Defining the origins and evolution of the chemokine/chemokine receptor system

Selection Pressure Regulates the Evolution-Structure-Function Paradigm of Monocyte Chemoattractant Protein Family

Monocyte chemoattractant proteins (MCPs) are involved in monocyte trafficking during severe inflammation by modulating the chemokine-glycosaminoglycan-receptor signaling axis. MCPs comprise a family of four chemokines (CCL2, CCL7, CCL8, and CCL13/12) that exhibit differential expression patterns in mammals, functional diversity, and receptor/glycosaminoglycan (GAG) binding promiscuity. In this context, the evolution-structure-function paradigm of MCP chemokines in mammals was established by assessing phylogeny, functional divergence, selection pressure, and coevolution in correlation with structural and surface characteristics. Comprehensive analyses were performed using an array of evolutionary and structural bioinformatic methods including molecular dynamics simulations. Our findings demonstrate that substitutions in receptor/GAG-interacting residues mediate episodic diversification and functional diversity in MCP chemokines. Additionally, a balanced interplay of selection pressures has driven the functional changes observed among MCP paralogs, with positive selection at various receptor/GAG-binding sites contributing to their promiscuous receptor/GAG interactions. Meanwhile, processes like purifying selection and coevolution maintain the classical chemokine structure and preserve the ancestral functions of MCP chemokines. Overall, this study suggests that selection pressure on sites within the N-terminal region [N-loop and 310-helix] and 40S loop of MCP chemokines alters surface properties to fine-tune the molecular interactions and functional characteristics without altering the overall chemokine structure.

SDF-1/CXCR4 axis maintains porcine prospermatogonia undifferentiated state through regulation of transcription suppressor PLZF

Prospermatogonia (ProSGs), the progenitors of spermatogonial stem cells in neonatal testes, undergo critical migration to the testicular microenvironment-a fundamental process for testicular development and subsequent spermatogenic capacity. The SDF-1/CXCR4 chemokine axis serves as an essential molecular guidance mechanism, directing ProSGs toward the basal membrane of seminiferous tubules. Nevertheless, the precise molecular mechanisms governing this axis remain incompletely understood. Utilizing a porcine in vitro model system, this investigation elucidated the molecular mechanisms underlying the SDF-1/CXCR4 axis in ProSGs fate determination. Through integrated molecular and transcriptomic analyses, we investigated the consequences of CXCR4 inhibition on ProSG cellular dynamics. Our findings demonstrated that the SDF-1/CXCR4 axis exerts regulatory control over ProSGs differentiation via the PI3K-AKT-AP-1 signaling cascade. This regulation significantly influences the transcriptional landscape of ProSGs, particularly modulating the expression of PLZF, a crucial suppressor of spermatogonial differentiation, and DMRT1, an essential mediator of germ cell differentiation. These findings elucidate the molecular mechanisms orchestrating ProSGs homing and emphasize the significance of maintaining male reproductive competence. Furthermore, this research could enhance our understanding of ProSGs biology and its relationship to boar fertility, while potentially facilitating the development of innovative reproductive technologies and sustainable livestock management strategies.

Immune Response of Silver Pomfret (Pampus argenteus) CC Chemokine Ligand Gene Family to Photobacterium damselae Subsp. Damselae and Nocardia seriolae Infections

Chemokines play a crucial role in immune responses by facilitating the migration of cells expressing corresponding chemokine receptors along concentration gradients. Photobacterium damselae subsp. Damselae (PDD) and Nocardia seriolae (NS) are known to induce substantial mortality in silver pomfret populations, yet there exists a dearth of research regarding the immune response of CCLs in PDD- or NS-infected silver pomfret. In our investigation, we identified 10 PaCCLs, which include one fish-specific CCL (PaCCL44). Phylogenetic analysis revealed considerable diversity in CCL types and copy numbers among various teleost fishes. Notably, silver pomfret lacks specific CCL genes, with most PaCCLs exhibiting heightened expression levels in immune-related organs such as the spleen and kidney, and some being expressed in mucosal immune-related organs like the skin and gills. Transcriptome analysis conducted on silver pomfret infected with NS and PDD elucidated that the expression changes of PaCCLs primarily manifested in the spleen during the initial stages of NS infection, shifting to the kidney in later stages. Conversely, the expression changes of PaCCLs following PDD infection predominantly occurred in the kidney. In vitro studies using silver pomfret spleen cell lines demonstrated an early peak in PaCCLs expression during infection, followed by gradual decline with NS treatment and rapid diminishment with PDD treatment. These findings suggest that PaCCLs primarily support the innate immunity of silver pomfret, potentially exhibiting chemotactic effects in the early infection stages, such as the synergistic action of PaCCL4 and PaCCL25, and later serving as direct antibacterial agents. NS invasion is characterised by a chronic infection affecting multiple organs, whereas PDD primarily inflicts severe damage to the kidney. PaCCL19a and PaCCL19b are specific to PDD, and their expression levels may decrease in the later stages of infection due to PDD immune escape. These data offer initial insights into understanding the mechanism underlying the innate immune response of the CCL gene family in silver pomfret and provide theoretical underpinnings for fish culture practices.

CXCL12/CXCR4 Axis Promotes the Chemotaxis and Phagocytosis of B Cells through the PI3K-AKT Signaling Pathway in an Early Vertebrate

Chemokines play crucial roles in the regulation of immune cell migration and development. The CXCL12/CXCR4 axis has been extensively studied in mammals, but its regulatory mechanism in teleost fish remains unclear. In this study, we used Nile tilapia (Oreochromis niloticus) as a teleost model to investigate the mediation of the CXCL12/CXCR4 axis in IgM+ B cells. Our findings demonstrate that the CXCL12/CXCR4 axis exhibits chemotactic activity on IgM+ B cells and promotes the phagocytosis of IgM+ B cells. Blocking CXCR4 severely impairs the chemotaxis and phagocytosis of IgM+ B cells in vitro and reduces the percentages and numbers of IgM+ B cells that migrate to peripheral blood after pathogen infection in vivo. This reduction in migration leads to a decrease in the inflammatory response, an increase in tissue bacterial load, and a decrease in survival rate. We also discovered that the evolutionarily conserved PI3K-AKT signaling pathway and Girdin are involved in the immune response during Streptococcus agalactiae infection. Inhibitors of the PI3K-AKT signaling pathway prevent the chemotaxis and phagocytosis of IgM+ B cells, impair the expression and phosphorylation levels of related proteins in vitro, and prevent IgM+ B cells chemotaxis into the peripheral blood after pathogen infection in vivo. Furthermore, CXCR4 blocking significantly downregulates the expression of AKT and Girdin. Overall, our study reveals the regulatory mechanism of the CXCL12/CXCR4 axis on IgM+ B cells via the PI3K-AKT signaling pathway in tilapia, suggesting that the functions of the CXCL12/CXCR4 axis in B cells may be conserved between mammals and teleost fish.

Redirecting NK cells to the lymph nodes to augment their lymphoma-targeting capacity

CAR-NK cells can induce remission in lymphoma patients. We speculate that the full potential of adoptive NK cell immunotherapy against lymphoma is restricted by their poor lymph node (LN) homing capacity. Here, we have utilized a clinically approved transfection method with the aim of redirecting NK cells to LNs. Electroporation of ex vivo expanded NK cells with mRNAs coding for CCR7, CXCR5, and CD62L resulted in increased in vitro migration towards chemokines and mouse LN-derived supernatant. Following infusion into SCID/Beige mice, modified NK cells showed enhanced LN homing. Importantly, lymphoma patient-derived NK cells were equally well expanded and engineered as healthy donor NK cells, highlighting their translational potential. Additionally, the introduction of high-affinity CD16, together with the homing molecules, also augmented their ADCC capacity against autologous lymphoma cells. Hence, genetic engineering can be utilized to enhance NK cell LN homing. The homing concept may synergize with CAR- or monoclonal/bi-/tri-specific antibody-based approaches.

Antibacterial efficacy and mechanism of Cyprinus carpio chemokine-derived L-10 against multidrug-resistant Escherichia coli infections

OBJECTIVES

Antimicrobial resistance has raised concerns regarding untreatable infections and poses a growing threat to public health. Rational design of new AMPs is an ideal solution to this threat.

