An angiogenic switch in macrophages involving synergy between Toll-like receptors 2, 4, 7, and 9 and adenosine A(2A) receptors

Global trends in publications regarding macrophages-related diabetic foot ulcers in the last two decades

BACKGROUND

Diabetic foot ulcers (DFUs) are one of the most severe and popular complications of diabetes. The persistent non-healing of DFUs is the leading cause of ampu-tation, which causes significant mental and financial stress to patients and their families. Macrophages are critical cells in wound healing and perform essential roles in all phases of wound healing. However, no studies have been carried out to systematically illustrate this area from a scientometric point of view. Although there have been some bibliometric studies on diabetes, reports focusing on the investigation of macrophages in DFUs are lacking.

AIM

To perform a bibliometric analysis to systematically assess the current state of research on macrophage-related DFUs.

METHODS

The publications of macrophage-related DFUs from January 1, 2004, to December 31, 2023, were retrieved from the Web of Science Core Collection on January 9, 2024. Four different analytical tools: VOSviewer (v1.6.19), CiteSpace (v6.2.R4), HistCite (v12.03.07), and Excel 2021 were used for the scientometric research.

RESULTS

A total of 330 articles on macrophage-related DFUs were retrieved. The most published countries, institutions, journals, and authors in this field were China, Shanghai Jiao Tong University of China, Wound Repair and Regeneration, and Aristidis Veves. Through the analysis of keyword co-occurrence networks, historical direct citation networks, thematic maps, and trend topics maps, we synthesized the prevailing research hotspots and emerging trends in this field.

CONCLUSION

Our bibliometric analysis provides a comprehensive overview of macrophage-related DFUs research and insights into promising upcoming research.

A Dose-Dependent Spatiotemporal Response of Angiogenesis Elicited by Zn Biodegradation during the Initial Stage of Bone Regeneration

Zinc (Zn) plays a crucial role in bone metabolism and imbues biodegradable Zn-based materials with the ability to promote bone regeneration in bone trauma. However, the impact of Zn biodegradation on bone repair, particularly its influence on angiogenesis, remains unexplored. This study reveals that Zn biodegradation induces a consistent dose-dependent spatiotemporal response in angiogenesis,both in vivo and in vitro. In a critical bone defect model, an increase in Zn release intensity from day 3 to 10 post-surgery is observed. By day 10, the CD31-positive area around the Zn implant significantly surpasses that of the Ti implant, indicating enhanced angiogenesis. Furthermore,angiogenesis exhibits a distance-dependent pattern closely mirroring the distribution of Zn signals from the implant. In vitro experiments demonstrate that Zn extraction fosters the proliferation and migration of human umbilical vein endothelial cells and upregulates the key genes associated with tube formation, such as HIF-1α and VEGF-A, peaking at a concentration of 22.5 µM. Additionally, Zn concentrations within the range of 11.25-45 µM promote the polarization of M0-type macrophages toward the M2-type, while inhibiting polarization toward the M1-type. These findings provide essential insights into the biological effects of Zn on bone repair, shedding light on its potential applications.

Research progress on the role of tumor‑associated macrophages in tumor development and their use as molecular targets (Review)

The tumor microenvironment (TME) is a complex system composed mainly of tumor cells, mesenchymal cells and immune cells. Macrophages, also known as tumor‑associated macrophages (TAMs), among innate immune cells, are some of the most abundant components of the TME. They may influence tumor growth and metastasis through interactions with other cell populations in the TME and have been associated with poor prognosis in a variety of tumors. Therefore, a better understanding of the role of TAMs in the TME may provide new insight into tumor therapy. In the present review, the origin and classification of TAMs in the TME were outlined and their polarization and dual effects on tumor cells, as well as emerging strategies for cancer therapies targeting TAMs, were discussed.

Adenosine, bridging chronic inflammation and tumor growth

Adenosine (Ado) is a well-known immunosuppressive agent that may be released or generated extracellularly by cells, via degrading ATP by the sequential actions of the ectonucleotides CD39 and CD73. During inflammation Ado is produced by leukocytes and tissue cells by different means to initiate the healing phase. Ado downregulates the activation and the effector functions of different leukocyte (sub-) populations and stimulates proliferation of fibroblasts for re-establishment of intact tissues. Therefore, the anti-inflammatory actions of Ado are already intrinsically triggered during each episode of inflammation. These tissue-regenerating and inflammation-tempering purposes of Ado can become counterproductive. In chronic inflammation, it is possible that Ado-driven anti-inflammatory actions sustain the inflammation and prevent the final clearance of the tissues from possible pathogens. These chronic infections are characterized by increased tissue damage, remodeling and accumulating DNA damage, and are thus prone for tumor formation. Developing tumors may further enhance immunosuppressive actions by producing Ado by themselves, or by "hijacking" CD39+/CD73+ cells that had already developed during chronic inflammation. This review describes different and mostly convergent mechanisms of how Ado-induced immune suppression, initially induced in inflammation, can lead to tumor formation and outgrowth.

Loss of adenosine A3 receptors accelerates skeletal muscle regeneration in mice following cardiotoxin-induced injury

Skeletal muscle regeneration is a complex process orchestrated by multiple interacting steps. An increasing number of reports indicate that inflammatory responses play a central role in linking initial muscle injury responses to timely muscle regeneration following injury. The nucleoside adenosine has been known for a long time as an endogenously produced anti-inflammatory molecule that is generated in high amounts during tissue injury. It mediates its physiological effects via four types of adenosine receptors. From these, adenosine A3 receptors (A3Rs) are not expressed by the skeletal muscle but are present on the surface of various inflammatory cells. In the present paper, the effect of the loss of A3Rs was investigated on the regeneration of the tibialis anterior (TA) muscle in mice following cardiotoxin-induced injury. Here we report that regeneration of the skeletal muscle from A3R-/- mice is characterized by a stronger initial inflammatory response resulting in a larger number of transmigrating inflammatory cells to the injury site, faster clearance of cell debris, enhanced proliferation and faster differentiation of the satellite cells (the muscle stem cells), and increased fusion of the generated myoblasts. This leads to accelerated skeletal muscle tissue repair and the formation of larger myofibers. Though the infiltrating immune cells expressed A3Rs and showed an increased inflammatory profile in the injured A3R-/- muscles, bone marrow transplantation experiments revealed that the increased response of the tissue-resident cells to tissue injury is responsible for the observed phenomenon. Altogether our data indicate that A3Rs are negative regulators of injury-related regenerative inflammation and consequently also that of the muscle fiber growth in the TA muscle. Thus, inhibiting A3Rs might have a therapeutic value during skeletal muscle regeneration following injury.

Enhancer of zeste homolog 2 promotes renal fibrosis after acute kidney injury by inducing epithelial-mesenchymal transition and activation of M2 macrophage polarization

Long-term follow-up data indicates that 1/4 patients with acute kidney injury (AKI) will develop to chronic kidney disease (CKD). Our previous studies have demonstrated that enhancer of zeste homolog 2 (EZH2) played an important role in AKI and CKD. However, the role and mechanisms of EZH2 in AKI-to-CKD transition are still unclear. Here, we demonstrated EZH2 and H3K27me3 highly upregulated in kidney from patients with ANCA-associated glomerulonephritis, and expressed positively with fibrotic lesion and negatively with renal function. Conditional EZH2 deletion or pharmacological inhibition with 3-DZNeP significantly improved renal function and attenuated pathological lesion in ischemia/reperfusion (I/R) or folic acid (FA) mice models (two models of AKI-to-CKD transition). Mechanistically, we used CUT & Tag technology to verify that EZH2 binding to the PTEN promoter and regulating its transcription, thus regulating its downstream signaling pathways. Genetic or pharmacological depletion of EZH2 upregulated PTEN expression and suppressed the phosphorylation of EGFR and its downstream signaling ERK1/2 and STAT3, consequently alleviating the partial epithelial-mesenchymal transition (EMT), G2/M arrest, and the aberrant secretion of profibrogenic and proinflammatory factors in vivo and vitro experiments. In addition, EZH2 promoted the EMT program induced loss of renal tubular epithelial cell transporters (OAT1, ATPase, and AQP1), and blockade of EZH2 prevented it. We further co-cultured macrophages with the medium of human renal tubular epithelial cells treated with H₂O₂ and found macrophages transferred to M2 phenotype, and EZH2 could regulate M2 macrophage polarization through STAT6 and PI3K/AKT pathways. These results were further verified in two mice models. Thus, targeted inhibition of EZH2 might be a novel therapy for ameliorating renal fibrosis after acute kidney injury by counteracting partial EMT and blockade of M2 macrophage polarization.

