Processing, signaling, and physiological function of chemerin

Adipokine receptor expression in mast cells is altered by specific ligands and proinflammatory cytokines

Adipokines play essential roles in regulating a range of biological processes, but growing evidence indicates that they are also fundamental in immunological mechanisms and, primarily, inflammatory responses. Adipokines mediate their actions through specific receptors. However, although adipokine receptors are widely distributed in many cell and tissue types, limited data are available on their expression in mast cells (MCs) and, consequently, adipokine's significance in the modulation of MC activity within the tissues. In this study, we demonstrate that rat peritoneal MCs constitutively express the leptin receptor (i.e. LEPR), adiponectin receptors (i.e. ADIPOR1 and ADIPOR2) and the chemerin receptor (i.e. CMKLR1). We also found that LEPR, ADIPOR1, ADIPOR2 and CMKLR1 expression in MCs changes in response to stimulation by their specific ligands and some cytokines with potent proinflammatory properties. Furthermore, the involvement of intracellular signaling molecules in leptin-, adiponectin- and chemerin-induced MC response was analyzed. Overall, our findings suggest that adipokines leptin, adiponectin and chemerin can significantly affect the activity of MCs in various processes, especially during inflammation. These observations may contribute significantly to understanding the relationship between adipokines, immune mechanisms and diseases or conditions with an inflammatory component.

Chemerin abundance in egg white and its expression with receptors in extra-embryonic annexes of Pekin ducks: implications for embryo development

Embryonic mortality is a significant problem in the commercial duck industry worldwide. Therefore, identification of new biomarkers for duck embryo development is necessary. In the chicken (order Galliformes), we previously showed that chemerin is a hormone locally produced by the reproductive tract in hens, particularly in the magnum area, leading to its accumulation in the egg white and within the embryo annexes during embryonic development. We therefore hypothesized that the chemerin concentration in egg white could be a biomarker of egg performance and reproductive parameters in Pekin ducks (order Anseriformes). Thus, we collected eggs from Pekin ducks over a 5-d period at three stages of the laying period (before the laying peak, after the laying peak, and at the end of the laying period) to measure the chemerin concentrations in egg white by enzyme-linked immunosorbent assay. The chemerin concentration in egg white decreased during the laying period and was not associated with reproductive parameters. We found negative correlations between the chemerin level in egg white and the albumen weight. Reverse-transcriptase quantitative polymerase chain reaction showed that chemerin and its three receptors CMKLR1, GPR1, and CCRL2 were expressed in the reproductive tract and within allantoic and amniotic annexes during embryo development. Chemerin concentrations strongly increased in amniotic fluid on embryonic day 16 (ED16) when the egg white was transferred into the amniotic sac. Finally, chemerin inhibition in egg white by in ovo injections of anti-chemerin antibodies (0.01, 0.1, and 1 µg) increased the embryo mortality rate. These data demonstrate the important role of the chemerin system during egg formation and embryo development in Pekin ducks, suggesting their potential use as biomarkers for determining the quality of poultry eggs and embryo development.

Adipokines in pregnancy

Reproductive success consists of a sequential events chronology, starting with the ovum fertilization, implantation of the embryo, placentation, and cellular processes like proliferation, apoptosis, angiogenesis, endocrinology, or metabolic changes, which taken together finally conduct the birth of healthy offspring. Currently, many factors are known that affect the regulation and proper maintenance of pregnancy in humans, domestic animals, or rodents. Among the determinants of reproductive success should be distinguished: the maternal microenvironment, genes, and proteins as well as numerous pregnancy hormones that regulate the most important processes and ensure organism homeostasis. It is well known that white adipose tissue, as the largest endocrine gland in our body, participates in the synthesis and secretion of numerous hormones belonging to the adipokine family, which also may regulate the course of pregnancy. Unfortunately, overweight and obesity lead to the expansion of adipose tissue in the body, and its excess in both women and animals contributes to changes in the synthesis and release of adipokines, which in turn translates into dramatic changes during pregnancy, including those taking place in the organ that is crucial for the proper progress of pregnancy, i.e. the placenta. In this chapter, we are summarizing the current knowledge about levels of adipokines and their role in the placenta, taking into account the physiological and pathological conditions of pregnancy, e.g. gestational diabetes mellitus, preeclampsia, or intrauterine growth restriction in humans, domestic animals, and rodents.

Chemerin affects the expression of angiogenesis-related factors in the porcine endometrium during early pregnancy and the oestrous cycle: an in vitro study

CONTEXT

The appropriate course of angiogenesis in the endometrium is crucial for pregnancy establishment and maintenance. Very little is known about the factors linking vessel formation and immune system functioning.

AIMS

We hypothesised that chemerin, an adipokine known for its involvement in the regulation of energy balance and immunological functions, may act as a potent regulator of endometrial angiogenesis during early pregnancy in pigs.

METHODS

Porcine endometrial tissue explants were obtained from pregnant pigs on days 10-11, 12-13, 15-16 and 27-28, and on days 10-12 of the oestrous cycle. The explants were in vitro cultured for 24h in the presence of chemerin (100, 200ng/mL) or in medium alone (control). We evaluated the in vitro effect of chemerin on the secretion of vascular endothelial growth factors A-D (VEGF-A-D), placental growth factor (PlGF), basic fibroblast growth factor (bFGF) and angiopoietin 1 and 2 (ANG-1, ANG-2) with the ELISA method. The protein abundance of angiogenesis-related factor receptors, VEGF receptors 1-3 (VEGFR1-3), FGF receptors 1 and 2 (FGFR1-2) and ANG receptor (TIE2) was evaluated with the Western blot (WB) method. We also analysed the influence of chemerin on the phosphorylation of AMPK using WB.

KEY RESULTS

We found that in the studied endometrial samples, chemerin up-regulated the secretion of VEGF-A, VEGF-B and PlGF, and protein expression of VEGFR3. The adipokine caused a decrease in VEGF-C, VEGF-D and ANG-1 release. Chemerin effect on bFGF and ANG-2 secretion, and protein content of VEGFR1, VEGFR2, FGFR1, FGFR2 and TIE2 were dependent on the stage of pregnancy. Chemerin was found to down-regulate AMPK phosphorylation.

CONCLUSIONS

The obtained in vitro results suggest that chemerin could be an important factor in the early pregnant uterus by its influence on angiogenic factors' secretion and signalling.

IMPLICATIONS

The obtained results on the role of chemerin in the process of endometrial angiogenesis may, in the long term perspective, contribute to the elaboration of more effective methods of modifying reproductive processes and maintaining energy homeostasis in farm animals.

The profile of adipokines associated with fibrosis and impaired microcirculation in systemic sclerosis

PURPOSE

Adipokines belong to a group of molecules mostly produced by adipose tissue. Abnormalities in the secretion of several adipokines have already implicated to play a pathogenic role in systemic sclerosis (SSc). However, the possible role of numerous molecules still needs to be clarified. The aim of the study was to determine whether the altered level of selected circulating adipokines might correlate with the intensity of fibrosis and vasculopathy in the course of SSc.

MATERIALS AND METHODS

Serum concentrations of chemerin, adipsin, retinol-binding protein 4, apelin, visfatin, omentin-1, and vaspin were determined with ELISA in the sera of patients with SSc (n ​= ​55) and healthy controls (n ​= ​25).

RESULTS

The serum concentration of adipsin (p ​= ​0.03) and visfatin (p ​= ​0.04) was significantly increased and the level of retinol-binding protein 4 (p ​= ​0.03) was decreased in diffuse compared to limited cutaneous SSc. Moreover, serum adipsin level correlated positively with the intensity of skin fibrosis measured with the modified Rodnan skin score (r ​= ​0.31, p ​= ​0.02) and was significantly higher in patients with pulmonary arterial hypertension than in those without the condition (p ​= ​0.03). The concentrations of adipsin (p ​= ​0.01) and visfatin (p ​= ​0.04) were significantly increased and the level of apelin (p ​= ​0.02) was decreased in patients with active digital ulcerations compared to individuals without this complication.

CONCLUSION

Adipsin may be considered a pivotal protein in the development of both fibrosis and impaired microcirculation. Its abnormal concentration reflects the intensity of skin thickening and the presence of pulmonary arterial hypertension. Adipsin, visfatin, and apelin are adipose tissue-derived molecules associated with digital vasculopathy.

Endothelial CCRL2 induced by disturbed flow promotes atherosclerosis via chemerin-dependent β2 integrin activation in monocytes

AIMS

Chemoattractants and their cognate receptors are essential for leucocyte recruitment during atherogenesis, and atherosclerotic plaques preferentially occur at predilection sites of the arterial wall with disturbed flow (d-flow). In profiling the endothelial expression of atypical chemoattractant receptors (ACKRs), we found that Ackr5 (CCRL2) was up-regulated in an endothelial subpopulation by atherosclerotic stimulation. We therefore investigated the role of CCRL2 and its ligand chemerin in atherosclerosis and the underlying mechanism.

