Abstract 4525: Monocyte Chemotactic Protein 1 is Epigenetically Activated Early After Experimental Aortic Aneurysm Induction and is Required for Aneurysm Formation and Smooth Muscle Phenotypic Modulation
Objectives: Our lab has recently documented that phenotypic modulation of smooth muscle cells (SMCs), characterized by downregulation of marker genes, is an early event in aortic aneurysm (AA) formation. We hypothesized SMC phenotype is epigenetically regulated early in AA and occurs in concert with epigenetic activation of inflammatory promoters such as MCP1, a factor previously found to be upregulated in human thoracic and abdominal aneurysms. We further hypothesized that MCP1 is crucial to AA formation and associated decreases in SMC marker genes.
Methods: Abdominal aortas from WT C57B6 mice and MCP1 knockout mice were perfused with elastase or saline (control) and harvested at 3, 7, and 14 days. Aortas were analyzed by chromatin immunoprecipitation (ChIP) at 3 days and by histology at 7 and 14 days. The effects of MCP1 on SMCs were tested in an aortic SMC culture.
Results: Elastase treated WT aortas had a mean diameter of 1.21+/−0.02 mm (n=8) at 14 days versus 0.91+/−0.05 mm for MCP1 KO aortas (n=8, p<0.0001) and 0.93+/−0.03 mm for WT saline controls (n=14). Preliminary ChIP analysis demonstrated >400-fold enrichment of H4 acetylation, an epigenetic mark associated with activation, at the MCP1 loci at 3 days in elastase perfused WT AAs compared to saline perfused WT aortas (n=10 pooled samples each). H4 acetylation was decreased 3-fold at the SMaA promoter and 2-fold at the promoter of pro-myogenic factor myocardin at 3 days. Protein levels of MCP1 were confirmed to be elevated in WT AAs by immunohistochemistry (IHC) at 14 days. IHC also demonstrated that the repression of SMaA and induction of MMP2, −9, and Mac2 seen in WT AAs was greatly abrogated in the MCP1 KOs at 14 days. Interestingly, in vitro studies demonstrated that MCP1 can act directly on SMCs to repress SMaA, SM-MHC, and SM22 and induce MMP9 despite no detectable expression of CCR2, the known MCP1 receptor, in our SMC culture.
Conclusions: MCP1 is required for experimental AA formation and its promoter acquires an epigenetic activation mark well before any aneurysm formation is evident in WT mice. While its role in promoting CCR2-dependent immune cell chemotaxis has been presumed to be its mechanism of action, here we show MCP1 is capable of acting directly on SMCs to affect AA-related gene expression changes.
This research has received full or partial funding support from the American Heart Association, Mid-Atlantic Affiliate (Maryland, North Carolina, South Carolina, Virginia & Washington, DC).