Men and women differ in circulating lipids and coronary artery disease (CAD). While sex hormones such as estrogens decrease CAD risk, hormone replacement therapy increases risk. Biological sex is determined by sex hormones and chromosomes, but effects of sex chromosomes on circulating lipids and atherosclerosis are unknown. Here, we use mouse models to separate effects of sex chromosomes and hormones on atherosclerosis, circulating lipids and intestinal fat metabolism. We assess atherosclerosis in multiple models and experimental paradigms that distinguish effects of sex chromosomes, and male or female gonads. Pro-atherogenic lipids and atherosclerosis are greater in XX than XY mice, indicating a primary effect of sex chromosomes. Small intestine expression of enzymes involved in lipid absorption and chylomicron assembly are greater in XX male and female mice with higher intestinal lipids. Together, our results show that an XX sex chromosome complement promotes the bioavailability of dietary fat to accelerate atherosclerosis.
Background Abdominal aortic aneurysms (AAAs) are a deadly pathology with strong sexual dimorphism. Similar to humans, female mice exhibit far lower incidences of angiotensin II (AngII)-induced AAAs than males. In addition to sex hormones, the X and Y sex chromosomes, and their unique complements of genes, may contribute to sexually dimorphic AAA pathology. Here, we defined the effect of female (XX) versus male (XY) sex chromosome complement on AngII-induced AAA formation and rupture in phenotypically female mice. Methods Female low density lipoprotein receptor (Ldlr) mice with an XX or XY sex chromosome complement were infused with AngII for 28 days to induce AAAs. Abdominal aortic lumen diameters were quantified by ultrasound, while AAA diameters were quantified at study endpoint. DNA microarrays were performed on abdominal aortas. To mimic males, female mice were administered a single dose of testosterone as neonates or as adults prior to AngII infusions. Results Female Ldlr−/− deficient mice with an XX and XY sex chromosome complement had similar sex organ weights and low serum testosterone concentrations. Abdominal aortas from female XY mice selectively expressed Y chromosome genes, while genes known to escape X-inactivation were higher in XX females. The majority of aortic gene differences in XY versus XX females fell within inflammatory pathways. AAA incidences doubled and aneurysms ruptured in XY females. AAAs from XY females exhibited inflammation, and plasma IL1β concentrations were increased in XY females. Moreover, aortas from XY females had augmented matrix metalloproteinase activity and increased oxidative stress. Finally, testosterone exposure applied chronically, or as a single bolus at postnatal day 1, markedly worsened AAA outcomes in XY compared to XX adult females. Conclusions An XY sex chromosome complement in phenotypic females profoundly influenced aortic gene expression profiles and promoted AAA severity. When XY females were exposed to testosterone, aneurysm rupture rates were striking. Mechanisms for augmented AAA severity in XY females include increased inflammation, augmented matrix metalloproteineases and oxidative stress. Our results demonstrate that genes on the sex chromosomes regulate aortic vascular biology and contribute to sexual dimorphism of AAAs. Sex chromosome genes may serve as novel targets for sex-specific AAA therapeutics.
An XY sex chromosome complement mediates diffuse aortic pathology, whereas an XX sex chromosome complement contributes to focal AngII-induced AAAs.
BackgroundAbdominal aortic aneurysms (AAAs) occur predominately in males. However, AAAs in females have rapid growth rates and rupture at smaller sizes. Mechanisms contributing to AAA progression in females are undefined. We defined effects of ovariectomy, with and without 17-β estradiol (E2), on progression of established angiotensin II (AngII)-induced AAAs in female mice.MethodsWe used neonatal testosterone exposures at 1 day of age to promote susceptibility to AngII-induced AAAs in adult female Ldlr−/− mice. Females were infused with AngII for 28 days to induce AAAs, and then stratified into groups that were sham, ovariectomized (Ovx, vehicle), or Ovx with E2 administration for 2 months of continued AngII infusions. Aortic lumen diameters were quantified by ultrasound and analyzed by linear mixed model, and maximal AAA diameters were analyzed by one-way ANOVA. Atherosclerosis was quantified en face in the aortic arch. AAA tissue sections were analyzed for cellular composition. We quantified effects of E2 on abdominal aortic smooth muscle cell (SMC) growth, α-actin and transforming growth factor-beta (TGF-β) production, and wound healing.ResultsSerum E2 concentrations were increased significantly by E2. Aortic lumen diameters increased over time in sham-operated and Ovx (vehicle) females, but not in Ovx females administered E2. At day 70, E2 administration decreased significantly aortic lumen diameters compared to Ovx vehicle and sham-operated females. Compared to Ovx females (vehicle), maximal AAA diameters were reduced significantly by E2. AAA tissue sections from Ovx females administered E2 exhibited significant increases in α-actin and decreases in neutrophils compared to Ovx females administered vehicle. In abdominal aortic SMCs, E2 resulted in a concentration-dependent increase in α-actin, elevated TGF-β, and more rapid wound healing. E2 administration to Ovx females also significantly reduced atherosclerotic lesions compared to sham-operated females. This effect was accompanied by significant reductions in serum cholesterol concentrations.ConclusionsE2 administration to Ovx females abolished progressive growth and decreased severity of AngII-induced AAAs. These effects were accompanied by increased SMC α-actin, elevated TGF-β, and reduced neutrophils. Similarly, E2 administration reduced AngII-induced atherosclerosis. These results suggest that loss of E2 in post-menopausal females may contribute to progressive growth of AAAs.Electronic supplementary materialThe online version of this article (doi:10.1186/s13293-015-0030-1) contains supplementary material, which is available to authorized users.
Objective: Turner syndrome women (monosomy X) have high risk of aortopathies consistent with a role for sex chromosomes in disease development. We demonstrated that sex chromosomes influence regional development of Ang II (angiotensin II)–induced aortopathies in mice. In this study, we determined if the number of X chromosomes regulates regional development of Ang II–induced aortopathies. Approach and Results: We used females with varying numbers of X chromosomes (XX female mice [XXF] or XO female mice [XOF]) on an C57BL/6J (ascending aortopathies) or low-density lipoprotein receptor deficient ( Ldlr −/− ) background (descending and abdominal aortopathies) compared with XY males (XYM). To induce aortopathies, mice were infused with Ang II. XOF (C57BL/6J) exhibited larger percent increases in ascending aortic lumen diameters than Ang II–infused XXF or XYM. Ang II–infused XOF ( Ldlr −/− ) exhibited similar incidences of thoracic (XOF, 50%; XYM, 71%) and abdominal aortopathies (XOF, 83%; XYM, 71%) as XYM, which were greater than XXF (XXF, 0%). Abdominal aortic lumen diameters and maximal external diameters were similar between XOF and XYM but greater than XXF, and these effects persisted with extended Ang II infusions. Larger aortic lumen diameters, abdominal aortopathy incidence (XXF, 20%; XOF, 75%), and maximal aneurysm diameters (XXF, 1.02±0.17; XOF, 1.96±0.32 mm; P =0.027) persisted in ovariectomized Ang II–infused XOF mice. Data from RNA-seq demonstrated that X chromosome genes that escape X-inactivation (histone lysine demethylases Kdm5c and Kdm6a ) exhibited lower mRNA abundance in aortas of XOF than XXF ( P =0.033 and 0.024, respectively). Conversely, DNA methylation was higher in aortas of XOF than XXF ( P =0.038). Conclusions: The absence of a second X chromosome promotes diffuse Ang II–induced aortopathies in females.
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