METHODS AND RESULTS

By analysing scRNA-seq data of the left carotid artery under d-flow and scRNA-seq datasets GSE131776 of ApoE-/- mice from the Gene Expression Omnibus database, we found that CCRL2 was up-regulated in one subpopulation of endothelial cells in response to d-flow stimulation and atherosclerosis. Using CCRL2-/-ApoE-/- mice, we showed that CCRL2 deficiency protected against plaque formation primarily in the d-flow areas of the aortic arch in ApoE-/- mice fed high-fat diet. Disturbed flow induced the expression of vascular endothelial CCRL2, recruiting chemerin, which caused leucocyte adhesion to the endothelium. Surprisingly, instead of binding to monocytic CMKLR1, chemerin was found to activate β2 integrin, enhancing ERK1/2 phosphorylation and monocyte adhesion. Moreover, chemerin was found to have protein disulfide isomerase-like enzymatic activity, which was responsible for the interaction of chemerin with β2 integrin, as identified by a Di-E-GSSG assay and a proximity ligation assay. For clinical relevance, relatively high serum levels of chemerin were found in patients with acute atherothrombotic stroke compared to healthy individuals.

CONCLUSIONS

Our findings indicate that d-flow-induced CCRL2 promotes atherosclerotic plaque formation via a novel CCRL2-chemerin-β2 integrin axis, providing potential targets for the prevention or therapeutic intervention of atherosclerosis.

Investigation of Gene Networks in Three Components of Immune System Provides Novel Insights into Immune Response Mechanisms against Edwardsiella tarda Infection in Paralichthys olivaceus

As a quintessential marine teleost, Paralichthys olivaceus demonstrates vulnerability to a range of pathogens. Long-term infection with Edwardsiella tarda significantly inhibits fish growth and even induces death. Gills, blood, and kidneys, pivotal components of the immune system in teleosts, elicit vital regulatory roles in immune response processes including immune cell differentiation, diseased cell clearance, and other immunity-related mechanisms. This study entailed infecting P. olivaceus with E. tarda for 48 h and examining transcriptome data from the three components at 0, 8, and 48 h post-infection employing weighted gene co-expression network analysis (WGCNA) and protein-protein interaction (PPI) network analysis. Network analyses revealed a series of immune response processes after infection and identified multiple key modules and key, core, and hub genes including xpo1, src, tlr13, stat1, and mefv. By innovatively amalgamating WGCNA and PPI network methodologies, our investigation facilitated an in-depth examination of immune response mechanisms within three significant P. olivaceus components post-E. tarda infection. Our results provided valuable genetic resources for understanding immunity in P. olivaceus immune-related components and assisted us in further exploring the molecular mechanisms of E. tarda infection in teleosts.

Role of Chemerin and Perivascular Adipose Tissue Characteristics on Cardiovascular Risk Assessment by Arterial Stiffness Markers in Patients with Morbid Obesity

BACKGROUND AND OBJECTIVE

The development of arterial stiffness (AS) in obesity is a multifactorial and complex process. The pleomorphic actions of adipokines and their local activity in perivascular adipose tissue (PVAT) are potential modulators of AS appearance and progression. We aimed to assess the correlations between two adipokines (chemerin, adiponectin), PVAT morphological changes (adipocyte size, blood vessel wall thickness) and AS parameters in the special subgroup of patients with morbid obesity.

MATERIAL AND METHODS

We enrolled 25 patients with morbid obesity and 25 non-obese patients, who were age- and gender-matched, untreated for cardiovascular risk factors, and admitted to hospital for laparoscopic surgical procedures (bariatric surgery for morbid obesity and non-inflammatory benign pathology surgery for non-obese patients). Before the surgical procedures, we evaluated demographic and anthropometric data and biochemical parameters including the studied adipokines. Arterial stiffness was evaluated using a Medexpert ArteriographTM TL2 device. In both groups, adipocyte size and vascular wall thickness as well as local adiponectin activity were analyzed in PVAT from intraoperative biopsies.

RESULTS

In our study, adiponectin (p = 0.0003), chemerin (p = 0.0001) and their ratio (p = 0.005) had statistically significant higher mean values in patients with morbid obesity compared to normal-weight patients. In patients with morbid obesity there were significant correlations between chemerin and AS parameters such as aortic pulse wave velocity (p = 0.006) and subendocardial viability index (p = 0.009). In the same group adipocyte size was significantly correlated with another AS parameter, namely, aortic systolic blood pressure (p = 0.030). In normal-weight patients, blood vessel wall thickness positively correlated with AS parameters such as brachial (p = 0.023) and aortic augmentation index (p = 0.023). An important finding was the negative adipoR1 and adipoR2 immunoexpression in PVAT adipocytes of patients with morbid obesity. Additionally, we found significant correlations between blood vessel wall thickness and blood fasting glucose (p < 0.05) in both groups.

CONCLUSIONS

Chemerin and adipocyte size could be predictive biomarkers for AS in patients with morbid obesity. Given the small number of patients included, our results need further validation.

The Role of Selected Adipocytokines in Ovarian Cancer and Endometrial Cancer

Due to their multidirectional influence, adipocytokines are currently the subject of numerous intensive studies. Significant impact applies to many processes, both physiological and pathological. Moreover, the role of adipocytokines in carcinogenesis seems particularly interesting and not fully understood. For this reason, ongoing research focuses on the role of these compounds in the network of interactions in the tumor microenvironment. Particular attention should be drawn to cancers that remain challenging for modern gynecological oncology-ovarian and endometrial cancer. This paper presents the role of selected adipocytokines, including leptin, adiponectin, visfatin, resistin, apelin, chemerin, omentin and vaspin in cancer, with a particular focus on ovarian and endometrial cancer, and their potential clinical relevance.

Chemerin Exacerbates Psoriasis by Stimulating Keratinocyte Proliferation and Cytokine Production

OBJECTIVE

Psoriasis is often combined with metabolic abnormalities, such as obesity and diabetes. The upregulation of chemerin, which is an essential protein produced primarily from white fat, is strongly correlated to the development of psoriasis. However, there is no clarification on its exact function and mechanism in disease pathogenesis. The present study aims to determine its function and mechanism in disease pathogenesis.

METHODS

The present study used a psoriasislike inflammatory cell model and imiquimod (IMQ)-induced mouse model to confirm whether chemerin is upregulated in psoriasis patients.

RESULTS

Chemerin enhanced the keratinocyte proliferation, inflammatory cytokine secretion, and activation of the MAPK signaling pathway. Crucially, the intraperitoneal injection of neutralizing anti-chemerin antibody (ChAb) diminished the epidermal proliferation and inflammation in the IMQ-induced mouse model.

CONCLUSION

The present results indicate that chemerin promotes keratinocyte proliferation, and enhances the production of inflammatory cytokines, thereby aggravating the psoriasis. Thus, chemerin can be a prospective target for the treatment of psoriasis.

Substrates, Cofactors, and Cellular Targets of Coagulation Factor XIa

Coagulation factor XI (FXI) has increasingly been shown to play an integral role in several physiologic and pathological processes. FXI is among several zymogens within the blood coagulation cascade that are activated by proteolytic cleavage, with FXI converting to the active serine protease form (FXIa). The evolutionary origins of FXI trace back to duplication of the gene that transcribes plasma prekallikrein, a key factor in the plasma kallikrein-kinin system, before further genetic divergence led to FXI playing a unique role in blood coagulation. While FXIa is canonically known for activating the intrinsic pathway of coagulation by catalyzing the conversion of FIX into FIXa, it is promiscuous in nature and has been shown to contribute to thrombin generation independent of FIX. In addition to its role in the intrinsic pathway of coagulation, FXI also interacts with platelets, endothelial cells, and mediates the inflammatory response through activation of FXII and cleavage of high-molecular-weight kininogen to generate bradykinin. In this manuscript, we critically review the current body of knowledge surrounding how FXI navigates the interplay of hemostasis, inflammatory processes, and the immune response and highlight future avenues for research. As FXI continues to be clinically explored as a druggable therapeutic target, understanding how this coagulation factor fits into physiological and disease mechanisms becomes increasingly important.