METHODS

In this study, we designed, modified, and synthesised an excellent AMP, L-10, based on the original sequence of the Cyprinus carpio chemokine. All experimental data were presented as the mean ± standard deviation (SD), and the two-tailed unpaired T-test method was used to analyze all data.

RESULTS

L-10 exhibited excellent antibacterial activity with negligible toxicity and improved the efficacy of a broad class of antibiotics against MDR Gram-negative pathogens, including tetracycline, meropenem, levofloxacin, and rifampin. Mechanistic studies have suggested that L-10 targets the bacterial membrane components, LPS and PG, to disrupt bacterial membrane integrity, thereby exerting antibacterial effects and enhancing the efficacy of antibiotics. Moreover, in animal infection models, L-10 significantly increased the survival rate of infected animals and effectively reduced the tissue bacterial load and inflammatory factor levels. In addition to its direct antibacterial activity, L-10 dramatically reduced pulmonary pathological alterations in a mouse model of endotoxemia and suppressed LPS-induced proinflammatory cytokines in vitro and in vivo. Lastly, L-10 was successfully expressed in Pichia pastoris and maintained antimicrobial activity against MDR Gram-negative pathogens in vivo and in vitro.

CONCLUSION

Collectively, these results reveal the potential of L-10 as an ideal candidate against MDR bacterial infections and provide new insights into the design, development, and clinical application of AMPs.

The origin, evolution, and molecular diversity of the chemokine system

Chemokine signalling performs key functions in cell migration via chemoattraction, such as attracting leukocytes to the site of infection during host defence. The system consists of a ligand, the chemokine, usually secreted outside the cell, and a chemokine receptor on the surface of a target cell that recognises the ligand. Several noncanonical components interact with the system. These include a variety of molecules that usually share some degree of sequence similarity with canonical components and, in some cases, are known to bind to canonical components and/or to modulate cell migration. Whereas canonical components have been described in vertebrate lineages, the distribution of the noncanonical components is less clear. Uncertainty over the relationships between canonical and noncanonical components hampers our understanding of the evolution of the system. We used phylogenetic methods, including gene-tree to species-tree reconciliation, to untangle the relationships between canonical and noncanonical components, identify gene duplication events, and clarify the origin of the system. We found that unrelated ligand groups independently evolved chemokine-like functions. We found noncanonical ligands outside vertebrates, such as TAFA "chemokines" found in urochordates. In contrast, all receptor groups are vertebrate-specific and all-except ACKR1-originated from a common ancestor in early vertebrates. Both ligand and receptor copy numbers expanded through gene duplication events at the base of jawed vertebrates, with subsequent waves of innovation occurring in bony fish and mammals.

The Teleost CXCL13-CXCR5 Axis Induces Inflammatory Cytokine Expression through the Akt-NF-κB, p38-AP-1, and p38-NF-κB Pathways

The ancestors of chemokines originate in the most primitive of vertebrates, which has recently attracted great interest in the immune functions and the underlying mechanisms of fish chemokines. In the current study, we identified an evolutionarily conserved chemokine, CiCXCL13, from a teleost fish, grass carp. CiCXCL13 was characterized by a typical SCY (small cytokine CXC) domain and four cysteine residues (C34, C36, C61, C77), with the first two cysteines separated by a random amino acid residue, although it shared 24.2-54.8% identity with the counterparts from other vertebrates. CiCXCL13 was an inducible chemokine, whose expression was significantly upregulated in the immune tissues of grass carps after grass carp reovirus infection. CiCXCL13 could bind to the membrane of grass carp head kidney leukocytes and promote cell migration, NO release, and the expression of >15 inflammatory cytokines, including IL-1β, TNF-α, IL-10 and TGF-β1, thus regulating the inflammatory response. Mechanistically, CiCXCL13 interacted with its evolutionarily conserved receptor CiCXCR5 and activated the Akt-NF-κB and p38-AP-1 pathways, as well as a previously unrevealed p38-NF-κB pathway, to efficiently induce inflammatory cytokine expression, which was distinct from that reported in mammals. Zebrafish CXCL13 induced inflammatory cytokine expression through Akt, p38, NF-κB, and AP-1 as CiCXCL13. Meanwhile, the CiCXCL13-CiCXCR5 axis-mediated inflammatory activity was negatively shaped by grass carp atypical chemokine receptor 2 (CiACKR2). The present study is, to our knowledge, the first to comprehensively define the immune function of CXCL13 in inflammatory regulation and the underlying mechanism in teleosts, and it provides a valuable perspective on the evolution and biology of fish chemokines.

How chemokines organize the tumour microenvironment

For our immune system to contain or eliminate malignant solid tumours, both myeloid and lymphoid haematopoietic cells must not only extravasate from the bloodstream into the tumour tissue but also further migrate to various specialized niches of the tumour microenvironment to functionally interact with each other, with non-haematopoietic stromal cells and, ultimately, with cancer cells. These interactions regulate local immune cell survival, proliferative expansion, differentiation and their execution of pro-tumour or antitumour effector functions, which collectively determine the outcome of spontaneous or therapeutically induced antitumour immune responses. None of these interactions occur randomly but are orchestrated and critically depend on migratory guidance cues provided by chemokines, a large family of chemotactic cytokines, and their receptors. Understanding the functional organization of the tumour immune microenvironment inevitably requires knowledge of the multifaceted roles of chemokines in the recruitment and positioning of its cellular constituents. Gaining such knowledge will not only generate new insights into the mechanisms underlying antitumour immunity or immune tolerance but also inform the development of biomarkers (or 'biopatterns') based on spatial tumour tissue analyses, as well as novel strategies to therapeutically engineer immune responses in patients with cancer. Here we will discuss recent observations on the role of chemokines in the tumour microenvironment in the context of our knowledge of their physiological functions in development, homeostasis and antimicrobial responses.

Mitochondrial Impairment: A Link for Inflammatory Responses Activation in the Cardiorenal Syndrome Type 4

Cardiorenal syndrome type 4 (CRS type 4) occurs when chronic kidney disease (CKD) leads to cardiovascular damage, resulting in high morbidity and mortality rates. Mitochondria, vital organelles responsible for essential cellular functions, can become dysfunctional in CKD. This dysfunction can trigger inflammatory responses in distant organs by releasing Damage-associated molecular patterns (DAMPs). These DAMPs are recognized by immune receptors within cells, including Toll-like receptors (TLR) like TLR2, TLR4, and TLR9, the nucleotide-binding domain, leucine-rich-containing family pyrin domain-containing-3 (NLRP3) inflammasome, and the cyclic guanosine monophosphate (cGMP)-adenosine monophosphate (AMP) synthase (cGAS)-stimulator of interferon genes (cGAS-STING) pathway. Activation of these immune receptors leads to the increased expression of cytokines and chemokines. Excessive chemokine stimulation results in the recruitment of inflammatory cells into tissues, causing chronic damage. Experimental studies have demonstrated that chemokines are upregulated in the heart during CKD, contributing to CRS type 4. Conversely, chemokine inhibitors have been shown to reduce chronic inflammation and prevent cardiorenal impairment. However, the molecular connection between mitochondrial DAMPs and inflammatory pathways responsible for chemokine overactivation in CRS type 4 has not been explored. In this review, we delve into mechanistic insights and discuss how various mitochondrial DAMPs released by the kidney during CKD can activate TLRs, NLRP3, and cGAS-STING immune pathways in the heart. This activation leads to the upregulation of chemokines, ultimately culminating in the establishment of CRS type 4. Furthermore, we propose using chemokine inhibitors as potential strategies for preventing CRS type 4.

