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Fan H, Song C, Zhang J. Sarm1 Controls the MYD88-Mediated Inflammatory Responses in Inflammatory Bowel Disease via the Regulation of TRAF3 Recruitment. Immunol Invest 2024:1-13. [PMID: 38651786 DOI: 10.1080/08820139.2024.2343889] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/25/2024]
Abstract
BACKGROUND Sterile alpha and TIR motif-containing 1 (Sarm1) is known as a negative regulator of inflammatory responses. However, its role in inflammatory bowel disease (IBD) is still unclear. OBJECTIVE This study aimed to explore the function of Sarm1 in IBD and its underlying mechanisms. Sarm1 and tumor necrosis factor (TNF) receptor associated factor 3 (TRAF3) knockout (KO) micewere established. METHODS The colitis was induced using dextran sulfate sodium (DSS). Bone marrow-derived macrophages (BMDMs) were isolated and stimulated with lipopolysaccharides (LPS) or cytidine phosphate guanosine(CpG). Inflammatory cytokines were measured viaELISA. qPCR and Western blotting were used to determine the levels of the mRNA and protein expression, respectively. RESULTS It was demonstrated that reduced expression of Sarm1 was correlated with the severity of IBD in ulcerative colitis patients, and also with the reduction of pro-inflammatory cytokines in the mouse model induced by DSS. It was further observed that Sarm1 KO enhanced the induction of pro-inflammatory cytokines in both animal and in vitro cell models. Sarm1 deficiency in macrophages increased the severity of colitis in the mouse model induced by DSS. Moreover, Sarm1 regulatedTRAF3 recruitment to myeloid differentiation primary response protein 88 (MyD88), which in turn controlled the MYD88-mediated inflammatory responses. CONCLUSIONS In summary, our data suggest that Sarm1 controls the MYD88-mediated inflammatory responses in IBD via its regulation of TRAF3 recruitment.
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Affiliation(s)
- Huijuan Fan
- Department of Gastroenterology, The Second Affiliated Hospital, Air Force Medical University, Xi'an, Shaanxi, China
| | - Chun Song
- Department of Gastroenterology, The Second Affiliated Hospital, Air Force Medical University, Xi'an, Shaanxi, China
| | - Jingyu Zhang
- Department of Gastroenterology, The Second Affiliated Hospital, Air Force Medical University, Xi'an, Shaanxi, China
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Baig MS, Barmpoutsi S, Bharti S, Weigert A, Hirani N, Atre R, Khabiya R, Sharma R, Sarup S, Savai R. Adaptor molecules mediate negative regulation of macrophage inflammatory pathways: a closer look. Front Immunol 2024; 15:1355012. [PMID: 38482001 PMCID: PMC10933033 DOI: 10.3389/fimmu.2024.1355012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Accepted: 01/22/2024] [Indexed: 04/13/2024] Open
Abstract
Macrophages play a central role in initiating, maintaining, and terminating inflammation. For that, macrophages respond to various external stimuli in changing environments through signaling pathways that are tightly regulated and interconnected. This process involves, among others, autoregulatory loops that activate and deactivate macrophages through various cytokines, stimulants, and other chemical mediators. Adaptor proteins play an indispensable role in facilitating various inflammatory signals. These proteins are dynamic and flexible modulators of immune cell signaling and act as molecular bridges between cell surface receptors and intracellular effector molecules. They are involved in regulating physiological inflammation and also contribute significantly to the development of chronic inflammatory processes. This is at least partly due to their involvement in the activation and deactivation of macrophages, leading to changes in the macrophages' activation/phenotype. This review provides a comprehensive overview of the 20 adaptor molecules and proteins that act as negative regulators of inflammation in macrophages and effectively suppress inflammatory signaling pathways. We emphasize the functional role of adaptors in signal transduction in macrophages and their influence on the phenotypic transition of macrophages from pro-inflammatory M1-like states to anti-inflammatory M2-like phenotypes. This endeavor mainly aims at highlighting and orchestrating the intricate dynamics of adaptor molecules by elucidating the associated key roles along with respective domains and opening avenues for therapeutic and investigative purposes in clinical practice.