Determinants of Arterial Stiffness in Patients with Morbid Obesity. The Role of Echocardiography and Carotid Ultrasound Imaging

Background and objective: Morbid obesity is accompanied by an increased cardiovascular (CV) risk, which justifies a multidisciplinary, integrative approach. Arterial stiffness has a well-defined additional role in refining individual CV risk. Given that echocardiography and carotid ultrasound are usual methods for CV risk characterization, we aimed to identify the imaging parameters with a predictive value for early-onset arterial stiffness. Material and methods: We conducted a study in which 50 patients (divided into two equal groups with morbid obesity and without obesity), age and gender matched, untreated for cardiovascular risk factors, were addressed to bariatric surgery or non-inflammatory benign pathology surgery. Before the surgical procedures, we evaluated demographics, anthropometric data and biochemical parameters including adipokines (chemerin, adiponectin). Arterial stiffness was evaluated using the Medexpert ArteriographTM TL2 device. Transthoracic echocardiography and carotid ultrasound were also performed. We also analyzed adipocyte size and vascular wall thickness in intraoperative biopsies. Results: Left ventricle (LV) mass index (p = 0.2851), LV ejection fraction (LVEF) (p = 0.0073), epicardial adipose tissue thickness (p = 0.0001) as echocardiographic parameters and carotid intima–media thickness (p = 0.0033), relative wall thickness (p = 0.0295), wall to lumen thickness ratio (p = 0.0930) and carotid cross-sectional area (p = 0.0042) as ultrasound parameters were significant measures in our groups and were assessed in relation to adipocyte size, blood vessel wall thickness and adipokines serum levels. Statistical analysis revealed directly proportional relationships between LV mass index (p = 0.008), carotid systolic thickness of the media (p = 0.009), diastolic thickness of the media (p = 0.007), cross-sectional area (p = 0.001) and blood vessel wall thickness. Carotid relative wall thickness positively correlates with adipocyte size (p = 0.023). In patients with morbid obesity, chemerin and adiponectin/chemerin ratio positively correlates with carotid intima–media thickness (p = 0.050), systolic thickness of the media (p = 0.015) and diastolic thickness of the media (p = 0.001). The multiple linear regression models revealed the role of epicardial adipose tissue thickness and carotid cross-sectional area in predicting adipocyte size which in turn is an independent factor for arterial stiffness parameters such as pulse wave velocity, subendocardial viability ratio and aortic augmentation index. Conclusions: Our results suggest that epicardial adipose tissue thickness, carotid intima–media thickness, relative wall thickness and carotid cross-sectional area might be useful imaging parameters for early prediction of arterial stiffness in patients with morbid obesity.

Chronic Resistance Training Effects on Serum Adipokines in Type 2 Diabetes Mellitus: A Systematic Review

(1) Background: Non-communicable diseases (NCD) are an important concern for public health because of their high rates of morbidity and mortality. A prevalent lifestyle-linked NCD is type 2 diabetes mellitus (T2D). Recently, molecular biomarkers secreted by adipocytes, called adipokines, have been linked with T2D and muscle function disturbances. However, the effects of resistance training (RT) interventions on adipokine levels in patients with T2D have not been systematically studied. (2) Methods: The PRISMA guidelines were followed. Searches for the studies were performed in the PubMed/MEDLINE and Web of Science electronic databases. Eligibility criteria included: (i) participants with T2D; (ii) RT interventions; (iii) randomized controlled trials; and (iv) measurement of serum adipokines. The PEDro scale was used to assess the methodological quality of the selected studies. Significant differences (p ≤ 0.05) and effect size were screened for each variable. (3) Results: Of the initial 2166 records, database search extraction yielded 14 studies to be included. The methodological quality of the included data was high (median PEDro score of 6.5). Analyzed adipokines in the included studies were leptin, adiponectin, visfatin, apelin, resistin, retinol-binding protein 4 (RBP4), vaspin, chemerin, and omentin. RT interventions (6-52 weeks; minimal effective duration >12 weeks) exert a meaningful effect on serum adipokine, (e.g., leptin) levels in T2D patients. (4) Conclusions: RT may be an alternative, but not an optimal, option in adipokine disruptions in T2D. Combined (i.e., aerobic and RT) long-term training may be considered the optimal intervention for treating adipokine level disturbances.

Chemerin levels in chronic kidney disease: A systematic review and meta-analysis

INTRODUCTION

Chemerin as an inflammatory biomarker has gained attention in its biomarker capability. Several studies measured its levels in chronic kidney disease (CKD), as one of the common non-communicable causes of mortality and morbidity. Hence, this systematic review and meta-analysis aimed to investigate this association.

METHODS

PubMed, Scopus, Embase, and the Web of Science databases were systematically searched for studies investigating chemerin levels in any CKD stage (including end-stage renal disease patients undergoing hemodialysis (HD)) and comparing it with healthy controls. Random effect meta-analysis was performed to calculate the standardized mean difference (SMD) and 95% confidence interval (CI).

RESULTS

A total of eight studies were included, comprised of 875 individuals, with a mean age of 56.92 ± 11.78 years. All studies had high quality based on the New Castle-Ottawa Scale (NOS). Meta-analysis revealed significantly higher levels of chemerin in CKD patients compared to healthy controls (SMD 2.15, 95% CI 0.83-3.48, p-value<0.01). Additionally, HD patients had statistically higher levels of chemerin than controls (SMD 2.10, 95% CI 0.58-3.62, p-value=0.01). In meta-regression, publication year accounted for 23.50% and 24.17% of heterogeneity for these analyses, respectively.

CONCLUSION

Chemerin can be potentially used as a biomarker in CKD patients, which can suggest the inflammatory pathways for the disease. Further research is warranted for the assessment of its clinical applications and enlightening its role in the pathophysiology of CKD.

Global hypo-methylation in a proportion of glioblastoma enriched for an astrocytic signature is associated with increased invasion and altered immune landscape

We describe a subset of glioblastoma, the most prevalent malignant adult brain tumour, harbouring a bias towards hypomethylation at defined differentially methylated regions. This epigenetic signature correlates with an enrichment for an astrocytic gene signature, which together with the identification of enriched predicted binding sites of transcription factors known to cause demethylation and to be involved in astrocytic/glial lineage specification, point to a shared ontogeny between these glioblastomas and astroglial progenitors. At functional level, increased invasiveness, at least in part mediated by SRPX2, and macrophage infiltration characterise this subset of glioblastoma.

Role of Chemerin in Cardiovascular Diseases

(1) Background: Obesity is closely connected to the pathophysiology of cardiovascular diseases (CVDs). Excess fat accumulation is associated with metabolic malfunctions that disrupt cardiovascular homeostasis by activating inflammatory processes that recruit immune cells to the site of injury and reduce nitric oxide levels, resulting in increased blood pressure, endothelial cell migration, proliferation, and apoptosis. Adipose tissue produces adipokines, such as chemerin, that may alter immune responses, lipid metabolism, vascular homeostasis, and angiogenesis. (2) Methods: We performed PubMed and MEDLINE searches for articles with English abstracts published between 1997 (when the first report on chemerin identification was published) and 2022. The search retrieved original peer-reviewed articles analyzed in the context of the role of chemerin in CVDs, explicitly focusing on the most recent findings published in the past five years. (3) Results: This review summarizes up-to-date findings related to mechanisms of chemerin action, its role in the development and progression of CVDs, and novel strategies for developing chemerin-targeting therapeutic agents for treating CVDs. (4) Conclusions: Extensive evidence points to chemerin's role in vascular inflammation, angiogenesis, and blood pressure modulation, which opens up exciting perspectives for developing chemerin-targeting therapeutic agents for the treatment of CVDs.

Urinary chemerin as a potential biomarker for inflammatory bowel disease

Purpose

Systemic levels of the adipokine chemerin are elevated in different inflammatory conditions such as inflammatory bowel disease (IBD). In IBD, chemerin protein expression in colon mucosa is induced and serum chemerin levels are increased. Aim of this study was to identify chemerin protein in human feces and/or urine and to evaluate a possible association with IBD activity.

Materials and methods

Feces and urine of 40 patients with IBD and the respective sera of 34 patients were collected. Chemerin levels were analyzed by immunoblot in feces and urine samples. In addition, enzyme-linked immunosorbent assay (ELISA) was used to measure chemerin in all urine, feces and serum samples of the patients and in urine of 17 healthy controls.

Results

Chemerin was not detectable in 80% of the human feces samples by ELISA. Chemerin in human urine was detected by immunoblot and ELISA. Compared to serum levels, urinary concentration was about 6,000-fold lower. Urinary chemerin did not differ between patients with ulcerative colitis (n = 15) and Crohn's disease (n = 25). Urinary chemerin was not related to its serum levels, did not correlate with serum C-reactive protein level and negatively correlated with serum creatinine. Of note, urinary chemerin of patients with a fecal calprotectin > 500 μg/g was significantly higher compared to patients with lower calprotectin levels and compared to healthy controls. Serum creatinine did not differ between the patient groups.

Conclusion

Urinary chemerin might present a novel non-invasive biomarker for monitoring IBD severity and clinical course.

The influence of selection in wild pheasant (Phasianus colchicus) breeding on reproduction and the involvement of the chemerin system

Chemerin is a hormone produced mainly by adipose tissue and liver. We have recently shown that it is locally produced in the reproductive tract in hens, particularly at the magnum level, leading to its accumulation in the egg albumen. We have also determined that chemerin is necessary for egg fertilization, embryo development, and angiogenesis within the chorio-allantoic membrane in chicken species. We, therefore, hypothesize that chemerin, widely present in various gallinacean species, could be a marker of egg fertility in this animal order. To demonstrate this, we used a model close to the hen: the pheasant. By RT-qPCR, we have shown that chemerin and its three receptors CMKLR1, GPR1, and CCRL2 are expressed in the reproductive tract of females. In addition, chemerin is also produced predominantly in the magnum and accumulates in the egg albumen as determined by immunoblot. We then compared two lines of pheasants with different reproductive characteristics: the F11 and F22 breeds. F22 lays more eggs than F11, but have significantly lower fertility and hatchability rates. In addition, F22 exhibit a significantly lower amount of chemerin protein in their magnum (P < 0.01) and in the egg albumen (P < 0.0001) compared to F11. Finally, we observed a positive correlation between the chemerin amount in the albumen of F11 eggs and the hatching rate of the eggs (r = 0.5; P = 0.04) as well as a negative correlation between the chemerin quantity in the albumen of F22 eggs and the rate of unfertilized eggs (r = -0.37; P = 0.04). Finally, chemerin system (ligand and receptors) is also expressed within embryo annexes (chorioallantoic and amniotic membranes) during incubation. These data demonstrate an interspecies conservation of chemerin production in the magnum, its accumulation in the egg albumen and its possible use as a marker for determining the quality of eggs in term of fertility and embryo development.

