Gonadotrophin-induced paracrine regulation of human oocyte maturation by BDNF and GDNF secreted by granulosa cells

BACKGROUND: In mammalian ovaries, diverse paracrine factors have been identified to mediate or modulate LH-induced changes during ovulation. Due to the difficulty in obtaining non-stimulated granulosa cells during IVF, little is known about the LH-induced paracrine factors in the human ovary. Based on earlier studies using murine ovarian cells showing the paracrine roles of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) in promoting oocyte maturation, we investigated the expression of these ligands in human granulosa cells and their regulation of human oocyte development. METHODS: Non-stimulated granulosa cells were obtained from non-stimulated IVM (in vitro maturation) patients after oocyte retrieval. Women undergoing non-stimulated IVM treatment at a mean age of 30.8+/-1.3 (n=10) were recruited for this study. Immature oocytes and granulosa cells were collected from IVF patients undergoing gonadotrophin stimulation and ICSI. Immunocytochemical analyses of granulosa cells were carried out to investigate expression profiles of BDNF and GDNF, together with real-time RT-PCR to analyze the gonadotrophin regulation of BDNF and GDNF transcript levels. In addition, immature oocytes were cultured to analyze the regulation of oocyte maturation by BDNF and GDNF. RESULTS: BDNF and GDNF were found to be expressed in non-stimulated granulosa cells. After gonadotrophin (FSH and/or hCG) treatment, transcripts levels for BDNF and GDNF were significantly increased (P<0.05). In cultured immature oocytes, treatment with BDNF or GDNF promoted total yields of metaphase II oocytes. CONCLUSIONS: These findings demonstrate that FSH and hCG treatments augment the expression of BDNF and GDNF by granulosa cells and that these granulosa-cell-derived factors are candidate paracrine factors capable of promoting oocyte maturation.