Adipocyte-secreted chemerin is processed to a variety of isoforms and influences MMP3 and chemokine secretion through an NFkB-dependent mechanism

The chemerin-CMKLR1 axis in keratinocytes impairs innate host defense against cutaneous Staphylococcus aureus infection

The skin is the most common site of Staphylococcus aureus infection, which can lead to various diseases, including invasive and life-threatening infections, through evasion of host defense. However, little is known about the host factors that facilitate the innate immune evasion of S. aureus in the skin. Chemerin, which is abundantly expressed in the skin and can be activated by proteases derived from S. aureus, has both direct bacteria-killing activity and immunomodulatory effects via interactions with its receptor CMKLR1. Here, we demonstrate that a lack of the chemerin/CMKLR1 axis increases the neutrophil-mediated host defense against S. aureus in a mouse model of cutaneous infection, whereas chemerin overexpression, which mimics high levels of chemerin in obese individuals, exacerbates S. aureus cutaneous infection. Mechanistically, we identified keratinocytes that express CMKLR1 as the main target of chemerin to suppress S. aureus-induced IL-33 expression, leading to impaired skin neutrophilia and bacterial clearance. CMKLR1 signaling specifically inhibits IL-33 expression induced by cell wall components but not secreted proteins of S. aureus by inhibiting Akt activation in mouse keratinocytes. Thus, our study revealed that the immunomodulatory effect of the chemerin/CMKLR1 axis mediates innate immune evasion of S. aureus in vivo and likely increases susceptibility to S. aureus infection in obese individuals.

Plasma Chemerin Is Induced in Critically Ill Patients with Gram-Positive Infections

Chemerin is a chemoattractant protein abundantly expressed in hepatocytes. Chemerin exerts pro- and anti-inflammatory effects and acts as a pro-resolving protein. Chemerin levels are low in patients with liver cirrhosis and are increased in sepsis. The aim of this study was to identify associations between plasma chemerin levels and underlying diseases as well as causes of severe illness. The cohort included 32 patients with liver cirrhosis who had low systemic chemerin, and who were not considered for further evaluation. Plasma chemerin levels were similar between the 27 patients with systemic inflammatory response syndrome (SIRS), the 34 patients with sepsis and the 63 patients with septic shock. Chemerin in plasma correlated with C-reactive protein and leukocyte count but not with procalcitonin, a clinical marker of bacterial infection. Plasma chemerin did not differ among patients with and without ventilation and patients with and without dialysis. Vasopressor therapy was not associated with altered plasma chemerin levels. Infection with severe acute respiratory syndrome coronavirus 2 had no effect on plasma chemerin levels. Baseline levels of plasma chemerin could not discriminate between survivors and non-survivors. Notably, Gram-positive infection was associated with higher chemerin levels. In summary, the current study suggests that plasma chemerin might serve as an early biomarker for the diagnosis of Gram-positive infections in patients with sepsis.

Chemerin Forms: Their Generation and Activity

Chemerin is the product of the RARRES2 gene which is secreted as a precursor of 143 amino acids. That precursor is inactive, but proteases from the coagulation and fibrinolytic cascades, as well as from inflammatory reactions, process the C-terminus of chemerin to first activate it and then subsequently inactivate it. Chemerin can signal via two G protein-coupled receptors, chem1 and chem2, as well as be bound to a third non-signaling receptor, CCRL2. Chemerin is produced by the liver and secreted into the circulation as a precursor, but it is also expressed in some tissues where it can be activated locally. This review discusses the specific tissue expression of the components of the chemerin system, and the role of different proteases in regulating the activation and inactivation of chemerin. Methods of identifying and determining the levels of different chemerin forms in both mass and activity assays are reviewed. The levels of chemerin in circulation are correlated with certain disease conditions, such as patients with obesity or diabetes, leading to the possibility of using chemerin as a biomarker.

