Role Of Efferocytosis Research Articles

Efferocytosis and Bone Dynamics.

This review summarizes the recently published scientific evidence regarding the role of efferocytosis in bone dynamics and skeletal health. Several types of efferocytes have been identified within the skeleton, with macrophages being the most extensively studied. Efferocytosis is not merely a 'clean-up' process vital for maintaining skeletal homeostasis; it also plays a crucial role in promoting resolution pathways and orchestrating bone dynamics, such as osteoblast-osteoclast coupling during bone remodeling. Impaired efferocytosis has been associated with aging-related bone loss and various skeletal pathologies, including osteoporosis, osteoarthritis, rheumatoid arthritis, and metastatic bone diseases. Accordingly, emerging evidence suggests that targeting efferocytic mechanisms has the potential to alleviate these conditions. While efferocytosis remains underexplored in the skeleton, recent discoveries have shed light on its pivotal role in bone dynamics, with important implications for skeletal health and pathology. However, there are several knowledge gaps and persisting technical limitations that must be addressed to fully unveil the contributions of efferocytosis in bone.

Role of efferocytosis in atherosclerosis

Role of efferocytosis in atherosclerosis

Role of Efferocytosis in Health and Diseases

Efferocytosis is the process of removal of apoptotic cells through phagocytosis by the specialized cells known as efferocytes. Clearance of dead cells also plays an important role in the defensive system of organisms as efferocytosis maintains homeostasis and repairing of tissues and organs. In this process, the dying cell releases signals for identification and engulfment which is further processed by macrophages. Efferocytosis prevents the secondary necrosis and release of pro-inflammatory cellular contents. This clearance process involves interplay of signaling molecules, receptors, and other mediators that ensures prompt recognitions and removal of dying cells. Dysregulation of efferocytosis has been implicated in various pathological conditions, including autoimmune diseases, chronic inflammation, and atherosclerosis. This review focuses on some common autoimmune diseases, cardiovascular diseases, respiratory disorders, and neurodegenerative disorders due to impaired efferocytosis. To describe the pathophysiology of efferocytosis in diseases more extensive studies are required.

TMIC-53. TRANSGLUTAMINASE 2 EXPRESSION IN GLIOBLASTOMA: EVIDENCE FOR A ROLE IN EFFEROCYTOSIS

Abstract Glioblastoma is the most common type of brain cancer in adults. It is currently incurable and there is a clear need for more effective treatments. The heterogeneity of this cancer and its ability to promote both local and systemic immunosuppression are major obstacles to the development of effective therapies. Previous studies have explored the use of transglutaminase 2 (TGM2) inhibitors for glioblastoma therapy. These studies focussed on TGM2 that is expressed in a subset of glioblastoma cells. We show here that glioblastoma-associated macrophages are a major source of TGM2 in glioblastoma tumours. Analysis of bulk and single cell RNAseq data showed that TGM2 mRNA was expressed at high levels in glioblastoma-associated macrophages. Immunohistochemical and immunofluorescence analysis of TGM2 expression was performed in a mouse xenograft model in which human mesenchymal subtype glioblastoma cells were grown intracerebrally in nude mice. In these xenograft tumours, glioblastoma cells were negative for TGM2 expression, while infiltrating macrophages were strongly positive. The most intense staining for TGM2 was observed in macrophages in the vicinity of necrotic regions. Apoptotic cells were frequently present within the necrotic regions and highly TGM2-positive macrophages were observed to be phagocytosing these. The same patterns of TGM2 expression were also observed in samples from glioblastoma patients. Consistent with a role in phagocytosis, TGM2 co-localized with the endosomal protein CD68 in glioblastoma-associated macrophages. The phagocytosis of apoptotic cells by macrophages, known as efferocytosis, is tolerogenic, both because it clears potentially antigenic material and because it induces an immunosuppressive phenotype in macrophages. As TGM2 has a previously established role in efferocytosis and autoimmunity suppression, our findings suggest that TGM2 has a role in maintaining the glioblastoma immunosuppressive environment and that its inhibition might enhance immunotherapy for this cancer.