Chicken white egg chemerin as a tool for genetic selection for egg weight and hen fertility

Embryo mortality rate, which can reach up to 40% in avian species, is a major issue for breeding. It is therefore important to identify new embryo development biomarkers for genetic selection to improve reproductive performances. We have recently shown that chemerin is expressed in the oviductal hen magnum, accumulates in egg white, is correlated with embryo survival and could thus be used as a molecular marker of embryo development. Eggs from seven hen breeds (n = 70) were collected during five successive days at the end of the laying period. After weighing eggs, yolk and albumen, an egg white sample from each egg was collected and a blood sample was taken from each hen. Chemerin concentrations in albumen and blood samples were measured by a specific home made ELISA assay. Hen's plasma and egg's albumen chemerin levels were found to be correlated with reproductive parameters such as fecundity, fertility, embryo mortality, hatchability and laying rates. The inter-hen chemerin level variability in albumen was higher than intra-hen except for one breed (R+). We observed significantly different levels of chemerin in egg white between breeds. However, chemerin concentrations in egg white were not significantly associated to variations of hen plasma chemerin levels. Interestingly, we observed negative correlations between albumen chemerin concentrations and egg weight (r = -0.43, p = 0.001), between albumen weight (r = -0.40, p = 0.002), and between yolk weight (r = -0.28, p = 0.03). We also showed negative correlations between egg white chemerin concentrations and fecundity (r = -0.32, p = 0.011) and fertility (r = -0.27, p = 0.04) whereas no significant correlation was observed with the laying rate. Taken together, these results suggest that egg white chemerin concentration might be a good biomarker for genetic selection for egg weight and fertility in hens, provided these data are confirmed on a larger scale.

Exploring CCRL2 chemerin binding using accelerated molecular dynamics

Chemokine (C–C motif) receptor‐like 2 (CCRL2), is a seven transmembrane receptor closely related to the chemokine receptors CCR1, CCR2, CCR3, and CCR5. Nevertheless, CCRL2 is unable to activate conventional G‐protein dependent signaling and to induce cell directional migration. The only commonly accepted CCRL2 ligand is the nonchemokine chemotactic protein chemerin (RARRES2). The chemerin binding to CCLR2 does induce leukocyte chemotaxis, yet, genetic targeting of CCRL2 was shown to modulate the inflammatory response in different experimental models. This mechanism was shown to be crucial for lung dendritic cell migration, neutrophil recruitment, and Natural Killer cell‐dependent immune surveillance in lung cancer. To gain more insight in the interactions involved in the CCRL2‐chemerin, the binding complexes were generated by protein–protein docking, then submitted to accelerated molecular dynamics. The obtained trajectories were inspected by principal component analyses followed by kernel density estimation to identify the ligand‐receptor regions most frequently involved in the binding. To conclude, the reported analyses led to the identification of the putative hot‐spot residues involved in CCRL2‐chemerin binding.

Divergence of Chemerin Reduction by an ATS9R Nanoparticle Targeting Adipose Tissue In Vitro vs. In Vivo in the Rat

Nanoparticles (NPs) can enable delivery of a drug to a targeted tissue. Previous studies have shown that an NP utilizing an adipose targeting sequence (ATS) peptide in conjunction with a drug can selectively deliver the drug to mouse adipose tissues, using the prohibitin protein expressed in adipose tissue as the target of the ATS. Adipose tissue is a major source of the adipokine chemerin, a prohypertensive protein. Liver-derived chemerin, the largest source of circulating chemerin, is biologically inactive in blood pressure regulation. Our goal is to understand if chemerin produced in adipose tissue contributes to blood pressure/hypertension. We hypothesize the ATS drug delivery system could be used specifically to reduce the levels of adipose tissue-derived chemerin. We created an NP consisting of an antisense oligonucleotide (ASO) against chemerin and a FITC-labeled ATS with a nine arginine sequence (ATS9R). In vitro studies showed that the ASO is functional when incorporated into an NP with ATS9R as it reduced chemerin mRNA expression in isolated epidydimal (Epi) and retroperitoneal (RP) fat adipocytes from Dahl SS rats. This same NP reduced chemerin in isolated whole fats. However, this NP was unable to selectively deliver the ASO to adipose tissue in vivo; liver delivery was dominant. Varying NP doses, administration route, and the concentration of components constituting the NP showed no improvement in ASO delivery to fats vs. the liver. Further studies are therefore needed to develop the ATS9R system to deliver an ASO to adipose beds in rats.

Chemerin is secreted by the chicken oviduct, accumulates in egg albumen and could promote embryo development

Understanding of the distribution of chemerin and its receptors, Chemokine-like Receptor 1 (CMKLR1), G Protein-coupled Receptor 1 (GPR1) and Chemokine (C–C motif) receptor-like 2 (CCRL2), in the egg and the embryonic annexes is currently lacking, and their role during embryogenesis remains unknown. By immunoblot using monoclonal anti-chicken antibodies and Enzyme Linked Immunosorbent Assays (ELISA), we found that chemerin is expressed 10 times higher in albumen eggs than in blood plasma, and it is also abundant in the perivitelline membrane but undetectable in yolk. Chicken chemerin can inhibit bacterial growth. By Reverse Transcription—quantitative Polymerisation Chain Reaction (RT-qPCR), western-blot, and immunofluorescence, we show that chemerin is locally produced by the oviduct magnum that participates in albumen formation. Using cultures of magnum explants, we demonstrate that progesterone (P4) and oestradiol (E2) treatment increases chemerin secretion into cultured media and expression in magnum. Chemerin and its three receptors are present in amniotic and Chorio Allantoic Membranes (CAM). Only CMKLR1 expression decreased from embryonic day (ED) 7 to ED11 and remained low until ED18. Chemerin concentrations strongly increased in amniotic fluid at D14 when egg albumen crossed the amniotic membrane. In ovo injections of neutralising chemerin and CMKLR1 antibodies (0.01, 0.1 and 1 µg) increased embryo mortality, which occurred mainly at ED12-13, in a dose-dependent manner. Chemerin treatment increased primary CAM viability. Finally, chemerin and CMKLR1 inhibition within the CAM led to a decrease in blood vessel development and associated angiogenic gene expression. Our results show an important function of the chemerin system during embryo development in chickens, suggesting the potential use of this adipokine as a predictive marker for egg fertility or hatchability.

Association of serum omentin-1, apelin and chemerin concentrations with the presence and severity of diabetic retinopathy in type 2 diabetes mellitus patients

Omentin-1 is a novel adipokine with anti-inflammatory functions. Apelin is associated with hyperinsulinemia and pathological angiogenesis. Chemerin has both pro- and anti-inflammatory actions and implicated in insulin resistance and metabolic syndrome. The aim of this study was to assess serum omentin-1, apelin and chemerin concentrations and to investigate their association with the presence and severity of DR in T2DM patients. Serum omentin-1, apelin and chemerin were measured in 112 patients with DR and 56 patients without DR. Bivariate analysis showed omentin-1 correlated negatively with hsCRP and TyG index; while apelin correlated positively with chemerin. Linear regression data showed that apelin and chemerin were independent predictors of DR severity. ROC curve revealed that omentin-1 was the best discriminant for DR while apelin was the best discriminant for vision threatening retinopathy. Serum omentin-1 concentration correlates negatively, while serum apelin and chemerin concentrations correlate positively with DR presence and severity in T2DM patients.

Chemerin Effect on the Endometrial Proteome of the Domestic Pig during Implantation Obtained by LC-MS/MS Analysis

Chemerin (CHEM) is a hormone mainly expressed in adipocytes involved in the regulation of energy homeostasis and inflammatory response. CHEM expression has been demonstrated in the structures of the porcine hypothalamic-pituitary-gonadal axis, as well as in the uterus, trophoblasts and conceptuses of pigs. In this study, we performed high-throughput proteomic analyses (liquid chromatography with tandem mass spectrometry, LC-MS/MS) to examine the influence of CHEM (400 ng/mL) on differentially regulated proteins (DRPs) in the porcine endometrial tissue explants during implantation (15 to 16 days of gestation). Among all 352 DRPs, 164 were up-regulated and 188 were down-regulated in CHEM-treated group. DRPs were assigned to 47 gene ontology (GO) terms (p-adjusted < 0.05). Validation of four DRPs (IFIT5, TGFβ1, ACO1 and PGRMC1) by Western blot analysis confirmed the veracity and accuracy of the LC-MS/MS method used in the present study. We suggest that CHEM, by modulating various protein expressions, takes part in the endometrial cell proliferation, migration and invasion at the time of implantation. It also regulates the endometrial immune response, sensitivity to P4 and the formation of new blood vessels. Additionally, CHEM appears to be an important factor involved in endothelial cell dysfunction during the pathogenesis of preeclampsia. The identification of a large number of DRPs under the influence of CHEM provides a valuable resource for understanding the molecular mechanisms of this hormone action during implantation, which is a prerequisite for better control of pig reproduction.

