Smooth muscle cell mineralocorticoid receptor does not contribute to atherosclerosis in male or female ApoE-knockout mice.

backgroundYoung women have a lower risk of myocardial infarction (MI) compared to age-matched men, protection that is lost with aging or obesity. There are sex differences in human plaque histopathology, where male plaques are more inflamed and female plaques have more smooth muscle cell (SMC) content. The hormone aldosterone activates the mineralocorticoid receptor (MR) to regulate gene transcription. Elevated aldosterone is seen with obesity and associates with significantly increased incidence of MI. Cell-type specific knockout (KO) of MR reveals a role for endothelial cell and myeloid MR in atherogenesis and plaque inflammation in male, but not in female, mice. SMC-KO of the MR did not impact plaque phenotype in male mice, but female mice have never been studied. Thus, the role of SMC-MR in atherosclerosis was tested for the first time in female mice, directly comparing male and female littermates to identify potential sex differences. METHODS AND

resultsAtheroprone male and female mice with SMC-specific MR deletion were generated by crossing ApoE-KO mice to MRflox/flox×SMA-Cre-ERT2+/- mice to generate ApoE-KO/SMC-MR-KO and ApoE-KO/SMC-MR-intact littermate controls. Significant knockdown of MR mRNA expression was confirmed in aorta from male and female littermates in this model. After 8 weeks high fat diet (HFD), SMC-MR-KO did not impact aldosterone levels, blood pressure, fasting glucose and cholesterol, or body weight, although males weighed significantly more than females. Atherosclerotic plaque size and phenotype were characterized histologically in aortic root sections. SMC-MR-KO did not significantly impact aortic root plaque area in male or female mice, although females had larger plaques than males. Analysis of Oil-Red-O-stained aortic root sections revealed no significant sex or genotype difference in the percentage of the plaque made up of necrotic core or neutral lipids. Analysis of Masson's Trichrome-stained sections showed no impact of SMC-MR-KO on the percentage of the plaque composed of fibrosis. Finally, immunofluorescent staining of aortic root sections showed no impact of SMC-MR-KO on the percentage of the plaque that was positive for smooth muscle actin or Mac2, neither of which differed significantly by sex.

conclusionIn ApoE-KO mice fed HFD for 8 weeks, SMC-MR-KO does not impact traditional cardiovascular risk factors or atherosclerotic plaque size or plaque composition in early atherosclerosis in either sex.