Pro-Resolving Factors Released by Macrophages After Efferocytosis Promote Mucosal Wound Healing in Inflammatory Bowel Disease

Resolvin E1 improves efferocytosis and rescues severe aplastic anemia in mice

Severe aplastic anemia (SAA) is a rare, fatal disease characterized by severe cytopenias and loss of hematopoietic stem cells (HSCs). Immune-mediated destruction and inflammation are known drivers of SAA, however, the underlying mechanisms driving persistent inflammation are unknown. Current treatments for SAA rely on immunosuppressive therapies or HSC transplantation, however, these treatments are not always effective. Using an established mouse model of SAA, we observed a significant increase in apoptotic cells within the bone marrow (BM) and impaired efferocytosis in SAA mice, relative to radiation controls. Single-cell transcriptomic analysis revealed heterogeneity among BM monocytes and unique populations emerged during SAA characterized by increased inflammatory signatures and significantly increased expression of Sirpa and Cd47. CD47, a "don't eat me" signal, was increased on both live and apoptotic BM cells, concurrent with markedly increased expression of signal regulatory protein alpha (SIRPα) on monocytes. Functionally, SIRPα blockade improved cell clearance and reduced accumulation of CD47-positive apoptotic cells. Lipidomic analysis revealed a reduction in the precursors of specialized pro-resolving lipid mediators (SPMs) and increased prostaglandins in the BM during SAA, indicative of impaired inflammation resolution. Specifically, 18-HEPE, a precursor of E-series resolvins, was significantly reduced in SAA-induced mice relative to radiation controls. Treatment of SAA mice with Resolvin E1 (RvE1) improved efferocytic function, BM cellularity, platelet output, and survival. Our data suggest that impaired efferocytosis and inflammation resolution contributes to SAA progression and demonstrate that SPMs, such as RvE1, offer new and/or complementary treatments for SAA that do not rely on immune suppression.

Efferocytosis by macrophages in physiological and pathological conditions: regulatory pathways and molecular mechanisms

Efferocytosis is defined as the highly effective phagocytic removal of apoptotic cells (ACs) by professional or non-professional phagocytes. Tissue-resident professional phagocytes ("efferocytes"), such as macrophages, have high phagocytic capacity and are crucial to resolve inflammation and aid in homeostasis. Recently, numerous exciting discoveries have revealed divergent (and even diametrically opposite) findings regarding metabolic immune reprogramming associated with efferocytosis by macrophages. In this review, we highlight the key metabolites involved in the three phases of efferocytosis and immune reprogramming of macrophages under physiological and pathological conditions. The next decade is expected to yield further breakthroughs in the regulatory pathways and molecular mechanisms connecting immunological outcomes to metabolic cues as well as avenues for "personalized" therapeutic intervention.

Macrophage and Neutrophil Dysregulation in Diabetic Wounds

SIGNIFICANCE

The incidence of diabetes continues to rise throughout the world in an alarming rate. Diabetic patients often develop diabetic foot ulcers (DFUs), many of which do not heal. Non-healing DFUs are a major cause of hospitalization, amputation, and increased morbidity. Understanding the underlying mechanisms of impaired healing in DFU is crucial for its management.

RECENT ADVANCES

This review focuses on the recent advancements in macrophage and neutrophils in diabetic wounds and DFUs. In particular, we will discuss diabetes-induced dysregulations and dysfunctions of macrophage and neutrophil functions.

CRITICAL ISSUES

It is well established that diabetic wounds are characterized by stalled inflammation that results in impaired healing. Recent findings in the field suggest that dysregulation of macrophages and neutrophils play a critical role in impaired healing in DFUs. The delineation of mechanisms that restore macrophage and neutrophil function in diabetic wound healing is the focus of intense investigation.

FUTURE DIRECTIONS

The breadth of recently generated knowledge on the activity of macrophages and neutrophils in diabetic wound healing is impressive. Experimental models have delineated pathways that hold promise for the treatment of diabetic wounds and DFUs. These pathways may be useful targets for further clinical investigation.

Efferocytosis: Current status and future prospects in the treatment of autoimmune diseases

Billions of apoptotic cells are swiftly removed from the human body daily. This clearance process is regulated by efferocytosis, an active anti-inflammatory process during which phagocytes engulf and remove apoptotic cells. However, impaired clearance of apoptotic cells is associated with the development of various autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, and inflammatory bowel disease. In this review, we conducted a comprehensive search of relevant studies published from January 1, 2000, to the present, focusing on efferocytosis, autoimmune disease pathogenesis, regulatory mechanisms governing efferocytosis, and potential treatments targeting this process. Our review highlights the key molecules involved in different stages of efferocytosis-namely, the "find me," "eat me," and "engulf and digest" phases-while elucidating their relevance to autoimmune disease pathology. Furthermore, we explore the therapeutic potential of modulating efferocytosis to restore immune homeostasis and mitigate autoimmune responses. By providing theoretical underpinnings for the targeting of efferocytosis in the treatment of autoimmune diseases, this review contributes to the advancement of therapeutic strategies in this field.

