Protective roles of the fractalkine/CX3CL1-CX3CR1 interactions in alkali-induced corneal neovascularization through enhanced antiangiogenic factor expression

CD47 and thrombospondin-1 contribute to immune evasion by Porphyromonas gingivalis

Porphyromonas gingivalis is a gram-negative anaerobic bacterium linked to periodontal disease. Remarkably, P. gingivalis thrives in an inflamed environment rich in activated neutrophils. Toll-like receptor 2 (TLR2) recognition is required for P. gingivalis to evade innate immune killing; however, the mechanisms through which P. gingivalis uncouples host inflammation from bactericidal activity are only partially known. Since integrin activation and alternative signaling are implicated in P. gingivalis TLR2-mediated immune escape, we explored the role of CD47, a widely expressed integrin-associated protein known to suppress phagocytosis and implicated as an interacting partner with other innate immune receptors. We found that CD47 associates with TLR2, and blocking CD47 leads to decreased intracellular P. gingivalis survival in macrophages in a manner dependent on the bacterial major fimbria. In vivo, CD47 knock-out mice cleared P. gingivalis more efficiently than wild-type mice. Next, we found increased expression and secretion of the CD47 ligand thrombospondin-1 (TSP-1) following P. gingivalis infection. Secreted TSP-1 broadly protected P. gingivalis and other periodontitis-associated bacterial species from neutrophil bactericidal activity. Therefore, CD47-TLR2 cosignaling in response to P. gingivalis induces TSP-1 that in turn suppresses neutrophil activity, an effect that can explain how species such as P. gingivalis survive in an inflamed environment and cause dysbiosis.

Role of macrophage in ocular neovascularization

Ocular neovascularization is the leading cause of blindness in clinical settings. Pathological angiogenesis of the eye can be divided into corneal neovascularization (CoNV), retinal neovascularization (RNV, including diabetic retinopathy and retinopathy of prematurity), and choroidal neovascularization (CNV) based on the anatomical location of abnormal neovascularization. Although anti-Vascular endothelial growth factor (VEGF) agents have wide-ranging clinical applications and are an effective treatment for neovascular eye disease, many deficiencies in this treatment strategy remain. Recently, emerging evidence has demonstrated that macrophages are vital during the process of physiological and pathological angiogenesis. Monocyte-macrophage lineage is diverse and plastic, they can shift between different activation modes and have different functions. Due to the obvious regulatory effect of macrophages on inflammation and angiogenesis, macrophages have been increasingly studied in the field of ophthalmology. Here, we detail how macrophage activated and the role of different subtypes of macrophages in the pathogenesis of ocular neovascularization. The complexity of macrophages has recently taken center stage owing to their subset diversity and tightly regulated molecular and metabolic phenotypes. In this review, we reveal the functional and phenotypic characterization of macrophage subsets associated with ocular neovascularization, more in-depth research is needed to explore the specific mechanisms by which macrophages regulate angiogenesis as well as macrophage polarization. Targeted regulation of macrophage differentiation based on their phenotype and function could be an effective approach to treat and manage ocular neovascularization in the future.

Pathogenesis of Alkali Injury-Induced Limbal Stem Cell Deficiency: A Literature Survey of Animal Models

Limbal stem cell deficiency (LSCD) is a debilitating ocular surface disease that eventuates from a depleted or dysfunctional limbal epithelial stem cell (LESC) pool, resulting in corneal epithelial failure and blindness. The leading cause of LSCD is a chemical burn, with alkali substances being the most common inciting agents. Characteristic features of alkali-induced LSCD include corneal conjunctivalization, inflammation, neovascularization and fibrosis. Over the past decades, animal models of corneal alkali burn and alkali-induced LSCD have been instrumental in improving our understanding of the pathophysiological mechanisms responsible for disease development. Through these paradigms, important insights have been gained with regards to signaling pathways that drive inflammation, neovascularization and fibrosis, including NF-κB, ERK, p38 MAPK, JNK, STAT3, PI3K/AKT, mTOR and WNT/β-catenin cascades. Nonetheless, the molecular and cellular events that underpin re-epithelialization and those that govern long-term epithelial behavior are poorly understood. This review provides an overview of the current mechanistic insights into the pathophysiology of alkali-induced LSCD. Moreover, we highlight limitations regarding existing animal models and knowledge gaps which, if addressed, would facilitate development of more efficacious therapeutic strategies for patients with alkali-induced LSCD.

Laser-induced microinjury of the corneal basal epithelium and imaging of resident macrophage responses in a live, whole-eye preparation

The corneal epithelium is continuously subjected to external stimuli that results in varying degrees of cellular damage. The use of live-cell imaging approaches has facilitated understanding of the cellular and molecular mechanisms underlying the corneal epithelial wound healing process. Here, we describe a live, ex vivo, whole-eye approach using laser scanning confocal microscopy to simultaneously induce and visualize short-term cellular responses following microdamage to the corneal epithelium. Live-cell imaging of corneal cell layers was enabled using the lipophilic fluorescent dyes, SGC5 or FM4-64, which, when injected into the anterior chamber of enucleated eyes, readily penetrated and labelled cell membranes. Necrotic microdamage to a defined region (30 μm x 30 μm) through the central plane of the corneal basal epithelium was induced by continuously scanning for at least one minute using high laser power and was dependent on the presence of lipophilic fluorescent dye. This whole-mount live-cell imaging and microdamage approach was used to examine the behavior of Cx3cr1:GFP-expressing resident corneal stromal macrophages (RCSMs). In undamaged corneas, RCSMs remained stationary, but exhibited a constant extension and retraction of short (~5 μm) semicircular, pseudopodia-like processes reminiscent of what has previously been reported in corneal dendritic cells. Within minutes of microdamage, nearby anterior RCSMs became highly polarized and extended projections towards the damaged region. The extension of the processes plateaued after about 30 minutes and remained stable over the course of 2-3 hours of imaging. Retrospective immunolabeling showed that these responding RCSMs were MHC class II+. This study adds to existing knowledge of immune cell behavior in response to corneal damage and introduces a simple corneal epithelial microdamage and wound healing paradigm.

Implications of fractalkine on glial function, ablation and glial proteins/receptors/markers—understanding its therapeutic usefulness in neurological settings: a narrative review

Background

Fractalkine (CX3CL1) is a chemokine predominantly released by neurons. As a signaling molecule, CX3CL1 facilitates talk between neurons and glia. CX3CL1 is considered as a potential target which could alleviate neuroinflammation. However, certain controversial results and ambiguous role of CX3CL1 make it inexorable to decipher the overall effects of CX3CL1 on the physiopathology of glial cells.

Main body of the abstract

Implications of cross-talk between CX3CL1 and different glial proteins/receptors/markers will give a bird eye view of the therapeutic significance of CX3CL1. Keeping with the need, this review identifies the effects of CX3CL1 on glial physiopathology, glial ablation, and gives a wide coverage on the effects of CX3CL1 on certain glial proteins/receptors/markers.

Short conclusion

Pinpoint prediction of the therapeutic effect of CX3CL1 on neuroinflammation needs further research. This is owing to certain obscure roles and implications of CX3CL1 on different glial proteins/receptors/markers, which are crucial under neurological settings. Further challenges are imposed due to the dichotomous roles played by CX3CL1. The age-old chemokine shows many newer scopes of research in near future. Thus, overall assessment of the effect of CX3CL1 becomes crucial prior to its administration in neuroinflammation.

