Molecular cloning and endometrial expression of porcine high density lipoprotein receptor SR-BI during the estrous cycle and early pregnancy.

During rapid development of the fetus, levels of high density lipoprotein (HDL) are elevated in pregnant women. The receptor for HDL, scavenger receptor class B type I (SR-BI), mediates selective cholesteryl ester uptake and is highly expressed in the human placenta. Because of the rapid growth of uterus during early pregnancy and differences in placentation between swine and humans, we hypothesized that SR-BI may be expressed in porcine endometrium to take up HDL cholesterol. The objectives of this study were to obtain the full coding region for porcine SR-BI, determine endometrial expression of SR-BI mRNA during the estrous cycle and early pregnancy, and map the gene. By iterative screening of a porcine expressed sequence tag library, we obtained the full coding region of SR-BI. Endometrial expression of SR-BI in White composite gilts (n = 3-4 each) was determined by Northern blotting on Days 10, 13, and 15 cyclic gilts and Days 10, 13, 15, 20, 30, and 40 pregnant gilts. In cyclic gilts, endometrial expression of SR-BI did not change between Days 10 and 13, but increased (P < 0.01) between Days 13 and 15. In pregnant gilts, endometrial expression of SR-BI increased (P < 0.01) between Days 10 and 13, remained elevated until Day 30, and decreased (P = 0.015) on Day 40. The SR-BI gene was mapped to 46.3 cM on chromosome 14. These results show that endometrial expression of SR-BI changes during the estrous cycle and early pregnancy, and suggest that SR-BI takes up HDL for endometrial development during early pregnancy.