Harnessing anti-inflammatory pathways and macrophage nano delivery to treat inflammatory and fibrotic disorders

Targeting specific organs and cell types using nanotechnology and sophisticated delivery methods has been at the forefront of applicative biomedical sciences lately. Macrophages are an appealing target for immunomodulation by nanodelivery as they are heavily involved in various aspects of many diseases and are highly plastic in their nature. Their continuum of functional "polarization" states has been a research focus for many years yielding a profound understanding of various aspects of these cells. The ability of monocyte-derived macrophages to metamorphose from pro-inflammatory to reparative and consequently to pro-resolving effectors has raised significant interest in its therapeutic potential. Here, we briefly survey macrophages' ontogeny and various polarization phenotypes, highlighting their function in the inflammation-resolution shift. We review their inducing mediators, signaling pathways, and biological programs with emphasis on the nucleic acid sensing-IFN-I axis. We also portray the polarization spectrum of macrophages and the characteristics of their transition between different subtypes. Finally, we highlighted different current drug delivery methods for targeting macrophages with emphasis on nanotargeting that might lead to breakthroughs in the treatment of wound healing, bone regeneration, autoimmune, and fibrotic diseases.

Intestinal macrophages in pathogenesis and treatment of gut leakage: current strategies and future perspectives

Macrophages play key roles in tissue homeostasis, defense, disease, and repair. Macrophages are highly plastic and exhibit distinct functional phenotypes based on micro-environmental stimuli. In spite of several advancements in understanding macrophage biology and their different functional phenotypes in various physiological and pathological conditions, currently available treatment strategies targeting macrophages are limited. Macrophages' high plasticity and diverse functional roles-including tissue injury and wound healing mechanisms-mark them as potential targets to mine for efficient therapeutics to treat diseases. Despite mounting evidence on association of gut leakage with several extraintestinal diseases, there is no targeted standard therapy to treat gut leakage. Therefore, there is an urgent need to develop therapeutic strategies to treat this condition. Macrophages are the cells that play the largest role in interacting with the gut microbiota in the intestinal compartment and exert their intended functions in injury and repair mechanisms. In this review, we have summarized the current knowledge on the origins and phenotypes of macrophages. The specific role of macrophages in intestinal barrier function, their role in tissue repair mechanisms, and their association with gut microbiota are discussed. In addition, currently available therapies and the putative tissue repair mediators of macrophages for treating microbiota dysbiosis induced gut leakage are also discussed. The overall aim of this review is to convey the intense need to screen for microbiota induced macrophage-released prorepair mediators, which could lead to the identification of potential candidates that could be developed for treating the leaky gut and associated diseases.

Scaffold Adhering to Peptide-Based Biomimetic Extracellular Matrix Composite Nanobioglass Promotes the Proliferation and Migration of Skin Fibroblasts Through the GSK-3β/β-Catenin Signaling Axis

Introduction

Nano-mesoporous bioactive glass and RGD peptide-coated collagen membranes have great potential in wound healing. However, the application of their compound has not been further studied. Our purpose is to prepare a novel bioactive collagen scaffold containing both NMBG stent and adhesion peptides (BM), which then proves its promising prospect the assessment of physical properties, biocompatibility, GSK-3β/β-catenin signaling axis and toxicological effects.

Methods

The structural and morphological changes of BM were analyzed using scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). In vivo, wound healing of BM was assessed in SD rats through dynamic monitoring and calculation of wound healing rate. Immunohistofluorescence (IHF), H&E, and Masson staining were utilized; in vitro, primary cell culture, and a variety of assays including CCK-8, Transwell, Scratch, Immunocytofluorescence (ICF), and Western blot (WB) were performed, both for morphology and molecular analysis.

Results and Discussion

Preparation of BM involved attaching NMBG to RGD-exposed collagen while avoiding the use of toxic chemical reagents. BM exhibited a distinctive superficial morphology with increased Si content, indicating successful NMBG attachment. In vivo studies on SD rats demonstrated the superior wound healing capability of BM, as evidenced by accelerated wound closure, thicker epithelial layers, and enhanced collagen deposition compared to the NC group. Additionally, BM promoted skin fibroblast migration and proliferation, possibly through activation of the GSK-3β/β-catenin signaling axis, which was crucial for tissue regeneration. This study underscored the potential of BM as an effective wound-healing dressing.

