Primordial GATA6 macrophages function as extravascular platelets in sterile injury

HuoXueTongFu formula induces M2c macrophages via the MerTK/PI3K/AKT pathway to eliminate NETs in intraperitoneal adhesion in mice

ETHNOPHARMACOLOGICAL RELEVANCE

HuoXueTongFu Formula (HXTF) is a traditional Chinese herbal formula that has been used as a supplement and alternative therapy for intraperitoneal adhesion (IA). However, its specific mechanism of action has not been fully understood.

AIM OF THE STUDY

In surgery, IA presents an inevitable challenge, significantly impacting patients' physical and mental well-being and increasing the financial burden. Our previous research has confirmed the preventive effects of HXTF on IA formation. However, the precise mechanism of its action still needs to be understood.

METHODS

In this study, the IA model was successfully established by using the Ischemic buttons and treated with HXTF for one week with or without Mer Tyrosine Kinase (MerTK) inhibitor. We evaluated the pharmacodynamic effect of HXTF on IA mice. The MerTK/phosphoinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway-associated proteins were detected by Western blotting. Neutrophil extracellular traps (NETs) were detected by immunofluorescence. Macrophage phenotype was assessed by immunohistochemistry and flow cytometry. Inflammatory cytokines were detected by Real Time Quantitative PCR and Western blotting.

RESULTS

HXTF reduced inflammatory response and alleviated IA. HXTF significantly enhanced MerTK expression, increased the number of M2c macrophages, and decreased the formation of NETs. In addition, the MerTK/PI3K/AKT pathway was significantly activated by HXTF. However, after using MerTK inhibitors, the role of HXTF in inducing M2c macrophage through activation of the PI3K/AKT pathway was suppressed and there was no inhibitory effect on NETs formation and inflammatory responses, resulting in diminished inhibition of adhesion.

CONCLUSION

HXTF may improve IA by activating the MerTK/PI3K/AKT pathway to induce M2c polarization, which removes excess NETs and attenuates the inflammatory response.

Intravital imaging: dynamic insights into liver immunity in health and disease

Inflammation is a critical component of most acute and chronic liver diseases. The liver is a unique immunological organ with a dense vascular network, leading to intense crosstalk between tissue-resident immune cells, passenger leucocytes and parenchymal cells. During acute and chronic liver diseases, the multifaceted immune response is involved in disease promoting and repair mechanisms, while upholding core liver immune functions. In recent years, single-cell technologies have unravelled a previously unknown heterogeneity of immune cells, reshaping the complexity of the hepatic immune response. However, inflammation is a dynamic biological process, encompassing various immune cells, orchestrated in temporal and spatial dimensions, and driven by multiorgan signals. Intravital microscopy (IVM) has emerged as a powerful tool to investigate immunity by visualising the dynamic interplay between different immune cells and their surroundings within a near-natural environment. In this review, we summarise the experimental considerations to perform IVM and highlight recent technological developments. Furthermore, we outline the unique contributions of IVM to our understanding of liver immunity. Through the lens of liver disease, we discuss novel immune-mediated disease mechanisms uncovered by imaging-based studies.

A ROS-responsive and scavenging hydrogel for postoperative abdominal adhesion prevention

Postoperative abdominal adhesion (PAA) widely occurs after abdominal surgery, which often produces severe complications. However, there were still no satisfactory anti-adhesive products including barriers and anti-adhesive agents. Herein, we developed a ROS-responsive and scavenging hydrogel barrier, termed AHBC/PSC, wherein the monomer AHBC was synthesized by phenylboronic acid (PBA)-modified hyaluronic acid (HA-PBA) further grafted with adipic dihydrazide (ADH) and PBA-based chlorogenic acid (CGA) via ROS-sensitive borate ester bond, and the other monomer PSC was constructed by polyvinyl alcohol (PVA) grafted with sulfated betaine (SB) and p-hydroxybenzaldehyde (CHO). Further, the double crosslinked AHBC/PSC hydrogel was successfully fabricated between AHBC and PSC via forming dynamic covalent acylhydrazone bonds and borate ester bonds. Results showed that AHBC/PSC hydrogel had in situ gelation behavior, satisfactory mechanical properties (storage modulus of about 1 kPa and loss factor Tan δ of about 0.5), suitable wet tissue adhesion strength of about 2.3 kPa on rat abdominal wall, and good biocompatibility, achieving an ideal physical barrier. Particularly, CGA could be responsively released from the hydrogel by breakage of borate ester bonds between CGA and PBA based on high reactive oxygen species (ROS) levels of damaged tissue and exhibited great ROS scavenging capability to regulate inflammation and promote the polarization of macrophages from pro-inflammatory M1 phenotype to anti-inflammatory M2 phenotype. Moreover, the grafted SB as a zwitterionic group could reduce protein adsorption and fibroblast adhesion. Finally, the in vivo experiments revealed that AHBC/PSC hydrogel with good safety and in vivo retention behavior of about 2 weeks, effectively prevented PAA by regulating the inflammatory microenvironment and alleviating the fibrosis process. In brief, the versatile AHBC/PSC hydrogel would provide a more convenient and efficient approach for PAA prevention. STATEMENT OF SIGNIFICANCE: Postoperative abdominal adhesion (PAA) widely occurs after surgery and is often accompanied by severe complications. Excessive inflammation and oxidative stress are very crucial for PAA formation. This study provides a ROS-responsive and scavenging hydrogel with suitable mechanical properties, good biocompatibility and biodegradability, and resistance to protein and fibroblast. The antioxidant and anti-inflammatory active ingredient could be responsively released from the hydrogel via triggering by the high ROS levels in the postoperative microenvironment thereby regulating the inflammatory balance. Finally, the hydrogel would effectively regulate the development process of PAA thereby achieving non-adhesion wound healing.

An injectable and antifouling hydrogel prevents the development of abdominal adhesions by inhibiting the CCL2/CCR2 interaction

Abdominal adhesion, a serious complication of abdominal surgery, often resists mitigation by current drug administration and physical barriers. To address this issue, we developed an injectable, antifouling hydrogel through the free-radical polymerization of methacrylate chondroitin sulfate (CS-GMA) and 2-methacryloyloxyethyl phosphorylcholine (MPC) monomers, dubbed the CGM hydrogel. We systematically analyzed its physicochemical properties, including rheological strength, biocompatibility, and antifouling capabilities. A rat abdominal cecum adhesion model was constructed to assess the effectiveness of CGM hydrogel in preventing postoperative adhesion and recurrent adhesion. In addition, multi-omics analyses identified the relationship between adhesion development and CCL2/CCR2 interaction. Notably, CGM hydrogel can thwart the recruitment and aggregation of fibroblasts and macrophages by inhibiting the CCL2/CCR2 interaction. Moreover, CGM hydrogel significantly dampens the activity of fibrosis-linked cytokines (TGF-βR1) and recalibrates extracellular matrix deposition-related cytokines (t-PA and PAI-1, Col Ⅰ and MMP-9). Cumulatively, the dual action of CGM hydrogel-as a physical barrier and cytokine regulator-highlights its promising potential in clinical application for abdominal adhesion prevention.

ROS-responsive sprayable hydrogel as ROS scavenger and GATA6+ macrophages trap for the prevention of postoperative abdominal adhesions

Postoperative abdominal adhesions are a common clinical problem after surgery and can cause many serious complications. Current most commonly used antiadhesion products are less effective due to their short residence time and focus primary on barrier function. Herein, we developed a sprayable hydrogel barrier (sHA-ADH/OHA-E) with self-regulated drug release based on ROS levels at the trauma site, to serve as a smart inflammatory microenvironment modulator and GATA6+ macrophages trap for non-adherent recovery from abdominal surgery. Sulfonated hyaluronic acid (HA) conjugates modified with adipic dihydrazide (sHA-ADH), and oxidized HA conjugates grafted with epigallocatechin-3-gallate (EGCG) via ROS-cleavable boronate bonds (OHA-E) were synthesized. sHA-ADH/OHA-E hydrogel was facilely fabricated within 5 s after simply mixing sHA-ADH and OHA-E through forming dynamic covalent acylhydrazones. With good biocompatibility, appropriate mechanical strength, tunable shear-thinning, self-healing, asymmetric adhesion, and reasonable in vivo retention time, sHA-ADH/OHA-E hydrogel meets the requirements of a perfect physical barrier. Intriguingly, sulfonic acid groups endowed the hydrogel with satisfactory anti-fibroblast and macrophage attachment capability, and were demonstrated for the first time to act as polyanion traps to prevent GATA6+ macrophages aggregation. Importantly, EGCG could be intelligently released by ROS triggering to alleviate oxidative stress and promote proinflammatory M1 macrophage polarize to antiinflammatory M2 phenotype. Further, the fibrinolytic system balance was restored to reduce fibrosis. Thanks to the above advantages, the sHA-ADH/OHA-E hydrogel exhibited excellent anti-adhesion effects in a rat sidewall defect-cecum abrasion model and is expected to be a promising and clinically translatable antiadhesion barrier.