CX3CL1-CX3CR1 Signaling Deficiency Exacerbates Obesity-induced Inflammation and Insulin Resistance in Male Mice

The CX3CL1-CX3CR1 system plays an important role in disease progression by regulating inflammation both positively and negatively. We reported previously that C-C chemokine receptors 2 and 5 promote obesity-associated adipose tissue inflammation and insulin resistance. Here, we demonstrate that CX3CL1-CX3CR1 signaling is involved in adipose tissue inflammation and insulin resistance in obese mice via adipose tissue macrophage recruitment and M1/M2 polarization. Cx3cl1 expression was persistently decreased in the epididymal white adipose tissue (eWAT) of high-fat diet-induced obese (DIO) mice, despite increased expression of other chemokines. Interestingly, in Cx3cr1-/- mice, glucose tolerance, insulin resistance, and hepatic steatosis induced by DIO or leptin deficiency were exacerbated. CX3CL1-CX3CR1 signaling deficiency resulted in reduced M2-polarized macrophage migration and an M1-dominant shift of macrophages within eWAT. Furthermore, transplantation of Cx3cr1-/- bone marrow was sufficient to impair glucose tolerance, insulin sensitivity, and regulation of M1/M2 status. Moreover, Cx3cl1 administration in vivo led to the attenuation of glucose intolerance and insulin resistance. Thus, therapy targeting the CX3CL1-CX3CR1 system may be beneficial in the treatment of type 2 diabetes by regulating M1/M2 macrophages.

Association of CX3CL1 and CX3CR1 Expression with Liver Fibrosis in a Mouse Model of Schistosomiasis

Immunopathological mechanisms of schistosomiasis, a debilitating parasitic disease, are still unclear. In this study, we investigated the involvement of CX3C chemokine ligand 1 (CX3CL1) and its sole receptor CX3CR1 in the development of liver fibrosis in schistosomiasis. The animal model of schistosomiasis was established by infection of C57BL/6 mice with Schistosoma japonicum cercariae; mice injected with carbon tetrachloride (CCl₄) were used as positive control of liver injury. After 4 and 8 weeks, the degree of liver lesions was assessed by hematoxylin and eosin staining, serum levels of hyaluronic acid (HA) were analyzed by a chemiluminescence immunoassay, liver fibrosis was evaluated by immunohistochemistry analysis of α-smooth muscle actin (α-SMA) expression, and CX3CL1 and CX3CR1 expression in the liver was measured by immunohistochemistry and real-time PCR. The results showed that at 8 weeks after Schistosoma infection, serum HA levels were increased and α-SMA-expressing cells appeared in the liver, indicating fibrogenesis. CX3CL1- and CX3CR1-positive cells were observed in the outer layer of granulomas formed around Schistosoma eggs in liver tissues, which was consistent with the significant upregulation of hepatic CX3CL1 and CX3CR1 mRNA expression at 4 and 8 weeks post-infection. Furthermore, correlation analysis revealed positive association between CX3CL1 and CX3CR1 expression and serum HA levels at 8 weeks post-infection, indicating a link between fibrogenesis and the CX3CL1/CX3CR1 axis in schistosomiasis. In conclusion, our data suggest the involvement of CX3CL1 and CX3CR1 in the progression of liver fibrosis caused by Schistosoma infection.

CX3CR1 regulates angiogenesis and activation of pro-angiogenic factors and triggers macrophage accumulation in experimental hepatopulmonary syndrome model

OBJECTIVE

Prevalence of hepatopulmonary syndrome (HPS) ranges from 4% to 47% in patients with cirrhosis. This study aimed to explore possible relationship between CX3CR1 and angiogenesis or macrophage accumulation in pathological process of HPS.

MATERIAL AND METHODS

Wide-type C57Bl/6 mice were divided into WT-sham, WT-common bile duct ligation (WT-CBDL), WT-CBDL plus antibody (WT-CBDL+Ab) and WT-CBDL plus Bevacizumab. The CX3CR1^GFP/GFP mice were grouping into CX3CR1 GFP/GFP-sham, CX3CR1 GFP/GFP-CBDL and CX3CR1 GFP/GFP-CBDL+Bevacizumab group. Intrapulmonary expression of Akt, pAkt, ERK, pERK, iNOS, VEGF, PDGF was measured using biological technology. Hematoxylin-eosin (H&E) staining and immunohistochemical analysis were used to evaluate changes of pulmonary tissues including pathological abnormality, angiogenesis and macrophage accumulation.

RESULTS

Blockade CX3CR1 pathway inhibited angiogenesis, macrophage accumulation and pathological changes of lung tissues. Blockade of CX3CR1 pathway reduced pAkt, pERK, iNOS, PDGF and VEGF activation. CX3CR1 contributed to the process of angiogenesis and activate the pro-angiogenic factors. CX3CR1 deficiency obviously reduced the macrophage accumulation. Inhibition of VEGF by Bevacizumab improved intrapulmonary angiogenesis and pathological changes of lung tissues. Inhibition of VEGF by Bevacizumab retarded the production of pAKt, PDGF, and iNOS. Inhibition of VEGF by Bevacizumab reduced CX3CL1 production.

CONCLUSION

CX3CR1 could regulate the angiogenesis and activation of pro-angiogenic factors, including pAKT, pERK, iNOS, VEGF and PDGF in the process of hepato-pulmonary syndrome. Moreover, CX3CR1 could also contribute to the macrophage accumulation.

Essential Contribution of Macrophage Tie2 Signalling in a Murine Model of Laser-Induced Choroidal Neovascularization

Wet age-related macular degeneration (AMD), which can cause progressive blindness, is characterised by choroid neovascularization (CNV) in the macular area. Although close attention has been paid to AMD, and anti-vascular endothelial growth factor (VEGF) drugs are available, its complex pathogenesis is still elusive. Tie2-expressing macrophages (TEMs) have been found to promote angiogenesis in remodel tissues and tumours. This study aimed to elucidate the role of macrophage Tie2 signalling in laser-induced CNV (LCNV). We observed that TEMs were responsible for the severity of CNV. Mechanistically, TEM deletion resulted in impaired LCNV due to the suppression of inflammatory angiogenesis and the promotion of apoptosis. We also observed that TEMs prevented apoptosis of b.End3 cells, but promoted their migration, proliferation and tube formation via VEGF, extracellular signal-regulated kinase (ERK) and v-akt murine thymoma viral oncogene (AKT)-dependent signalling pathways. The flow cytometry results comparing dry AMD patients and healthy controls with wet AMD patients showed that the percentage of Tie2⁺CD14⁺ cells was higher in the wet AMD patients’ peripheral blood. This study demonstrates that Tie2 expression by macrophages intensifies CNV in LCNV murine models, thereby proposing an additional intervention option to inhibit CNV.

Functional Annotations of Single-Nucleotide Polymorphism (SNP)-Based and Gene-Based Genome-Wide Association Studies Show Genes Affecting Keratitis Susceptibility

Background

Keratitis is a complex condition in humans and is the second most common cause of legal blindness worldwide.

Material/Methods

To reveal the genomic loci underlying keratitis, we performed functional annotations of SNP-based and gene-based genome-wide association studies of keratitis in the UK Biobank (UKB) cohort with 337 199 subjects of European ancestry.

