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Shu LX, Cao LL, Guo X, Wang ZB, Wang SZ. Mechanism of efferocytosis in atherosclerosis. J Mol Med (Berl) 2024; 102:831-840. [PMID: 38727748 DOI: 10.1007/s00109-024-02439-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Revised: 02/26/2024] [Accepted: 03/13/2024] [Indexed: 06/29/2024]
Abstract
Atherosclerosis (AS) is a chronic inflammatory vascular disease that occurs in the intima of large and medium-sized arteries with the immune system's involvement. It is a common pathological basis for high morbidity and mortality of cardiovascular diseases. Abnormal proliferation of apoptotic cells and necrotic cells leads to AS plaque expansion, necrotic core formation, and rupture. In the early stage of AS, macrophages exert an efferocytosis effect to engulf and degrade apoptotic, dead, damaged, or senescent cells by efferocytosis, thus enabling the regulation of the organism. In the early stage of AS, macrophages rely on this effect to slow down the process of AS. However, in the advanced stage of AS, the efferocytosis of macrophages within the plaque is impaired, which leads to the inability of macrophages to promptly remove the apoptotic cells (ACs) from the organism promptly, causing exacerbation of AS. Moreover, upregulation of CD47 expression in AS plaques also protects ACs from phagocytosis by macrophages, resulting in a large amount of residual ACs in the plaque, further expanding the necrotic core. In this review, we discussed the molecular mechanisms involved in the process of efferocytosis and how efferocytosis is impaired and regulated during AS, hoping to provide new insights for treating AS.
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Affiliation(s)
- Li-Xia Shu
- Institute of Pharmacy and Pharmacology, School of Pharmaceutical Sciences, Hengyang Medical School, University of South China, Hengyang, 421001, China
- Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, University of South China, Hengyang, 421001, China
| | - Liu-Li Cao
- Institute of Pharmacy and Pharmacology, School of Pharmaceutical Sciences, Hengyang Medical School, University of South China, Hengyang, 421001, China
- Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, University of South China, Hengyang, 421001, China
| | - Xin Guo
- Institute of Pharmacy and Pharmacology, School of Pharmaceutical Sciences, Hengyang Medical School, University of South China, Hengyang, 421001, China
- Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, University of South China, Hengyang, 421001, China
| | - Zong-Bao Wang
- Institute of Pharmacy and Pharmacology, School of Pharmaceutical Sciences, Hengyang Medical School, University of South China, Hengyang, 421001, China
- Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, University of South China, Hengyang, 421001, China
| | - Shu-Zhi Wang
- Institute of Pharmacy and Pharmacology, School of Pharmaceutical Sciences, Hengyang Medical School, University of South China, Hengyang, 421001, China.
- Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, University of South China, Hengyang, 421001, China.
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2
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De Meyer GRY, Zurek M, Puylaert P, Martinet W. Programmed death of macrophages in atherosclerosis: mechanisms and therapeutic targets. Nat Rev Cardiol 2024; 21:312-325. [PMID: 38163815 DOI: 10.1038/s41569-023-00957-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 11/02/2023] [Indexed: 01/03/2024]
Abstract
Atherosclerosis is a progressive inflammatory disorder of the arterial vessel wall characterized by substantial infiltration of macrophages, which exert both favourable and detrimental functions. Early in atherogenesis, macrophages can clear cytotoxic lipoproteins and dead cells, preventing cytotoxicity. Efferocytosis - the efficient clearance of dead cells by macrophages - is crucial for preventing secondary necrosis and stimulating the release of anti-inflammatory cytokines. In addition, macrophages can promote tissue repair and proliferation of vascular smooth muscle cells, thereby increasing plaque stability. However, advanced atherosclerotic plaques contain large numbers of pro-inflammatory macrophages that secrete matrix-degrading enzymes, induce death in surrounding cells and contribute to plaque destabilization and rupture. Importantly, macrophages in the plaque can undergo apoptosis and several forms of regulated necrosis, including necroptosis, pyroptosis and ferroptosis. Regulated necrosis has an important role in the formation and expansion of the necrotic core during plaque progression, and several triggers for necrosis are present within atherosclerotic plaques. This Review focuses on the various forms of programmed macrophage death in atherosclerosis and the pharmacological interventions that target them as a potential means of stabilizing vulnerable plaques and improving the efficacy of currently available anti-atherosclerotic therapies.