Conclusion

A new method for synthesizing ECM-like membranes has been developed using nano-mesoporous bioactive glass and collagen-derived peptides. This approach enhances the bioactivity of biomaterials through surface functionalization and growth factor-free therapy.

Osteopathic manipulative treatment for chronic inflammatory diseases

Chronic inflammatory diseases (CIDs) are debilitating and potentially lethal illnesses that affect a large proportion of the global population. Osteopathic manipulative treatment (OMT) is a manual therapy technique developed and performed by osteopathic physicians that facilitates the body's innate healing processes. Therefore, OMT may prove a beneficial anti-inflammatory modality useful in the management and treatment of CIDs. This work aims to objectively evaluate the therapeutic benefits of OMT in patients with various CIDs. In this review, a structured literature search was performed. The included studies involving asthma, chronic obstructive pulmonary disease, irritable bowel syndrome, ankylosing spondylitis, and peripheral arterial disease were selected for this work. Various OMT modalities, including lymphatic, still, counterstain, and muscle energy techniques, were utilized. Control treatments included sham techniques, routine care, or no treatment. OMT utilization led to variable patient outcomes in individuals with pathologies linked to CID.

Role reversals: non-canonical roles for immune and non-immune cells in the gut

The intestine is home to an intertwined network of epithelial, immune, and neuronal cells as well as the microbiome, with implications for immunity, systemic metabolism, and behavior. While the complexity of this microenvironment has long since been acknowledged, recent technological advances have propelled our understanding to an unprecedented level. Notably, the microbiota and non-immune or structural cells have emerged as important conductors of intestinal immunity, and by contrast, cells of both the innate and adaptive immune systems have demonstrated non-canonical roles in tissue repair and metabolism. This review highlights recent works in the following two streams: non-immune cells of the intestine performing immunological functions; and traditional immune cells exhibiting non-immune functions in the gut.

Macrophage-based therapeutic approaches for cardiovascular diseases

Despite the advances in treatment options, cardiovascular disease (CVDs) remains the leading cause of death over the world. Chronic inflammatory response and irreversible fibrosis are the main underlying pathophysiological causes of progression of CVDs. In recent decades, cardiac macrophages have been recognized as main regulatory players in the development of these complex pathophysiological conditions. Numerous approaches aimed at macrophages have been devised, leading to novel prospects for therapeutic interventions. Our review covers the advancements in macrophage-centric treatment plans for various pathologic conditions and examines the potential consequences and obstacles of employing macrophage-targeted techniques in cardiac diseases.

Stromal Cell Regulation of Intestinal Inflammatory Fibrosis

Intestinal inflammatory fibrosis is a severe consequence of inflammatory bowel diseases (IBDs). There is currently no cure for the treatment of intestinal fibrosis in IBD. Although inflammation is necessary for triggering fibrosis, the anti-inflammatory agents used to treat IBD are ineffective in preventing the progression of intestinal fibrosis and stricture formation once initiated, suggesting that inflammatory signals are not the sole drivers of fibrosis progression once it is established. Among multiple mechanisms involved in the initiation and progression of intestinal fibrosis in IBD, stromal cells play critical roles in mediating the process. In this review, we summarize recent progress on how stromal cells regulate intestinal fibrosis in IBD and how they are regulated by focusing on immune regulation and gut microbiota. We also outline the challenges moving forward in the field.

Amelioration of experimental autoimmune encephalomyelitis by in vivo reprogramming of macrophages using pro-resolving factors

BACKGROUND

Reinstating inflammation resolution represents an innovative concept to regain inflammation control in diseases marked by chronic inflammation. While most therapeutics target inflammatory molecules and inflammatory effector cells and mediators, targeting macrophages to initiate inflammation resolution to control neuroinflammation has not yet been attempted. Resolution-phase macrophages are critical in the resolution process to regain tissue homeostasis, and are programmed through the presence and elimination of apoptotic leukocytes. Hence, inducing resolution-phase macrophages might represent an innovative therapeutic approach to control and terminate dysregulated neuroinflammation.

METHODS

Here, we investigated if the factors released by in vitro induced resolution-phase macrophages (their secretome) are able to therapeutically reprogram macrophages to control neuroinflammation in the model of experimental autoimmune encephalomyelitis (EAE).

RESULTS

We found that injection of the pro-resolutive secretome reduced demyelination and decreased inflammatory cell infiltration in the CNS, notably through the in vivo reprogramming of macrophages at the epigenetic level. Adoptive transfer experiments with in vivo or in vitro reprogrammed macrophages using such pro-resolutive secretome confirmed the stability and transferability of this acquired therapeutic activity.

