Histone deacetylases 1 and 2 redundantly regulate cardiac morphogenesis, growth, and contractility
Abstract
Histone deacetylases (HDACs) tighten chromatin structure and repress gene expression through the removal of acetyl groups from histone tails. The class I HDACs, HDAC1 and HDAC2, are expressed ubiquitously, but their potential roles in tissue-specific gene expression and organogenesis have not been defined. To explore the functions of HDAC1 and HDAC2 in vivo, we generated mice with conditional null alleles of both genes. Whereas global deletion of HDAC1 results in death by embryonic day 9.5, mice lacking HDAC2 survive until the perinatal period, when they succumb to a spectrum of cardiac defects, including obliteration of the lumen of the right ventricle, excessive hyperplasia and apoptosis of cardiomyocytes, and bradycardia. Cardiac-specific deletion of either HDAC1 or HDAC2 does not evoke a phenotype, whereas cardiac-specific deletion of both genes results in neonatal lethality, accompanied by cardiac arrhythmias, dilated cardiomyopathy, and up-regulation of genes encoding skeletal muscle-specific contractile proteins and calcium channels. Our results reveal cell-autonomous and non-cell-autonomous functions for HDAC1 and HDAC2 in the control of myocardial growth, morphogenesis, and contractility, which reflect partially redundant roles of these enzymes in tissue-specific transcriptional repression.
Chromatin-modifying enzymes control gene expression through reversible post-translational modifications of histone tails within nucleosomes (Jenuwein and Allis 2001). Histone acetyltransferases catalyze the transfer of acetyl groups from acetyl coenzyme A to ε-amino groups of lysine residues of histone tails. Acetylation results in a loss of positive charge, relaxing chromatin structure and allowing access of transcription factors to their target genes (Roth et al. 2001). Histone deacetylases (HDACs) oppose the activity of histone acetyltransferases by catalyzing the removal of acetyl groups from histone tails, resulting in compaction of chromatin and transcriptional repression (Grozinger and Schreiber 2002).
There are four classes of HDACs that comprise an ancient enzyme family conserved from bacteria to humans (Gregoretti et al. 2004). Class I HDACs (HDAC1, HDAC2, HDAC3, and HDAC8) are highly homologous to the yeast HDAC RPD3 and are ubiquitously expressed (Yang et al. 1997). The class II HDACs (HDAC4, HDAC5, HDAC7, and HDAC9) are homologous to the yeast protein HDA1 and are enriched in muscle and neural tissues (Grozinger et al. 1999; Verdin et al. 2003). Class II HDACs regulate tissue growth through signal-dependent repression of MEF2 and other transcription factors (McKinsey et al. 2000). Class III HDACs, or sirtuins, require NAD for deacetylation and are related to the yeast repressor Sir2 (Grozinger and Schreiber 2002). Class IV HDACs, a recently identified family of deacetylases, share homology with human HDAC11 (Gao et al. 2002).
The functions of class I HDACs in mammals have been largely inferred from studies in cultured cells, but relatively little is known of their potential roles in vivo. HDAC1 and HDAC2 share 85% amino acid homology and are found together in almost all repressive transcriptional complexes (Grozinger and Schreiber 2002). Mouse embryos deficient in HDAC1 die before embryonic day 10.5 (E10.5) due to proliferative defects (Lagger et al. 2002), precluding an analysis of its potential functions later in development or after birth. An HDAC2 mutant mouse generated from a lacZ insertion was recently reported to be viable (Trivedi et al. 2007), although as discussed below, our findings differ from the conclusions of that study.
To examine the functions of HDAC1 and HDAC2 in vivo, we generated mice with conditional null alleles for both genes. We show that global deletion of HDAC2 results in perinatal lethality with severe cardiac defects that appear to reflect a non-myocyte-autonomous function of HDAC2, since cardiac-specific deletion of either HDAC1 or HDAC2 alone has no discernable effect on cardiac function. However, cardiac deletion of both HDAC1 and HDAC2 genes results in dilated cardiomyopathy, arrhythmias, and neonatal lethality, accompanied by up-regulation of genes encoding skeletal muscle-specific myofibrillar proteins and calcium channels. Our findings suggest that HDAC1 and HDAC2 are functionally redundant in cardiac growth and development and maintain cardiomyocyte identity and function, at least in part, through repression of genes encoding skeletal muscle-specific myofibrillar proteins and calcium channels.
Acknowledgments
We are grateful to Alisha Tizenor for graphics, and to Nik Munshi for advice on electrophysiology. Supported by grants from the National Institutes of Health, the Donald W. Reynolds Clinical Cardiovascular Research Center, and the Robert A. Welch Foundation to E.N.O. M.H. was supported by a grant from the Deutsche Forschungsgemeinschaft (DFG, HA 3335/2-1). J.F. was supported by the Muscular Dystrophy Association.
Footnotes
Supplemental material is available at http://www.genesdev.org.
Article is online at http://www.genesdev.org/cgi/doi/10.1101/gad.1563807