Whole-genome resequencing of Hu sheep identifies candidate genes associated with agronomic traits

The phenotypic diversity resulting from artificial or natural selection of sheep has made a significant contribution to human civilization. Hu sheep are a local sheep breed unique to China with high reproductive rates and rapid growth. Genomic selection signatures have been widely used to investigate the genetic mechanisms underlying phenotypic variation in livestock. Here, we conduct whole-genome sequencing of 207 Hu sheep and compare them with the wild ancestors of domestic sheep (Asiatic mouflon) to investigate the genetic characteristics and selection signatures of Hu sheep. Based on six signatures of selection approaches, we detect genomic regions containing genes related to reproduction (BMPR1B, BMP2, PGFS, CYP19, CAMK4, GGT5, and GNAQ), vision (ALDH1A2, SAG, and PDE6B), nervous system (NAV1), and immune response (GPR35, SH2B2, PIK3R3, and HRAS). Association analysis with a population of 1299 Hu sheep reveal those missense mutations in the GPR35 (GPR35 g.952651 A>G; GPR35 g.952496 C>T) and NAV1 (NAV1 g.84216190 C>T; NAV1 g.84227412 G>A) genes are significantly associated (P < 0.05) with immune and growth traits in Hu sheep, respectively. This research offers unique insights into the selection characteristics of Hu sheep and facilitates further genetic improvement and molecular investigations.

From orphan to oncogene: The role of GPR35 in cancer and immune modulation

G protein-coupled receptors (GPCRs) are well-studied and the most traceable cell surface receptors for drug discovery. One of the intriguing members of this family is G protein-coupled receptors 35 (GPR35), which belongs to the class A rhodopsin-like family of GPCRs identified over two decades ago. GPR35 presents interesting features such as ubiquitous expression and distinct isoforms. Moreover, functional and genome-wide association studies on its widespread expression have linked GPR35 with pathophysiological disease progression. Various pieces of evidence have been accumulated regarding the independent or endogenous ligand-dependent role of GPR35 in cancer progression and metastasis. In the current scenario, the relationship of this versatile receptor and its putative endogenous ligands for the activation of oncogenic signal transduction pathways at the cellular level is an active area of research. These intriguing features offered by GPR35 make it an oncological target, justifying its uniqueness at the physiological and pathophysiological levels concerning other GPCRs. For pharmacologically targeting receptor-induced signaling, few potential competitive antagonists have been discovered that offer high selectivity at a human level. In addition to its fascinating features, targeting GPR35 at rodent and human orthologue levels is distinct, thus contributing to the sub-species selectivity. Strategies to modulate these issues will help us understand and truly target GPR35 at the therapeutic level. In this article, we have provided prospects on each topic mentioned above and suggestions to overcome the challenges. This review discusses the molecular mechanism and signal transduction pathways activated by endogenous ligands or spontaneous auto-activation of GPR35 that contributes towards disease progression. Furthermore, we have highlighted the GPR35 structure, ubiquitous expression, its role in immunomodulation, and at the pathophysiological level, especially in cancer, indicating its status as a versatile receptor. Subsequently, we discussed the various proposed ligands and their mechanism of interaction with GPR35. Additionally, we have summarized the GPR35 antagonist that provides insights into the opportunities for therapeutically targeting this receptor.

Gallic acid induces osteoblast differentiation and alleviates inflammatory response through GPR35/GSK3β/β-catenin signaling pathway in human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Gallic acid (GA) possesses various beneficial functions including antioxidant, anticancer, anti-inflammatory as well as inhibiting osteoclastogeneis. However, effects on osteogenic differentiation, especially in human ligament periodontal (hPDL) cells, remain unclear. Thus, the aim of this study was to evaluate the function of GA on osteogenesis and anti-inflammation in hPDL cells and to explore the involved underlying mechanism.

METHODS

Porphyromonas gingivalis lipopolysaccharide (Pg-LPS) treatment was used as a model for periodontitis. ROS production was determined by H2DCFDA staining. Trans-well and wound healing assays were performed for checking the migration effect of GA. Alizarin red and alkaline phosphatase activity (ALP) assays were performed to evaluate osteogenic differentiation. Osteogenesis and inflammatory-related genes and proteins were measured by real-time PCR and western blot.

RESULTS

Our results showed that GA-treated hPDL cells had higher proliferation and migration effect. GA inhibited ROS production-induced by Pg-LPS. Besides, GA abolished Pg-LPS-induced inflammation cytokines (il-6, il-1β) and inflammasome targets (Caspase-1, NLRP3). In addition, GA promoted ALP activity and mineralization in hPDL cells, lead to enhance osteoblast differentiation process. The effect of GA is related to G-protein-coupled receptor 35 (GPR35)/GSK3β/β-catenin signaling pathway.

CONCLUSION

GA attenuated Pg-LPS-induced inflammatory responses and periodontitis in hPDL cells. Taken together, GA may be targeted for therapeutic interventions in periodontal diseases.

Discovery of a novel GPR35 agonist with high and equipotent species potency for oral treatment of IBD

The G protein-coupled receptor 35 (GPR35) has been identified as a potential target in the treatment of inflammatory bowel disease (IBD). However, the lack of high and equipotent agonists on both human and mouse GPR35 has limited the in vivo study of GPR35 agonists in mouse models of IBD. In this study, structural modifications to lodoxamide provides a series of high and equivalent agonists on human, mouse, and rat GPR35. These molecules eliminate the species selectivity of human to mouse and rat orthologs that have been prevalent with GPR35 agonists including lodoxamide. The cLogP properties are also optimized to make the compounds more obedient to drug-like rules, yielding compound 4b (cLogP = 2.41), which activates human, mouse or rat GPR35 with EC50 values of 76.0, 63.7 and 77.8 nM, respectively. Oral administration of compound 4b at 20 mg/kg alleviates clinical symptoms of DSS-induced IBD in mice, and is slightly more effective than 5-ASA at 200 mg/kg. In summary, it can serve as a new start point for exploiting more potent GPR35 agonists without species differences for the treatment of IBD, and warrants further study.

Pamoic acid-induced peripheral GPR35 activation improves pruritus and dermatitis

BACKGROUND AND PURPOSE

Pruritic dermatitis is a disease with a considerable unmet need for treatment and appears to present with not only epidermal but also peripheral neuronal complications. Here, we propose a novel pharmacological modulation targeting both peripheral dorsal root ganglion (DRG) sensory neurons and skin keratinocytes. GPR35 is an orphan G-protein-coupled receptor expressed in DRG neurons and has been predicted to downregulate neuronal excitability when activated. Modulator information is currently increasing for GPR35, and pamoic acid (PA), a salt-forming agent for drugs, has been shown to be an activator solely specific for GPR35. Here, we investigated its effects on dermatitic pathology.

EXPERIMENTAL APPROACH

We confirmed GPR35 expression in peripheral neurons and tissues. The effect of PA treatment was pharmacologically evaluated in cultured cells in vitro and in in vivo animal models for acute and chronic pruritus.

KEY RESULTS

Local PA application mitigated acute non-histaminergic itch and, consistently, obstructed DRG neuronal responses. Keratinocyte fragmentation under dermatitic simulation was also dampened following PA incubation. Chronic pruritus in 1-chloro-2,4-dinitrobenzene and psoriasis models were also moderately but significantly reversed by the repeated applications of PA. Dermatitic scores in the 1-chloro-2,4-dinitrobenzene and psoriatic models were also improved by its application, indicating that it is beneficial for mitigating disease pathology.

CONCLUSION AND IMPLICATIONS

Our findings suggest that pamoic acid activation of peripheral GPR35 can contribute to the improvement of pruritus and its associated diseases.