CONCLUSIONS

Overall, our data confirm the therapeutic activity of a pro-resolution secretome in the treatment of ongoing CNS inflammation, via the epigenetic reprogramming of macrophages and open with that a new therapeutic avenue for diseases marked by neuroinflammation.

Role of glycolysis in inflammatory bowel disease and its associated colorectal cancer

Inflammatory bowel disease (IBD) has been referred to as the "green cancer," and its progression to colorectal cancer (CRC) poses a significant challenge for the medical community. A common factor in their development is glycolysis, a crucial metabolic mechanism of living organisms, which is also involved in other diseases. In IBD, glycolysis affects gastrointestinal components such as the intestinal microbiota, mucosal barrier function, and the immune system, including macrophages, dendritic cells, T cells, and neutrophils, while in CRC, it is linked to various pathways, such as phosphatidylinositol-3-kinase (PI3K)/AKT, AMP-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), and transcription factors such as p53, Hypoxia-inducible factor (HIF), and c-Myc. Thus, a comprehensive study of glycolysis is essential for a better understanding of the pathogenesis and therapeutic targets of both IBD and CRC. This paper reviews the role of glycolysis in diseases, particularly IBD and CRC, via its effects on the intestinal microbiota, immunity, barrier integrity, signaling pathways, transcription factors and some therapeutic strategies targeting glycolytic enzymes.

Human breast milk: A promising treatment for necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a severe gastrointestinal disorder occurring in newborns, with a mortality rate ranging from 20 % to 30 %. The existing therapeutic approaches for NEC are limited in their effectiveness. Various factors contribute to the development of NEC, including disruption of barrier function, dysregulation of the intestinal immune system, and abnormal colonization of the intestinal microbiota. Researchers have shown considerable interest in exploring the therapeutic potential of the constituents present in human breast milk (HBM) for treating NEC. HBM contains numerous bioactive components, such as exosomes, growth factors, and oligosaccharides. However, the precise mechanisms by which HBM exerts its protective effects against NEC remain incompletely understood. In this study, our objective was to comprehensively review the bioactive substances present in HBM, aiming to facilitate the development of novel therapeutic strategies for NEC.

Interaction Between Blood Vasculatures and Lymphatic Vasculatures During Inflammation

Physiological activity cannot be regulated without the blood and lymphatic vasculatures, which play complementary roles in maintaining the body's homeostasis and immune responses. Inflammation is the body's initial response to pathological injury and is responsible for protecting the body, removing damaged tissues, and restoring and maintaining homeostasis in the body. A growing number of researches have shown that blood and lymphatic vessels play an essential role in a variety of inflammatory diseases. In the inflammatory state, the permeability of blood vessels and lymphatic vessels is altered, and angiogenesis and lymphangiogenesis subsequently occur. The blood vascular and lymphatic vascular systems interact to determine the development or resolution of inflammation. In this review, we discuss the changes that occur in the blood vascular and lymphatic vascular systems of several organs during inflammation, describe the different scenarios of angiogenesis and lymphangiogenesis at different sites of inflammation, and demonstrate the prospect of targeting the blood vasculature and lymphatic vasculature systems to limit the development of inflammation and promote the resolution of inflammation in inflammatory diseases.

Resolvin E1 improves efferocytosis and rescues severe aplastic anemia in mice

Current treatments for severe aplastic anemia (SAA) rely on hematopoietic stem cell (HSC) transplantation and immunosuppressive therapies, however these treatments are not always effective. While immune-mediated destruction and inflammation are known drivers of SAA, the underlying mechanisms that lead to persistent inflammation are unknown. Using an established mouse model of SAA, we observed a significant increase in apoptotic cells within the bone marrow (BM) and demonstrate impaired efferocytosis in SAA mice, as compared to radiation controls. Single-cell transcriptomic analysis revealed heterogeneity among BM monocytes and unique populations emerged during SAA characterized by increased inflammatory signatures and significantly increased expression of Sirpa and Cd47. CD47, a "don't eat me" signal, was increased on both live and apoptotic BM cells, concurrent with markedly increased expression of signal regulatory protein alpha (SIRPα) on monocytes. Functionally, SIRPα blockade improved cell clearance and reduced accumulation of CD47-positive apoptotic cells. Lipidomic analysis revealed a reduction in the precursors of specialized pro-resolving lipid mediators (SPMs) and increased prostaglandins in the BM during SAA, indicative of impaired inflammation resolution. Specifically, 18-HEPE, a precursor of E-series resolvins, was significantly reduced in SAA-induced mice relative to radiation controls. Treatment of SAA mice with Resolvin E1 (RvE1) improved efferocytic function, BM cellularity, platelet output, and survival. Our data suggest that impaired efferocytosis and inflammation resolution contributes to SAA progression and demonstrate that SPMs, such as RvE1, offer new and/or complementary treatments for SAA that do not rely on immune suppression.

