358 EXCESS EXPRESSION OF 11β-HSD1 CONTRIBUTES TO LETHALITY THROUGH DYSFUNCTION IN ENERGY BALANCE BETWEEN ANABOLIC PROCESS AND ENERGY RECOVERY PROCESS

Abstract

11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) effectively amplifies glucocorticoid action in liver, adipose tissue, and brain. This enzyme converts the inactive 11-keto form into a glucocorticoid (e.g. cortisol). Glucocorticoids (GC) are steroid hormones found in the body and produced by the adrenal cortex, the outer layer of the adrenal glands. Glucocorticoids are lipophilic and readily access their intracellular receptors. Glucocorticoids regulate carbohydrate, fat, and protein metabolism. In a previous study, we constructed a vector composed of 2 parts: the 11β-HSD1 expression cassette and the selection cassette containing EGFP and Neo resistant genes. Porcine fibroblasts overexpressing 11β-HSD1 under the control of adipose tissue-specific aP2 promoter were established and used in somatic cell nuclear transfer (SCNT). Somatic cells from the resulting stillborn transgenic piglets were used in a second round of SCNT. Non-obese, transgenic piglets overexpressing 11β-HSD1 were obtained and were identified through PCR-based methods using specific primers for the targeting cassettes from the genomic DNA of piglets. Six live piglets, 1 stillborn piglet, and 3 mummies were born. Integration of target gene into the genomic DNA was confirmed for all of them. However, all 6 live piglets died within 1 month. All of the piglets had displayed hypoglycemia. Increased expression of 11β-HSD1 in metabolic tissues induced up-regulation of gluconeogenesis-related genes (G6PT, G6Pase, PEPCK, HNF4a, FOXO1) in liver and kidney, and showed up-regulation of lipogenesis-related genes (SREBP1c, FASN, DGAT, ACC, SCD) in muscle. The AMPK and SIRT signalling, which controls energy balance and mitochondrial biogenesis, was also stimulated. We propose that overexpression of 11β-HSD1 evokes the excess production and action of glucocorticoid or its receptors, and activates gluconeogenic and lipogenic pathways. For this reason, AMPK and SIRT1 signalling was induced. Also, in compensation of energy loss by anabolic processes, the expression of mitochondrial biogenesis-related genes was increased. Finally, the constitutive expression of 11β-HSD1 might continuously activate complementary energy-gaining processes, and these problems could develop into more fatal diseases that resulted in the piglets' death.