GPR35 acts a dual role and therapeutic target in inflammation

GPR35 is a G protein-coupled receptor with notable involvement in modulating inflammatory responses. Although the precise role of GPR35 in inflammation is not yet fully understood, studies have suggested that it may have both pro- and anti-inflammatory effects depending on the specific cellular environment. Some studies have shown that GPR35 activation can stimulate the production of pro-inflammatory cytokines and facilitate the movement of immune cells towards inflammatory tissues or infected areas. Conversely, other investigations have suggested that GPR35 may possess anti-inflammatory properties in the gastrointestinal tract, liver and certain other tissues by curbing the generation of inflammatory mediators and endorsing the differentiation of regulatory T cells. The intricate role of GPR35 in inflammation underscores the requirement for more in-depth research to thoroughly comprehend its functional mechanisms and its potential significance as a therapeutic target for inflammatory diseases. The purpose of this review is to concurrently investigate the pro-inflammatory and anti-inflammatory roles of GPR35, thus illuminating both facets of this complex issue.

G protein-receptor kinases 5/6 are the key regulators of G protein-coupled receptor 35-arrestin interactions

Human G protein-coupled receptor 35 is regulated by agonist-mediated phosphorylation of a set of five phospho-acceptor amino acids within its C-terminal tail. Alteration of both Ser300 and Ser303 to alanine in the GPR35a isoform greatly reduces the ability of receptor agonists to promote interactions with arrestin adapter proteins. Here, we have integrated the use of cell lines genome edited to lack expression of combinations of G protein receptor kinases (GRKs), selective small molecule inhibitors of subsets of these kinases, and antisera able to specifically identify either human GPR35a or mouse GPR35 only when Ser300 and Ser303 (orce; the equivalent residues in mouse GPR35) have become phosphorylated to demonstrate that GRK5 and GRK6 cause agonist-dependent phosphorylation of these residues. Extensions of these studies demonstrated the importance of the GRK5/6-mediated phosphorylation of these amino acids for agonist-induced internalization of the receptor. Homology and predictive modeling of the interaction of human GPR35 with GRKs showed that the N terminus of GRK5 is likely to dock in the same methionine pocket on the intracellular face of GPR35 as the C terminus of the α5 helix of Gα13 and, that while this is also the case for GRK6, GRK2 and GRK3 are unable to do so effectively. These studies provide unique and wide-ranging insights into modes of regulation of GPR35, a receptor that is currently attracting considerable interest as a novel therapeutic target in diseases including ulcerative colitis.

The gut microbiota-induced kynurenic acid recruits GPR35-positive macrophages to promote experimental encephalitis

The intricate interplay between gut microbes and the onset of experimental autoimmune encephalomyelitis (EAE) remains poorly understood. Here, we uncover remarkable similarities between CD4+ T cells in the spinal cord and their counterparts in the small intestine. Furthermore, we unveil a synergistic relationship between the microbiota, particularly enriched with the tryptophan metabolism gene EC:1.13.11.11, and intestinal cells. This symbiotic collaboration results in the biosynthesis of kynurenic acid (KYNA), which modulates the recruitment and aggregation of GPR35-positive macrophages. Subsequently, a robust T helper 17 (Th17) immune response is activated, ultimately triggering the onset of EAE. Conversely, modulating the KYNA-mediated GPR35 signaling in Cx3cr1+ macrophages leads to a remarkable amelioration of EAE. These findings shed light on the crucial role of microbial-derived tryptophan metabolites in regulating immune responses within extraintestinal tissues.

GPR35-mediated kynurenic acid sensing contributes to maintenance of gut microbiota homeostasis in ulcerative colitis

Ulcerative colitis (UC) is a recurrent inflammatory disease related to gut microbiota disorder. Metabolites and their sensors play an important role in the communication between gut microbes and their host. Our previous study revealed that G protein-coupled receptor 35 (GPR35) is a key guardian of kynurenic acid (KA) and a core element of the defense responses against gut damage. However, the mechanism remains unknown. In this study, a DSS-induced rat colitis model was established and 16S rRNA sequencing was applied to explore the influence of GPR35-mediated KA sensing on gut microbiota homeostasis. Our results demonstrated that GPR35-mediated KA sensing is a necessary component in maintaining gut barrier integrity against DSS-induced damage. Furthermore, we provide compelling evidence suggesting that GPR35-mediated KA sensing plays a crucial role in maintaining gut microbiota homeostasis, which contributes to alleviation of DSS-induced colitis. In addition, five classes (Actinobacteria, Beta-/Gamma-proteobacteria, Erysipelotrichi and Coriobacteriia) and six genera (Corynebacterium, Allobaculum, Parabacteroides, Sutterella, Shigella and Xenorhabdus) were identified as the marked bacterial taxa that characterized the progression and outcome of colitis and are regulated by GPR35-mediated KA sensing. Our findings highlight that GPR35-mediated KA sensing is an essential defense mechanism against disorder of gut microbiota in UC. The results provide insights into the key role of specific metabolites and their monitor in maintaining gut homeostasis.

Modulation of T cells by tryptophan metabolites in the kynurenine pathway

Lymphocytes maturing in the thymus (T cells) are key factors in adaptive immunity and the regulation of inflammation. The kynurenine pathway of tryptophan metabolism includes several enzymes and compounds that can modulate T cell function, but manipulating these pharmacologically has not achieved the expected therapeutic activity for the treatment of autoimmune disorders and cancer. With increasing knowledge of other pathways interacting with kynurenines, the expansion of screening methods, and the application of virtual techniques to understanding enzyme structures and mechanisms, details of interactions between kynurenines and other pathways are being revealed. This review surveys some of these alternative approaches to influence T cell function indirectly via the kynurenine pathway and summarizes the most recent work on the development of compounds acting directly on the kynurenine pathway.

Platelets and mast cells promote pathogenic eosinophil recruitment during invasive fungal infection via the 5-HIAA-GPR35 ligand-receptor system

Cryptococcus neoformans is the leading cause of fungal meningitis and is characterized by pathogenic eosinophil accumulation in the context of type-2 inflammation. The chemoattractant receptor GPR35 is expressed by granulocytes and promotes their migration to the inflammatory mediator 5-hydroxyindoleacetic acid (5-HIAA), a serotonin metabolite. Given the inflammatory nature of cryptococcal infection, we examined the role of GPR35 in the circuitry underlying cell recruitment to the lung. GPR35 deficiency dampened eosinophil recruitment and fungal growth, whereas overexpression promoted eosinophil homing to airways and fungal replication. Activated platelets and mast cells were the sources of GPR35 ligand activity and pharmacological inhibition of serotonin conversion to 5-HIAA, or genetic deficiency in 5-HIAA production by platelets and mast cells resulted in more efficient clearance of Cryptococcus. Thus, the 5-HIAA-GPR35 axis is an eosinophil chemoattractant receptor system that modulates the clearance of a lethal fungal pathogen, with implications for the use of serotonin metabolism inhibitors in the treatment of fungal infections.

Recent advances in GPR35 pharmacology; 5-HIAA serotonin metabolite becomes a ligand

GPR35, an orphan receptor, has been waiting for its ligand since its cloning in 1998. Many endogenous and exogenous molecules have been suggested to act as agonists of GPR35 including kynurenic acid, zaprinast, lysophosphatidic acid, and CXCL17. However, complex and controversial responses to ligands among species have become a huge hurdle in the development of therapeutics in addition to the orphan state. Recently, a serotonin metabolite, 5-hydroxyindoleacetic acid (5-HIAA), is reported to be a high potency ligand for GPR35 by investigating the increased expression of GPR35 in neutrophils. In addition, a transgenic knock-in mouse line is developed, in which GPR35 was replaced with a human ortholog, making it possible not only to overcome the different selectivity of agonists among species but also to conduct therapeutic experiments on human GPR35 in mouse models. In the present article, I review the recent advances and prospective therapeutic directions in GPR35 research. Especially, I'd like to draw attention of readers to the finding of 5-HIAA as a ligand of GPR35 and lead to apply the 5-HIAA and human GPR35 knock-in mice to their research fields in a variety of pathophysiological conditions.