Epithelial chemerin-CMKLR1 signaling restricts microbiota-driven colonic neutrophilia and tumorigenesis by up-regulating lactoperoxidase

Intestinal barrier immunity is essential for controlling gut microbiota without eliciting harmful immune responses, while its defect contributes to the breakdown of intestinal homeostasis and colitis development. Chemerin, which is abundantly expressed in barrier tissues, has been demonstrated to regulate tissue inflammation via CMKLR1, its functional receptor. Several studies have reported the association between increased expression of chemerin-CMKLR1 and disease severity and immunotherapy resistance in inflammatory bowel disease (IBD) patients. However, the pathophysiological role of endogenous chemerin-CMKLR1 signaling in intestinal homeostasis remains elusive. We herein demonstrated that deficiency of chemerin or intestinal epithelial cell (IEC)-specific CMKLR1 conferred high susceptibility to microbiota-driven neutrophilic colon inflammation and subsequent tumorigenesis in mice following epithelial injury. Unexpectedly, we found that lack of chemerin-CMKLR1 signaling specifically reduced expression of lactoperoxidase (LPO), a peroxidase that is predominantly expressed in colonic ECs and utilizes H₂O₂ to oxidize thiocyanates to the antibiotic compound, thereby leading to the outgrowth and mucosal invasion of gram-negative bacteria and dysregulated CXCL1/2-mediated neutrophilia. Importantly, decreased LPO expression was causally linked to aggravated microbiota-driven colitis and associated tumorigenesis, as LPO supplementation could completely rescue such phenotypes in mice deficient in epithelial chemerin-CMKLR1 signaling. Moreover, epithelial chemerin-CMKLR1 signaling is necessary for early host defense against bacterial infection in an LPO-dependent manner. Collectively, our study reveals that the chemerin-CMKLR1/LPO axis represents an unrecognized immune mechanism that potentiates epithelial antimicrobial defense and restricts harmful colonic neutrophilia and suggests that LPO supplementation may be beneficial for microbiota dysbiosis in IBD patients with a defective innate antimicrobial mechanism.

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.

Microglia become hypofunctional and release metalloproteases and tau seeds when phagocytosing live neurons with P301S tau aggregates

The microtubule-associated protein tau aggregates in multiple neurodegenerative diseases, causing inflammation and changing the inflammatory signature of microglia by unknown mechanisms. We have shown that microglia phagocytose live neurons containing tau aggregates cultured from P301S tau mice due to neuronal tau aggregate-induced exposure of the “eat me” signal phosphatidylserine. Here, we show that after phagocytosing tau aggregate-bearing neurons, microglia become hypophagocytic while releasing seed-competent insoluble tau aggregates. These microglia express a senescence-like phenotype, demonstrated by acidic β-galactosidase activity, secretion of paracrine senescence-associated cytokines, and maturation of matrix remodeling enzymes, results that are corroborated in P301S mouse brains and ex vivo brain slices. In particular, the nuclear factor κB–dependent activation of matrix metalloprotease 3 (MMP3/stromelysin1) was replicated in brains from patients with tauopathy. These data show that microglia that have been activated to ingest live tau aggregates-bearing neurons behave hormetically, becoming hypofunctional while acting as vectors of tau aggregate spreading.

The chemerin-CMKLR1 axis limits thermogenesis by controlling a beige adipocyte/IL-33/type 2 innate immunity circuit