Results

The publicly available SNP-based association results showed a total of 34 SNPs, from 14 distinct loci, associated with keratitis in the UKB. Gene-based association analysis identified 2 significant genes: IQCF3 (p=2.0×10⁻⁶) and SOD3 (p=2.0×10⁻⁶). Thirty-two candidate genes were then prioritized using information from multiple sources. The overlap of IQCF3 in these 2 analyses resulted in a total of 33 hub genes. Functional annotation of hub genes was performed and transcriptional factors of IQCF3 and SOD3 were predicted.

Conclusions

A total of 34 SNPs from 14 distinct loci were identified as being associated with keratitis, and 32 candidate genes were then prioritized. In addition, IQCF3 and SOD3 were identified by their p values through gene-based tests on the basis of individual SNP-based tests. The functional relationship between these suspect genes and keratitis suggest that IQCF3 and SOD3 are candidate genes underlying keratitis.

Essential contribution of macrophage Tie2 signal mediated autophagy in laser-induced choroidal neovascularization

Autophagy plays critical roles in various ocular diseases, including age-related macular degeneration (AMD). Tie2-expressing macrophages (TEMs) play crucial roles in angiogenesis. To investigate the role of TEMs and autophagy in the development of AMD, we employed macrophage-specific Tie2 knockout mice and used a laser-induced choroidal neovascularization (CNV). The results showed that TEMs can promote CNV formation by up-regulating the level of autophagy. These results were further verified by in vitro cell experiments that peritoneal macrophages from Tie2 knockout mice can inhibit the expression of autophagy-related factors and inhibit the expression of angiogenic factor of VEGF by activating AMPK signaling pathway. Our results suggest that TEMs and macrophage Tie2 signal mediated-autophagy play critical role in experimental CNV, and they may be novel preventive targets for AMD treatment.

Cathepsin S activation contributes to elevated CX3CL1 (fractalkine) levels in tears of a Sjögren's syndrome murine model

Autoimmune dacryoadenitis and altered lacrimal gland (LG) secretion are features of Sjögren's syndrome (SS). Activity of cathepsin S (CTSS), a cysteine protease, is significantly and specifically increased in SS patient tears. The soluble chemokine, CX3CL1 (fractalkine), is cleaved from membrane-bound CX3CL1 by proteases including CTSS. We show that CX3CL1 is significantly elevated by 2.5-fold in tears (p = 0.0116) and 1.4-fold in LG acinar cells (LGAC)(p = 0.0026) from male NOD mice, a model of autoimmune dacryoadenitis in SS, relative to BALB/c controls. Primary mouse LGAC and human corneal epithelial cells (HCE-T cells) exposed to interferon-gamma, a cytokine elevated in SS, showed up to 9.6-fold (p ≤ 0.0001) and 25-fold (p ≤ 0.0001) increases in CX3CL1 gene expression, and 1.9-fold (p = 0.0005) and 196-fold (p ≤ 0.0001) increases in CX3CL1 protein expression, respectively. Moreover, exposure of HCE-T cells to recombinant human CTSS at activity equivalent to that in SS patient tears increased cellular CX3CL1 gene and protein expression by 2.8-fold (p = 0.0021) and 5.1-fold (p ≤ 0.0001), while increasing CX3CL1 in culture medium by 5.8-fold (p ≤ 0.0001). Flow cytometry demonstrated a 4.5-fold increase in CX3CR1-expressing immune cells (p ≤ 0.0001), including increased T-cells and macrophages, in LG from NOD mice relative to BALB/c. CTSS-mediated induction/cleavage of CX3CL1 may contribute to ocular surface and LG inflammation in SS.

Role of CX3CL1/CX3CR1 Signaling Axis Activity in Osteoporosis

Osteoporosis is a civilization disease which is still challenging for contemporary medicine in terms of treatment and prophylaxis. It results from excessive activation of the osteoclastic cell line and immune cells like macrophages and lymphocytes. Cell-to-cell inflammatory information transfer occurs via factors including cytokines which form a complex network of cell humoral correlation, called cytokine network. Recently conducted studies revealed the participation of CX3CL1 chemokine in the pathogenesis of osteoporosis. CX3CL1 and its receptor CX3CR1 present unique properties among over 50 described chemokines. Apart from its chemotactic activity, CX3CL1 is the only chemokine which may function as an adhesion molecule which facilitates easier penetration of immune system cells through the vascular endothelium to the area of inflammation. The present study, based on world literature review, sums and describes convincing evidences of a significant role of the CX3CL1/CX3CR1 axis in processes leading to bone mineral density (BMD) reduction. The CX3CL1/CX3CR1 axis plays a principal role in osteoclast maturation and binding them with immune cells to the surface of the bone tissue. It promotes the development of inflammation and production of many inflammatory cytokines near the bone surface (i.e., TNF-α, IL-1β, and IL-6). High concentrations of CX3CL1 in serum are directly proportional to increased concentrations of bone turnover and inflammatory factors in human blood serum (TRACP-5b, NTx, IL-1β, and IL-6). Regarding the fact that acting against the CX3CL1/CX3CR1 axis is a potential target of immune treatment in osteoporosis, the number of available papers tackling the topic is certainly insufficient. Therefore, it seems justified to continue research which would precisely determine its role in the metabolism of the bone tissue as one of the most promising targets in osteoporosis therapy.

Bone Marrow CX3CL1/Fractalkine is a New Player of the Pro-Angiogenic Microenvironment in Multiple Myeloma Patients

C-X3-C motif chemokine ligand 1 (CX3CL1)/fractalkine is a chemokine released after cleavage by two metalloproteases, ADAM metallopeptidase domain 10 (ADAM10) and ADAM metallopeptidase domain 17 (ADAM17), involved in inflammation and angiogenesis in the cancer microenvironment. The role of the CX3CL1/ C-X3-C motif chemokine receptor 1(CX3CR1) axis in the multiple myeloma (MM) microenvironment is still unknown. Firstly, we analyzed bone marrow (BM) plasma levels of CX3CL1 in 111 patients with plasma cell disorders including 70 with active MM, 25 with smoldering myeloma (SMM), and 16 with monoclonal gammopathy of undetermined significance (MGUS). We found that BM CX3CL1 levels were significantly increased in MM patients compared to SMM and MGUS and correlated with BM microvessel density. Secondly, we explored the source of CX3CL1 in MM and BM microenvironment cells. Primary CD138⁺ cells did not express CXC3L1 but up-regulated its production by endothelial cells (ECs) through the involvement of tumor necrosis factor alpha (TNFα). Lastly, we demonstrated the presence of CX3CR1 on BM CD14⁺CD16⁺ monocytes of MM patients and on ECs, but not on MM cells. The role of CX3CL1 in MM-induced angiogenesis was finally demonstrated in both in vivo chick embryo chorioallantoic membrane and in vitro angiogenesis assays. Our data indicate that CX3CL1, present at a high level in the BM of MM patients, is a new player of the MM microenvironment involved in MM-induced angiogenesis.

