Pivotal Involvement of the CX3CL1-CX3CR1 Axis for the Recruitment of M2 Tumor-Associated Macrophages in Skin Carcinogenesis

Targeting tumor-associated macrophages: Novel insights into immunotherapy of skin cancer

BACKGROUND

The incidence of skin cancer is currently increasing, and conventional treatment options inadequately address the demands of disease management. Fortunately, the recent rapid advancement of immunotherapy, particularly immune checkpoint inhibitors (ICIs), has ushered in a new era for numerous cancer patients. However, the efficacy of immunotherapy remains suboptimal due to the impact of the tumor microenvironment (TME). Tumor-associated macrophages (TAMs), a major component of the TME, play crucial roles in tumor invasion, metastasis, angiogenesis, and immune evasion, significantly impacting tumor development. Consequently, TAMs have gained considerable attention in recent years, and their roles have been extensively studied in various tumors. However, the specific roles of TAMs and their regulatory mechanisms in skin cancer remain unclear.

AIM OF REVIEW

This paper aims to elucidate the origin and classification of TAMs, investigate the interactions between TAMs and various immune cells, comprehensively understand the precise mechanisms by which TAMs contribute to the pathogenesis of different types of skin cancer, and finally discuss current strategies for targeting TAMs in the treatment of skin cancer.

KEY SCIENTIFIC CONCEPTS OF OVERVIEW

With a specific emphasis on the interrelationship between TAMs and skin cancer, this paper posits that therapeutic modalities centered on TAMs hold promise in augmenting and harmonizing with prevailing clinical interventions for skin cancer, thereby charting a novel trajectory for advancing the landscape of immunotherapeutic approaches for skin cancer.

CX3CR1+CD8+ T cells: Key players in antitumor immunity

CX3CR1 functions as the specific receptor for the chemokine CX3CL1, demonstrating expression across a broad spectrum of immune cells. This underscores its pivotal role in communication and response mechanisms within the immune system. Upon engagement with CX3CL1, CX3CR1 initiates a cascade of downstream signaling pathways that regulate various biological functions. In the context of tumor progression, the intricate and inhibitory nature of the tumor microenvironment presents a significant challenge to current clinical treatment techniques. This review aims to comprehensively explore the tumor-destructive potential shown by CX3CR1+CD8+ T cells. Simultaneously, it investigates the promising prospects of utilizing CX3CR1 in future tumor immunotherapies.

Pravastatin prevents colitis-associated carcinogenesis by reducing CX3CR1high M2-like fibrocyte counts in the inflamed colon

Colorectal cancer (CRC) resulting from chronic inflammation is a crucial issue in patients with inflammatory bowel disease (IBD). Although many reports established that intestinal resident CX3CR1high macrophages play an essential role in suppressing intestinal inflammation, their function in colitis-related CRC remains unclear. In this study, we found that colonic CX3CR1high macrophages, which were positive for MHC-II, F4/80 and CD319, promoted colitis-associated CRC. They highly expressed Col1a1, Tgfb, II10, and II4, and were considered to be fibrocytes with an immunosuppressive M2-like phenotype. CX3CR1 deficiency led to reductions in the absolute numbers of CX3CR1high fibrocytes through increased apoptosis, thereby preventing the development of colitis-associated CRC. We next focused statins as drugs targeting CX3CR1high fibrocytes. Statins have been actively discussed for patients with IBD and reported to suppress the CX3CL1/CX3CR1 axis. Statin treatment after azoxymethane/dextran sulfate sodium-induced inflammation reduced CX3CR1high fibrocyte counts and suppressed colitis-associated CRC. Therefore, CX3CR1high fibrocytes represent a potential target for carcinogenesis-preventing therapy, and statins could be safe therapeutic candidates for IBD.

Chemokine receptors in COVID-19 infection

Chemokine receptors play diverse roles in the immune response against pathogens by recruiting innate and adaptive immune cells to sites of infection. However, their involvement could also be detrimental, causing tissue damage and exacerbating respiratory diseases by triggering histological alterations such as fibrosis and remodeling. This chapter reviews the role of chemokine receptors in the immune defense against SARS-CoV-2 infection. In COVID-19, CXCR3 is expressed mainly in T cells, and its upregulation is related to an increase in SARS-CoV-2-specific antibodies but also to COVID-19 severity. CCR5 is a key player in T-cell recruitment, and its suppression leads to reduced inflammation and viremia levels. Conversely, CXCR6 is implicated in the aberrant migration of memory T cells within airways. On the other hand, increased CCR4+ cells in the blood and decreased CCR4+ cells in lung cells are associated with severe COVID-19. Additionally, CCR2 is associated with an increase in macrophage recruitment to lung tissues. Elevated levels of CXCR1 and CXCR2, which are predominantly expressed in neutrophils, are associated with the severity of the disease, and finally, the expression of CX3CR1 in cytotoxic T lymphocytes affects the retention of these cells in lung tissues, thereby impacting the severity of COVID-19. Despite the efforts of many clinical trials to find effective therapies for COVID-19 using chemokine receptor inhibitors, no conclusive results have been found due to the small number of patients, redundancy, and co-expression of chemokine receptors by immune cells, which explains the difficulty in finding a single therapeutic target or effective treatment.