Interaction, immune infiltration characteristics and prognostic modeling of efferocytosis-related subtypes in glioblastoma

BackgroundEfferocytosis is a biological process in which phagocytes remove apoptotic cells and vesicles from tissues. This process is initiated by the release of inflammatory mediators from apoptotic cells and plays a crucial role in resolving inflammation. The signals associated with efferocytosis have been found to regulate the inflammatory response and the tumor microenvironment (TME), which promotes the immune escape of tumor cells. However, the role of efferocytosis in glioblastoma multiforme (GBM) is not well understood and requires further investigation.MethodsIn this study, we conducted a comprehensive analysis of 22 efferocytosis-related genes (ERGs) by searching for studies related to efferocytosis. Using bulk RNA-Seq and single-cell sequencing data, we analyzed the expression and mutational characteristics of these ERGs. By using an unsupervised clustering algorithm, we obtained ERG clusters from 549 GBM patients and evaluated the immune infiltration characteristics of each cluster. We then identified differential genes (DEGs) in the two ERG clusters and classified GBM patients into different gene clusters using univariate cox analysis and unsupervised clustering algorithms. Finally, we utilized the Boruta algorithm to screen for prognostic genes and reduce dimensionality, and the PCA algorithm was applied to create a novel efferocytosis-related scoring system.ResultsDifferential expression of ERGs in glioma cell lines and normal cells was analyzed by rt-PCR. Cell function experiments, on the other hand, validated TIMD4 as a tumor risk factor in GBM. We found that different ERG clusters and gene clusters have distinct prognostic and immune infiltration profiles. The ERG signature we developed provides insight into the tumor microenvironment of GBM. Patients with lower ERG scores have a better survival rate and a higher likelihood of benefiting from immunotherapy.ConclusionsOur novel efferocytosis-related signature has the potential to be used in clinical practice for risk stratification of GBM patients and for selecting individuals who are likely to respond to immunotherapy. This can help clinicians design appropriate targeted therapies before initiating clinical treatment.

The role of efferocytosis and transplant rejection: Strategies in promoting transplantation tolerance using apoptotic cell therapy and/or synthetic particles.

Recently, efforts have been made to recognize the precise reason(s) for transplant failure and the process of rejection utilizing the molecular signature. Most transplant recipients do not appreciate the unknown length of survival of allogeneic grafts with the existing standard of care. Two noteworthy immunological pathways occur during allogeneic transplant rejection. A nonspecific innate immune response predominates in the early stages of the immune reaction, and allogeneic antigens initiate a donor-specific adaptive reaction. Though the adaptive response is the major cause of allograft rejection, earlier pro-inflammatory responses that are part of the innate immune response are also regarded as significant in graft loss. The onset of the innate and adaptive immune response causes chronic and acute transplant rejection. Currently employed immunosuppressive medications have shown little or no influence on chronic rejection and, as a result, on overall long-term transplant survival. Furthermore, long-term pharmaceutical immunosuppression is associated with side effects, toxicity, and an increased risk of developing diseases, both infectious and metabolic. As a result, there is a need for the development of innovative donor-specific immunosuppressive medications to regulate the allorecognition pathways that induce graft loss and to reduce the side effects of immunosuppression. Efferocytosis is an immunomodulatory mechanism with fast and efficient clearance of apoptotic cells (ACs). As such, AC therapy strategies have been suggested to limit transplant-related sequelae. Efferocytosis-based medicines/treatments can also decrease the use of immunosuppressive drugs and have no detrimental side effects. Thus, this review aims to investigate the impact of efferocytosis on transplant rejection/tolerance and identify approaches using AC clearance to increase transplant viability.

The role of efferocytosis in neuro-degenerative diseases.

Efferocytosis has a critical role in maintaining tissues and organs' homeostasis by removing apoptotic cells. It is essential for human health, and disturbances in efferocytosis may result indifferent illnesses. In case of inadequate clearance of the dead cells, the content in the cells would be released. In fact, it induces some damages to the tissue and leads to the prolonged inflammation, so unsuitable phagocytosis of the apoptotic cells is involved in occurrence as well as expansion of numerous human chronic inflammatory diseases. Studies have shown age dependence of the neuro-degenerative diseases, which are largely due to the neuro-inflammation and the loss of neurons and thus cause the brain's functional disorders. Efferocytosis is coupled to anti-inflammatory responses that contribute to the elimination of the dying neurons in neuro-degenerative diseases, so its disruption may make a risk factor in numerous human chronic inflammatory diseases such as multiple sclerosis, Alzheimer's disease, glioblastoma, and Rett syndrome. This study is a review of the efferocytosis molecular pathways and their role in neuro-degenerative diseases in order to discover a new treatment option to cure patients.