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Affiliation(s)
- Guido R Y De Meyer
- Laboratory of Physiopharmacology, University of Antwerp, Antwerp, Belgium.
| | - Michelle Zurek
- Laboratory of Physiopharmacology, University of Antwerp, Antwerp, Belgium
| | - Pauline Puylaert
- Laboratory of Physiopharmacology, University of Antwerp, Antwerp, Belgium
| | - Wim Martinet
- Laboratory of Physiopharmacology, University of Antwerp, Antwerp, Belgium
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3
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Maffia P, Mauro C, Case A, Kemper C. Canonical and non-canonical roles of complement in atherosclerosis. Nat Rev Cardiol 2024:10.1038/s41569-024-01016-y. [PMID: 38600367 DOI: 10.1038/s41569-024-01016-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 03/18/2024] [Indexed: 04/12/2024]
Abstract
Cardiovascular diseases are the leading cause of death globally, and atherosclerosis is the major contributor to the development and progression of cardiovascular diseases. Immune responses have a central role in the pathogenesis of atherosclerosis, with the complement system being an acknowledged contributor. Chronic activation of liver-derived and serum-circulating canonical complement sustains endothelial inflammation and innate immune cell activation, and deposition of complement activation fragments on inflamed endothelial cells is a hallmark of atherosclerotic plaques. However, increasing evidence indicates that liver-independent, cell-autonomous and non-canonical complement activities are underappreciated contributors to atherosclerosis. Furthermore, complement activation can also have atheroprotective properties. These specific detrimental or beneficial contributions of the complement system to the pathogenesis of atherosclerosis are dictated by the location of complement activation and engagement of its canonical versus non-canonical functions in a temporal fashion during atherosclerosis progression. In this Review, we summarize the classical and the emerging non-classical roles of the complement system in the pathogenesis of atherosclerosis and discuss potential strategies for therapeutic modulation of complement for the prevention and treatment of atherosclerotic cardiovascular disease.
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Affiliation(s)
- Pasquale Maffia
- School of Infection & Immunity, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
- Department of Pharmacy, School of Medicine and Surgery, University of Naples Federico II, Naples, Italy
- Africa-Europe Cluster of Research Excellence (CoRE) in Non-Communicable Diseases & Multimorbidity, African Research Universities Alliance (ARUA) & The Guild, Accra, Ghana
| | - Claudio Mauro
- Institute of Inflammation and Ageing, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Ayden Case
- Heart and Lung Research Institute, University of Cambridge, Cambridge, UK
- Complement and Inflammation Research Section, National Heart, Lung, and Blood Institute (NHLBI), National Institutes of Health (NIH), Bethesda, MD, USA
| | - Claudia Kemper
- Complement and Inflammation Research Section, National Heart, Lung, and Blood Institute (NHLBI), National Institutes of Health (NIH), Bethesda, MD, USA.
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Stroope C, Nettersheim FS, Coon B, Finney AC, Schwartz MA, Ley K, Rom O, Yurdagul A. Dysregulated cellular metabolism in atherosclerosis: mediators and therapeutic opportunities. Nat Metab 2024; 6:617-638. [PMID: 38532071 PMCID: PMC11055680 DOI: 10.1038/s42255-024-01015-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/05/2023] [Accepted: 02/20/2024] [Indexed: 03/28/2024]
Abstract
Accumulating evidence over the past decades has revealed an intricate relationship between dysregulation of cellular metabolism and the progression of atherosclerotic cardiovascular disease. However, an integrated understanding of dysregulated cellular metabolism in atherosclerotic cardiovascular disease and its potential value as a therapeutic target is missing. In this Review, we (1) summarize recent advances concerning the role of metabolic dysregulation during atherosclerosis progression in lesional cells, including endothelial cells, vascular smooth muscle cells, macrophages and T cells; (2) explore the complexity of metabolic cross-talk between these lesional cells; (3) highlight emerging technologies that promise to illuminate unknown aspects of metabolism in atherosclerosis; and (4) suggest strategies for targeting these underexplored metabolic alterations to mitigate atherosclerosis progression and stabilize rupture-prone atheromas with a potential new generation of cardiovascular therapeutics.