Streptozotocin‑induced diabetic mice exhibit reduced experimental choroidal neovascularization but not corneal neovascularization

The present study aimed to investigate the effects of diabetes mellitus (DM) on the generation of experimental corneal neovascularization (CrNV) and choroidal neovascularization (ChNV). Diabetes was induced in mice by intraperitoneal injection of streptozotocin (STZ). Experimental CrNV and ChNV were induced by alkali injury and laser photocoagulation, respectively. CrNV and ChNV were compared between the STZ‑induced diabetic mice and control mice two weeks after injury. Relative expression of angiogenic factors was quantified by reverse transcription‑quantitative polymerase chain reaction, and progenitor cell or macrophage accumulation in the early phase following injury was examined by flow cytometric analysis. Compared with the alkali‑injured normal mice, the alkali‑injured diabetic mice (STZ‑induced) exhibited no significant difference in CrNV occurrence, whereas the laser‑injured diabetic mice exhibited significantly reduced levels of ChNV compared with those of the laser‑injured control animals. The laser‑induced intrachoroidal mRNA expression levels of angiogenic factors, including vascular endothelial growth factor, hypoxia‑induced factor‑1α, chemokine (C‑C motif) ligand 3, and stromal cell‑derived factor‑1α, were reduced in the laser‑injured diabetic mice when compared with laser‑injured control mice. Furthermore, the laser‑induced intrachoroidal infiltration of c‑Kit+ progenitor cells was impaired in the laser‑injured diabetic mice compared with the laser‑injured control mice. Overall, diabetes did not exert a significant effect on the generation of experimental CrNV. However, diabetes reduced laser‑induced ChNV through downregulation of intrachoroidal progenitor cell infiltration and angiogenic factor expression.

B-cell leukemia/lymphoma 10 promotes angiogenesis in an experimental corneal neovascularization model

PURPOSE

Corneal neovascularization (CrNV) arises from many causes including corneal inflammatory, infectious, or traumatic insult, and frequently leads to impaired vision. This study seeks to determine the role of B-cell leukemia/lymphoma 10 (BCL-10) in the development of experimental CrNV.

METHODS

Corneas from BCL-10 knockout (KO) mice and wild-type (WT) mice were burned by sodium hydroxide (NaOH) to create the CrNV model and neovascular formation in the corneas was assessed 2 weeks later. Intracorneal macrophage accumulation and the expression of angiogenic factors were quantified by flow cytometric analysis (FCM) and real-time PCR, respectively.

RESULTS

The amount of CrNV was determined 2 weeks after alkali burn. Compared to WT mice, the amount of CrNV in BCL-10 KO mice was significantly decreased. FCM revealed that F4/80-positive macrophages were markedly decreased in BCL-10 KO mice compared with WT mice. Reverse transcription PCR showed that the mRNA expression levels of intracorneal vascular endothelial growth factor-A (VEGF-A), basic fibroblast growth factor (bFGF) and monocyte chemotactic protein 1 were reduced in BCL-10 KO mice compared with WT mice.

CONCLUSION

BCL-10 KO mice exhibited reduced alkali-induced CrNV by suppressing intracorneal macrophage infiltration, which subsequently led to decreased VEGF-A and bFGF expression, suggesting that BCL-10 may become a potential clinical intervening target of CrNV.

Monocyte chemoattractant protein 1 and fractalkine play opposite roles in angiogenesis via recruitment of different macrophage subtypes

AIM

To explore the interaction between macrophages and chemokines [monocyte chemoattractant protein 1 (MCP-1/CCL2) and fractalkine/CX3CL1] and the effects of their interaction on neovascularization.

METHODS

Human peripheral blood mononuclear cells, donated by healthy volunteers, were separated and cultured in RPMI-1640 medium containing 10% fetal bovine serum, then induced into macrophages by stimulation with 30 µg/L granulocyte macrophage-colony stimulating factor (GM-CSF). The expression of CCR2 and/or CX3CR1 in the macrophages was examined using flow cytometry. Macrophages were then stimulated with recombinant human CCL2 (rh-CCL2) or recombinant human CX3CL1 (rh-CX3CL1). The expression of angiogenesis-related genes, including VEGF-A, THBS-1 and ADAMTS-1 were examined using real-time quantitative polymerase chain reaction (PCR). Supernatants from stimulated macrophages were used in an assay of human retinal endothelial cell (HREC) proliferation. Finally, stimulated macrophages were co-cultured with HREC in a migration assay.

RESULTS

The expression rate of CCR2 in macrophages stimulated by GM-CSF was 42%±1.9%. The expression rate of CX3CR1 was 71%±3.3%. Compared with vehicle-treated groups, gene expression of VEGF-A in the macrophages was greater in 150 mg/L CCL2-treated groups (P<0.05), while expression of THBS-1 and ADAMTS-1 was significantly lower (P<0.05). By contrast, compared with vehicle-treated groups, expression of VEGF-A in 150 mg/L CX3CL1-treated groups was significantly lower (P<0.05), while expression of THBS-1 and ADAMTS-1 was greater (P<0.05). Supernatants from CCL2 treated macrophages promoted proliferation of HREC (P<0.05), while supernatants from CX3CL1-treated macrophages inhibited the proliferation of HREC (P<0.05). HREC migration increased when co-cultured with CCL2-treated macrophages, but decreased with CX3CL1-treated macrophages (P<0.05).

CONCLUSION

CCL2 and CX3CL1 exert different effects in regulation of macrophage in expression of angiogenesis-related factors, including VEGF-A, THBS-1 and ADAMTS-1. Our findings suggest that CCL2 and CX3CL1 may be candidate proteins for further exploration of novel targets for treatment of ocular neovascularization.

Essential involvement of the CX3CL1-CX3CR1 axis in bleomycin-induced pulmonary fibrosis via regulation of fibrocyte and M2 macrophage migration

The potential role of macrophages in pulmonary fibrosis (PF) prompted us to evaluate the roles of CX3CR1, a chemokine receptor abundantly expressed in macrophages during bleomycin (BLM)-induced PF. Intratracheal BLM injection induced infiltration of leukocytes such as macrophages into the lungs, which eventually resulted in fibrosis. CX3CR1 expression was mainly detected in the majority of macrophages and in a small portion of α-smooth muscle actin-positive cells in the lungs, while CX3CL1 was expressed in macrophages. BLM-induced fibrotic changes in the lungs were reduced without any changes in the number of leukocytes in Cx3cr1 -/- mice, as compared with those in the wild-type (WT) mice. However, intrapulmonary CX3CR1+ macrophages displayed pro-fibrotic M2 phenotypes; lack of CX3CR1 skewed their phenotypes toward M1 in BLM-challenged lungs. Moreover, fibrocytes expressed CX3CR1, and were increased in BLM-challenged WT lungs. The number of intrapulmonary fibrocytes was decreased in Cx3cr1 -/- mice. Thus, locally-produced CX3CL1 can promote PF development primarily by attracting CX3CR1-expressing M2 macrophages and fibrocytes into the lungs.