IL-33-associated type 2 innate immunity has been shown to support beige fat formation and thermogenesis in subcutaneous inguinal white adipose tissue (iWAT), but little is known about how it is regulated in iWAT. Chemerin, as a newly identified adipokine, is clinically associated with obesity and metabolic disorders. We here show that cold exposure specifically reduces chemerin and its receptor chemerin chemokine-like receptor 1 (CMKLR1) expression in iWAT. Lack of chemerin or adipocytic CMKLR1 enhances cold-induced thermogenic beige fat via potentiating type 2 innate immune responses. Mechanistically, we identify adipocytes, particularly beige adipocytes, as the main source for cold-induced IL-33, which is restricted by the chemerin-CMKLR1 axis via dampening cAMP-PKA signaling, thereby interrupting a feed-forward circuit between beige adipocytes and type 2 innate immunity that is required for cold-induced beige fat and thermogenesis. Moreover, specific deletion of adipocytic IL-33 inhibits cold-induced beige fat and type 2 innate immune responses. Last, genetic blockade of adipocytic CMKLR1 protects against diet-induced obesity and enhances the metabolic benefits of cold stimulation in preestablished obese mice. Thus, our study identifies the chemerin-CMKLR1 axis as a physiological negative regulator of thermogenic beige fat via interrupting adipose-immune communication and suggests targeting adipose CMKLR1 as a potential therapeutic strategy for obesity-related metabolic disorders.

Chemerin-156 is the Active Isoform in Human Hepatic Stellate Cells

The chemokine chemerin exists as C-terminally processed isoforms whose biological functions are mostly unknown. A highly active human chemerin variant (huChem-157) was protective in experimental hepatocellular carcinoma (HCC) models. Hepatic stellate cells (HSCs) are central mediators of hepatic fibrogenesis and carcinogenesis and express the chemerin receptors chemokine-like receptor 1 (CMKLR1) and G protein-coupled receptor 1 (GPR1). Here we aimed to analyse the effect of chemerin isoforms on the viability, proliferation and secretome of the human HSC cell line LX-2. Therefore, huChem-157, 156 and 155 were over-expressed in LX-2 cells, which have low endogenous chemerin levels. HuChem-157 produced in LX-2 cells activated CMKLR1 and GPR1, and huChem-156 modestly induced GPR1 signaling. HuChem-155 is an inactive chemerin variant. Chemerin isoforms had no effect on cell viability and proliferation. Cellular expression of the fibrotic proteins galectin-3 and alpha-smooth muscle actin was not regulated by any chemerin isoform. HuChem-156 increased IL-6, IL-8 and galectin-3 in cell media. HuChem-157 was ineffective, and accordingly, did not enhance levels of these proteins in media of primary human hepatic stellate cells when added exogenously. These analyses provide evidence that huChem-156 is the biologic active chemerin variant in hepatic stellate cells and acts as a pro-inflammatory factor.

Chemerin isoform analysis in human biofluids using an LC/MRM-MS-based targeted proteomics approach with stable isotope-labeled standard

Targeted proteomics has advantages over earlier conventional technologies for protein detection. We developed and validated an LC/MRM-MS-based targeted proteomic method combined with immunoaffinity precipitation for the enrichment and detection of low abundance chemerin isoforms in human biofluids. After tryptic digestion, each chemerin isoform was characterized by isoform-specific peptides, and the absolute quantification was achieved by using stable isotope-labeled peptides as internal standards. In serum, follicular fluid and synovial fluid, a total of 6 chemerin isoforms were identified and quantified, among which a novel natural isoform 153Q was discovered for the first time. The relative content of the six chemerin isoforms in human serum was 157S ≫ 156F ≫ 158K > 154F ≥ 155A > 153Q in the ratio of 25:17:5:2.5:2.2:1, respectively. The absolute contents were in the range of 88-3.5 ng/mL. This distribution remained consistent among the 3 biofluids analyzed. Total chemerin were found to be increased in both polycystic ovary syndrome (serum and follicular fluid) and rheumatoid arthritis (serum) patients. However, chemerin isoform analysis revealed that only 156F & 157S were increased in the former, while 155A, 156F & 157S were increased in the latter. This demonstrates the potential of this method in detailed characterization of changes in chemerin isoforms that may be of clinical relevance.