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Affiliation(s)
- Mirza S. Baig
- Department of Biosciences and Biomedical Engineering (BSBE), Indian Institute of Technology Indore (IITI), Indore, India
| | - Spyridoula Barmpoutsi
- Lung Microenvironmental Niche in Cancerogenesis, Institute for Lung Health (ILH), Justus Liebig University, Giessen, Germany
- Max Planck Institute for Heart and Lung Research, Member of the German Center for Lung Research (DZL), Member of the Cardio-Pulmonary Institute (CPI), Bad Nauheim, Germany
| | - Shreya Bharti
- Department of Biosciences and Biomedical Engineering (BSBE), Indian Institute of Technology Indore (IITI), Indore, India
| | - Andreas Weigert
- Institute of Biochemistry I, Faculty of Medicine, Goethe University Frankfurt, Frankfurt, Germany
- Frankfurt Cancer Institute (FCI), Goethe University Frankfurt, Frankfurt, Germany
| | - Nik Hirani
- MRC Centre for Inflammation Research, Queen’s Medical Research Institute, University of Edinburgh, Edinburgh, United Kingdom
| | - Rajat Atre
- Department of Biosciences and Biomedical Engineering (BSBE), Indian Institute of Technology Indore (IITI), Indore, India
| | - Rakhi Khabiya
- Department of Biosciences and Biomedical Engineering (BSBE), Indian Institute of Technology Indore (IITI), Indore, India
| | - Rahul Sharma
- Department of Biosciences and Biomedical Engineering (BSBE), Indian Institute of Technology Indore (IITI), Indore, India
| | - Shivmuni Sarup
- Department of Biosciences and Biomedical Engineering (BSBE), Indian Institute of Technology Indore (IITI), Indore, India
| | - Rajkumar Savai
- Lung Microenvironmental Niche in Cancerogenesis, Institute for Lung Health (ILH), Justus Liebig University, Giessen, Germany
- Max Planck Institute for Heart and Lung Research, Member of the German Center for Lung Research (DZL), Member of the Cardio-Pulmonary Institute (CPI), Bad Nauheim, Germany
- Frankfurt Cancer Institute (FCI), Goethe University Frankfurt, Frankfurt, Germany
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Shanahan KA, Davis GM, Doran CG, Sugisawa R, Davey GP, Bowie AG. SARM1 regulates NAD +-linked metabolism and select immune genes in macrophages. J Biol Chem 2024; 300:105620. [PMID: 38176648 PMCID: PMC10847163 DOI: 10.1016/j.jbc.2023.105620] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2023] [Revised: 12/23/2023] [Accepted: 12/27/2023] [Indexed: 01/06/2024] Open
Abstract
Sterile alpha and HEAT/armadillo motif-containing protein (SARM1) was recently described as a NAD+-consuming enzyme and has previously been shown to regulate immune responses in macrophages. Neuronal SARM1 is known to contribute to axon degeneration due to its NADase activity. However, how SARM1 affects macrophage metabolism has not been explored. Here, we show that macrophages from Sarm1-/- mice display elevated NAD+ concentrations and lower cyclic ADP-ribose, a known product of SARM1-dependent NAD+ catabolism. Further, SARM1-deficient macrophages showed an increase in the reserve capacity of oxidative phosphorylation and glycolysis compared to WT cells. Stimulation of macrophages to a proinflammatory state by lipopolysaccharide (LPS) revealed that SARM1 restricts the ability of macrophages to upregulate glycolysis and limits the expression of the proinflammatory gene interleukin (Il) 1b, but boosts expression of anti-inflammatory Il10. In contrast, we show macrophages lacking SARM1 induced to an anti-inflammatory state by IL-4 stimulation display increased oxidative phosphorylation and glycolysis, and reduced expression of the anti-inflammatory gene, Fizz1. Overall, these data show that SARM1 fine-tunes immune gene transcription in macrophages via consumption of NAD+ and altered macrophage metabolism.
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Affiliation(s)
- Katharine A Shanahan
- School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin, Ireland
| | - Gavin M Davis
- School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin, Ireland
| | - Ciara G Doran
- School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin, Ireland
| | - Ryoichi Sugisawa
- School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin, Ireland
| | - Gavin P Davey
- School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin, Ireland
| | - Andrew G Bowie
- School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin, Ireland.
