Endoplasmic Reticulum-Derived Multilamellar Bodies in Oocytes of Mouse Follicle Cultures under Oxidized Low-Density Lipoprotein Treatment

Objective: Multilamellar bodies associated with an organized endoplasmic reticulum (ER) arise in various somatic cell types, and a subtype called multivesicular bodies is described in oocytes. Both entities, so far undetermined in significance, may occur in oocytesof folliclesunder oxidative stress. In preovulatory follicles, oxidative stress appears to be caused by oxidized low-density lipoprotein (ox-LDL). Method: Culturesof preantral mouse follicleswere treated with 100 µg/ml ox-LDL or normal LDL (n-LDL) for 12–48 h or for 12 days during antral folliclegrowth followed by in vitro ovulation and harvest of cumulus oophoruscomplexes (COCs) with metaphase II (MII) oocyteson day 13. Preantral follicles, COCs, or MII oocyteswere immunostained with anti-tubulin antibody or stained with actin-binding phalloidinfor confocal microscopy. Ultrathin sections were prepared for electron microscopy. Results: Preantral folliclesexposed to n-LDL or ox-LDL developed normally, and MII oocytesin COCs possessed normal spindles with well-aligned chromosomes. In contrast, treated cumulus cells underwent apoptosis. Only the ox-LDL-treated preantral follicle oocytesshowed ER-derived multilamellar bodies (EMBs) of type I, consisting of rough ER membranesfor the envelope. The MII oocytesof COCs showed type II EMBs consisting of smooth/vesicular ER and were more prominent after ox-LDL than after n-LDL exposure. Degenerating mitochondria were prominent in oocytesof the ox-LDL group and judged as a sign of oxidative stress. Conclusion: Oxidative stress presumably induces damage of proteins and organelles in the oocytes. The EMBs might sequester the damaged structures for oocytesurvival. Thus, EMBs could represent a novel form of autophagy.