As a multifaceted adipokine, chemerin has been found to perform functions vital for immunity, adiposity, and metabolism through its three known receptors (chemokine-like receptor 1, CMKLR1; G-protein-coupled receptor 1, GPR1; C-C motif chemokine receptor-like 2, CCRL2). Chemerin and the cognate receptors are also expressed in the hypothalamus, pituitary gland, testis, ovary, and placenta. Accumulating studies suggest that chemerin participates in normal reproduction and underlies the pathological mechanisms of certain reproductive system diseases, including polycystic ovary syndrome (PCOS), preeclampsia, and breast cancer. Herein, we present a comprehensive review of the roles of the chemerin system in multiple reproductive processes and human reproductive diseases, with a brief discussion and perspectives on future clinical applications.

Hyperandrogenism is a key pathological feature of polycystic ovarian syndrome (PCOS). Excess androgen can lead to PCOS-like cell hypertrophy in the ovaries and adipose tissue of rodents. Here, we established a dihydrotestosterone (DHT)-induced hyperandrogenic mouse model to analyze the differences in gene expression and signaling pathways of the ovaries and gonad fat pads of mice treated with or without DHT by RNA microarray analysis. From the results, we focused on the overlapping differentially expressed gene—Col6a5—and the major differentially enriched signaling pathway—lipid metabolism. We employed DHT-induced mouse ovarian stromal cell, adipogenic 3T3-L1 cell and hepatic cell line NCTC1469 models to investigate whether androgens directly mediate lipid accumulation and hypertrophy. We found that DHT increased lipid droplet accumulation in ovarian stromal cells and adipogenic 3T3-L1 cells but not NCTC1469 cells. DHT significantly altered stromal cell cholesterol metabolism and steroidogenesis, as indicated by changes in cholesterol levels and the expression of related genes, but these effects were not observed in 3T3-L1 cells. Moreover, Col6a5 expression was significantly increased in ovaries and gonadal fat pads of DHT-treated mice, and Col6a5 inhibition alleviated DHT-induced excess lipid accumulation and hypertrophy of ovarian stromal cells and adipogenic 3T3-L1 cells, even improved lipid metabolism in overnourished NCTC1469 cells. Our results indicate that Col6a5 plays important roles in the pathogenesis of DHT-induced lipid metabolism disorder and the hypertrophy of ovarian stromal cells and adipocytes.

Background: Placental metabolic dysfunction is associated with pregnancy complications, including preeclampsia, gestational diabetes mellitus, and fetal growth restriction. However, little is known about how the metabolic processes regulate placental development and trophoblast differentiation. The adipokine chemerin, whose serum level is elevated during pregnancy, regulates the placental lipid metabolism and may influence placental development and trophoblast differentiation. Results: In this study, we observed the increased chemerin expression in the serum and placenta of the pregnant mice. Chemerin is highly expressed in the extraembryonic primary parietal trophoblast giant cells and the ectoplacental cone (EPC) trophoblast cells. Excessive chemerin treatment in mice results in increased placental lipid accumulation, promotes the expansion of glycogen trophoblast cell (GlyT) and syncytiotrophoblast, and restricts the growth of spongiotrophoblast (SpT) and sinusoidal trophoblast giant cell (S-TGC). Chemerin deficiency led to increased expression of placental fatty acid oxidation enzymes and disrupted the proliferation of SpT and S-TGC in the labyrinth. Furthermore, we utilized the fatty acid oxidation inhibitor etomoxir and demonstrated that blocking fatty acid oxidation hinders the proliferation of SpT and S-TGC in the labyrinth. Conclusions: Our study demonstrated that chemerin-related lipid metabolism is crucial for EPC trophoblast differentiation during placental development, providing evidence that chemerin determines the growth of SpT and S-TGC through fatty acid oxidation. These findings also imply a possible pathological mechanism for pregnancy complications associated with chemerin.

Chemerin and GPR1 show increased on serum and placental in mice during pregnancy. Interestingly, we observed increased serum chemerin levels and decreased GPR1 expression in HFD-fed mice placental compared to chow at GD 18. GPR1 protein and gene levels were significantly decreased in GDM patient placentas. It was previously reported that serum chemerin levels are markedly increased in obese and gestational diabetes mellitus (GDM) patients and positively associated with the risk of GDM in the first trimester, and loss of GPR1, a chemerin receptor, could result in glucose intolerance in obese mice. Therefore, we hypothesized that chemerin/GPR1 signaling might participate in the pathogenic mechanism of GDM. Our study is the first report on the expression of GPR1, and on the characterization of its direct biological effects in humans and mice, including the molecular mechanism that indicates the role of GPR1 signaling in maternal metabolism during pregnancy. Decreased GPR1 levels were measured in GDM patient placentas. Meanwhile, it was confirmed that GPR1 knockdown exacerbated glucose intolerance and disrupted lipid metabolism. These findings indicate a novel feedback mechanism to regulate glucose balance during pregnancy, and GPR1 could be a potential target for the detection, prevention, and therapy of GDM.

Trophoblast invasion is crucial for the establishment of a functional placenta. Defects in this process can cause adverse pregnancy outcomes, such as miscarriage and preeclampsia. Aldo-keto reductase family 1 member B10 (AKR1B10), a key cytoplasmic oxidoreductase that converts retinoids, retinaldehyde isoprenoids, and lipid peroxidation-derived reactive aldehydes into their corresponding alcohols, regulates cell proliferation, inflammation, and metastasis in cancers. Here, our results demonstrated that AKR1B10 is highly expressed in the ectoplacental cone (EPC) of the mouse placenta. Deficiency of AKR1B10 leads to excessive trophoblast giant cell (TGC) invasion, impaired trophoblast cell differentiation of the junctional zone, and accelerated maternal spiral artery remodeling. Mechanistically, loss of AKR1B10 suppressed extracellular regulated protein kinase (ERK) phosphorylation in both murine placentas and human HTR8/SVneo cells, further promoting HTR8 cell migration and invasion in vitro. Our findings identify AKR1B10 as a critical regulator that restrains trophoblast invasion in the placenta, suggesting it as a new therapeutic target for placental disorders.