Symposium review: Adipose tissue endocrinology in the periparturient period of dairy cows

The involvement of adipose tissue (AT) in metabolism is not limited to energy storage but turned out to be much more complex. We now know that in addition to lipid metabolism, AT is important in glucose homeostasis and AA metabolism and also has a role in inflammatory processes. With the discovery of leptin in 1994, the concept of AT being able to secrete messenger molecules collectively termed as adipokines, and acting in an endo-, para-, and autocrine manner emerged. Moreover, based on its asset of receptors, many stimuli from other tissues reaching AT via the bloodstream can also elicit distinct responses and thus integrate AT as a control element in the regulatory circuits of the whole body's functions. The protein secretome of human differentiated adipocytes was described to comprise more than 400 different proteins. However, in dairy cows, the characterization of the physiological time course of adipokines in AT during the transition from pregnancy to lactation is largely limited to the mRNA level; for the protein level, the analytical methods are limited and available assays often lack sound validation. In addition to proteinaceous adipokines, small compounds such as steroids can also be secreted from AT. Due to the lipophilic nature of steroids, they are stored in AT, but during the past years, AT became also known as being able to metabolize and even to generate steroid hormones de novo. In high-yielding dairy cows, AT is substantially mobilized due to increased energy requirements related to lactation. As to whether the steroidogenic system in AT is affected and may change during the common loss of body fat is largely unknown. Moreover, most research about AT in transition dairy cows is based on subcutaneous AT, whereas other depots have scarcely been investigated. This contribution aims to review the changes in adipokine mRNA and-where available-protein expression with time relative to calving in high-yielding dairy cows at different conditions, including parity, body condition, diet, specific feed supplements, and health disorders. In addition, the review provides insights into steroidogenic pathways in dairy cows AT, and addresses differences between fat depots where possible.

Deep transcriptome analysis using RNA-Seq suggests novel insights into molecular aspects of fat-tail metabolism in sheep

Fat-tail content of sheep breeds is varied and the molecular mechanisms regulating fat-tail development have not been well characterized. Aiming at better identifying the important candidate genes and their functional pathways contributing to fat deposition in the tail, a comparative transcriptome analysis was performed between fat- (Lori-Bakhtiari) and thin-tailed (Zel) Iranian sheep breeds using RNA-seq. The experiment was conducted on six male lambs (three lambs per each breed) at seven months of age. Four different combinations of aligners and statistical methods including Hisat2 + edgeR, Hisat2 + DESeq2, STAR + edgeR and STAR + DESeq2 were used to identify the differentially expressed genes (DEGs). The DEGs were selected for functional enrichment analysis and protein-protein interaction (PPI) network construction. Module analysis was also conducted to mine the functional sub-networks from the PPI network. In total, 264 genes including 80 up- and 184 down-regulated genes were identified as DEGs. The RNA-Seq results were validated by Q-RT-PCR. Functional analysis of DEGs and the module analysis of PPI network demonstrated that in addition to pathways affecting lipid metabolism, a series of enriched functional terms related to "response to interleukin", "MAPK signaling pathways", "Wnt signaling pathway", "ECM-receptor interaction", "regulation of actin cytoskeleton", and "response to cAMP" might contribute to the deposition of fat in tails of sheep. Overall results using RNA-Seq analysis characterized important candidate genes involved in the fatty acid metabolism and regulation of fat deposition, suggesting novel insights into molecular aspects of fat-tail metabolism in sheep. Selected DEGs should be further investigated as potential markers associated with the fat-tail development in sheep breeds.