The expression patterns of different cell types and their interactions in the tumor microenvironment are predictive of breast cancer patient response to neoadjuvant chemotherapy

The tumor microenvironment (TME) is a complex ecosystem of diverse cell types whose interactions govern tumor growth and clinical outcome. While the TME's impact on immunotherapy has been extensively studied, its role in chemotherapy response remains less explored. To address this, we developed DECODEM (DEcoupling Cell-type-specific Outcomes using DEconvolution and Machine learning), a generic computational framework leveraging cellular deconvolution of bulk transcriptomics to associate the gene expression of individual cell types in the TME with clinical response. Employing DECODEM to analyze the gene expression of breast cancer (BC) patients treated with neoadjuvant chemotherapy, we find that the gene expression of specific immune cells (myeloid, plasmablasts, B-cells) and stromal cells (endothelial, normal epithelial, CAFs) are highly predictive of chemotherapy response, going beyond that of the malignant cells. These findings are further tested and validated in a single-cell cohort of triple negative breast cancer. To investigate the possible role of immune cell-cell interactions (CCIs) in mediating chemotherapy response, we extended DECODEM to DECODEMi to identify such CCIs, validated in single-cell data. Our findings highlight the importance of active pre-treatment immune infiltration for chemotherapy success. The tools developed here are made publicly available and are applicable for studying the role of the TME in mediating response from readily available bulk tumor expression in a wide range of cancer treatments and indications.

Proliferating macrophages in human tumours show characteristics of monocytes responding to myelopoietic growth factors

Macrophages play essential roles in maintaining tissue homeostasis and immune defence. However, their extensive infiltration into tumours has been linked to adverse outcomes in multiple human cancers. Within the tumour microenvironment (TME), tumour-associated macrophages (TAMs) promote tumour growth and metastasis, making them prime targets for cancer immunotherapy. Recent single-cell analysis suggest that proliferating TAMs accumulate in human cancers, yet their origins and differentiation pathways remain uncertain. Here, we show that a subpopulation of CD163+ TAMs proliferates in situ within the TME of melanoma, lung cancer, and breast cancer. Consistent with their potential role in suppressing anti-tumour activities of T cells, CD163+ TAMs express a range of potent immunosuppressive molecules, including PD-L1, PD-L2, IL-10, and TGF-β. Other phenotypic markers strongly suggested that these cells originate from CD14+ CCR2+ monocytes, a cell population believed to have minimal capacity for proliferation. However, we demonstrate in vitro that certain myelopoietic cytokines commonly available within the TME induce robust proliferation of human monocytes, especially the combination of interleukin 3 (IL-3) and Macrophage Colony-Stimulating Factor 1 (M-CSF). Monocytic cells cultured with these cytokines efficiently modulate T cell proliferation, and their molecular phenotype recapitulates that of CD163+ TAMs. IL-3-driven proliferation of monocytic cells can be completely blocked by IL-4, associated with the induction of CDKN1A, alongside the upregulation of transcription factors linked to dendritic cell function, such as BATF3 and IRF4. Taken together, our work suggests several novel therapeutic routes to reducing immunosuppressive TAMs in human tumours, from blocking chemokine-mediated recruitment of monocytes to blocking their proliferation.

Metabolic regulation of tumor-associated macrophage heterogeneity: insights into the tumor microenvironment and immunotherapeutic opportunities

Tumor-associated macrophages (TAMs) are a heterogeneous population that play diverse functions in tumors. Their identity is determined not only by intrinsic factors, such as origins and transcription factors, but also by external signals from the tumor microenvironment (TME), such as inflammatory signals and metabolic reprogramming. Metabolic reprogramming has rendered TAM to exhibit a spectrum of activities ranging from pro-tumorigenic to anti-tumorigenic, closely associated with tumor progression and clinical prognosis. This review implicates the diversity of TAM phenotypes and functions, how this heterogeneity has been re-evaluated with the advent of single-cell technologies, and the impact of TME metabolic reprogramming on TAMs. We also review current therapies targeting TAM metabolism and offer new insights for TAM-dependent anti-tumor immunotherapy by focusing on the critical role of different metabolic programs in TAMs.