Latent Epigenetic Programs in Müller Glia Contribute to Stress, Injury, and Disease Response in the Retina

Previous studies have demonstrated the dynamic changes in chromatin structure during retinal development that correlate with changes in gene expression. However, a major limitation of those prior studies was the lack of cellular resolution. Here, we integrate single-cell (sc) RNA-seq and scATAC-seq with bulk retinal data sets to identify cell type-specific changes in the chromatin structure during development. Although most genes' promoter activity is strongly correlated with chromatin accessibility, we discovered several hundred genes that were transcriptionally silent but had accessible chromatin at their promoters. Most of those silent/accessible gene promoters were in the Müller glial cells. The Müller cells are radial glia of the retina and perform a variety of essential functions to maintain retinal homeostasis and respond to stress, injury, or disease. The silent/accessible genes in Müller glia are enriched in pathways related to inflammation, angiogenesis, and other types of cell-cell signaling and were rapidly activated when we tested 15 different physiologically relevant conditions to mimic retinal stress, injury, or disease in human and murine retinae. We refer to these as "pliancy genes" because they allow the Müller glia to rapidly change their gene expression and cellular state in response to different types of retinal insults. The Müller glial cell pliancy program is established during development, and we demonstrate that pliancy genes are necessary and sufficient for regulating inflammation in the murine retina in vivo. In zebrafish, Müller glia can de-differentiate and form retinal progenitor cells that replace lost neurons. The pro-inflammatory pliancy gene cascade is not activated in zebrafish Müller glia following injury, and we propose a model in which species-specific pliancy programs underly the differential response to retinal damage in species that can regenerate retinal neurons (zebrafish) versus those that cannot (humans and mice).

Molecular characterization, structural and expression analysis of twelve CXC chemokines and eight CXC chemokine receptors in largemouth bass (Micropterus salmoides)

The chemokine-receptor system plays important roles in the leukocyte trafficking, inflammation, immune cell differentiation, cancer and other biological processes. In the present study, the sequence features, structures and expression patterns of twelve CXC chemokine ligands (CXCL8a.1, CXCL8a.2, CXCL8b.1, CXCL8b.2, CXCL12a, CXCL12b, CXCL13.1, CXCL13.2, CXCL14, CXCL18a, CXCL18b and CXCL19) and eight CXC chemokine receptors (CXCR1, CXCR2, CXCR3.1, CXCR3.2, CXCR3.3, CXCR4a, CXCR4b and CXCR5) of largemouth bass (Micropterus salmoides) were analyzed. All the CXCLs and CXCRs of largemouth bass shared high sequence identities with their teleost counterparts and possessed conserved motifs and structures of CXCLs and CXCRs family. Realtime qPCR revealed that these CXCLs and CXCRs were ubiquitously expressed in all examined tissues, with high expression levels in the immune-related tissues (spleen, head kidney, and gill). Following lipopolysaccharide (LPS) and polyinosinic-polycytidylic acid (polyI:C) stimulations, most of these CXCLs and CXCRs were significantly up-regulated in spleen. In addition, the potential interacted molecules of these CXCLs and CXCRs were analyzed by protein-protein interaction network analysis. To the best of our knowledge, this is the first study that in detail analyzes the CXCLs and CXCRs of largemouth bass. Our results provide valuable basis for study the function and mechanism of chemokine-receptor system in largemouth bass.

Structural and Phylogenetic Analysis of CXCR4 Protein Reveals New Insights into Its Role in Emerging and Re-Emerging Diseases in Mammals

Chemokine receptor type 4 (CXCR4) is a G protein-coupled receptor that plays an essential role in immune system function and disease processes. Our study aims to conduct a comparative structural and phylogenetic analysis of the CXCR4 protein to gain insights into its role in emerging and re-emerging diseases that impact the health of mammals. In this study, we analyzed the evolution of CXCR4 genes across a wide range of mammalian species. The phylogenetic study showed species-specific evolutionary patterns. Our analysis revealed novel insights into the evolutionary history of CXCR4, including genetic changes that may have led to functional differences in the protein. This study revealed that the structural homologous human proteins and mammalian CXCR4 shared many characteristics. We also examined the three-dimensional structure of CXCR4 and its interactions with other molecules in the cell. Our findings provide new insights into the genomic landscape of CXCR4 in the context of emerging and re-emerging diseases, which could inform the development of more effective treatments or prevention strategies. Overall, our study sheds light on the vital role of CXCR4 in mammalian health and disease, highlighting its potential as a therapeutic target for various diseases impacting human and animal health. These findings provided insight into the study of human immunological disorders by indicating that Chemokines may have activities identical to or similar to those in humans and several mammalian species.

Chemokine clouding and liver cancer heterogeneity: Does it impact clinical outcomes?

Tumor heterogeneity is a predominant feature of hepatocellular carcinoma (HCC) that plays a crucial role in chemoresistance and limits the efficacy of available chemo/immunotherapy regimens. Thus, a better understanding regarding the molecular determinants of tumor heterogeneity will help in developing newer strategies for effective HCC management. Chemokines, a sub-family of cytokines are one of the key molecular determinants of tumor heterogeneity in HCC and are involved in cell survival, growth, migration, and angiogenesis. Herein, we provide a panoramic insight into the role of chemokines in HCC heterogeneity at genetic, epigenetic, metabolic, immune cell composition, and tumor microenvironment levels and its impact on clinical outcomes. Interestingly, our in-silico analysis data showed that expression of chemokine receptors impacts infiltration of various immune cell populations into the liver tumor and leads to heterogeneity. Thus, it is evident that aberrant chemokines clouding impacts HCC tumor heterogeneity and understanding this phenomenon in depth could be harnessed for the development of personalized medicine strategies in future.

Genome-wide identification, evolutionary analysis, and antimicrobial activity prediction of CC chemokines in allotetraploid common carp, Cyprinus carpio

Chemokines are a group of secreted small molecules which are essential for cell migration in physiological and pathological conditions by binding to specific chemokine receptors. They are structurally classified into five groups, namely CXC, CC, CX3C, XC and CX. CC chemokine group is the largest one among them. In this study, we identified and characterized 61 CC chemokines from allotetraploid common carp (Cyprinus carpio). The sequence analyses showed that the majority of CC chemokines had an N-terminal signal peptide, and an SCY domain, and all CC chemokines were located in the extracellular region. Phylogenetic, evolutionary and syntenic analyses confirmed that CC chemokines were annotated as 11 different types (CCL19, CCL20, CCL25, CCL27, CCL32, CCL33, CCL34, CCL35, CCL36, CCL39, and CCL44), which exhibited unique gene arrangement pattern and chromosomal location respectively. Furthermore, genome synteny analyses between common carp and four representative teleost species indicated expansion of common carp CC chemokines resulted from the whole genome duplication (WGD) event. Additionally, the continuous evolution of gene CCL25s in teleost afforded a novel viewpoint to explain the WGD event in teleost. Then, we predicted the three-dimensional structures and probable function regions of common carp CC chemokines. All the CC chemokines core structures were constituted of an N-loop, a three-stranded β-sheet, and a C-terminal helix. Finally, 43 CC chemokines were predicted to have probable general antimicrobial activity. Their tertiary structures, cationic and amphiphilic physicochemical property supported the viewpoint. To verify the prediction, six recombinant CCL19s proteins were prepared and the antibacterial activity against Escherichia coli and Aeromonas hydrophila were verified. The results supported our prediction that rCCL19a.1s (rCCL19a.1_a, rCCL19a.1_b) and rCCL19bs (rCCL19b_a, rCCL19b_b), especially rCCL19bs, exhibited extremely significant inhibition to the growth of both E. coli and A. hydrophila. On the contrary, two rCCL19a.2s had no significant inhibitory effect. These studies suggested that CC chemokines were essential in immune system evolution and not monofunctional during pathogen infection.

Cytokine Receptor Diversity in the Lamprey Predicts the Minimal Essential Cytokine Networks of Vertebrates

The vertebrate adaptive immune systems (Agnatha and Gnathostomata) use sets of T and B lymphocyte lineages that somatically generate highly diverse repertoires of Ag-specific receptors and Abs. In Gnathostomata, cytokine networks regulate the activation of lymphoid and myeloid cells, whereas little is known about these components in Agnathans. Most gnathostome cytokines are four-helix bundle cytokines with poorly conserved primary sequences. In contrast, sequence conservation across bilaterians has been observed for cognate cytokine receptor chains, allowing their structural classification into two classes, and for downstream JAK/STAT signaling mediators. With conserved numbers among Gnathostomata, human cytokine receptor chains (comprising 34 class I and 12 class II) are able to interact with 28 class I helical cytokines (including most ILs) and 16 class II cytokines (including all IFNs), respectively. Hypothesizing that the arsenal of cytokine receptors and transducers may reflect homologous cytokine networks, we analyzed the lamprey genome and transcriptome to identify genes and transcripts for 23 class I and five class II cytokine receptors alongside one JAK signal mediator and four STAT transcription factors. On the basis of deduction of their respective orthologs, we predict that these receptors may interact with 16 class I and 3 class II helical cytokines (including IL-4, IL-6, IL-7, IL-12, IL-10, IFN-γ, and thymic stromal lymphoprotein homologs). On the basis of their respective activities in mammals, this analysis suggests the existence of lamprey cytokine networks that may regulate myeloid and lymphoid cell differentiation, including potential Th1/Th2 polarization. The predicted networks thus appear remarkably homologous to those of Gnathostomata, albeit reduced to essential functions.

