Barbara Kaminska

Visfatin/NAMPT (VIS), the hormone exerting a pleiotropic effect, is also perceived as an important factor in the regulation of reproductive processes and pregnancy maintenance. Previous studies confirmed its involvement in the control of porcine pituitary and ovary function. In this study, we hypothesized that VIS may affect the global transcriptome of luteal cells and thus regulate the functioning of the ovaries. Illumina’s NovaSeq 6000 RNA sequencing was performed to investigate the differentially expressed genes (DEGs) and long non-coding RNAs (DELs) as well as the occurrence of differential alternative splicing events (DASs) in the porcine luteal cells exposed to VIS (100 ng/mL) during the implantation period. The obtained results revealed 170 DEGs (99 up- and 71 downregulated) assigned to 45 functional annotations. Moreover, we revealed 40 DELs, of which 3 were known and 37 were described for the first time. We identified 169 DASs events. The obtained results confirmed a significant effect of VIS on the transcriptome and spliceosome of luteal cells, including the genes involved in the processes crucial for successful implantation and pregnancy maintenance as angiogenesis, steroidogenesis, inflammation, cell development, migration, and proliferation.

The pituitary gland is a key endocrine gland in all classes of vertebrates, including mammals. The pituitary gland is an important component of hypothalamus–pituitary–target organ hormonal regulatory axes and forms a functional link between the nervous system and the endocrine system. In response to hypothalamic stimuli, the pituitary gland secretes a number of hormones involved in the regulation of metabolism, stress reactions and environmental adaptation, growth and development, as well as reproductive processes and lactation. In turn, hormones secreted by target organs at the lowest levels of the hormonal regulatory axes regulate the functions of the pituitary gland in the process of hormonal feedback. The pituitary also responds to other peripheral signals, including adipose-tissue-derived factors. These substances are a broad group of peptides known as adipocytokines or adipokines that act as endocrine hormones mainly involved in energy homeostasis. Adipokines, including adiponectin, resistin, apelin, chemerin, visfatin, and irisin, are also expressed in the pituitary gland, and they influence the secretory functions of this gland. This review is an overview of the existing knowledge of the relationship between chosen adipose-derived factors and endocrine functions of the pituitary gland, with an emphasis on the pituitary control of reproductive processes.

Visfatin (VIS), also known as nicotinamide phosphoribosyltransferase (NAMPT), is the rate-limiting enzyme in the biosynthesis of nicotinamide adenine dinucleotide (NAD+). Recently, VIS has been also recognized as an adipokine. Our previous study revealed that VIS is produced in the anterior and posterior lobes of the porcine pituitary. Moreover, the expression and secretion of VIS are dependent on the phase of the estrous cycle and/or the stage of early pregnancy. Based on this, we hypothesized that VIS may regulate porcine pituitary function. This study was conducted on anterior pituitary (AP) glands harvested from pigs during specific phases of the estrous cycle. We have shown the modulatory effect of VIS in vitro on LH and FSH secretion by porcine AP cells (determined by ELISA). VIS was also found to stimulate cell proliferation (determined by Alamar Blue) without affecting apoptosis in these cells (determined using flow cytometry technique). Moreover, it was indicated that VIS may act in porcine AP cells through the INSR, AKT/PI3K, MAPK/ERK1/2, and AMPK signaling pathways (determined by ELISA or Western Blot). This observation was further supported by the finding that simultaneous treatment of cells with VIS and inhibitors of these pathways abolished the observed VIS impact on LH and FSH secretion (determined by ELISA). In addition, our research indicated that VIS affected the mentioned processes in a manner that was dependent on the dose of VIS and/or the phase of the estrous cycle. Thus, these findings suggest that VIS may regulate the functioning of the porcine pituitary gland during the estrous cycle.

The corpus luteum is a small gland of great importance because its proper functioning determines not only the appropriate course of the estrous/menstrual cycle and embryo implantation, but also the subsequent maintenance of pregnancy. Among the well-known regulators of luteal tissue functions, increasing attention is focused on the role of neuropeptides and adipose tissue hormones—adipokines. Growing evidence points to the expression of these factors in the corpus luteum of women and different animal species, and their involvement in corpus luteum formation, endocrine function, angiogenesis, cells proliferation, apoptosis, and finally, regression. In the present review, we summarize the current knowledge about the expression and role of adipokines, such as adiponectin, leptin, apelin, vaspin, visfatin, chemerin, and neuropeptides like ghrelin, orexins, kisspeptin, and phoenixin in the physiological regulation of the corpus luteum function, as well as their potential involvement in pathologies affecting the luteal cells that disrupt the estrous cycle.

BackgroundVisfatin exists in two forms: the intracellular form which is a rate limiting enzyme engaged in nicotinamide adenine dinucleotide biosynthesis and the extracellular form considered as an adipokine, produced mainly by the adipose tissue. Visfatin could be an energy sensor involved in regulating female fertility, which creates a hormonal link integrating the control of energy homeostasis and reproduction. MethodsThe study compares the expression levels of visfatin gene (quantitative real time PCR) and protein (Western blotting and fluorescent immunohistochemistry) in the selected areas of the porcine hypothalamus responsible for gonadotropin releasing hormone synthesis: the mediobasal hypothalamus (MBH) and preoptic area (POA), and visfatin concentrations in the blood plasma (enzyme-linked immunosorbent assay). The tissue samples were harvested from gilts on days 2-3, 10-12, 14-16 and 17-19 of the estrous cycle, and on days 10-11, 12-13, 15-16, 27-28 of pregnancy. Differences between groups were analyzed by one-way ANOVA followed by Tukey’s post hoc test. ResultsDuring the estrous cycle, visfatin mRNA expression in the MBH was higher on days 2-3 and 17-19, while the visfatin protein concentration on days 17-19. During early pregnancy, the most pronounced gene and protein expression in the MBH was found on days 15-16 and 10-11, respectively. In the POA during the estrous cycle, visfatin gene expression was the highest on days 17-19, and the protein level of visfatin on days 14-16. During early pregnancy, the highest expression of visfatin gene in the POA was observed on days 15-16, whereas the protein concentrations on days 27-28. Blood plasma concentrations of visfatin during the estrous cycle were higher on days 2-3 in relation to other studied phases of the cycle. During early pregnancy, the highest visfatin contents in the blood plasma were observed on days 12-13. Visfatin gene and protein expression in MBH and POA, and visfatin plasma concentrations differed during early pregnancy in relation to days 10-12 of the cycle. ConclusionsThis study demonstrated visfatin expression in the porcine hypothalamus and its dependence on hormonal milieu related to the estrous cycle and early pregnancy.