Efferocytes release extracellular vesicles to resolve inflammation and tissue injury via prosaposin-GPR37 signaling

Macrophages release soluble mediators following efferocytic clearance of apoptotic cells to facilitate intercellular communication and promote the resolution of inflammation. However, whether inflammation resolution is modulated by extracellular vesicles (EVs) and vesicular mediators released by efferocytes is not known. We report that efferocyte-derived EVs express prosaposin, which binds to macrophage GPR37 to increase expression of the efferocytosis receptor Tim4 via an ERK-AP1-dependent signaling axis, leading to increased macrophage efferocytosis efficiency and accelerated resolution of inflammation. Neutralization and knockdown of prosaposin or blocking GRP37 abrogates the pro-resolution effects of efferocyte-derived EVs in vivo. Administration of efferocyte-derived EVs in a murine model of atherosclerosis is associated with an increase in lesional macrophage efferocytosis efficiency and a decrease in plaque necrosis and lesional inflammation. Thus, we establish a critical role for efferocyte-derived vesicular mediators in increasing macrophage efferocytosis efficiency and accelerating the resolution of inflammation and tissue injury.

Involvement of Abnormal p-α-syn Accumulation and TLR2-Mediated Inflammation of Schwann Cells in Enteric Autonomic Nerve Dysfunction of Parkinson's Disease: an Animal Model Study

The study was designed to investigate the pathogenesis of gastrointestinal (GI) impairment in Parkinson's disease (PD). We utilized 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 20 mg/kg) and probenecid (250 mg/kg) to prepare a PD mice model. MPTP modeling was first confirmed. GI motility was measured using stool collection test and enteric plexus loss was also detected. Intestinal phosphorylated α-synuclein (p-α-syn), inflammation, and S100 were assessed using western blotting. Association between Toll-like receptor 2(TLR2) and GI function was validated by Pearson's correlations. Immunofluorescence was applied to show co-localizations of intestinal p-α-syn, inflammation, and Schwann cells (SCs). CU-CPT22 (3 mg/kg, a TLR1/TLR2 inhibitor) was adopted then. Success in modeling, damaged GI neuron and function, and activated intestinal p-α-syn, inflammation, and SCs responses were observed in MPTP group, with TLR2 related to GI damage. Increased p-α-syn and inflammatory factors were shown in SCs of myenteron for MPTP mice. Recovered fecal water content and depression of inflammation, p-α-syn deposition, and SCs activity were noticed after TLR2 suppression. The study investigates a novel mechanism of PD GI autonomic dysfunction, demonstrating that p-α-syn accumulation and TLR2 signaling of SCs were involved in disrupted gut homeostasis and treatments targeting TLR2-mediated pathway might be a possible therapy for PD.

The Impact of Phase-Specific Macrophage Depletion on Intestinal Anastomotic Healing

Intestinal anastomotic healing (AH) is critical in colorectal surgery, since disruptive AH leads to anastomotic leakage, a feared postoperative complication. Macrophages are innate immune cells and are instrumental in orchestrating intestinal wound healing, displaying a functional dichotomy as effectors of both tissue injury and repair. The aim of this study was to investigate the phase-specific function and plasticity of macrophages during intestinal AH. Transgenic CD11b diphtheria toxin receptor (CD11b-DTR) mice were used to deplete intestinal macrophages in a temporally controlled manner. Distal colonic end-to-end anastomoses were created in CD11b-DTR, and wild-type mice and macrophages were selectively depleted during either the inflammatory (day 0–3), proliferative (day 4–10), or reparative (day 11–20) phase of intestinal AH, respectively. For each time point, histological and functional analysis as well as gene set enrichment analysis (GSEA) of RNA-sequencing data were performed. Macrophage depletion during the inflammatory phase significantly reduced the associated inflammatory state without compromising microscopic AH. When intestinal macrophages were depleted during the proliferative phase, AH was improved, despite significantly reduced perianastomotic neoangiogenesis. Lastly, macrophages were depleted during the reparative phase and GSEA revealed macrophage-dependent pathways involved in collagen remodeling, cell proliferation, and extracellular matrix composition. However, AH remained comparable at this late timepoint. These results demonstrate that during intestinal AH, macrophages elicit phase-specific effects, and that therapeutic interventions must critically balance their dual and timely defined role.