CC and CXC chemokines in turbot (Scophthalmus maximus L.): Identification, evolutionary analyses, and expression profiling after Aeromonas salmonicida infection

Chemokines are a superfamily of structurally related cytokines, which exert essential roles in guiding cell migration in development, homeostasis, and immunity. CC and CXC chemokines are the two major subfamilies in teleost species. In this study, a total of seventeen CC and CXC chemokines, with inclusion of twelve CC and five CXC chemokines, were systematically identified from the turbot genome, making turbot the teleost harboring the least number of CC and CXC chemokines among all teleost species ever reported. Phylogeny, synteny, and genomic organization analyses were performed to annotate these genes, and multiple chemokine genes were identified in the turbot genome, due to the tandem duplications (CCL19 and CCL20), the whole genome duplications (CCL20, CCL25, and CXCL12), and the teleost-specific members (CCL34-36, CCL44, and CXCL18). In addition, chemokines were ubiquitously expressed in nine examined healthy tissues, with high expression levels observed in liver, gill, and spleen. Moreover, most chemokines were significantly differentially expressed in gill and spleen after Aeromonas salmonicida infection, and exhibited tissue-specific and time-dependent manner. Finally, protein-protein interaction network (PPI) analysis indicated that turbot chemokines interacted with a few immune-related genes such as interleukins, cathepsins, stats, and TLRs. These results should be valuable for comparative immunological studies and provide insights for further functional characterization of chemokines in teleost.

Migratory regulation by MTA homologous genes is essential for the uniform distribution of planarian adult pluripotent stem cells

The migration of adult stem cells in vivo is an important issue, but the complex tissue structures involved, and limited accessibility of the cells hinder a detailed investigation. To overcome these problems, the freshwater planarian Dugesia japonica was used because it has a simple body plan and abundant adult pluripotent stem cells (neoblasts) distributed uniformly throughout its body. To investigate the migratory mechanisms of neoblasts, two planarian homologous genes of metastatic tumor antigen (MTA-A and MTA-B), a protein involved in cancer metastasis that functions through histone deacetylation, were identified, and their function was analyzed using RNA interference (RNAi). MTA-A or MTA-B knockdown disrupted homeostatic tissue turnover and regeneration in planarians. Whereas neoblasts in MTA-A (RNAi) and MTA-B (RNAi) animals were maintained, neoblast differentiation was inhibited. Furthermore, the normal uniform neoblast distribution pattern changed to a branch-like pattern in MTA-A (RNAi) and MTA-B (RNAi) animals. To examine the neoblast migratory ability, a partial X-ray irradiation assay was performed in D. japonica. Using this assay system, the MTA-A knockdown neoblasts migrated collectively in a branch-like pattern, and the MTA-B knockdown neoblasts were not able to migrate. These results indicated that MTA-A was required for the exit of neoblasts from the branch-like region, and that MTA-B was required for neoblast migration. Thus, the migration mediated by MTA-A and MTA-B enabled uniform neoblast distribution and was required for neoblast differentiation to achieve tissue homeostasis and regeneration.

GPR15-C10ORF99 functional pairing initiates colonic Treg homing in amniotes

Regulatory T lymphocyte (Treg) homing reactions mediated by G protein-coupled receptor (GPCR)-ligand interactions play a central role in maintaining intestinal immune homeostasis by restraining inappropriate immune responses in the gastrointestinal tract. However, the origin of Treg homing to the colon remains mysterious. Here, we report that the C10ORF99 peptide (also known as CPR15L and AP57), a cognate ligand of GPR15 that controls Treg homing to the colon, originates from a duplication of the flanking CDHR1 gene and is functionally paired with GPR15 in amniotes. Evolutionary analysis and experimental data indicate that the GPR15-C10ORF99 pair is functionally conserved to mediate colonic Treg homing in amniotes and their expression patterns are positively correlated with herbivore diet in the colon. With the first herbivorous diet in early amniotes, a new biological process (herbivorous diet short-chain fatty acid-C10ORF99/GPR15-induced Treg homing colon immune homeostasis) emerged, and we propose an evolutionary model whereby GPR15-C10ORF99 functional pairing has initiated the first colonic Treg homing reaction in amniotes. Our findings also highlight that GPCR-ligand pairing leads to physiological adaptation during vertebrate evolution.

Gene Structure Analysis of Chemokines and Their Receptors in Allotetraploid Frog, Xenopus laevis

Chemokines, relatively small secreted proteins, are involved in cell migration and function in various biological events, including immunity, morphogenesis, and disease. Due to their nature, chemokines tend to be a target of hijacking of immunity by virus and therefore show an exceptionally high mutation rate. Xenopus laevis is considered an excellent model to investigate the effect of whole-genome duplication for gene family evolution. Because its allotetraploidization occurred around 17–18 million years ago, ancestral subgenomes L and S were well conserved. Based on the gene model of human and diploid frog Xenopus tropicalis, we identified 52 chemokine genes and 26 chemokine receptors in X. laevis. The retention rate of the gene in the X. laevis L and S subgenomes was 96% (45/47) and 68% (32/47), respectively. We conducted molecular phylogenetic analysis and found clear orthologies in all receptor genes but not in the ligand genes, suggesting rapid divergences of the ligand. dN/dS calculation demonstrated that dN/dS ratio greater than one was observed in the four ligand genes, cxcl8b.1.S, cxcl18.S, ccl21.S, and xcl1.L, but nothing in receptor genes. These results revealed that the whole-genome duplication promotes diversification of chemokine ligands in X. laevis while conserving the genes necessary for homeostasis, suggesting that selective pressure also supports a rapid divergence of the chemokines in amphibians.

Galactose-Binding C-Type Lectin Promotes Cellular Aggregation of Coelomocytes in Sea Cucumber

Echinoderms have a large coelomic cavity containing coelomocytes. When the coelomic fluid is removed from the cavity, the cells aggregate immediately. We found that a fraction or an extract of the intestine of the sea cucumber, Apostichopus japonicus, markedly accelerated cellular movement and aggregation on a glass slide, and this effect was clearly inhibited by galactose. We successfully purified the aggregation-promoting factor, a 16 kDa protein, from the intestine. TOF-MS analysis followed by de novo sequencing revealed that the protein is a C-type lectin. RNA-seq data and cDNA cloning demonstrated the factor to be a novel lectin, named AjGBCL, consisting of 158 aa residues in the mature form. Microscopic observation revealed that most of the aggregating cells moved toward aggregates and not to an intestinal fragment, suggesting that AjGBCL is not a chemoattractant but a cellular aggregation-inducing factor that may induce aggregates to release chemoattractant. We report, for the first time, an endogenous molecule that promotes coelomocyte aggregation in echinoderms.

Molecular and Cellular Mechanisms of Vascular Development in Zebrafish

The establishment of a functional cardiovascular system is crucial for the development of all vertebrates. Defects in the development of the cardiovascular system lead to cardiovascular diseases, which are among the top 10 causes of death worldwide. However, we are just beginning to understand which signaling pathways guide blood vessel growth in different tissues and organs. The advantages of the model organism zebrafish (Danio rerio) helped to identify novel cellular and molecular mechanisms of vascular growth. In this review we will discuss the current knowledge of vasculogenesis and angiogenesis in the zebrafish embryo. In particular, we describe the molecular mechanisms that contribute to the formation of blood vessels in different vascular beds within the embryo.

