Fatty acid oxidation is an important energy source for the oocyte; however, little is known about how this metabolic pathway is regulated in cumulus-oocyte complexes. Analysis of genes involved in fatty acid oxidation showed that many are regulated by the luteinizing hormone surge during in vivo maturation, including acyl-CoA synthetases, carnitine transporters, acyl-CoA dehydrogenases and acetyl-CoA transferase, but that many are dysregulated when cumulus-oocyte complexes are matured under in vitro maturation conditions using follicle stimulating hormone and epidermal growth factor. Fatty acid oxidation, measured as production of 3H2O from [3H]palmitic acid, occurs in mouse cumulus-oocyte complexes in response to the luteinizing hormone surge but is significantly reduced in cumulus-oocyte complexes matured in vitro. Thus we sought to determine whether fatty acid oxidation in cumulus-oocyte complexes could be modulated during in vitro maturation by lipid metabolism regulators, namely peroxisome proliferator activated receptor (PPAR) agonists bezafibrate and rosiglitazone. Bezafibrate showed no effect with increasing dose, while rosiglitazone dose dependently inhibited fatty acid oxidation in cumulus-oocyte complexes during in vitro maturation. To determine the impact of rosiglitazone on oocyte developmental competence, cumulus-oocyte complexes were treated with rosiglitazone during in vitro maturation and gene expression, oocyte mitochondrial activity and embryo development following in vitro fertilization were assessed. Rosiglitazone restored Acsl1, Cpt1b and Acaa2 levels in cumulus-oocyte complexes and increased oocyte mitochondrial membrane potential yet resulted in significantly fewer embryos reaching the morula and hatching blastocyst stages. Thus fatty acid oxidation is increased in cumulus-oocyte complexes matured in vivo and deficient during in vitro maturation, a known model of poor oocyte quality. That rosiglitazone further decreased fatty acid oxidation during in vitro maturation and resulted in poor embryo development points to the developmental importance of fatty acid oxidation and the need for it to be optimized during in vitro maturation to improve this reproductive technology.

In vitro maturation of oocytes is suboptimal to in vivo maturation with altered gene expression and compromised oocyte quality. The large proteoglycan versican is abundant in mouse cumulus-oocyte complexes (COCs) matured in vivo but is absent in cultured COCs. Versican is also positively correlated with human oocyte quality. Versican contains an epidermal growth factor (EGF) motif, and based on EGF-like activities in other systems we hypothesized that versican acts as an EGF-like signaling factor during COC maturation. Here, we purified recombinant versican and compared its function with that of EGF during in vitro maturation (IVM). Versican significantly increased cumulus expansion and induced cumulus-specific genes Ptgs2, Tnfaip6, and Has2, which was blocked by EGF receptor antagonist. Microarray analysis revealed that versican has overlapping function with EGF; however, a subset of genes was uniquely altered following 6 h of IVM with either treatment. Following 6 h of IVM, both Areg and Ereg were significantly increased by both treatments, whereas Egln3, Nr4a1, Nr4a2, Nr4a3, and Adamts5 were significantly higher following versican treatment compared with EGF. In contrast, Sprr1a and Aqp3 were increased after 6 h of EGF but not versican treatment. To determine whether there were temporal differences, COCs were cultured with EGF or versican for 0-12 h. Versican-induced expression occurred later but remained elevated for longer compared with EGF for Ptgs2, Ereg, and Nr4a3. The unique expression profiles of Aqp3 and Nr4a3 during IVM were similarly regulated in vivo. These data indicate that versican has EGF-like effects on COC gene expression, but with distinct temporal characteristics.