Therapeutic effects of zerumbone in an alkali-burned corneal wound healing model

Cornea is an avascular transparent tissue. Ocular trauma caused by a corneal alkali burn induces corneal neovascularization (CNV), inflammation, and fibrosis, leading to vision loss. The purpose of this study was to examine the effects of Zerumbone (ZER) on corneal wound healing caused by alkali burns in mice. CNV was induced by alkali-burn injury in BALB/C female mice. Topical ZER (three times per day, 3μl each time, at concentrations of 5, 15, and 30μM) was applied to treat alkali-burned mouse corneas for 14 consecutive days. Histopathologically, ZER treatment suppressed alkali burn-induced CNV and decreased corneal epithelial defects induced by alkali burns. Corneal tissue treated with ZER showed reduced mRNA levels of pro-angiogenic genes, including vascular endothelial growth factor, matrix metalloproteinase-2 and 9, and pro-fibrotic factors such as alpha smooth muscle actin and transforming growth factor-1 and 2. Immunohistochemical analysis demonstrated that the infiltration of F4/80 and/or CCR2 positive cells was significantly decreased in ZER-treated corneas. ZER markedly inhibited the mRNA and protein levels of monocyte chemoattractant protein-1 (MCP-1) in human corneal fibroblasts and murine peritoneal macrophages. Immunoblot analysis revealed that ZER decreased the activation of signal transducer and activator of transcription 3 (STAT3), with consequent reduction of MCP-1 production by these cells. In conclusion, topical administration of ZER accelerated corneal wound healing by inhibition of STAT3 and MCP-1 production.

CX3CR1 deficiency accelerates the development of retinopathy in a rodent model of type 1 diabetes

In this study, the role of CX3CR1 in the progression of diabetic retinopathy (DR) was investigated. The retinas of wild-type (WT), CX3CR1 null (CX3CR1gfp/gfp, KO), and heterozygous (CX3CR1+/gfp, Het) mice were compared in the presence and absence of streptozotocin (STZ)-induced diabetes. CX3CR1 deficiency in STZ-KO increased vascular pathology at 4 months of diabetes, as a significant increase in acellular capillaries was observed only in the STZ-KO group. CX3CR1 deficiency and diabetes had similar effects on retinal neurodegeneration measured by an increase in DNA fragmentation. Retinal vascular pathology in STZ-KO mice was associated with increased numbers of monocyte-derived macrophages in the retina. Furthermore, compared to STZ-WT, STZ-KO mice exhibited increased numbers of inflammatory monocytes in the bone marrow and impaired homing of monocytes to the spleen. The induction of retinal IL-10 expression by diabetes was significantly less in KO mice, and when bone marrow-derived macrophages from KO mice were maintained in high glucose, they expressed significantly less IL-10 and more TNF-α in response to LPS stimulation. These findings support that CX3CR1 deficiency accelerates the development of vascular pathology in DR through increased recruitment of proinflammatory myeloid cells that demonstrate reduced expression of anti-inflammatory IL-10.

KEY MESSAGES

• CX3CR1 deletion in STZ-diabetic mice accelerated the onset of diabetic retinopathy (DR). • The early onset of DR was associated with increased retinal cell apoptosis. • The early onset of DR was associated with increased recruitment of bone marrow-derived macrophages to the retina. • Bone marrow-derived macrophages from CX3CR1 KO diabetic mice expressed more TNF-α and less IL-10. • The role of IL-10 in protection from progression of DR is highlighted.

Host immune cellular reactions in corneal neovascularization

Corneal neovascularization (CNV) is a global important cause of visual impairment. The immune mechanisms leading to corneal heme- and lymphangiogenesis have been extensively studied over the past years as more attempts were made to develop better prophylactic and therapeutic measures. This article aims to discuss immune cells of particular relevance to CNV, with a focus on macrophages, Th17 cells, dendritic cells and the underlying immunology of common pathologies involving neovascularization of the cornea. Hopefully, a thorough understanding of these topics would propel the efforts to halt the detrimental effects of CNV.

Adenosine A1 receptors contribute to immune regulation after neonatal hypoxic ischemic brain injury

Neonatal brain hypoxic ischemia (HI) often results in long-term motor and cognitive impairments. Post-ischemic inflammation greatly effects outcome and adenosine receptor signaling modulates both HI and immune cell function. Here, we investigated the influence of adenosine A1 receptor deficiency (A1R(-/-)) on key immune cell populations in a neonatal brain HI model. Ten-day-old mice were subjected to HI. Functional outcome was assessed by open locomotion and beam walking test and infarction size evaluated. Flow cytometry was performed on brain-infiltrating cells, and semi-automated analysis of flow cytometric data was applied. A1R(-/-) mice displayed larger infarctions (+33%, p < 0.05) and performed worse in beam walking tests (44% more mistakes, p < 0.05) than wild-type (WT) mice. Myeloid cell activation after injury was enhanced in A1R(-/-) versus WT brains. Activated B lymphocytes expressing IL-10 infiltrated the brain after HI in WT, but were less activated and did not increase in relative frequency in A1R(-/-). Also, A1R(-/-) B lymphocytes expressed less IL-10 than their WT counterparts, the A1R antagonist DPCPX decreased IL-10 expression whereas the A1R agonist CPA increased it. CD4(+) T lymphocytes including FoxP3(+) T regulatory cells, were unaffected by genotype, whereas CD8(+) T lymphocyte responses were smaller in A1R(-/-) mice. Using PCA to characterize the immune profile, we could discriminate the A1R(-/-) and WT genotypes as well as sham operated from HI-subjected animals. We conclude that A1R signaling modulates IL-10 expression by immune cells, influences the activation of these cells in vivo, and affects outcome after HI.

Nestin depletion induces melanoma matrix metalloproteinases and invasion

Matrix metalloproteinases (MMPs) are key biological mediators of processes as diverse as wound healing, embryogenesis, and cancer progression. Although MMPs may be induced through multiple signaling pathways, the precise mechanisms for their regulation in cancer are incompletely understood. Because cytoskeletal changes are known to accompany MMP expression, we sought to examine the potential role of the poorly understood cytoskeletal protein, nestin, in modulating melanoma MMPs. Nestin knockdown (KD) upregulated the expression of specific MMPs and MMP-dependent invasion both through extracellular matrix barriers in vitro and in peritumoral connective tissue of xenografts in vivo. The development of three-dimensional melanospheres that in vitro partially recapitulate noninvasive tumorigenic melanoma growth was inhibited by nestin KD, although ECM invasion by aberrant melanospheres that did form was enhanced. Mechanistically, nestin KD-dependent melanoma invasion was associated with intracellular redistribution of phosphorylated focal adhesion kinase and increased melanoma cell responsiveness to transforming growth factor-beta, both implicated in pathways of melanoma invasion. The results suggest that the heretofore poorly understood intermediate filament, nestin, may serve as a novel mediator of MMPs critical to melanoma virulence.

Critical Role of IP-10 on Reducing Experimental Corneal Neovascularization

AIM AND SCOPE

To address the role of interferon-induced protein of 10 kDa (IP-10) in the course of corneal neovascularization (CrNV) in a mouse model of experimental corneal neovascularization.

MATERIAL AND METHOD

BALB/c mice that were 7- to 8-week-old male were included in the study. Corneal injury was induced by NaOH. Mice were randomly divided into 2 groups of IP-10 and vehicle. The alkali-treated eyes received 5 μl of 5 μg/ml IP-10 dissolved in 0.2% sodium hyaluronate for IP-10-treated group, or 5 μl of 0.2% sodium hyaluronate for vehicle-treated group twice a day for 7 days immediately after the alkali injury. 2 weeks after alkali injury, corneas were removed and used for whole mount CD31 staining. The percentages of neovascularization on corneal photographs were examined with digital image analysis. In other experiments, at indicated time intervals, the corneas were removed. Angiogenic factor expression in the early phase after injury was quantified by real-time PCR and western blot. The VEGF expression in macrophages infiltrating into burned corneas was examined by Flow cytometry (FCM) and immunofluorescence. Tube formation and cell proliferation of human retinal endothelial cells (HRECs) were detected after being stimulated with IP-10 in vitro.