Bfc, a novel serpent co-factor for the expression of croquemort, regulates efferocytosis in Drosophila melanogaster.

Efferocytosis is the process by which phagocytes recognize, engulf, and digest (or clear) apoptotic cells during development. Impaired efferocytosis is associated with developmental defects and autoimmune diseases. In Drosophila melanogaster, recognition of apoptotic cells requires phagocyte surface receptors, including the scavenger receptor CD36-related protein, Croquemort (Crq, encoded by crq). In fact, Crq expression is upregulated in the presence of apoptotic cells, as well as in response to excessive apoptosis. Here, we identified a novel gene bfc (booster for croquemort), which plays a role in efferocytosis, specifically the regulation of the crq expression. We found that Bfc protein interacts with the zinc finger domain of the GATA transcription factor Serpent (Srp), to enhance its direct binding to the crq promoter; thus, they function together in regulating crq expression and efferocytosis. Overall, we show that Bfc serves as a Srp co-factor to upregulate the transcription of the crq encoded receptor, and consequently boosts macrophage efferocytosis in response to excessive apoptosis. Therefore, this study clarifies how phagocytes integrate apoptotic cell signals to mediate efferocytosis.

Efferocytosis during Skeletal Muscle Regeneration.

Efferocytosis, i.e., engulfment of dead cells by macrophages, is a crucial step during tissue repair after an injury. Efferocytosis delineates the transition from the pro-inflammatory phase of the inflammatory response to the recovery phase that ensures tissue reconstruction. We present here the role of efferocytosis during skeletal muscle regeneration, which is a paradigm of sterile tissue injury followed by a complete regeneration. We present the molecular mechanisms that have been described to control this process, and particularly the metabolic control of efferocytosis during skeletal muscle regeneration.

Abstract 1735: The potent and selective MERTK/AXL inhibitor PF-5807/ARRY-067 activates dendritic cells to cross-prime CD8+ T cells for anti-tumor activity

Abstract The TAM family of receptor tyrosine kinases (MERTK, AXL, and TYRO3) are expressed on DCs and macrophages, and they serve a critical role in efferocytosis, by which apoptotic bodies are cleared by engulfment. Their activation drives phagocytic activity concomitant to promoting an immuno-suppressive, tolerogenic state in DCs and the M2 polarization of macrophages. This dual signaling mechanism allows for the clearance of cells undergoing non-pathologic apoptotic turnover without inappropriately breaking self-tolerance and driving auto-immunity. Unlike most immuno-therapy targets, the KOs of the TAM kinases, PD-1, and CTLA-4 share common auto-immune disease phenotypes such as splenomegaly, immune infiltration of the liver, arthritis, and lupus. Furthermore, viruses have evolved to promote PD-1/CTLA-4 signaling to suppress the anti-viral immune response, and they similarly target the TAM receptors via apoptotic mimicry to reduce the inflammatory response. This confluence of immune phenotypes provided the biological rationale for the discovery of PF-5807/ARRY-067, a potent and selective inhibitor of MERTK/AXL as a DC-activating immuno-oncology therapeutic. Based on the IC50 for inhibition of phospho-MERTK/AXL in cell-based assays, our mouse PK and PK/PD studies determined that 50 mg/kg PF-5807 provided IC90 plasma coverage for 12 hours. This PK profile supported a twice-daily dosing schedule for maintaining continuous suppression of MERTK and AXL, which was used for mechanistic and efficacy studies in mouse models. To investigate DC and T cell responses to PF-5807, mice were adoptively-transferred with OT-I T cells and challenged with ovalbumin immunization; flow cytometry analysis indicated that PF-5807 treatment increased the fraction of activated, Class II MHC-positive DCs, as well as cross-primed IFNγ+ TNFα+ OT-I T cells. Also, we found that cytotoxic T lymphocytes were necessary for tumor control in the E0771 mouse syngeneic tumor model, as depletion of CD8+ T cells abrogated all activity by PF-5807 in inhibiting tumor growth. This anti-tumor activity was further demonstrated in the MC-38 and EMT6 tumor models, where single agent PF-5807 effected 57-88% TGI and a 13-38% cure rate, while combination with PD-1 blockade drove 99-100% TGI and a 75-100% cure rate. Finally, these complete responders rejected tumor re-challenge without further treatment, resulting in extended survival and durable cures that corroborate the development of immunologic memory. Therefore, we find that PF-5807 activates DCs to cross-prime CD8+ T cells, which are necessary for tumor control and are likely responsible for the establishment of tumor-specific memory T cells. PF-5807 is currently in an ongoing Phase I clinical trial in patients with advanced or metastatic solid tumors, with the intent to explore combination with anti-PD-1/anti-PD-L1 antibodies. Citation Format: Jim Wong, Jacqueline Harrison, Karyn Bouhana, Nhan Nguyen, Namir Shaabani, Vincent F. Vartabedian, LouAnn Cable, Robert Rieger, Lisa Pieti Opie, Shelley Allen, Adam Cook, Joshua Dahlke, Ronald Hinklin, David Chantry, Shannon Winski, John Teijaro. The potent and selective MERTK/AXL inhibitor PF-5807/ARRY-067 activates dendritic cells to cross-prime CD8+ T cells for anti-tumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1735.

