Abstract
BackgroundPhenotypic alteration of vascular smooth muscle cells (SMC) in response to injury or inflammation is an essential component of vascular disease. Evidence suggests that this process is dependent on epigenetic regulatory processes. P300, a histone acetyltransferase (HAT), activates crucial muscle-specific promoters in terminal (non-SMC) myocyte differentiation, and may be essential to SMC modulation as well.ResultsWe performed a subanalysis examining transcriptional time-course microarray data obtained using the A404 model of SMC differentiation. Numerous chromatin remodeling genes (up to 62% of such genes on our array platform) showed significant regulation during differentiation. Members of several chromatin-remodeling families demonstrated involvement, including factors instrumental in histone modification, chromatin assembly-disassembly and DNA silencing, suggesting complex, multi-level systemic epigenetic regulation. Further, trichostatin A, a histone deacetylase inhibitor, accelerated expression of SMC differentiation markers in this model. Ontology analysis indicated a high degree of p300 involvement in SMC differentiation, with 60.7% of the known p300 interactome showing significant expression changes. Knockdown of p300 expression accelerated SMC differentiation in A404 cells and human SMCs, while inhibition of p300 HAT activity blunted SMC differentiation. The results suggest a central but complex role for p300 in SMC phenotypic modulation.ConclusionsOur results support the hypothesis that chromatin remodeling is important for SMC phenotypic switching, and detail wide-ranging involvement of several epigenetic modification families. Additionally, the transcriptional coactivator p300 may be partially degraded during SMC differentiation, leaving an activated subpopulation with increased HAT activity and SMC differentiation-gene specificity.
Highlights
The ability of mature vascular smooth muscle cells (SMC) to modulate their phenotype is responsible in large part for many of the specific manifestations and genesis of vascular diseases such as hypertension, atherosclerosis, and post-angioplasty restenosis [1,2,3]
Chromatin remodeling genes show widespread regulation with in vitro SMC differentiation In previously published work, A404 P19 mouse embryonal carcinoma cells were induced to differentiate into SMCs using alltrans retinoic acid (RA) treatment for 96 hours, followed by hours of puromycin, and RNA-harvested for microarray transcriptional profiling [26]
We used a 60-mer microarray platform (Agilent, Palo Alto, CA) with 20,280 mouse transcripts derived from the National Institute on Aging clone set, and identified 2,739 genes that were significantly upregulated from untreated cells after differentiation was completed (FDR,1), as well as 2,227 downregulated genes
Summary
The ability of mature vascular smooth muscle cells (SMC) to modulate their phenotype is responsible in large part for many of the specific manifestations and genesis of vascular diseases such as hypertension, atherosclerosis, and post-angioplasty restenosis [1,2,3]. The amino-terminal portions of core histones contain flexible protease-sensitive tails which are evolutionarily conserved sites for post-translational modifications, including methylation, acetylation, phosphorylation, ubiquitylation, and ADP-ribosylation [9,10, 11]. These modifications are correlated with replication, chromatin assembly, and transcription [7,12]. Phenotypic alteration of vascular smooth muscle cells (SMC) in response to injury or inflammation is an essential component of vascular disease Evidence suggests that this process is dependent on epigenetic regulatory processes. P300, a histone acetyltransferase (HAT), activates crucial muscle-specific promoters in terminal (non-SMC) myocyte differentiation, and may be essential to SMC modulation as well
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