Membrane damage by MBP-1 is mediated by pore formation and amplified by mtDNA

Eosinophils play a crucial role in host defense while also contributing to immunopathology through the release of inflammatory mediators. Characterized by distinctive cytoplasmic granules, eosinophils securely store and rapidly release various proteins exhibiting high toxicity upon extracellular release. Among these, major basic protein 1 (MBP-1) emerges as an important mediator in eosinophil function against pathogens and in eosinophil-associated diseases. While MBP-1 targets both microorganisms and host cells, its precise mechanism remains elusive. We demonstrate that formation of small pores by MBP-1 in lipid bilayers induces membrane permeabilization and disrupts potassium balance. Additionally, we reveal that mitochondrial DNA (mtDNA) present in eosinophil extracellular traps (EETs) amplifies MBP-1 toxic effects, underscoring the pivotal role of mtDNA in EETs. Furthermore, we present evidence indicating that absence of CpG methylation in mtDNA contributes to the regulation of MBP-1-mediated toxicity. Taken together, our data suggest that the mtDNA scaffold within extracellular traps promotes MBP-1 toxicity.

Neutrophil Extracellular Traps-Inhibiting and Fouling-Resistant Polysulfoxides Potently Prevent Postoperative Adhesion, Tumor Recurrence, and Metastasis

Peritoneal metastasis (PM) is considered one of the most dreaded forms of cancer metastases for both patients and physicians. Aggressive cytoreductive surgery (CRS) is the primary treatment for peritoneal metastasis. Unfortunately, this intensive treatment frequently causes clinical complications, such as postoperative recurrence, metastasis, and adhesion formation. Emerging evidence suggests that neutrophil extracellular traps (NETs) released by inflammatory neutrophils contribute to these complications. Effective NET-targeting strategies thus show considerable potential in counteracting these complications but remain challenging. Here, one type of sulfoxide-containing homopolymer, PMeSEA, with potent fouling-resistant and NET-inhibiting capabilities, is synthesized and screened. Hydrating sulfoxide groups endow PMeSEA with superior nonfouling ability, significantly inhibiting protein/cell adhesion. Besides, the polysulfoxides can be selectively oxidized by ClO- which is required to stabilize the NETs rather than H2O2, and ClO- scavenging effectively inhibits NETs formation without disturbing redox homeostasis in tumor cells and quiescent neutrophils. As a result, PMeSEA potently prevents postoperative adhesions, significantly suppresses peritoneal metastasis, and shows synergetic antitumor activity with chemotherapeutic 5-Fluorouracil. Moreover, coupling CRS with PMeSEA potently inhibits CRS-induced tumor metastatic relapse and postoperative adhesions. Notably, PMeSEA exhibits low in vivo acute and subacute toxicities, implying significant potential for clinical postoperative adjuvant treatment.

Injectable Asymmetric Adhesive-Antifouling Bifunctional Hydrogel for Peritoneal Adhesion Prevention

Peritoneal adhesion is a common problem after abdominal surgery and can lead to various medical problems. In response to the lack of in situ retention and pro-wound healing properties of existing anti-adhesion barriers, this work reports an injectable adhesive-antifouling bifunctional hydrogel (AAB-hydrogel). This AAB-hydrogel can be constructed by "two-step" injection. The tissue adhesive hydrogel based on gallic acid-modified chitosan and aldehyde-modified dextran is prepared as the bottom hydrogel (B-hydrogel) by Schiff base reaction. The aldehyde-modified zwitterionic dextran/carboxymethyl chitosan-based hydrogel is formed on the B-hydrogel surface as the antifouling top hydrogel (T-hydrogel). The AAB-hydrogel exhibits good bilayer binding and asymmetric properties, including tissue adhesive, antifouling, and antimicrobial properties. To evaluate the anti-adhesion effect in vivo, the prepared hydrogels are injected onto the wound surface of a mouse abdominal wall abrasion-cecum defect model. Results suggest that the AAB-hydrogel has antioxidant capacity and can reduce the postoperative inflammatory response by modulating the macrophage phenotype. Moreover, the AAB-hydrogel could effectively inhibit the formation of postoperative adhesions by reducing protein deposition, and resisting fibroblast adhesions and bacteria attacking. Therefore, AAB-hydrogel is a promising candidate for the prevention of postoperative peritoneal adhesions.

IL-4-induced M2 macrophages inhibit fibrosis of endometrial stromal cells

BACKGROUND

Intrauterine adhesions (IUA) refers to endometrial fibrosis caused by irreversible damage of the endometrial basal layer. As the key regulators in tissue repair, regeneration, and fibrosis, macrophages play an essential role in endometrial regeneration and repair during the normal menstrual cycle. However, the mechanism of macrophages involved in IUA remains unclear.

METHODS

In the late stages of proliferation, the endometrium was collected to make paraffin sections. HE and Masson staining were used to observing endometrial morphology and endometrial fibrosis. Immunohistochemistry and Western blotting were used to detect the expression level of fibrosis indexes COL1A1 and α-SMA. The macrophage infiltration was evaluated by immunohistochemistry for the expression levels of CD 206 and CD163. Next, we cultured the primary human endometrial stromal cells (HESCs), and then an IUA cell model was established with 10 ng/ml TGF-β1 for 72 h. THP 1 cells were differentiated by 100 ng/ml PMA into macrophages for 48 h, then macrophages were polarized to M2 macrophages by 20 ng/ml IL-4 for 24 h. The culture supernatants (M(IL-4) -S) of M2 macrophages were applied to the IUA cell model. The expression of fibrosis markers was then assessed using immunofluorescence and Western blotting.

RESULTS

The results show that Patients with IUA have fewer endometrial glands and significantly increased fibrosis levels. Moreover, the infiltration of CD206-positive (M2) macrophages was significantly reduced in IUA patients, and negatively correlated with the expression of endometrial fibrosis indexes α-SMA and COL1A1. In addition, the primary HESCs treated with 10 ng/ml TGF-β1 for 72 h were found to have significantly increased levels of fibrosis indexes. Furthermore, supernatants from IL4-induced M2 macrophages inhibit the TGF-β1-induced fibrosis of HESCs.

CONCLUSIONS

M2 macrophages may negatively regulate the expression of COL1A1 and α-SMA, inhibiting the TGF-β1-induced fibrosis of HESCs. Our study suggests that targeting macrophage phenotypes and promoting the polarization of macrophages to M2 may become a novel strategy for the clinical treatment of IUA.

Dynamic Multiplex Tissue Imaging in Inflammation Research

Inflammation is a highly dynamic process with immune cells that continuously interact with each other and parenchymal components as they migrate through tissue. The dynamic cellular responses and interaction patterns are a function of the complex tissue environment that cannot be fully reconstructed ex vivo, making it necessary to assess cell dynamics and changing spatial patterning in vivo. These dynamics often play out deep within tissues, requiring the optical focus to be placed far below the surface of an opaque organ. With the emergence of commercially available two-photon excitation lasers that can be combined with existing imaging systems, new avenues for imaging deep tissues over long periods of time have become available. We discuss a selected subset of studies illustrating how two-photon microscopy (2PM) has helped to relate the dynamics of immune cells to their in situ function and to understand the molecular patterns that govern their behavior in vivo. We also review some key practical aspects of 2PM methods and point out issues that can confound the results, so that readers can better evaluate the reliability of conclusions drawn using this technology.