Cellular Responses to the Efferocytosis of Apoptotic Cells.

The rapid and efficient phagocytic clearance of apoptotic cells, termed efferocytosis, is a critical mechanism in the maintenance of tissue homeostasis. Removal of apoptotic cells through efferocytosis prevents secondary necrosis and the resultant inflammation caused by the release of intracellular contents. The importance of efferocytosis in homeostasis is underscored by the large number of inflammatory and autoimmune disorders, including atherosclerosis and systemic lupus erythematosus, that are characterized by defective apoptotic cell clearance. Although mechanistically similar to the phagocytic clearance of pathogens, efferocytosis differs from phagocytosis in that it is immunologically silent and induces a tissue repair response. Efferocytes face unique challenges resulting from the internalization of apoptotic cells, including degradation of the apoptotic cell, dealing with the extra metabolic load imposed by the processing of apoptotic cell contents, and the coordination of an anti-inflammatory, pro-tissue repair response. This review will discuss recent advances in our understanding of the cellular response to apoptotic cell uptake, including trafficking of apoptotic cell cargo and antigen presentation, signaling and transcriptional events initiated by efferocytosis, the coordination of an anti-inflammatory response and tissue repair, unique cellular metabolic responses and the role of efferocytosis in host defense. A better understanding of how efferocytic cells respond to apoptotic cell uptake will be critical in unraveling the complex connections between apoptotic cell removal and inflammation resolution and maintenance of tissue homeostasis.

TAM Receptor Inhibition–Implications for Cancer and the Immune System

Simple SummaryTAM receptors are a family of receptor tyrosine kinases, comprising Tyro3, Axl and MerTK. Their primary role is in digestion of dying cells by macrophages without alarming the immune system. TAM receptors are also expressed by cancer cells in which signaling is oncogenic, and for this reason there is growing interest and research into TAM inhibition. This approach to cancer treatment may, however, come into conflict with beneficial and costimulatory TAM receptor signaling in T cells and natural killer (NK) cells. The aim of this review is to explore in detail the effects of TAM receptor inhibition on cancer cells and immune cells, and how the ramifications of this inhibition may affect cancer treatment in humans.Tyro3, Axl and MerTK (TAM) receptors are receptor tyrosine kinases which play important roles in efferocytosis and in the balancing of immune responses and inflammation. TAM receptor activation is induced upon binding of the ligands protein S (Pros1) or growth arrest-specific protein 6 (Gas6) which act as bridging molecules for binding of phosphatidyl serine (PtdSer) exposed on apoptotic cell membranes. Upon clearance of apoptotic cell material, TAM receptor activation on innate cells suppresses proinflammatory functions, thereby ensuring the immunologically silent removal of apoptotic material in the absence of deleterious immune responses. However, in T cells, MerTK signaling is costimulatory and promotes activation and functional output of the cell. MerTK and Axl are also aberrantly expressed in a range of both hematological and solid tumor malignancies, including breast, lung, melanoma and acute myeloid leukemia, where they have a role in oncogenic signaling. Consequently, TAM receptors are being investigated as therapeutic targets using small molecule inhibitors and have already demonstrated efficacy in mouse tumor models. Thus, inhibition of TAM signaling in cancer cells could have therapeutic value but given the opposing roles of TAM signaling in innate cells and T cells, TAM inhibition could also jeopardize anticancer immune responses. This conflict is discussed in this review, describing the effects of TAM inhibition on cancer cells as well as immune cells, while also examining the intricate interplay of cancer and immune cells in the tumor microenvironment.

