Leptin Gene and Protein Expression in the Ovary During the Oestrous Cycle and Early Pregnancy in Pigs

Abstract

Leptin, the product of the obese gene, is the hormone originally identified in adipocytes. It is involved in the control of satiety and energy metabolism. More recent observations suggest that leptin plays an important role in reproduction. Leptin mRNA and protein have been found in the human and the murine ovary. However, the expression of leptin in the porcine ovary has not been examined. Therefore, the aim of the present work was to compare the expression levels of porcine leptin mRNA by semiquantitative RT-PCR and in situ hybridization, as well as leptin protein by Western blotting in the corpus luteum (CL) and ovarian stroma (OS) during mid- and late-luteal phase of the oestrous cycle as well as during days 14-16 and 30-32 of pregnancy. Leptin gene and protein expression in CL was increased on days 14-16 of the cycle compared with pregnant animals. Leptin gene expression in OS was higher during the late-luteal phase of the cycle than on days 30-32 after conception. However, comparison of leptin protein expression in OS between days 14-16 of the cycle and days 30-32 of pregnancy indicates a higher protein expression during pregnancy. Moreover, leptin gene expression was higher in porcine CL and OS on days 14-16 of pregnancy in comparison to days 30-32. Contrary to leptin mRNA expression, a higher leptin protein expression was observed on days 30-32 compared with days 14-16 after conception. In summary, the present study provides the first evidence that leptin mRNA and protein occur in porcine ovary and vary during the oestrous cycle and pregnancy. Moreover, the obtained results indicate that also locally synthesized leptin may participate in the control of pig reproduction by exercising its action at the ovarian level.

Expression of leptin and its receptor genes in the ovarian follicles of cycling and early pregnant pigs

“…The leptin concentration in blood increased during the luteal phase in women (Lukaszuk et al, 1998). Leptin mRNA expression in GC (present paper) and in OS (Smolinska et al, 2010) has been shown to be higher on days 10 to 12 than that on days 14 to 16 of the cycle. OB-Rb protein expression in OS is also higher on days 10 to 12 than days 14 to 16 (Smolinska et al, 2007a).…”

“…The lack of differences in the expression of leptin and OB-Rb in TIC during pregnancy and between the cycle and pregnancy seems to indicate that the leptin system existing in TIC is not involved in the regulation of pregnancy. The differences in both leptin (present study, Smolinska et al, 2007b and2010) and OB-Rb (present study, Smolinska et al, 2007a and) gene and protein expression in the reproductive organs of pregnant pigs on days 14 to 32 of pregnancy, a period in which implantation and embryo development take place, may indicate that leptin plays a role in the control of these processes.…”

“…In our study, however, OB-Rb mRNA expression in GC was higher during the late-luteal phase than on days 10 to 12 of the cycle. Our previous research has also shown that this is true for leptin gene and protein expression in the CL (Smolinska et al, 2010). In addition, ovarian leptin protein levels in rats increased from estrus to metestrus and decreased in diestrus (Archanco et al, 2003).…”

“…We have previously shown that, during the luteal phase and early pregnancy in the porcine CL and OS, leptin mRNA and protein (Smolinska et al, 2010), and OB-Rb mRNA and protein are expressed (Smolinska et al, 2007a), as is OB-Ra mRNA (Bogacka et al, 2006). This study, our previous findings and the results obtained in other species support the conclusion that the ovary is an important source of leptin, that the hormone may act within the ovary as an autocrine factor or a paracrine factor or both and that leptin plays a direct role in the regulation of ovarian functions.…”

“…The ovary is also believed to be a site of leptin synthesis. The presence of leptin mRNA and protein was observed in human GC and theca cells, follicular fluid, oocytes and CL Cioffi et al, 1997;Loffler et al, 2001;Welt et al, 2003), in murine GC and theca cells, oocytes, CL and OS Ryan et al, 2002 andArchanco et al, 2003) and in porcine CL and OS (Smolinska et al, 2010). The expression of leptin and OB-Rb in porcine ovarian follicles during the cycle and in early pregnancy (implantation) has scarcely been investigated to date.…”