Obesity-related Plasma CXCL10 Drives CX3CR1-dependent Monocytic Secretion of Macrophage Migration Inhibitory Factor

Obesity is characterized by excessive body fat accumulation and comorbidities such as diabetes mellitus, cardiovascular disease, and obstructive sleep apnea syndrome (OSAS). Both obesity and OSAS are associated with immune disturbance, alterations of systemic inflammatory mediators, and immune cell recruitment to metabolic tissues. Chemokine CXCL10 is an important regulator of proinflammatory immune responses and is significantly increased in patients with severe obesity. This research project aims to investigate the impact of CXCL10 on human monocytes in patients with obesity. We studied the distribution of the CD14/CD16 monocyte subsets as well as their CX3CR1 expression patterns in whole-blood measurements from 92 patients with obesity and/or OSAS with regard to plasma CXCL10 values and individual clinical parameters. Furthermore, cytokine secretion by THP-1 monocytes in response to CXCL10 was analyzed. Data revealed significantly elevated plasma CXCL10 in patients with obesity with an additive effect of OSAS. CXCL10 was found to drive monocytic secretion of macrophage migration inhibitory factor via receptor protein CX3CR1, which significantly correlated with the individual body mass index. Our data show, for the first time, to our knowledge, that CX3CR1 is involved in alternative CXCL10 signaling in human monocytes in obesity-related inflammation. Obesity is a multifactorial disease, and further investigations regarding the complex interplay between obesity-related inflammatory mediators and systemic immune balances will help to better understand and improve the individual situation of our patients.

CX3CR1-Expressing Immune Cells Infiltrate the Tumor Microenvironment and Promote Radiation Resistance in a Mouse Model of Lung Cancer

INTRODUCTION

Chemokine (C-X3-C Motif) Receptor 1 (CX3CR1) is present in a subset of the immune cells in the tumor microenvironment (TME) and plays an essential and diverse role in cancer progression. However, its potential function in the irradiated TME remains unknown.

MATERIALS AND METHODS

A mouse lung cancer model was performed by subcutaneously inoculating Lewis Lung Carcinoma (LLC) cells expressing luciferase (Luc-2) and mCherry cells in CX3CR1GFP/GFP, CX3CR1DTR/+, and wild-type (WT) mice. Bioluminescence imaging, clonogenic assay, and flow cytometry were used to assess tumor progression, proliferation, and cell composition after radiation.

RESULTS

Radiation provoked a significant influx of CX3CR1-expressing immune cells, notably monocytes and macrophages, into the TME. Co-culturing irradiated LLC cells with CX3CR1-deficient monocytes, and macrophages resulted in reduced clonogenic survival and increased apoptosis of the cancer cells. Interestingly, deficiency of CX3CR1 in macrophages led to a redistribution of the irradiated LLC cells in the S-phase, parallel to increased expression of cyclin E1, required for cell cycle G1/S transition. In addition, the deficiency of CX3CR1 expression in macrophages altered the cytokine secretion with a decrease in interleukin 6, a crucial mediator of cancer cell survival and proliferation. Next, LLC cells were injected subcutaneously into CX3CR1DTR/+ mice, sensitive to diphtheria toxin (DT), and WT mice. After injection, tumors were irradiated with 8 Gy, and mice were treated with DT, leading to conditional ablation of CX3CR1-expressing cells. After three weeks, CX3CR1-depleted mice displayed reduced tumor progression. Furthermore, combining the S-phase-specific chemotherapeutic gemcitabine with CX3CR1 cell ablation resulted in additional attenuation of tumor progression.

CONCLUSIONS

CX3CR1-expressing mononuclear cells invade the TME after radiation therapy in a mouse lung cancer model. CX3CR1 cell depletion attenuates tumor progression following radiation and sensitizes the tumor to S-phase-specific chemotherapy. Thus, we propose a novel strategy to improve radiation sensitivity by targeting the CX3CR1-expressing immune cells.

Tumor-associated macrophage-derived exosomes LINC01592 induce the immune escape of esophageal cancer by decreasing MHC-I surface expression

BACKGROUND

TAMs (tumor-associated macrophages) infiltration promotes the progression of esophageal cancer (EC). However, the underlying mechanisms remain unclear.

METHODS

Abnormal expression of LINC01592 from EC microarrays of the TCGA database was analyzed. LINC01592 expression level was validated in both EC cell lines and tissues. Stable LINC01592 knockdown and overexpression of EC cell lines were established. In vitro and in vivo trials were conducted to test the impact of LINC01592 knockdown and overexpression on EC cells. RNA binding protein immunoprecipitation (RIP), RNA pulldown assays, and Immunofluorescence (IF) were used to verify the combination of E2F6 and LINC01592. The combination of E2F6 and NBR1 was verified through the utilization of ChIP and dual luciferase reporter assays.