Adipose-derived mesenchymal stem cells promote the malignant phenotype of cervical cancer

Epidemiological studies indicate that obesity negatively affects the progression and treatment of cervical-uterine cancer. Recent evidence shows that a subpopulation of adipose-derived stem cells can alter cancer properties. In the present project, we described for the first time the impact of adipose-derived stem cells over the malignant behavior of cervical cancer cells. The transcriptome of cancer cells cultured in the presence of stem cells was analyzed using RNA-seq. Changes in gene expression were validated using digital-PCR. Bioinformatics tools were used to identify the main transduction pathways disrupted in cancer cells due to the presence of stem cells. In vitro and in vivo assays were conducted to validate cellular and molecular processes altered in cervical cancer cells owing to stem cells. Our results show that the expression of 95 RNAs was altered in cancer cells as a result of adipose-derived stem cells. Experimental assays indicate that stem cells provoke an increment in migration, invasion, angiogenesis, and tumorigenesis of cancer cells; however, no alterations were found in proliferation. Bioinformatics and experimental analyses demonstrated that the NF-kappa B signaling pathway is enriched in cancer cells due to the influence of adipose-derived stem cells. Interestingly, the tumor cells shift their epithelial to a mesenchymal morphology, which was reflected by the increased expression of specific mesenchymal markers. In addition, stem cells also promote a stemness phenotype in the cervical cancer cells. In conclusion, our results suggest that adipose-derived stem cells induce cervical cancer cells to acquire malignant features where NF-kappa B plays a key role.

CXCL13 is a differentiation- and hypoxia-induced adipocytokine that exacerbates the inflammatory phenotype of adipocytes through PHLPP1 induction

Hypoxia in adipose tissue is regarded as a trigger that induces dysregulation of the secretory profile in adipocytes. Similarly, local dysregulation of adipocytokine secretion is an initial event in the deleterious effects of obesity on metabolism. We previously reported that CXCL13 is highly produced during adipogenesis, however little is known about the roles of CXCL13 in adipocytes. Here, we found that hypoxia, as modeled by 1% O2 or exposure to the hypoxia-mimetic reagent desferrioxamine (DFO) has strong inductive effects on the expression of CXCL13 and CXCR5, a CXCL13 receptor, in both undifferentiated and differentiated adipocytes and in organ-cultured white adipose tissue (WAT). CXCL13 was also highly expressed in WAT from high fat diet-fed mice. Hypoxic profile, typified by increased expression of interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1) and decreased expression of adiponectin, was significantly induced by CXCL13 treatment during adipogenic differentiation. Conversely, the treatment of adipocytes with a neutralizing-antibody against CXCL13 as well as CXCR5 knockdown by specific siRNA effectively inhibited DFO-induced inflammation. The phosphorylation of Akt2, a protective factor of adipose inflammation, was significantly inhibited by CXCL13 treatment during adipogenic differentiation. Mechanistically, CXCL13 induces the expression of PHLPP1, an Akt2 phosphatase, through focal adhesion kinase (FAK) signaling; and correspondingly we show that CXCL13 and DFO-induced IL-6 and PAI-1 expression was blocked by Phlpp1 knockdown. Furthermore, we revealed the functional binding sites of PPARγ2 and HIF1-α within the Cxcl13 promoter. Taken together, these results indicate that CXCL13 is an adipocytokine that facilitates hypoxia-induced inflammation in adipocytes through FAK-mediated induction of PHLPP1 in autocrine and/or paracrine manner.

Selenium deficiency causes immune damage by activating the DUSP1/NF-κB pathway and endoplasmic reticulum stress in chicken spleen