Immunosenescence, Inflammaging, and Frailty: Role of Myeloid Cells in Age-Related Diseases

The immune system is the central regulator of tissue homeostasis, ensuring tissue regeneration and protection against both pathogens and the neoformation of cancer cells. Its proper functioning requires homeostatic properties, which are maintained by an adequate balance of myeloid and lymphoid responses. Aging progressively undermines this ability and compromises the correct activation of immune responses, as well as the resolution of the inflammatory response. A subclinical syndrome of "homeostatic frailty" appears as a distinctive trait of the elderly, which predisposes to immune debilitation and chronic low-grade inflammation (inflammaging), causing the uncontrolled development of chronic and degenerative diseases. The innate immune compartment, in particular, undergoes to a sequela of age-dependent functional alterations, encompassing steps of myeloid progenitor differentiation and altered responses to endogenous and exogenous threats. Here, we will review the age-dependent evolution of myeloid populations, as well as their impact on frailty and diseases of the elderly.

Cannabidiol's neuroprotective properties and potential treatment of traumatic brain injuries

Cannabidiol (CBD) has numerous pharmacological targets that initiate anti-inflammatory, antioxidative, and antiepileptic properties. These neuroprotective benefits have generated interest in CBD's therapeutic potential against the secondary injury cascade from traumatic brain injury (TBI). There are currently no effective broad treatment strategies for combating the damaging mechanisms that follow the primary injury and lead to lasting neurological consequences or death. However, CBD's effects on different neurotransmitter systems, the blood brain barrier, oxidative stress mechanisms, and the inflammatory response provides mechanistic support for CBD's clinical utility in TBI. This review describes the cascades of damage caused by TBI and CBD's neuroprotective mechanisms to counter them. We also present challenges in the clinical treatment of TBI and discuss important future clinical research directions for integrating CBD in treatment protocols. The mechanistic evidence provided by pre-clinical research shows great potential for CBD as a much-needed improvement in the clinical treatment of TBI. Upcoming clinical trials sponsored by major professional sport leagues are the first attempts to test the efficacy of CBD in head injury treatment protocols and highlight the need for further clinical research.

The generation, activation, and polarization of monocyte-derived macrophages in human malignancies

Macrophages are immune cells that originate from embryogenesis or from the differentiation of monocytes. They can adopt numerous phenotypes depending on their origin, tissue distribution and in response to different stimuli and tissue environment. Thus, in vivo, macrophages are endowed with a continuum of phenotypes that are rarely strictly pro-inflammatory or anti-inflammatory and exhibit a broad expression profile that sweeps over the whole polarization spectrum. Schematically, three main macrophage subpopulations coexist in human tissues: naïve macrophages also called M0, pro-inflammatory macrophages referred as M1 macrophages, and anti-inflammatory macrophages also known as M2 macrophages. Naïve macrophages display phagocytic functions, recognize pathogenic agents, and rapidly undergo polarization towards pro or anti-inflammatory macrophages to acquire their full panel of functions. Pro-inflammatory macrophages are widely involved in inflammatory response, during which they exert anti-microbial and anti-tumoral functions. By contrast, anti-inflammatory macrophages are implicated in the resolution of inflammation, the phagocytosis of cell debris and tissue reparation following injuries. Macrophages also play important deleterious or beneficial roles in the initiation and progression of different pathophysiological settings including solid and hematopoietic cancers. A better understanding of the molecular mechanisms involved in the generation, activation and polarization of macrophages is a prerequisite for the development of new therapeutic strategies to modulate macrophages functions in pathological situations.

A composite hydrogel containing resveratrol-laden nanoparticles and platelet-derived extracellular vesicles promotes wound healing in diabetic mice

Diabetic wounds are difficult to heal because of persistent inflammation and limited angiogenesis. Resveratrol (RES) is an anti-inflammatory and antioxidant agent. Platelet-derived extracellular vesicles (PDEVs) are rich in growth factors and cytokines, which promote proliferation and angiogenesis. However, single drug treatment has limited efficacy and delivery efficiency. Bioengineering can improve the limited effect of single drugs by combining drugs and materials to obtain complementary or cooperative bioengineered drugs. In this study, gelatin methacrylate (GelMA) and silk fibroin glycidyl methacrylate (SFMA) were used to synthesize GelMA/SFMA composite hydrogels with suitable mechanical properties, swelling ratio and biodegradability. The composite hydrogel was used as a wound dressing for sustained drug release. RES was loaded into mesoporous silica nanoparticles (MSNs) to synthesize MSN-RES to enhance the release dynamic, and MSN-RES and PDEVs were combined with the composite hydrogels to form GelMA/SFMA/MSN-RES/PDEVs hydrogels. The GelMA/SFMA/MSN-RES/PDEVs had low cytotoxicity and good biocompatibility, inhibited macrophage iNOS expression, and promoted the tube formation by human umbilical vein endothelial cells (HUVECs) in vitro. In a diabetic mouse wound model, the GelMA/SFMA/MSN-RES/PDEVs hydrogels decreased the expression of pro-inflammatory factors TNF-α and iNOS, increased the expression of anti-inflammatory factors TGF-β1 and Arg-1, promoted angiogenesis, and accelerated wound healing. Interestingly, the GelMA/SFMA/MSN-RES/PDEVs hydrogels promoted the expression of extracellular purinergic signaling pathway-related CD73 and adenosine 2A receptor (A2A-R). Therefore, the GelMA/SFMA/MSN-RES/PDEVs hydrogels could be used as wound dressings to regulate the inflammation and angiogenesis of diabetic wounds and accelerate wound healing. STATEMENT OF SIGNIFICANCE: Drugs often fail to function because of a continuous oxidative stress microenvironment and inflammation. Here, a GelMA/SFMA hydrogel, with enhanced mechanical properties and liquid absorption ability, is proposed for sustained release of drugs. In addition to carrying platelet-derived extracellular vesicles (PDEVs) with pro-angiogenic effects, the hydrogels were also loaded with nanoparticle-encapsulated resveratrol with anti-inflammatory activities, aiming to reduce inflammation and oxidative stress in the wound microenvironment, such that the wound could receive proliferative repair signals to achieve sequential treatment and heal quickly. We also experimentally predicted that the regulatory mechanism of the GelMA/SFMA/MSN-RES/PDEVs in wound healing might be related to the extracellular purinergic signaling pathway.

Plasticity towards Rigidity: A Macrophage Conundrum in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive, chronic, and ultimately fatal diffuse parenchymal lung disease. The molecular mechanisms of fibrosis in IPF patients are not fully understood and there is a lack of effective treatments. For decades, different types of drugs such as immunosuppressants and antioxidants have been tested, usually with unsuccessful results. Although two antifibrotic drugs (Nintedanib and Pirfenidone) are approved and used for the treatment of IPF, side effects are common, and they only slow down disease progression without improving patients’ survival. Macrophages are central to lung homeostasis, wound healing, and injury. Depending on the stimulus in the microenvironment, macrophages may contribute to fibrosis, but also, they may play a role in the amelioration of fibrosis. In this review, we explore the role of macrophages in IPF in relation to the fibrotic processes, epithelial–mesenchymal transition (EMT), and their crosstalk with resident and recruited cells and we emphasized the importance of macrophages in finding new treatments.

Functional Phenotypes of Intraplaque Macrophages and Their Distinct Roles in Atherosclerosis Development and Atheroinflammation

Macrophages are the key inflammatory cell type involved in all stages of atherosclerosis development and progression, as demonstrated by numerous studies. Correspondingly, macrophages are currently regarded as a promising therapeutic target for the development of new treatment approaches. The macrophage population is heterogeneous and dynamic, as these cells can switch between a number of distinct functional states with pro- and anti-atherogenic activity in response to various stimuli. An atherosclerotic plaque microenvironment defined by cytokine levels, cell-to-cell interactions, lipid accumulation, hypoxia, neoangiogenesis, and intraplaque haemorrhage may guide local macrophage polarization processes within the lesion. In this review, we discuss known functional phenotypes of intraplaque macrophages and their distinct contribution to ahteroinflammation.