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4
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Brazill JM, Shen IR, Craft CS, Magee KL, Park JS, Lorenz M, Strickland A, Wee NK, Zhang X, Beeve AT, Meyer GA, Milbrandt J, DiAntonio A, Scheller EL. Sarm1 knockout prevents type 1 diabetic bone disease in females independent of neuropathy. JCI Insight 2024; 9:e175159. [PMID: 38175722 DOI: 10.1172/jci.insight.175159] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Accepted: 01/03/2024] [Indexed: 01/05/2024] Open
Abstract
Patients with diabetes have a high risk of developing skeletal diseases accompanied by diabetic peripheral neuropathy (DPN). In this study, we isolated the role of DPN in skeletal disease with global and conditional knockout models of sterile-α and TIR-motif-containing protein-1 (Sarm1). SARM1, an NADase highly expressed in the nervous system, regulates axon degeneration upon a range of insults, including DPN. Global knockout of Sarm1 prevented DPN, but not skeletal disease, in male mice with type 1 diabetes (T1D). Female wild-type mice also developed diabetic bone disease but without DPN. Unexpectedly, global Sarm1 knockout completely protected female mice from T1D-associated bone suppression and skeletal fragility despite comparable muscle atrophy and hyperglycemia. Global Sarm1 knockout rescued bone health through sustained osteoblast function with abrogation of local oxidative stress responses. This was independent of the neural actions of SARM1, as beneficial effects on bone were lost with neural conditional Sarm1 knockout. This study demonstrates that the onset of skeletal disease occurs rapidly in both male and female mice with T1D completely independently of DPN. In addition, this reveals that clinical SARM1 inhibitors, currently being developed for treatment of neuropathy, may also have benefits for diabetic bone through actions outside of the nervous system.
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Affiliation(s)
| | - Ivana R Shen
- Division of Bone and Mineral Diseases, Department of Medicine, and
| | - Clarissa S Craft
- Division of Bone and Mineral Diseases, Department of Medicine, and
| | - Kristann L Magee
- Division of Bone and Mineral Diseases, Department of Medicine, and
| | - Jay S Park
- Division of Bone and Mineral Diseases, Department of Medicine, and
| | - Madelyn Lorenz
- Division of Bone and Mineral Diseases, Department of Medicine, and
| | - Amy Strickland
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Natalie K Wee
- Division of Bone and Mineral Diseases, Department of Medicine, and
| | - Xiao Zhang
- Division of Bone and Mineral Diseases, Department of Medicine, and
- Department of Biomedical Engineering, McKelvey School of Engineering, Washington University, St. Louis, Missouri, USA
| | - Alec T Beeve
- Division of Bone and Mineral Diseases, Department of Medicine, and
- Department of Biomedical Engineering, McKelvey School of Engineering, Washington University, St. Louis, Missouri, USA
| | | | - Jeffrey Milbrandt
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, USA
| | | | - Erica L Scheller
- Division of Bone and Mineral Diseases, Department of Medicine, and
- Department of Biomedical Engineering, McKelvey School of Engineering, Washington University, St. Louis, Missouri, USA
- Department of Developmental Biology, and
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri, USA
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5
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McGuinness HY, Gu W, Shi Y, Kobe B, Ve T. SARM1-Dependent Axon Degeneration: Nucleotide Signaling, Neurodegenerative Disorders, Toxicity, and Therapeutic Opportunities. Neuroscientist 2023:10738584231162508. [DOI: 10.1177/10738584231162508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2023]
Abstract
Axons are an essential component of the nervous system, and axon degeneration is an early feature of many neurodegenerative disorders. The NAD+ metabolome plays an essential role in regulating axonal integrity. Axonal levels of NAD+ and its precursor NMN are controlled in large part by the NAD+ synthesizing survival factor NMNAT2 and the pro-neurodegenerative NADase SARM1, whose activation triggers axon destruction. SARM1 has emerged as a promising axon-specific target for therapeutic intervention, and its function, regulation, structure, and role in neurodegenerative diseases have been extensively characterized in recent years. In this review, we first introduce the key molecular players involved in the SARM1-dependent axon degeneration program. Next, we summarize recent major advances in our understanding of how SARM1 is kept inactive in healthy neurons and how it becomes activated in injured or diseased neurons, which has involved important insights from structural biology. Finally, we discuss the role of SARM1 in neurodegenerative disorders and environmental neurotoxicity and its potential as a therapeutic target.
