Mihir Sarkar1,2, S Schilffarth1, D Schams1, HHD Meyer1, M W Pfaffl1, S Ulbrich1, B Berisha1,3
1Technical University Munich, Germany; 2Physiology & Climatology, Indian Veterinary Research Institute, Izatnagar, Bareilly, Uttar Pradesh, India; 3Faculty of Agriculture and Veterinary, University of Prishtina, Prishtine, Kosovo
Leptin, the hormonal product of the obese (ob) gene, circulates in the blood at levels paralleling those of fat reserves and regulates satiety. In cattle, leptin has also been implicated in the control of ovarian function, but its local production in the ovary and role in the control of ovarian function in autocrine/paracrine manner is unknown. Similarly, Thrombopoietin (TPO) is known to be involved in mega-karyocytopoiesis, but its role in the control of ovarian function is unknown in cattle. The aims of this study were to demonstrate the expression of Leptin, its receptor (Ob-R), TPO and its receptor (c-MPL) in detail in bovine corpus luteum (CL) obtained from different stages of the oestrous cycle and during pregnancy – and to demonstrate that leptin/Ob-R and TPO⁄ c-MPL systems are expressed clearly in bovine follicles. Real-time RT-PCR (qPCR) and ELISA were applied to investigate mRNA expression of examined factors and leptin & TPO protein, respectively. In general, we demonstrated leptin and its receptor transcripts and leptin protein are consistent with in vivo luteinisation of bovine CL and decline coincidental with luteal regression. The highest co-expression of leptin/Ob-R system was observed in TI and GC of the smallest follicles with E2 concentration <0.5 ng/ml followed by significant down regulation in growing follicles with the increase of follicular size and E2 content in the follicular fluid. Furthermore, expression of the leptin/Ob-R system does not show any significant variation in the CL throughout pregnancy. In this investigation, increases in the concentrations of TPO protein and the mRNA expression of TPO and c-MPL were noticed during both early luteal stage and late luteal stage of the oestrous cycle. Furthermore, the expression of TPO⁄ c-MPL system does not show any significant regulation in the CL throughout pregnancy. Highest co-expression of TPO⁄ c-MPL system in both theca interna (TI) and granulosa cells (GC) in small follicles (<10 mm in diameter) was observed in this study that may suggest the possible role of TPO⁄ c-MPL system in proliferation of TI and GC cells. To conclude, our results are the first to demonstrate the possible involvement of locally produced leptin/Ob-R and TPO⁄ c-MPL system in the bovine ovary, suggesting possible involvement of leptin/Ob-R system in the function and/or development of the CL and growth of small follicles in an autocrine/ paracrine fashion and of TPO⁄ c-MPL system as a ‘physiological filter’ in bovine ovary where they may promote cell selection by inducing proliferation of viable cells and scavenging non-viable cells and thereby may play an important role in modulation of ovarian function.
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