Inactivation of AUF1 in Myeloid Cells Protects From Allergic Airway and Tumor Infiltration and Impairs the Adenosine-Induced Polarization of Pro-Angiogenic Macrophages

The four isoforms of the RNA-binding protein hnRNPD/AUF1 have been proposed to limit the use of inflammatory mRNAs in innate immune cells. Mice engineered to lack AUF1s in all tissues are sensitive to acute inflammatory assaults; however, they also manifest complex degenerations obscuring assessment of AUF1s’ roles in innate immune cells. Here, we restricted a debilitating AUF1 mutation to the mouse myeloid lineage and performed disease-oriented phenotypic analyses to assess the requirement of AUF1s in variable contexts of innate immune reactivity. Contrary to the whole-body mutants, the myeloid mutants of AUF1s did not show differences in their susceptibility to cytokine storms occurring during endotoxemia; neither in type-I cell-mediated reactions driving intestinal inflammation by chemical irritants. Instead, they were resistant to allergic airway inflammation and displayed reductions in inflammatory infiltrates and an altered T-helper balance. The ex-vivo analysis of macrophages revealed that the loss of AUF1s had a minimal effect on their proinflammatory gene expression. Moreover, AUF1s were dispensable for the classical polarization of cultured macrophages by LPS & IFNγ correlating with the unchanged response of mutant mice to systemic and intestinal inflammation. Notably, AUF1s were also dispensable for the alternative polarization of macrophages by IL4, TGFβ and IL10, known to be engaged in allergic reactions. In contrast, they were required to switch proinflammatory macrophages towards a pro-angiogenic phenotype induced by adenosine receptor signals. Congruent to this, the myeloid mutants of AUF1 displayed lower levels of vascular remodeling factors in exudates from allergen exposed lungs; were unable to support the growth and inflammatory infiltration of transplanted melanoma tumors; and failed to vascularize inert grafts unless supplemented with angiogenic factors. Mechanistically, adenosine receptor signals enhanced the association of AUF1s with the Vegfa, Il12b, and Tnf mRNAs to differentially regulate and facilitate the pro-angiogenic switch. Our data collectively demonstrates that AUF1s do not act as general anti-inflammatory factors in innate immune cells but have more specialized roles in regulons allowing specific innate immune cell transitions to support tissue infiltration and remodeling processes.

Expression of the Adenosine A2A-A3 Receptor Heteromer in Different Brain Regions and Marked Upregulation in the Microglia of the Transgenic APPSw,Ind Alzheimer’s Disease Model

Adenosine (Ado) receptors have been instrumental in the detection of heteromers and other higher-order receptor structures, mainly via interactions with other cell surface G-protein-coupled receptors. Apart from the first report of the A₁ Ado receptor interacting with the A_2A Ado receptor, there has been more recent data on the possibility that every Ado receptor type, A₁, A_2A, A_2B, and A₃, may interact with each other. The aim of this paper was to look for the expression and function of the A_2A/A₃ receptor heteromer (A_2AA₃Het) in neurons and microglia. In situ proximity ligation assays (PLA), performed in primary cells, showed that A_2AA₃Het expression was markedly higher in striatal than in cortical and hippocampal neurons, whereas it was similar in resting and activated microglia. Signaling assays demonstrated that the effect of the A_2AR agonist, PSB 777, was reduced in the presence of the A₃R agonist, 2-Cl-IB-MECA, whereas the effect of the A₃R agonist was potentiated by the A_2AR antagonist, SCH 58261. Interestingly, the expression of the heteromer was markedly enhanced in microglia from the APP_Sw,Ind model of Alzheimer’s disease. The functionality of the heteromer in primary microglia from APP_Sw,Ind mice was more similar to that found in resting microglia from control mice.

Recovery of Altered Diabetic Myofibroblast Heterogeneity and Gene Expression Are Associated with CD301b+ Macrophages

Diabetic wound healing is associated with impaired function and reduced numbers of myofibroblasts, a heterogeneous cell population with varying capacities to promote repair. To determine how diabetes alters myofibroblast composition, we performed flow cytometry and spatial tissue analysis of myofibroblast subsets throughout the healing process in diabetic (db/db) and control (db/+) mouse skin. We observed reduced numbers of profibrotic SCA1+; CD34+; CD26+ myofibroblasts in diabetic wounds five days after injury, with decreased expression of fibrosis-associated genes compared to myofibroblasts from db/+ mouse wounds. While the abundance of myofibroblasts remained reduced in db/db mouse wounds compared to controls, the altered myofibroblast heterogeneity and gene expression in diabetic mice was improved seven days after injury. The natural correction of myofibroblast composition and gene expression in db/db wound beds temporally corresponds with a macrophage phenotypic switch. Correlation analysis from individual wound beds revealed that wound healing in control mice is associated with CD206+ macrophages, while the rescued myofibroblast phenotypes in diabetic wounds are correlated with increased CD301b+ macrophage numbers. These data demonstrate how diabetes impacts specific subsets of myofibroblasts and indicate that signaling capable of rescuing impaired diabetic wound healing could be different from signals that regulate wound healing under nonpathological conditions.

Mesothelioma Malignancy and the Microenvironment: Molecular Mechanisms

Several studies have reported that cellular and soluble components of the tumor microenvironment (TME) play a key role in cancer-initiation and progression. Considering the relevance and the complexity of TME in cancer biology, recent research has focused on the investigation of the TME content, in terms of players and informational exchange. Understanding the crosstalk between tumor and non-tumor cells is crucial to design more beneficial anti-cancer therapeutic strategies. Malignant pleural mesothelioma (MPM) is a complex and heterogenous tumor mainly caused by asbestos exposure with few treatment options and low life expectancy after standard therapy. MPM leukocyte infiltration is rich in macrophages. Given the failure of macrophages to eliminate asbestos fibers, these immune cells accumulate in pleural cavity leading to the establishment of a unique inflammatory environment and to the malignant transformation of mesothelial cells. In this inflammatory landscape, stromal and immune cells play a driven role to support tumor development and progression via a bidirectional communication with tumor cells. Characterization of the MPM microenvironment (MPM-ME) may be useful to understand the complexity of mesothelioma biology, such as to identify new molecular druggable targets, with the aim to improve the outcome of the disease. In this review, we summarize the known evidence about the MPM-ME network, including its prognostic and therapeutic relevance.

The multifaceted roles of macrophages in bone regeneration: A story of polarization, activation and time

To present knowledge, macrophages are found in all tissues of the human body. They are a cell population with high plasticity which come with a multitude of functions which appear to be adapted to the respective tissue niche and micro-environment in which they reside. Bone harbors multiple macrophage subpopulations, with the osteoclasts as classical representative of a bone resorbing cells and osteomacs as a bone tissue resident macrophage first described by the expression of F4/80. Both subtypes are found throughout all phases in bone healing. In vivo data on bone regeneration have demonstrated their essential role in initiating the healing cascade (inflammatory phase) but also of the later phases of healing (e.g. endochondral and intramembranous bone formation). To participate in such diverse processes macrophages have to be highly plastic in their functionality. Thus, the widely used M1/M2 paradigm to distinguish macrophage subpopulations may not mirror the comprehensive role of the dynamics of macrophage plasticity. From a clinical perspective it is especially relevant to distinguish what drives macrophages in impaired healing scenarios, implant loosening or infections, where their specific role of a misbalanced inflammatory setting is so far only partially known. With this review we aim at illustrating current knowledge and gaps of knowledge on macrophage plasticity and function during the cascades of regeneration and reconstitution of bone tissue. We propose aspects of the known biological mechanisms of macrophages and their specific subsets that might serve as targets to control their function in impaired healing and eventually support a scar-free regeneration. STATEMENT OF SIGNIFICANCE: Macrophages are essential for successful regeneration. In scar-free healing such as in bone, a complete failure of healing was shown if macrophages were depleted; the M1/M2 switch appears to be key to the progression from pro-inflammation to regeneration. However, experimental data illustrate that the classical M1/M2 paradigm does not completely mirror the complexity of observed macrophage functions during bone healing and thus demands a broader perspective. Within this review we discuss the high degree of plasticity of macrophages and the relevant contribution of the different and more specific M2 subtypes (M2a-M2f) during (bone) regeneration. It summarizes the versatile roles of macrophages in skeletal regeneration and thereby highlights potential target points for immunomodulatory approaches to enable or even foster bone repair.