Abstract PO032: TIM3 regulation by phosphatidylserine

Abstract Immune responses have been successfully reactivated in cancer by targeting inhibitory receptors such as PD-1 on exhausted T cells to block immune checkpoints. Many patients do not respond, however, and a key challenge in immuno-oncology is to identify and understand new immune-regulatory targets to increase response rates. One other co-inhibitory receptor in T cells is TIM3, which – like PD-1 – is upregulated on exhausted T cells in the tumor microenvironment. TIM3 belongs to a family of phosphatidylserine (PS) receptors with well-documented roles in efferocytosis by phagocytes. However, the role of PS in regulating TIM3 remains unclear. Previous studies have shown that TIM3 can variously enhance or inhibit T cell signaling, though exactly how TIM3 accomplishes this range of activity is unknown. We therefore investigated how TIM3 levels modulate T cell signaling, and how PS in turn influences TIM3 activity. We found that TIM3 promoted T cell activity in a Jurkat T cell model when expressed at high – but not low – levels on the cell surface. We also confirmed the ability of human TIM3 to bind PS with low micromolar affinity using surface plasmon resonance. To investigate how PS affects the ability of TIM3 to promote T cell signaling in this model, we employed several approaches, including adding PS to the cell culture, manipulating TIM3 to reduce or abrogate PS binding (using chimeric receptors and TIM3 mutants), and pharmacological blockade of PS binding using a functional TIM3 antibody. Together, these studies supported a role for PS in regulating TIM3 activity, where decreased or abrogated PS binding prevented TIM3 from promoting T cell signaling. We also sought to understand what changes in T cell receptor (TCR) signaling might account for the TIM3-dependent effects we observed. We found that TIM3 did not impact phosphorylation of downstream components in the TCR signaling cascade. Rather, cells expressing high – but not low – surface levels of TIM3 displayed enhanced phosphorylation of receptor components in the TCR signaling pathway, similar to what has been reported for PD-1. We hypothesize that TIM3 modulates TCR signaling by modifying the localization and/or dwell time of one or more signaling effector proteins (e.g. phosphatases) in a manner dependent on PS engagement. The consequences of this are then determined by surface levels of TIM3. Our results demonstrate that PS does function as a ligand capable of modulating TIM3 activity, and provide new mechanistic insight into how TIM3 modulates TCR signaling. Citation Format: Courtney M. Smith, Alice Li, Nithya Krishnamurthy, Mark A. Lemmon. TIM3 regulation by phosphatidylserine [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO032.

Potential Mechanisms and Effects of Efferocytosis in Atherosclerosis.

Atherosclerosis (AS) is the main pathological basis for the development of cardio-cerebrovascular diseases. Abnormal accumulation of apoptotic and necrotic cells resulted in plaque enlargement, necrotic core formation and plaque rupture in AS. Under physiological conditions, apoptotic cells (ACs) could be effectively phagocytized and cleared by phagocyte-mediated efferocytosis. In contrast, the clearance efficiency of ACs in AS plaque was much lower because of the impaired efferocytosis in AS. Recent findings have made great progress on the molecular mechanisms of efferocytosis process and dynamic regulation, and its dysfunction on organismal health. Yet, there are still few effective treatments for this process. This article reviews the mechanism of efferocytosis and the role of efferocytosis in AS, highlighting a novel therapeutic strategy for AS, which mainly prevents the progression of plaque by targeting efferocytosis.

Ca2+ Flux: Searching for a Role in Efferocytosis of Apoptotic Cells in Atherosclerosis.