Selenium (Se) is an essential trace element and its deficiency can lead to immune dysfunction. Many studies have investigated the immune damage caused by Se deficiency in chickens, but its mechanism still needs to be explored. In this study, we fed 1-day-old Hyline male chickens with Se deficient diets (the Se content was 0.008 mg kg^-1 of diet) and a basal diet (the Se content was 0.15 mg kg^-1 of diet). The spleen was collected at the sixth week and used for subsequent experiments. The pathological analysis showed that Se deficiency leads to the destruction of the normal nuclear structure of the spleen cell, and we can observe obvious chromatin condensation and nuclear debris. We constructed a transcriptome database and analyzed the abundance of various genes in the spleen by transcriptome sequence. The analysis of differentially expressed genes (DEGS) showed significant changes in 337 genes, including 210 up-regulations and 127 down-regulations after feeding Se deficient diets. Se deficiency can significantly change oxidative stress and inflammatory response genes in chicken spleen. This study confirmed that Se deficiency increased the IL-2 levels, whereas it down-regulated IL-17, IFN-γ and Foxp3, which indicates that the immune dysfunction of the spleen and Th1/Th2 is imbalanced. We also found that Se deficiency down-regulated some related genes for endoplasmic reticulum Ca²⁺ transport, leading to endoplasmic reticulum stress (ERS). Moreover, we determined that Se deficiency triggered the low expression of DUSP1/NF-κB. In summary, our results indicate that Se deficiency can inhibit the spleen immune function of chickens by regulating the DUSP1/NF-κB pathway and ERS, leading to spleen damage in chickens. Based on transcriptomics research, our results will help further study the harmful effects of Se deficiency.

More Than an Adipokine: The Complex Roles of Chemerin Signaling in Cancer

Chemerin is widely recognized as an adipokine, with diverse biological roles in cellular differentiation and metabolism, as well as a leukocyte chemoattractant. Research investigating the role of chemerin in the obesity-cancer relationship has provided evidence both for pro- and anti-cancer effects. The tumor-promoting effects of chemerin primarily involve direct effects on migration, invasion, and metastasis as well as growth and proliferation of cancer cells. Chemerin can also promote tumor growth via the recruitment of tumor-supporting mesenchymal stromal cells and stimulation of angiogenesis pathways in endothelial cells. In contrast, the majority of evidence supports that the tumor-suppressing effects of chemerin are immune-mediated and result in a shift from immunosuppressive to immunogenic cell populations within the tumor microenvironment. Systemic chemerin and chemerin produced within the tumor microenvironment may contribute to these effects via signaling through CMKLR1 (chemerin₁), GPR1 (chemerin₂), and CCLR2 on target cells. As such, inhibition or activation of chemerin signaling could be beneficial as a therapeutic approach depending on the type of cancer. Additional studies are required to determine if obesity influences cancer initiation or progression through increased adipose tissue production of chemerin and/or altered chemerin processing that leads to changes in chemerin signaling in the tumor microenvironment.

Chemerin partly mediates tumor-inhibitory effect of all-trans retinoic acid via CMKLR1-dependent natural killer cell recruitment

Down-regulated chemerin expression has been reported to correlate with poor prognosis of several types of cancer including melanoma. All-trans retinoic acid (atRA) is a potent inducer of chemerin, and we previously reported that atRA inhibited murine melanoma growth through enhancement of anti-tumor T-cell immunity. Here, we aimed to investigate whether loss of endogenous chemerin accelerated melanoma growth and whether chemerin was involved in the melanoma-inhibitory effect of atRA. We demonstrated that chemerin was constitutively expressed in the skin, which was down-regulated during murine melanoma growth. Rarres2^-/- mice, which are deficient in chemerin, exhibited aggravated tumor growth and impaired tumor-infiltrating natural killer (NK) cells that express CMKLR1, the functional receptor of chemerin. Topical treatment with atRA up-regulated skin chemerin expression, which was primarily derived from dermal cells. Moreover, atRA treatment significantly enhanced tumor-infiltrating NK cells, which was completely abrogated in Rarres2^-/- mice and Cmklr1^-/- mice, suggesting a dependency of NK cell recruitment on the chemerin-CMKLR1 axis in melanoma. Despite comparable melanoma growth detected in wild-type mice and Cmklr1^-/- mice, lack of CMKLR1 partially abrogated the melanoma-inhibitory effect of atRA. This may be due to the inability to enhance tumor-infiltrating NK cells in Cmklr1^-/- mice following atRA treatment. Collectively, our study suggests that down-regulation of chemerin could be a strategy used by cancers such as melanoma to impair anti-tumor NK cell immunity and identifies a new anti-tumor mechanism of atRA by up-regulating chemerin to enhance CMKLR1-dependent NK cell recruitment.