The CC and CXC chemokine receptors in turbot (Scophthalmus maximus L.) and their response to Aeromonas salmonicida infection

Chemokines are crucial regulators of cell mobilization for development, homeostasis, and immunity. Chemokines signal through binding to chemokine receptors, a superfamily of seven-transmembrane domain G-coupled receptors. In the present study, eleven CC chemokine receptors (CCRs) and seven CXC chemokine receptors (CXCRs) were identified from turbot genome. Phylogenetic and syntenic analyses were performed to annotate these genes, indicating the closest relationship between the turbot chemokine receptors and their counterparts of Japanese flounders (Paralichthys olivaceus). Evolutionary analyses revealed that the tandem duplications of CCR8 and CXCR3, the whole genome duplications of CCR6, CCR9, CCR12, and CXCR4, and the teleost-specific CCR12 led to the expansion of turbot chemokine receptors. In addition, turbot chemokine receptors were ubiquitously expressed in nine examined healthy tissues, with high expression levels observed in spleen, gill, and head kidney. Moreover, most turbot chemokine receptors were significantly differentially expressed in spleen and gill after Aeromonas salmonicida infection, and exhibited general down-regulations at early time points and then gradually up-regulated. Finally, protein-protein interaction network (PPI) analyses indicated that chemokine receptors interacted with a few immune-related genes such as interleukins, Grk genes, CD genes, etc. These results should be valuable for comparative immunological studies and provide insights for further functional characterization of chemokine receptors in turbots.

CCL19 variants mediate chemotactic response via CCR7 in grass carp Ctenopharyngodon idella

CC chemokine ligand 19 (CCL19) plays a key role in the regulation of immune responses including homeostasis, inflammation, and immune tolerance. In this study, two variants of CCL19 homologues (CCL19a2 and CCL19b) and CCR7 were investigated in grass carp Ctenopharyngodon idella. The three genes were widely expressed in immune tissues and could be modulated by stimulation with LPS, PHA and poly(I:C), and infection with Flavobacterium columnare and grass carp reovirus. In an in vitro chemotaxis assay, the recombinant CCL19a2 and CCL19b were active to promote the migration of HEK293 T cells expressing CCR7 and leucocytes isolated from the gills, head kidney and spleen. Moreover, their chemotactive effects were validated in vivo. We found that the cells recruited by CCL19a2 and CCl19b are mainly monocytes/macrophages expressing high levels of IL-1β, IFN-γ, colony stimulating factor 1 receptor (CSF1R) and MHC II. Our work suggests that CCL19a2 and CCl19b are involved in recruitment of antigen presenting cells in fish.

Neuromodulation by the immune system: a focus on cytokines

Interactions between the immune system and the nervous system have been described mostly in the context of diseases. More recent studies have begun to reveal how certain immune cell-derived soluble effectors, the cytokines, can influence host behaviour even in the absence of infection. In this Review, we contemplate how the immune system shapes nervous system function and how it controls the manifestation of host behaviour. Interactions between these two highly complex systems are discussed here also in the context of evolution, as both may have evolved to maximize an organism's ability to respond to environmental threats in order to survive. We describe how the immune system relays information to the nervous system and how cytokine signalling occurs in neurons. We also speculate on how the brain may be hardwired to receive and process information from the immune system. Finally, we propose a unified theory depicting a co-evolution of the immune system and host behaviour in response to the evolutionary pressure of pathogens.

CXC chemokines and their receptors in black rockfish (Sebastes schlegelii): Characterization, evolution analyses, and expression pattern after Aeromonas salmonicida infection

Chemokines are crucial regulators of cell mobilization for development, homeostasis, and immunity. Chemokines signal through binding to chemokine receptors, a superfamily of seven-transmembrane domain G-coupled receptors. In the present study, seventeen CXC chemokine ligands (SsCXCLs) and nine CXC chemokine receptors (SsCXCRs) were systematically identified from Sebastes schlegelii genome. Phylogeny, synteny, and evolutionary analyses were performed to annotate these genes, indicating that the tandem duplications (CXCL8, CXCL11, CXCL32, CXCR2, and CXCR3), the whole genome duplications (CXCL8, CXCL12, CXCL18, and CXCR4), and the teleost-specific members (CXCL18, CXCL19, and CXCL32) led to the expansion of SsCXCLs and SsCXCRs. In addition, SsCXCLs and SsCXCRs were ubiquitously expressed in nine examined healthy tissues, with high expression levels observed in head kidney, liver, gill and spleen. Moreover, most SsCXCLs and SsCXCRs were significantly differentially expressed in head kidney, liver, and gill after Aeromonas salmonicida infection, and exhibited tissue-specific and time-dependent manner. Finally, protein-protein interaction network (PPI) analysis indicated that SsCXCLs and SsCXCRs interacted with a few immune-related genes such as interleukins, cathepsins, CD genes, and TLRs, etc. These results should be valuable for comparative immunological studies and provide insights for further functional characterization of chemokines and receptors in teleost.

Genetic variation analyses indicate conserved SARS-CoV-2-host interaction and varied genetic adaptation in immune response factors in modern human evolution

Coronavirus disease 2019 (COVID‐19), caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), is a pandemic as of early 2020. Upon infection, SARS‐CoV‐2 attaches to its receptor, that is, angiotensin‐converting enzyme 2 (ACE2), on the surface of host cells and is then internalized into host cells via enzymatic machineries. This subsequently stimulates immune response factors. Since the host immune response and severity of COVID‐19 vary among individuals, genetic risk factors for severe COVID‐19 cases have been investigated. Our research group recently conducted a survey of genetic variants among SARS‐CoV‐2‐interacting molecules across populations, noting near absence of difference in allele frequency spectrum between populations in these genes. Recent genome‐wide association studies have identified genetic risk factors for severe COVID‐19 cases in a segment of chromosome 3 that involves six genes encoding three immune‐regulatory chemokine receptors and another three molecules. The risk haplotype seemed to be inherited from Neanderthals, suggesting genetic adaptation against pathogens in modern human evolution. Therefore, SARS‐CoV‐2 uses highly conserved molecules as its virion interaction, whereas its immune response appears to be genetically biased in individuals to some extent. We herein review the molecular process of SARS‐CoV‐2 infection as well as our further survey of genetic variants of its related immune effectors. We also discuss aspects of modern human evolution.

The evolution and functional characterization of CXC chemokines and receptors in lamprey

Chemokines are a large family of soluble peptides guiding cell migration in development and immune defense. They interact with chemokine receptors and are essential for the coordination of cell migration in diverse physiological processes. The CXC subfamily is one of the largest groups in the chemokine family and consists of multiple members. In this study, we identified homologues of three chemokine ligands (CXCL8, CXCL_F5 and CXCL12) and two CXC receptor like molecules (CXCR_L1 and CXCR_L2) in lamprey. Sequence analysis revealed that they share the same genomic organization with their counterparts in jawed vertebrates but synteny was not conserved. Lamprey CXCL8 and CXCL12 have four conserved cysteine residues whilst the CXCL_F5 has two additional cysteine residues. In addition, CXCL_F5 is evolutionarily related to the fish specific CXC chemokine groups previously identified and contains multiple cationic aa residues in the extended C- terminal region. The two CXCRs possess seven transmembrane domains and conserved structural elements for receptor activation and signaling, including the DRYXXI(V)Y motif in TM2, the disulphide bond connecting ECL2 and TM3, the WXP motif in TM6 and NPXXY motif in TM7. The identified CXC chemokines and receptors were constitutively expressed in tissues including the liver, kidney, intestine, heart, gills, supraneural body and primary leukocytes, but exhibited distinct expression patterns. Relatively high expression was detected in the gills for CXCL8, CXCL_F5 and CXCR_L1 and in the supraneural body for CXCL12 and CXCR_L2. All the genes except CXCL12 were upregulated by stimulation with LPS, pokeweed and bacterial infection, and the CXCL8 and CXCL_F5 was induced by poly (I:C). Functional analysis showed that the CXCL8 and CXCL_F5 specifically interacted with CXCR_L1 and CXCR_L2, respectively. Our results demonstrate that the CXC chemokine system had diversified in jawless fish.

Review of inflammation in fish and value of the zebrafish model

Inflammation is a crucial step in the development of chronic diseases in humans. Understanding the inflammation environment and its intrinsic mechanisms when it is produced by harmful stimuli may be a key element in the development of human disease diagnosis. In recent decades, zebrafish (Danio rerio) have been widely used in research, due to their exceptional characteristics, as a model of various human diseases. Interestingly, the mediators released during the inflammatory response of both the immune system and nervous system, after its integration in the hypothalamus, could also facilitate the detection of injury through the register of behavioural changes in the fish. Although there are many studies that give well-defined information separately on such elements as the recruitment of cells, the release of pro- and anti-inflammatory mediators or the type of neurotransmitters released against different triggers, to the best of our knowledge there are no reviews that put all this knowledge together. In the present review, the main available information on inflammation in zebrafish is presented in order to facilitate knowledge about this important process of innate immunity, as well as the stress responses and behavioural changes derived from it.