RESULTS

The mRNA and protein expression of IP-10 and C-X-C motif chemokine receptor 3 (CXCR3) was augmented after the alkali injury (p < 0.05). Compared with vehicle-treated mice, IP-10-treated mice exhibited reduced CrNV 2 weeks after injury, as evidenced by diminished CD31-positive areas (p < 0.05). Concomitantly, the intracorneal mRNA and protein expression enhancement of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) was lower in IP-10-treated mice than in vehicle-treated mice after injury (p < 0.05). Moreover, IP-10 inhibited HREC tube formation and proliferation in vitro.

CONCLUSION

IP-10-treated mice exhibited reduced alkali-induced CrNV through decreasing intracorneal VEGF and bFGF expression, and inhibiting endothelial cell proliferation and tube formation.

Protective effects of matrix metalloproteinase-12 following corneal injury

Corneal scarring due to injury is a leading cause of blindness worldwide and results from dysregulated inflammation and angiogenesis during wound healing. Here we demonstrate that the extracellular matrix metalloproteinase MMP12 (macrophage metalloelastase) is an important regulator of these repair processes. Chemical injury resulted in higher expression of the fibrotic markers α-smooth muscle actin and type I collagen, and increased levels of angiogenesis in corneas of Mmp12(-/-) mice compared with corneas of wild-type mice. In vivo, we observed altered immune cell dynamics in Mmp12(-/-) corneas by confocal imaging. We determined that the altered dynamics were the result of an altered inflammatory response, with delayed neutrophil infiltration during the first day and excessive macrophage infiltration 6 days later, mediated by altered expression levels of chemokines CXCL1 and CCL2, respectively. Corneal repair returned to normal upon inhibition of these chemokines. Taken together, these data show that MMP12 has a protective effect on corneal fibrosis during wound repair through regulation of immune cell infiltration and angiogenesis.

Crucial involvement of tumor-associated neutrophils in the regulation of chronic colitis-associated carcinogenesis in mice

Ulcerative colitis (UC) is a major form of chronic inflammation that can frequently progress to colon cancer. Several studies have demonstrated massive infiltration of neutrophils and macrophages into the lamina propria and submucosa in the progression of UC-associated colon carcinogenesis. Macrophages contribute to the development of colitis-associated colon cancer (CAC). However, the role of neutrophils is not well understood. To better understand the involvement of tumor-associated neutrophils (TANs) in the regulation of CAC, we used a mouse CAC model produced by administering azoxymethane (AOM), followed by repeated dextran sulfate sodium (DSS) ingestion. This causes severe colonic inflammation and subsequent development of multiple tumors in mice colon. We observed that colorectal mucosal inflammation became increasingly severe with AOM and DSS treatment. Macrophages infiltrated the lamina propria and submucosa, together with a marked increase in neutrophil infiltration. The chemokine CXCL2 increased in the lamina propria and submucosal regions of the colons of the treated mice, together with the infiltration of neutrophils expressing CXCR2, a specific receptor for CXCL2. This process was followed by neoplastic transformation. After AOM and DSS treatment, the mice showed enhanced production of metalloproteinase (MMP)-9 and neutrophil elastase (NE), accompanied by excessive vessel generation and cell proliferation. Moreover, CXCL2 promoted neutrophil recruitment and induced neutrophils to express MMP-9 and NE in vitro. Furthermore, administration of neutrophil-neutralizing antibodies after the last DSS cycle markedly reduced the number and size of tumors and decreased the expression of CXCR2, CXCL2, MMP-9, and NE. These observations indicate a crucial role for TANs in the initiation and progression of CAC and suggest that the CXCL2-CXCR2 axis might be useful in reducing the risk of UC-associated colon cancer.

Radial coherence of diffusion tractography in the cerebral white matter of the human fetus: neuroanatomic insights

High angular resolution diffusion imaging (HARDI) demonstrates transient radial coherence of telencephalic white matter in the human fetus. Our objective was to define the neuroanatomic basis of this radial coherence through correlative HARDI- and postmortem tissue analyses. Applying immunomarkers to radial glial fibers (RGFs), axons, and blood vessels in 18 cases (19 gestational weeks to 3 postnatal years), we compared their developmental profiles to HARDI tractography in brains of comparable ages (n = 11). At midgestation, radial coherence corresponded with the presence of RGFs. At 30-31 weeks, the transition from HARDI-defined radial coherence to corticocortical coherence began simultaneously with the transformation of RGFs to astrocytes. By term, both radial coherence and RGFs had disappeared. White matter axons were radial, tangential, and oblique over the second half of gestation, whereas penetrating blood vessels were consistently radial. Thus, radial coherence in the fetal white matter likely reflects a composite of RGFs, penetrating blood vessels, and radial axons of which its transient expression most closely matches that of RGFs. This study provides baseline information for interpreting radial coherence in tractography studies of the preterm brain in the assessment of the encephalopathy of prematurity.

CX3CL1 expression in the conjunctiva is involved in immune cell trafficking during toxic ocular surface inflammation

Inappropriate expression of the chemokine CX3CL1 is reportedly known to act on inflammatory conditions in extraocular immune diseases. We studied the expression and effects of CX3CL1 in human patients, cultured human conjunctival cells, and transgenic mice exposed to benzalkonium chloride (BAC), a commonly used preservative in ophthalmic medications despite its proinflammatory properties, to determine whether CX3CL1 is involved in conjunctival inflammation. We report that CX3CL1 expression is increased in the conjunctiva of patients receiving BAC-containing medication, and correlates with clinical inflammation. BAC enhances the production of CX3CL1 in a conjunctival epithelial cell line, through the tumor-necrosis factor-α pathway, which attracts specific leukocyte subsets. In vivo, BAC-induced macrophage infiltration and subsequent inflammation of the conjunctiva is decreased in CX3CR1-deficient mice as compared with CX3CR1(+/+) controls. This translational study opens new avenue to investigate ocular surface disorders by focusing on chemokine-related inflammation and immune cell trafficking in the ocular conjunctival mucosa.

Inhibitory effect of CCR3 signal on alkali-induced corneal neovascularization

AIM

To investigate the effect of CC chemokine receptor 3 (CCR3) signal on corneal neovascularization (CRNV) induced by alkali burn and to explore its mechanism.

METHODS

Specific pathogen-free male BALB/C mice (aged 6-8 weeks) were randomly divided into CCR3-antagonist treated group (experimental group) and control group. CRNV was induced by alkali burn in mice. The time kinetic CCR3 expression in injured corneas was examined by reverse transcription polymerase chain reaction (RT-PCR). CCR3-antagonist (SB-328437 at different concentration of 125µg/mL, 250µg/mL, and 500µg/mL) was locally administrated after alkali injury. The formation of CRNV was assessed by CD31 corneal whole mount staining at two weeks after injury. Monocyte chemotactic protein 1 (MCP-1), monocyte chemotactic protein 3 (MCP-3) expressions in the early phase after injury were quantified and compared by RT-PCR. Macrophage intracorneal accumulation in the early phase after injury was evaluated and compared by immunohistochemistry.