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Affiliation(s)
- Helen Y. McGuinness
- School of Chemistry and Molecular Biosciences, Institute for Molecular Bioscience and Australian Infectious Diseases Research Centre, University of Queensland, Saint Lucia, Australia
| | - Weixi Gu
- School of Chemistry and Molecular Biosciences, Institute for Molecular Bioscience and Australian Infectious Diseases Research Centre, University of Queensland, Saint Lucia, Australia
| | - Yun Shi
- Institute for Glycomics, Griffith University, Gold Coast, Australia
| | - Bostjan Kobe
- School of Chemistry and Molecular Biosciences, Institute for Molecular Bioscience and Australian Infectious Diseases Research Centre, University of Queensland, Saint Lucia, Australia
| | - Thomas Ve
- Institute for Glycomics, Griffith University, Gold Coast, Australia
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Ji X, Zheng M, Yu T, Kang J, Fan T, Xu B. NAD(+)-Consuming Enzymes in Stem Cell Homeostasis. Oxid Med Cell Longev 2023; 2023:4985726. [PMID: 36819783 DOI: 10.1155/2023/4985726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/11/2022] [Revised: 12/27/2022] [Accepted: 01/06/2023] [Indexed: 02/10/2023]
Abstract
Nicotinamide adenine dinucleotide (NAD+) is a coenzyme used in redox reactions, energy metabolism, and mitochondrial biogenesis. NAD+ is also required as a cofactor by nonredox NAD+-dependent enzymes. Hundreds of enzymes that consume NAD+ have been identified. The NAD+-consuming enzymes are involved in a variety of cellular processes such as signal transduction, DNA repair, cellular senescence, and stem cell (SC) homeostasis. In this review, we discussed how different types of NAD+-consuming enzymes regulate SC functions and summarized current research on the roles of the NAD+ consumers in SC homeostasis. We hope to provide a more global and integrative insight to the mechanism and intervention of SC homeostasis via the regulation of the NAD+-consuming enzymes.
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Feriotti C, Sá-Pessoa J, Calderón-González R, Gu L, Morris B, Sugisawa R, Insua JL, Carty M, Dumigan A, Ingram RJ, Kissenpfening A, Bowie AG, Bengoechea JA. Klebsiella pneumoniae hijacks the Toll-IL-1R protein SARM1 in a type I IFN-dependent manner to antagonize host immunity. Cell Rep 2022; 40:111167. [PMID: 35947948 PMCID: PMC9638020 DOI: 10.1016/j.celrep.2022.111167] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Revised: 05/18/2022] [Accepted: 07/14/2022] [Indexed: 02/06/2023] Open
Abstract
Many bacterial pathogens antagonize host defense responses by translocating effector proteins into cells. It remains an open question how those pathogens not encoding effectors counteract anti-bacterial immunity. Here, we show that Klebsiella pneumoniae exploits the evolutionary conserved innate protein SARM1 to regulate negatively MyD88- and TRIF-governed inflammation, and the activation of the MAP kinases ERK and JNK. SARM1 is required for Klebsiella induction of interleukin-10 (IL-10) by fine-tuning the p38-type I interferon (IFN) axis. SARM1 inhibits the activation of Klebsiella-induced absent in melanoma 2 inflammasome to limit IL-1β production, suppressing further inflammation. Klebsiella exploits type I IFNs to induce SARM1 in a capsule and lipopolysaccharide O-polysaccharide-dependent manner via the TLR4-TRAM-TRIF-IRF3-IFNAR1 pathway. Absence of SARM1 reduces the intracellular survival of K. pneumoniae in macrophages, whereas sarm1-deficient mice control the infection. Altogether, our results illustrate an anti-immunology strategy deployed by a human pathogen. SARM1 inhibition will show a beneficial effect to treat Klebsiella infections. SARM1 is an evolutionary conserved innate immune protein with a TIR domain Klebsiella pneumoniae induces SARM1 to limit inflammation, and to induce IL-10 SARM1 inhibits the action of AIM2 inflammasome to limit IL-1β production In vivo, absence of SARM1 facilitates the clearance of Klebsiella pneumoniae
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Affiliation(s)
- Claudia Feriotti
- Wellcome-Wolfson Institute for Experimental Medicine, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast, UK
| | - Joana Sá-Pessoa
- Wellcome-Wolfson Institute for Experimental Medicine, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast, UK
| | - Ricardo Calderón-González
- Wellcome-Wolfson Institute for Experimental Medicine, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast, UK
| | - Lili Gu
- School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland
| | - Brenda Morris
- Wellcome-Wolfson Institute for Experimental Medicine, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast, UK
| | - Ryoichi Sugisawa
- School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland
| | - Jose L Insua
- Wellcome-Wolfson Institute for Experimental Medicine, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast, UK
| | - Michael Carty
- School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland
| | - Amy Dumigan
- Wellcome-Wolfson Institute for Experimental Medicine, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast, UK
| | - Rebecca J Ingram
- Wellcome-Wolfson Institute for Experimental Medicine, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast, UK
| | - Adrien Kissenpfening
- Wellcome-Wolfson Institute for Experimental Medicine, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast, UK
| | - Andrew G Bowie
- School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland
| | - José A Bengoechea
- Wellcome-Wolfson Institute for Experimental Medicine, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast, UK.
