Abstract 14216: Myocyte-Specific Gene Targeting and RNASeq Reveal a Selective Requirement for P300 For Basal Expression of Myh7 and the Induction of Cardiac Hypertrophy After Pressure Overload
Background: Acetyltransferase p300 is required for cardiac myocyte-specific gene expression and embryonic growth, and is induced by stress in the adult heart.
Objective: To determine the functional and transcriptional consequences of myocyte-specific loss of p300 at baseline and under mechanical stress.
Methods: Mice harboring the a-MHC Mer-Cre-Mer transgene and 0, 1 or 2 p300 floxed alleles were induced with tamoxifen (TA) at 8 -12 weeks of age (25mg/kg/d for 2 x 7d.) Loss of p300 was confirmed by Western blot and RT-PCR. Cardiac function was evaluated using high-resolution echocardiography and MRI. Histological analysis and In-situ cell death detection was performed at sacrifice. RNASeq analysis was performed on an Illumina Genome Analyzer IIX. Pressure overload was induced by transverse aortic coarctation (TAC) and pressure gradients were quantitated by Doppler flow/velocity.
Results: Homozygous p300fl/fl, MCM+ (KO) and heterozygous p300+/fl, MCM+ (HET) expressed 0.29±0.03 fold (p<0.001, n=3), and 0.71±0.06x (p<0.05, n=3), of p300 mRNA levels in p300+/+, MCM+ (MCM) mice after TA induction, with corresponding reductions in p300 protein content. KO and HET, but not MCM mice, developed an initial cardiac dysfunction with LVEF decreasing to 55% (±5.3, p<0.05, n= 4) in KO and 54.4% (±5.1 p<0.05, n=5) in HET at day 35. However EF recovered to near normal by day 80 in both genotypes (KO and HET). MCM mice maintained EF 67%-70% at all time points. No apoptotic cell death or fibrosis was seen in KO or HET mice at 35d. RNASeq revealed increased expression of HDAC11 (1.28x, p< 0.05) and Bcorl1 (1.65 fold, p<0.01). Remarkably, Myh7 (β-MHC) was strongly downregulated in KO myocardium (0.34 fold of MCM, p<0.001), with no corresponding change in ANP, Myh6, a-skeletal or a-cardiac actin, and upregulation of BNP (2.23x, p<0.001), indicating a selective dependence of this hypertrophy-associated gene on p300 availability. TAC induced significant myocyte growth by d20 in MCM (2.31x ± 0.27 of sham) but not in KO (1.02x ± 0.4 of sham), without evidence of impaired survival or cardiac function in KO mice.
Conclusion: Myocyte p300 is required for hypertrophic growth and expression of β-MHC but is not required for basal function or survival.
- © 2011 by American Heart Association, Inc.