RESULTS

Alkali injury induced the time kinetic intracorneal CCR3 expression. 500µg/mL of CCR3-antagonist treatment in the early phase but not the late phase resulted in significant impaired CRNV as compared to control group (P<0.05). CCR3-antagonist treatment in the early phase significantly reduced the intracorneal MCP-1 and MCP-3 enhancement compare to control group at day 2 and day 4 (P<0.05). Moreover, the number of intracorneal macrophage infiltration in the experimental group was reduced than those in control group at day 4 (P<0.05).

CONCLUSION

CCR3 signal is involved in alkali-induced CRNV. CCR3-antagonist can inhibit alkali-induced CRNV by reducing the intracorneal MCP-1 and MCP-3 mRNA expression and the intracorneal macrophage infiltration.

Inhibited experimental corneal neovascularization by neutralizing anti-SDF-1α antibody

AIM

To explore the effect of SDF-1α on the development of experimental corneal neovascularization (CRNV).

METHODS

CRNV was induced by alkali injury in mice. The expression of SDF-1α and CXCR4 in burned corneas was examined by Flow Cytometry. Neutralizing anti-mouse SDF-1α antibody was locally administrated after alkali injury and the formation of CRNV 2 weeks after injury was assessed by Immunohistochemistry. The expression of VEGF and C-Kit in burned corneas was detected by RT-PCR.

RESULTS

The number of CRNV peaks at 2 weeks after alkali injury. Compared to control group, SDF-1α neutralizing antibody treatment significantly decreased the number of CRNV. RT-PCR confirmed that SDF-1α neutralizing antibody treatment resulted in decreased intracorneal VEGF and C-Kit expression.

CONCLUSION

SDF-1α neutralizing antibody treated mice exhibited impaired experimental CRNV through down regulated VEGF and C-Kit expression.

Therapies using anti-angiogenic peptide mimetics of thrombospondin-1

INTRODUCTION

The role of hrombospondin-1 (TSP1) as a major endogenous angiogenesis inhibitor has been confirmed by numerous studies and subsequent mechanistic discoveries. It has yielded a new class of potential drugs against cancer and other angiogenesis-driven diseases.

AREAS COVERED

An overview of TSP1 functions and molecular mechanisms, including regulation and signaling. Functions in endothelial and non-endothelial cells, with emphasis on the role of TSP1 in the regulation of angiogenesis and inflammation. The utility of duplicating these activities for drug discovery. Past and current literature on endogenous TSP1 and its role in the progression of cancer and non-cancerous pathological conditions is summarized, as well as the research undertaken to identify and optimize short bioactive peptides derived from the two TSP1 anti-angiogenic domains, which bind CD47 and CD36 cell surface receptors. Lastly, there is an overview of the efficacy of some of these peptides in pre-clinical and clinical models of angiogenesis-dependent disease.

EXPERT OPINION

It is concluded that TSP1-derived peptides and peptide mimetics hold great promise as future agents for the treatment of cancer and other diseases driven by excessive angiogenesis. They may fulfill unmet medical needs including neovascular ocular disease and the diseases of the female reproductive tract including ovarian cancer.

Fractalkine and its receptor, CX3CR1, promote hypertensive interstitial fibrosis in the kidney

Hypertension promotes and escalates kidney injury, including kidney fibrosis. Fractalkine/CX3CL1 is a unique chemokine that works as a leukocyte chemoattractant and an adhesion molecule. Recently, fractalkine/CX3CL1 has been reported to promote tissue fibrosis via its cognate receptor, CX3CR1. However, the involvement of the fractalkine-CX3CR1 axis in the pathogenesis of hypertensive kidney fibrosis remains unclear. The impacts of the fractalkine-CX3CR1 axis on hypertensive kidney fibrosis were investigated in a deoxycorticosterone acetate (DOCA)-salt hypertensive model in CX3CR1-deficient mice, which were sacrificed on day 28. The blood pressure levels were similarly elevated in both CX3CR1-/- C57BL/6 and wild-type C57BL/6 mice. Fractalkine and CX3CR1 were upregulated in kidneys that were damaged by hypertension. Deficiency in CX3CR1 inhibited kidney fibrosis, as evidenced by a decrease in the presence of interstitial fibrotic area detected by type I collagen in Mallory-Azan staining, concomitant with the downregulation of transforming growth factor (TGF)-β(1) and type I procollagen mRNA expression in damaged kidneys. The CX3CR1 blockade also decreased the number of infiltrating F4/80-positive macrophages in damaged kidneys. These results suggest that the fractalkine-CX3CR1 axis contributes to kidney fibrosis in a hypertensive mouse model, possibly by the upregulation of macrophage infiltration and the expression of TGF-β(1) and type I collagen.

Protective roles of CX3CR1-mediated signals in toxin A-induced enteritis through the induction of heme oxygenase-1 expression

The injection of Clostridium difficile toxin A into the ileal loops caused fluid accumulation with the destruction of intestinal epithelial structure and the recruitment of neutrophils and macrophages. Concomitantly, intraileal gene expression of CX3CL1/fractalkine (FKN) and its receptor, CX3CR1, was enhanced. When treated with toxin A in a similar manner, CX3CR1-deficient (CX3CR1(-/-)) mice exhibited exaggerated fluid accumulation, histopathological alterations, and neutrophil recruitment, but not macrophage infiltration. Mice reconstituted with CX3CR1(-/-) mouse-derived bone marrow cells exhibited exacerbated toxin A-induced enteritis, indicating that the lack of the CX3CR1 gene for hematopoietic cells aggravated toxin A-induced enteritis. A heme oxygenase-1 (HO-1) inhibitor, tin-protoporphyrin-IX, markedly increased fluid accumulation in toxin A-treated wild-type mice, indicating the protective roles of HO-1 in this situation. HO-1 expression was detected mainly in F4/80-positive cells expressing CX3CR1, and CX3CR1(-/-) mice failed to increase HO-1 expression after toxin A treatment. Moreover, CX3CL1/FKN induced HO-1 gene expression by isolated lamina propria-derived macrophages or a mouse macrophage cell line, RAW264.7, through the activation of the ERK signal pathway. Thus, CX3CL1/FKN could induce CX3CR1-expressing macrophages to express HO-1, thereby ameliorating toxin A-induced enteritis.

Chemokines in angiogenesis

Chemokines are a family of small heparin-binding proteins, mostly known for their role in inflammation and immune surveillance, which have emerged as important regulators of angiogenesis. Chemokines influence angiogenesis either through recruitment of pro-angiogenic immune cells and endothelial progenitors to the neo-vascular niche or via direct regulation of endothelial function downstream of activation of G-protein coupled chemokine receptors. The dual function of chemokines in regulating immune response and angiogenesis confers a central role in modulating the tissue microenvironment. Therefore, chemokines may constitute attractive targets for therapeutic intervention in several pathological disorders. This review will summarize the current understanding of the role of chemokines in angiogenesis, and give an overview of angiostatic and angiogenic chemokines and their crosstalk with other angiogenic factors.