Possible involvement of the RARRES2/CMKLR1-system in metabolic and reproductive parameters in Holstein dairy cows

BACKGROUND

In dairy cows, the energy cost of milk yield results in a negative energy balance (EB) and body fat mobilization that impairs reproductive efficiency. Emerging evidence suggests that the novel adipokines, Retinoic acid receptor responder protein 2 (RARRES2), and its main receptor, Chemokine-like receptor 1 (CMKLR1) are involved in the regulation of metabolic and ovarian functions. So, we investigated in a first experiment the plasma RARRES2, and RARRES2 and CMKLR1 mRNA expression levels in subcutaneous adipose tissue (SAT) and granulosa cells (GC) at different times of body fat mobilization in dairy cows (4, 8, 20 and 44 weeks postpartum, wk. pp. for SAT and 8, 20 and 44 wk. pp. for GC). Then, in a second experiment we examined the effect of high (HE) and low energy (LE) diets on the RARRES2 system and its links with metabolic and reproductive parameters.

METHODS

The first experiment included 9 animals fed with HE diet from 4 to 44 wk. pp. and the second one included animals fed either a HE diet (n = 8) or a LE diet (n = 8) from - 4 to 16 wk. peripartum. In both experiments, various metabolic and reproductive parameters were determined and associated with plasma RARRES2 as measured by bovine ELISA. RARRES2 and CMKLR1 mRNA expression levels were analyzed by RT-qPCR in SAT after biopsy and GC after aspiration of follicles.

RESULTS

Plasma RARRES2 levels were higher at 4 wk. pp. as compared to 20 and 44 wk. pp. and they were positively correlated with body fat mobilization and milk yield. RARRES2 and CMKLR1 mRNA expression levels increased from 4 to 8 wk. pp. (fat mobilization, EB < 0) and remained unchanged at 20 and 44 wk. pp. (fat reconstitution, EB > 0) as compared to 4 wk. pp. in SAT. RARRES2 and CMKLR1 mRNA levels decreased from 8 to 44 wk. pp. in GC from small follicles. In the second experiment, plasma RARRES2 increased from - 4 to 8 wk. peripartum similarly in both LE and HE cows. In addition, the area under of plasma RARRES2 curve was highly negatively associated with the number of small follicles obtained in HE animals during the cycle before the first artificial insemination. In SAT of HE cows, RARRES2 mRNA expression decreased at 1 wk. pp. compared to - 4 and 16 wk. peripartum whereas opposite expression patterns were obtained for CMKLR1. Similar results were observed for CMKLR1 mRNA expression in LE cows while there was no variation in RARRES2 mRNA expression. Moreover, RARRES2 mRNA was higher expressed in LE than in HE cows at 1 wk. pp.

CONCLUSIONS

The lactation-induced fat and energy mobilization influenced plasma RARRES2 profile and mRNA expression pattern of RARRES2 and CMKLR1 similarly in both SAT and GC. In addition, the energy content of the diet did not affect plasma RARRES2 but it altered RARRES2 mRNA expression in SAT and the area under the curve of plasma RARRES2 that was negatively associated to the number of small follicles in HE animals. Thus, RARRES2 could be a metabolic or ovarian signal involved in the interactions between metabolic and reproductive functions in dairy cows.

Downregulated angiopoietin-like protein 8 production at calving related to changes in lipid metabolism in dairy cows

Acute physiological adaptation of lipid metabolism during the postpartum transition period of cows facilitates peripheral metabolic regulation. Hepatokines, which are hormones secreted from hepatocytes, are presumed to play a critical role in systemic metabolic regulation. Angiopoietin-like protein 8 (ANGPTL8) has been identified as a novel hepatokine associated with circulating triglyceride concentrations in mice and humans. However, regulation of ANGPTL8 and its physiological effects is still unknown in cattle. The present study aimed to reveal changes in ANGPTL8 expression and secretion during the periparturient period, and to investigate its regulatory effect on adipocytes and mammary epithelial cells. In the peripartum period, liver ANGPTL8 mRNA expression was lesser on the day of parturition and 1 wk postpartum than it was 1 wk before parturition (P < 0.05). Moreover, plasma ANGPTL8 concentrations decreased on the day of parturition as compared with that 1 wk before parturition (P < 0.05). In addition, ANGPTL8 expression in cultured bovine hepatocytes was downregulated after oleate and palmitate treatment but upregulated after insulin treatment (P < 0.05). ANGPTL8 decreased hormone-sensitive lipase (HSL) expression in differentiated adipocytes and cluster of differentiation 36 (CD36), fatty acid synthase (FAS), acetyl-coa carboxylase (ACC), and stearoyl-coa desaturase (SCD) in cultured bovine mammary epithelial cells (P < 0.05). These data suggest that hepatic ANGPTL8 production was downregulated postpartum when the cows experienced a negative energy balance. This downregulation was associated with increased concentrations of NEFA and decreased concentrations of insulin in lactating cows, and it facilitated lipid mobilization from adipose tissue to the mammary glands. We speculate that ANGPTL8 might have beneficial effects in reverting or improving the physiological adaptation and pathological processes of lipid metabolism during the peripartum period.