RESULTS

LINC01592 is carried and transferred by exosomes secreted by M2-TAMs to tumor cells. The molecular mechanism underlying the promotion of NBR1 transcription involves the direct binding of LINC01592 to E2F6, which facilitates the nuclear entry of E2F6. The collaborative action of LINC01592 and E2F6 results in improved NBR1 transcription. The elevation of NBR1 binding to the ubiquitinated protein MHC-I via the ubiquitin domain caused a higher degradation of MHC-I in autophagolysosomes and a reduction in MHC-I expression on the exterior of cancerous cell. Consequently, this caused cancerous cells to escape from CD8+ CTL immune attack. The tumor-promoting impacts of LINC01592, as well as the growth of M2-type macrophage-driven tumors, were significantly suppressed by the interruption of E2F6/NBR1/MHC-I signaling through the effect of siRNA or the corresponding antibody blockade. Significantly, the suppression of LINC01592 resulted in an upregulation of MHC-I expression on the tumor cell membrane, thereby enhancing the efficacy of CD8+ T cell reinfusion therapy.

CONCLUSIONS

The investigation conducted has revealed a significant molecular interaction between TAMs and EC via the LINC01592/E2F6/NBR1/MHC-I axis, which facilitates the progression of malignant tumors. This suggests that a therapeutic intervention targeting this axis may hold promise for the treatment of the disease.

The CX3CL1-CX3CR1 chemokine axis can contribute to tumor immune evasion and blockade with a novel CX3CR1 monoclonal antibody enhances response to anti-PD-1 immunotherapy

CX3CL1 secreted in the tumor microenvironment serves as a chemoattractant playing a critical role in metastasis of CX3CR1 expressing cancer cells. CX3CR1 can be expressed in both cancer and immune-inhibitory myeloid cells to facilitate their migration. We generated a novel monoclonal antibody against mouse CX3CR1 that binds to CX3CR1 and blocks the CX3CL1-CX3CR1 interaction. We next explored the immune evasion strategies implemented by the CX3CL1-CX3CR1 axis and find that it initiates a resistance program in cancer cells that results in 1) facilitation of tumor cell migration, 2) secretion of soluble mediators to generate a pro-metastatic niche, 3) secretion of soluble mediators to attract myeloid populations, and 4) generation of tumor-inflammasome. The CX3CR1 monoclonal antibody reduces migration of tumor cells and decreases secretion of immune suppressive soluble mediators by tumor cells. In combination with anti-PD-1 immunotherapy, this CX3CR1 monoclonal antibody enhances survival in an immunocompetent mouse colon carcinoma model through a decrease in tumor-promoting myeloid populations. Thus, this axis is involved in the mechanisms of resistance to anti-PD-1 immunotherapy and the combination therapy can overcome a portion of the resistance mechanisms to anti-PD-1.

Role of chemokines in the crosstalk between tumor and tumor-associated macrophages

Tumor microenvironment (TME) consists of a dynamic network of non-tumoral stromal cells, including cancer-associated fibroblasts, endothelial cells, tumor-associated macrophages (TAMs), B and T cells. In the TME, TAMs support tumor initiation, progression, invasion and metastasis by promoting angiogenesis and immunosuppression of the tumor cells. There is close crosstalk between TAMs and tumor cells. Notably, chemokines are a significant messenger mediating the crosstalk between tumor cells and TAMs. TAMs can promote tumor progression via secretion of chemokines. Various chemokines secreted by tumors are involved in the generation and polarization of TAMs, the infiltration of TAMs in tumors, and the development of TAMs' suppressive function. This paper reviews CCL2-CCR2, CCL3/5-CCR5, CCL15-CCR1, CCL18-CCR8, CX3CL1/CCL26-CX3CR1, CXCL8-CXCR1/2, CXCL12-CXCR4/CXCR7 signaling pathways, their role in the recruitment, polarization and exertion of TAMs, and their correlation with tumor development, metastasis and prognosis. Furthermore, we present the current research progress on modulating the effects of TAMs with chemokine antagonists and discuss the prospects and potential challenges of using chemokine antagonists as therapeutic tools for cancer treatment. The TAMs targeting by chemokine receptor antagonists in combination with chemotherapy drugs, immune checkpoint inhibitors or radiotherapy appears to be a promising approach.