Competitive Hybridization of a Microarray Identifies CMKLR1 as an Up-Regulated Gene in Human Bone Marrow-Derived Mesenchymal Stem Cells Compared to Human Embryonic Fibroblasts

Mesenchymal stem cells (MSCs) have been widely applied to the regeneration of damaged tissue and the modulation of immune response. The purity of MSC preparation and the delivery of MSCs to a target region are critical factors for success in therapeutic application. In order to define the molecular identity of an MSC, the gene expression pattern of a human bone marrow-derived mesenchymal stem cell (hBMSC) was compared with that of a human embryonic fibroblast (hEF) by competitive hybridization of a microarray. A total of 270 and 173 genes were two-fold up- and down-regulated with FDR < 0.05 in the hBMSC compared to the hEF, respectively. The overexpressed genes in the hBMSC over the hEF, including transcription factors, were enriched for biological processes such as axial pattern formation, face morphogenesis and skeletal system development, which could be expected from the differentiation potential of MSCs. CD70 and CD339 were identified as additional CD markers that were up-regulated in the hBMSC over the hEF. The differential expression of CD70 and CD339 might be exploited to distinguish hEF and hBMSC. CMKLR1, a chemokine receptor, was up-regulated in the hBMSC compared to the hEF. RARRES2, a CMKLR1 ligand, stimulated specific migration of the hBMSC, but not of the hEF. RARRES2 manifested as ~two-fold less effective than SDF-1α in the directional migration of the hBMSC. The expression of CMKLR1 was decreased upon the osteoblastic differentiation of the hBMSC. However, the RARRES2-loaded 10% HA-silk scaffold did not recruit endogenous cells to the scaffold in vivo. The RARRES2−CMKLR1 axis could be employed in recruiting systemically delivered or endogenous MSCs to a specific target lesion.

New Aspects of Corpus Luteum Regulation in Physiological and Pathological Conditions: Involvement of Adipokines and Neuropeptides

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.

Chemerin Impact on Alternative mRNA Transcription in the Porcine Luteal Cells

Chemerin participates in the regulation of processes related to physiological and disorder mechanisms in mammals, including metabolism, obesity, inflammation, and reproduction. In this study, we have investigated chemerin influence on alternative mRNA transcription within the porcine luteal cell transcriptome, such as differential expression of long non-coding RNAs (DELs) and their interactions with differentially expressed genes (DEGs), differences in alternative splicing of transcripts (DASs), and allele-specific expression (ASEs) related to the single nucleotide variants (SNVs) frequency. Luteal cells were collected from gilts during the mid-luteal phase of the oestrous cycle. After in vitro culture of cells un-/treated with chemerin, the total RNA was isolated and sequenced using the high-throughput method. The in silico analyses revealed 24 DELs cis interacting with 6 DEGs and trans-correlated with 300 DEGs, 137 DASs events, and 18 ASEs. The results enabled us to analyse metabolic and signalling pathways in detail, providing new insights into the effects of chemerin on the corpus luteum functions related to inflammatory response, leukocyte infiltration, the occurrence of luteotropic and luteolytic signals (leading to apoptosis and/or necroptosis). Validation of the results using qPCR confirmed the predicted expression changes. Chemerin at physiological concentrations significantly modifies the transcription processes in the porcine luteal cells.

Circulating Chemerin and Its Kinetics May Be a Useful Diagnostic and Prognostic Biomarker in Critically Ill Patients with Sepsis: A Prospective Study

Chemerin, a novel adipokine, is a potent chemoattractant molecule with antimicrobial properties, implicated in immune responses. Our aim was to investigate circulating chemerin and its kinetics, early in sepsis in critically ill patients and its association with severity and prognosis. Serum chemerin was determined in a cohort of 102 critically ill patients with sepsis during the first 48 h from sepsis onset and one week later, and in 102 age- and gender-matched healthy controls. Patients were followed for 28 days and their outcomes were recorded. Circulating chemerin was significantly higher in septic patients at onset compared to controls (342.3 ± 108.1 vs. 200.8 ± 40.1 μg/L, p < 0.001). Chemerin decreased significantly from sepsis onset to one week later (342.3 ± 108.1 vs. 308.2 ± 108.5 μg/L, p < 0.001), but remained higher than in controls. Chemerin was higher in patients presenting with septic shock than those with sepsis (sepsis onset: 403.2 ± 89.9 vs. 299.7 ± 99.5 μg/L, p < 0.001; one week after: 374.9 ± 95.3 vs. 261.6 ± 91.9 μg/L, p < 0.001), and in nonsurvivors than survivors (sepsis onset: 427.2 ± 96.7 vs. 306.9 ± 92.1 μg/L, p < 0.001; one week after: 414.1 ± 94.5 vs. 264.2 ± 79.9 μg/L, p < 0.001). Moreover, patients with septic shock and nonsurvivors, presented a significantly lower absolute and relative decrease in chemerin one week after sepsis onset compared to baseline (p < 0.001). Based on ROC curve analyses, the diagnostic performance of chemerin (AUC 0.78, 95% CI 0.69–0.87) was similar to C-reactive protein (CRP) (AUC 0.78, 95% CI 0.68–0.87) in discriminating sepsis severity. However, increased chemerin at sepsis onset and one week later was an independent predictor of 28-day mortality (sepsis onset: HR 3.58, 95% CI 1.48–8.65, p = 0.005; one week after: HR 10.01, 95% CI 4.32–23.20, p < 0.001). Finally, serum chemerin exhibited significant correlations with the severity scores, white blood cells, lactate, CRP and procalcitonin, as well as with biomarkers of glucose homeostasis, but not with cytokines and soluble urokinase-type plasminogen activator receptor (suPAR). Circulating chemerin is increased early in sepsis and its kinetics may have diagnostic and prognostic value in critically ill patients. Further studies are needed to shed light on the role of chemerin in sepsis.

Role of chemerin in the control of glucose homeostasis

Chemerin is an adipokine produced by the white adipose tissue and other tissues, which plays various roles in the pathogenesis of inflammatory and metabolic diseases in multiple organs. The present review aims at gathering scientific evidence reported in the last ten years, concerning the relationship of chemerin with alterations of glycaemic control, such as insulin resistance, type 2 diabetes and gestational diabetes in humans. Although the vast majority of the studies have shown a positive correlation between the chemerin level and a bad glycaemic control, a general consensus has not been reached. The reported results come from case-control and observational longitudinal studies, thereby limiting their interpretation. In fact, it cannot be stated whether insulin resistance and diabetes lead to an increase in chemerin levels or, on the contrary, if high levels of chemerin contribute to an impaired glycaemic control. Elevated levels of circulating chemerin are also associated with gestational diabetes mellitus. Chemerin gene polymorphisms could be proposed as mediators of glucose-related diseases. Nevertheless, to date very little is known about their implication in glucose metabolism. With regard to the mechanisms of action, chemerin impairs insulin cascade signaling by acting on several proteins of this cascade and by inducing inflammation.

Placental Trophoblast Specific Overexpression of Chemerin Induces Preeclampsia-like Symptoms

Maternal circulating levels of the adipokine chemerin are elevated in preeclampsia, but its origin and contribution to preeclampsia remain unknown. We therefore studied 1) placental chemerin expression and release in human pregnancy, and 2) the consequences of chemerin overexpression via lentivirus-mediated trophoblast-specific gene manipulation in both mice and immortalized human trophoblast. Placental chemerin expression and release were increased in women with preeclampsia, and their circulating chemerin levels correlated positively with the soluble Fms-like tyrosine kinase-1 (sFlt-1)/placental growth factor ratio, a well-known biomarker of preeclampsia severity. Placental trophoblast chemerin overexpression in mice induced a preeclampsia-like syndrome, involving hypertension, proteinuria, and endotheliosis, combined with diminished trophoblast invasion, a disorganized labyrinth layer, and upregulation of sFlt-1 and the inflammation markers nuclear factor-kappa B, tumor necrosis factor-α and interleukin-1β. It also led to embryo resorption, while maternal serum chemerin levels correlated negatively with fetal weight in mice. Chemerin overexpression in human trophoblasts upregulated sFlt-1, reduced vascular endothelial factor-A, and inhibited migration and invasion, as well as tube formation during co-culture with human umbilical vein endothelial cells. The chemokine-like receptor 1 (CMKLR1) antagonist α-NETA prevented the latter phenomena, although it did not reverse the chemerin-induced downregulation of the phosphoinositide 3-kinase/Akt pathway. In conclusion, upregulation of placental chemerin synthesis disturbs normal placental development via its CMKLR1 receptor, thereby contributing to fetal growth restriction/resorption and the development of preeclampsia. Chemerin might be a novel biomarker of preeclampsia, and inhibition of the chemerin/CMKLR1 pathway is a promising novel therapeutic strategy to treat preeclampsia.