Activation of the IL-17 signalling pathway by the CXCL17-GPR35 axis affects drug resistance and colorectal cancer tumorigenesis

Colorectal cancer (CRC) is one of the most commonly diagnosed cancers, and drug resistance following prolonged treatment leads to downregulation of the efficacy of chemotherapy against CRC. CXCL17 is an inflammatory factor that plays a crucial role in tumorigenesis. However, the function of the CXCL17-GPR35 axis in CRC and resistance to chemotherapy is not entirely clear. Bioinformatic analysis was used to identify differentially expressed genes (DEGs) in oxaliplatin (OXA)-resistant CRC tumour tissues compared to OXA-sensitive counterparts. To further determine the function of CXCL17 in taxol-resistant CRC cells (HCT15), proliferation, migration, invasion, cell cycle, and apoptosis were analysed by CCK-8, wound healing, Transwell^®, and flow cytometry assays, respectively. In addition, RNA sequencing, western blotting, CCK-8, wound healing, and Transwell^® assays were used to further identify and confirm the downstream effects of CXCL17 regulation on taxol resistance. Our study found that CXCL17 and GPR35 were upregulated in OXA-resistant tumour tissues compared to in OXA-sensitive tissues. CXCL17 silencing significantly decreased the viability, migration, and invasion of taxol-resistant CRC cells. CXCL17 silencing arrested taxol-resistant CRC cells in the G2/M phase and promoted apoptosis. The IL-17 signalling pathway is involved in regulation of the CXCL17-GPR35 biological axis in HCT15 cells, and the addition of IL-17A distinctly reversed the decreased proliferation, migration, and the enhanced apoptosis of HCT15 cells upon CXCL17 deletion. In summary, these findings demonstrate that the CXCL17-GPR35 axis and IL-17 signalling pathway are involved in mediating CRC tumorigenesis and drug-resistance. Inhibition of the CXCL17-GPR35 axis and IL-17 may hence be promising therapeutic targets for CRC resistance to OXA.

Aminosalicylates target GPR35, partly contributing to the prevention of DSS-induced colitis

GPR35, a class A G-protein-coupled receptor, is considered an orphan receptor; the endogenous ligand and precise physiological function of GPR35 remain obscure. GPR35 is expressed relatively highly in the gastrointestinal tract and immune cells. It plays a role in colorectal diseases like inflammatory bowel diseases (IBDs) and colon cancer. More recently, the development of GPR35 targeting anti-IBD drugs is in solid request. Nevertheless, the development process is in stagnation due to the lack of a highly potent GPR35 agonist that is also active comparably in both human and mouse orthologs. Therefore, we proposed to find compounds for GPR35 agonist development, especially for the human ortholog of GPR35. As an efficient way to pick up a safe and effective GPR35 targeting anti-IBD drug, we screened Food and Drug Administration (FDA)-approved 1850 drugs using a two-step DMR assay. Interestingly, we found aminosalicylates, first-line medicine for IBDs whose precise target remains unknown, exhibited activity on both human and mouse GPR35. Among these, pro-drug olsalazine showed the most potency on GPR35 agonism, inducing ERK phosphorylation and β-arrestin2 translocation. In dextran sodium sulfate (DSS)-induced colitis, the protective effect on disease progression and inhibitory effect on TNFα mRNA expression, NF-κB and JAK-STAT3 pathway of olsalazine are compromised in GPR35 knock-out mice. The present study identified a target for first-line medicine aminosalicylates, highlighted that uncleaved pro-drug olsalazine is effective, and provided a new concept for the design of aminosalicylic GPR35 targeting anti-IBD drug.

Neuroglobin plays as tumor suppressor by disrupting the stability of GPR35 in colorectal cancer

BACKGROUND

The incidence of colorectal cancer (CRC) has increased in recent years. Identification of accurate tumor markers has become the focus of CRC research. Early and frequent DNA methylation tends to occur in cancer. Thus, identifying accurate methylation biomarkers would improve the efficacy of CRC treatment. Neuroglobin (NGB) is involved in neurological and oncological diseases. However, there are currently no reports on epigenetic regulation involvement of NGB in CRC.

RESULTS

NGB was downregulated or silenced in majority CRC tissues and cell lines. The hypermethylation of NGB was detected in tumor tissue, but no or a very low methylation frequency in normal tissues. Overexpression of NGB induced G2/M phase arrest and apoptosis, suppressed proliferation, migration, invasion in vitro, and inhibited CRC tumor growth and angiogenesis in vivo. Isobaric tag for relative and absolute quantitation (Itraq)-based proteomics identified approximately 40% proteins related to cell-cell adhesion, invasion, and tumor vessel formation in the tumor microenvironment, among which GPR35 was proved critical for NGB-regulated tumor angiogenesis suppression in CRC.

CONCLUSIONS

NGB, an epigenetically silenced factor, inhibits metastasis through the GPR35 in CRC. It is expected to grow into a potential cancer risk assessment factor and a valuable biomarker for early diagnosis and prognosis assessment of CRC.

Increased GPR35 expression in human colorectal and pancreatic cancer samples: A preliminary clinical validation of a new biomarker

BACKGROUND

G protein-coupled receptor 35 (GPR35) is involved in carcinogenesis; however, limited experimental data are available on its actual expression in patients with colorectal cancer (CRC) and pancreatic adenocarcinoma (PDAC).

OBJECTIVES

We aimed to measure the relative expression of GPR35 in samples from patients with CRC or PDAC.

MATERIAL AND METHODS

Using real-time polymerase chain reaction (RT-PCR), we have examined GPR35 expression in surgery samples from 40 CRC and 17 PDAC patients, and performed analysis of the results.

RESULTS

The analysis of GPR35 expression in patients with CRC revealed correlations between relative GPR35 mRNA expression and several tumor characteristics, with statistical significance for higher American Joint Committee on Cancer (AJCC) stages, T stages and histological grades. GPR35 expression was significantly higher in tumor samples compared to the paired healthy samples collected from the same patient. Similar, although not statistically significant trends were found in PDAC tumor samples for sex (lower expression in women) and for samples with no nodal involvement (lower expression). Samples with higher tumor T stages and higher histological grades or considered inoperable had higher GPR35 expression.

CONCLUSIONS

We have identified correlations which confirm our expectation of high GPR35 expression in CRC and PDAC. Our findings suggest the prognostic value of GPR35 testing in patients with an increased risk of CRC or PDAC development, and warrant further clinical confirmation.

GPR35 antagonist CID-2745687 attenuates anchorage-independent cell growth by inhibiting YAP/TAZ activity in colorectal cancer cells

Background and purpose: GPR35, a member of the orphan G-protein-coupled receptor, was recently implicated in colorectal cancer (CRC). However, whether targeting GPR35 by antagonists can inhibit its pro-cancer role has yet to be answered. Experimental approach: We applied antagonist CID-2745687 (CID) in established GPR35 overexpressing and knock-down CRC cell lines to understand its anti-cell proliferation property and the underlying mechanism. Key results: Although GPR35 did not promote cell proliferation in 2D conditions, it promoted anchorage-independent growth in soft-agar, which was reduced by GPR35 knock-down and CID treatment. Furthermore, YAP/TAZ target genes were expressed relatively higher in GPR35 overexpressed cells and lower in GPR35 knock-down cells. YAP/TAZ activity is required for anchorage-independent growth of CRC cells. By detecting YAP/TAZ target genes, performing TEAD4 luciferase reporter assay, and examining YAP phosphorylation and TAZ protein expression level, we found YAP/TAZ activity is positively correlated to GPR35 expression level, which CID disrupted in GPR35 overexpressed cells, but not in GPR35 knock-down cells. Intriguingly, GPR35 agonists did not promote YAP/TAZ activity but ameliorated CID's inhibitory effect; GPR35-promoted YAP/TAZ activity was only partly attenuated by ROCK1/2 inhibitor. Conclusion and implications: GPR35 promoted YAP/TAZ activity partly through Rho-GTPase with its agonist-independent constitutive activity, and CID exhibited its inhibitory effect. GPR35 antagonists are promising anti-cancer agents that target hyperactivation and overexpression of YAP/TAZ in CRC.