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Affiliation(s)
- Chad Stroope
- Department of Molecular and Cellular Physiology, Louisiana State University Health Sciences Center, Shreveport, LA, USA
| | - Felix Sebastian Nettersheim
- La Jolla Institute for Immunology, La Jolla, CA, USA
- Department of Cardiology, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne, Germany
| | - Brian Coon
- Yale Cardiovascular Research Center, Division of Cardiovascular Medicine, Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
- Cardiovascular Biology Research Program, OMRF, Oklahoma City, OK, USA
- Department of Cell Biology, Oklahoma University Health Sciences Center, Oklahoma City, OK, USA
| | - Alexandra C Finney
- Department of Pathology and Translational Pathobiology, Louisiana State University Health Sciences Center, Shreveport, LA, USA
| | - Martin A Schwartz
- Yale Cardiovascular Research Center, Division of Cardiovascular Medicine, Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
- Departments of Cell Biology and Biomedical Engineering, Yale University, New Haven, CT, USA
| | - Klaus Ley
- La Jolla Institute for Immunology, La Jolla, CA, USA
- Department of Bioengineering, University of California, San Diego, San Diego, CA, USA
- Immunology Center of Georgia (IMMCG), Augusta University Immunology Center of Georgia, Augusta, GA, USA
| | - Oren Rom
- Department of Molecular and Cellular Physiology, Louisiana State University Health Sciences Center, Shreveport, LA, USA
- Department of Pathology and Translational Pathobiology, Louisiana State University Health Sciences Center, Shreveport, LA, USA
| | - Arif Yurdagul
- Department of Molecular and Cellular Physiology, Louisiana State University Health Sciences Center, Shreveport, LA, USA.
- Department of Pathology and Translational Pathobiology, Louisiana State University Health Sciences Center, Shreveport, LA, USA.
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Xie XD, Dong SS, Liu RJ, Shi LL, Zhu T. Mechanism of Efferocytosis in Determining Ischaemic Stroke Resolution-Diving into Microglia/Macrophage Functions and Therapeutic Modality. Mol Neurobiol 2024:10.1007/s12035-024-04060-4. [PMID: 38409642 DOI: 10.1007/s12035-024-04060-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Accepted: 02/17/2024] [Indexed: 02/28/2024]
Abstract
After ischaemic cerebral vascular injury, efferocytosis-a process known as the efficient clearance of apoptotic cells (ACs) by various phagocytes in both physiological and pathological states-is crucial for maintaining central nervous system (CNS) homeostasis and regaining prognosis. The mechanisms of efferocytosis in ischaemic stroke and its influence on preventing inflammation progression from secondary injury were still not fully understood, despite the fact that the fundamental process of efferocytosis has been described in a series of phases, including AC recognition, phagocyte engulfment, and subsequent degradation. The genetic reprogramming of macrophages and brain-resident microglia after an ischaemic stroke has been equated by some researchers to that of the peripheral blood and brain. Based on previous studies, some molecules, such as signal transducer and activator of transcription 6 (STAT6), peroxisome proliferator-activated receptor γ (PPARG), CD300A, and sigma non-opioid intracellular receptor 1 (SIGMAR1), were discovered to be largely associated with aspects of apoptotic cell elimination and accompanying neuroinflammation, such as inflammatory cytokine release, phenotype transformation, and suppressing of antigen presentation. Exacerbated stroke outcomes are brought on by defective efferocytosis and improper modulation of pertinent signalling pathways in blood-borne macrophages and brain microglia, which also results in subsequent tissue inflammatory damage. This review focuses on recent researches which contain a number of recently discovered mechanisms, such as studies on the relationship between benign efferocytosis and the regulation of inflammation in ischaemic stroke, the roles of some risk factors in disease progression, and current immune approaches that aim to promote efferocytosis to treat some autoimmune diseases. Understanding these pathways provides insight into novel pathophysiological processes and fresh characteristics, which can be used to build cerebral ischaemia targeting techniques.