HIF-1α-Overexpressing Mesenchymal Stem Cells Attenuate Colitis by Regulating M1-like Macrophages Polarization toward M2-like Macrophages

A modified mesenchymal stem cell (MSC) transplantation is a highly effective and precise treatment for inflammatory bowel disease (IBD), with a significant curative effect. Thus, we aim to examine the efficacy of hypoxia-inducible factor (HIF)–1α-overexpressing MSC (HIF-MSC) transplantation in experimental colitis and investigate the immunity regulation mechanisms of HIF-MSC through macrophages. A chronic experimental colitis mouse model was established using 2,4,6-trinitrobenzene sulfonic acid. HIF-MSC transplantation significantly attenuated colitis in weight loss rate, disease activity index (DAI), colon length, and pathology score and effectively rebuilt the local and systemic immune balance. Macrophage depletion significantly impaired the benefits of HIF-MSCs on mice with colitis. Immunofluorescence analysis revealed that HIF-MSCs significantly decreased the number of M1-like macrophages and increased the number of M2-like macrophages in colon tissues. In vitro, co-culturing with HIF-MSCs significantly decreased the expression of pro-inflammatory factors, C-C chemokine receptor 7 (CCR-7), and inducible nitric oxide synthase (INOS) and increased the expression of anti-inflammatory factors and arginase I (Arg-1) in induced M1-like macrophages. Flow cytometry revealed that co-culturing with HIF-MSCs led to a decrease in the proportions of M1-like macrophages and an increase in that of M2-like macrophages. HIF-MSCs treatment notably upregulated the expression of downstream molecular targets of phosphatidylinositol 3-kinase-γ (PI3K-γ), including HIF-1α and p-AKT/AKT in the colon tissue. A selected PI3K-γ inhibitor, IPI549, attenuated these effects, as well as the effect on M2-like macrophage polarization and inflammatory cytokines in colitis mice. In vitro, HIF-MSCs notably upregulated the expression of C/EBPβ and AKT1/AKT2, and PI3K-γ inhibition blocked this effect. Modified MSCs stably overexpressed HIF-1α, which effectively regulated macrophage polarization through PI3K-γ. HIF-MSC transplantation may be a potentially effective precision therapy for IBD.

Mucosal healing and inflammatory bowel disease: Therapeutic implications and new targets

Mucosal healing (MH) is vital in maintaining homeostasis within the gut and protecting against injury and infections. Multiple factors and signaling pathways contribute in a dynamic and coordinated manner to maintain intestinal homeostasis and mucosal regeneration/repair. However, when intestinal homeostasis becomes chronically disturbed and an inflammatory immune response is constitutively active due to impairment of the intestinal epithelial barrier autoimmune disease results, particularly inflammatory bowel disease (IBD). Many proteins and signaling pathways become dysregulated or impaired during these pathological conditions, with the mechanisms of regulation just beginning to be understood. Consequently, there remains a relative lack of broadly effective therapeutics that can restore MH due to the complexity of both the disease and healing processes, so tissue damage in the gastrointestinal tract of patients, even those in clinical remission, persists. With increased understanding of the molecular mechanisms of IBD and MH, tissue damage from autoimmune disease may in the future be ameliorated by developing therapeutics that enhance the body’s own healing response. In this review, we introduce the concept of mucosal healing and its relevance in IBD as well as discuss the mechanisms of IBD and potential strategies for altering these processes and inducing MH.

Cellular mechanisms underlying the impairment of macrophage efferocytosis

The phagocytosis and clearance of dying cells by macrophages, a process termed efferocytosis, is essential for both maintaining homeostasis and promoting tissue repair after infection or sterile injury. If not removed in a timely manner, uncleared cells can undergo secondary necrosis, and necrotic cells lose membrane integrity, release toxic intracellular components, and potentially induce inflammation or autoimmune diseases. Efferocytosis also initiates the repair process by producing a wide range of pro-reparative factors. Accumulating evidence has revealed that macrophage efferocytosis defects are involved in the development and progression of a variety of inflammatory and autoimmune diseases. The underlying mechanisms of efferocytosis impairment are complex, disease-dependent, and incompletely understood. In this review, we will first summarize the current knowledge about the normal signaling and metabolic processes of macrophage efferocytosis and its importance in maintaining tissue homeostasis and repair. We then will focus on analyzing the molecular and cellular mechanisms underlying efferocytotic abnormality (impairment) in disease or injury conditions. Next, we will discuss the potential molecular targets for enhanced efferocytosis in animal models of disease. To provide a balanced view, we will also discuss some deleterious effects of efferocytosis.