Involvement of CXCL17 and GPR35 in Gastric Cancer Initiation and Progression

The expression of CXC motif chemokine 17 (CXCL17) and its reported membrane receptor G-protein-coupled receptor 35 (GPR35) in different gastric pathological lesions and their clinical implications are largely unknown. In this study, a total of 860 pathological sections were immune-stained with either anti-CXCL17 or anti-GPR35 antibodies. Their expression was scored within the area of the normal gastric gland of non-atrophic gastritis (NAG-NOR), intestinal metaplasia of atrophic gastritis (AG-IM), IM adjacent to GC (GC-IM), and GC tissue. The clinical significance and potential function of CXCL17 and GPR35 were explored using multiple methods. Our results suggested that CXCL17 expression was gradually upregulated during the pathological progress of gastric diseases (NAG-NOR < AG-IM < GC-IM), but significantly downregulated when GC occurred. GPR35 had a similar expression pattern but its expression in GC remained abundant. High CXCL17 expression in GC was associated with less malignant behavior and was an independent biomarker of favorable prognosis. Overexpressing CXCL17 in HGC27 cells significantly upregulated CCL20 expression. TCGA analysis identified that CXCL17 was negatively correlated with some cancer-promoting pathways and involved in inflammatory activities. CTRP analysis revealed that gastric cell lines expressing less CXCL17 and were more sensitive to the CXCR2 inhibitor SB-225002.

Kynurenic acid ameliorates NLRP3 inflammasome activation by blocking calcium mobilization via GPR35

The inflammasome has been linked to diverse inflammatory and metabolic diseases, and tight control of inflammasome activation is necessary to avoid excessive inflammation. Kynurenic acid (KA) is a tryptophan metabolite in the kynurenine pathway. However, the roles and mechanisms of the regulation of inflammasome activation by KA have not yet been fully elucidated. Here, we found that KA suppressed caspase-1 activation and IL-1β production in macrophages by specifically inhibiting canonical and noncanonical activation of the NLRP3 inflammasome. Mechanistically, KA reduced calcium mobilization through G-protein receptor 35 (GPR35), resulting in reduced mitochondrial damage and decreased mtROS production, thus blocking NLRP3 inflammasome assembly and activation. Importantly, KA prevented lipopolysaccharide-induced systemic inflammation, monosodium urate-induced peritoneal inflammation, and high-fat diet-induced metabolic disorder. Thus, KA ameliorated inflammation and metabolic disorders by blocking calcium mobilization-mediated NLRP3 inflammasome activation via GPR35. Our data reveal a novel mechanism for KA in the modulation of inflammasome activation and suggest that GPR35 might be a promising target for improving NLRP3 inflammasome-associated diseases by regulating calcium mobilization.

A comprehensive review of chemokine CXC17 (VCC1) in cancer, infection, and inflammation

A crucial component of the immune system are chemokiness. Chemokine's dysregulation has been linked to a number of pathological diseases. Recently, CXCL17, a chemokine belonging to the CXC subfamily, was identified. With regard to a number of physiological conditions and disorders, CXCL17 either has homeostatic or pathogenic effects. Some research suggests that CXCL17 is an orphan ligand, despite the fact that G protein-coupled receptor (GPR) 35 has been suggested as a possible receptor for CXCL17. Since CXCL17 is primarily secreted by mucosal epithelia, such as those in the digestive and respiratory tracts, under physiological circumstances, this chemokine is referred to as a mucosal chemokine. Macrophages and monocytes are the cells that express GPR35 and hence react to CXCL17. In homeostatic conditions, this chemokine has anti-inflammatory, antibacterial, and chemotactic properties. CXCL17 promotes angiogenesis, metastasis, and cell proliferation in pathologic circumstances like malignancies. However, other studies suggest that CXCL17 may have anti-tumor properties. Additionally, studies have shown that CXCL17 may have a role in conditions such as idiopathic pulmonary fibrosis, multiple sclerosis, asthma, and systemic sclerosis. Additionally, deregulation of CXCL17 in some diseases may serve as a biomarker for diagnosis and prognosis. Clarifying the underlying mechanism of CXCL17's activity in homeostatic and pathological situations may thus increase our understanding of its role and hold promise for the development of novel treatment strategies.

The GPR35 expression pattern is associated with overall survival in male patients with colorectal cancer

BACKGROUND

G protein-coupled receptor 35 (GPR35) is involved in the carcinogenesis; however, limited data exist on its relevance for overall survival (OS) and disease-specific survival (DSS) in patients with cancer.

METHODS

We have examined The Cancer Genome Atlas dataset to check the relations between GPR35 expression pattern and OS or DSS of patients with colorectal cancer (CRC).

RESULTS

The performed analysis showed a negative association between positive GPR35 expression Z score and OS in males, which remains statistically significant in advanced stages of colon (COAD) and rectal (READ) adenocarcinoma combined.

CONCLUSIONS

These findings suggest the prognostic value of early testing of GPR35 in male patients with an increased risk of CRC development and warrant further clinical confirmation.

GPR35 promotes neutrophil recruitment in response to serotonin metabolite 5-HIAA

Rapid neutrophil recruitment to sites of inflammation is crucial for innate immune responses. Here, we reveal that the G-protein-coupled receptor GPR35 is upregulated in activated neutrophils, and it promotes their migration. GPR35-deficient neutrophils are less recruited from blood vessels into inflamed tissue, and the mice are less efficient in clearing peritoneal bacteria. Using a bioassay, we find that serum and activated platelet supernatant stimulate GPR35, and we identify the platelet-derived serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) as a GPR35 ligand. GPR35 function in neutrophil recruitment is strongly dependent on platelets, with the receptor promoting transmigration across platelet-coated endothelium. Mast cells also attract GPR35⁺ cells via 5-HIAA. Mice deficient in 5-HIAA show a loss of GPR35-mediated neutrophil recruitment to inflamed tissue. These findings identify 5-HIAA as a GPR35 ligand and neutrophil chemoattractant and establish a role for platelet- and mast cell-produced 5-HIAA in cell recruitment to the sites of inflammation and bacterial clearance.

Agonist-induced phosphorylation of orthologues of the orphan receptor GPR35 functions as an activation sensor

G protein-coupled receptor 35 (GPR35) is poorly characterized but nevertheless has been revealed to have diverse roles in areas including lower gut inflammation and pain. The development of novel reagents and tools will greatly enhance analysis of GPR35 functions in health and disease. Here, we used mass spectrometry, mutagenesis, and [³²P] orthophosphate labeling to identify that all five hydroxy-amino acids in the C-terminal tail of human GPR35a became phosphorylated in response to agonist occupancy of the receptor and that, apart from Ser²⁹⁴, each of these contributed to interactions with arretin-3, which inhibits further G protein-coupled receptor signaling. We found that Ser³⁰³ was key to such interactions; the serine corresponding to human GPR35a residue 303 also played a dominant role in arrestin-3 interactions for both mouse and rat GPR35. We also demonstrated that fully phospho-site–deficient mutants of human GPR35a and mouse GPR35 failed to interact effectively with arrestin-3, and the human phospho-deficient variant was not internalized from the surface of cells in response to agonist treatment. Even in cells stably expressing species orthologues of GPR35, a substantial proportion of the expressed protein(s) was determined to be immature. Finally, phospho-site–specific antisera targeting the region encompassing Ser³⁰³ in human (Ser³⁰¹ in mouse) GPR35a identified only the mature forms of GPR35 and provided effective sensors of the activation status of the receptors both in immunoblotting and immunocytochemical studies. Such antisera may be useful tools to evaluate target engagement in drug discovery and target validation programs.

