Expression and localization of apelin and apelin receptor (APJ) in buffalo ovarian follicles and corpus luteum and the in-vitro effect of apelin on steroidogenesis and survival of granulosa cells

Apelin is an adipose tissue-derived hormone with many physiological functions, including the regulation of female reproduction. It acts through an orphan G protein-coupled receptor APJ/APLNR. The present study aimed to investigate the expression of apelin and its receptor APJ in the ovarian follicles and corpus luteum (CL) and the role of apelin on steroidogenesis and cell survival. Ovarian follicles were classified into four groups based on size and estradiol (E₂) level in the follicular fluid as follows: (i) F1 (4-6 mm; <0.5 ng/mL) (ii) F2 (7-9 mm; 0.5-5 ng/mL) (iii) F3 (10-13 mm; 5-40 ng/mL) and (iv) F4 (dominant/pre-ovulatory follicle) (>13 mm; >180 ng/mL). The corpora lutea (CL) were categorized into early (CL1), mid (CL2), late luteal (CL3), and regressing (CL4) CL stages. Expression of apelin increased with follicle size, with significantly greatest in the dominant or pre-ovulatory follicle (P < 0.05). Expression of APJ was greater in large and dominant follicles than in small and medium follicles (P < 0.05). In CL, the mRNA and protein abundance of apelin and apelin receptor was greater during mid (CL2) and late luteal (CL3) stages as compared to early (CL1) and regressing (CL4) stages (P < 0.05). Both the factors were localized in granulosa and theca cells of follicles and small and large luteal cells of CL. The pattern of the intensity of immunofluorescence was similar to mRNA and protein expression. Granulosa cells were cultured in vitro and treated at 1, 10, and 10 ng/mL apelin-13 either alone or in the presence of the follicle-stimulating hormone (FSH) (30 ng/mL) or insulin-like growth factor-I (IGF-I) (10 ng/mL) for 48 h. The luteal cells were treated with apelin-13 at 1, 10, and 100 ng/mL doses for 48 h. Apelin treatment at 10 and 100 ng/ml significantly (P < 0.05) increased E₂ secretion, cytochrome P450 aromatase or CYP19A1 expression in GC. In luteal cells, apelin at 10 ng/mL and 100 ng/mL significantly (P < 0.05) increased progesterone (P₄) secretion and HSD3B1 expression. In GCs, apelin, either alone or in combination, increased PCNA expression and inhibited CASPASE3 expression suggesting its role in cell survival. In conclusion, this study provides novel evidence for the presence of apelin and receptor APJ in ovarian follicles and corpora lutea and the stimulatory effect on E₂ and P₄ production and promotes GC survival in buffalo, suggesting the role of apelin in follicular and luteal functions in buffalo.

Transcriptional and translational abundance of visfatin (NAMPT) in buffalo ovary during estrous cycle and its in vitro effect on steroidogenesis

Visfatin is a highly conserved adipokine protein having multiple biological effects, including regulation of reproduction. Evidence in recent years has shown a pivotal role of visfatin in ovarian functions. The present study was conducted to evaluate the mRNA and protein abundance of visfatin in ovarian follicles and corpora lutea (CL) during different stages of their development in the ovary of water buffalo (Bubalus bubalis) and to investigate the role of visfatin on estradiol (E₂) and progesterone (P₄) secretion. Ovarian follicles were categorized in to small (F1), medium (F2), large (F3), and preovulatory (F4) follicles, whereas the CL were categorized into early (CL1), mid (CL2), late (CL3), and regressing (CL4) CL stage. In follicles, the mRNA and protein abundance of visfatin increased with an increase in follicle size in granulosa cells (GCs) and theca interna (TI) cells. In CL, the transcript of visfatin was significantly (P < 0.05) higher in the late luteal phase (CL3) than that in other phases. The translational abundance of visfatin was significantly higher in the mid and late luteal phase. Visfatin was localized in the cytoplasm of GC and TI of ovarian follicles and small and large luteal cells of CL. GCs were cultured in vitro and treated at 0, 1, and 10 ng/mL visfatin either alone or in the presence of FSH (30 ng/mL) or IGF-I (10 ng/mL) for 48 h. The luteal cells were treated with visfatin at 0, 1, and 10 ng/mL dose for 48h. There was significant (P < 0.05) increase in estradiol (E₂) secretion from GCs at 10 ng/mL dose of visfatin and visfatin (10 ng/mL) +IGF-I (10 ng/mL). Visfatin also increased (P < 0.05) progesterone (P₄) secretion from cultured luteal cells at both 1 and 10 ng/mL dose. In GCs, visfatin in the presence of IGF-I increased the transcriptional abundance of cytochrome P45019A1 (CYP19A1), the gene for key enzyme aromatase. In luteal cells, the visfatin increased mRNA abundance of factors involved in progesterone synthesis viz. steroidogenic acute regulatory protein (StAR), cytochrome P45011A1 (CYP11A1), 3beta-hydroxysteroid dehydrogenase (HSD3B1). The present study provided evidence that visfatin is expressed in ovarian follicles and CL of buffalo ovary and visfatin has a stimulatory effect on estradiol and progesterone secretion in ovarian cells of water buffalo.