Post-prandial decrease in plasma growth hormone levels is not related to the increase in plasma insulin levels in goats

Objective

In the present study, we examined whether the post-prandial reduction in plasma growth hormone (GH) levels is related to the increase in plasma insulin levels in ruminants.

Methods

We performed two experiments: intravenous bolus injection of insulin (0.2 IU/kg body weight) or glucose (1.0 mmol/kg body weight) was administered to increase the plasma insulin levels in male Shiba goats.

Results

In the insulin injection experiment, significant (p<0.05) increase in GH concentrations was observed, 15 to 20 min after the injection; it was accompanied with a significant (p<0.01) increase in cortisol concentrations at 45 to 90 min, when compared to the concentrations in the saline-injected controls. The glucose injection significantly (p<0.05) increased the plasma GH concentration at 20 to 45 min; this was not accompanied by significantly higher cortisol concentrations than were observed for the saline-injected control. Hypoglycemia induced by the insulin injection, which causes the excitation of the adrenal cortex, might be involved in the increase in insulin levels.

Conclusion

Based on these results, we conclude that post-prandial increases in plasma insulin or glucose levels do not induce a decrease in GH concentration after feeding in the ruminants.

Postweaning changes in the expression of chemerin and its receptors in calves are associated with the modification of glucose metabolism

Chemerin, originally known as a chemoattractant derived from adipose tissue and the liver, has been reported to have regulatory functions in gluconeogenesis, peripheral insulin sensitivity, and insulin secretion. This study was conducted to assess the postweaning changes in expression of this cytokine and its physiological role in the modification of glucose metabolism associated with weaning. Eighteen tissue samples were collected from Holstein calves (90 d of age; n = 4) to investigate the tissue distributions of chemerin and its receptors genes. was highly expressed in the liver, and secreted chemerin protein was found in the plasma. Among the receptors of chemerin, and were ubiquitously expressed whereas was predominantly expressed in the liver. The changes in glucose metabolism and expression of these genes after weaning were assessed by comparing suckling calves (n = 6) and weaned calves (n = 8) of Japanese Black cattle. No significant difference was observed in plasma glucose levels between suckling and weaned calves (P = 0.22), whereas the plasma level of total ketone bodies was significantly higher in weaned calves (P < 0.01). Plasma levels of insulin and cortisol did not differ between suckling and weaned calves. The mRNA levels of certain key enzymes involved in hepatic gluconeogenesis were also altered; for instance, level was lower in postweaning calves (P < 0.05) and () level tended to be higher after weaning (P = 0.08). However, was not altered after weaning. The plasma levels of hepatic stress indicators were also changed, with aspartate transaminase, alanine transaminase, and lactate dehydrogenase being significantly elevated in postweaning calves (P < 0.05). Chemerin protein in liver tissue was less abundant in weaned calves (P < 0.05), although there were no changes in its transcript levels. The abundance of plasma chemerin protein did not change after weaning (P = 0.95). In summary, these data indicate that as a consequence of weaning, which causes physiological stress and alters hepatic metabolism, chemerin protein expression within the liver is downregulated, indicating that chemerin plays a role in the upregulation of hepatic expression via its inhibitory effect on hepatic gluconeogenesis.