C1q+ tumor-associated macrophages contribute to immunosuppression through fatty acid metabolic reprogramming in malignant pleural effusion

BACKGROUND

Although immune checkpoint blockade (ICB) therapy has shown remarkable benefits in cancers, a subset of patients with cancer exhibits unresponsiveness or develop acquired resistance due to the existence of abundant immunosuppressive cells. Tumor-associated macrophages (TAMs), as the dominant immunosuppressive population, impede the antitumor immune response; however, the underlying mechanisms have not been fully elucidated yet.

METHODS

Single-cell RNA sequencing analysis was performed to portray macrophage landscape and revealed the underlying mechanism of component 1q (C1q)+ TAMs. Malignant pleural effusion (MPE) of human and mouse was used to explore the phenotypes and functions of C1q+ TAMs.

RESULTS

C1q+ TAMs highly expressed multiple inhibitory molecules and their high infiltration was significantly correlated with poor prognosis. C1q+ TAMs promote MPE immunosuppression through impairing the antitumor effects of CD8+ T cells. Mechanistically, C1q+ TAMs enhance fatty acid binding protein 5 (FABP5)-mediated fatty acid metabolism, which activate transcription factor peroxisome proliferator-activated receptor-gamma, increasing the gene expression of inhibitory molecules. A high-fat diet increases the expression of inhibitory molecules in C1q+ TAMs and the immunosuppression of MPE microenvironment, whereas a low-fat diet ameliorates these effects. Moreover, FABP5 inhibition represses the expression of inhibitory molecules in TAMs and tumor progression, while enhancing the efficacy of ICB therapy in MPE and lung cancer.

CONCLUSIONS

C1q+ TAMs impede antitumor effects of CD8+ T cells promoting MPE immunosuppression. Targeting C1q+ TAMs effectively alleviates the immunosuppression and enhances the efficacy of ICB therapy. C1q+ TAMs subset has great potential to be a therapeutic target for cancer immunotherapy.

CX3CR1+ Macrophage Facilitates the Resolution of Allergic Lung Inflammation via Interacting CCL26

Rationale: The resolution of inflammation is an active process coordinated by mediators and immune cells to restore tissue homeostasis. However, the mechanisms for resolving eosinophilic allergic lung inflammation triggered by inhaled allergens have not been fully elucidated. Objectives: Our objectives were to investigate the cellular mechanism of tissue-resident macrophages involved in the resolution process of eosinophilic lung inflammation. Methods: For the study, we used the institutional review board-approved protocol for human subsegmental bronchoprovocation with allergen, mouse models for allergic lung inflammation, and novel transgenic mice, including a conditional CCL26 knockout. The samples were analyzed using mass cytometry, single-cell RNA sequencing, and biophysical and immunological analyses. Measurements and Main Results: We compared alveolar macrophage (AM) subsets in the BAL before and after allergen provocation. In response to provocation with inhaled allergens, the subsets of AMs are dynamically changed in humans and mice. In the steady state, the AM subset expressing CX3CR1 is a relatively small fraction in bronchoalveolar space and lung tissue but drastically increases after allergen challenges. This subset presents unique patterns of gene expression compared with classical AMs, expressing high C1q family genes. CX3CR1+ macrophages are activated by airway epithelial cell-derived CCL26 via a receptor-ligand interaction. The binding of CCL26 to the CX3CR1+ receptor induces CX3CR1+ macrophages to secrete C1q, subsequently facilitating the clearance of eosinophils. Furthermore, the depletion of CX3CR1 macrophages or CCL26 in airway epithelial cells delays the resolution of allergic lung inflammation displaying prolonged tissue eosinophilia. Conclusions: These findings indicate that the CCL26-CX3CR1 pathway is pivotal in resolving eosinophilic allergic lung inflammation.

M1 macrophage-derived exosomes containing miR-150 inhibit glioma progression by targeting MMP16

A large amount of clinical and experimental evidence indicates that M1 macrophages can inhibit tumor progression and expansion; however, the molecular mechanism by which macrophage-derived exosomes inhibit the proliferation of glioblastoma cells has not yet been elucidated. Here, we used M1 macrophage exosomes encapsulating microRNAs to inhibit the proliferation of glioma cells. Exosomes derived from M1 macrophages exhibited high expression levels of miR-150, and the inhibition of glioma cell proliferation mediated by exosomes derived from M1 macrophages was dependent on this microRNA. Mechanistically, miR-150 is transferred to glioblastoma cells through M1 macrophages and binds to MMP16, downregulating its expression and inhibiting glioma progression. Overall, these findings indicate that M1 macrophage-derived exosomes carrying miR-150 inhibit the proliferation of glioblastoma cells through targeted binding to MMP16. This dynamic mutual influence between glioblastoma cells and M1 macrophages provides new opportunities for the treatment of glioma.

