The effect of glycosaminoglycans on rat gametes in vitro and the associated signal pathway

The effects of adding the extracellular glycosaminoglycans (GAGs), hyaluronic acid (HA) and chondroitin sulphate (CS) to rat in vitro fertilisation (IVF) media were assessed. Metaphase II (MII) oocytes were also incubated in GAG-supplemented modified rat 1-cell embryo culture medium (mR1 ECM + BSA) for 3 days. Cytoplasmic fragmentation was significantly reduced in mR1 ECM + BSA with HA (39.0-48.0%) compared with the control (82.0%). In IVF experiments, neither HA (8.0-30.8%) nor CS (9.7-42.5%) improved fertilisation rates compared with controls fertilised in M16 (47.2%) or enriched Krebs-Ringer bicarbonate solution (61.5%). RT-PCR and Western blot were used to probe for CD44 mRNA and protein in Sprague-Dawley gametes and cumulus cells. CD44 was identified in cumulus cells, suggesting a role for oocyte maturation and cumulus expansion. The CD44 protein was also present on caudal epididymal spermatozoa that were highly stimulated by CS in vitro implicating a role in fertilisation for CS and CD44.