Physiological Roles of Adipokines, Hepatokines, and Myokines in Ruminants

Since the discovery of leptin secreted from adipocytes, specialized tissues and cells have been found that secrete the several peptides (or cytokines) that are characterized to negatively and positively regulate the metabolic process. Different types of adipokines, hepatokines, and myokines, which act as cytokines, are secreted from adipose, liver, and muscle tissue, respectively, and have been identified and examined for their physiological roles in humans and disease in animal models. Recently, various studies of these cytokines have been conducted in ruminants, including dairy cattle, beef cattle, sheep, and goat. Interestingly, a few cytokines from these tissues in ruminants play an important role in the post-parturition, lactation, and fattening (marbling) periods. Thus, understanding these hormones is important for improving nutritional management in dairy cows and beef cattle. However, to our knowledge, there have been no reviews of the characteristics of these cytokines in beef and dairy products in ruminants. In particular, lipid and glucose metabolism in adipose tissue, liver tissue, and muscle tissue are very important for energy storage, production, and synthesis, which are regulated by these cytokines in ruminant production. In this review, we summarize the physiological roles of adipokines, hepatokines, and myokines in ruminants. This discussion provides a foundation for understanding the role of cytokines in animal production of ruminants.

Are serum chemerin levels different between obese and non-obese polycystic ovary syndrome women?

The objective of this study is to measure serum chemerin levels in women with polycystic ovary syndrome (PCOS) and assess their relationship with clinical, metabolic, and hormonal parameters. One hundred eighteen PCOS women and 114 healthy women were recruited in this study. Their blood pressure, body mass index (BMI), waist circumference and waist-to-hip ratio (WHR), fasting insulin (FIN), fasting plasma glucose (FPG), blood serum sex hormone, and blood lipid were measured. Serum chemerin, leptin, and adiponectin were measured by ELISA. Serum chemerin was significantly higher in the obese PCOS group (47.62 ± 11.27 ng/mL) compared with non-obese PCOS (37.10 ± 9.55 ng/mL) and the obese (33.71 ± 6.17 ng/mL) and non-obese (25.78 ± 6.93 ng/mL) control groups (p < 0.05). Serum chemerin was positively related to BMI, waist circumference, WHR, testosterone (T), FPG, FIN, homeostasis model assessment of insulin resistance (HOMA-IR), total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL-C), LDL-C/high-density lipoprotein(HDL-C), TC/HDL-C and serum leptin, while negatively related to glucose-to-insulin ratio (G/I), HDL-C, and adiponectin levels. Multiple linear regression analysis revealed HOMA-IR, leptin, and TC were the significant influencing factors of chemerin levels (p < 0.05). Increased serum chemerin in PCOS woman with or without obesity suggested that chemerin may be involved in the development of the pathogenesis of PCOS.

Chemerin is a novel regulator of lactogenesis in bovine mammary epithelial cells

Chemerin is a chemoattractant cytokine (chemokine) produced by adipocytes and hepatocytes; it regulates insulin sensitivity and adipocyte differentiation. The objective of this study was to investigate the effect of chemerin on the expression of genes related to lactogenesis and the regulators of chemerin signaling in a bovine mammary epithelial cell line (MAC-T). Two types of chemerin receptors, chemokine like-receptor 1 (CMKLR1) and chemokine (C-C motif) receptor-like 2 (CCRL2), were detected in cultured MAC-T cells, whereas chemerin was not detected. G protein-coupled receptor 1 (GPR1), another receptor of chemerin, was undetectable in MAC-T cells. Chemerin upregulated transcript expression of CMKLR1, CCRL2, and genes associated with fatty acid synthesis, glucose uptake, insulin signaling, and casein synthesis in MAC-T cells. Lactogenic hormones (insulin, growth hormone, and prolactin) downregulated the expression of CMKLR1 in MAC-T cells. Adiponectin suppressed CMKLR1 expression. TNF-α suppressed CMKLR1, but induced CCRL2 expression. These data suggest chemerin is a novel regulator of lactogenesis via its own receptor in bovine mammary epithelial cells.