In atherosclerosis, macrophages in the arterial wall ingest plasma lipoprotein-derived lipids and become lipid-filled foam cells with a limited lifespan. Thus, efficient removal of apoptotic foam cells by efferocytic macrophages is vital to preventing the dying foam cells from forming a large necrotic lipid core, which, otherwise, would render the atherosclerotic plaque vulnerable to rupture and would cause clinical complications. Ca2+ plays a role in macrophage migration, survival, and foam cell generation. Importantly, in efferocytic macrophages, Ca2+ induces actin polymerization, thereby promoting the formation of a phagocytic cup necessary for efferocytosis. Moreover, in the efferocytic macrophages, Ca2+ enhances the secretion of anti-inflammatory cytokines. Various Ca2+ antagonists have been seminal for the demonstration of the role of Ca2+ in the multiple steps of efferocytosis by macrophages. Moreover, in vitro and in vivo experiments and clinical investigations have revealed the capability of Ca2+ antagonists in attenuating the development of atherosclerotic plaques by interfering with the deposition of lipids in macrophages and by reducing plaque calcification. However, the regulation of cellular Ca2+ fluxes in the processes of efferocytic clearance of apoptotic foam cells and in the extracellular calcification in atherosclerosis remains unknown. Here, we attempted to unravel the molecular links between Ca2+ and efferocytosis in atherosclerosis and to evaluate cellular Ca2+ fluxes as potential treatment targets in atherosclerotic cardiovascular diseases.

Abstract 4556: Targeting the TAM receptors on prostate cancer tumor-associated macrophages

Abstract Tumor growth and progression is influenced by the composition of the tumor microenvironment including host stromal cells and immune cells. In prostate cancer, a large proportion of the tumor volume is made up of macrophages, and high macrophage infiltrate correlates with poor prognosis. Macrophages can be polarized to various subtypes including M1 and M2 in response to stimuli in their environment. M1 macrophages have anti-tumor functions such as immune stimulation. M2 macrophages have pro-tumor functions such as promoting angiogenesis, extracellular matrix remodeling and immune suppression. The majority of prostate cancer tumor-associated macrophages exhibit M2-like characteristics. Thus, targeting M2 tumor-associated macrophages is a promising strategy for cancer therapy. M2 macrophages engage in efferocytosis, or phagocytosis of apoptotic cells. This process is an anti-inflammatory, immunosuppressive event that promotes tissue remodeling and tumor growth. The TAM receptors (Tyro3, Axl, MerTK) are a family of receptor tyrosine kinases whose role in efferocytosis has been well described in the literature. The TAM receptors bind phosphatidylserine on apoptotic cells using their ligands Gas6 and Protein S as bridging proteins. Following binding to phosphatidylserine, TAM receptor signaling induces a cytoskeleton rearrangement to engulf the apoptotic cell. Since efferocytosis is a tumor promoting process, we hypothesize targeting the TAM receptors on M2 macrophages may be a beneficial anti-cancer strategy. We are characterizing TAM receptor expression on M1 and M2 macrophages using two complementary in vitro methods: macrophage polarization of monocytes derived from healthy human donors and of the acute monocytic leukemia cell line THP-1. Cell surface markers of M1 macrophages (CD86) and M2 macrophages (CD163 and CD206) were measured to assess polarization by flow cytometry. We are currently further confirming the degree of polarization by measuring cytokine secretion and mRNA expression of M1- and M2-associated genes. We used flow cytometry analysis to assess TAM receptor expression on the in vitro polarized M1 and M2 macrophages. In the human monocyte derived model, we detected higher levels of expression of MerTK and Tyro3 on M2 macrophages in several biological replicates. We also found that M2 THP-1 macrophages express higher levels of MerTK and Tyro3 than M1 THP-1 macrophages, consistent with macrophages from the monocyte derived model. In conclusion, these data support the TAM receptors as a relevant therapeutic target for inhibiting M2 pro-tumor functions. Further work by qRT-PCR, western blot and immunofluorescence staining will be used to confirm higher levels of the MerTK and Tyro3 on M2 macrophages and further investigate expression of Axl on M1 and M2 macrophages. Citation Format: Kayla V. Myers, Kenneth J. Pienta. Targeting the TAM receptors on prostate cancer tumor-associated macrophages [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4556.