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Abstract
In the 20th century, researchers studying animal and plant signaling pathways discovered a protein domain shared across diverse innate immune systems: the Toll/Interleukin-1/Resistance-gene (TIR) domain. The TIR domain is found in several protein architectures and was defined as an adaptor mediating protein-protein interactions in animal innate immunity and developmental signaling pathways. However, studies of nerve degeneration in animals, and subsequent breakthroughs in plant, bacterial and archaeal systems, revealed that TIR domains possess enzymatic activities. We provide a synthesis of TIR functions and the role of various related TIR enzymatic products in evolutionarily diverse immune systems. These studies may ultimately guide interventions that would span the tree of life, from treating human neurodegenerative disorders and bacterial infections, to preventing plant diseases.
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Affiliation(s)
- Kow Essuman
- Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
| | - Jeffrey Milbrandt
- Department of Genetics, Washington University School of Medicine in St. Louis, St. Louis, MO 63110, USA
- Needleman Center for Neurometabolism and Axonal Therapeutics, Washington University School of Medicine in St. Louis, St. Louis, MO 63110, USA
- McDonnell Genome Institute, Washington University School of Medicine in St. Louis, St. Louis, MO 63110, USA
| | - Jeffery L. Dangl
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
- Howard Hughes Medical Institute, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Marc T. Nishimura
- Department of Biology, Colorado State University, Fort Collins, CO 80523, USA
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Msheik Z, El Massry M, Rovini A, Billet F, Desmoulière A. The macrophage: a key player in the pathophysiology of peripheral neuropathies. J Neuroinflammation 2022; 19:97. [PMID: 35429971 PMCID: PMC9013246 DOI: 10.1186/s12974-022-02454-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2021] [Accepted: 03/29/2022] [Indexed: 12/22/2022] Open
Abstract
Macrophages are present in all mammalian tissues and coexist with various cell types in order to respond to different environmental cues. However, the role of these cells has been underestimated in the context of peripheral nerve damage. More importantly, macrophages display divergent characteristics, associated with their origin, and in response to the modulatory effects of their microenvironment. Interestingly, the advent of new techniques such as fate mapping and single-cell transcriptomics and their synergistic use has helped characterize in detail the origin and fate of tissue-resident macrophages in the peripheral nervous system (PNS). Furthermore, these techniques have allowed a better understanding of their functions from simple homeostatic supervisors to chief regulators in peripheral neuropathies. In this review, we summarize the latest knowledge about macrophage ontogeny, function and tissue identity, with a particular focus on PNS-associated cells, as well as their interaction with reactive oxygen species under physiological and pathological conditions. We then revisit the process of Wallerian degeneration, describing the events accompanying axon degeneration, Schwann cell activation and most importantly, macrophage recruitment to the site of injury. Finally, we review these processes in light of internal and external insults to peripheral nerves leading to peripheral neuropathies, the involvement of macrophages and the potential benefit of the targeting of specific macrophages for the alleviation of functional defects in the PNS.
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