Formation of the hyaluronan–serum-derived hyaluronan-associated protein complex during cumulus expansion contributes to in vitro maturation of porcine oocytes

Context Serum-derived hyaluronan-associated proteins (SHAPs), which are identical to the heavy chains of the inter-α-trypsin inhibitor (ITI) family of proteins, bind to hyaluronan produced by cumulus cells, thus forming the hyaluronan–SHAP complex, which stabilises the hyaluronan-rich matrix of cumulus–oocyte complexes (COCs) during cumulus expansion. However, the role of the hyaluronan–SHAP complex in inducing oocyte maturation is still poorly understood. Aims Hence, this study was conducted to investigate the effects of hyaluronan retention within COCs on the formation of the hyaluronan–SHAP complex during cumulus expansion in porcine oocytes matured in vitro. Methods Western blot analysis and enzyme-linked immunosorbent assays were performed to detect SHAPs in porcine follicular fluid (pFF) and to quantify hyaluronan respectively. Key results The degree of cumulus expansion and oocyte maturation rates were proportional to the amount of hyaluronan retained within the COCs. SHAP was detected in pFF used for in vitro oocyte maturation and in the matrix of expanded COCs. Furthermore, immunodepletion of the ITI family proteins from pFF not only inhibited the formation of the hyaluronan-rich COC matrix, but also decreased oocyte maturation rates in a concentration-dependent manner. Conclusions These results suggest that hyaluronan–SHAP complex formation during cumulus expansion may contribute to oocyte maturation. Implications This finding is important for improving the culture system for porcine oocyte maturation in vitro.