Molecular Basis for CCRL2 Regulation of Leukocyte Migration

CCRL2 is a seven-transmembrane domain receptor that belongs to the chemokine receptor family. At difference from other members of this family, CCRL2 does not promote chemotaxis and shares structural features with atypical chemokine receptors (ACKRs). However, CCRL2 also differs from ACKRs since it does not bind chemokines and is devoid of scavenging functions. The only commonly recognized CCRL2 ligand is chemerin, a non-chemokine chemotactic protein. CCRL2 is expressed both by leukocytes and non-hematopoietic cells. The genetic ablation of CCRL2 has been instrumental to elucidate the role of this receptor as positive or negative regulator of inflammation. CCRL2 modulates leukocyte migration by two main mechanisms. First, when CCRL2 is expressed by barrier cells, such endothelial, and epithelial cells, it acts as a presenting molecule, contributing to the formation of a non-soluble chemotactic gradient for leukocytes expressing CMKLR1, the functional chemerin receptor. This mechanism was shown to be crucial in the induction of NK cell-dependent immune surveillance in lung cancer progression and metastasis. Second, by forming heterocomplexes with other chemokine receptors. For instance, CCRL2/CXCR2 heterodimers were shown to regulate the activation of β2-integrins in mouse neutrophils. This mini-review summarizes the current understanding of CCRL2 biology, based on experimental evidence obtained by the genetic deletion of this receptor in in vivo experimental models. Further studies are required to highlight the complex functional role of CCRL2 in different organs and pathological conditions.

Molecular insights into the differential structure-dynamics-stability features of interleukin-8 orthologs: Implications to functional specificity

Chemokines are a sub-group of chemotactic cytokines that regulate the leukocyte migration by binding to G-protein coupled receptors (GPCRs) and cell surface glycosaminoglycans (GAGs). Interleukin-8 (CXCL8/IL8) is one of the most essential CXC chemokine that has been reported to be involved in various pathophysiological conditions. Structure-function relationships of human IL8 have been studied extensively. However, no such detailed information is available on IL8 orthologs, although they exhibit significant functional divergence. In order to unravel the differential structure-dynamics-stability-function relationship of IL8 orthologs, comparative molecular analysis was performed on canine (laurasians) and human (primates) IL8 proteins using in-silico molecular evolutionary analysis and solution NMR spectroscopy methods. The residue level NMR studies suggested that, although the overall structural architecture of canine IL8 is similar to that of human IL8, systematic differences were observed in their backbone dynamics and low-energy excited states due to amino acid substitutions. Further, these substitutions also resulted in attenuation of stability and heparin binding affinity in the canine IL8 as compared to its human counterpart. Indeed, structural and sequence analysis evidenced for specificity of molecular interactions with cognate receptor (CXCR1) and glycosaminoglycan (heparin), thus providing evidence for a noticeable functional specificity and divergence between the two IL8 orthologs.

The chemokine X-factor: Structure-function analysis of the CXC motif at CXCR4 and ACKR3

The human chemokine family consists of 46 protein ligands that induce chemotactic cell migration by activating a family of 23 G protein-coupled receptors. The two major chemokine subfamilies, CC and CXC, bind distinct receptor subsets. A sequence motif defining these families, the X position in the CXC motif, is not predicted to make significant contacts with the receptor, but instead links structural elements associated with binding and activation. Here, we use comparative analysis of chemokine NMR structures, structural modeling, and molecular dynamic simulations that suggested the X position reorients the chemokine N terminus. Using CXCL12 as a model CXC chemokine, deletion of the X residue (Pro-10) had little to no impact on the folded chemokine structure but diminished CXCR4 agonist activity as measured by ERK phosphorylation, chemotaxis, and G_i/o-mediated cAMP inhibition. Functional impairment was attributed to over 100-fold loss of CXCR4 binding affinity. Binding to the other CXCL12 receptor, ACKR3, was diminished nearly 500-fold. Deletion of Pro-10 had little effect on CXCL12 binding to the CXCR4 N terminus, a major component of the chemokine-GPCR interface. Replacement of the X residue with the most frequent amino acid at this position (P10Q) had an intermediate effect between WT and P10del in each assay, with ACKR3 having a higher tolerance for this mutation. This work shows that the X residue helps to position the CXCL12 N terminus for optimal docking into the orthosteric pocket of CXCR4 and suggests that the CC/CXC motif contributes directly to receptor selectivity by orienting the chemokine N terminus in a subfamily-specific direction.

Elucidating the Molecular Interactions of Chemokine CCL2 Orthologs with Flavonoid Baicalin

An integrated and controlled migration of leukocytes is necessary for the legitimate functioning and maintenance of the immune system. Chemokines and their receptors play a decisive role in regulating the leukocyte migration to the site of inflammation, a phenomena often referred to as chemotaxis. Chemokines and their receptors have become significant targets for therapeutic intervention considering their potential to regulate the immune system. Monocyte chemoattractant protein-1 (MCP-1/CCL2) is a preeminent member of CC chemokine family that facilitates crucial roles by orchestrating the recruitment of monocytes into inflamed tissues. Baicalin (BA), a major bioactive flavonoid, has been reported to attenuate chemokine-regulated leukocyte trafficking. However, no molecular details pertaining to its direct binding to chemokine(s)/receptor(s) are available till date. In the current study, using an array of monomers/dimers of human and murine CCL2 orthologs (hCCL2/mCCL2), we have shown that BA binds to the CCL2 protein specifically with nanomolar affinity (K _d = 270 ± 20 nM). NMR-based studies established that BA binds CCL2 in a specific pocket involving the N-terminal, β1- and β3-sheets. Docking studies suggested that the residues T16, N17, R18, I20, R24, K49, E50, I51, and C52 are majorly involved in complex formation through a combination of H-bonds and hydrophobic interactions. As the residues R18, R24, and K49 of hCCL2 are crucial determinants of monocyte trafficking through receptor/glycosaminoglycans (GAG) binding in CCL2 human/murine orthologs, we propose that baicalin engaging these residues in complex formation will result in attenuation of CCL2 binding to the receptor/GAGs, thus inhibiting the chemokine-regulated leukocyte trafficking.

Molecular characterization and expression analysis of chemokine (CXCL12) from Nile tilapia (Oreochromis niloticus)

Chemokines are a class of small molecular weight cytokines of 6-14 kDa, exerting important roles in the regulation of various inflammatory diseases and immune cell migration. In this study, we have identified the CXCL12 gene from Nile tilapia (Oreochromis niloticus), including CXCL12a (OnCXCL12a) and CXCL12b (OnCXCL12b). The open reading frames of OnCXCL12a and OnCXCL12b are 309 and 297 bp, encoding 102 and 98 amino acids, respectively. Multiple alignment showed that OnCXCL12a and OnCXCL12b have characteristics of CXC chemokines and share high identity with CXCL12 amino acid sequences from the known species. Tissue distribution in the healthy fish indicated that OnCXCL12a and OnCXCL12b expressed in all examined tissues, with the highest expression in muscle and anterior kidney, respectively. After challenged by Streptococcus agalactiae, Poly(I:C) and LPS in vivo and in vitro, OnCXCL12 is transcriptionally up-regulated in immune tissues and cells significantly. The recombinant OnCXCL12 proteins, (r)OnCXCL12a and (r)OnCXCL12b, enhance the release of nitric oxide and increase the expression of inflammatory cytokines (TNF-α, IL-6, and IL-10) in anterior kidney leukocytes, as well as exhibit chemotactic activity for leukocytes from anterior kidney. Summarizing, these results indicate that OnCXCL12 is involved in the immune response of Nile tilapia against pathogen infection and may play an important role in mediating inflammatory response.