Breaking through the basement membrane barrier to improve nanotherapeutic delivery to tumours

An effective nanotherapeutic transport from the vasculature to the tumour is crucial for cancer treatment with minimal side effects. Here we demonstrate that, in addition to the endothelial barrier, the tumour vascular basement membrane surrounding the endothelium acts as a formidable mechanical barrier that entraps nanoparticles (NPs) in the subendothelial void, forming perivascular NP pools. Breaking through this basement membrane barrier substantially increases NP extravasation. Using inflammation triggered by local hyperthermia, we develop a cooperative immunodriven strategy to overcome the basement membrane barrier that leads to robust tumour killing. Hyperthermia-triggered accumulation and inflammation of platelets attract neutrophils to the NP pools. The subsequent movement of neutrophils through the basement membrane can release the NPs entrapped in the subendothelial void, resulting in increased NP penetration into deeper tumours. We show the necessity of considering the tumour vascular basement membrane barrier when delivering nanotherapeutics. Understanding this barrier will contribute to developing more effective antitumour therapies.

Human serous cavity macrophages and dendritic cells possess counterparts in the mouse with a distinct distribution between species

In mouse peritoneal and other serous cavities, the transcription factor GATA6 drives the identity of the major cavity resident population of macrophages, with a smaller subset of cavity-resident macrophages dependent on the transcription factor IRF4. Here we showed that GATA6+ macrophages in the human peritoneum were rare, regardless of age. Instead, more human peritoneal macrophages aligned with mouse CD206+ LYVE1+ cavity macrophages that represent a differentiation stage just preceding expression of GATA6. A low abundance of CD206+ macrophages was retained in C57BL/6J mice fed a high-fat diet and in wild-captured mice, suggesting that differences between serous cavity-resident macrophages in humans and mice were not environmental. IRF4-dependent mouse serous cavity macrophages aligned closely with human CD1c+CD14+CD64+ peritoneal cells, which, in turn, resembled human peritoneal CD1c+CD14-CD64- cDC2. Thus, major populations of serous cavity-resident mononuclear phagocytes in humans and mice shared common features, but the proportions of different macrophage differentiation stages greatly differ between the two species, and dendritic cell (DC2)-like cells were especially prominent in humans.

Neutrophil extracellular traps and DNases orchestrate formation of peritoneal adhesions

Peritoneal adhesions are poorly understood but highly prevalent conditions that can cause intestinal obstruction and pelvic pain requiring surgery. While there is consensus that stress-induced inflammation triggers peritoneal adhesions, the molecular processes of their formation still remain elusive. We performed murine models and analyzed human samples to monitor the formation of adhesions and the treatment with DNases. Various molecular analyses were used to evaluate the adhesions. The experimental peritoneal adhesions of the murine models and biopsy material from humans are largely based on neutrophil extracellular traps (NETs). Treatment with DNASE1 (Dornase alfa) and the human DNASE1L3 analog (NTR-10), significantly reduced peritoneal adhesions in experimental models. We conclude that NETs serve as essential scaffold for the formation of adhesions; DNases interfere with this process. Herein, we show that therapeutic application of DNases can be employed to prevent the formation of murine peritoneal adhesions. If this can be translated into the human situation requires clinical studies.

A Zwitterionic Hydrogel with Anti-Oxidative and Anti-Inflammatory Properties for the Prevention of Peritoneal Adhesion by Inhibiting Mesothelial-Mesenchymal Transition

Postoperative peritoneal adhesion is a serious clinical complication. Various hydrogel barriers have been developed to prevent peritoneal adhesion. However, it remains a challenge to design a hydrogel with desirable physicochemical properties and bioactivities. In this study, a zwitterionic polysaccharide-based multifunctional hydrogel is developed using epigallocatechin-3-gallate (EGCG) to prevent postoperative abdominal adhesion. This hydrogel is simple to use and has desirable properties, such as excellent injectability, self-healing, and non-swelling properties. The hydrogel also has ultralow fouling capabilities, such as superior bactericidal performance, cell and protein adhesion, and low immunogenicity resistance. Moreover, the hydrogel exhibits good antioxidant activity, which is attributed to the integration of EGCG. Furthermore, the detailed mechanism from in vivo and in vitro experimental studies illustrates that hydrogel compositions can synergistically prevent adhesion formation through multiple pathways, including anti-inflammatory and antioxidant capabilities and inhibition effects on the mesothelial-mesenchymal transition (MMT) process induced by transforming growth factor (TGF-β). In summary, this zwitterionic multifunctional hydrogel has great potential to prevent postoperative adhesion formation in the clinical setting.

Techniques for navigating postsurgical adhesions: Insights into mechanisms and future directions

Postsurgical adhesions are a common complication of surgical procedures that can lead to postoperative pain, bowel obstruction, infertility, as well as complications with future procedures. Several agents have been developed to prevent adhesion formation, such as barriers, anti-inflammatory and fibrinolytic agents. The Food and Drug Administration (FDA) has approved the use of physical barrier agents, but they have been associated with conflicting clinical studies and controversy in the clinical utilization of anti-adhesion barriers. In this review, we summarize the human anatomy of the peritoneum, the pathophysiology of adhesion formation, the current prevention agents, as well as the current research progress on adhesion prevention. The early cellular events starting with injured mesothelial cells and incorporating macrophage response have recently been found to be associated with adhesion formation. This may provide the key component for developing future adhesion prevention methods. The current use of physical barriers to separate tissues, such as Seprafilm®, composed of hyaluronic acid and carboxymethylcellulose, can only reduce the risk of adhesion formation at the end stage. Other anti-inflammatory or fibrinolytic agents for preventing adhesions have only been studied within the context of current research models, which is limited by the lack of in-vitro model systems as well as in-depth study of in-vivo models to evaluate the efficiency of anti-adhesion agents. In addition, we explore emerging therapies, such as gene therapy and stem cell-based approaches, that may offer new strategies for preventing adhesion formation. In conclusion, anti-adhesion agents represent a promising approach for reducing the burden of adhesion-related complications in surgical patients. Further research is needed to optimize their use and develop new therapies for this challenging clinical problem.

Targeting CD301+ macrophages inhibits endometrial fibrosis and improves pregnancy outcome

Macrophages are a key and heterogeneous cell population involved in endometrial repair and regeneration during the menstrual cycle, but their role in the development of intrauterine adhesion (IUA) and sequential endometrial fibrosis remains unclear. Here, we reported that CD301+ macrophages were significantly increased and showed their most active interaction with profibrotic cells in the endometria of IUA patients compared with the normal endometria by single-cell RNA sequencing, bulk RNA sequencing, and experimental verification. Increasing CD301+ macrophages promoted the differentiation of endometrial stromal cells into myofibroblasts and resulted in extracellular matrix accumulation, which destroyed the physiological architecture of endometrial tissue, drove endometrial fibrosis, and ultimately led to female infertility or adverse pregnancy outcomes. Mechanistically, CD301+ macrophages secreted GAS6 to activate the AXL/NF-κB pathway, upregulating the profibrotic protein synthesis. Targeted deletion of CD301+ macrophages or inhibition of AXL by Bemcentinib blunted the pathology and improved the outcomes of pregnancy in mice, supporting the therapeutic potential of targeting CD301+ macrophages for treating endometrial fibrosis.

Kupffer cell-like syncytia replenish resident macrophage function in the fibrotic liver

Kupffer cells (KCs) are localized in liver sinusoids but extend pseudopods to parenchymal cells to maintain their identity and serve as the body's central bacterial filter. Liver cirrhosis drastically alters vascular architecture, but how KCs adapt is unclear. We used a mouse model of liver fibrosis and human tissue to examine immune adaptation. Fibrosis forced KCs to lose contact with parenchymal cells, down-regulating "KC identity," which rendered them incapable of clearing bacteria. Commensals stimulated the recruitment of monocytes through CD44 to a spatially distinct vascular compartment. There, recruited monocytes formed large aggregates of multinucleated cells (syncytia) that expressed phenotypical KC markers and displayed enhanced bacterial capture ability. Syncytia formed via CD36 and were observed in human cirrhosis as a possible antimicrobial defense that evolved with fibrosis.

