Nogo receptor expression in microglia/macrophages during experimental autoimmune encephalomyelitis progression

Abstract

Myelin-associated inhibitory factors within the central nervous system (CNS) are considered to be one of the main obstacles for axonal regeneration following disease or injury. The nogo receptor 1 (NgR1) has been well documented to play a key role in limiting axonal regrowth in the injured and diseased mammalian CNS. However, the role of nogo receptor in immune cell activation during CNS inflammation is yet to be mechanistically elucidated. Microglia/macrophages are immune cells that are regarded as pathogenic contributors to inflammatory demyelinating lesions in multiple sclerosis (MS). In this study, the animal model of MS, experimental autoimmune encephalomyelitis (EAE) was induced in ngr1+/+ and ngr1–/– female mice following injection with the myelin oligodendrocyte glycoprotein (MOG35–55) peptide. A fate-map analysis of microglia/macrophages was performed throughout spinal cord sections of EAE-induced mice at clinical scores of 0, 1, 2 and 3, respectively (increasing locomotor disability) from both genotypes, using the CD11b and Iba1 cell markers. Western immunoblotting using lysates from isolated spinal cord microglia/macrophages, along with immunohistochemistry and flow cytometric analysis, was performed to demonstrate the expression of nogo receptor and its two homologs during EAE progression. Myelin protein engulfment during EAE progression in ngr1+/+ and ngr1–/– mice was demonstrated by western immunblotting of lysates from isolated spinal cord microglia/macrophages, detecting levels of Nogo-A and MOG. The numbers of M1 and M2 microglia/macrophage phenotypes present in the spinal cords of EAE-induced ngr1+/+ and ngr1–/– mice, were assessed by flow cytometric analysis using CD38 and Erg-2 markers. A significant difference in microglia/macrophage numbers between ngr1+/+ and ngr1–/– mice was identified during the progression of the clinical symptoms of EAE, in the white versus gray matter regions of the spinal cord. This difference was unrelated to the expression of NgR on these macrophage/microglial cells. We have identified that as EAE progresses, the phagocytic activity of microglia/macrophages with myelin debris, in ngr1–/– mice, was enhanced. Moreover, we show a modulation from a predominant M1-pathogenic to the M2-neurotrophic cell phenotype in the ngr1–/– mice during EAE progression. These findings suggest that CNS-specific macrophages and microglia of ngr1–/– mice may exhibit an enhanced capacity to clear inhibitory molecules that are sequestered in inflammatory lesions.

Central nervous system demyelinating diseases: glial cells at the hub of pathology

“…When Nogo-A was depleted from the visual cortex of mice by acute cuprizone treatment, astrocytes released a higher concentration of synaptogenic factors and excitatory synapses proliferated ( Figure 2 ). Although we have not evaluated the case of microglia, previous articles have shown that these cells actively respond to Nogo-A, modulating functions such as cell migration, focal adhesion and inflammation ( 60 , 61 ), while Nogo-A may impair microglial phagocytic capacity ( 62 ). We understand this is further evidence that myelin inhibitory proteins, such as Nogo-A, may serve as a converging point between inflammation, synaptopathy and glial cells in demyelinating diseases, as is described in Figure 3 .…”

Dynamic roles of neutrophils in post‐stroke neuroinflammation

“…Microglia can produce and respond to pro‐inflammatory cytokines such as IL‐1, IL‐2 and TNFα 74 . The dysfunction of microglia leads to a wide variety of neurodegenerative diseases including multiple sclerosis, 75 Parkinson’s, 76 Huntington’s 77 and Alzheimer’s disease 78 . In addition, microglia also exhibit distinct interactions with neutrophils during the neuroinflammatory process after stroke.…”

That’s a Wrap! Molecular Drivers Governing Neuronal Nogo Receptor-Dependent Myelin Plasticity and Integrity

“…A surprising finding in our study which investigated axo-glial dynamics of ngr1 −/− mice (Lee et al, 2017 ), was that although there was increased cleavage of Caspr, no reduction of full-length Caspr was found in the spinal cords of ngr1 −/− mice, implicating consistent expression and possibly a potential regulation of turnover of myelin by NgR1. We have recently reported that ngr1 −/− mice also exhibit a sustained expansion of microglia without neuroinflammatory challenge and these cells exhibit increased levels of engulfed myelin proteins (Alrehaili et al, 2018 ). Furthermore, this observation is consistent with the different expression patterns of Nogo-A found along with the axo-glial units in the spinal cords of ngr1 −/− mice, as mice deficient in Nogo-A exhibited faster remyelination upon lysolecithin-induced demyelination when compared to wild-type (Chong et al, 2012 ).…”