ECTOPIC EXPRESSION OF THE CRF-BINDING PROTEIN - MINOR IMPACT ON HPA AXIS REGULATION BUT INDUCTION OF SEXUALLY DIMORPHIC WEIGHT-GAIN

Corticotrophin-releasing factor (CRF) and urocortin possess a high-aff inity binding protein. Although the CRF binding protein (BP) can seque ster these ligands and inhibit their activity, the endogenous activity of this protein is not understood. Therefore, transgenic mouse lines that over-express the CRF-BP were created, The transgene was construct ed by ligating rat CRF-BP cDNA (1.1 kb) between a mouse metallothionei n-I promoter (1.8 kb) and a nonfunctional human growth hormone gene se quence (2.1 kb) in a modified pBR322 plasmid and microinjecting the tr ansgene into C57BL/6 x SJL hybrid ova. The transgene was expressed in 50% in both male and female progeny, All transgenic lines were maintai ned by crossing transgenic animals with wild-type C57BL/6 mates. Rever se-transcriptase (RT) PCR of the CRF-BP transgene showed that it is wi dely expressed not only in the brain and pituitary, but also periphera l tissues including the liver, kidney and spleen. Transgenic animals o f both sexes showed significant increases in weight gain as establishe d by analysis of variance; however, the weight gain profiles for each sex were distinct. High levels of circulating CRF-BP were detected in the transgenic animals, but the basal ACTH and corticosterone levels w ere not significantly decreased compared to wild-type littermates. The hypothalamopituitary-adrenal (HPA) axis was stimulated by systemic in flammation induced with lipopolysaccharide (LPS). An expected increase in transgene expression was observed and was accompanied by a signifi cant attenuation of ACTH secretion at 3 h after LPS injection in the t ransgenic males but not the females. These data suggest that HPA axis regulation is significantly affected only with very high circulating l evels of CRF-BP, Moreover, this work supports previous studies that im plicate CRF and urocortin in the regulation of appetite and the bindin g protein expression may play a sexually dimorphic role in regulating this and other responses.