Chemerin Isoforms and Activity in Obesity

Overweight and adiposity are risk factors for several diseases, like type 2 diabetes and cancer. White adipose tissue is a major source for adipokines, comprising a diverse group of proteins exerting various functions. Chemerin is one of these proteins whose systemic levels are increased in obesity. Chemerin is involved in different physiological and pathophysiological processes and it regulates adipogenesis, insulin sensitivity, and immune response, suggesting a vital role in metabolic health. The majority of serum chemerin is biologically inert. Different proteases are involved in the C-terminal processing of chemerin and generate diverse isoforms that vary in their activity. Distribution of chemerin variants was analyzed in adipose tissues and plasma of lean and obese humans and mice. The Tango bioassay, which is suitable to monitor the activation of the beta-arrestin 2 pathway, was used to determine the ex-vivo activation of chemerin receptors by systemic chemerin. Further, the expression of the chemerin receptors was analyzed in adipose tissue, liver, and skeletal muscle. Present investigations assume that increased systemic chemerin in human obesity is not accompanied by higher biologic activity. More research is needed to fully understand the pathways that control chemerin processing and chemerin signaling.

Ex vivo analysis of serum chemerin activity in murine models of obesity

OBJECTIVES

Chemerin is an adipokine with established roles in inflammation, adipogenesis and the regulation of glucose and lipid homeostasis. Extracellular proteolytic processing of chemerin generates a spectrum of isoforms that differ significantly with respect to the ability to activate the cognate receptors chemokine-like receptor 1 (CMKLR1) and G-protein-coupled receptor 1 (GPR1). Increased total serum chemerin has been widely reported in obese humans as well as in preclinical rodent models of adiposity. However, very little information is available regarding the correspondence, if any, of changes in total serum chemerin protein with chemerin bioactivity.

METHODS

Total serum chemerin and ex vivo CMKLR1 and GPR1 activation was compared using two widely used murine obesity models: high fat diet feeding (HFD) and leptin deficiency (ob/ob).

RESULTS

Total serum chemerin levels and ex vivo CMKLR1 and GPR1 activation were significantly induced in HFD. The bioactivity ratio (bioactive chemerin/total chemerin) was also increased when measured with CMKLR1, but not GPR1. In contrast, while ob/ob mice exhibited increased total serum chemerin protein, ex vivo receptor activation was observed with GPR1, but not CMKLR1. There was no change in bioactivity ratio for either receptor. Of note, GPR1 but not CMKLR1 bioactivity positively correlated with adipose tissue inflammation.

CONCLUSIONS

While increased total serum chemerin is a consistent finding among rodent obesity models, this may not accurately reflect changes in chemerin bioactivity which is the major determinant of biological effects.

Systemic Inflammation as a Driver of Brain Injury: the Astrocyte as an Emerging Player

Severe systemic inflammation has strong effects on brain functions, promoting permanent neurocognitive dysfunction and high mortality rates. Additionally, hippocampal damage seems to be directly involved in this process and astrocytes play an important role in neuroinflammation and in the neuroimmune response. However, the contribution of the astrocytes to the pathology of acute brain dysfunction is not well understood. Recently, our group established a protocol for obtaining astrocyte cultures from mature brain to allow the characterization of these cells and their functions under pathologic conditions. The present study was designed to characterize astrocyte function after acute systemic inflammation induced by cecal ligation and perforation (CLP). Hippocampal astrocyte cultures from CLP animals presented increased levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, IL-18, and cyclooxygenase-2 and decreased levels of IL-10. This proinflammatory profile was accompanied by an increase in Toll-like receptor (TLR)2 mRNA expression levels and no change either in TLR4 or in vascular endothelial growth factor (VEGF) gene expression. These alterations were associated with increased expressions of p21, nuclear factor kappa B (NFκB), and inducible nitric oxide synthase (iNOS) in astrocytes from CLP animals. The same parameters were also evaluated in whole hippocampal tissue, but differences in this profile were found compared to hippocampal astrocyte cultures from CLP, reflecting an interaction between other central nervous system cell types, which may mask specific astrocytic changes. These results improve our understanding of the mechanisms by which astrocytes react against systemic inflammation, and suggest these cells to be potential targets for therapeutic modulation.