MERTK tyrosine kinase receptor together with TIM4 phosphatidylserine receptor mediates distinct signal transduction pathways for efferocytosis and cell proliferation

Apoptotic cells expose phosphatidylserine (PtdSer) on their surface, leading to efferocytosis, i.e. their engulfment by resident macrophages that express the PtdSer receptor T cell immunoglobulin mucin receptor 4 (TIM4) and TAM family receptor tyrosine kinase receptors (MERTK, AXL, and TYRO3). TAM family receptors stimulate cell proliferation, and the many aspects of the growth signaling pathway downstream of TAM family receptors have been elucidated previously. However, the signaling cascade for TAM receptor-mediated efferocytosis has been elusive. Here we observed that efferocytosis by mouse-resident peritoneal macrophages was blocked by inhibitors against the MERTK, mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK), AKT Ser/Thr kinase (AKT), focal adhesion kinase (FAK), or STAT6 pathway. Accordingly, apoptotic cells stimulated the phosphorylation of MERTK, ERK, AKT, FAK, and STAT6, but not of IκB or STAT5. A reconstituted efferocytosis system using MERTK- and TIM4-expressing NIH3T3-derived cells revealed that the juxtamembrane and C-terminal regions of MERTK have redundant roles in efferocytosis. The transformation of murine IL-3-dependent Ba/F3 cells (a pro-B cell line) with MERTK and TIM4 enabled them to proliferate in response to apoptotic cells in a PtdSer-dependent manner. This apoptotic cell-induced MERTK-mediated proliferation required both MERTK's juxtamembrane and C-terminal regions and was blocked by inhibitors of not only ERK, AKT, FAK, and STAT6 but also of NF-κB and STAT5 signaling. These results suggest that apoptotic cells stimulate distinct sets of signal transduction pathways via MERTK to induce either efferocytosis or proliferation.

Macrophagic Stabilin-1 Restored Disruption of Vascular Integrity Caused by Sepsis.

Sepsis develops because of overwhelming inflammatory responses to bacterial infection, and disrupts vascular integrity. Stabilin-1 (STAB-1) is a phagocytic receptor, which mediates efferocytosis in a phosphatidylserine (PS)-dependent manner. STAB-1 is expected to play important roles in efferocytosis during sepsis. Here, we determined the role of STAB-1 in maintaining and restoring vascular integrity. Macrophages and vascular endothelial cells were used to assess the effect of STAB-1 on survival rate, phagocytic activity, vascular permeability and transendothelial migration (TEM). Additionally, we investigated whether the high-mobility group box 1 (HMGB1)-receptor for advanced glycated end products complex interfered with the binding of Stab1 to PS. Mortality rate was higher in the Stab1-knockout mice than in the wild-type mice, and STAB-1 deficiency was related to reduced macrophage-mediated efferocytosis and the disruption of vascular integrity, which increased vascular permeability, and enhanced TEM. STAB-1 deficiency promoted lung injury, and elevated the expression of sepsis markers. The exogenous application of the anti-HMGB1 neutralizing antibody improved efferocytosis, vascular integrity and survival rate in sepsis. Collectively, our findings indicated that STAB-1 regulated and maintained vascular integrity through the clearance of infected apoptotic endothelial cells. Moreover, our results suggested that interventions targeting vascular integrity by STAB-1 signalling are promising therapeutic approaches to sepsis.

The Role of Efferocytosis in Autoimmune Diseases.

Apoptosis happens continuously for millions of cells along with the active removal of apoptotic debris in order to maintain tissue homeostasis. In this respect, efferocytosis, i.e., the process of dead cell clearance, is orchestrated through cell exposure of a set of “find me,” “eat me,” and “tolerate me” signals facilitating the engulfment of dying cells through phagocytosis by macrophages and dendritic cells. The clearance of dead cells via phagocytes is of utmost importance to maintain the immune system tolerance to self-antigens. Accordingly, this biological activity prevents the release of autoantigens by dead cells, thus potentially suppressing the undesirable autoreactivity of immune cells and the appearance of inflammatory autoimmune disorders as systemic lupus erythematous and rheumatoid arthritis. In the present study, the apoptosis pathways and their immune regulation were reviewed. Moreover, efferocytosis process and its impairment in association with some autoimmune diseases were discussed.

Meet the First Authors.

