Obesity-Related Modification of Ovarian Gene Expression and Glucocorticoid Metabolism in Aging Lethal Yellow Mice.

Abstract

Mice possessing the lethal yellow (LY) agouti mutation (C57BL/6J Ay/a) exhibit adult-onset obesity, altered metabolic regulation, and early reproductive senescence. We have previously reported that aging (180-day-old) LY mice exhibit altered ovarian expression of genes involved in sterol synthesis and metabolism relative to age-matched lean non-mutant black mice (B; C57BL/6J a/a). The present study was designed to test the hypothesis that the altered expression of ovarian genes is related to acquired obesity rather than to a direct consequence of the agouti mutation. Differential gene expression in young (90-day-old) LY and B mice, which have similar body weights, were compared with aging mice in which the LY animals are obese. To synchronize ovarian state and exclude gonadotropin-mediated effects, 90-day-old diestrous LY (n = 3) and B (n = 3) mice were suppressed with GnRH antagonist (Antide, Sigma, St. Louis, MO) for five days, then injected with 5 IU eCG (Sigma). Mice were killed 36 h after eCG, and ovaries were immediately removed, carefully trimmed of adhering tissue, and placed in RNALater (Ambion, Austin, TX ) for subsequent RNA extraction. cRNA derived from RNA extracts were run individually on Codelink Mouse Whole Genome Bioarrays (GE Healthcare Life Sciences). Relative gene expression was compared between B and LY mice by t-test using GeneSpring software. Unnamed genes, EST, genes whose expression was below sensitivity limits, and those with less than a 2-fold difference in expression between groups were excluded from further analysis. After these exclusions, 45 genes were differentially expressed in young B and LY mice, compared to 110 differentially expressed genes in aging mice. Both 90- and 180-day-old LY mice exhibited elevated ovarian expression relative to B mice of the agouti gene (330x,350x) as expected. In contrast, numerous genes whose expression was elevated in aging LY mice relative to B mice, e.g. leptin, HMG-CoA reductase, CYP51, and steroidogenic acute regulatory protein (StAR), were not differentially expressed in young LY and B mice. Notably, aging LY mice had a 2-fold greater expression of 11β-HSD type 1 and a 2-fold lesser expression of 11β-HSD type 2 relative to B mice. There was no difference in expression of these genes in young B and LY mice. Consistent with altered 11β-HSD gene expression, ovarian concentrations of corticosterone (C) were elevated in aging LY mice relative to B mice (1.7 ng/mg vs. 0.8 ng/mg, respectively), but C levels were similar in young B and LY mice (0.8 ng/mg vs. 0.9 ng/mg). Results suggest that differential ovarian gene expression and glucocorticoid metabolism observed in aging LY mice is directly related to acquired obesity. (Supported by NIH INBRE 2P20RR016479, NIH R15 HD044438, and Sanford Research/USD)