Abstract
Apelin (APLN), as a ligand for APJ (an orphan G-protein-coupled receptor), is an adipokine with pleiotropic effects in many physiological processes of the body. It has an important role in the control of reproduction particularly in females (mainly in control of ovarian function). This study was carried out to investigate the mRNA and protein amounts of APLN/APJ in granulose cells (GCs) of ovarian follicles with small (SF), medium (MF), and large (LF) sizes of buffalo (Bubalus bubalis) and the effect of IGF1 and follicle-stimulating hormone (FSH) on the expression levels of APLN/APJ. In addition, we evaluated the effect of various doses of APLN (isoforms -13 and -17) singly or in combination with IGF1 and FSH on estradiol (E2) and progesterone (P4) secretion in GCs. The mRNA and protein abundance of APLN was the highest in GCs of LF while the APJ expression enhanced with follicle enlargement in GCs (p-value <0.01). IGF1 and FSH elevated the mRNA and protein amounts of APLN and FSH, and IGF1 increased the expression of APJ in buffalo GCs (p-value <0.01). Both isoforms of APLN (-13/-17) singly or in the presence of IGF1 or FSH increased the secretion of E2 and P4 with or without preincubation of cells with APJ antagonist (ML221 10 µM), although we had some variation in the effects. Concurrently, APLN-13/-17 significantly increased the mRNA and protein expression of CYP19A1 and StAR (p-value <0.01). ML221 substantially diminished the secretion of E2 and P4 and also the expression of CY19A1 and StAR in buffalo GCs (p-value <0.01). We also revealed that APLN-13/-17 (10-9 M), singly or in response to IGF1 and FSH, increased the production of E2 and P4 in different times of stimulation. In conclusion, APLN may play a crucial role in steroidogenesis and follicular development in ovarian GCs of buffalo.
Highlights
As the largest endocrine gland, adipose tissue secretes different bioactive peptides that are mainly named adipokines (1)
To assess the relative mRNA expression levels of APLN and APJ in ovarian granulose cells (GCs), two cDNA fragments of 106 and 100 bp were amplified by qRTPCR corresponding to APLN and APJ, respectively
Along with some discrepancies with the literature, our findings revealed that APLN in combination with IGF1 and follicle-stimulating hormone (FSH) has a positive effect on steroidogenesis in GCs
Summary
As the largest endocrine gland, adipose tissue secretes different bioactive peptides that are mainly named adipokines (1). APLN and APJ are involved in several different basic biological processes, such as cell proliferation, cardiovascular function, angiogenesis, food intake, fluid homeostasis, and regulation of energy metabolism (5, 8–10). They have been detected in the reproductive organs as well as in nucleus of the hypothalamus (the arcuate, supraoptic, and paraventricular hypothalamic), addressing their key roles in the regulation of reproduction (11). Some literature showed that APLN singly or with IGF1 and FSH has some effects on the secretion of progesterone (P4) in cattle (16) and porcine (15) It exerts its effects through various signaling pathways. APLN led to an increase of the basal levels of estrogen (E2) and P4 via AMPKa activation and enhanced the concentration of HSD3B protein, and it decreased the IGF1- and FSH-induced steroid secretion in human and porcine GCs (14–16)
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