Hepatic chemerin mRNA expression is reduced in human nonalcoholic steatohepatitis

BACKGROUND

Chemerin is associated with insulin resistance and is expressed in the liver. Nonalcoholic fatty liver disease (NAFLD) is related to impaired insulin sensitivity, but studies evaluating hepatic and serum chemerin in NAFLD resulted in discordant data.

MATERIALS AND METHODS

Chemerin mRNA was determined in the liver tissue obtained from 33 controls and 76 NAFLD patients. Chemerin serum levels were measured in a different cohort of patients with ultrasound-diagnosed NAFLD and the respective controls. Hepatic stellate cells and hepatocytes were exposed to selected metabolites and nuclear receptor agonists to study the regulation of chemerin. Effect of recombinant chemerin on hepatocyte released proteins was analysed.

RESULTS

Hepatic chemerin expression was not related to BMI, gender, type 2 diabetes and hypertension. Chemerin mRNA did not correlate with steatosis and was negatively associated with inflammation, fibrosis and nonalcoholic steatohepatitis (NASH) score. Patients with NASH had lower chemerin mRNA compared to those with borderline NASH and controls. Factors with a role in NASH mostly did not regulate chemerin in the liver cells. Of note, liver X receptor agonist reduced chemerin protein. Serum chemerin was not changed in NAFLD. Levels positively correlated with age, waist-to-hip ratio, systolic blood pressure, serum FGF21 and lipocalin 2, and negatively with transferrin saturation. Chemerin induced FGF21 in supernatants of primary human hepatocytes. Hepcidin, a major regulator of iron homoeostasis and lipocalin 2, were not regulated by chemerin.

CONCLUSION

Chemerin mRNA is reduced in the liver of NASH patients, and liver X receptor seems to have a role herein.

CMKLR1 activation ex vivo does not increase proportionally to serum total chemerin in obese humans

Prochemerin is the inactive precursor of the adipokine chemerin. Proteolytic processing is obligatory for the conversion of prochemerin into active chemerin and subsequent regulation of cellular processes via the chemokine-like receptor 1 (CMKLR1). Elevated plasma or serum chemerin concentrations and differential processing of prochemerin have been reported in obese humans. The impact of these changes on CMKLR1 signalling in humans is unknown. The objective of this pilot study was to develop a cellular bioassay to measure CMKLR1 activation by chemerin present in human serum and to characterise how obesity modifies serum activation of CMKLR1 under fasted and fed conditions. Blood samples were collected from control (N = 4, BMI 20-25) and obese (N = 4, BMI >30) female subjects after an overnight fast (n = 2) and at regular intervals (n = 7) following consumption of breakfast over a period of 6 h. A cellular CMKLR1-luminescent reporter assay and a pan-chemerin ELISA were used to determine CMKLR1 activation and total chemerin concentrations, respectively. Serum total chemerin concentration (averaged across all samples) was higher in obese vs control subjects (17.9 ± 1.8 vs 10.9 ± 0.5 nM, P < 0.05), but serum activation of CMKLR1 was similar in both groups. The CMKLR1 activation/total chemerin ratio was lower in obese vs control subjects (0.33 ± 0.04 vs 0.58 ± 0.05, P < 0.05). After breakfast, serum total chemerin or CMKLR1 activation did not differ from baseline values. In conclusion, the unexpected observation that obese serum activation of CMKLR1 did not match increased total chemerin concentrations suggests impaired processing to and/or enhanced degradation of active chemerin in serum of obese humans.