Corticosteroid-binding globulin (SERPINA6) consolidates sexual dimorphism of adult rat liver

Produced by the liver, corticosteroid-binding globulin (CBG) regulates the plasma distribution and actions of glucocorticoids. A sex difference in pituitary growth hormone secretion patterns established during puberty in rats results in increased hepatic CBG production and two-fold higher plasma corticosterone levels in females. Glucocorticoids control hepatic development and metabolic activities, and we have therefore examined how disrupting the SerpinA6 gene encoding CBG influences plasma corticosterone dynamics, as well as liver gene expression in male and female rats before and after puberty. Comparisons of corticosterone plasma clearance and hepatic uptake in adult rats, with or without CBG, indicated that CBG limits corticosterone clearance by reducing its hepatic uptake. Hepatic transcriptomic profiling revealed minor sex differences (207 differentially expressed genes) and minimal effect of CBG deficiency in 30-day-old rats before puberty. While liver transcriptomes in 60-day-old males lacking CBG remained essentially unchanged, 2,710 genes were differentially expressed in wild-type female versus male livers at this age. Importantly, ~10% of these genes lost their sexually dimorphic expression in adult females lacking CBG, including those related to cholesterol biosynthesis, inflammation, and lipid and amino acid catabolism. Another 203 genes were altered by the loss of CBG specifically in adult females, including those related to xenobiotic metabolism, circadian rhythm, and gluconeogenesis. Our findings reveal that CBG consolidates the sexual dimorphism of the rat liver initiated by sex differences in growth hormone secretion patterns and provide insight into how CBG deficiencies are linked to glucocorticoid-dependent diseases. To investigate the role of CBG in liver function, we generated CBG-deficient rats using a CRISPR/cas9 strategy to ablate SerpinA6 gene expression. We then performed gene expression profiling analysis using data obtained from RNA-seq of rat livers at 30 and 60 days of age, under basal conditions. Male and female wild-type (Cbg+/+) and CBG-knockout (Cbg-/-) rats were employed (n=4).