Melanocortin therapies to resolve fibroblast-mediated diseases

Stromal cells have emerged as central drivers in multiple and diverse diseases, and consequently, as potential new cellular targets for the development of novel therapeutic strategies. In this review we revise the main roles of fibroblasts, not only as structural cells but also as players and regulators of immune responses. Important aspects like fibroblast heterogeneity, functional specialization and cellular plasticity are also discussed as well as the implications that these aspects may have in disease and in the design of novel therapeutics. An extensive revision of the actions of fibroblasts on different conditions uncovers the existence of numerous diseases in which this cell type plays a pathogenic role, either due to an exacerbation of their 'structural' side, or a dysregulation of their 'immune side'. In both cases, opportunities for the development of innovative therapeutic approaches exist. In this regard, here we revise the existing evidence pointing at the melanocortin pathway as a potential new strategy for the treatment and management of diseases mediated by aberrantly activated fibroblasts, including scleroderma or rheumatoid arthritis. This evidence derives from studies involving models of in vitro primary fibroblasts, in vivo models of disease as well as ongoing human clinical trials. Melanocortin drugs, which are pro-resolving mediators, have shown ability to reduce collagen deposition, activation of myofibroblasts, reduction of pro-inflammatory mediators and reduced scar formation. Here we also discuss existing challenges, both in approaching fibroblasts as therapeutic targets, and in the development of novel melanocortin drug candidates, that may help advance the field and deliver new medicines for the management of diseases with high medical needs.

Targeting macrophage autophagy for inflammation resolution and tissue repair in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic, non-specific, recurrent inflammatory disease, majorly affecting the gastrointestinal tract. Due to its unclear pathogenesis, the current therapeutic strategy for IBD is focused on symptoms alleviation. Autophagy is a lysosome-mediated catabolic process for maintaining cellular homeostasis. Genome-wide association studies and subsequent functional studies have highlighted the critical role of autophagy in IBD via a number of mechanisms, including modulating macrophage function. Macrophages are the gatekeepers of intestinal immune homeostasis, especially involved in regulating inflammation remission and tissue repair. Interestingly, many autophagic proteins and IBD-related genes have been revealed to regulate macrophage function, suggesting that macrophage autophagy is a potentially important process implicated in IBD regulation. Here, we have summarized current understanding of macrophage autophagy function in pathogen and apoptotic cell clearance, inflammation remission and tissue repair regulation in IBD, and discuss how this knowledge can be used as a strategy for IBD treatment.

IFN-γ and TGF-β, Crucial Players in Immune Responses: A Tribute to Howard Young

Interferon gamma (IFN-γ) and transforming growth factor beta (TGF-β), both pleiotropic cytokines, have been long studied and described as critical mediators of the immune response, notably in T cells. One of the investigators who made seminal and critical discoveries in the field of IFN-γ biology is Dr. Howard Young. In this review, we provide an overview of the biology of IFN-γ as well as its role in cancer and autoimmunity with an emphasis on Dr. Young's critical work in the field. We also describe how Dr. Young's work influenced our own research studying the role of TGF-β in the modulation of immune responses.

Long COVID and the Neuroendocrinology of Microbial Translocation Outside the GI Tract: Some Treatment Strategies

Similar to previous pandemics, COVID-19 has been succeeded by well-documented post-infectious sequelae, including chronic fatigue, cough, shortness of breath, myalgia, and concentration difficulties, which may last 5 to 12 weeks or longer after the acute phase of illness. Both the psychological stress of SARS-CoV-2 infection and being diagnosed with COVID-19 can upregulate cortisol, a stress hormone that disrupts the efferocytosis effectors, macrophages, and natural killer cells, leading to the excessive accumulation of senescent cells and disruption of biological barriers. This has been well-established in cancer patients who often experience unrelenting fatigue as well as gut and blood–brain barrier dysfunction upon treatment with senescence-inducing radiation or chemotherapy. In our previous research from 2020 and 2021, we linked COVID-19 to myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) via angiotensin II upregulation, premature endothelial senescence, intestinal barrier dysfunction, and microbial translocation from the gastrointestinal tract into the systemic circulation. In 2021 and 2022, these hypotheses were validated and SARS-CoV-2-induced cellular senescence as well as microbial translocation were documented in both acute SARS-CoV-2 infection, long COVID, and ME/CFS, connecting intestinal barrier dysfunction to disabling fatigue and specific infectious events. The purpose of this narrative review is to summarize what is currently known about host immune responses to translocated gut microbes and how these responses relate to fatiguing illnesses, including long COVID. To accomplish this goal, we examine the role of intestinal and blood–brain barriers in long COVID and other illnesses typified by chronic fatigue, with a special emphasis on commensal microbes functioning as viral reservoirs. Furthermore, we discuss the role of SARS-CoV-2/Mycoplasma coinfection in dysfunctional efferocytosis, emphasizing some potential novel treatment strategies, including the use of senotherapeutic drugs, HMGB1 inhibitors, Toll-like receptor 4 (TLR4) blockers, and membrane lipid replacement.

