Abstract
Chemerin (CHEM) may act as an important link integrating energy homeostasis and reproductive functions of females, and its actions are mediated by three receptors: chemokine-like receptor 1 (CMKLR1), G protein-coupled receptor 1 (GPR1), and C-C motif chemokine receptor-like 2 (CCRL2). The aim of the current study was to compare the expression of CHEM and its receptor (CHEM system) mRNAs (quantitative real-time PCR) and proteins (Western blotting and fluorescent immunohistochemistry) in the selected areas of the porcine hypothalamus responsible for gonadotropin-releasing hormone production and secretion: the mediobasal hypothalamus, preoptic area and stalk median eminence during the oestrous cycle and early pregnancy. Moreover, plasma CHEM concentrations were determined using ELISA. The expression of CHEM system has been demonstrated in the porcine hypothalamus throughout the luteal phase and follicular phase of the oestrous cycle, and during early pregnancy from days 10 to 28. Plasma CHEM levels and concentrations of transcripts and proteins of CHEM system components in the hypothalamus fluctuated throughout pregnancy and the oestrous cycle. Our study was the first experiment to demonstrate the presence of CHEM system mRNAs and proteins in the porcine hypothalamus and the correlations between the expression levels and physiological hormonal milieu related to the oestrous cycle and early pregnancy.
Highlights
Chemerin (CHEM), encoded by the gene retinoic acid receptor responder 2 (RARRES2) or tazarotene-induced gene 2 (TIG2), is a chemotactic factor for immune cells engaged in the processes of innate and acquired immunity [1]
The immunofluorescence staining has shown the presence of CHEM and its 3 receptors—chemokine-like receptor 1 (CMKLR1), G protein-coupled receptor 1 (GPR1) and chemokine receptor-like 2 (CCRL2)—in some regions of the pig hypothalamus both during the oestrous cycle as well as during early gestation
CHEM-immunoreactive (CHEM-IR) (Figure 1G,H and Figure 3G,H), GPR1-immunoreactive (GPR1-IR) (Figure 1C,D and Figure 3C,D) and CCRL2-immunoreactive (CCRL2-IR) (Figure 1E,F and Figure 3E,F) neurons were the most abundant in the paraventricular nucleus, which is the part of MBH, both during early gestation and during the oestrous cycle
Summary
Chemerin (CHEM), encoded by the gene retinoic acid receptor responder 2 (RARRES2) or tazarotene-induced gene 2 (TIG2), is a chemotactic factor for immune cells engaged in the processes of innate and acquired immunity [1]. CHEM is initially synthesised as a 163 amino acid (aa) pre-prochemerin. Several isoforms of CHEM have been reported that are dependent on the proteolytic cleavage at its C-terminus by various serine and cysteine proteases. This process serves as a key regulatory mechanism to determine the local and systemic concentrations of active CHEM which exerts local biological actions [4]. The different CHEM isoforms in human blood (CHEM-A155, -S157 and -K158), cerebrospinal fluid (CHEM-K158), hemofiltrate (CHEM-F154) and synovial fluid (CHEM-K158) have been reported, indicating that complex prochemerin processing occurs in vivo [5]
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