Effects of different roughage sources and feeding levels on adipogenesis of ovine adipocytes

The objective of the present study was to conduct an adipogenic evaluation of different roughage sources and feeding levels during ruminant adipocyte differentiation in vitro. Six wether sheep were divided into a timothy hay feeding group (TFG, n = 3) and an Italian ryegrass straw feeding group (IFG, n = 3). The sheep were fed high-roughage (HR), medium roughage (MR) and low-roughage (LR) diets in a one-way layout design each over a 6-day period. Sheep serum samples collected on the last day of each dietary treatment were added to an adipogenic induction medium for differentiation of preadipocytes derived from sheep subcutaneous adipose tissue. The cytoplasmic lipid accumulations in the TFG serum-treated preadipocytes were significantly higher than those of the IFG-serum treated preadipocytes on day 12. Messenger RNA expression of CCAAT/enhancer-binding protein (C/EBP)-α, C/EBP-β, C/EBP-δ, fatty-acid-binding protein (aP2) and stearoyl-coenzyme A desaturase (SCD) were regulated by each serum treatment. This study shows that different roughage source diets and roughage-to-concentrate ratio diets can regulate adipocyte differentiation via ruminant blood composition.

Single Nucleotide Polymorphism in the Coding Region of Bovine Chemerin Gene and Their Associations with Carcass Traits in Japanese Black Cattle

Chemerin, highly expressed in adipose and liver tissues, regulates glucose and lipid metabolism and immunity in these tissues in ruminants and mice. Our previous reports showed that chemerin is involved in adipogenesis and lipid metabolism in adipose tissue as an adipokine. The aim of the present study was to identify single nucleotide polymorphisms (SNPs) in the coding region of the chemerin gene and to analyze their effects on carcass traits and intramuscular fatty acid compositions in Japanese Black cattle. The SNPs in the bovine chemerin gene were detected in 232 Japanese Black steers (n = 161) and heifers (n = 71) using DNA sequencing. The results revealed five novel silent mutations: NM_001046020: c.12A>G (4aa), c.165G<A (55aa), c.276C>T (92aa), c.321 A>G (107aa), and c.396C>T (132aa). There was no association between 4 of the SNPs (c.12A>G [4aa], c.165G<A [55aa], c.321 A>G [107aa], and c.396C>T) and carcass traits or intramuscular fatty acid compositions. Regarding the remaining SNP, c.276C>T, we found that cattle with genotype CC had a higher beef marbling score than that of cattle with genotype CT, whereas cattle with genotype CT had a higher body condition score (p<0.10). Further, cattle with genotype CC had significantly higher C18:0 content in their intramuscular fat tissue than that of cattle with genotype CT (p<0.05). On the other hand, cattle with genotype CT had significantly higher C14:0 and C16:0 content in their intramuscular fat tissue (p<0.05). Moreover, the number of individuals carrying the minor allele of c.276C>T SNP is small. It is suggested that the c.276C>T SNP of the chemerin gene has potential in cattle breeding using modern methods, such as marker assisted selection. So, further functional and physiological research elucidating the impact of the chemerin gene on bovine lipid metabolism including fatty acid synthesis will help in understanding these results.

Soluble extract of soybean fermented with Aspergillus oryzae GB107 inhibits fat accumulation in cultured 3T3-L1 adipocytes

BACKGROUND/OBJECTIVES

This study was conducted to investigate the effects of fermented soybean (FS) extract on adipocyte differentiation and fat accumulation using cultured 3T3-L1 adipocytes.

MATERIALS/METHODS

3T3-L1 adipocytes were treated with FS and nonfermented soybean (NFS) extract during differentiation for 10 days in vitro. Oil red O staining was performed and glycerol-3-phosphate dehydrogenase (GPDH) activity was measured for analysis of fat accumulation. Expressions of adipogenic genes were measured.