Macrophages in Skeletal Muscle Dystrophies, An Entangled Partner

While skeletal muscle remodeling happens throughout life, diseases that result in its dysfunction are accountable for many deaths. Indeed, skeletal muscle is exceptionally capable to respond to stimuli modifying its homeostasis, such as in atrophy, hypertrophy, regeneration and repair. In particular conditions such as genetic diseases (muscular dystrophies), skeletal muscle’s capacity to remodel is strongly affected and undergoes continuous cycles of chronic damage. This induces scarring, fatty infiltration, as well as loss of contractibility and of the ability to generate force. In this context, inflammation, primarily mediated by macrophages, plays a central pathogenic role. Macrophages contribute as the primary regulators of inflammation during skeletal muscle regeneration, affecting tissue-resident cells such as myogenic cells and endothelial cells, but also fibro-adipogenic progenitors, which are the main source of the fibro fatty scar. During skeletal muscle regeneration their function is tightly orchestrated, while in dystrophies their fate is strongly disturbed, resulting in chronic inflammation. In this review, we will discuss the latest findings on the role of macrophages in skeletal muscle diseases, and how they are regulated.

DAMPening COVID-19 Severity by Attenuating Danger Signals

COVID-19 might lead to multi-organ failure and, in some cases, to death. The COVID-19 severity is associated with a “cytokine storm.” Danger-associated molecular patterns (DAMPs) are proinflammatory molecules that can activate pattern recognition receptors, such as toll-like receptors (TLRs). DAMPs and TLRs have not received much attention in COVID-19 but can explain some of the gender-, weight- and age-dependent effects. In females and males, TLRs are differentially expressed, likely contributing to higher COVID-19 severity in males. DAMPs and cytokines associated with COVID-19 mortality are elevated in obese and elderly individuals, which might explain the higher risk for severer COVID-19 in these groups. Adenosine signaling inhibits the TLR/NF-κB pathway and, through this, decreases inflammation and DAMPs’ effects. As vaccines will not be effective in all susceptible individuals and as new vaccine-resistant SARS-CoV-2 mutants might develop, it remains mandatory to find means to dampen COVID-19 disease severity, especially in high-risk groups. We propose that the regulation of DAMPs via adenosine signaling enhancement might be an effective way to lower the severity of COVID-19 and prevent multiple organ failure in the absence of severe side effects.

TLR2 signaling contributes to the angiogenesis of oxygen-induced retinopathy

PURPOSE

To evaluate the role of Toll-like receptor 2 (TLR2) signaling in retinal neovascularization in a mouse model of oxygen-induced retinopathy (OIR).

MATERIALS AND METHODS

The OIR model was established in C57BL/6J wild type (WT) mice and TLR2^-/- mice. Retinal neovascularization in the OIR model was measured by counting new vascular cell nuclei above the internal limiting membrane and analyzing flat-mounted retinas perfused with fluorescein dextran and immunostained with Griffonia Simplicifolia (GS) isolectin. The expression of TLR2 and VEGF in the retina was detected by immunofluorescence. Expression of TGF- β1, b-FGF, and IL-6 mRNA in the retina was measured by quantitative real-time PCR.

RESULTS

Compared to WT OIR mice, retinal neovascularization was attenuated in TLR2^-/- OIR mice. The co-expressions of TLR2 and VEGF were remarkably and consistently increased in WT OIR mice; however, there was no expression of TLR2 and a significant decrease in VEGF expression in TLR2^-/- OIR mice. These results suggest that TLR2 plays a central role in OIR model angiogenesis. Expression of TGF- β1, b-FGF, and IL-6 mRNA were reduced in the TLR2^-/- OIR mice, suggesting that the inflammatory response induced by TLR2 relates to angiogenesis.

CONCLUSION

TLR2 signaling in the retina is associated with neovascularization in mice. Inflammation contributes to the activation of angiogenesis and is partially mediated through the TLR2-VEGF retinal signaling pathway.

Effective Actions of Ion Release from Mesoporous Bioactive Glass and Macrophage Mediators on the Differentiation of Osteoprogenitor and Endothelial Progenitor Cells

Due to their specific mesoporous structure and large surface area, mesoporous bioactive glasses (MBGs) possess both drug-delivery ability and effective ionic release to promote bone regeneration by stimulating osteogenesis and angiogenesis. Macrophages secrete mediators that can affect both processes, depending on their phenotype. In this work, the action of ion release from MBG-75S, with a molar composition of 75SiO₂-20CaO-5P₂O₅, on osteogenesis and angiogenesis and the modulatory role of macrophages have been assessed in vitro with MC3T3-E1 pre-osteoblasts and endothelial progenitor cells (EPCs) in monoculture and in coculture with RAW 264.7 macrophages. Ca²⁺, phosphorous, and silicon ions released from MBG-75S were measured in the culture medium during both differentiation processes. Alkaline phosphatase activity and matrix mineralization were quantified as the key markers of osteogenic differentiation in MC3T3-E1 cells. The expression of CD31, CD34, VEGFR2, eNOS, and vWF was evaluated to characterize the EPC differentiation into mature endothelial cells. Other cellular parameters analyzed included the cell size and complexity, intracellular calcium, and intracellular content of the reactive oxygen species. The results obtained indicate that the ions released by MBG-75S promote osteogenesis and angiogenesis in vitro, evidencing a macrophage inhibitory role in these processes and demonstrating the high potential of MBG-75S for the preparation of implants for bone regeneration.

Effects of Ipriflavone-Loaded Mesoporous Nanospheres on the Differentiation of Endothelial Progenitor Cells and Their Modulation by Macrophages

Angiogenic biomaterials are designed to promote vascularization and tissue regeneration. Nanoparticles of bioactive materials loaded with drugs represent an interesting strategy to stimulate osteogenesis and angiogenesis and to inhibit bone resorption. In this work, porcine endothelial progenitor cells (EPCs), essential for blood vessel formation, were isolated and characterized to evaluate the in vitro effects of unloaded (NanoMBGs) and ipriflavone-loaded nanospheres (NanoMBG-IPs), which were designed to prevent osteoporosis. The expression of vascular endothelial growth factor receptor 2 (VEGFR2) was studied in EPCs under different culture conditions: (a) treatment with NanoMBGs or NanoMBG-IPs, (b) culture with media from basal, M1, and M2 macrophages previously treated with NanoMBGs or NanoMBG-IPs, (c) coculture with macrophages in the presence of NanoMBGs or NanoMBG-IPs, and (d) coculture with M2d angiogenic macrophages. The endocytic mechanisms for nanosphere incorporation by EPCs were identified using six different endocytosis inhibitors. The results evidence the great potential of these nanomaterials to enhance VEGFR2 expression and angiogenesis, after intracellular incorporation by EPCs through clathrin-dependent endocytosis, phagocytosis, and caveolae-mediated uptake. The treatment of EPCs with basal, M1, and M2 macrophage culture media and EPC/macrophage coculture studies also confirmed the angiogenic effect of these nanospheres on EPCs, even in the presence of phagocytic cells.

Distinct toll-like receptor signaling in the salamander response to tissue damage

BACKGROUND

Efficient wound healing or pathogen clearance both rely on balanced inflammatory responses. Inflammation is essential for effective innate immune-cell recruitment; however, excessive inflammation will result in local tissue destruction, pathogen egress, and ineffective pathogen clearance. Sterile and nonsterile inflammation operate with competing functional priorities but share common receptors and overlapping signal transduction pathways. In regenerative organisms such as the salamander, whole limbs can be replaced after amputation while exposed to a nonsterile environment. In mammals, exposure to sterile-injury Damage Associated Molecular Patterns (DAMPS) alters innate immune-cell responsiveness to secondary Pathogen Associated Molecular Pattern (PAMP) exposure.

RESULTS

Using new phospho-flow cytometry techniques to measure signaling in individual cell subsets we compared mouse to salamander inflammation. These studies demonstrated evolutionarily conserved responses to PAMP ligands through toll-like receptors (TLRs) but identified key differences in response to DAMP ligands. Co-exposure of macrophages to DAMPs/PAMPs suppressed MAPK signaling in mammals, but not salamanders, which activate sustained MAPK stimulation in the presence of endogenous DAMPS.

CONCLUSIONS

These results reveal an alternative signal transduction network compatible with regeneration that may ultimately lead to the promotion of enhanced tissue repair in mammals.