Targeting the NF-κB pathway enhances responsiveness of mammary tumors to JAK inhibitors

Interactions between tumor cells and the tumor microenvironment are critical for tumor growth, progression, and response to therapy. Effective targeting of oncogenic signaling pathways in tumors requires an understanding of how these therapies impact both tumor cells and cells within the tumor microenvironment. One such pathway is the janus kinase (JAK)/signal transducer and activator or transcription (STAT) pathway, which is activated in both breast cancer cells and in tumor associated macrophages. This study demonstrates that exposure of macrophages to JAK inhibitors leads to activation of NF-κB signaling, which results in increased expression of genes known to be associated with therapeutic resistance. Furthermore, inhibition of the NF-κB pathway improves the ability of ruxolitinib to reduce mammary tumor growth in vivo. Thus, the impact of the tumor microenvironment is an important consideration in studying breast cancer and understanding such mechanisms of resistance is critical to development of effective targeted therapies.

Nucleus Pulposus Cells Induce M2 Polarization of RAW264.7 via CX3CL1/CX3CR1 Pathway and M2 Macrophages Promote Proliferation and Anabolism of Nucleus Pulposus Cells

Background

The mechanisms underlying M2 macrophage polarization induced by nucleus pulposus (NP) cells are unclear. The effects that M2-polarized macrophages have on NP cells are also controversial.

Methods

Transcriptome sequencing was performed to detect the gene change profiles between NP cells from ruptured intervertebral disc (IVD) and normal IVD. The main difference on biological activities between the two cell groups were analyzed by GO analysis and KEGG analysis. Virus transduction, flow cytometry, immunofluorescence, RT-PCR, western blot, CCK-8, TUNEL staining, and AO/EB staining were performed to explore the interactions between NP cells and RAW264.7 macrophages. Statistics were performed using SPSS26.

Results

801 upregulated and 276 downregulated genes were identified in NP cells from ruptured IVD in mouse models. According to GO and KEGG analysis, we found that the differentially expressed genes (DEG) were dominantly enriched in inflammatory response, extracellular matrix degradation, blood vessel morphogenesis, immune effector process, ossification, chemokine signaling pathway, macrophage activation, etc. CX3CL1 was one of the top 20% DEG, and we confirmed that both NP tissue and cells expressed remarkably higher level of CX3CL1 in mouse models (p < 0.001∗). Besides, we further revealed that both the recombinant CX3CL1 and NP cells remarkably induced M2 polarization of RAW264.7 (p < 0.001∗), respectively, while this effect was significantly reversed by si-CX3CL1 or JMS-17-2 (p < 0.001∗). Furthermore, we found that M2 macrophages significantly decreased the apoptosis rate (p < 0.001∗) and the catabolic gene levels (p < 0.001∗) of NP cells, while increased the viability, proliferation as well as the anabolic gene levels of NP cells (p < 0.01∗).

Conclusions

Via regulating CX3CL1/CX3CR1 pathway, NP cells can induce the M2 macrophage polarization. M2 polarized macrophages can further promote NP cell viability, proliferation, and anabolism, while inhibit NP cell apoptosis and catabolism.

Inflammatory stimulus worsens the effects of UV-A exposure on J774 cells

UV-A radiation affects skin homeostasis by promoting oxidative distress. Endogenous photosensitizers in the dermis and epidermis of human skin absorb UV-A radiation forming excited states (singlet and triplet) and reactive oxygen species (ROS) producing oxidized compounds that trigger biological responses. The activation of NF-kB induces the expression of pro-inflammatory cytokines and can intensify the generation of ROS. However, there is no studies evaluating the cross talks between inflammatory stimulus and UV-A exposure on the levels of redox misbalance and inflammation. In here, we evaluated the effects of UV-A exposure on J774 macrophage cells previously challenged with LPS in terms of oxidative distress, release of pro-inflammatory cytokines, and activation of regulated cell death pathways. Our results showed that LPS potentiates the dose-dependent UV-A-induced oxidative distress and cytokine release, in addition to amplifying the regulated (autophagy and apoptosis) and non-regulated (necrosis) mechanisms of cell death, indicating that a previous inflammatory stimulus potentiates UV-A-induced cell damage. We discuss these results in terms of the current-available skin care strategies.