Resolution therapy: Harnessing efferocytic macrophages to trigger the resolution of inflammation

Several chronic inflammatory diseases are associated with non-resolving inflammation. Conventional anti-inflammatory drugs fail to completely cure these diseases. Resolution pharmacology is a new therapeutic approach based on the use of pro-resolving mediators that accelerate the resolution phase of inflammation by targeting the productive phase of inflammation. Indeed, pro-resolving mediators prevent leukocyte recruitment and induce apoptosis of accumulated leukocytes. This approach is now called resolution therapy with the introduction of complex biological drugs and cell-based therapies. The main objective of resolution therapy is to specifically reduce the duration of the resolution phase to accelerate the return to homeostasis. Under physiological conditions, macrophages play a critical role in the resolution of inflammation. Indeed, after the removal of apoptotic cells (a process called efferocytosis), macrophages display anti-inflammatory reprogramming and subsequently secrete multiple pro-resolving factors. These factors can be used as resolution therapy. Here, we review the different mechanisms leading to anti-inflammatory reprogramming of macrophages after efferocytosis and the pro-resolving factors released by these efferocytic macrophages. We classify these mechanisms in three different categories: macrophage reprogramming induced by apoptotic cell-derived factors, by molecules expressed by apoptotic cells (i.e., "eat-me" signals), and induced by the digestion of apoptotic cell-derived materials. We also evoke that macrophage reprogramming may result from cooperative mechanisms, for instance, implicating the apoptotic cell-induced microenvironment (including cellular metabolites, specific cytokines or immune cells). Then, we describe a new drug candidate belonging to this resolution therapy. This candidate, called SuperMApo, corresponds to the secretome of efferocytic macrophages. We discuss its production, the pro-resolving factors present in this drug, as well as the results obtained in experimental models of chronic (e.g., arthritis, colitis) and acute (e.g., peritonitis or xenogeneic graft-versus-host disease) inflammatory diseases.

Mechanisms of efferocytosis in determining inflammation resolution: Therapeutic potential and the association with cardiovascular disease

Efferocytosis is defined as the clearance of apoptotic cells (ACs) in physiological and pathological states and is performed by efferocytes, such as macrophages. Efferocytosis can lead to the resolution of inflammation and restore tissue homoeostasis; however, the mechanisms of efferocytosis in determining inflammation resolution are still not completely understood, and the effects of efferocytosis on other proresolving properties need to be explored and explained. In this review, the process of efferocytosis will be summarized briefly, and then these mechanisms and effects will be thoroughly discussed. In addition, the association between the mechanisms of efferocytosis in determining inflammation resolution and cardiovascular diseases will also be reviewed, as an understanding of this association may provide information on novel treatment targets.

Glucocorticoid-Induced Leucine Zipper Alleviates Lung Inflammation and Enhances Bacterial Clearance During Pneumococcal Pneumonia

Pneumonia is a leading cause of morbidity and mortality. While inflammation is a host protective response that ensures bacterial clearance, a finely regulated response is necessary to prevent bystander tissue damage. Glucocorticoid (GC)-induced leucine zipper (GILZ) is a GC-induced protein with anti-inflammatory and proresolving bioactions, yet the therapeutical role of GILZ in infectious diseases remains unexplored. Herein, we investigate the role and effects of GILZ during acute lung injury (ALI) induced by LPS and Streptococcus pneumoniae infection. GILZ deficient mice (GILZ^−/−) presented more severe ALI, characterized by increased inflammation, decreased macrophage efferocytosis and pronounced lung damage. In contrast, pulmonary inflammation, and damage were attenuated in WT mice treated with TAT-GILZ fusion protein. During pneumococcal pneumonia, TAT-GILZ reduced neutrophilic inflammation and prevented the associated lung damage. There was also enhanced macrophage efferocytosis and bacterial clearance in TAT-GILZ-treated mice. Mechanistically, TAT-GILZ enhanced macrophage phagocytosis of pneumococcus, which was lower in GILZ^−/− macrophages. Noteworthy, early treatment with TAT-GILZ rescued 30% of S. pneumoniae-infected mice from lethal pneumonia. Altogether, we present evidence that TAT-GILZ enhances host resilience and resistance to pneumococcal pneumonia by controlling pulmonary inflammation and bacterial loads leading to decreased lethality. Exploiting GILZ pathways holds promise for the treatment of severe respiratory infections.