocyte proliferation and early heart failure. In contrast, transgenic BRAP overexpression lead to enhanced myocardial mass and to higher cell cycle activity in neonatal cardiomyocytes. Thus, via cell cylce control, BRAP is an essential regulator of cardiomycyte function and proliferation.
- © 2012 by American Heart Association, Inc.