Cooperative phagocytosis of solid tumours by macrophages triggers durable anti-tumour responses

In solid tumours, the abundance of macrophages is typically associated with a poor prognosis. However, macrophage clusters in tumour-cell nests have been associated with survival in some tumour types. Here, by using tumour organoids comprising macrophages and cancer cells opsonized via a monoclonal antibody, we show that highly ordered clusters of macrophages cooperatively phagocytose cancer cells to suppress tumour growth. In mice with poorly immunogenic tumours, the systemic delivery of macrophages with signal-regulatory protein alpha (SIRPα) genetically knocked out or else with blockade of the CD47-SIRPα macrophage checkpoint was combined with the monoclonal antibody and subsequently triggered the production of endogenous tumour-opsonizing immunoglobulin G, substantially increased the survival of the animals and helped confer durable protection from tumour re-challenge and metastasis. Maximizing phagocytic potency by increasing macrophage numbers, by tumour-cell opsonization and by disrupting the phagocytic checkpoint CD47-SIRPα may lead to durable anti-tumour responses in solid cancers.

Injectable photocurable Janus hydrogel delivering hiPSC cardiomyocyte-derived exosome for post-heart surgery adhesion reduction

Postsurgical pericardial adhesions pose increased risks of sequelae, prolonged reoperation time, and reduced visibility in the surgical field. Here, we introduce an injectable Janus hydrogel, which exhibits asymmetric adhesiveness properties after photocrosslinking, sustained delivering induced pluripotent stem cell-derived cardiomyocyte exosomes (iCM-EXOs) for post-heart surgery adhesion reduction. Our findings reveal that iCM-EXOs effectively attenuate oxidative stress in hydrogen peroxide-treated primary cardiomyocytes by inhibiting the activation of the transcription factor nuclear factor erythroid 2-related factor 2. Notably, in rat cardiac postsurgery models, the Janus hydrogels loaded with iCM-EXOs demonstrate dual functionality, acting as antioxidants and antipericardial adhesion agents. These hydrogels effectively protect iCM-EXOs from GATA6+ cavity macrophage clearance by inhibiting the recruitment of macrophages from the thoracic cavity. These results highlight the promising potential of iCM-EXO-laden Janus hydrogels for clinical safety and efficacy validation in trials involving heart surgery patients, with the ultimate goal of routine administration during open-heart surgeries.

Abdominal wall hernia repair: from prosthetic meshes to smart materials

Hernia reconstruction is one of the most frequently practiced surgical procedures worldwide. Plastic surgery plays a pivotal role in reestablishing desired abdominal wall structure and function without the drawbacks traditionally associated with general surgery as excessive tension, postoperative pain, poor repair outcomes, and frequent recurrence. Surgical meshes have been the preferential choice for abdominal wall hernia repair to achieve the physical integrity and equivalent components of musculofascial layers. Despite the relevant progress in recent years, there are still unsolved challenges in surgical mesh design and complication settlement. This review provides a systemic summary of the hernia surgical mesh development deeply related to abdominal wall hernia pathology and classification. Commercial meshes, the first-generation prosthetic materials, and the most commonly used repair materials in the clinic are described in detail, addressing constrain side effects and rational strategies to establish characteristics of ideal hernia repair meshes. The engineered prosthetics are defined as a transit to the biomimetic smart hernia repair scaffolds with specific advantages and disadvantages, including hydrogel scaffolds, electrospinning membranes, and three-dimensional patches. Lastly, this review critically outlines the future research direction for successful hernia repair solutions by combing state-of-the-art techniques and materials.

Prevention strategies of postoperative adhesion in soft tissues by applying biomaterials: Based on the mechanisms of occurrence and development of adhesions

Postoperative adhesion (POA) widely occurs in soft tissues and usually leads to chronic pain, dysfunction of adjacent organs and some acute complications, seriously reducing patients' quality of life and even being life-threatening. Except for adhesiolysis, there are few effective methods to release existing adhesion. However, it requires a second operation and inpatient care and usually triggers recurrent adhesion in a great incidence. Hence, preventing POA formation has been regarded as the most effective clinical strategy. Biomaterials have attracted great attention in preventing POA because they can act as both barriers and drug carriers. Nevertheless, even though much reported research has been demonstrated their efficacy on POA inhibition to a certain extent, thoroughly preventing POA formation is still challenging. Meanwhile, most biomaterials for POA prevention were designed based on limited experiences, not a solid theoretical basis, showing blindness. Hence, we aimed to provide guidance for designing anti-adhesion materials applied in different soft tissues based on the mechanisms of POA occurrence and development. We first classified the postoperative adhesions into four categories according to the different components of diverse adhesion tissues, and named them as "membranous adhesion", "vascular adhesion", "adhesive adhesion" and "scarred adhesion", respectively. Then, the process of the occurrence and development of POA were analyzed, and the main influencing factors in different stages were clarified. Further, we proposed seven strategies for POA prevention by using biomaterials according to these influencing factors. Meanwhile, the relevant practices were summarized according to the corresponding strategies and the future perspectives were analyzed.

Degradable Temperature-Sensitive Hydrogel Loaded with Heparin Effectively Prevents Post-Operative Tissue Adhesions

Tissue adhesions could occur following surgeries, and severe tissue adhesions can lead to serious complications. Medical hydrogels could be applied at surgical sites as a physical barrier to prevent tissue adhesion. For practical reasons, spreadable, degradable, and self-healable gels are highly demanded. To meet these requirements, we applied carboxymethyl chitosan (CMCS) to poloxamer-based hydrogels to generate low Poloxamer₃₃₈ (P₃₃₈) content gels displaying low viscosity at refrigerator temperature and improved mechanical strength at body temperature. Heparin, an effective adhesion inhibitor, was also added to construct P₃₃₈/CMCS-heparin composite hydrogel (PCHgel). PCHgel presents as a flowable liquid below 20 °C and could rapidly transform into gel when spread on the surface of damaged tissue due to temperature change. The introduction of CMCS enabled hydrogels to form a stable self-healable barrier at injured positions and slowly release heparin during the wound healing period before being degraded after ∼14 days. Ultimately, PCHgel significantly reduced tissue adhesion in model rats and displayed higher efficiency than P₃₃₈/CMCS gel without heparin. Its adhesion suppression mechanism was verified, and it also displayed good biosafety. Therefore, PCHgel showed good clinical transformation potential with high efficacy, good safety, and ease of use.

GATA6 triggers fibroblast activation and tracheal fibrosis through the Wnt/β-catenin pathway

Tracheal fibrosis is a key abnormal repair process leading to fatal stenosis, characterized by excessive fibroblast activation and extracellular matrix (ECM) deposition. GATA6, a zinc finger-containing transcription factor, is involved in fibroblast activation, while its role in tracheal fibrosis remains obscure. The present study investigated the potential role of GATA6 as a novel regulator of tracheal fibrosis. It was found that GATA6 and α-smooth muscle actin (α-SMA) were obviously increased in tracheal fibrotic granulations and in TGFβ1-treated primary tracheal fibroblasts. GATA6 silencing inhibited TGFβ1-stimulated fibroblast proliferation and ECM synthesis, promoted cell apoptosis, and inactivated Wnt/β-catenin pathway, whereas GATA6 overexpression showed the reverse effects. SKL2001, an agonist of Wnt/β-catenin signaling, restored collagen1a1 and α-SMA expression which was suppressed by GATA6 silencing. Furthermore, in vivo, knockdown of GATA6 ameliorated tracheal fibrosis, as manifested by reduced tracheal stenosis and ECM deposition. GATA6 inhibition in rat tracheas also impaired granulation proliferation, increased apoptosis, and inactivated Wnt/β-catenin pathway. In conclusion, our findings indicate that GATA6 triggers fibroblast activation, cell proliferation, and apoptosis resistance in tracheal fibrosis via the Wnt/β-catenin signaling pathway. Targeting GATA6 may represent a promising therapeutic approach for tracheal fibrosis.

