O-8: Critical Role of Hyaluronan System in Pre-Implantation Embryo Development and Establishment of Pregnancy

Background: Hyaluronan (HA) is a structural component of extracellular matrix synthesised by HA synthases HAS1-3, which produce HA of different molecular sizes with distinct biological functions associated with reproductive processes. Hyaluronidase (HYAL) cleaves the HA into biologically active small fragments which are known to regulate cell proliferation through CD44 receptor signaling. HA is currently used a supplement in embryo transfer media as a “glue” to improve embryo attachment. We have determined developmental pattern of expression and critical role of HA system in pre-implantation embryos. We have also investigated the effect of HA or HA-synthesis inhibitor on endometrial receptivity and embryo attachment. Materials and Methods: Pattern of HA production and expression of HA system (HAS1-3, and HYAL2) in the embryos at different stages of development and also HYAL2 in the oviduct was assessed. Effects of HA sizes including HA fragments produced by HYAL2 on development to blastocyst stage and blastocysts quality of in vitro produced bovine and ovine embryos (in vitro and in vivo) were analysed in the presence or absence of HA synthesis inhibitor methylumbelliferone (4MU) and involvement of CD44 and MAPK signaling in HYAL-2 promoted blastocyst rate was investigated. In addition, the effect of HA on embryo implantation was determined in an in vivo study using sheep and uterine infusion of Saline (control), HA (0.5 mg/ml) or 4MU (HA-synthesis inhibitor; 1mM) on day 14 of pregnancy (3 days before embryo attachment). Animals were then euthanized on day 17 when the uteri were fixed for histological and immunohistochemical analysis. Results: Immunostaining for HA was detected at all stages embryos to blastocyst. HAS1-3 mRNAs were expressed at all stages of embryos and showed specific pattern. Interestingly, HYAL2 mRNA expression was detected in the oviduct at early luteal phase but was only detected in the embryos at morula and blastocyst stages. In contrast to 4MU which inhibited blastocyst formation, HYAL2 improved blastocyst rate in vitro and increased embryo cell numbers (p<0.05). Addition of Anti-CD44 antibody or MAPK inhibitor abrogated the positive effects of HYAL2 on blastocyst rates (p<0.05). HA infusion resulted in failure of embryo, whereas all embryos in the 4MU infused group were attached on day 17. In contrast to HA infusion, the 4MU infusion inhibited HA synthesis in the endometrium and blocked mucin-1 (MUC-1) production, but increased adhesion molecules osteopontin (OPN) and CD44 expression at the uterusembryo interface. Conclusion: HAS and HYAL2 are differentially expressed in different stages of early embryo development and HYAL2 supplementation is required to maximize blastocyst yield and improve its quality in vitro. Presence of high molecular weight HA in the uterus inhibits embryo attachment and its removal may enhance pregnancy rate.