Synthesis and Accumulation of Hyaluronic Acid and Proteoglycans in the Mouse Cumulus Cell-oocyte Complex during Follicle-stimulating Hormone-induced Mucification

In most mammalian ovaries, the cumulus cell-oocyte complex (COC) expands at the time of ovulation by depositing an extensive extracellular matrix between the cumulus cells. This phenomenon can be reproduced in vitro by culturing COCs with follicle-stimulating hormone (FSH) and serum. Biosynthesis of hyaluronic acid (HA) and proteoglycans by mouse COCs in vitro was studied using [3H]glucosamine and [35S]sulfate as metabolic precursors. Radiolabeled complex carbohydrates were analyzed by ion exchange chromatography, specific enzyme digestion followed by high performance liquid chromatography, and gel filtration. The specific activities of [3H]hexosamines in the labeled molecules were determined by measuring the incorporation of 3H and 35S into chondroitin 4-sulfate disaccharides. When COCs were stimulated with FSH, HA biosynthesis increased 20–30-fold between 3–12 h later when expansion occurs, reaching a maximum rate of ∼ 780 pmol (as glucosamine)/COC/h compared with the unstimulated rate of ∼ 26 pmol/COC/h. The final concentration of HA in the expanded COC was calculated to be ∼ 250 µg/ml. The effects of dibutyryl cyclic AMP (Bt2cAMP) on COC expansion and HA synthesis were similar to those of FSH, suggesting that the effects of FSH are mediated by cAMP. However, FSH significantly decreased the specific activity of the incorporated hexosamines while Bt2cAMP did not. Serum is necessary for the accumulation of HA in the COC matrix. HA synthesis in FSH-stimulated COCs was as high or higher in the absence of serum, but most was recovered in the medium and not in the COC matrix. The molecular size of the HA was >2 million dalton in either case, suggesting that the serum did not alter physical properties of HA. Stimulation of proteoglycan biosynthesis by either FSH or Bt2cAMP was less pronounced (three to four times control) than for HA and was sustained throughout an 18-h culture period. A reduction of 80% in the deposition of newly synthesized PGs in the COC matrix by 0.5 mM β-xyloside treatment did not affect the expansion of the cumulus.