Macrophage 3D migration: A potential therapeutic target for inflammation and deleterious progression in diseases

Macrophages are heterogeneous cells that have different physiological functions, such as chemotaxis, phagocytosis, endocytosis, and secretion of various factors. All physiological functions of macrophages are integral to homeostasis, immune defense and tissue repair. However, in several diseases, macrophages are recruited from the blood towards inflammatory sites. This process is called macrophage migration, which promotes deleterious disease progression. Macrophage migration is a key player in many inflammatory diseases, autoimmune diseases and cancers because it contributes to the accumulation of proinflammatory factors, the destruction of tissues and the development of tumors. Therefore, macrophage migration is proposed to be a potential therapeutic target. Macrophages migrate between two-dimensional (2D) and three-dimensional (3D) environments, implying that distinct migratory features and mechanisms are involved. Compared with the 2D migration of macrophages, 3D migration involves more complex variations in cellular morphology and dynamics. The structure of the extracellular matrix, a key factor, is modified in diseases that influence macrophage 3D migration. Macrophage 3D migration relates to disease pathology. Research that focuses on macrophage 3D migration is an emerging field and was reviewed in this article to indicate the molecular and cellular mechanisms of macrophage migration in 3D environments and to provide potential targets for controlling disease progression associated with this migration.

Dermal Drivers of Injury-Induced Inflammation: Contribution of Adipocytes and Fibroblasts

Irregular inflammatory responses are a major contributor to tissue dysfunction and inefficient repair. Skin has proven to be a powerful model to study mechanisms that regulate inflammation. In particular, skin wound healing is dependent on a rapid, robust immune response and subsequent dampening of inflammatory signaling. While injury-induced inflammation has historically been attributed to keratinocytes and immune cells, a vast body of evidence supports the ability of non-immune cells to coordinate inflammation in numerous tissues and diseases. In this review, we concentrate on the active participation of tissue-resident adipocytes and fibroblasts in pro-inflammatory signaling after injury, and how altered cellular communication from these cells can contribute to irregular inflammation associated with aberrant wound healing. Furthering our understanding of how tissue-resident mesenchymal cells contribute to inflammation will likely reveal new targets that can be manipulated to regulate inflammation and repair.

From Inflammation to the Onset of Fibrosis through A2A Receptors in Kidneys from Deceased Donors

Pretransplant graft inflammation could be involved in the worse prognosis of deceased donor (DD) kidney transplants. A2A adenosine receptor (A_2AR) can stimulate anti-inflammatory M2 macrophages, leading to fibrosis if injury and inflammation persist. Pre-implantation biopsies of kidney donors (47 DD and 21 living donors (LD)) were used to analyze expression levels and activated intracellular pathways related to inflammatory and pro-fibrotic processes. A_2AR expression and PKA pathway were enhanced in DD kidneys. A_2AR gene expression correlated with TGF-β1 and other profibrotic markers, as well as CD163, C/EBPβ, and Col1A1, which are highly expressed in DD kidneys. TNF-α mRNA levels correlated with profibrotic and anti-inflammatory factors such as TGF-β1 and A_2AR. Experiments with THP-1 cells point to the involvement of the TNF-α/NF-κB pathway in the up-regulation of A_2AR, which induces the M2 phenotype increasing CD163 and TGF-β1 expression. In DD kidneys, the TNF-α/NF-κB pathway could be involved in the increase of A_2AR expression, which would activate the PKA–CREB axis, inducing the macrophage M2 phenotype, TGF-β1 production, and ultimately, fibrosis. Thus, in inflamed DD kidneys, an increase in A_2AR expression is associated with the onset of fibrosis, which may contribute to graft dysfunction and prognostic differences between DD and LD transplants.

Cross-Talk Between Alveolar Macrophages and Lung Epithelial Cells is Essential to Maintain Lung Homeostasis

The main function of the lung is to perform gas exchange while maintaining lung homeostasis despite environmental pathogenic and non-pathogenic elements contained in inhaled air. Resident cells must keep lung homeostasis and eliminate pathogens by inducing protective immune response and silently remove innocuous particles. Which lung cell type is crucial for this function is still subject to debate, with reports favoring either alveolar macrophages (AMs) or lung epithelial cells (ECs) including airway and alveolar ECs. AMs are the main immune cells in the lung in steady-state and their function is mainly to dampen inflammatory responses. In addition, they phagocytose inhaled particles and apoptotic cells and can initiate and resolve inflammatory responses to pathogens. Although AMs release a plethora of mediators that modulate immune responses, ECs also play an essential role as they are more than just a physical barrier. They produce anti-microbial peptides and can secrete a variety of mediators that can modulate immune responses and AM functions. Furthermore, ECs can maintain AMs in a quiescent state by expressing anti-inflammatory membrane proteins such as CD200. Thus, AMs and ECs are both very important to maintain lung homeostasis and have to coordinate their action to protect the organism against infection. Thus, AMs and lung ECs communicate with each other using different mechanisms including mediators, membrane glycoproteins and their receptors, gap junction channels, and extracellular vesicles. This review will revisit characteristics and functions of AMs and lung ECs as well as different communication mechanisms these cells utilize to maintain lung immune balance and response to pathogens. A better understanding of the cross-talk between AMs and lung ECs may help develop new therapeutic strategies for lung pathogenesis.

Modulation of myeloid cells by adenosine signaling

Hypoxia, metabolic activity, cell death and immune responses influence the adenosine concentrations in the extracellular space. Cellular responses to hypoxia and inflammation in myeloid cells promote activation of adenosine sensing circuit, which involves increased expression of ectoenzymes that converts phospho-nucleotides such as ATP to adenosine and increased expression of G protein-coupled adenosine receptors. Adenosine sensing circuitry also involves feedforward signaling, which leads to increased expression of hypoxia-inducible factor 1-alpha (HIF1 and feedback signaling, which leads to the suppression of inflammatory transcription factor, the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation. In this review we will discuss how different subsets of myeloid cells sense adenosine accumulation and how adenosine sensing by myeloid cells influence progression of different immune-related conditions including cancer.

Macrophages and the maintenance of homeostasis

There have been many chapters written about macrophage polarization. These chapters generally focus on the role of macrophages in orchestrating immune responses by highlighting the T-cell-derived cytokines that shape these polarizing responses. This bias toward immunity is understandable, given the importance of macrophages to host defense. However, macrophages are ubiquitous and are involved in many different cellular processes, and describing them as immune cells is undoubtedly an oversimplification. It disregards their important roles in development, tissue remodeling, wound healing, angiogenesis, and metabolism, to name just a few processes. In this chapter, we propose that macrophages function as transducers in the body. According to Wikipedia, “A transducer is a device that converts energy from one form to another.” The word transducer is a term used to describe both the “sensor,” which can interpret a wide range of energy forms, and the “actuator,” which can switch voltages or currents to affect the environment. Macrophages are able to sense a seemingly endless variety of inputs from their environment and transduce these inputs into a variety of different response outcomes. Thus, rather than functioning as immune cells, they should be considered more broadly as cellular transducers that interpret microenvironmental changes and actuate vital tissue responses. In this chapter, we will describe some of the sensory stimuli that macrophages perceive and the responses they make to these stimuli to achieve their prime directive, which is the maintenance of homeostasis.

The Role of Specialized Pro-Resolving Mediators in Cystic Fibrosis Airways Disease

Cystic Fibrosis (CF) is a recessive genetic disease due to mutations of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene encoding the CFTR chloride channel. The ion transport abnormalities related to CFTR mutation generate a dehydrated airway surface liquid (ASL) layer, which is responsible for an altered mucociliary clearance, favors infections and persistent inflammation that lead to progressive lung destruction and respiratory failure. The inflammatory response is normally followed by an active resolution phase to return to tissue homeostasis, which involves specialized pro-resolving mediators (SPMs). SPMs promote resolution of inflammation, clearance of microbes, tissue regeneration and reduce pain, but do not evoke unwanted immunosuppression. The airways of CF patients showed a decreased production of SPMs even in the absence of pathogens. SPMs levels in the airway correlated with CF patients' lung function. The prognosis for CF has greatly improved but there remains a critical need for more effective treatments that prevent excessive inflammation, lung damage, and declining pulmonary function for all CF patients. This review aims to highlight the recent understanding of CF airway inflammation and the possible impact of SPMs on functions that are altered in CF airways.

