The literature suggests that adiponectin has

The literature suggests that adiponectin has a steroidogenic effect on ovarian function. In pigs, in vitro studies have shown that adiponectin reduced basal testosterone secretion in internal theca cells; in granulosa cells, it increased secretion of estradiol and, in combination with insulin, increased secretion of progesterone [23]. In human primary granulosa cells, adiponectin increased IGF-1-induced secretion of progesterone and estradiol [20]. In chickens, adiponectin was also shown to modify the progesterone secretion pattern induced by LH, FSH or IGF-1 in granulosa 5-Methoxy-UTP [16]. This adipokine effect was also verified in oocyte maturation in vitro. In pigs, adiponectin promoted nuclear maturation of treated oocytes [18]; however this effect was not observed in cattle [15], [24]. Regarding caprine species, no reports were found on the adiponectin system and its influence on female reproduction. Thus, the objective of this work was first to investigate mRNA and protein expression of the adiponectin system (adiponectin, AdipoR1 and AdipoR2) in goat ovary and second to study the effects of recombinant adiponectin on goat oocyte maturation in vitro.
Materials and methods
Results
Discussion Our results demonstrated that adiponectin was not expressed at detectable levels in oocytes of small and large goat antral follicles or cumulus cells from large antral follicles. These results differ from those reported by Maillard et al. [15] and Tabandeh et al. [30], who found adiponectin expression in oocytes and cumulus cells of bovine antral follicles, indicating that there may be species-specific differences in ovarian expression of the adiponectin gene. Quantitatively, relative adiponectin expression in cumulus cells was significantly higher than that in GCs and TCs from small follicles. In large follicles, relative expression in GCs was significantly higher compared with that in TCs. These data differ from what has been observed in chicken ovaries, in which the expression of adiponectin in TCs was 10–30-fold higher than that in GCs [16]. In addition, adiponectin expression was also low in GCs of mice [17]. However, Maillard et al. [15] observed good adiponectin expression in bovine GCs. Receptor expression analysis showed decreased expression of AdipoR1 and Adipo2 in TCs of large follicles compared with expression of receptors in GCs. These results differ from those found by Tabandeh et al. [30] in cattle, where AdipoR1 and AdipoR2 expression was higher in large follicle TCs than that in GCs. Our findings also differ from results observed in mice, in which receptor expression in GCs was lower than in TCs [17]. However, similar results were observed in chickens, where AdipoR1 expression was twice as high in GCs as that in TCs, and AdipoR2 expression was similar in both cell types [16]. This discrepancy suggests a species-specific mode of action of the adiponectin system on follicular development. In the present study, adiponectin and its receptors AdipoR1 and AdipoR2 were immunolocalized in oocytes, cumulus cells, GCs and TCs in ovarian follicles at all stages of development. These findings corroborate those obtained in bovines [15], mice [17] and humans [21] and further support the physiological relevance of this hormone on ovarian function. Adiponectin protein was detected in the oocytes by immunohistochemistry, although no mRNA was observed, indicating that adiponectin must be produced elsewhere and then transported to the oocyte. This is likely because adiponectin is a secreted protein, is found in follicular fluid [29], and binds to its receptors on granulosa, cumulus and oocyte cells; receptor-bound adiponectin has been shown to be internalized in several cell lines [31], [32]. The detection of adiponectin appears to be specific because preincubation of the antibody with blocking peptide abolished staining. In the present work, we demonstrated that adiponectin addition (5 or 10 μg/mL) during IVM affected goat oocyte meiotic maturation. However, conflicting results have been reported in the literature. In cattle, supplementation of IVM medium with adiponectin (5 or 10 μg/mL) did not affect bovine oocyte meiotic maturation [15], [24]. In pigs, however, Chappaz et al. [18] reported that recombinant porcine adiponectin (30 μg/mL) significantly decreased the proportion of immature oocytes, suggesting that adiponectin accelerated porcine oocyte meiotic maturation.