511. THE EFFECTS OF HIGH FAT DIET ON LIPID LOCALISATION IN THE PERI-OVULATORY CUMULUS OOCYTE COMPLEX

Abstract

Intracellular neutral lipids are stored in discrete droplets that are surrounded by lipid associated proteins, such as adipophilin and perilipin, which control cellular lipid metabolism by regulating the access of lipases. The role of lipids in oocyte maturation is unclear, although they have a potential role as an energy source for the oocyte and early embryo. To elucidate potential mechanisms controlling lipid utilisation in the peri-ovulatory cumulus-oocyte-complex (COC) we 1) localised lipid droplets by immunohistochemistry for adipophilin and perilipin and direct staining of neutral lipids with BODIPY and 2) investigated whether a high fat diet can alter oocyte lipid quantity or localisation. Ovaries were isolated from 21 day old mice before and 10h after the ovulation stimulus hCG. Adipophilin and perilipin were both detected by immunohistochemistry in peri-ovulatory follicles with similar localisation before and after hCG. In separate experiments, adult mice were fed a high fat or control diet for 4 weeks and COCs were isolated from preovulatory follicles prior to hCG or from the oviduct 13h after hCG stimulation followed by BODIPY staining and quantification with confocal microscopy. BODIPY staining showed that COCs possess low levels of lipids evenly distributed in the oocyte before hCG but increased lipid assembled as droplets in the oocyte after ovulation. In mice fed a high fat diet, intracellular lipids were markedly increased in both the cumulus cells and oocytes from preovulatory and ovulated COCs. The ubiquitous expression of lipid droplet proteins in the peri-ovulatory follicle together with the changes in neutral lipid storage concurrent with ovulation suggests that lipid metabolism play an important role in oocyte release, transport and/or developmental competence. Furthermore, the dramatic effect of dietary fat on COC lipid content may contribute to the impaired oocyte quality we have observed in obese mice as well as reduced fertility in obese women