Chemerin - exploring a versatile adipokine

Chemerin is a small chemotactic protein and a key player in initiating the early immune response. As an adipokine, chemerin is also involved in energy homeostasis and the regulation of reproductive functions. Secreted as inactive prochemerin, it relies on proteolytic activation by serine proteases to exert biological activity. Chemerin binds to three distinct G protein-coupled receptors (GPCR), namely chemokine-like receptor 1 (CMKLR1, recently named chemerin₁), G protein-coupled receptor 1 (GPR1, recently named chemerin₂), and CC-motif chemokine receptor-like 2 (CCRL2). Only CMKLR1 displays conventional G protein signaling, while GPR1 only recruits arrestin in response to ligand stimulation, and no CCRL2-mediated signaling events have been described to date. However, GPR1 undergoes constitutive endocytosis, making this receptor perfectly adapted as decoy receptor. Here, we discuss expression pattern, activation, and receptor binding of chemerin. Moreover, we review the current literature regarding the involvement of chemerin in cancer and several obesity-related diseases, as well as recent developments in therapeutic targeting of the chemerin system.

Chemerin Affects P4 and E2 Synthesis in the Porcine Endometrium during Early Pregnancy

Chemerin, belonging to the adipokine family, exhibits pleiotropic activity. We hypothesised that the adipokine could be involved in the regulation of steroidogenesis in the porcine endometrium. Thus, the aim of this study was to determine the effect of chemerin on the key steroidogenic enzyme proteins' abundance (Western blot), as well as on P4 and E2 secretion (radioimmunoassay) by the porcine endometrium during early pregnancy and the mid-luteal phase of the oestrous cycle. Moreover, we investigated the hormone impact on Erk and Akt signalling pathway activation (Western blot). Chemerin stimulated E2 production on days 10 to 11 of pregnancy. On days 10 to 11 and 15 to 16 of gestation, and on days 10 to 11 of the cycle, chemerin enhanced the expression of StAR and all steroidogenic enzyme proteins. On days 12 to 13 of pregnancy, chemerin decreased StAR and most of the steroidogenic enzyme proteins' abundance, whereas the P450C17 abundance was increased. On days 27 to 28 of pregnancy, chemerin increased StAR and P450C17 protein contents and decreased 3βHSD protein amounts. It was noted that the adipokine inhibited Erk1/2 and stimulated Akt phosphorylation. The obtained results indicate that chemerin affected P4 and E2 synthesis through the Erk1/2 and Akt signalling pathways.

Development of metabolic dysfunction in mice lacking chemerin

Chemerin, an adipocyte-secreted adipokine, is hypothesized to participate in energy homeostasis and glucoregulation. However, the physiologic effect of endogenous chemerin on glucose metabolism is unclear. The present studies tested the hypotheses that chemerin deficiency alters whole-body glucose homeostasis following switches to high-fat diet. Adult, male chemerin knockout and C57BL/6J control wild type mice were studied. During the following 4 weeks, chow- or high-fat diet maintained chemerin knockout mice showed elevated fasting glucose levels and glucose intolerance as well as insulin intolerance. Chemerin deficiency impaired adaptation to glucose and insulin challenge, leading to increased glucose levels. Moreover, the mRNA and protein levels of GLUT4 and PGC-1α expression in both skeletal muscle and adipose tissue were significantly decreased in chemerin knockout mice relative to the wild type, respectively. Taken together, the results support the hypotheses that chemerin helps adapt glucose metabolism to changes in dietary fat and modulates glucose consumption in mice by activation of PGC-1α/GLUT4 axis. Chemerin may play a significant role in elevation of glucose uptake and insulin sensitivity to promote glucose clearance.

Adipokines in metabolic and reproductive functions in birds: An overview of current knowns and unknowns

Adipose tissue is now recognized as an active endocrine organ, which synthesizes and secretes numerous peptides factors called adipokines. In mammals, they exert pleiotropic effects affecting energy metabolism but also fertility. In mammals, secretion of adipokines is altered in adipose tissue dysfunctions and may participate to obesity-associated disorders. Thus, adipokines are promising candidates both for novel pharmacological treatment strategies and as diagnostic tools. As compared to mammals, birds exhibit several unique physiological features, which make them an interesting model for comparative studies on endocrine control of metabolism and adiposity and reproductive functions. Some adipokines such as leptin and visfatin may have different roles in avian species as compared to mammals. In addition, some of them found in mammals such as CCL2 (chemokine ligand 2), resistin, omentin and FGF21 (Fibroblast Growth factor 21) have not yet been mapped to the chicken genome model and among its annotated gene models. This brief review aims to summarize data (structure, metabolic and reproductive roles and molecular mechanisms involved) related to main avian adipokines (leptin, adiponectin, visfatin, and chemerin) and we will briefly discuss the adipokines that are still lacking in avian species.

Fetal programming by androgen excess impairs liver lipid content and PPARg expression in adult rats

It is known that prenatal hyperandrogenization induces alterations since early stages of life, contributing to the development of polycystic ovary syndrome affecting the reproductive axis and the metabolic status, thus promoting others associated disorders, such as dyslipidemia, insulin resistance, liver dysfunction, and even steatosis. In this study, we aimed to evaluate the effect of fetal programming by androgen excess on the hepatic lipid content and metabolic mediators at adult life. Pregnant rats were hyperandrogenized with daily subcutaneous injections of 1 mg of free testosterone from days 16 to 19 of pregnancy. The prenatally hyperandrogenized (PH) female offspring displayed two phenotypes: irregular ovulatory phenotype (PHiov) and anovulatory phenotype (PHanov), with different metabolic and endocrine features. We evaluated the liver lipid content and the main aspect of the balance between fatty acid (FA) synthesis and oxidation. We investigated the status of the peroxisomal proliferator-activated receptors (PPARs) alpha and gamma, which act as lipid mediators, and the adipokine chemerin, one marker of liver alterations. We found that prenatal hyperandrogenization altered the liver lipid profile with increased FAs levels in the PHanov phenotype and decreased cholesterol content in the PHiov phenotype. FA metabolism was also disturbed, including decreased mRNA and protein PPARgamma levels and impaired gene expression of the main enzymes involved in lipid metabolism. Moreover, we found low chemerin protein levels in both PH phenotypes. In conclusion, these data suggest that prenatal hyperandrogenization exerts a negative effect on the liver and alters lipid content and metabolic mediators' expression at adult age.

Ligand-binding and -scavenging of the chemerin receptor GPR1

Tight regulation of cytokines is essential for the initiation and resolution of inflammation. Chemerin, a mediator of innate immunity, mainly acts on chemokine-like receptor 1 (CMKLR1) to induce the migration of macrophages and dendritic cells. The role of the second chemerin receptor, G protein-coupled receptor 1 (GPR1), is still unclear. Here we demonstrate that GPR1 shows ligand-induced arrestin3 recruitment and internalization. The chemerin C-terminus triggers this activation by folding into a loop structure, binding to aromatic residues in the extracellular loops of GPR1. While this overall binding mode is shared between GPR1 and CMKLR1, differences in their respective extracellular loop 2 allowed for the design of the first GPR1-selective peptide. However, our results suggest that ligand-induced arrestin recruitment is not the only mode of action of GPR1. This receptor also displays constitutive internalization, which allows GPR1 to internalize inactive peptides efficiently by an activation-independent pathway. Our results demonstrate that GPR1 takes a dual role in regulating chemerin activity: as a signaling receptor for arrestin-based signaling on one hand, and as a scavenging receptor with broader ligand specificity on the other.

Adipokines as biomarkers of postpartum subclinical endometritis in dairy cows

Adipokines emerged as regulators of metabolism and inflammation in several scenarios. This study evaluated the relationship between adipokines (adiponectin, chemerin and visfatin) and cytological (subclinical) endometritis, by comparing healthy (without), transient (recovered by 45 days postpartum (DPP)) and persistent (until 45 DPP) endometritis cows (n = 49). Cows with persistent endometritis had higher adiponectin concentrations in plasma (at 21 DPP, P < 0.05 and at 45 DPP, P < 0.01) and in uterine fluid (at 45 DPP, P < 0.001), and higher chemerin concentrations in plasma (P < 0.05) and uterine fluid (P < 0.01) at 45 DPP than healthy cows. Cows with persistent endometritis had higher gene transcription in the cellular pellet of uterine fluid and protein expression in the endometrium of these adipokines and their receptors than healthy cows. Adiponectin plasma concentrations allowed to discriminate healthy from persistent endometritis cows, in 87% (21 DPP) and 98% (45 DPP) of cases, and adiponectin and chemerin uterine fluid concentrations at 45 DPP allowed for this discrimination in 100% of cases. Cows with concentrations above the cutoff were a minimum of 3.5 (plasma 21 DPP), 20.4 (plasma 45 DPP), and 33.3 (uterine fluid 45 DPP) times more at risk of evidencing persistent endometritis at 45 DPP than cows with concentrations below the cutoff. Overall, results indicate a relationship between adipokine signalling and the inflammatory status of the postpartum uterus of dairy cows, evidencing that adipokines represent suitable biomarkers of subclinical endometritis, able to predict the risk of persistence of inflammation.

