XX sex chromosome complement promotes hyperlipidemia and atherosclerosis in mice

It is well recognized that men and women differ in circulating lipid profiles and consequently coronary artery disease (CAD). While sex hormones like estrogens are thought to protect women from CAD risk by promoting protective lipid profiles, hormone replacement therapy in women paradoxically increases CAD risk. Biological sex is determined by both sex chromosomes and sex hormones. We used mouse models to separate effects of sex chromosomes and hormones on atherosclerosis, circulating lipids and intestinal fat metabolism. We found that an XX sex chromosome complement increases food intake, body weight, fat absorption, serum lipid concentrations and atherosclerosis in gonadal male and female mice, indicating a primary effect of sex chromosome complement. Small intestine expression of enzymes involved in lipid absorption and chylomicron assembly were increased in XX male and female mice with elevated intestinal lipids. These results reveal that an XX sex chromosome complement promotes the absorption and bioavailability of dietary fat to accelerate the development of atherosclerosis. Liver tissue was harvested from 24-28 week old Ldlr-/- male and female mice with an XX or XY chromosomal complement that had been surgically gonadectomized at 8-12 weeks of age and then fed a Western high fat diet for 16 weeks (n = 5 female XX, n = 5 female XY, n = 4 male XX, n = 5 male XY; no technical replicates were performed). Harvested liver RNA samples were of sufficient quality and did not differ significantly among treatment groups (Agilent Bioanalyzer RNA Integrity Number [RIN]: 9.55 ± 0.05 – p > 0.29; two-way ANOVA main effect of Sex p = 0.25; main effect of chromosome p = 0.13; interaction p = 0.42). Extracted RNA was labeled and hybridized to Affymetrix Mouse Transcriptome Array 1.0 (MTA-1.0; one array per subject). Signal intensities were calculated using the Robust Multi-array Average (RMA) algorithm at the transcript level in Genomics Suite (Partek, St Louis). Data were transferred to flat files in Excel and associated with Gene Expression Omnibus annotations for this microarray platform (GPL20775). Pre-statistical filtering retained unique, annotated probe sets with signal intensity ≥ 4.2 on at least 2 arrays in the study. Filtered signal intensities were analyzed by two-way ANOVA to identify significant main effects of genotype (XX versus XY), phenotypic sex (Male vs Female), as well as Interaction. The False Discovery Rate (FDR) procedure, as modified by Storey was used to control for the error of multiple testing (q ≤ 0.01).