RESULTS

Soluble extract of soybean fermented with Aspergillus oryzae GB107 contained higher levels of low-molecular-weight protein than conventional soybean protein did. FS extract (50 µg/ml) inhibited adipocyte differentiation and fat accumulation during differentiation of 3T3-L1 preadipocytes for 10 days in vitro. Significantly lower GPDH activity was observed in differentiated adipocytes treated with the FS extract than those treated with NFS extract. Treatment with FS extract resulted in decreased expression levels of leptin, adiponectin, and adipogenin genes, which are associated with adipogenesis.

CONCLUSIONS

This report is the first to demonstrate that the water-soluble extract from FS inhibits fat accumulation and lipid storage in 3T3-L1 adipocytes. Thus, the soybean extract fermented with A. oryzae GB107 could be used to control lipid accumulation in adipocytes.

The regulation of oxytocin receptor gene expression during adipogenesis

Although it has been reported that oxytocin stimulates lipolysis in adipocytes, changes in the expression of oxytocin receptor (OTR) mRNA in adipogenesis are still unknown. The present study aimed to investigate the expression of OTR mRNA during adipocyte differentiation and fat accumulation in adipocytes. OTR mRNA was highly expressed in adipocytes prepared from mouse adipose tissues compared to stromal-vascular cells. OTR mRNA expression was increased during the adipocyte differentiation of 3T3-L1 cells. OTR expression levels were higher in subcutaneous and epididymal adipose tissues of 14-week-old male mice compared to 7-week-old male mice. Levels of OTR mRNA expression were higher in adipose tissues at four different sites of mice fed a high-fat diet than in those of mice fed a normal diet. The OTR expression level was also increased by refeeding for 4 h after fasting for 16 h. Oxytocin significantly induced lipolysis in 3T3-L1 adipocytes. In conclusion, a new regulatory mechanism is demonstrated for oxytocin to control the differentiation and fat accumulation in adipocytes via activation of OTR as a part of the hypothalamic-pituitary-adipose axis.

Apelin-13 decreases lipid storage in hypertrophic adipocytes in vitro through the upregulation of AQP7 expression by the PI3K signaling pathway

BACKGROUND

Adipocyte-secreted apelin contributes to decreased adiposity and to improved insulin resistance, but the mechanisms remain unknown. The present study aimed to assess if apelin-13 is an upstream signal regulation factor of aquaporin 7 (AQP7), a water-glycerol transporter present in the plasma membrane of adipocytes that plays a key role in the regulation of lipid accumulation.

MATERIAL/METHODS

3T3-L1 pre-adipocytes were induced to fully differentiated adipocytes; hypertrophic adipocytes were then induced using palmitate. The effects of apelin-13 on AQP7 expression in hypertrophic adipocytes were investigated before and after treatment with LY249002, a PI3K inhibitor. Accumulation of cytoplasmic triglycerides (TG) in hypertrophic adipocytes was also determined.

RESULTS

We found that 0.1 mM of palmitate induced a model of hypertrophic adipocytes with a lower AQP7 expression (0.26±0.07 vs. 0.46±0.04, P<0.05). Apelin-13 100 nM or 1000 nM upregulated AQP7 mRNA expression (100 nM: 0.54±0.06 and 1000 nM: 0.58±0.09 vs. control: 0.33±0.04, both P<0.05), and decreased accumulation of cytoplasmic triglycerides in hypertrophic adipocytes. Pretreatment using 10 µM LY294002 prevented the increase in AQP7 expression observed when using apelin-13 alone (apelin-13 + LY49002: 0.38±0.03 vs. apelin-13: 0.54±0.06, P<0.05), as well as the decreased cytoplasmic TG accumulation (apelin-13 + LY294002: 3.79±0.04 µM per µg/ml vs. apelin-13: 3.32±0.08 µM per µg/ml, P<0.05).

