Posttranslational removal of α-dystroglycan N terminus by PC5/6 cleavage is important for uterine preparation for embryo implantation in women

Embryo implantation requires a healthy embryo and a receptive endometrium (inner lining of the uterus); endometrial receptivity acquisition involves considerable epithelial surface remodeling. Dystroglycan (DG), a large cell surface glycoprotein, consists of alpha- and beta-subunits; beta-DG anchors within the plasma membrane whereas alpha-DG attaches extracellularly to beta-DG. The glycosylated central alpha-DG mediates adhesion, but it is obstructed by its large N terminus (alpha-DG-N); alpha-DG-N removal enables DG's adhesive function. We demonstrate here that full-length alpha-DG in the human endometrial epithelium is a barrier for embryo attachment and that removal of alpha-DG-N by proprotein convertase 5/6 (PC6; a protease critical for implantation) regulates receptivity. This was evidenced by: 1) alpha-DG contains a PC6-cleavage site near alpha-DG-N, and PC6 cleaves a peptide harboring such a site; 2) PC6 knockdown reduces alpha-DG-N removal from endometrial epithelial cell surface and blastocyst adhesion; 3) mutating the PC6-cleavage site prevents alpha-DG-N removal, causing cell surface retention of full-length alpha-DG and loss of adhesiveness; 4) alpha-DG-N is removed from endometrial tissue in vivo for receptivity and uterine fluid alpha-DG-N reflects tissue removal and receptivity. We thus identified alpha-DGN removal as an important posttranslational control of endometrial receptivity and uterine fluid alpha-DG-N as a potential biomarker for receptivity in women.