Lysophosphatidylcholine (17:0) Improves HFD-Induced Hyperglycemia & Insulin Resistance: A Mechanistic Mice Model Study

PURPOSE

Type 2 diabetes mellitus is characterized by the dysregulation of glucose homeostasis and insulin sensitivity, resulting in hyperglycemia. The exploration of a complex regulatory network in host metabolism homeostasis may raise a novel strategy for the prevention of T2D. A variety of metabolites serve as the endogenous ligand of G protein-coupled receptors (GPCR) and play an important role in the pathophysiological process of T2D and insulin resistance, however, the roles of remaining endogenous metabolites in insulin resistance and GPCRs still need to be explored.

PATIENTS AND METHODS

The effect of LPC (17:0) on hyperglycemia were proved in high fat diet (HFD) mice, and qPCR with Western blot technology was used to verify the downstream targets.

RESULTS

Herein, we found that LPC (17:0) reduced blood glucose and alleviated insulin resistance and related metabolic disorders in high-fat diet induced (HFD) mice through activating GLP-1 and promoting insulin secretion. Further, the LPC (17:0) was found to stimulate intestinal GPR120, GPR35 and CALCR, with potential effect on GLP-1 stimulation.

CONCLUSION

The above observation revealed LPC (17:0) as an endogenous protective factor with potential role on GPCRs, and it provided theoretical support for the development of LPC (17:0) as a potent drug candidate or health food additive for insulin resistance and hyperglycemia.

GPR35 in Intestinal Diseases: From Risk Gene to Function

Diet and gut microbial metabolites mediate host immune responses and are central to the maintenance of intestinal health. The metabolite-sensing G-protein coupled receptors (GPCRs) bind metabolites and trigger signals that are important for the host cell function, survival, proliferation and expansion. On the contrary, inadequate signaling of these metabolite-sensing GPCRs most likely participate to the development of diseases including inflammatory bowel diseases (IBD). In the intestine, metabolite-sensing GPCRs are highly expressed by epithelial cells and by specific subsets of immune cells. Such receptors provide an important link between immune system, gut microbiota and metabolic system. Member of these receptors, GPR35, a class A rhodopsin-like GPCR, has been shown to be activated by the metabolites tryptophan-derived kynurenic acid (KYNA), the chemokine CXCL17 and phospholipid derivate lysophosphatidic acid (LPA) species. There have been studies on GPR35 in the context of intestinal diseases since its identification as a risk gene for IBD. In this review, we discuss the pharmacology of GPR35 including its proposed endogenous and synthetic ligands as well as its antagonists. We elaborate on the risk variants of GPR35 implicated in gut-related diseases and the mechanisms by which GPR35 contribute to intestinal homeostasis.

Disruption of GPR35 Signaling in Bone Marrow-Derived Cells Does Not Influence Vascular Inflammation and Atherosclerosis in Hyperlipidemic Mice

G-protein-coupled receptor-35 (GPR35) has been identified as a receptor for the tryptophan metabolite kynurenic acid (KynA) and suggested to modulate macrophage polarization in metabolic tissues. Whether GPR35 can influence vascular inflammation and atherosclerosis has however never been tested. Lethally irradiated LdlrKO mice were randomized to receive GPR35KO or wild type (WT) bone marrow transplants and fed a high cholesterol diet for eight weeks to develop atherosclerosis. GPR35KO and WT chimeric mice presented no difference in the size of atherosclerotic lesions in the aortic arch (2.37 ± 0.58% vs. 1.95 ± 0.46%, respectively) or in the aortic roots (14.77 ± 3.33% vs. 11.57 ± 2.49%, respectively). In line with these data, no changes in the percentage of VCAM-1+, IA^b + cells, and CD3+ T cells, as well as alpha smooth muscle cell actin expression, was observed between groups. Interestingly, the GPR35KO group presented a small but significant increase in CD68+ macrophage infiltration in the plaque. However, in vitro culture experiments using bone marrow-derived macrophages from both groups indicated that GPR35 plays no role in modulating the secretion of major inflammatory cytokines. Our study indicates that GPR35 expression does not play a direct role in macrophage activation, vascular inflammation, and the development of atherosclerosis.

Lysophosphatidic Acid-Mediated GPR35 Signaling in CX3CR1+ Macrophages Regulates Intestinal Homeostasis

Single-nucleotide polymorphisms in the gene encoding G protein-coupled receptor 35 (GPR35) are associated with increased risk of inflammatory bowel disease. However, the mechanisms by which GPR35 modulates intestinal immune homeostasis remain undefined. Here, integrating zebrafish and mouse experimental models, we demonstrate that intestinal Gpr35 expression is microbiota dependent and enhanced upon inflammation. Moreover, murine GPR35⁺ colonic macrophages are characterized by enhanced production of pro-inflammatory cytokines. We identify lysophosphatidic acid (LPA) as a potential endogenous ligand produced during intestinal inflammation, acting through GPR35 to induce tumor necrosis factor (Tnf) expression in macrophages. Mice lacking Gpr35 in CX3CR1⁺ macrophages aggravate colitis when exposed to dextran sodium sulfate, which is associated with decreased transcript levels of the corticosterone-generating gene Cyp11b1 and macrophage-derived Tnf. Administration of TNF in these mice restores Cyp11b1 expression and intestinal corticosterone production and ameliorates DSS-induced colitis. Our findings indicate that LPA signals through GPR35 in CX3CR1⁺ macrophages to maintain TNF-mediated intestinal homeostasis.

GPR35 regulates osteogenesis via the Wnt/GSK3β/β-catenin signaling pathway

It is well known that osteoporosis is a significant chronic disease with the increase of the aging population. Here, we report that expression of G protein-coupled receptor 35 (GPR35) in bone marrow mesenchymal stem cells (BMSCs) is suppressed in diagnosed osteoporosis patients and osteoporotic mice. The expression of GPR35 on BMSCs is enhanced during osteogenic differentiation. GPR35 knockout suppresses the proliferation and osteogenesis of BMSCs and deteriorates bone mass in both sham-treated and ovariectomized mice. Moreover, GPR35 deficiency reduces β-catenin activity in BMSCs. In contrast, the overexpression of GPR35 contributes to these processes in BMSCs. Finally, using zaprinast, a synthetic GPR35 agonist, we show that zaprinast rescues OVX-induced bone loss and promotes bone generation in mice. Thus, GPR35 may as a new target and its agonist zaprinast may serve as a novel treatment for osteoporosis.

Functional metabolomics reveal the role of AHR/GPR35 mediated kynurenic acid gradient sensing in chemotherapy-induced intestinal damage

Intestinal toxicity induced by chemotherapeutics has become an important reason for the interruption of therapy and withdrawal of approved agents. In this study, we demonstrated that chemotherapeutics-induced intestinal damage were commonly characterized by the sharp upregulation of tryptophan (Trp)−kynurenine (KYN)−kynurenic acid (KA) axis metabolism. Mechanistically, chemotherapy-induced intestinal damage triggered the formation of an interleukin-6 (IL-6)−indoleamine 2,3-dioxygenase 1 (IDO1)−aryl hydrocarbon receptor (AHR) positive feedback loop, which accelerated kynurenine pathway metabolism in gut. Besides, AHR and G protein-coupled receptor 35 (GPR35) negative feedback regulates intestinal damage and inflammation to maintain intestinal integrity and homeostasis through gradually sensing kynurenic acid level in gut and macrophage, respectively. Moreover, based on virtual screening and biological verification, vardenafil and linagliptin as GPR35 and AHR agonists respectively were discovered from 2388 approved drugs. Importantly, the results that vardenafil and linagliptin significantly alleviated chemotherapy-induced intestinal toxicity in vivo suggests that chemotherapeutics combined with the two could be a promising therapeutic strategy for cancer patients in clinic. This work highlights GPR35 and AHR as the guardian of kynurenine pathway metabolism and core component of defense responses against intestinal damage.