Macrophage polarity and wound age determination

We investigated the dynamics of the gene expression of M1 and M2 macrophage markers during skin wound healing in mice. Expression of M1-macrophage markers, such as Il12a, Tnf, Il6, Il1b, and Nos2 was upregulated after wounding and peaked at 1 or 3 days after injury, and that of M2-macrophage markers such as Mrc1, Cd163, Ccl17, Arg, and Tgfb1, peaked at 6 days after injury. Consistent with these findings, using triple-color immunofluorescence analysis revealed that F4/80⁺CD80⁺ M1 macrophages were more abundant than F4/80⁺CD206⁺ M2 macrophages on day 3 in mouse wound specimens, and that M2 macrophages were prominently detected in day 6 wounds. For application in forensic practice, we examined macrophage polarization using human wound specimens. The average ratios of CD68⁺iNOS⁺ M1 macrophages to CD68⁺CD163⁺ M2 macrophages (M1/M2 ratios) were greater than 2.5 for the wounds aged 2-5 days. Out of 11 wounds aged 1-5 days, five samples had the M1/M2 ratios of > 3.0. These observations propose that the M1/M2 ratios of 3.0 would indicate a wound age of 1-5 days as the forensic opinion. This study showed that M1 and M2 macrophages in human skin wound might be a promising marker for wound age determination.

Tertiary Lymphoid Structures and Chemokine Landscape in Virus-Positive and Virus-Negative Merkel Cell Carcinoma

Tertiary lymphoid structures (TLSs) are used as biomarkers in many cancers for predicting the prognosis and assessing the response to immunotherapy. In Merkel cell carcinoma (MCC), TLSs have only been examined in MCPyV-positive cases. Here, we examined the prognostic value of the presence or absence of TLSs in 61 patients with MCC, including MCPyV-positive and MCPyV-negative cases. TLS-positive samples had a significantly better prognosis than TLS-negative samples. MCPyV-positive samples had a good prognosis with or without TLSs, and MCPyV-negative/TLS-positive samples had a similarly good prognosis as MCPyV-positive samples. Only MCPyV-negative/TLS-negative samples had a significantly poor prognosis. All cases with spontaneous regression were MCPyV-positive/TLS-positive. We also performed a comprehensive analysis of the chemokines associated with TLS formation using next-generation sequencing (NGS). The RNA sequencing results revealed 5 chemokine genes, CCL5, CCR2, CCR7, CXCL9, and CXCL13, with significantly high expression in TLS-positive samples compared with TLS-negative samples in both MCPyV-positive and MCPyV-negative samples. Only 2 chemokine genes, CXCL10 and CX3CR1, had significantly different expression levels in the presence or absence of MCPyV infection in TLS-negative samples. Patients with high CXCL13 or CCL5 expression have a significantly better prognosis than those with low expression. In conclusion, the presence of TLSs can be a potential prognostic marker even in cohorts that include MCPyV-negative cases. Chemokine profiles may help us understand the tumor microenvironment in patients with MCPyV-positive or MCPyV-negative MCC and may be a useful prognostic marker in their own right.

Apoptosis - Fueling the oncogenic fire

Apoptosis, the most extensively studied form of programmed cell death, is essential for organismal homeostasis. Apoptotic cell death has widely been reported as a tumor suppressor mechanism. However, recent studies have shown that apoptosis exerts noncanonical functions and may paradoxically promote tumor growth and metastasis. The hijacking of apoptosis by cancer cells may arise at different levels, either via the interaction of apoptotic cells with their local or distant microenvironment, or through the abnormal pro-oncogenic roles of the main apoptosis effectors, namely caspases and mitochondria, particularly upon failed apoptosis. In this review, we highlight some of the recently described mechanisms by which apoptosis and these effectors may promote cancer aggressiveness. We believe that a better understanding of the noncanonical roles of apoptosis may be crucial for developing more efficient cancer therapies.

Tumor-Associated Macrophages: A Potential Target for Cancer Therapy

Macrophages, an important class of innate immune cells that maintain body homeostasis and ward off foreign pathogens, exhibit a high degree of plasticity and play a supportive role in different tissues and organs. Thus, dysfunction of macrophages may contribute to advancement of several diseases, including cancer. Macrophages within the tumor microenvironment are known as tumor-associated macrophages (TAMs), which typically promote cancer cell initiation and proliferation, accelerate angiogenesis, and tame anti-tumor immunity to promote tumor progression and metastasis. Massive infiltration of TAMs or enrichment of TAM-related markers usually indicates cancer progression and a poor prognosis, and consequently tumor immunotherapies targeting TAMs have gained significant attention. Here, we review the interaction between TAMs and cancer cells, discuss the origin, differentiation and phenotype of TAMs, and highlight the role of TAMs in pro-cancer functions such as tumor initiation and development, invasive metastasis, and immunosuppression. Finally, we review therapies targeting TAMs, which are very promising therapeutic strategies for malignant tumors.

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.