HomeCirculation ResearchVol. 121, No. 8Meet the First Authors Free AccessIn BriefPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessIn BriefPDF/EPUBMeet the First Authors Originally published29 Sep 2017https://doi.org/10.1161/RES.0000000000000176Circulation Research. 2017;121:894–895Genome Editing Therapy for DMD Cardiomyopathy (p 923)Download figureDownload PowerPointDr Mona El Refaey earned her BS from Cairo University in Egypt and then she moved to the United States to pursue advanced training in research. She received her PhD in Molecular and Regenerative Medicine from Georgia Regents University (under the mentorship of Dr Carlos M. Isales), where she studied mesenchymal stem cells and the effect of aging on their major signaling pathways and environment. Then, she moved to The Ohio State University for postdoctoral training (in the Dorothy M. Davis Heart and Lung Research Institute under the leadership of Dr Peter J. Mohler). Currently, she is focusing on recent technologies like gene editing, their use in therapeutics and molecular mechanisms underlying heart diseases. Outside work, she likes reading and traveling. Her dream is to translate science to the bedside.Resident MerTK Cleavage in Heart (p 930)Download figureDownload PowerPointDr Matthew DeBerge is currently a postdoctoral fellow in Edward Thorp’s laboratory in the Department of Pathology in the Feinberg School of Medicine at Northwestern University. He completed his undergraduate studies at Illinois State University and obtained his PhD from the Geisel School of Medicine at Dartmouth College. Matt’s current research focuses on the role of efferocytosis by cardiac macrophages in tissue repair and inflammation resolution after cardiac injury. He hopes this will lead to an independent research career investigating the evolutionary significance of inflammatory responses and their relationship to homeostasis and disease. Outside of the lab, Matt enjoys spending time with his wife and son, working out, and watching the defending World Champion Chicago Cubs.Mast Cells Granule Contents Exacerbate DVT in Mice (p 941)Download figureDownload PowerPointDr Tatyana Ponomaryov earned her MSc in Organic Chemistry, and then completed her PhD in hematopoietic stem cells at the Weizmann Institute of Science with Dr Tsvee Lapidot. She is fascinated by niche signals that guide stem cells’ fate. During her postdoctoral training at the Dana-Farber Cancer Institute, Boston with Prof Rosalind Segal, she investigated how stem cells originating in brain tumors would respond to targeted therapy. Upon moving across the pond to the University of Birmingham, she returned to studying vascular stem cells, this time investigating their role in venous thrombosis. Her motto is, “go out of your comfort zone and bring a fresh vision,” something she finds easy to do spending time with her family and three kids, changing countries and learning new things.TLR2 Promotes Thrombosis in Hyperlipidemia (p 951)Download figureDownload PowerPointDr Sudipta Biswas earned her BS and MS in Biology from the University of Kalyani, India, and her PhD from Jawaharlal Nehru University, India. Currently she is working as a Research Associate in Dr Podrez’s laboratory in the Department of Molecular Cardiology at Cleveland Clinic. Sudipta’s current research focuses on the role of platelet innate immune signaling cascade in the prothrombotic phenotype associated with hyperlipidemia. Sudipta has been awarded a Postdoctoral Fellowship from the American Heart Association for her research. In the future, she wants to investigate the specific role of platelets in immunity. Besides science, she loves hiking, outdoor activities, photography, gardening, and experimental cooking.miRNAs as Biomarkers After Stroke (p 970)Download figureDownload PowerPointDr Steffen Tiedt earned his MD from Ludwig-Maximilians-University Munich under the supervision of Dr Madgalena Götz investigating the stem cell capacity of reactive astrocytes. Intent on becoming a clinician-scientist, he is now a PhD candidate in the Graduate School of Systemic Neurosciences at the Institute for Stroke and Dementia Research under the supervision of Dr Martin Dichgans and a resident in neurology. His research focuses on using blood-based biomarkers in ischemic stroke patients to guide clinical decision-making in the future. Outside the lab, he loves to escape city life by running trails in the mountains, just thinking about the next step. Previous Back to top Next FiguresReferencesRelatedDetails September 29, 2017Vol 121, Issue 8 Advertisement Article InformationMetrics © 2017 American Heart Association, Inc.https://doi.org/10.1161/RES.0000000000000176PMID: 28963181 Originally publishedSeptember 29, 2017 PDF download Advertisement