Inflammatory bowel disease susceptible gene GPR35 promotes bowel inflammation in mice

Inflammatory bowel disease (IBD) has emerged as a public health challenge with high incidence, recurrence rates and low cure rate. Moreover, sustained inflammation increases the risk of colorectal cancer. The occurrence and progression of IBD are closely related to the genetic mutation. Previous genome-wide association studies (GWAS) analysis demonstrated that the susceptibility loci rs4676410, rs3749171, and rs3749172 in theGPR35 gene locus increase the risk of IBD, but no direct evidence on the function ofGPR35 in IBD progression has been shown. To investigate the role ofGPR35 in IBD, CRISPR/Cas9 technology was employed to construct aGpr35 knockout mouse strain. TheGpr35^-/- mice exhibited lower susceptibility to dextran sodium sulfate-induced IBD model than the wildtype group with a significant reduction in body weight loss, DAI score, intestinal epithelial injury, and macrophage cell infiltration. To explore how the IBD susceptibility loci rs3749171 and rs3749172 regulate GPR35 activity, two mutant forms of GPR35 (T108M and S294R) were constructed. By analyzing the activity of GPR35 downstream signaling pathway, the two mutation forms of GPR35 exhibited higher receptor activity to Zaprinast than the wildtype GPR35. Finally, the Western blotting analysis found an elevated phosphorylation level of ERK1/2 inGpr35^-/- colon epithelial after DSS treatment, demonstrating that the loss function ofGpr35 alleviates the IBD syndrome by activating the ERK1/2 signaling pathway. In summary, the IBD susceptibility loci rs3749171 and rs3749172 may promote the disease progression by activating GPR35 activity, providing a potential drug target for the treatment of inflammatory bowel disease.

Prognostic value of CXCL17 and CXCR8 expression in patients with colon cancer

C-X-C motif chemokine ligand 17 (CXCL17) is a mucous chemokine and its expression is highly correlated with that of G protein-coupled receptor 35 (GPR35), which has been confirmed as its receptor and named C-X-C motif chemokine receptor 8 (CXCR8). CXCL17 is upregulated in several types of cancer. However, the biological role of this chemokine in colon cancer remains unknown. In the present study, the expression levels of CXCL17 and CXCR8 were examined using immunohistochemistry in 101 colon cancer tissues and 79 healthy tumour-adjacent tissues. CXCL17 and CXCR8 expression levels were increased in the colon cancer samples compared with tumour-adjacent samples. Patients with high CXCL17 expression had longer overall survival (OS) compared with patients with low expression of CXCL17 (log-rank test; P=0.027). However, CXCR8 expression, but not CXCL17, was an independent prognostic factor for OS in patients with colon cancer. The expression of CXCR8 correlated positively with that of CXCL17 in colon cancer samples (ρ=0.295; P=0.003). Furthermore, the combined high expression of CXCL17 and CXCR8 was a significant independent prognostic factor for OS in patients with colon cancer (P=0.001). In subgroups with a TNM stage of I–II, the patients with combined high expression of CXCL17 and CXCR8 had a longer survival compared with those without combined high expression (P=0.001). However, this difference was not observed in subgroups with a TNM stage of III–IV. Collectively, these findings suggest that CXCL17/CXCR8 signalling may be involved in colon cancer and contribute to improved patient outcomes.

Kynurenic acid and cancer: facts and controversies

Kynurenic acid (KYNA) is an endogenous tryptophan metabolite exerting neuroprotective and anticonvulsant properties in the brain. However, its importance on the periphery is still not fully elucidated. KYNA is produced endogenously in various types of peripheral cells, tissues and by gastrointestinal microbiota. Furthermore, it was found in several products of daily human diet and its absorption in the digestive tract was evidenced. More recent studies were focused on the potential role of KYNA in carcinogenesis and cancer therapy; however, the results were ambiguous and the biological activity of KYNA in these processes has not been unequivocally established. This review aims to summarize the current views on the relationship between KYNA and cancer. The differences in KYNA concentration between physiological conditions and cancer, as well as KYNA production by both normal and cancer cells, will be discussed. The review also describes the effect of KYNA on cancer cell proliferation and the known potential molecular mechanisms of this activity.

Kynurenic acid/GPR35 axis restricts NLRP3 inflammasome activation and exacerbates colitis in mice with social stress

Psychological stress is well known to increase colitis susceptibility and promote relapse. Metabolic changes are commonly observed under psychological stress, but little is known how this relates to the progression of colitis. Here we show that kynurenic acid (KA) is an endogenous driver of social stress-exacerbated colitis via regulating the magnitude of NLRP3 inflammasome. Chronic social defeat stress (CSDS) in mice induced colonic accumulation of KA, and mice receiving KA during CSDS had defects in colonic NLRP3 inflammasome activation. Mechanistically, KA activated GPR35 signaling to induce autophagy-dependent degradation of NLRP3 in macrophages, thereby suppressing IL-1β production. Socially defeated mice with KA treatment displayed enhanced vulnerability to subsequent dextran sulphate sodium (DSS)-induced colonic injury and inflammatory disturbance, and this effect was reversed by autophagic inhibition that blocked the NLRP3-suppressive effect of KA. Thus, our research describes a mechanism by which KA/GPR35 signaling represses adaptive NLRP3 inflammasome activation to increase colitis susceptibility and suggests a potential metabolic target for the intervention of stress-related colonic disorder.

Receptor selectivity between the G proteins Gα12 and Gα13 is defined by a single leucine-to-isoleucine variation

Despite recent advances in structural definition of GPCR-G protein complexes, the basis of receptor selectivity between G proteins remains unclear. The Gα₁₂ and Gα₁₃ subtypes together form the least studied group of heterotrimeric G proteins. G protein-coupled receptor 35 (GPR35) has been suggested to couple efficiently to Gα₁₃ but weakly to Gα₁₂. Using combinations of cells genome-edited to not express G proteins and bioluminescence resonance energy transfer-based sensors, we confirmed marked selectivity of GPR35 for Gα₁₃. Incorporating Gα₁₂/Gα₁₃ chimeras and individual residue swap mutations into these sensors defined that selectivity between Gα₁₃ and Gα₁₂ was imbued largely by a single leucine-to-isoleucine variation at position G.H5.23. Indeed, leucine could not be substituted by other amino acids in Gα₁₃ without almost complete loss of GPR35 coupling. The critical importance of leucine at G.H5.23 for GPR35-G protein interaction was further demonstrated by introduction of this leucine into Gα_q, resulting in the gain of coupling to GPR35. These studies demonstrate that Gα₁₃ is markedly the most effective G protein for interaction with GPR35 and that selection between Gα₁₃ and Gα₁₂ is dictated largely by a single conservative amino acid variation.-Mackenzie, A. E., Quon, T., Lin, L.-C., Hauser, A. S., Jenkins, L., Inoue, A., Tobin, A. B., Gloriam, D. E., Hudson, B. D., Milligan, G. Receptor selectivity between the G proteins Gα₁₂ and Gα₁₃ is defined by a single leucine-to-isoleucine variation.

The weight of nutrients: kynurenine metabolites in obesity and exercise

Obesity ultimately results from an imbalance between energy intake and expenditure. However, in addition to their bioenergetic value, nutrients and their metabolites can function as important signalling molecules in energy homeostasis. Indeed, macronutrients and their metabolites can be direct regulators of metabolism through their actions on different organs. In turn, target organs can decide to use, store or transform the incoming nutrients depending on their physiological context and in coordination with other cell types. Tryptophan-kynurenine metabolites are an example of a family of compounds that can serve as systemic integrators of energy metabolism by signalling to different cell types. These include adipocytes, immune cells and muscle fibres, in addition to the well-known effects of kynurenine metabolites on the central nervous system. In the context of energy metabolism, several of the effects elicited by kynurenic acid are mediated by the G-protein-coupled receptor, GPR35. As GPR35 is expressed in tissues such as the adipose tissue, immune cells and the gastrointestinal tract, this receptor could be a potential therapeutic target for the treatment of obesity, diabetes and other metabolic diseases. In addition, metabolic disorders often coincide with states of chronic inflammation, which further highlights GPR35 as an integration node in conditions where inflammation skews metabolism. Defining the molecular interplay between different tissues in the regulation of energy homeostasis can help us understand interindividual variability in the response to nutrient intake and develop safe and efficient therapies to fight obesity and metabolic disease.