Hallmarks of Aging in Macrophages: Consequences to Skin Inflammaging

The skin is our largest organ and the outermost protective barrier. Its aging reflects both intrinsic and extrinsic processes resulting from the constant insults it is exposed to. Aging in the skin is accompanied by specific epigenetic modifications, accumulation of senescent cells, reduced cellular proliferation/tissue renewal, altered extracellular matrix, and a proinflammatory environment favoring undesirable conditions, including disease onset. Macrophages (Mφ) are the most abundant immune cell type in the skin and comprise a group of heterogeneous and plastic cells that are key for skin homeostasis and host defense. However, they have also been implicated in orchestrating chronic inflammation during aging. Since Mφ are related to innate and adaptive immunity, it is possible that age-modified skin Mφ promote adaptive immunity exacerbation and exhaustion, favoring the emergence of proinflammatory pathologies, such as skin cancer. In this review, we will highlight recent findings pertaining to the effects of aging hallmarks over Mφ, supporting the recognition of such cell types as a driving force in skin inflammaging and age-related diseases. We will also present recent research targeting Mφ as potential therapeutic interventions in inflammatory skin disorders and cancer.

Bacteria induce skin regeneration via IL-1β signaling

Environmental factors that enhance regeneration are largely unknown. The immune system and microbiome are attributed roles in repairing and regenerating structure but their precise interplay is unclear. Here, we assessed the function of skin bacteria in wound healing and wound-induced hair follicle neogenesis (WIHN), a rare adult organogenesis model. WIHN levels and stem cell markers correlate with bacterial counts, being lowest in germ-free (GF), intermediate in conventional specific pathogen-free (SPF), and highest in wild-type mice, even those infected with pathogenic Staphylococcus aureus. Reducing skin microbiota via cage changes or topical antibiotics decreased WIHN. Inflammatory cytokine IL-1β and keratinocyte-dependent IL-1R-MyD88 signaling are necessary and sufficient for bacteria to promote regeneration. Finally, in a small trial, a topical broad-spectrum antibiotic also slowed skin wound healing in adult volunteers. These results demonstrate a role for IL-1β to control morphogenesis and support the need to reconsider routine applications of topical prophylactic antibiotics.

Tumor-associated macrophages: A promising target for a cancer immunotherapeutic strategy

Macrophages, a type of myeloid immune cell, play essential roles in fighting against pathogenic invasion and activating T cell-mediated adaptive immune responses. As a major constituent of the tumor microenvironment (TME), macrophages play a complex role in tumorigenesis and tumor progression. They can inhibit tumor growth by releasing proinflammatory cytokines and exerting cytotoxic activities but principally contribute to tumor progression by promoting tumor proliferation, angiogenesis, and metastasis. The tumor-promoting hallmarks of macrophages have aroused widespread interest in targeting tumor-associated macrophages (TAMs) for cancer immunotherapy. Increasing preclinical and clinical studies suggest that TAMs are a promising target for cancer immunotherapy. To date, TAM-targeted therapeutic strategies have mainly been divided into two kinds: inhibiting pro-tumor TAMs and activating anti-tumor TAMs. We reviewed the heterogeneous and plastic characteristics of macrophages in the TME and the feasible strategies to target TAMs in cancer immunotherapy and summarized the complementary effect of TAM-targeted therapy with traditional treatments or other immunotherapies.

Development, Characterization and Use of Liposomes as Amphipathic Transporters of Bioactive Compounds for Melanoma Treatment and Reduction of Skin Inflammation: A Review

The skin is the largest organ in the human body, providing a barrier to the external environment. It is composed of three layers: epidermis, dermis and hypodermis. The most external epidermis is exposed to stress factors that may lead to skin conditions such as photo-aging and skin cancer. Some treatments for skin disease utilize the incorporation of drugs or bioactive compounds into nanocarriers known as liposomes. Liposomes are membranes whose sizes range from nano to micrometers and are composed mostly of phospholipids and cholesterol, forming similar structures to cell membranes. Thus, skin treatments with liposomes have lower toxicity in comparison to traditional treatment routes such as parenteral and oral. Furthermore, addition of edge activators to the liposomes decreases the rigidity of the bilayer structure making it deformable, thereby improving skin permeability. Liposomes are composed of an aqueous core and a lipidic bilayer, which confers their amphiphilic property. Thus, they can carry hydrophobic and hydrophilic compounds, even simultaneously. Current applications of these nanocarriers are mainly in the cosmetic and pharmaceutic industries. Nevertheless, new research has revealed promising results regarding the effectiveness of liposomes for transporting bioactive compounds through the skin. Liposomes have been well studied; however, additional research is needed on the efficacy of liposomes loaded with bioactive peptides for skin delivery. The objective of this review is to provide an up-to-date description of existing techniques for the development of liposomes and their use as transporters of bioactive compounds in skin conditions such as melanoma and skin inflammation. Furthermore, to gain an understanding of the behavior of liposomes during the process of skin delivery of bioactive compounds into skin cells.