Discovery of chemerin as the new chemoattractant of human mesenchymal stem cells

Background

The homing capacity of human mesenchymal stem cells (hMSCs) to the injured sites enables systemic administration of hMSCs in clinical practice. In reality, only a small proportion of MSCs are detected in the target tissue, which is a major bottleneck for MSC-based therapies. We still don’t know the mechanism how MSCs are chemo-attracted to certain target organ and engrafted through trans-endothelial migration. In this study, we aimed to determine the mechanism how the circulating hMSCs home to the injured liver.

Methods and results

When we compare the cytokine array between normal and injured mouse liver at 1-day thioacetamide (TAA)-treatment, we found that chemerin, CXCL2, and CXCL10 were higher in the injured liver than normal one. Among three, only chemerin was the chemoattractant of hMSCs in 2D- and 3D-migration assay. Analysis of the signal transduction pathways in hMSCs showed that chemerin activated the phosphorylation of JNK1/2, ERK1/2 and p38, and finally upregulated CD44, ITGA4, and MMP-2 that are involved in the transendothelial migration and extravasation of MSCs. Upstream transcription regulators of CD44, ITGA4, and MMP-2 after chemerin treatment were MZF1, GATA3, STAT3, and STAT5A. To develop chemerin as a chemoattractant tool, we cloned gene encoding the active chemerin under the CMV promoter (CMV-aChemerin). We analyzed the migration of hMSCs in the 3D model for space of the Disse, which mimics transmigration of hMSCs in the liver. CMV-aChemerin-transfected hepatocytes were more effective to attract hMSC than control hepatocytes, leading to the enhanced transendothelial migration and homing of hMSCs to liver. The homing efficiency of the intravascularly-delivered hMSCs to liver was evaluated after systemic introduction of the CMV-aChemerin plasmid packed in liposome-vitamin A conjugates which target liver. CMV-aChemerin plasmid targeting liver significantly enhanced homing efficiency of hMSCs to liver compared with control plasmid vector.

Conclusions

Chemerin is the newly found chemoattractant of hMSCs and may be a useful tool to manipulate the homing of the intravascularly-administered hMSC to the specific target organ.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00631-3.

CHEMERIN as a modulator of angiogenesis and apoptosis processes in the corpus luteum of pigs: An in vitro study

The corpus luteum (CL) undergoes rapid changes, and its functional capabilities are influenced by processes such as angiogenesis and apoptosis. According to the literature, chemerin - a protein which participates in the regulation of energy homeostasis and the immune response, may also affect angiogenesis and apoptosis. Therefore, the aim of this study was to investigate the in vitro effect of chemerin on angiogenesis and apoptosis in porcine luteal cells (Lc) during specific phases related to CL physiology. Luteal cells were harvested from gilts during the early-, mid-, and late-luteal phases of the estrous cycle. The cells were preincubated for 48 h and incubated for 24 h with chemerin or a serum-free medium (controls). The abundance of angiogenesis- and apoptosis-related proteins was determined by ELISA in spent culture media, or by ELISA and Western Blot in protein extracts. The current study demonstrated that chemerin stimulates the production of VEGF-A and bFGF by porcine Lc and increases the protein abundance of angiogenic factors receptors (VEGFR1, VEGFR2, VEGFR3, FGFR1, FGFR2) in these cells. The study also revealed that chemerin exerts a modulatory effect (stimulatory/inhibitory, depending on the phase of the cycle) on the protein abundance of Fas, FasL, Bcl-2 and caspase-3 in porcine Lc. These results imply that chemerin may affect angiogenesis and apoptosis processes in the porcine CL, as evidenced by its modulatory effect of chemerin on the protein abundance of crucial angiogenesis- and apoptosis-related factors, observed in an in vitro study of porcine Lc.

Preoperative Chemerin Level Is Predictive of Inflammatory Status 1 Year After Bariatric Surgery

BACKGROUND

Obesity is associated with chronic low-grade inflammation, which has been linked to increased morbidity. However, inflammation variably and unpredictably improves after bariatric surgery. This study aimed at (1) evaluating the relationship between amplitude of weight loss and variation of inflammatory parameters after bariatric surgery, and (2) identifying, among clinical and biological baseline parameters, predictive factors of variation in inflammatory parameters.

METHODS

In a prospective cohort of patients who underwent bariatric surgery, serum concentrations of interleukin (IL)-6, IL-10, resistin, leptin, adiponectin chemerin, and C-reactive protein (CRP) were measured preoperatively and 1 year after surgery, and routine clinical and biochemical parameters were retrieved. Univariate and multivariate analyses (partial least square method) were performed to assess how parameters were associated with weight loss and to predict improvement of inflammatory parameters.

RESULTS

Eighty-seven patients were included (mean weight ± SD 136.3 ± 3.2 kg, 35 gastric bypasses, 52 sleeve gastrectomies). In parallel with weight loss (39.5 ± 13.8 kg), pro-inflammatory markers (IL-6, CRP, leptin, resistin) significantly decreased, and anti-inflammatory markers (IL-10, adiponectin) increased. Multivariate analysis revealed a significant association between weight loss and improvement in inflammatory parameters. Among all the clinical and biological preoperative parameters, baseline chemerin level was the only parameter that was significantly associated with global improvement of the inflammatory status after surgery.

CONCLUSION

The amplitude of weight loss 1 year after bariatric surgery was strongly correlated with improvement of inflammatory profile, which could be predicted by baseline plasma level of chemerin. This suggests a key role of chemerin in obesity-driven inflammation, and a potential use as a biomarker.

Chemerin impairs food intake and body weight in chicken: Focus on hypothalamic neuropeptides gene expression and AMPK signaling pathway

Unlike mammals, the role of adipokines and more particularly of chemerin in the regulation of food intake is totally unknown in avian species. Here we investigated the effect of chemerin on the food and water consumption and on the body weight in chicken. We studied the effects on the plasma glucose and insulin concentrations and the hypothalamic neuropeptides and AMPK signaling pathway. Female broiler chickens were intraperitoneally injected, daily for 13 days with either vehicle (saline; n = 25) or chemerin (8 μg/kg; n = 25 and 16 μg/kg; n = 25). Food and water intakes were recorded 24 h after each administration. Overnight fasted animals were sacrificed at day 13 (D13), 24 h after the last injection and hypothalamus and left cerebral hemispheres were collected. Chemerin and its receptors protein levels were determined by western-blot. Gene expression of neuropeptide Y (Npy), agouti-related peptide (Agrp), corticotrophin releasing hormone (Crh), pro-opiomelanocortin (Pomc), cocaine and amphetamine-regulated transcript (Cart) and Taste 1 Receptor Member 1 (Tas1r1) were evaluated by RT-qPCR. In chicken, we found that the protein amount of chemerin, CCRL2 and GPR1 was similar in left cerebral hemisphere and hypothalamus whereas CMKLR1 was higher in hypothalamus. Chemerin administration (8 and 16 μg/kg) decreased both food intake and body weight compared to vehicle without affecting water intake and the size or volume of different brain subdivisions as determined by magnetic resonance imaging. It also increased plasma insulin levels whereas glucose levels were decreased. These data were associated with an increase in Npy and Agrp expressions and a decrease in Crh, Tas1r1 mRNA expression within the hypothalamus. Furthermore, chemerin decreased hypothalamic CMKLR1 protein expression and AMPK activation. Taken together, these results support that chemerin could be a peripheral appetite-regulating signal through modulation of hypothalamic peptides expression in chicken.

The complex role of adipokines in obesity, inflammation, and autoimmunity

The global obesity epidemic is a major contributor to chronic disease and disability in the world today. Since the discovery of leptin in 1994, a multitude of studies have characterized the pathological changes that occur within adipose tissue in the obese state. One significant change is the dysregulation of adipokine production. Adipokines are an indispensable link between metabolism and optimal immune system function; however, their dysregulation in obesity contributes to chronic low-grade inflammation and disease pathology. Herein, I will highlight current knowledge on adipokine structure and physiological function, and focus on the known roles of these factors in the modulation of the immune response. I will also discuss adipokines in rheumatic and autoimmune diseases.

Cyclic Analogues of the Chemerin C-Terminus Mimic a Loop Conformation Essential for Activating the Chemokine-like Receptor 1

The chemokine-like receptor 1 (CMKLR1) is a promising target for treating autoinflammatory diseases, cancer, and reproductive disorders. However, the interaction between CMKLR1 and its protein-ligand chemerin remains uncharacterized, and no drugs targeting this interaction have passed clinical trials. Here, we identify the binding mode of chemerin-9, the C-terminus of chemerin, at the receptor by combining complementary mutagenesis with structure-based modeling. Incorporating our experimental data, we present a detailed model of this binding site, including experimentally confirmed pairwise interactions for the most critical ligand residues: Chemerin-9 residue F⁸ binds to a hydrophobic pocket in CMKLR1 formed by the extracellular loop (ECL) 2, while F⁶ interacts with Y^2.68, suggesting a turn-like structure. On the basis of this model, we created the first cyclic peptide with nanomolar activity, confirming the overall binding conformation. This constrained agonist mimics the loop conformation adopted by the natural ligand and can serve as a lead compound for future drug design.

