The extracellular matrix (ECM) exerts itself in a structural and signalling manner during implantation and placentation that, when impaired, can lead to pregnancy complications. Hyaluronic acid (HA) is a major component of the ECM that is synthesized in a two-step biosynthetic process by UDP-glucose 6-dehydrogenase and HA Synthases (HAS1-3). Whereas Hyaluronidases (Hyal1-3) depolymerise HA into smaller fragments that are known to have roles in signalling and angiogenesis. Research has shown that deletion HA synthases (HAS2), and not hyaluronidases, causes embryonic lethality: leading to the current dogma that HA processing is not required for embryogenesis. Our laboratory identified a novel hyaluronidase, Cemip2, that is required for normal cardiac development. However, the role of CEMIP2 or the requirements of HA in implantation and placentation has not been explored, which is the focus of this study.
We have generated numerous mouse lines to explore the role of HA modulation in implantation and placentation. These lines allow us to examine the effect high-molecular weight HA (due to Cemip2 deletion; Cemip2floxed) and no HA (due to Ugdh deletion; Ugdhfloxed) has on implantation and placentation by spatially and temporally controlling deletion when crossed with different Cre-driver lines.
Whole-body Cemip2 knockout reduced Mendelian ratios at embryonic day (E) 9.5; consistent with defective implantation. Implantation sites are currently being analysed to identify the defective process/es. When Cemip2 is deleted in endothelial cells (using Tie2Cre), while embryos survive implantation, Mendelian ratios are reduced at E14.5; consistent with defective placentation. Gross placental morphology of Cemip2:Tie2Cre embryos show impaired angiogenesis and reduced branchpoints at E14.5. Preliminary stereology analysis suggests perturbed placental morphology. Analysis of Ugdh implantation sites and placenta are currently underway.
This study highlights the requirements for HA processing for pregnancy. Importantly, it demonstrates that CEMIP2 is the hyaluronidase required for pregnancy success.