Overexpression of GPR35 confers drug resistance in NSCLC cells by β-arrestin/Akt signaling

Background

Non-small-cell lung cancer (NSCLC) is the major leading cause of cancer-related death around the world. The resistance to chemotherapy limits the effects of clinical treatment. The aim of this study was to identify novel mechanisms involved in NSCLC chemoresistance.

Materials and methods

We explored the public database and commercial tissue microarray to evaluate the expression of G protein-coupled receptor 35 (GPR35). We established the chemoresistant A549 cell line to further investigate the biological function of GPR35 in vitro and in vivo. Then, we measured the altered signalings that GPR35 knocking down by Western blot assay.

Results

We demonstrated that GPR35 expression was significantly elevated in NSCLC tissues and correlated with poor prognosis. GPR35 was upregulated in our in vitro chemoresistance cell model. GPR35 depletion reduced the half maximal inhibitory concentration of chemodrugs and restored the sensitivity both in vitro and in vivo. Mechanically, we found that GPR35-mediated chemoresistance occurred partially via β-arrestin-2/Akt signaling. Furthermore, inhibition of β-arrestin-2 or Akt activation could suppress the GPR35 expression and overcome chemoresistance.

Conclusion

Our results suggested that GPR35 might serve as a novel therapeutic target to enhance the chemotherapy efficacy in NSCLC.

The Anti-allergic Cromones: Past, Present, and Future

The anti-allergic cromones were originally synthesized in the 1960s by Fisons Plc, and the first drug to emerge from this program, disodium cromoglycate was subsequently marketed for the treatment of asthma and other allergic conditions. Whilst early studies demonstrated that the ability of the cromones to prevent allergic reactions was due to their 'mast cell stabilizing' properties, the exact pharmacological mechanism by which this occurred, remained a mystery. Here, we briefly review the history of these drugs, recount some aspects of their pharmacology, and discuss two new explanations for their unique actions. We further suggest how these findings could be used to predict further uses for the cromones.

The role and clinical significance of the CXCL17-CXCR8 (GPR35) axis in breast cancer

BACKGROUND

Chemokine (C-X-C motif) ligand 17 (CXCL17) is the latest member of the chemokine family. However, its function in various cancer types is unknown. The G protein-coupled receptor 35 (GPR35) was identified as the receptor of CXCL17 and named recently as CXCR8. The function of the CXCL17-CXCR8 (GPR35) biological axis in cancer has not been reported.

METHODS

The expression of CXCL17 and CXCR8 (GPR35) in breast cancer cell lines and a tissue microarray (TMA) was detected through western blot and immunohistochemistry (IHC). Expression data in IHC were analyzed using clinicopatholigical and survival information.

RESULTS

CXCL17 and CXCR8 (GPR35) were found to be variably expressed in breast cancer cell lines. Both expressed higher in breast cancer tissue than normal adjacent tissue. Although CXCL17 can interact with CXCR8 (GPR35) in breast cancer cells in vitro, the expression correlation between these two markers in breast cancer tissue was not found to be significant. As to clinical significance, CXCR8 (GPR35) expression was found to be significantly associated with advanced histological grade and higher proliferation rate indicated by Ki-67 expression. Although CXCL17 was not found to statistically correlate with any clinicopathological characteristics, it was found to be associated with shorter overall survival and is an independent marker of poor prognosis in breast cancer. In addition, CXCL17 was found to promote proliferation and migration of breast cancer cells in vitro and in vivo.

CONCLUSIONS

We investigated the role of the CXCL17-CXCR8 (GPR35) axis in breast cancer for the first time. CXCL17 is a potential oncogene and promising therapeutic target, is an independent biomarker of poor prognosis in patients with breast cancer, and can promote proliferation and migration of breast cancer cells in vitro and in vivo.

G protein-coupled receptor 35 contributes to mucosal repair in mice via migration of colonic epithelial cells

G protein-coupled receptor 35 (GPR35), a receptor for lysophosphatidic acid, is highly expressed in the gastrointestinal tract. Recently, GPR35 has been implicated in the onset of inflammatory bowel disease (IBD), but its role in physiological and pathological processes in the colon remains undefined. In this study, we investigated the contribution of GPR35-mediated signalling to mucosal repair of colonic epithelium in IBD. GPR35 function was examined in a wound healing model, using young adult mouse colon epithelium (YAMC) cells, and in a dextran sulphate sodium (DSS)-induced mouse model of colitis. Cell proliferation, mRNA expression, extracellular signal-regulated kinase (ERK) activation, and protein localization were determined by MTT assay, quantitative RT-PCR, western blotting, and immunohistochemistry, respectively. GPR35 agonists (YE120, zaprinast, and pamoic acid) promoted wound repair in a concentration-dependent manner independently of cell proliferation, whereas a specific GPR35 antagonist CID2745687, forskolin, and pertussis toxin reversed the YE120-induced effect. YE120 increased the mRNA expression of fibronectin and its receptor integrin α5, and ERK1/2 phosphorylation, but these responses were attenuated by CID2745687 and forskolin. Furthermore, the severity of DSS-induced colitis was significantly reduced by daily injections of pamoic acid via upregulation of fibronectin and integrin α5 in the colonic epithelium. GPR35 signalling promotes mucosal repair by inducing fibronectin and integrin α5 expression, coupling to Gi protein, and activating ERK1/2 in colonic epithelial cells. These findings define GPR35 as a candidate therapeutic target in IBD.

Structure-activity relationships of benzothiazole GPR35 antagonists

The first structure-activity relationships for a benzothiazole scaffold acting as an antagonist at GPR35 is presented. Analogues were designed based on a lead compound that was previously determined to have selective activity as a GPR35 antagonist. The synthetic route was modular in nature to independently explore the role of the middle and both ends of the scaffold. The activities of the analogues illustrate the importance of all three segments of the compound.

Kynurenic acid and zaprinast induce analgesia by modulating HCN channels through GPR35 activation

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels have a key role in the control of cellular excitability. HCN2, a subgroup of the HCN family channels, are heavily expressed in small dorsal root ganglia (DRG) neurons and their activation seems to be important in the determination of pain intensity. Intracellular elevation of cAMP levels activates HCN-mediated current (Ih) and small DRG neurons excitability. GPR35, a Gi/o coupled receptor, is highly expressed in small DRG neurons, and we hypothesized that its activation, mediated by endogenous or exogenous ligands, could lead to pain control trough a reduction of Ih current. Patch clamp recordings were carried out in primary cultures of rat DRG neurons and the effects of GPR35 activation on Ih current and neuronal excitability were studied in control conditions and after adenylate cyclase activation with either forskolin or prostaglandin E2 (PGE2). We found that both kynurenic acid (KYNA) and zaprinast, the endogenous and synthetic GPR35 agonist respectively, were able to antagonize the forskolin-induced depolarization of resting membrane potential by reducing Ih-mediated depolarization. Similar results were obtained when PGE2 was used to activate adenylate cyclase and to increase Ih current and the overall neuronal excitability. Finally, we tested the analgesic effect of both GPR35 agonists in an in vivo model of PGE2-induced thermal hyperalgesia. In accord with the hypothesis, both KYNA and zaprinast showed a dose dependent analgesic effect. In conclusion, GPR35 activation leads to a reduced excitability of small DRG neurons in vitro and causes a dose-dependent analgesia in vivo. GPR35 agonists, by reducing adenylate cyclase activity and inhibiting Ih in DRG neurons may represent a promising new group of analgesic drugs.