Aldh1a2 + fibroblastic reticular cells regulate lymphocyte recruitment in omental milky spots

Lymphoid clusters in visceral adipose tissue omentum, known as milky spots, play a central role in the immunological defense in the abdomen. Milky spots exhibit hybrid nature between secondary lymph organs and ectopic lymphoid tissues, yet their development and maturation mechanisms are poorly understood. Here, we identified a subset of fibroblastic reticular cells (FRCs) that are uniquely present in omental milky spots. These FRCs were characterized by the expression of retinoic acid-converting enzyme, Aldh1a2, and endothelial cell marker, Tie2, in addition to canonical FRC-associated genes. Diphtheria toxin-mediated ablation of Aldh1a2+ FRCs resulted in the alteration in milky spot structure with a significant reduction in size and cellularity. Mechanistically, Aldh1a2+ FRCs regulated the display of chemokine CXCL12 on high endothelial venules (HEVs), which recruit blood-borne lymphocytes from circulation. We further found that Aldh1a2+ FRCs are required for the maintenance of peritoneal lymphocyte composition. These results illustrate the homeostatic roles of FRCs in the formation of non-classical lymphoid tissues.

Intraperitoneal metastasis of ovarian cancer: new insights on resident macrophages in the peritoneal cavity

Ovarian cancer metastasis occurs primarily in the peritoneal cavity. Orchestration of cancer cells with various cell types, particularly macrophages, in the peritoneal cavity creates a metastasis-favorable environment. In the past decade, macrophage heterogeneities in different organs as well as their diverse roles in tumor settings have been an emerging field. This review highlights the unique microenvironment of the peritoneal cavity, consisting of the peritoneal fluid, peritoneum, and omentum, as well as their own resident macrophage populations. Contributions of resident macrophages in ovarian cancer metastasis are summarized; potential therapeutic strategies by targeting such cells are discussed. A better understanding of the immunological microenvironment in the peritoneal cavity will provide a stepping-stone to new strategies for developing macrophage-based therapies and is a key step toward the unattainable eradication of intraperitoneal metastasis of ovarian cancer.

Adjuvant-Free COVID-19 Vaccine with Glycoprotein Antigen Oxidized by Periodate Rapidly Elicits Potent Immune Responses

Modification of antigens to improve their immunogenicity represents a promising direction for the development of protein vaccine. Here, we designed facilely prepared adjuvant-free vaccines in which the N-glycan of SARS-CoV-2 receptor-binding domain (RBD) glycoprotein was oxidized by sodium periodate. This strategy only minimally modifies the glycans and does not interfere with the epitope peptides. The RBD glycoprotein oxidized by high concentrations of periodate (RBDHO) significantly enhanced antigen uptake mediated by scavenger receptors and promoted the activation of antigen-presenting cells. Without any external adjuvant, two doses of RBDHO elicited 324- and 27-fold increases in IgG antibody titers and neutralizing antibody titers, respectively, compared to the unmodified RBD antigen. Meanwhile, the RBDHO vaccine could cross-neutralize all of the SARS-CoV-2 variants of concern. In addition, RBDHO effectively enhanced cellular immune responses. This study provides a new insight for the development of adjuvant-free protein vaccines.

Mouse Tissue-Resident Peritoneal Macrophages in Homeostasis, Repair, Infection, and Tumor Metastasis

Large peritoneal macrophages (LPMs) are long-lived, tissue-resident macrophages, formed during embryonic life, developmentally and functionally confined to the peritoneal cavity. LPMs provide the first line of defense against life-threatening pathologies of the peritoneal cavity, such as abdominal sepsis, peritoneal metastatic tumor growth, or peritoneal injuries caused by trauma, or abdominal surgery. Apart from their primary phagocytic function, reminiscent of primitive defense mechanisms sustained by coelomocytes in the coelomic cavity of invertebrates, LPMs fulfill an essential homeostatic function by achieving an efficient clearance of apoptotic, that is crucial for the maintenance of self-tolerance. Research performed over the last few years, in mice, has unveiled the mechanisms by which LPMs fulfill a crucial role in repairing peritoneal injuries and controlling microbial and parasitic infections, reflecting that the GATA6-driven LPM transcriptional program can be modulated by extracellular signals associated with pathological conditions. In contrast, recent experimental evidence supports that peritoneal tumors can subvert LPM metabolism and function, leading to the acquisition of a tumor-promoting potential. The remarkable functional plasticity of LPMs can be nevertheless exploited to revert tumor-induced LPM protumor potential, providing the basis for the development of novel immunotherapeutic approaches against peritoneal tumor metastasis based on macrophage reprogramming.

Whole-mount immunofluorescence imaging and isolation of mesothelium-bound immune cell aggregates during mouse peritoneal inflammation

Resident peritoneal macrophages (resMØs) are crucial for repairing peritoneal injuries and controlling infections by forming mesothelium-bound resMØ-aggregates in the peritoneal wall and omentum. Here we present a protocol to analyze these structures in mouse models of peritoneal inflammation. We describe the dissection, fixation, immunofluorescent staining, and mounting of whole peritoneal wall and omentum samples and subsequent confocal microscopy imaging of resMØ-aggregates. We also detail the steps to isolate resMØ-aggregates for additional studies, including flow cytometry and electron-microscopy-based analysis. For complete details on the use and execution of this protocol, please refer to Vega-Pérez et al. (2021).1.

Neutrophil interactions with T cells, platelets, endothelial cells, and of course tumor cells

Neutrophils sense microbes and host inflammatory mediators, and traffic to sites of infection where they direct a broad armamentarium of antimicrobial products against pathogens. Neutrophils are also activated by damage-associated molecular patterns (DAMPs), which are products of cellular injury that stimulate the innate immune system through pathways that are similar to those activated by microbes. Neutrophils and platelets become activated by injury, and cluster and cross-signal to each other with the cumulative effect of driving antimicrobial defense and hemostasis. In addition, neutrophil extracellular traps are extracellular chromatin and granular constituents that are generated in response to microbial and damage motifs and are pro-thrombotic and injurious. Although neutrophils can worsen tissue injury, neutrophils may also have a role in facilitating wound repair following injury. A central theme of this review relates to how critical functions of neutrophils that evolved to respond to infection and damage modulate the tumor microenvironment (TME) in ways that can promote or limit tumor progression. Neutrophils are reprogrammed by the TME, and, in turn, can cross-signal to tumor cells and reshape the immune landscape of tumors. Importantly, promising new therapeutic strategies have been developed to target neutrophil recruitment and function to make cancer immunotherapy more effective.

Multifunctional Microgel-Based Cream Hydrogels for Postoperative Abdominal Adhesion Prevention

Postoperative abdominal adhesions are a common problem after surgery and can produce serious complications. Current antiadhesive strategies focus mostly on physical barriers and are unsatisfactory and inefficient. In this study, we designed and synthesized advanced injectable cream-like hydrogels with multiple functionalities, including rapid gelation, self-healing, antioxidation, anti-inflammation, and anti-cell adhesion. The multifunctional hydrogels were facilely formed by the conjugation reaction of epigallocatechin-3-gallate (EGCG) and hyaluronic acid (HA)-based microgels and poly(vinyl alcohol) (PVA) based on the dynamic boronic ester bond. The physicochemical properties of the hydrogels including antioxidative and anti-inflammatory activities were systematically characterized. A mouse cecum-abdominal wall adhesion model was implemented to investigate the efficacy of our microgel-based hydrogels in preventing postoperative abdominal adhesions. The hydrogels, with a high molecular weight HA, significantly decreased the inflammation, oxidative stress, and fibrosis and reduced the abdominal adhesion formation, compared to the commercial Seprafilm group or Injury-only group. Label-free quantitative proteomics analysis demonstrated that S100A8 and S100A9 expressions were associated with adhesion formation; the microgel-containing hydrogels inhibited these expressions. The microgel-containing hydrogels with multifunctionality decreased the formation of postoperative intra-abdominal adhesions in a murine model, demonstrating promise for clinical applications.