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Affiliation(s)
- Xiao-Di Xie
- Department of Pathophysiology, School of Basic Medicine, Institute of Neuroregeneration & Neurorehabilitation, Qingdao University, No. 308 Ningxia Road, Qingdao, China
| | - Shan-Shan Dong
- Department of Pathophysiology, School of Basic Medicine, Institute of Neuroregeneration & Neurorehabilitation, Qingdao University, No. 308 Ningxia Road, Qingdao, China
- Department of Rehabilitation Medicine, The Affiliated Hospital of Qingdao University, Qingdao, China
| | - Ru-Juan Liu
- Department of Pathophysiology, School of Basic Medicine, Institute of Neuroregeneration & Neurorehabilitation, Qingdao University, No. 308 Ningxia Road, Qingdao, China
- Department of Rehabilitation Medicine, The Affiliated Hospital of Qingdao University, Qingdao, China
| | - Liu-Liu Shi
- Department of Pathophysiology, School of Basic Medicine, Institute of Neuroregeneration & Neurorehabilitation, Qingdao University, No. 308 Ningxia Road, Qingdao, China
- Department of Neurosurgery, The Affiliated Hospital of Qingdao University, Qingdao, China
| | - Ting Zhu
- Department of Pathophysiology, School of Basic Medicine, Institute of Neuroregeneration & Neurorehabilitation, Qingdao University, No. 308 Ningxia Road, Qingdao, China.
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Coronelli MM, Coppi F, Mattioli AV. Inflammation, atherosclerosis and hypertension: the impact of depression and stress on their complex relationship. Future Cardiol 2024; 20:27-33. [PMID: 38127553 DOI: 10.2217/fca-2023-0030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2023] [Accepted: 11/28/2023] [Indexed: 12/23/2023] Open
Abstract
This future perspective analyzes the complex relationship between inflammation and atherosclerosis and arterial hypertension. The involvement of inflammation in atherosclerosis has led to research therapies that target inflammation to prevent or treat cardiovascular disease. This aspect has recently been included in the treatment management of residual cardiovascular risk. The recent pandemic has exacerbated cardiovascular risk both through an increase in unhealthy lifestyle behaviors and through the reduction of cardiovascular screening. What actions to take? Primary prevention campaigns for healthy subjects with specific attention to young people.
