Effect of Obesity on the Preovulatory Follicle and Lipid Fingerprint of Equine Oocytes1

Obesity is associated with disrupted reproductive cycles in mares, but the impact of obesity on follicles and oocytes has received minimal attention. We investigated the impact of obesity on 1) expression of selected genes in follicle cells for carbohydrate metabolism, inflammatory cytokines, lipid homeostasis, endoplasmic reticulum stress, and mitochondrial function; 2) follicular fluid content of metabolic hormones and metabolites; and 3) lipid fingerprint of oocytes. Mares (9–13 yr) were classified as control (n = 8, normal weight, body condition score [BCS] 5.1, 10.4% body fat) or obese (n = 9, BCS 7.9, 16.2% body fat). Gene expression from granulosa cells (GC) and cumulus cells (CC) was evaluated by RT-PCR. Serum and follicular fluid were evaluated for insulin, leptin, adiponectin, and metabolite profiling. Oocyte lipid fingerprints were acquired using matrix-assisted laser desorption/ionization mass spectrometry. Several genes for lipid homeostasis, endoplasmic reticulum stress, and mitochondrial function were different between groups in GC and CC. Obese had (P < 0.05) or tended to have (0.05 < P < 0.1) lower insulin sensitivity and higher insulin and leptin in serum and follicular fluid. Many metabolites differed between control and obese in serum and/or follicular fluid and correlated with BCS and/or insulin sensitivity. Oocytes from control had greater concentrations of lipids consistent with phosphatidylcholines, phosphatidylethanolamines, and sphingomyelins, while lipids consistent with triglycerides tended to be higher in obese. These findings suggest that maternal obesity causes alterations in the follicle and oocyte; the extent to which these alterations impact the conceptus and offspring is still to be determined.