CONCLUSIONS

Apelin-13 decreases lipid storage in hypertrophic adipocytes in vitro, possibly through the upregulation of AQP7 expression by the PI3K signaling pathway. Treatment using apelin-13 and AQP modulators might represent novel treatment strategies against obesity and its related complications.

The Regulation of Chemerin and CMKLR1 Genes Expression by TNF-α, Adiponectin, and Chemerin Analog in Bovine Differentiated Adipocytes

Adipokines, adipocyte-derived protein, have important roles in various kinds of physiology including energy homeostasis. Chemerin, one of adipocyte-derived adipokines, is highly expressed in differentiated adipocytes and is known to induce macrophage chemotaxis and glucose intolerance. The objective of the present study was to investigate the changes of chemerin and the chemokine-like-receptor 1 (CMKLR1) gene expression levels during differentiation of the bovine adipocyte and in differentiated adipocytes treated with tumor necrosis factor-α (TNF-α), adiponectin, leptin, and chemerin (peptide analog). The expression levels of the chemerin gene increased at d 6 and 12 of the differentiation period accompanied by increased cytoplasm lipid droplets. From d 6 onward, peroxisome proliferator-activated receptor-γ2 (PPAR-γ2) gene expression levels were significantly higher than that of d 0 and 3. In contrast, CMKLR1 expression levels decreased at the end of the differentiation period. In fully differentiated adipocytes (i.e. at d 12), the treatment of TNF-α and adiponectin upregulated both chemerin and CMKLR1 gene expression levels, although leptin did not show such effects. Moreover, chemerin analog treatment was shown to upregulate chemerin gene expression levels regardless of doses. These results suggest that the expression of chemerin in bovine adipocyte might be regulated by chemerin itself and other adipokines, which indicates its possible role in modulating the adipokine secretions in adipose tissues.

CHEMERIN (RARRES2) decreases in vitro granulosa cell steroidogenesis and blocks oocyte meiotic progression in bovine species

CHEMERIN, or RARRES2, is a new adipokine that is involved in the regulation of adipogenesis, energy metabolism, and inflammation. Recent data suggest that it also plays a role in reproductive function in rats and humans. Here we studied the expression of CHEMERIN and its three receptors (CMKLR1, GPR1, and CCRL2) in the bovine ovary and investigated the in vitro effects of this hormone on granulosa cell steroidogenesis and oocyte maturation. By RT-PCR, immunoblotting, and immunohistochemistry, we found CHEMERIN, CMKLR1, GPR1, and CCRL2 in various ovarian cells, including granulosa and theca cells, corpus luteum, and oocytes. In cultured bovine granulosa cells, INSULIN, IGF1, and two insulin sensitizers-metformin and rosiglitazone-increased rarres2 mRNA expression whereas they decreased cmklr1, gpr1, and cclr2 mRNA expression. Furthermore, TNF alpha and ADIPONECTIN significantly increased rarres2 and cmklr1 expression, respectively. In cultured bovine granulosa cells, human recombinant CHEMERIN (hRec, 200 ng/ml) reduced production of both progesterone and estradiol, cholesterol content, STAR abundance, CYP19A1 and HMGCR proteins, and the phosphorylation levels of MAPK3/MAPK1 in the presence or absence of FSH (10(-8) M) and IGF1 (10(-8) M). All of these effects were abolished by using an anti-CMKLR1 antibody. In bovine cumulus-oocyte complexes, the addition of hRec (200 ng/ml) in the maturation medium arrested most oocytes at the germinal vesicle stage, and this was associated with a decrease in MAPK3/1 phosphorylation in both oocytes and cumulus cells. Thus, in cultured bovine granulosa cells, hRec decreases steroidogenesis, cholesterol synthesis, and MAPK3/1 phosphorylation, probably through CMKLR1. Moreover, in cumulus-oocyte complexes, it blocked meiotic progression at the germinal vesicle stage and inhibited MAPK3/1 phosphorylation in both the oocytes and cumulus cells during in vitro maturation.