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Affiliation(s)
| | - Francesca Coppi
- Department of Medical & Surgical Sciences for Children & Adults, University of Modena & Reggio Emilia, Modena, 41100, Italy
| | - Anna Vittoria Mattioli
- Department of Medical & Surgical Sciences for Children & Adults, University of Modena & Reggio Emilia, Modena, 41100, Italy
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Soliman E, Leonard J, Basso EKG, Gershenson I, Ju J, Mills J, de Jager C, Kaloss AM, Elhassanny M, Pereira D, Chen M, Wang X, Theus MH. Efferocytosis is restricted by axon guidance molecule EphA4 via ERK/Stat6/MERTK signaling following brain injury. J Neuroinflammation 2023; 20:256. [PMID: 37941008 PMCID: PMC10633953 DOI: 10.1186/s12974-023-02940-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2023] [Accepted: 10/30/2023] [Indexed: 11/10/2023] Open
Abstract
BACKGROUND Efferocytosis is a process that removes apoptotic cells and cellular debris. Clearance of these cells alleviates neuroinflammation, prevents the release of inflammatory molecules, and promotes the production of anti-inflammatory cytokines to help maintain tissue homeostasis. The underlying mechanisms by which this occurs in the brain after injury remain ill-defined. METHODS We used GFP bone marrow chimeric knockout (KO) mice to demonstrate that the axon guidance molecule EphA4 receptor tyrosine kinase is involved in suppressing MERTK in the brain to restrict efferocytosis of resident microglia and peripheral-derived monocyte/macrophages. RESULTS Single-cell RNAseq identified MERTK expression, the primary receptor involved in efferocytosis, on monocytes, microglia, and a subset of astrocytes in the damaged cortex following brain injury. Loss of EphA4 on infiltrating GFP-expressing immune cells improved functional outcome concomitant with enhanced efferocytosis and overall protein expression of p-MERTK, p-ERK, and p-Stat6. The percentage of GFP+ monocyte/macrophages and resident microglia engulfing NeuN+ or TUNEL+ cells was significantly higher in KO chimeric mice. Importantly, mRNA expression of Mertk and its cognate ligand Gas6 was significantly elevated in these mice compared to the wild-type. Analysis of cell-specific expression showed that p-ERK and p-Stat6 co-localized with MERTK-expressing GFP + cells in the peri-lesional area of the cortex following brain injury. Using an in vitro efferocytosis assay, co-culturing pHrodo-labeled apoptotic Jurkat cells and bone marrow (BM)-derived macrophages, we demonstrate that efferocytosis efficiency and mRNA expression of Mertk and Gas6 was enhanced in the absence of EphA4. Selective inhibitors of ERK and Stat6 attenuated this effect, confirming that EphA4 suppresses monocyte/macrophage efferocytosis via inhibition of the ERK/Stat6 pathway. CONCLUSIONS Our findings implicate the ERK/Stat6/MERTK axis as a novel regulator of apoptotic debris clearance in brain injury that is restricted by peripheral myeloid-derived EphA4 to prevent the resolution of inflammation.
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Affiliation(s)
- Eman Soliman
- Department of Biomedical Sciences and Pathobiology, Virginia Tech, Blacksburg, VA, 24061, USA
- Department of Pharmacology and Toxicology, Faculty of Pharmacy, Zagazig University, Zagazig, Egypt
| | - John Leonard
- Department of Biomedical Sciences and Pathobiology, Virginia Tech, Blacksburg, VA, 24061, USA
| | | | - Ilana Gershenson
- Department of Biomedical Sciences and Pathobiology, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Jing Ju
- Department of Biomedical Sciences and Pathobiology, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Jatia Mills
- Department of Biomedical Sciences and Pathobiology, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Caroline de Jager
- Translational Biology Medicine and Health Graduate Program, Roanoke, VA, 24001, USA
| | - Alexandra M Kaloss
- Department of Biomedical Sciences and Pathobiology, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Mohamed Elhassanny
- Department of Biomedical Sciences and Pathobiology, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Daniela Pereira
- Department of Biomedical Sciences and Pathobiology, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Michael Chen
- Department of Biomedical Sciences and Pathobiology, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Xia Wang
- Department of Biomedical Sciences and Pathobiology, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Michelle H Theus
- Department of Biomedical Sciences and Pathobiology, Virginia Tech, Blacksburg, VA, 24061, USA.
- Translational Biology Medicine and Health Graduate Program, Roanoke, VA, 24001, USA.
- Center for Engineered Health, Virginia Tech, Blacksburg, VA, 24061, USA.
- VT-Biomedical Engineering and School of Neuroscience, 970 Washington Street SW, Life Sciences I; Rm 249 (MC0910), Blacksburg, VA, 24061, USA.
