The investigators created ApoE-knockout mice carrying a tamoxifen-inducible, smooth muscle cell-specific Cre recombinase crossed to floxed MR alleles. They treated both Cre+ and Cre– littermates with tamoxifen and confirmed significant reduction of MR mRNA in whole aortas by RT-qPCR in male and female SMC-MR-KO mice. The model therefore achieved SMC-targeted MR knockdown across sexes. The source did not report protein-level confirmation in isolated SMCs, only the aortic MR mRNA measurement.
After eight weeks of high fat diet (HFD), the study team measured established systemic risk markers. They reported no significant effect of SMC-MR deletion on plasma aldosterone concentration, fasting glucose, fasting total cholesterol, or systolic blood pressure. Body weight was higher in males than females, but genotype did not change weight. These results indicate that, under the conditions studied, SMC-MR-KO did not alter the traditional metabolic or hemodynamic drivers typically linked with atherogenesis.
Histologic analysis focused on aortic root cryosections after 8 weeks HFD. Representative Oil-Red-O and H&E images were quantified. The cohort showed that females developed larger aortic root plaque cross-sectional areas than males, consistent with prior reports. Despite this sex difference in absolute plaque area, SMC-MR-KO did not significantly change plaque cross-sectional area in either sex. Measurement of the percentage of plaque composed of neutral lipids and of necrotic core likewise showed no significant differences by genotype or by sex. The authors used three serial sections per mouse per stain, averaged for each animal, and quantification was performed blinded to group.
The team evaluated plaque fibrosis with Masson’s Trichrome and cellular composition via immunofluorescence for smooth muscle actin (SMA) and Mac-2. Quantitative analysis revealed that the percentage of plaque area composed of collagen-containing fibrosis did not differ by SMC genotype or sex. The proportion of the lesion positive for SMA, a marker of differentiated SMCs that can influence fibrous cap structure, was unchanged by SMC-MR deletion. Similarly, the percentage of Mac-2–positive area, reflecting activated macrophage content, did not vary between SMC-MR-KO and SMC-MR-intact mice in either sex. In short, SMC-MR deletion did not materially alter markers of plaque stability or inflammation in the aortic root at this early disease time point.
The cohort-wide observation that female ApoE-KO mice on HFD developed larger aortic root plaques than males was reaffirmed here. Despite larger lesions in females, the relative composition of those plaques—lipid fraction, necrotic core fraction, collagen content, SMA positivity, and Mac-2 positivity—remained statistically similar across sexes. Thus, lesion size diverged by sex, but lesion phenotype percentages did not. The authors compared male and female littermates directly in order to identify sex-specific contributions of SMC-MR; none were detected under the tested conditions.
All experimental inferences are limited to the conditions reported. The source documents that the study analyzed early atherosclerosis after eight weeks of HFD in ApoE-KO mice; effects at later time points or with different dietary or pharmacologic interventions were not reported. The authors noted that aldosterone infusion has increased plaque size and inflammation in male mice in prior work, but that such infusion has not been tested in females within this model—this remains an unanswered experimental question. The manuscript did not report protein-level MR verification specifically in isolated SMCs, nor did it assess coronary artery plaques because ApoE-KO mice do not develop coronary lesions under these conditions. The study design included at least three independent cohorts and blinded quantification, and all datasets are archived in the Harvard Dataverse as cited by the authors. No regulatory milestones were cited by the authors. Future experimental steps explicitly mentioned in the source would include testing other cell-type MR contributions, temporal extension of HFD exposure, and sex-specific aldosterone challenge studies to determine whether SMC-MR contributes under alternative pro-atherogenic stimuli.
Limitations therefore restrict conclusions to early aortic root atherosclerosis in this genetic and dietary mouse model. The data, as reported, indicate that deletion of the mineralocorticoid receptor from vascular smooth muscle cells does not alter aortic root plaque burden or composition in male or female ApoE-KO mice after eight weeks of high fat feeding. The study leaves specific mechanistic and sex-specific aldosterone-response questions open for further investigation.