Chemerin in inflammatory diseases

Obesity is associated with a series of health problems. Adipocytes are a huge repository of energy as well as an important source of many adipokines. In obesity, adipocytes are dysfunctional with excessive production and secretion of pro-inflammatory adipokines, such as tumor necrosis factor α (TNF-α), leptin, and chemerin. Recent studies have revealed that chemerin plays an important role in modulating physiologic as well as pathophysiologic processes. For example, chemerin stimulates maturation and differentiation of pre-adipocytes, acts as a chemoattractant and facilitates innate and acquired immunity. Furthermore, chemerin participates in the early stage of acute inflammation by reacting with the ChemR23 receptor. In various inflammatory diseases, the serum chemerin is significantly increased. Additionally, chemerin is also considered as an important biomarker for benign and malignant tumors. Thus, elucidating the pathologic mechanisms of chemerin action may facilitate the development of new therapeutic modalities to treat diverse inflammatory diseases. In this review, we summarize current knowledge of chemerin and its role as an important regulator in modulating various inflammatory diseases. Mechanisms underlying chemerin function in diverse diseases are explored to better understand its biochemistry and mechanisms of action.

Chemerin/ChemR23 regulates cementoblast function and tooth resorption in mice via inflammatory factors

BACKGROUND

Periodontitis and orthodontic treatment can lead to inflammatory root resorption (IRR) through an unclear mechanism. Chemerin, a novel chemoattractant protein, is closely associated with inflammation, affects osteoblast and osteoclast differentiation, and may play a role in IRR. We aimed to explore possible roles of the chemerin/ChemR23 interaction in cementoblast function and IRR and reveal a new IRR therapeutic target.

METHODS

Cementoblast function-related gene and protein expression in the immortalized murine cementoblast cell line OCCM-30 after treatment with chemerin and siChemR23 was examined by qRT-PCR and Western blotting.The roles of the MAPK and PI3K-Akt signaling pathways were studied using specific inhibitors. Cementoblast cytokine production under different treatment conditions was measured by ELISA and qRT-PCR. Additionally, we modeled IRR in wild-type and chemerin-overexpressing mice and injected transgenic mice with anti-ChemR23 antibody to block ChemR23. We then calculated the root resorption volume and examined periodontal tissue cathepsin K, Runx2, TNF-α, and IL-6 expression.

RESULT

Chemerin suppressed cementoblast differentiation and mineralization and exerted a proinflammatory effect on cementoblasts. These effects were partially reversed by siChemR23 and reversed to different extents by p38, Erk1/2 and PI3K-Akt pathway inhibition, suggesting p38, Erk1/2 and PI3K-Akt pathways as signaling pathways downstream of chemerin/ChemR23. In vivo, chemerin overexpression worsened IRR. Moreover, chemerin expression was positively correlated with TNF-α, IL-6, and cathepsin K expression and negatively correlated with Runx2 expression. ChemR23 downregulation reversed these effects.

CONCLUSION

Chemerin/ChemR23 induced TNF-α and IL-6 expression dependent on Erk1/2, p38 MAPK and PI3K-Akt signaling pathway activation, thereby regulating cementoblast function and affecting IRR. This article is protected by copyright. All rights reserved.

Chemerin as a modulator of ovarian steroidogenesis in pigs: an in vitro study

Chemerin has been shown to participate in the regulation of ovarian steroidogenesis in women, rats, mice and cows. Even though pigs are one of the most economically important livestock species, there is a general lack of data on the effects of chemerin in this species. Therefore, this study aimed to investigate the in vitro effect of chemerin on basal and luteinizing hormone/follicle-stimulating hormone- and/or insulin-induced secretion of progesterone (P₄), androstenedione (A₄), testosterone (T), estrone (E₁) and estradiol (E₂) by the porcine ovarian cells during the estrous cycle and early pregnancy. Granulosa (G) and theca interna (Th) cells were collected from gilts during the follicular phase. Luteal cells (Lc) were harvested from pigs during the early-luteal, mid-luteal and late-luteal phases, as well as during the maternal recognition of pregnancy and beginning of implantation. Cells were preincubated for 24 h (G and Th) or 48 h (Lc) and subsequently incubated for 24 h with or without treatments. Then, the concentrations of steroid hormones in the culture media were determined by radioimmunoassay. The results were analyzed by one-way analysis of variance, followed by Duncan's post hoc test. The study demonstrated that chemerin exerts a modulatory effect on de novo synthesis of steroid hormones in pigs. Chemerin stimulated basal and/or induced secretion of P₄ by the porcine Lc during the early-, mid- and late-luteal phases of the estrous cycle, as well as during both studied periods of early pregnancy. Further, chemerin caused an increase in the induced secretion of A₄, T and E₁ by the porcine Lc during the maternal recognition of pregnancy. Moreover, chemerin inhibited induced secretion of E₂ by the porcine Lc during the early-, mid- and late-luteal phases, as well as during the maternal recognition of pregnancy. During the follicular phase, chemerin stimulated basal and induced secretion of P₄ and inhibited induced secretion of E₂ by the porcine G, as well as decreased induced secretion of A₄, and T by the porcine Th. Therefore, chemerin appears to be a modulator of ovarian steroidogenesis in pigs, whereas its varied effects (stimulatory or inhibitory) on the secretion of steroid hormones may be due to the heterogeneity of factors regulating ovarian functions, possible interactions between these factors, and specific processes related to the ovarian physiology during different phases of the estrous cycle/pregnancy. Chemerin may also affect ovarian steroidogenesis in pigs by regulating the expression/activity of steroidogenic enzymes.

Chemerin as a Driver of Hypertension: A Consideration

The protein chemerin (tazarotene-induced gene, TIG2; RARRES2) is a relatively new adipokine. Many studies support that circulating chemerin levels associate strongly and positively with body mass index, visceral fat, and blood pressure. Here, we focus on the specific relationship of chemerin and blood pressure with the goal of understanding whether and how chemerin drives (pathological) changes in blood pressure such that it could be interfered with therapeutically. We dissect the biosynthesis of chemerin and how current antihypertensive medications change chemerin metabolism. This is followed with a review of what is known about where chemerin is synthesized in the body and what chemerin and its receptors can do to the physiological function of organs important to blood pressure determination (e.g., brain, heart, kidneys, blood vessels, adrenal, and sympathetic nervous system). We synthesize from the literature our best understanding of the mechanisms by which chemerin modifies blood pressure, with knowledge that plasma/serum levels of chemerin may be limited in their pathological relevance. This review reveals several gaps in our knowledge of chemerin biology that could be filled by the collective work of protein chemists, biologists, pharmacologists, and clinicians.

Adipokines and Inflammation: Focus on Cardiovascular Diseases

It is well established that adipose tissue, apart from its energy storage function, acts as an endocrine organ that produces and secretes a number of bioactive substances, including hormones commonly known as adipokines. Obesity is a major risk factor for the development of cardiovascular diseases, mainly due to a low grade of inflammation and the excessive fat accumulation produced in this state. The adipose tissue dysfunction in obesity leads to an aberrant release of adipokines, some of them with direct cardiovascular and inflammatory regulatory functions. Inflammation is a common link between obesity and cardiovascular diseases, so this review will summarise the role of the main adipokines implicated in the regulation of the inflammatory processes occurring under the scenario of cardiovascular diseases.

Chemerin Added to Endothelin-1 Promotes Rat Pulmonary Artery Smooth Muscle Cell Proliferation and Migration

Background

While chemerin has been shown to increase proliferation and migration of systemic vascular smooth muscle cells (SMCs) contributing therefore to the development of hypertension, this remains to be clarified for the pulmonary circulation.

Methods

Expression of chemerin and its three receptors (CMKRL1, CCRL2, GPR1) was examined by immunohistochemistry and RTq-PCR in lungs, pulmonary artery, and thoracic aorta from Wistar rats. Primary cultured rat pulmonary artery and thoracic aorta SMCs treated with recombinant chemerin (tested from 5.10^–9 to 10^–7 mol/L) were assessed for proliferation and migration (both with 10^–7 mol/L endothelin-1), as well as for staurosporine-induced apoptosis.

Results

In pulmonary artery and thoracic aorta, CMKLR1 expression was detected in both endothelial cells and SMCs. In primary cultured pulmonary artery SMCs, chemerin and its three receptors were expressed, and CMKLR1 expression was higher than those of CCRL2 and GPR1. Chemerin added to endothelin-1 increased pulmonary artery SMC proliferation, while chemerin or endothelin-1 alone did not. This effect was less pronounced in thoracic aorta SMCs. Chemerin induced pulmonary artery and thoracic aorta SMC migration, which was exacerbated by endothelin-1 and more pronounced in thoracic aorta SMCs. Chemerin concentration-dependently reduced staurosporine-induced apoptosis in both pulmonary artery and thoracic aorta SMCs. In pulmonary artery SMCs, endothelin-1 treatment increased the expression of CMKLR1, CCRL2, and GPR1, while these expressions were not altered in thoracic aorta SMCs.

Conclusion

Chemerin/CMKRL1 signaling, in conjunction with a key mediator in the pathogenesis of pulmonary hypertensive diseases, endothelin-1, stimulated proliferation and migration, and increased resistance to apoptosis in rat primary cultured pulmonary artery SMCs. Our results suggest that this signaling could play a role in pulmonary artery remodeling observed in pulmonary hypertension.