Gata6+ large peritoneal macrophages: an evolutionarily conserved sentinel and effector system for infection and injury

There are striking similarities between the sea urchin cavity macrophage-like phagocytes (coelomocytes) and mammalian cavity macrophages in not only their location, but also their behaviors. These cells are crucial for maintaining homeostasis within the cavity following a breach, filling the gap and functioning as a barrier between vital organs and the environment. In this review, we summarize the evolving literature regarding these Gata6⁺ large peritoneal macrophages (GLPMs), focusing on ontogeny, their responses to perturbations, including their rapid aggregation via coagulation, as well as scavenger receptor cysteine-rich domains and their potential roles in diseases, such as cancer. We challenge the 50-year old phenomenon of the 'macrophage disappearance reaction' (MDR) and propose the new term 'macrophage disturbance of homeostasis reaction' (MDHR), which may better describe this complex phenomenon.

Distinctive role of inflammation in tissue repair and regeneration

Inflammation is an essential host defense mechanism in response to microbial infection and tissue injury. In addition to its well-established role in infection, inflammation is actively involved in the repair of damaged tissues and restoration of homeostatic conditions after tissue injury. The intensity of the inflammatory response and types of cells involved in inflammation have a significant impact on the quality of tissue repair. Numerous immune cell subtypes participate in tissue repair and regeneration. In particular, immune cell-derived secretants, including cytokines and growth factors, can actively modulate the proliferation of resident stem cells or progenitor cells to facilitate tissue regeneration. These findings highlight the importance of inflammation during tissue repair and regeneration; however, the precise role of immune cells in tissue regeneration remains unclear. In this review, we summarize the current knowledge on the contribution of specific immune cell types to tissue repair and regeneration. We also discuss how inflammation affects the final outcome of tissue regeneration.

Macrophage differentiation is marked by increased abundance of the mRNA 3' end processing machinery, altered poly(A) site usage, and sensitivity to the level of CstF64

Regulation of mRNA polyadenylation is important for response to external signals and differentiation in several cell types, and results in mRNA isoforms that vary in the amount of coding sequence or 3' UTR regulatory elements. However, its role in differentiation of monocytes to macrophages has not been investigated. Macrophages are key effectors of the innate immune system that help control infection and promote tissue-repair. However, overactivity of macrophages contributes to pathogenesis of many diseases. In this study, we show that macrophage differentiation is characterized by shortening and lengthening of mRNAs in relevant cellular pathways. The cleavage/polyadenylation (C/P) proteins increase during differentiation, suggesting a possible mechanism for the observed changes in poly(A) site usage. This was surprising since higher C/P protein levels correlate with higher proliferation rates in other systems, but monocytes stop dividing after induction of differentiation. Depletion of CstF64, a C/P protein and known regulator of polyadenylation efficiency, delayed macrophage marker expression, cell cycle exit, attachment, and acquisition of structural complexity, and impeded shortening of mRNAs with functions relevant to macrophage biology. Conversely, CstF64 overexpression increased use of promoter-proximal poly(A) sites and caused the appearance of differentiated phenotypes in the absence of induction. Our findings indicate that regulation of polyadenylation plays an important role in macrophage differentiation.

Spatiotemporal multiplexed immunofluorescence imaging of living cells and tissues with bioorthogonal cycling of fluorescent probes

Cells in complex organisms undergo frequent functional changes, but few methods allow comprehensive longitudinal profiling of living cells. Here we introduce scission-accelerated fluorophore exchange (SAFE), a method for multiplexed temporospatial imaging of living cells with immunofluorescence. SAFE uses a rapid bioorthogonal click chemistry to remove immunofluorescent signals from the surface of labeled cells, cycling the nanomolar-concentration reagents in seconds and enabling multiple rounds of staining of the same samples. It is non-toxic and functional in both dispersed cells and intact living tissues. We demonstrate multiparameter (n ≥ 14), non-disruptive imaging of murine peripheral blood mononuclear and bone marrow cells to profile cellular differentiation. We also show longitudinal multiplexed imaging of bone marrow progenitor cells as they develop into neutrophils over 6 days and real-time multiplexed cycling of living mouse hepatic tissues. We anticipate that SAFE will find broad utility for investigating physiologic dynamics in living systems.

The role of platelet mediated thromboinflammation in acute liver injury

Acute liver injuries have wide and varied etiologies and they occur both in patients with and without pre-existent chronic liver disease. Whilst the pathophysiological mechanisms remain distinct, both acute and acute-on-chronic liver injury is typified by deranged serum transaminase levels and if severe or persistent can result in liver failure manifest by a combination of jaundice, coagulopathy and encephalopathy. It is well established that platelets exhibit diverse functions as immune cells and are active participants in inflammation through processes including immunothrombosis or thromboinflammation. Growing evidence suggests platelets play a dualistic role in liver inflammation, shaping the immune response through direct interactions and release of soluble mediators modulating function of liver sinusoidal endothelial cells, stromal cells as well as migrating and tissue-resident leucocytes. Elucidating the pathways involved in initiation, propagation and resolution of the immune response are of interest to identify therapeutic targets. In this review the provocative role of platelets is outlined, highlighting beneficial and detrimental effects in a spatial, temporal and disease-specific manner.

Intraperitoneal injection of class A TLR9 agonist enhances anti-PD-1 immunotherapy in colorectal peritoneal metastases

Peritoneal metastases are associated with a low response rate to immune checkpoint blockade (ICB) therapy. The numbers of peritoneal resident macrophages (PRMs) are reversely correlated with the response rate to ICB therapy. We have previously shown that TLR9 in fibroblastic reticular cells (FRCs) plays a critical role in regulating peritoneal immune cell recruitment. However, the role of TLR9 in FRCs in regulating PRMs is unclear. Here, we demonstrated that the class A TLR9 agonist, ODN1585, markedly enhanced the efficacy of anti-PD-1 therapy in mouse models of colorectal peritoneal metastases. ODN1585 injected i.p. reduced the numbers of Tim4+ PRMs and enhanced CD8+ T cell antitumor immunity. Mechanistically, treatment of ODN1585 suppressed the expression of genes required for retinoid metabolism in FRCs, and this was associated with reduced expression of the PRM lineage-defining transcription factor GATA6. Selective deletion of TLR9 in FRCs diminished the benefit of ODN1585 in anti-PD-1 therapy in reducing peritoneal metastases. The crosstalk between PRMs and FRCs may be utilized to develop new strategies to improve the efficacy of ICB therapy for peritoneal metastases.

Unbalanced Arginine pathway and altered maturation of pleural macrophages in Th2-deficient mice during Litomosoides sigmodontis filarial infection

Filarial parasites are tissue dwelling worms transmitted by hematophagous vectors. Understanding the mechanisms regulating microfilariae (the parasite offspring) development is a prerequisite for controlling transmission in filarial infections. Th2 immune responses are key for building efficient anti-parasite responses but have been shown to also lead to detrimental tissue damage in the presence of microfilariae. Litomosoides sigmodontis, a rodent filaria residing in the pleural cavity was therefore used to characterize pleuropulmonary pathology and associated immune responses in wild-type and Th2 deficient mice. Wild-type and Th2-deficient mice (Il-4rα^-/-/Il-5^-/-) were infected with L. sigmodontis and parasite outcome was analyzed during the patent phase (when microfilariae are in the general circulation). Pleuropulmonary manifestations were investigated and pleural and bronchoalveolar cells were characterized by RNA analysis, imaging and/or flow cytometry focusing on macrophages. Il-4rα^-/-/Il-5^-/- mice were hypermicrofilaremic and showed an enhanced filarial survival but also displayed a drastic reduction of microfilaria-driven pleural cavity pathologies. In parallel, pleural macrophages from Il-4rα^-/-/Il-5^-/- mice lacked expression of prototypical alternative activation markers RELMα and Chil3 and showed an altered balance of some markers of the arginine metabolic pathway. In addition, monocytes-derived F4/80^intermediate macrophages from infected Il-4rα^-/-/Il-5^-/- mice failed to mature into resident F4/80^high large macrophages. Altogether these data emphasize that the presence of both microfilariae and IL-4R/IL-5 signaling are critical in the development of the pathology and in the phenotype of macrophages. In Il-4rα^-/-/Il-5^-/- mice, the balance is in favor of parasite development while limiting the pathology associated with the host immune response.

