A novel approach to quantifying ovarian cell lipid content and lipid accumulation in vitro by confocal microscopy in lean women undergoing ovarian stimulation for in vitro fertilization (IVF)

Abstract

Differential uptake or utilization of lipid by CC and MGC occurs during oocyte maturation and steroidogenesis, respectively, with the amount of lipid present in ovarian cells a function of both the follicular microenvironment at the time of the oocyte retrieval and the capacity of these cells to accumulate lipid in vitro over time.

Oocyte environment: follicular fluid and cumulus cells are critical for oocyte health

“…Steroidogenesis is crucial for the synchronization of follicle growth and oocyte development, beginning with uptake of cholesterol from circulating lipoproteins and storage of cholesterol as esters in cellular lipid droplets (14)(15)(16)(17). Ovarian cellular cholesterol initially is transported into mitochondria via the steroidogenic acute regulatory protein.…”

“…1) (69,70). In the presence of LH/hCG, cortisone can be converted to cortisol in the periovulatory follicle by NADP-dependent type 1 11b-hydroxysteroid dehydrogenase (11bHSD1), which may promote cumulus cell lipid metabolism as an energy source for oocyte meiotic resumption, fertilization, and early embryogenesis (17,(71)(72)(73)(74)(75)(76)(77) (Fig. 3).…”

Intrafollicular cortisol levels inversely correlate with cumulus cell lipid content as a possible energy source during oocyte meiotic resumption in women undergoing ovarian stimulation for in vitro fertilization

“…Exclusion criteria were galactorrhea, endometriomas, or ovarian cysts greater than 18 mm in diameter as possible modifiers of ovarian responsiveness to gonadotropin therapy (25, 26). Women undergoing IVF who were obese (BMI ≥ 30) were also excluded to eliminate confouding effects of obesity on ovarian cell lipid content or steroidogenesis (8, 27, 28). …”

“…Images were captured using the Leica TCS-SP2-AOBS confocal microscope with x63 oil objective, using identical magnification and gain settings, as previously described (8, 29). The 488-line argon laser was used at 667 V to capture the BODIPY® FL C 16 lipid stain; the diode 405 nm laser was used at 436 V to capture DAPI nuclear stain.…”

“…Crucial for this process is cumulus cell-oocyte signaling, which relies upon free fatty acid (FFA) beta-oxidation as an energy source for meiosis through adenosine triphosphate (ATP) production by the mitochondrial tricarboxylic acid (TCA) cycle and electron transport chain (2, 3, 4, 5, 6, 7). These FFAs likely originate from cumulus cells themselves, which contain abundant lipid as a source of energy for FFA oxidation during oocyte meiotic resumption (8, 9). …”