The effects of polydeoxyribonucleotide on wound healing and tissue regeneration: a systematic review of the literature

Aim: The present study evaluated the effects of polydeoxyribonucleotide (PDRN) on tissue regeneration, paying special attention to the molecular mechanisms that underlie its tissue remodeling actions to better identify its effective therapeutic potential in wound healing. Materials & methods: Strategic searches were conducted through MEDLINE/PubMed, Google Scholar, Scopus, Web of Science and the Cochrane Central Register of Controlled Trials, from their earliest available dates to March 2020. The studies were included with the following eligibility criteria: studies evaluating tissue regeneration, and being an in vitro, in vivo and clinical study. Results: Out of more than 90 articles, 34 fulfilled the eligibility criteria. All data obtained proved the ability of PDRN in promoting a physiological tissue repair through salvage pathway and adenosine A2A receptor activation. Conclusion: Up to date PDRN has proved promising results in term of wound regeneration, healing time and absence of side effects.

MicroRNA sequences modulating inflammation and lipid accumulation in macrophage “foam” cells: Implications for atherosclerosis

Accumulation of macrophage “foam” cells, laden with cholesterol and cholesteryl ester, within the intima of large arteries, is a hallmark of early “fatty streak” lesions which can progress to complex, multicellular atheromatous plaques, involving lipoproteins from the bloodstream and cells of the innate and adaptive immune response. Sterol accumulation triggers induction of genes encoding proteins mediating the atheroprotective cholesterol efflux pathway. Within the arterial intima, however, this mechanism is overwhelmed, leading to distinct changes in macrophage phenotype and inflammatory status. Over the last decade marked gains have been made in understanding of the epigenetic landscape which influence macrophage function, and in particular the importance of small non-coding micro-RNA (miRNA) sequences in this context. This review identifies some of the miRNA sequences which play a key role in regulating “foam” cell formation and atherogenesis, highlighting sequences involved in cholesterol accumulation, those influencing inflammation in sterol-loaded cells, and novel sequences and pathways which may offer new strategies to influence macrophage function within atherosclerotic lesions.

Using Cytometry for Investigation of Purinergic Signaling in Tumor-Associated Macrophages

Tumor-associated macrophages are widely recognized for their importance in guiding pro-tumoral or antitumoral responses. Mediating inflammation or immunosuppression, these cells support many key events in cancer progression: cell growth, chemotaxis, invasiveness, angiogenesis and cell death. The communication between cells in the tumor microenvironment strongly relies on the secretion and recognition of several molecules, including damage-associated molecular patterns (DAMPs), such as adenosine triphosphate (ATP). Extracellular ATP (eATP) and its degradation products act as signaling molecules and have extensively described roles in immune response and inflammation, as well as in cancer biology. These multiple functions highlight the purinergic system as a promising target to investigate the interplay between macrophages and cancer cells. Here, we reviewed purinergic signaling pathways connecting cancer cells and macrophages, a yet poorly investigated field. Finally, we present a new tool for the characterization of macrophage phenotype within the tumor. Image cytometry emerges as a cutting-edge tool, capable of providing a broad set of information on cell morphology, expression of specific markers, and its cellular or subcellular localization, preserving cell-cell interactions within the tumor section and providing high statistical strength in small-sized experiments. Thus, image cytometry allows deeper investigation of tumor heterogeneity and interactions between these cells. © 2020 International Society for Advancement of Cytometry.

Targeting of G-protein coupled receptors in sepsis

The Third International Consensus Definitions (Sepsis-3) define sepsis as life-threatening multi-organ dysfunction caused by a dysregulated host response to infection. Sepsis can progress to septic shock-an even more lethal condition associated with profound circulatory, cellular and metabolic abnormalities. Septic shock remains a leading cause of death in intensive care units and carries a mortality of almost 25%. Despite significant advances in our understanding of the pathobiology of sepsis, therapeutic interventions have not translated into tangible differences in the overall outcome for patients. Clinical trials of antagonists of various pro-inflammatory mediators in sepsis have been largely unsuccessful in the past. Given the diverse physiologic roles played by G-protein coupled receptors (GPCR), modulation of GPCR signaling for the treatment of sepsis has also been explored. Traditional pharmacologic approaches have mainly focused on ligands targeting the extracellular domains of GPCR. However, novel techniques aimed at modulating GPCR intracellularly through aptamers, pepducins and intrabodies have opened a fresh avenue of therapeutic possibilities. In this review, we summarize the diverse roles played by various subfamilies of GPCR in the pathogenesis of sepsis and identify potential targets for pharmacotherapy through these novel approaches.

Regulation of tumor infiltrated innate immune cells by adenosine

Cancer has the ability to escape the immune system using different molecular actors. Adenosine is known to be involved in mechanisms which control inflammatory reactions and prevent excessive immune response. This purine nucleoside can be translocated from the cell or produced in the extracellular space by 5'-ectonucleotidases. Once bound to its receptors on the surface of immune effector cells, adenosine activates various molecular pathways, which lead to functional inhibition of the cell or its death. Some tumors are infiltrated by the different cells of immune system but are able to use adenosine as an immunosuppressive molecule and thus inhibit immune anticancer response. This mechanism is well described on adaptive cells, but much less on innate cells. This review outlines major effects of adenosine on innate immune cells, its consequences on cancer progression, and possible ways to block the adenosine-dependent immunosuppressive effect.

Immune-Inflammatory Responses in Atherosclerosis: The Role of Myeloid Cells

Inflammation plays a key role in the initiation and progression of atherosclerosis and can be caused by multiple agents, including increased concentration of circulating low-density lipoprotein (LDL) cholesterol. Areas of the arterial wall affected by atherosclerosis are enriched with lymphocytes and dendritic cells (DCs). Atherosclerotic plaques contain a variety of proinflammatory immune cells, such as macrophages, DCs, T cells, natural killer cells, neutrophils and others. Intracellular lipid accumulation in atherosclerotic plaque leads to formation of so-called foam cells, the cytoplasm of which is filled with lipid droplets. According to current understanding, these cells can also derive from the immune cells that engulf lipids by means of phagocytosis. Macrophages play a crucial role in the initial stages of atherogenesis by engulfing oxidized LDL (oxLDL) in the intima that leads to their transformation to foam cells. Dying macrophages inside the plaque form a necrotic core that further aggravates the lesion. Proinflammatory DCs prime differentiation of naïve T cells to proinflammatory Th1 and Th17 subsets. In this review, we discuss the roles of cell types of myeloid origin in atherosclerosis-associated inflammation.

Imaging the Vascular Bone Marrow Niche During Inflammatory Stress

RATIONALE

Inflammatory stress induced by exposure to bacterial lipopolysaccharide causes hematopoietic stem cell expansion in the bone marrow niche, generating a cellular immune response. As an integral component of the hematopoietic stem cell niche, the bone marrow vasculature regulates the production and release of blood leukocytes, which protect the host against infection but also fuel inflammatory diseases.

OBJECTIVE

We aimed to develop imaging tools to explore vascular changes in the bone marrow niche during acute inflammation.

METHODS AND RESULTS

Using the TLR (Toll-like receptor) ligand lipopolysaccharide as a prototypical danger signal, we applied multiparametric, multimodality and multiscale imaging to characterize how the bone marrow vasculature adapts when hematopoiesis boosts leukocyte supply. In response to lipopolysaccharide, ex vivo flow cytometry and histology showed vascular changes to the bone marrow niche. Specifically, proliferating endothelial cells gave rise to new vasculature in the bone marrow during hypoxic conditions. We studied these vascular changes with complementary intravital microscopy and positron emission tomography/magnetic resonance imaging. Fluorescence and positron emission tomography integrin αVβ3 imaging signal increased during lipopolysaccharide-induced vascular remodeling. Vascular leakiness, quantified by albumin-based in vivo microscopy and magnetic resonance imaging, rose when neutrophils departed and hematopoietic stem and progenitor cells proliferated more vigorously.

CONCLUSIONS

Introducing a tool set to image bone marrow either with cellular resolution or noninvasively within the entire skeleton, this work sheds light on angiogenic responses that accompany emergency hematopoiesis. Understanding and monitoring bone marrow vasculature may provide a key to unlock therapeutic targets regulating systemic inflammation.

