Dynamics of expression and localization of the cannabinoid system in granulosa cells during oocyte nuclear maturation

Abstract

Objective: To describe the expression of cannabinoid receptors CB1 and CB2 and cannabinoid-degrading enzymes fatty acid amide hydrolase (FAAH) and monoglyceride lipase (MGLL) in human granulosa cells and to investigate their differential distribution with respect to CB1 at various stages during the nuclear maturation of the oocyte.

Design: Analysis of granulosa cells from germinal vesicle (GV), metaphase I (MI), and MII oocytes by quantitative reverse transcriptase-polymerase chain reaction, Western blot, and indirect immunofluorescence assays.

Setting: Academic research laboratory.

Patient(s): Patients from the Human Reproduction Unit of Cruces University Hospital undergoing intracytoplasmic sperm injection.

Intervention(s): We analyzed the granulosa cells of 300 oocytes from 53 patients. The oocyte maturation stages were 75 at GV stage, 51 at MI, and 174 at MII.

Main outcome measure(s): The mRNA and protein expression of CB1, CB2, FAAH, and MGLL and localization in granulosa cells at each oocyte maturation stage.

Result(s): CB1, FAAH, and MGLL are present in human granulosa cells during oocyte maturation, but the presence of CB2 receptor is not entirely clear in those cells. CB1 and FAAH were detected in the periphery of the granulosa cells from the GV to the MII oocytes, and they colocalized in some portions of the cell membrane. On the other hand, MGLL immunostaining was more homogeneous across the cell and overlapped with CB1 only weakly.

Conclusion(s): The presence of the cannabinoid system in granulosa cells suggests a possible role of this system in the nuclear maturation of the oocyte.

Keywords: Cannabinoid; granulosa cells; oocyte maturation.