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Liu X, Liu H, Deng Y. Efferocytosis: An Emerging Therapeutic Strategy for Type 2 Diabetes Mellitus and Diabetes Complications. J Inflamm Res 2023; 16:2801-2815. [PMID: 37440994 PMCID: PMC10335275 DOI: 10.2147/jir.s418334] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2023] [Accepted: 06/24/2023] [Indexed: 07/15/2023] Open
Abstract
Increasing evidence indicates that chronic, low-grade inflammation is a significant contributor to the fundamental pathogenesis of type 2 diabetes mellitus (T2DM). Efferocytosis, an effective way to eliminate apoptotic cells (ACs), plays a critical role in inflammation resolution. Massive accumulation of ACs and the proliferation of persistent inflammation caused by defective efferocytosis have been proven to be closely associated with pancreatic islet β cell destruction, adipose tissue inflammation, skeletal muscle dysfunction, and liver metabolism abnormalities, which together are considered the most fundamental pathological mechanism underlying T2DM. Therefore, here we outline the association between the molecular mechanisms of efferocytosis in glucose homeostasis, T2DM, and its complications, and we analyzed the present constraints and potential future prospects for therapeutic targets in T2DM and its complications.
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Affiliation(s)
- Xun Liu
- Hunan University of Chinese Medicine, Changsha, Hunan, 410208, People’s Republic of China
| | - Hua Liu
- Southern Theater General Hospital of the Chinese People’s Liberation Army, Guangzhou, Guangdong, 510010, People’s Republic of China
| | - Yihui Deng
- Hunan University of Chinese Medicine, Changsha, Hunan, 410208, People’s Republic of China
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Soliman E, Leonard J, Basso EK, Gershenson I, Ju J, Mills J, Jager C, Kaloss AM, Elhassanny M, Pereira D, Chen M, Wang X, Theus MH. Efferocytosis is restricted by axon guidance molecule EphA4 via ERK/Stat6/Mertk signaling following brain injury. RESEARCH SQUARE 2023:rs.3.rs-3079466. [PMID: 37461720 PMCID: PMC10350120 DOI: 10.21203/rs.3.rs-3079466/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/24/2023]
Abstract
Background Efferocytosis is a process that removes apoptotic cells and cellular debris. Clearance of these cells alleviates neuroinflammation and prevents the release of inflammatory molecules and promotes the production of anti-inflammatory cytokines to help maintain tissue homeostasis. The underlying mechanisms by which this occurs in the brain after injury remains ill-defined. Methods We demonstrate using GFP bone marrow chimeric knockout (KO) mice, that the axon guidance molecule EphA4 receptor tyrosine kinase is involved in suppressing Mertk signaling in the brain to restrict the function of efferocytosis on resident microglia and peripheral-derived monocyte/macrophages. Results Single-cell RNAseq identified Mertk expression, the primary receptor involved in efferocytosis, on monocytes, microglia, and a subset of astrocytes in the damaged cortex following brain injury. Loss of EphA4 on infiltrating GFP-expressing immune cells improved functional outcome concomitant with enhanced efferocytosis, and overall protein expression of p-Mertk, p-ERK, and p-Stat6. The percentage of GFP+ monocyte/macrophages and resident microglia engulfing NeuN+ or TUNEL+ cells was significantly higher in KO chimeric mice. Importantly, mRNA expression of Mertk and its cognate ligand Gas6 was significantly elevated in these mice compared to wild-type. Analysis of cell-specific expression showed that p-ERK and p-Stat6 co-localized with Mertk-expressing GFP + cells in the peri-lesional area of the cortex following brain injury. Using an in vitro efferocytosis assay, co-culturing pHrodo-labeled apoptotic Jurkat cells and bone marrow (BM)-derived macrophages, we demonstrate that efferocytosis efficiency and mRNA expression of Mertk and Gas6 was enhanced in the absence of EphA4. Select inhibitors of ERK and Stat6 attenuated this effect confirming that EphA4 suppresses monocyte/macrophage efferocytosis via inhibition of the ERK/Stat6 pathway. Conclusions Our findings implicate the Mertk/ERK/Stat6 axis as a novel regulator of apoptotic debris clearance in brain injury that is restricted by peripheral myeloid-derived EphA4 to prevent the resolution of inflammation.
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