Molecular Characterization and Chemotactic Function of CXCL8 in Northeast Chinese Lamprey (Lethenteron morii)

Chemokine-induced chemotaxis of leukocytes is an important part of the innate immunity and has been shown to mediate inflammation in all groups of jawed vertebrates. For jawless vertebrates, hagfish leukocytes are known to show chemotaxis toward mammalian complement anaphylotoxin and Gram-negative bacteria lipopolysaccharide. However, whether chemokines mediate chemotaxis of leukocytes in jawless vertebrates has not been conclusively examined. Here, we show C-X-C motif chemokine ligand 8 (CXCL8, also named interleukin 8) of the Northeast Chinese lamprey (Lethenteron morii) (designated as LmCXCL8) induces chemotaxis in its leukocytes. We identified LmCXCL8 and found it possesses the characteristic N-terminal cysteine residues and GGR (Gly-Gly-Arg) motif. The Lmcxcl8 gene was found to be expressed in all examined tissues, and its expression was inducible in the lamprey challenged by an infectious bacterium, Pseudomonas aeruginosa. A recombinant LmCXCL8 protein elicited concentration-dependent chemotaxis in peripheral blood leukocytes isolated from the Northeast Chinese lamprey. Based on these results, we conclude that LmCXCL8 is a constitutive and inducible acute-phase cytokine that mediates immune defense and trace the chemotactic function of chemokine to basal vertebrates.

A Zika virus primary isolate induces neuroinflammation, compromises the blood-brain barrier and upregulates CXCL12 in adult macaques

Zika virus (ZIKV) is a flavivirus that can cause neuropathogenesis in adults and fetal neurologic malformation following the infection of pregnant women. We used a nonhuman primate model, the Indian-origin Rhesus macaque (IRM), to gain insight into virus-associated hallmarks of ZIKV-induced adult neuropathology. We find that the virus causes prevalent acute and chronic neuroinflammation and chronic disruption of the blood-brain barrier (BBB) in adult animals. ZIKV infection resulted in specific short- and long-term augmented expression of the chemokine CXCL12 in the central nervous system (CNS)of adult IRMs. Moreover, CXCL12 expression persists long after the initial viral infection is apparently cleared. CXCL12 plays a key role both in regulating lymphocyte trafficking through the BBB to the CNS and in mediating repair of damaged neural tissue including remyelination. Understanding how CXCL12 expression is controlled will likely be of central importance in the definition of ZIKV-associated neuropathology in adults.

What Is the Evolutionary Fingerprint in Neutrophil Granulocytes?

Over the years of evolution, thousands of different animal species have evolved. All these species require an immune system to defend themselves against invading pathogens. Nevertheless, the immune systems of different species are obviously counteracting against the same pathogen with different efficiency. Therefore, the question arises if the process that was leading to the clades of vertebrates in the animal kingdom-namely mammals, birds, amphibians, reptiles, and fish-was also leading to different functions of immune cells. One cell type of the innate immune system that is transmigrating as first line of defense in infected tissue and counteracts against pathogens is the neutrophil granulocyte. During the host-pathogen interaction they can undergo phagocytosis, apoptosis, degranulation, and form neutrophil extracellular traps (NETs). In this review, we summarize a wide spectrum of information about neutrophils in humans and animals, with a focus on vertebrates. Special attention is kept on the development, morphology, composition, and functions of these cells, but also on dysfunctions and options for cell culture or storage.

The role of chemokines and chemokine receptors in multiple sclerosis

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Summarize the study of the role of chemokines and their receptors in multiple sclerosis (MS) patients and MS animal models.

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Discuss their potential significance in inflammatory injury and repair of MS.

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Summarize the progress in the research of MS antagonists in recent years with chemokine receptors as targets.

Multiple sclerosis (MS) is a chronic inflammatory disease that is characterized by leukocyte infiltration and subsequent axonal damage, demyelinating inflammation, and formation of sclerosing plaques in brain tissue. The results of various studies in patients indicate that autoimmunity and inflammation make an important impact on the pathogenesis of MS. Chemokines are key mediators of inflammation development and cell migration, mediating various immune cell responses, including chemotaxis and immune activation, and are important in immunity and inflammation, therefore we focus on chemokines and their receptors in multiple sclerosis. In this article, we summarize the study of the role of prominent chemokines and their receptors in MS patients and MS animal modelsand discuss their potential significance in inflammatory injury and repair of MS. We have also summarized the progress in the treatment of multiple sclerosis antagonists in recent years with chemokine receptors as targets.

Chemokine Receptors and Phagocyte Biology in Zebrafish

Phagocytes are highly motile immune cells that ingest and clear microbial invaders, harmful substances, and dying cells. Their function is critically dependent on the expression of chemokine receptors, a class of G-protein-coupled receptors (GPCRs). Chemokine receptors coordinate the recruitment of phagocytes and other immune cells to sites of infection and damage, modulate inflammatory and wound healing responses, and direct cell differentiation, proliferation, and polarization. Besides, a structurally diverse group of atypical chemokine receptors (ACKRs) are unable to signal in G-protein-dependent fashion themselves but can shape chemokine gradients by fine-tuning the activity of conventional chemokine receptors. The optically transparent zebrafish embryos and larvae provide a powerful in vivo system to visualize phagocytes during development and study them as key elements of the immune response in real-time. In this review, we discuss how the zebrafish model has furthered our understanding of the role of two main classes of chemokine receptors, the CC and CXC subtypes, in phagocyte biology. We address the roles of the receptors in the migratory properties of phagocytes in zebrafish models for cancer, infectious disease, and inflammation. We illustrate how studies in zebrafish enable visualizing the contribution of chemokine receptors and ACKRs in shaping self-generated chemokine gradients of migrating cells. Taking the functional antagonism between two paralogs of the CXCR3 family as an example, we discuss how the duplication of chemokine receptor genes in zebrafish poses challenges, but also provides opportunities to study sub-functionalization or loss-of-function events. We emphasize how the zebrafish model has been instrumental to prove that the major determinant for the functional outcome of a chemokine receptor-ligand interaction is the cell-type expressing the receptor. Finally, we highlight relevant homologies and analogies between mammalian and zebrafish phagocyte function and discuss the potential of zebrafish models to further advance our understanding of chemokine receptors in innate immunity and disease.

Using evasins to target the chemokine network in inflammation

Inflammation, is driven by a network comprising cytokines, chemokines, their target receptors and leukocytes, and is a major pathologic mechanism that adversely affects organ function in diverse human diseases. Despite being supported by substantial target validation, no successful anti-chemokine therapeutic to treat inflammatory disease has yet been developed. This is in part because of the robustness of the chemokine network, which emerges from a large total chemokine load in disease, promiscuous expression of receptors on leukocytes, promiscuous and synergistic interactions between chemokines and receptors, and feedforward loops created by secretion of chemokines by leukocytes themselves. Many parasites, including viruses, helminths and ticks, evade the chemokine network by producing proteins that bind promiscuously to chemokines or their receptors. Evasins - three small glycoproteins identified in the saliva of the brown dog tick - bind multiple chemokines, and are active in several animal models of inflammatory disease. Over 50 evasin homologs have recently been identified from diverse tick species. Characterization of the chemokine binding patterns of evasins show that several have anti-chemokine activities that extend substantially beyond those previously described. These studies indicate that evasins function at the site of the tick bite by reducing total chemokine load. This not only reduces chemokine signaling to receptors, but also interrupts feedforward loops, thus disabling the chemokine network. Taking the lead from nature, a goal for the development of new anti-chemokine therapeutics would be to reduce the total chemokine load in disease. This could be achieved by administering appropriate evasin combinations or by smaller peptides that mimic evasin action.

Unraveling the evolutionary origin of ELR motif using fish CXC chemokine CXCL8

Chemokines are chemotactic proteins involved in host defense through the migration of immune-regulatory cells to the site of infection. Interleukin-8 (CXCL8/IL8) is the most studied "ELR-CXC chemokine/neutrophil activating chemokine (NAC) that regulate neutrophil trafficking during infections and inflammation by binding to its cognate G-protein coupled receptors CXCR1/CXCR2. The "ELR" motif of NAC chemokines is essential for the CXCR1/CXCR2 receptor activation. In order to understand the evolutionary origin of "ELR" motif in the CXC chemokines, a thorough evolutionary study of CXCL8 gene from various fishes and primates was performed. Phylogenetic analysis revealed that the CXCL8 gene can be classified into four distinct lineages (CXCL8-L1a, CXCL8-L1b, CXCL8-L2, and CXCL8-L3), where CXCL8-L1a is the fastest evolving lineage and CXCL8-L3 is the slowest. Selection analysis suggested that The "ELR/DLR" motif containing branches (gadoid and coelacanth) are positively selected. The probable evolutionary trend of "ELR" motif suggested that this motif in ancestor CXCL8 is evolved from the GGR of Lamprey (Agnatha), followed by duplication giving rise to two main motifs in CXCL8 "NXH" in L3 lineage and "ELR/DLR" in L1a/L1b lineages. Although, structural analysis suggested that the overall topology of the CXCL8 proteins is similar, differences do exist at the individual structural elements among the members of different lineages. Functional distance analysis suggested that the CXCL8-L3 lineage is more distant compared to the CXCL8-L1a and L1b lineages from the inferred ancestor. Functional divergence analysis between different lineages suggested that most of the selected residues are important for receptor or glycosaminoglycan binding. Such a functional diversification can be attributed to the novel set of functions adopted by CXCL8 in various species.