CX3CL1-CX3CR1 interaction prevents carbon tetrachloride-induced liver inflammation and fibrosis in mice

Chronic liver disease is associated with hepatocyte injury, inflammation, and fibrosis. Chemokines and chemokine receptors are key factors for the migration of inflammatory cells such as macrophages and noninflammatory cells such as hepatic stellate cells (HSCs). The expression of CX3CR1 and its ligand, CX3CL1, is up-regulated in chronic liver diseases such as chronic hepatitis C. However, the precise role of CX3CR1 in the liver is still unclear. Here we investigated the role of the CX3CL1-CX3CR1 interaction in a carbon tetrachloride (CCl(4))-induced liver inflammation and fibrosis model. CX3CR1 was dominantly expressed in Kupffer cells in the liver. In contrast, the main source of CX3CL1 was HSCs. Mice deficient in CX3CR1 showed significant increases in inflammatory cell recruitment and cytokine production [including tumor necrosis factor α (TNF-α); monocyte chemoattractant protein 1; macrophage inflammatory protein 1β; and regulated upon activation, normal T cell expressed, and secreted (RANTES)] after CCl(4) treatment versus wild-type (WT) mice. This suggested that CX3CR1 signaling prevented liver inflammation. Kupffer cells in CX3CR1-deficient mice after CCl(4) treatment showed increased expression of TNF-α and transforming growth factor β and reduced expression of the anti-inflammatory markers interleukin-10 (IL-10) and arginase-1. Coculture experiments showed that HSCs experienced significantly greater activation by Kupffer cells from CCl(4)-treated CX3CR1-deficient mice versus WT mice. Indeed, augmented fibrosis was observed in CX3CR1-deficient mice versus WT mice after CCl(4) treatment. Finally, CX3CL1 treatment induced the expression of IL-10 and arginase-1 in WT cultured Kupffer cells through CX3CR1, which in turn suppressed HSC activation.

CONCLUSION

The CX3CL1-CX3CR1 interaction inhibits inflammatory properties in Kupffer cells/macrophages and results in decreased liver inflammation and fibrosis.

Crucial involvement of the CX3CR1-CX3CL1 axis in dextran sulfate sodium-mediated acute colitis in mice

Ingestion of DSS solution can induce in rodents acute colitis with a massive infiltration of neutrophils and macropahges, mimicking pathological changes observed in the acute phase of UC patients. Concomitantly, DSS ingestion enhanced the expression of a potent macrophage-tropic chemokine, CX3CL1/fractalkine, and its receptor, CX3CR1, in the colon. WT but not CX3CR1-deficient mice exhibited marked body weight loss and shortening of the colon after DSS ingestion. Moreover, inflammatory cell infiltration was attenuated in CX3CR1-deficient mice together with reduced destruction of glandular architecture compared with WT mice. DSS ingestion enhanced intracolonic iNOS expression by macrophages and nitrotyrosine generation in WT mice, but iNOS expression and nitrotyrosine generation were attenuated in CX3CR1-deficient mice. The analysis on bone marrow chimeric mice revealed that bone marrow-derived but not non-bone marrow-derived CX3CR1-expressing cells were a major source of iNOS. These observations would indicate that the CX3CL1-CX3CR1 axis can regulate the expression of iNOS, a crucial mediator of DSS-induced colitis. Thus, targeting the CX3CL1-CX3CR1 axis may be effective for the treatment of IBDs such as UC.

Opposite roles of CCR2 and CX3CR1 macrophages in alkali-induced corneal neovascularization

PURPOSE

The purpose of this study was to investigate the role of infiltrating macrophages in the development of experimental corneal neovascularization.

METHODS

Corneal neovascularization was induced by alkali injury in mice deficient in a macrophage-tropic chemokine receptor, CCR2 or CX3CR1, or in mice treated with clodronate-liposomes (Cl2MDP-lip), which can selectively deplete monocytes/macrophages. Corneal neovascularization 2 weeks after alkali injury was assessed by immunostaining with anti-CD31 antibody. Intracorneal expression of proangiogenic and antiangiogenic factors was determined by reverse transcription-polymerase chain reaction.

RESULTS

CCR2-deficient mice exhibited reduced alkali-induced corneal neovascularization with reduced macrophage infiltration, whereas CX3CR1-deficient mice developed a more severe form of alkali-induced corneal neovascularization with reduced macrophage infiltration. Selective macrophage depletion by Cl2MDP-lip treatment failed to affect alkali-induced corneal neovascularization as evidenced by immunohistochemical analysis using anti-CD31 antibody, whereas intracorneal macrophage infiltration was markedly reduced. Alkali injury enhanced the expression of proangiogenic molecules, including matrix metalloproteinase-2, matrix metalloproteinase-9, and tumor necrosis factor alpha, and antiangiogenic factors, including a disintegrin and metalloprotease with thrombospondin (ADAMTS)-1, thrombospondin-1, and thrombospondin-2. Cl2MDP-lip-treated mice exhibited a reduction in the messenger RNA expression of these molecules.

CONCLUSION

Because CCR2- and CX3CR1-expressing macrophages exhibit opposite activities in angiogenesis, depletion of macrophages as a whole may not have apparent effects on alkali-induced corneal neovascularization.

Retinal vascular repair and neovascularization are not dependent on CX3CR1 signaling in a model of ischemic retinopathy

Proliferative retinal neovascularization occurring in response to ischemia is a common mechanism underlying many retinal diseases. In recent studies, retinal microglia have been shown to influence pathological neovascularization, likely through an exchange of cellular signals with associated vascular elements. CX3CR1 is a chemokine receptor located specifically on microglia; its ligand, CX3CL1 (also known as fractalkine or neurotactin) displays pro-angiogenic activity both in in vivo and in vitro. Discovering the regulatory role, if any, that CX3CR1 signaling may have in ischemic retinopathy will shed light on the molecular nature of microglial-vascular interactions and clarify potential targets for future therapy. In this study, we examined this question by inducing and comparing ischemic vascular changes in transgenic mice in which CX3CR1 signaling is either preserved or ablated. Using a well-known oxygen-induced retinopathy (OIR) model, we induced ischemic retinopathy in transgenic mice in which the gene for CX3CR1 has been replaced by green fluorescent protein (GFP) and their wild type controls. CX3CR1(+/+), CX3CR1(+/GFP), and CX3CR1(GFP/GFP) transgenic mice were exposed to 75% oxygen for 5 days starting from postnatal day (P) 7, and then transferred back to room air. At P12 and P17, the extents of vascular repair and neovascularization, and associated changes in retinal microglia distribution, were quantified and compared between mice of different genotypes. Neuronal loss in the retina following ischemia was also evaluated in paraffin sections. Our results show that: (1) CX3CR1 signaling is not required for normal vascular, microglial, and neuronal development in the retina in the first postnatal week, (2) the processes of retinal vascular repair and neovascularization following ischemia occur similarly with and without CX3CR1 signaling, (3) microglia redistribution in the retina and their association with vascular elements occurring concurrently is independent of CX3CR1, and (4) CX3CR1 does not influence the extent of neuronal cell loss in the retina following ischemia. Taken together, our findings indicate that the regulatory signals exchanged between microglia and vascular elements in the ischemic retinopathy animal model are unlikely to involve CX3CR1. These results have implications on therapeutic approaches to, pathological neovascularization involving the modulation of chemokine signaling in general, and the regulation of CX3CR1 signaling specifically.