Targeting Adenosine in Cancer Immunotherapy to Enhance T-Cell Function

T cells play a critical role in cancer control, but a range of potent immunosuppressive mechanisms can be upregulated in the tumor microenvironment (TME) to abrogate their activity. While various immunotherapies (IMTs) aiming at re-invigorating the T-cell-mediated anti-tumor response, such as immune checkpoint blockade (ICB), and the adoptive cell transfer (ACT) of natural or gene-engineered ex vivo expanded tumor-specific T cells, have led to unprecedented clinical responses, only a small proportion of cancer patients benefit from these treatments. Important research efforts are thus underway to identify biomarkers of response, as well as to develop personalized combinatorial approaches that can target other inhibitory mechanisms at play in the TME. In recent years, adenosinergic signaling has emerged as a powerful immuno-metabolic checkpoint in tumors. Like several other barriers in the TME, such as the PD-1/PDL-1 axis, CTLA-4, and indoleamine 2,3-dioxygenase (IDO-1), adenosine plays important physiologic roles, but has been co-opted by tumors to promote their growth and impair immunity. Several agents counteracting the adenosine axis have been developed, and pre-clinical studies have demonstrated important anti-tumor activity, alone and in combination with other IMTs including ICB and ACT. Here we review the regulation of adenosine levels and mechanisms by which it promotes tumor growth and broadly suppresses protective immunity, with extra focus on the attenuation of T cell function. Finally, we present an overview of promising pre-clinical and clinical approaches being explored for blocking the adenosine axis for enhanced control of solid tumors.

Adenosine A2a receptor promotes lymphangiogenesis and lymph node metastasis

The formation of new lymphatic vessels, or lymphangiogenesis, is a critical step of the tissue repair program. In pathological conditions involving chronic inflammation or tumorigenesis, this process is often dysregulated and can contribute to disease progression. Yet, lymphangiogenesis is still incompletely understood. In this study, we identified A2a adenosinergic signaling as an important regulator of inflammatory and tumor-associated lymphangiogenesis. Using Adora2a (A2a)-deficient mice, we demonstrated that A2a signaling was involved in the formation of new lymphatic vessels in the context of peritoneal inflammation. We also demonstrated that tumor-associated and sentinel lymph node lymphangiogenesis were impaired in A2a-deficient mice, protecting them from lymph node metastasis. Notably, A2a signaling in both hematopoietic and non-hematopoietic cells contributed to sentinel lymph node metastasis. In A2a-deficient tumor-draining lymph nodes, impaired lymphangiogenesis was associated with a reduced accumulation of B cells and decreased VEGF-C levels. Supporting a role for non-hematopoietic A2a signaling, we observed that primary murine lymphatic endothelial cells (LEC) predominantly expressed A2a receptor and that A2a signaling blockade altered LEC capillary tube formation in vitro. Finally, we observed that Adora2a, Nt5e and Entpd1 gene expression positively correlated with Lyve1, Pdpn and Vegfc in several human cancers, thereby supporting the notion that adenosine production and A2a receptor activation might promote lymphangiogenesis in human tumors. In conclusion, our study highlights a novel pathway regulating lymphangiogenesis and further supports the use of A2a or adenosine blocking agents to inhibit pathological lymphangiogenesis in cancers and block the dissemination of tumor cells through the lymphatic system.

Regulating IRFs in IFN Driven Disease

The Interferon regulatory factors (IRFs) are a family of transcription factors that play pivotal roles in many aspects of the immune response, including immune cell development and differentiation and regulating responses to pathogens. Three family members, IRF3, IRF5, and IRF7, are critical to production of type I interferons downstream of pathogen recognition receptors that detect viral RNA and DNA. A fourth family member, IRF9, regulates interferon-driven gene expression. In addition, IRF4, IRF8, and IRF5 regulate myeloid cell development and phenotype, thus playing important roles in regulating inflammatory responses. Thus, understanding how their levels and activity is regulated is of critical importance given that perturbations in either can result in dysregulated immune responses and potential autoimmune disease. This review will focus the role of IRF family members in regulating type I IFN production and responses and myeloid cell development or differentiation, with particular emphasis on how regulation of their levels and activity by ubiquitination and microRNAs may impact autoimmune disease.

4-Hexylresorcinol and silk sericin increase the expression of vascular endothelial growth factor via different pathways

Angiogenesis plays an important role in active inflammation and wound healing. Our results showed that silk sericin and 4-hexylresorcinol (4HR) increased vascular endothelial growth factor (VEGF) expression in a dose-dependent manner in RAW264.7 cells. Unlike 4HR, silk sericin increased the expression of hypoxia inducible factor-1α (HIF-1α) and HIF-2α. Pretreatment with an HIF inhibitor decreased the sericin-induced increase in VEGF expression. However, the HIF inhibitor did not affect the 4HR-induced increase in VEGF expression. An inhibitor of matrix metalloproteinase (MMP) declined the 4HR-induced increase in VEGF expression. Silk sericin increased production of reactive oxygen species (ROS), whereas 4HR decreased ROS. M1 markers were increased by silk sericin treatment, and M2 markers were increased by 4HR treatment. VEGF and angiogenin expression were higher in rats treated with a 4HR-incorporated silk mat than in rats treated with a silk mat alone. In conclusion, silk sericin and 4HR increased VEGF expression in RAW264.7 cells via HIF-mediated and MMP-mediated pathways, respectively. Silk sericin exerted like pro-oxidant effects and 4HR exerted anti-oxidant effects. Rats treated with a 4HR-incorporated silk mat showed higher levels of VEGF and angiogenin than those treated with a silk mat alone.

Macrophage biology in the peripheral nervous system after injury

Neuroinflammation has positive and negative effects. This review focuses on the roles of macrophage in the PNS. Transection of PNS axons leads to degeneration and clearance of the distal nerve and to changes in the region of the axotomized cell bodies. In both locations, resident and infiltrating macrophages are found. Macrophages enter these areas in response to expression of the chemokine CCL2 acting on the macrophage receptor CCR2. In the distal nerve, macrophages and other phagocytes are involved in clearance of axonal debris, which removes molecules that inhibit nerve regeneration. In the cell body region, macrophage trigger the conditioning lesion response, a process in which neurons increase their regeneration after a prior lesion. In mice in which the genes for CCL2 or CCR2 are deleted, neither macrophage infiltration nor the conditioning lesion response occurs in dorsal root ganglia (DRG). Macrophages exist in different phenotypes depending on their environment. These phenotypes have different effects on axonal clearance and neurite outgrowth. The mechanism by which macrophages affect neuronal cell bodies is still under study. Overexpression of CCL2 in DRG in uninjured animals leads to macrophage accumulation in the ganglia and to an increase in the growth potential of DRG neurons. This increased growth requires activation of neuronal STAT3. In contrast, in acute demyelinating neuropathies, macrophages are involved in stripping myelin from peripheral axons. The molecular mechanisms that trigger macrophage action after trauma and in autoimmune disease are receiving increased attention and should lead to avenues to promote regeneration and protect axonal integrity.

Immunology of Wound Healing

Purpose of Review

Chronic wounds are a tremendous burden on the healthcare system and lead to significant patient morbidity and mortality. Normal cutaneous wound healing occurs through an intricate and delicate interplay between the immune system, keratinocytes, and dermal cells. Each cell type contributes signals that drive the normal phases of wound healing: hemostasis, inflammation, proliferation, and remodeling. This paper reviews how various immunological cell types and signaling molecules influence the way wounds develop, persist, and heal.

Recent Findings

Concurrent with the achievement of hemostasis, neutrophils are the first cells to migrate to the wound bed, brought in by pro-inflammatory signals including IL-8. Their apoptosis and engulfment by macrophages (efferocytosis) provides a key signal to the local immune milieu, including macrophages, to transition to an anti-inflammatory, pro-repair state, where angiogenesis occurs and granulation tissue is laid down. Myofibroblasts, activated through contractile forces and signaling molecules, then drive remodeling, where granulation tissue becomes scar. Unchecked inflammation at this stage can result in abnormal scar formation.

Summary

Although the derangement of immune signals at any stage can result in impaired wound healing, recent research has shown that the key transition point lies between the inflammatory and the proliferative phases. This review summarizes the events that facilitate this transition and discusses how this process can be disrupted, leading to chronic, non-healing wounds.