Label-Free Cell Phenotypic Identification of D-Luciferin as an Agonist for GPR35

D-Luciferin (also known as beetle or firefly luciferin) is one of the most widely used bioluminescent reporters for monitoring in vitro or in vivo luciferase activity. The identification of several natural phenols and thieno[3,2-b]thiophene-2-carboxylic acid derivatives as agonists for GPR35, an orphan G protein-coupled receptor, had motivated us to examine the pharmacological activity of D-Luciferin, given that it also contains phenol and carboxylic acid moieties. Here, we describe label-free cell phenotypic assays that ascertain D-Luciferin as a partial agonist for GPR35. The agonistic activity of D-Luciferin at the GPR35 shall evoke careful interpretation of biological data when D-Luciferin or its analogues are used as probes.

The therapeutic potential of orphan GPCRs, GPR35 and GPR55

The G protein-coupled receptor (GPCR) superfamily of integral proteins is the largest family of signal transducers, comprised of ∼1000 members. Considering their prevalence and functional importance, it’s not surprising that ∼60% of drugs target GPCRs. Regardless, there exists a subset of the GPCR superfamily that is largely uncharacterized and poorly understood; specifically, more than 140 GPCRs have unknown endogenous ligands—the so-called orphan GPCRs. Orphan GPCRs offer tremendous promise, as they may provide novel therapeutic targets that may be more selective than currently known receptors, resulting in the potential reduction in side effects. In addition, they may provide access to signal transduction pathways currently unknown, allowing for new strategies in drug design. Regardless, orphan GPCRs are an important area of inquiry, as they represent a large gap in our understanding of signal transduction at the cellular level. Here, we focus on the therapeutic potential of two recently deorphanized GPCRs: GPR35/CXCR8 and GPR55. First, GPR35/CXCR8 has been observed in numerous tissues/organ systems, including the gastrointestinal tract, liver, immune system, central nervous system, and cardiovascular system. Not surprisingly, GPR35/CXCR8 has been implicated in numerous pathologies involving these tissues/systems. While several endogenous ligands have been identified, GPR35/CXCR8 has recently been observed to bind the chemokine CXCL17. Second, GPR55 has been observed to be expressed in the central nervous system, adrenal glands, gastrointestinal tract, lung, liver, uterus, bladder, kidney, and bone, as well as, other tissues/organ systems. Likewise, it is not surprising that GPR55 has been implicated in pathologies involving these tissues/systems. GPR55 was initially deorphanized as a cannabinoid receptor and this receptor does bind many cannabinoid compounds. However, the GPR55 endogenous ligand has been found to be a non-cannabinoid, lysophophatidylinositol (LPI) and subsequent high throughput assays have identified other GPR55 ligands that are not cannabinoids and do not bind to either the cannabinoid CB1 and CB2 receptors. Here, we review reports that suggest that GPR35/CXCR8 and GPR55 may be promising therapeutic targets, with diverse physiological roles.

G protein-coupled receptor 35: an emerging target in inflammatory and cardiovascular disease

G protein-coupled receptor 35 (GPR35) is an orphan receptor, discovered in 1998, that has garnered interest as a potential therapeutic target through its association with a range of diseases. However, a lack of pharmacological tools and the absence of convincingly defined endogenous ligands have hampered the understanding of function necessary to exploit it therapeutically. Although several endogenous molecules can activate GPR35 none has yet been confirmed as the key endogenous ligand due to reasons that include lack of biological specificity, non-physiologically relevant potency and species ortholog selectivity. Recent advances have identified several highly potent synthetic agonists and antagonists, as well as agonists with equivalent potency at rodent and human orthologs, which will be useful as tool compounds. Homology modeling and mutagenesis studies have provided insight into the mode of ligand binding and possible reasons for the species selectivity of some ligands. Advances have also been made in determining the role of the receptor in disease. In the past, genome-wide association studies have associated GPR35 with diseases such as inflammatory bowel disease, type 2 diabetes, and coronary artery disease. More recent functional studies have implicated it in processes as diverse as heart failure and hypoxia, inflammation, pain transduction and synaptic transmission. In this review, we summarize the progress made in understanding the molecular pharmacology, downstream signaling and physiological function of GPR35, and discuss its emerging potential applications as a therapeutic target.

Hypoxia-inducible factor 1-induced G protein-coupled receptor 35 expression is an early marker of progressive cardiac remodelling

AIMS

G protein-coupled receptor 35 (GPR35) has been characterized to be one of the genes that are up-regulated in human heart failure. Since mechanisms controlling GPR35 expression are not known, we investigated the regulation of GPR35 gene and protein expression in cardiac myocytes and in the mouse models of cardiac failure.

METHODS AND RESULTS

In cardiac myocytes, GPR35 gene expression was found to be exceptionally sensitive to hypoxia and induced by hypoxia-inducible factor-1 (HIF-1) activation. HIF-1-dependent regulation was established by genetic (HIF-1/VP16, Inhibitory Per/Arnt/Sim domain protein) and chemical [desferrioxamine (DFO)] modulation of the HIF-1 pathway and further confirmed by mutation analysis of the GPR35 promoter and by demonstrating direct binding of endogenous HIF-1 to the gene promoter. Hypoxia increased the number and density of GPR35 receptors on the cardiomyocyte cell membranes. Chemical GPR35 agonist Zaprinast caused GPR35 activation and receptor internalization in cardiac myocytes. In addition, overexpressed GPR35 disrupted actin cytoskeleton arrangement and caused morphological changes in cultured cardiomyocytes. GPR35 gene and protein expressions were also induced in mouse models of cardiac failure; the acute phase of myocardial infarction and during the compensatory and decompensatory phase of pressure-load induced cardiac hypertrophy.

CONCLUSIONS

Cardiac expression of GPR35 is regulated by hypoxia through activation of HIF-1. The expression of GPR35 in mouse models of cardiac infarction and pressure load suggests that GPR35 could be used as an early marker of progressive cardiac failure.

Synthesis and Agonistic Activity at the GPR35 of 5,6-Dihydroxyindole-2-carboxylic Acid Analogues

5,6-Dihydroxyindole-2-carboxylic acid (DHICA), an intermediate of melanin synthesis and an eumelanin building block, was recently discovered to be a GPR35 agonist with moderate potency. Here, we report the synthesis and pharmacological characterization of a series of DHICA analogues against GPR35 using both label-free dynamic mass redistribution and Tango β-arrestin translocation assays. This led to identification of novel GPR35 agonists with improved potency and/or having biased agonism.

Discovery of Natural Phenols as G Protein-Coupled Receptor-35 (GPR35) Agonists

We report the discovery and characterization of natural phenols as G protein-coupled receptor-35 (GPR35) agonists. Pharmacological characterization using label-free dynamic mass redistribution and Tango β-arrestin translocation assays revealed that GPR35-active natural phenols are divergent in their biased agonism.

GPR35 as a Novel Therapeutic Target

G protein-coupled receptors (GPCRs) remain the best studied class of cell surface receptors and the most tractable family of proteins for novel small molecule drug discovery. Despite this, a considerable number of GPCRs remain poorly characterized and in a significant number of cases, endogenous ligand(s) that activate them remain undefined or are of questionable physiological relevance. GPR35 was initially discovered over a decade ago but has remained an "orphan" receptor. Recent publications have highlighted novel ligands, both endogenously produced and synthetic, which demonstrate significant potency at this receptor. Furthermore, evidence is accumulating which highlights potential roles for GPR35 in disease and therefore, efforts to characterize GPR35 more fully and develop it as a novel therapeutic target in conditions that range from diabetes and hypertension to asthma are increasing. Recently identified ligands have shown marked species selective properties, indicating major challenges for future drug development. As we begin to understand these issues, the continuing efforts to identify novel agonist and antagonist ligands for GPR35 will help to decipher its true physiological relevance; translating multiple assay systems in vitro, to animal disease systems in vivo and finally to man.