Mechanisms of Peritoneal Mesothelial Cells in Peritoneal Adhesion

A peritoneal adhesion (PA) is a fibrotic tissue connecting the abdominal or visceral organs to the peritoneum. The formation of PAs can induce a variety of clinical diseases. However, there is currently no effective strategy for the prevention and treatment of PAs. Damage to peritoneal mesothelial cells (PMCs) is believed to cause PAs by promoting inflammation, fibrin deposition, and fibrosis formation. In the early stages of PA formation, PMCs undergo mesothelial–mesenchymal transition and have the ability to produce an extracellular matrix. The PMCs may transdifferentiate into myofibroblasts and accelerate the formation of PAs. Therefore, the aim of this review was to understand the mechanism of action of PMCs in PAs, and to offer a theoretical foundation for the treatment and prevention of PAs.

Monocyte-derived peritoneal macrophages protect C57BL/6 mice against surgery-induced adhesions

Peritoneal adhesions commonly occur after abdominal or pelvic surgery. These scars join internal organs to each other or to the cavity wall and can present with abdominal or pelvic pain, and bowel obstruction or female infertility. The mechanisms underlying adhesion formation remain unclear and thus, effective treatments are not forthcoming. Peritoneal macrophages accumulate after surgery and previous studies have attributed either pro- or anti-scarring properties to these cells. We propose that there are complex and nuanced responses after surgery with respect to both resident and also monocyte-derived peritoneal macrophage subpopulations. Moreover, we contend that differences in responses of specific macrophage subpopulations in part explain the risk of developing peritoneal scars. We characterized alterations in peritoneal macrophage subpopulations after surgery-induced injury using two strains of mice, BALB/c and C57BL/6, with known differences in macrophage response post-infection. At 14 days post-surgery, BALB/c mice displayed more adhesions compared with C57BL/6 mice. This increase in scarring correlated with a lower influx of monocyte-derived macrophages at day 3 post-surgery. Moreover, BALB/c mice showed distinct macrophage repopulation dynamics after surgery. To confirm a role for monocyte-derived macrophages, we used Ccr2-deficient mice as well as antibody-mediated depletion of CCR2 expressing cells during initial stages of adhesion formation. Both Ccr2-deficient and CCR2-depleted mice showed a significant increase in adhesion formation associated with the loss of peritoneal monocyte influx. These findings revealed an important protective role for monocyte-derived cells in reducing adhesion formation after surgery.

Activating SIRT3 in peritoneal mesothelial cells alleviates postsurgical peritoneal adhesion formation by decreasing oxidative stress and inhibiting the NLRP3 inflammasome

Peritoneal adhesions (PAs) are a serious complication of abdominal surgery and negatively affect the quality of life of millions of people worldwide. However, a clear molecular mechanism and a standard therapeutic strategy for PAs have not been established. Here, we developed a standardized method to mimic the pathological changes in PAs and found that sirtuin 3 (SIRT3) expression was severely decreased in adhesion tissues, which was consistent with our bioinformatics analysis and patient adhesion tissue analysis. Thus, we hypothesized that activating SIRT3 could alleviate postsurgical PAs. Sirt3-deficient (Sirt3^−/−) mice exhibited many more PAs after standardized abdominal surgery. Furthermore, compared with wild-type (Sirt3^+/+) mice, Sirt3-deficient (Sirt3^−/−) mice showed more prominent reactive oxygen species (ROS) accumulation, increased levels of inflammatory factors, and exacerbated mitochondrial damage and fragmentation. In addition, we observed NLRP3 inflammasome activation in the adhesion tissues of Sirt3^−/− but, not Sirt3^+/+ mice. Furthermore, mesothelial cells sorted from Sirt3^−/− mice exhibited impaired mitochondrial bioenergetics and redox homeostasis. Honokiol (HKL), a natural compound found in several species of the genus Magnolia, could activate SIRT3 in vitro. Then, we demonstrated that treatment with HKL could reduce oxidative stress and the levels of inflammatory factors and suppress NLRP3 activation in vivo, reducing the occurrence of postsurgical PAs. In vitro treatment with HKL also restored mitochondrial bioenergetics and promoted mesothelial cell viability under oxidative stress conditions. Taken together, our findings show that the rescue of SIRT3 by HKL may be a new therapeutic strategy to alleviate and block postsurgical PA formation.

Treatment with honokiol, a compound found in magnolia tree bark, significantly reduces formation of internal scar tissue after abdominal surgery in mice. Healing of incisions in the peritoneum, the connective tissue lining the abdomen, can result in scar tissue bonds known as peritoneal adhesions (PA), causing complications such as infertility or bowel obstructions. The mechanism of PA formation is unknown, and no therapies are available. Xuqi Li at The First Affiliated Hospital of Xi’an Jiaotong University, China, and co-workers found that PA tissues in both mice and human patients had decreased levels of SIRT3, a stress-response protein. Mice lacking SIRT3 showed increased inflammation and PA formation. When mice were treated with honokiol the day after surgery in order to boost SIRT3 levels, PA formation was significantly decreased. These results suggest a possible preventative treatment for post-surgical PAs.

Macrophages Rapidly Seal off the Punctured Zebrafish Larval Brain through a Vital Honeycomb Network Structure

There is accumulating evidence that macrophages play additional important roles in tissue damage besides their typical phagocytosis. Although the aggregation of macrophages on injured sites has long been observed, few researchers have focused on the role of the overall structure of macrophage aggregation. In this study, we developed a standardized traumatic brain injury (TBI) model in zebrafish larvae to mimic edema and brain tissue spillage symptoms after severe brain trauma. Using time-lapse imaging, we showed that macrophages/microglia in zebrafish larvae responded rapidly and dominated the surface of injured tissue, forming a meaningful honeycomb network structure through their compact aggregation and connection. Disrupting this structure led to fatal edema-like symptoms with severe loss of brain tissue. Using the RNA-Seq, together with the manipulation of in vitro cell lines, we found that collagen IV was indispensable to the formation of honeycomb network structures. Our study thus revealed a novel perspective regarding macrophages forming a protective compact structure with collagen IV. This honeycomb network structure acted as a physical barrier to prevent tissue loss and maintain brain homeostasis after TBI. This study may provide new evidence of macrophages’ function for the rapid protection of brain tissue after brain injury.

Tumor-associated macrophages in liver cancer: From mechanisms to therapy

Multidimensional analyses have demonstrated the presence of a unique tumor microenvironment (TME) in liver cancer. Tumor-associated macrophages (TAMs) are among the most abundant immune cells infiltrating the TME and are present at all stages of liver cancer progression, and targeting TAMs has become one of the most favored immunotherapy strategies. In addition, macrophages and liver cancer cells have distinct origins. At the early stage of liver cancer, macrophages can provide a niche for the maintenance of liver cancer stem cells. In contrast, cancer stem cells (CSCs) or poorly differentiated tumor cells are key factors modulating macrophage activation. In the present review, we first propose the origin connection between precursor macrophages and liver cancer cells. Macrophages undergo dynamic phenotypic transition during carcinogenesis. In this course of such transition, it is critical to determine the appropriate timing for therapy and block specific markers to suppress pro-tumoral TAMs. The present review provides a more detailed discussion of transition trends of such surface markers than previous reviews. Complex crosstalk occurs between TAMs and liver cancer cells. TAMs play indispensable roles in tumor progression, angiogenesis, and autophagy due to their heterogeneity and robust plasticity. In addition, macrophages in the TME interact with other immune cells by directing cell-to-cell contact or secreting various effector molecules. Similarly, tumor cells combined with other immune cells can drive macrophage recruitment and polarization. Despite the latest achievements and the advancements in treatment strategies following TAMs studies, comprehensive discussions on the communication between macrophages and cancer cells or immune cells in liver cancer are currently lacking. In this review, we discussed the interactions between TAMs and liver cancer cells (from cell origin to maturation), the latest therapeutic strategies (including chimeric antigen receptor macrophages), and critical clinical trials for hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (iCCA) to provide a rationale for further clinical investigation of TAMs as a potential target for treating patients with liver cancer.