Expansion and loss events characterized the occurrence of MIF-like genes in bivalves

Macrophage migration inhibitory factor (MIF) dynamically connects innate and adaptive immune systems in vertebrate animals, allowing highly orchestrated systemic responses to various insults. The occurrence of MIF-like genes in non-vertebrate organisms suggests its origin from an ancestral metazoan gene, whose function is still a matter of debate. In the present work, by analyzing available genomic and transcriptomic data from bivalve mollusks, we identified 137 MIF-like sequences, which were classified into three types, based on phylogeny and conservation of key residues: MIF, D-DT, and the lineage-specific type MDL. Comparative genomics revealed syntenic conservation of homologous genes at the family level, the loss of D-DT in the Ostreidae family as well as the expansion of MIF-like genes in the Mytilidae family, possibly underpinning the neofunctionalization of duplicated gene copies. In M. galloprovincialis, MIF and one D-DT were mostly expressed in haemocytes and mantle rim of untreated animals, while D-DT paralogs often showed very limited expression, suggesting an accessory role or their persistence as relict genes.

Cartography of rhodopsin-like G protein-coupled receptors across vertebrate genomes

We conduct a cartography of rhodopsin-like non-olfactory G protein-coupled receptors in the Ensembl database. The most recent genomic data (releases 90–92, 90 vertebrate genomes) are analyzed through the online interface and receptors mapped on phylogenetic guide trees that were constructed based on a set of ~14.000 amino acid sequences. This snapshot of genomic data suggest vertebrate genomes to harbour 142 clades of GPCRs without human orthologues. Among those, 69 have not to our knowledge been mentioned or studied previously in the literature, of which 28 are distant from existing receptors and likely new orphans. These newly identified receptors are candidates for more focused evolutionary studies such as chromosomal mapping as well for in-depth pharmacological characterization. Interestingly, we also show that 37 of the 72 human orphan (or recently deorphanized) receptors included in this study cluster into nineteen closely related groups, which implies that there are less ligands to be identified than previously anticipated. Altogether, this work has significant implications when discussing nomenclature issues for GPCRs.

Mechanistic insights and therapeutic opportunities of antimicrobial chemokines

Chemokines are a family of small proteins best known for their ability to orchestrate immune cell trafficking and recruitment to sites of infection. Their role in promoting host defense is multiplied by a number of additional receptor-dependent biological activities, and most, but not all, chemokines have been found to mediate direct antimicrobial effects against a broad range of microorganisms. The molecular mechanism(s) by which antimicrobial chemokines kill bacteria remains unknown; however, recent observations have expanded our fundamental understanding of chemokine-mediated bactericidal activity to reveal increasingly diverse and complex actions. In the current review, we present and consider mechanistic insights of chemokine-mediated antimicrobial activity against bacteria. We also discuss how contemporary advances are reshaping traditional paradigms and opening up new and innovative avenues of research with translational implications. Towards this end, we highlight a developing framework for leveraging chemokine-mediated bactericidal and immunomodulatory effects to advance pioneering therapeutic approaches for treating bacterial infections, including those caused by multidrug-resistant pathogens.

Regeneration associated transcriptional signature of retinal microglia and macrophages

Zebrafish have the remarkable capacity to regenerate retinal neurons following a variety of damage paradigms. Following initial tissue insult and a period of cell death, a proliferative phase ensues that generates neuronal progenitors, which ultimately regenerate damaged neurons. Recent work has revealed that Müller glia are the source of regenerated neurons in zebrafish. However, the roles of another important class of glia present in the retina, microglia, during this regenerative phase remain elusive. Here, we examine retinal tissue and perform QuantSeq. 3'mRNA sequencing/transcriptome analysis to reveal localization and putative functions, respectively, of mpeg1 expressing cells (microglia/macrophages) during Müller glia-mediated regeneration, corresponding to a time of progenitor proliferation and production of new neurons. Our results indicate that in this regenerative state, mpeg1-expressing cells are located in regions containing regenerative Müller glia and are likely engaged in active vesicle trafficking. Further, mpeg1+ cells congregate at and around the optic nerve head. Our transcriptome analysis reveals several novel genes not previously described in microglia. This dataset represents the first report, to our knowledge, to use RNA sequencing to probe the microglial transcriptome in such context, and therefore provides a resource towards understanding microglia/macrophage function during successful retinal (and central nervous tissue) regeneration.

A Novel ACKR2-Dependent Role of Fibroblast-Derived CXCL14 in Epithelial-to-Mesenchymal Transition and Metastasis of Breast Cancer

PURPOSE

Fibroblasts expressing the orphan chemokine CXCL14 have been previously shown to associate with poor breast cancer prognosis and promote cancer growth. This study explores the mechanism underlying the poor survival associations of stromal CXCL14.

EXPERIMENTAL DESIGN

Tumor cell epithelial-to-mesenchymal transition (EMT), invasion, and metastasis were studied in in vitro and in vivo models together with fibroblasts overexpressing CXCL14. An approach for CXCL14 receptor identification included loss-of-function studies followed by molecular and functional endpoints. The clinical relevance was further explored in publicly available gene expression datasets.

RESULTS

CXCL14 fibroblasts stimulated breast cancer EMT, migration, and invasion in breast cancer cells and in a xenograft model. Furthermore, tumor cells primed by CXCL14 fibroblasts displayed enhanced lung colonization after tail-vein injection. By loss-of function experiments, the atypical G-protein-coupled receptor ACKR2 was identified to mediate CXCL14-stimulated responses. Downregulation of ACKR2, or CXCL14-induced NOS1, attenuated the pro-EMT and migratory capacity. CXCL14/ACKR2 expression correlated with EMT and survival in gene expression datasets.

CONCLUSIONS

Collectively, the findings imply an autocrine fibroblast CXCL14/ACKR2 pathway as a clinically relevant stimulator of EMT, tumor cell invasion, and metastasis. The study also identifies ACKR2 as a novel mediator for CXCL14 function and thereby defines a pathway with drug target potential.See related commentary by Zhang et al., p. 3476.

The CXC chemokines and CXC chemokine receptors in orange-spotted grouper (Epinephelus coioides) and their expression after Singapore grouper iridovirus infection

Chemokines comprise a group of small molecular weight (6-14 kDa) cytokines; chemokine receptors are a superfamily of seven transmembrane domain G-coupled receptors. Both chemokines and their receptors have important roles in immune surveillance, inflammation, and development. Recently, 9 CXC chemokine ligands (CXCLs) and 8 CXC chemokine receptors (CXCRs) were identified and cloned from orange-spotted grouper (Epinephelus coioides) and annotated by phylogenetic and syntenic analyses. We detected mRNA transcripts for CXCLs and CXCRs in healthy tissues of E. coioides. Our data show that CXCL genes are highly expressed in the spleen, kidney and liver and that CXCR genes are ubiquitously expressed, rather than being expressed only in immune organs. Analysis of gene expression after Singapore grouper iridovirus infection indicated that CXCL and CXCR genes are regulated in a gene-specific manner. CXCL8 and CXCL12a were significantly upregulated in the spleen, kidney and liver of resistant fish, indicating potential roles in immunity against the pathogen. Additionally, CXCR4a was upregulated in all three organs in resistant fish, suggesting that CXCL8 or CXCL12a may participate in the immune response via interaction with CXCR4a. In addition, the new orange-spotted grouper receptor CXCR1b was found to be upregulated in the spleen and kidney of resistant fish, indicating that this receptor plays an important role in immune responses to viral infection. These results are valuable for comparative immunological studies and provide insight into the roles of these genes in viral infection.