Obesity and insulin resistance (IR) negativley impact cumulus oocyte complex (COC) quality

Abstract

OBJECTIVE: Women with Type 2 diabetes and/or IR and obesity are at increased risk for miscarriage and congenital malformations. Other studies suggest this may be due to differences in the hormonal intrafollicular environment. Our aim was to determine the differences in oocyte quality and COCs in two murine models of obesity and IR. DESIGN: A comparison of COCs from two IR/obese mouse models, the Tally-Ho(TH) and the high fat diet(HFD) mice vs controls. MATERIALS AND METHODS: Female C57 mice age 3 weeks were fed either HFD(58% fat) or control diet(11% fat) for 4 weeks. We also compared female TH mice age 6-7 weeks to FVB controls. MRI was performed to evaluate percentage total body fat. Mice were superovulated and sacrificed 48 hours later for COC collection. Oocytes were microscopically assessed for maturity and diameter. Confocal immunofluorescent microscopy evaluated Connexin 43(Cx43) localization. Western blot analysis quantified Cx43 levels. Apoptosis was evaluated via TUNEL assay. Fluorescence Recovery after Photobleaching (FRAP) assessed gap junction communication. Data were analyzed with Students t test and Chi squared. RESULTS: MRI showed higher body fat percentage in TH(28.3% vs 20.7%; p=0.01) and HFD mice(29.9% vs 18.9%; p=0.006). Microscopic evaluation of TH oocytes revealed smaller volume (219 vs 334 μM3; p<0.001) and fewer mature oocytes (7.4 vs 13.8%; p<0.001). Confocal microscopy showed Cx43 in COCs of TH, HFD, and controls. Western analysis revealed decreased Cx43 protein levels in the TH and HFD mice vs controls. Gap junction communication via FRAP was similar between HFD (16.2% vs 18%, p=0.79), and TH (9.4% vs 8.4%; p=0.82) vs controls. TUNEL staining trended towards increased apoptotic nuclei/COC in TH mice (20.2 vs 15.7, p=0.16). CONCLUSION: IR and obesity affect oocyte size, maturation, and Cx43 protein levels suggesting that maternal hormonal environment impacts oocyte developmental competence.