The M2a macrophage subset may be critically involved in the fibrogenesis of endometriosis in mice

RESEARCH QUESTION

Recent research has shown that endometriotic lesions are essentially wounds that undergo repeated tissue injury and repair, which results in epithelial-mesenchymal transition, fibroblast-to-myofibroblast transdifferentiation, smooth muscle metaplasia and ultimately fibrosis. Macrophages are a key regulator of tissue repair and fibrogenesis. But do macrophages also play a role in fibrogenesis of endometriosis, and, if yes, which subset of macrophages?

DESIGN

To elucidate the role of macrophages in fibrogenesis of endometriosis, we conducted three experiments in mice. In experiment 1, endometriotic tissue samples from female Balb/C mice with induced endometriosis were serially harvested to evaluate the role of macrophages in fibrogenesis. In experiments 2 and 3, female transgenic mice (C57BL/6J background) expressing the human diphtheria toxin receptor under the control of the CD11b promoter had macrophage depletion by diphtheria toxin injection after induction of endometriosis. Additionally, in experiment 3, adoptive transfer of different subsets of macrophage was carried out after macrophage depletion.

RESULTS

Lesional infiltration of M2 macrophages increased progressively as lesions progressed undisturbed, concomitant with progressive epithelial-mesenchymal transition, fibroblast-to-myofibroblast transdifferentiation and fibrosis. Macrophage depletion after induction of endometriosis significantly reduced lesional infiltration of total macrophages, significantly reduced lesional infiltration of M2 macrophages and significantly reduced lesional fibrotic content and lesion weight (P < 0.05). Finally, adoptive transfer of M2a, but not M1 or M2c macrophages, systemically after macrophage depletion significantly increased the extent of fibrosis in lesions (P = 1.6 × 10^-10).

CONCLUSIONS

The identification of a particular macrophage subset in fibrogenesis of endometriosis should further help to shed new light on the pathophysiology of endometriosis.

The Kat in the HAT: The Histone Acetyl Transferase Kat6b (MYST4) Is Downregulated in Murine Macrophages in Response to LPS

Epigenetic modulators, including histone methylases, demethylases, and deacetylases, have been implicated previously in the regulation of classical and alternative macrophage activation pathways. In this study, we show that the histone acetyl transferase (HAT) Kat6B (MYST4) is strongly suppressed (>80%) in macrophages by lipopolysaccharide (LPS) (M1 activation), while Kat6A, its partner in the MOZ/MORF complex, is reciprocally upregulated. This pattern of expression is not altered by LPS together with the adenosine receptor agonist NECA (M2d activation). This is despite the observation that miR-487b, a putative regulator of Kat6B expression, is mildly stimulated by LPS, but strongly suppressed by LPS/NECA. Other members of the MYST family of HATs (Kat5, Kat7, and Kat8) are unaffected by LPS treatment. Using the pLightswitch 3′UTR reporter plasmid, the miR-487b binding site in the Kat6b 3′UTR was found to play a role in the LPS-mediated suppression of Kat6B expression, but other as-yet unidentified factors are also involved. As Kat6B is a HAT that has the potential to modulate gene expression by its effects on chromatin accessibility, we are continuing our studies into the potential roles of this epigenetic modulator in macrophage activation pathways.

Adenosine A2A Receptor Signaling in the Immunopathogenesis of Experimental Autoimmune Encephalomyelitis

Our increasing appreciation of adenosine as an endogenous signaling molecule that terminates inflammation has generated excitement regarding the potential to target adenosine receptors (ARs) in the treatment of multiple sclerosis (MS), a disease of chronic neuroinflammation. Of the four G protein-coupled ARs, A2ARs are the principal mediator of adenosine’s anti-inflammatory effects and accordingly, there is a growing body of evidence surrounding the role of A2ARs in experimental autoimmune encephalomyelitis (EAE), the dominant animal model of MS. Such evidence points to a complex, often paradoxical role for A2ARs in the immunopathogenesis of EAE, where they have the ability to both exacerbate and alleviate disease severity. This review seeks to interpret these paradoxical findings and evaluate the therapeutic promise of A2ARs. In essence, the complexities of A2AR signaling arise from two properties. Firstly, A2AR signaling downregulates the inflammatory potential of TH lymphocytes whilst simultaneously facilitating the recruitment of these cells into the CNS. Secondly, A2AR expression by myeloid cells – infiltrating macrophages and CNS-resident microglia – has the capacity to promote both tissue injury and repair in chronic neuroinflammation. Consequently, the therapeutic potential of targeting A2ARs is greatly undermined by the risk of collateral tissue damage in the periphery and/or CNS.

Sustained reversal of central neuropathic pain induced by a single intrathecal injection of adenosine A2A receptor agonists

Central neuropathic pain is a debilitating outcome of spinal cord injury (SCI) and current treatments to alleviate this pain condition are ineffective. A growing body of literature suggests that activating adenosine A_2A receptors (A_2ARs) decreases the production of proinflammatory cytokines and increases the production of anti-inflammatory cytokines. Here, the effect of administering intrathecal A_2AR agonists on central neuropathic pain was measured using hindpaw mechanical allodynia in a rat model of SCI termed spinal neuropathic avulsion pain (SNAP). Other models of SCI cause extensive damage to the spinal cord, resulting in paralysis and health problems. SNAP rats with unilateral low thoracic (T13)/high lumbar (L1) dorsal root avulsion develop below-level bilateral allodynia, without concomitant motor or health problems. A single intrathecal injection of the A_2AR agonist 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamido adenosine HCl (CGS21680) reversed SCI-induced allodynia for at least 6 weeks. The reversal is likely in part mediated by interleukin (IL)-10, as intrathecally administering neutralizing IL-10 antibodies 1 week after CGS21680 abolished the anti-allodynic effect of CGS21680. Dorsal spinal cord tissue from the ipsilateral site of SCI (T13/L1) was assayed 1 and 6 weeks after CGS21680 for IL-10, CD11b, and tumor necrosis factor (TNF) gene expression. CGS21680 treatment did not change IL-10 gene expression but did significantly decrease CD11b and TNF gene expression at both timepoints. A second A_2AR agonist, 4-(3-(6-amino-9-(5-cyclopropylcarbamoyl-3,4-dihydroxytetrahydrofuran-2-yl)-9H-purin-2-yl)prop-2-ynyl)piperidine-1-carboxylic acid methyl ester (ATL313), was also able to significantly prevent and reverse SCI-induced allodynia for several weeks after a single intrathecal injection, providing converging lines of evidence of A_2AR involvement. The enduring pain reversal after a single intrathecal injection of A_2AR agonists suggests that A_2AR agonists could be exciting new candidates for treating SCI-induced central neuropathic pain.

Macrophage plasticity, polarization, and function in health and disease

Macrophages are heterogeneous and their phenotype and functions are regulated by the surrounding micro-environment. Macrophages commonly exist in two distinct subsets: 1) Classically activated or M1 macrophages, which are pro-inflammatory and polarized by lipopolysaccharide (LPS) either alone or in association with Th1 cytokines such as IFN-γ, GM-CSF, and produce pro-inflammatory cytokines such as interleukin-1β (IL-1β), IL-6, IL-12, IL-23, and TNF-α; and 2) Alternatively activated or M2 macrophages, which are anti-inflammatory and immunoregulatory and polarized by Th2 cytokines such as IL-4 and IL-13 and produce anti-inflammatory cytokines such as IL-10 and TGF-β. M1 and M2 macrophages have different functions and transcriptional profiles. They have unique abilities by destroying pathogens or repair the inflammation-associated injury. It is known that M1/M2 macrophage balance polarization governs the fate of an organ in inflammation or injury. When the infection or inflammation is severe enough to affect an organ, macrophages first exhibit the M1 phenotype to release TNF-α, IL-1β, IL-12, and IL-23 against the stimulus. But, if M1 phase continues, it can cause tissue damage. Therefore, M2 macrophages secrete high amounts of IL-10 and TGF-β to suppress the inflammation, contribute to tissue repair, remodeling, vasculogenesis, and retain homeostasis. In this review, we first discuss the basic biology of macrophages including origin, differentiation and activation, tissue distribution, plasticity and polarization, migration, antigen presentation capacity, cytokine and chemokine production, metabolism, and involvement of microRNAs in macrophage polarization and function. Secondly, we discuss the protective and pathogenic role of the macrophage subsets in normal and pathological pregnancy, anti-microbial defense, anti-tumor immunity, metabolic disease and obesity, asthma and allergy, atherosclerosis, fibrosis, wound healing, and autoimmunity.