The Essential Role of FoxO1 in the Regulation of Macrophage Function

Macrophages are widely distributed in various tissues and organs. They not only participate in the regulation of innate and adaptive immune response, but also play an important role in tissue homeostasis. Dysregulation of macrophage function is closely related to the initiation, development and prognosis of multiple diseases, including infection and tumorigenesis. Forkhead box transcription factor O1 (FoxO1) is an important member among the forkhead box transcription factor family. Through directly binding to the promoter regions of downstream target genes, FoxO1 is implicated in cell proliferation, apoptosis, metabolic activities and other biological processes. In this review, we summarized the regulatory role of FoxO1 in macrophage phagocytosis, migration, differentiation and inflammatory activation. We also emphasized that macrophage reciprocally modulated FoxO1 activity via a post-translational modification (PTM) dominant manner.

Cell origin and niche availability dictate the capacity of peritoneal macrophages to colonize the cavity and omentum

The relationship between macrophages of the peritoneal cavity and the adjacent omentum remains poorly understood. Here, we describe two populations of omental macrophages distinguished by CD102 expression and use an adoptive cell transfer approach to investigate whether these arise from peritoneal macrophages, and whether this depends upon inflammatory status, the origin of peritoneal macrophages and availability of the omental niches. We show that whereas established resident peritoneal macrophages largely fail to migrate to the omentum, monocyte-derived resident cells readily migrate and form a substantial component of omental CD102⁺ macrophages in the months following resolution of peritoneal inflammation. In contrast, both populations had the capacity to migrate to the omentum in the absence of endogenous peritoneal and omental macrophages. However, inflammatory macrophages expanded more effectively and more efficiently repopulated both CD102⁺ and CD102^- omental populations, whereas established resident macrophages partially reconstituted the omental niche via recruitment of monocytes. Hence, cell origin determines the migration of peritoneal macrophages to the omentum and predisposes established resident macrophages to drive infiltration of monocyte-derived cells.

CD11c identifies microbiota and EGR2-dependent MHCII+ serous cavity macrophages with sexually dimorphic fate in mice

The murine serous cavities contain a rare and enigmatic population of short-lived F4/80lo MHCII+ macrophages but what regulates their development, survival, and fate is unclear. Here, we show that mature F4/80lo MHCII+ peritoneal macrophages arise after birth, but that this occurs largely independently of colonization by microbiota. Rather, microbiota specifically regulate development of a subpopulation of CD11c+ cells that express the immunoregulatory cytokine RELM-α, are reliant on the transcription factor EGR2, and develop independently of the growth factor CSF1. Furthermore, we demonstrate that intrinsic expression of RELM-α, a signature marker shared by CD11c+ and CD11c- F4/80lo MHCII+ cavity macrophages, regulates survival and differentiation of these cells in the peritoneal cavity in a sex-specific manner. Thus, we identify a previously unappreciated diversity in serous cavity F4/80lo MHCII+ macrophages that is regulated by microbiota, and describe a novel sex and site-specific function for RELM-α in regulating macrophage endurance that reveals the unique survival challenge presented to monocyte-derived macrophages by the female peritoneal environment.

Gata6+ resident peritoneal macrophages promote the growth of liver metastasis

Emerging evidence suggests that resident macrophages within tissues are enablers of tumor growth. However, a second population of resident macrophages surrounds all visceral organs within the cavities and nothing is known about these GATA6⁺ large peritoneal macrophages (GLPMs) despite their ability to invade injured visceral organs by sensing danger signals. Here, we show that GLPMs invade growing metastases that breach the visceral mesothelium of the liver via the "find me signal", ATP. Depleting GLPMs either by pharmacological or genetic tools, reduces metastases growth. Apoptotic bodies from tumor cells induces programmed cell death ligand 1 (PD-L1) upregulation on GLPMs which block CD8⁺ T cell function. Direct targeting of GLPMs by intraperitoneal but not intravenous administration of anti-PD-L1 reduces tumor growth. Thermal ablation of liver metastases recruits huge numbers of GLPMs and enables rapid regrowth of tumors. GLPMs contribute to metastatic growth and tumor recurrence.

Peritoneal GATA6+ macrophage drives hepatic immunopathogenesis and maintains the Treg cell niche in the liver

The source of macrophages that contribute to human liver disease remains poorly understood. The purpose of this study is to investigate the functional mechanism of peritoneal macrophages in the development of hepatic immunopathology. By performing the natural infection with the blood fluke Schistosoma japonicum (S. japonicum) and the chemically carbon tetrachloride (CCl₄ )-induced liver injured mouse model, we identified the peritoneal cavity as an essential source of hepatic macrophages. Here, we show that a large number of F4/80⁺ macrophages was accumulated in the peritoneal cavity during liver injury. An unknown source population of macrophages, which highly expressed GATA6 that is specific to peritoneal macrophages, was found to exist in the injured livers. Peritoneal macrophage deletion by injection with clodronate-containing liposomes led to an attenuated hepatic pathology and the inflammatory microenvironment, while adoptive transfer of macrophages into the abdominal cavity, by contrast, results in restoring liver pathology. Importantly, there are set genes of monocyte chemoattractant protein (MCP)-1, -2, and -3 that are highly related to recruit GATA6⁺ macrophages during S. japonicum infection, while administration of bindarit, a selective inhibitor of MCPs synthesis, dramatically decreased the hepatic expression of GATA6⁺ macrophages and thus attenuated hepatic pathology. Furthermore, in vivo study showed that peritoneal macrophages promote hepatic immunopathology is dependent on the accumulation of regulatory T cells (Tregs) in the liver. Altogether, these data provide the first clear evidence that GATA6⁺ peritoneal macrophages play critical roles in both the formation of hepatic immunopathology and the accumulation of Tregs cells.

Genetic Lineage Tracing of Pericardial Cavity Macrophages in the Injured Heart

BACKGROUND

Macrophages play an important role in cardiac repair after myocardial infarction (MI). In addition to the resident macrophages and blood-derived monocytes, Gata6⁺ cavity macrophages located in the pericardial space were recently reported to relocate to the injured myocardium and prevent cardiac fibrosis. However, there is no direct genetic evidence to support it.

METHODS

We used dual recombinases (Cre and Dre) to specifically label Gata6⁺ pericardial macrophages (GPCMs) in vivo. For functional study, we generated genetic systems to specifically ablate GPCMs by induced expression of diphtheria toxin receptor or knockout of Gata6 (GATA binding protein 6) gene in GPCMs. We used these genetic systems to study GPCMs in pericardium intact MI model.

RESULTS

Dual recombinases-mediated genetic system targeted GPCMs specifically and efficiently. Lineage tracing study revealed accumulation of GPCMs on the surface of MI heart without deep penetration into the myocardium. We did not detect significant change of cardiac fibrosis or function of MI hearts after cell ablation or Gata6 knockout in GPCMs.

CONCLUSIONS

GPCMs minimally invade the injured heart after MI. Nor do they prevent cardiac fibrosis and exhibit reparative function on injured heart. This study also underlines the importance of using specific genetic tool for studying in vivo cell fates and functions.

GATA6+ Peritoneal Resident Macrophage: The Immune Custodian in the Peritoneal Cavity

Peritoneal resident macrophages (PRMs) have been a prominent topic in the research field of immunology due to their critical roles in immune surveillance in the peritoneal cavity. PRMs initially develop from embryonic progenitor cells and are replenished by bone marrow origin monocytes during inflammation and aging. Furthermore, PRMs have been shown to crosstalk with other cells in the peritoneal cavity to control the immune response during infection, injury, and tumorigenesis. With the advance in genetic studies, GATA-binding factor 6 (GATA6) has been identified as a lineage determining transcription factor of PRMs controlling the phenotypic and functional features of PRMs. Here, we review recent advances in the developmental origin, the phenotypic identity, and functions of PRMs, emphasizing the role of GATA6 in the pathobiology of PRMs in host defense, tissue repairing, and peritoneal tumorigenesis.