Author Of 1 Presentation
PS02.03 - Targeted Depletion of Alternatively-Activated Myeloid Cells Exacerbates Adoptive Transfer EAE
Abstract
Background
A significant proportion of the inflammatory cells that infiltrate the central nervous system (CNS) of patients with multiple sclerosis (MS) and animals with experimental autoimmune encephalomyelitis (EAE), are myeloid cells, including monocyte-derived macrophages and dendritic cells. A large body of literature supports a pathogenic role of these subsets during the acute phase of CNS demyelinating lesion formation. However, we and others have shown that CNS-infiltrating myeloid cells are more heterogeneous than traditionally thought, and that their phenotype evolves during the clinical course. Arginase 1 (Arg1) is an inhibitor of nitric oxide (NO) and a canonical marker of alternatively activated myeloid cells (AAMC) with anti-inflammatory properties. Arg1+ myeloid cells accumulate in the CNS from peak EAE through remission, but are not detectable in the blood or peripheral tissues. Furthermore, myeloid cells expressing AAMC markers are dominant in the quiescent core, as opposed to the active demyelinating rim, of MS lesions.
Objectives
The objective of this study is to determine the role of AAMCs in the resolution of inflammation and recovery of neurological function in a relapsing-remitting model of EAE.
Methods
To address that hypothesis, we constructed a transgenic mouse strain with the human diphtheria toxin receptor (hDTR) gene (Hbegf) linked to the Arg1 promoter (Arg1-hDTR mice). In order to restrict hDTR expression to hematopoietic cells we reconstituted lethally irradiated WT mice with bone marrow cells from Arg1-hDTR donors. EAE was induced in Arg1-hDTR→WT and WT→WT chimeric mice by the adoptive transfer of purified myelin-reactive CD4+ TH17 cells and treated with diphtheria toxin (DT). CNS inflammatory cell composition was evaluated via flow cytometry and cell subsets were isolated via FACS for transcriptional analysis.
Results
Depletion of Arg1+ inflammatory cells in Arg1-hDTR→WT chimeric mice exacerbated EAE induced by the transfer of encephalitogenic TH17 cells, and resulted in a high mortality rate compared with PBS-treatment and WT→WT controls. Monocyte-derived dendritic cells (mDC) possessing an anti-inflammatory phenotype were most susceptible to depletion. The more severe clinical course observed following depletion was associated with an increase in the absolute number of Arg1- inflammatory macrophages present in the spinal cord at peak disease, coincident with elevated levels of proinflammatory cytokines and chemokines in spinal cord homogenates. Conversely, targeted depletion of Arg1 in immune cells had no impact on EAE incidence or severity.
Conclusions
This study suggests that CNS accumulation of AAMC during later stages of autoimmune demyelinating disease suppresses the local inflammatory response and ameliorates neurological deficits by an Arg1- independent mechanism.
Author Of 1 Presentation
LB1236 - The role of ten eleven translocase 2 (TET2) in the regulation of autoimmune demyelinating disease (ID 2117)
Abstract
Background
Ten-Eleven Translocase 2 (TET2) is a Fe(III)-, α-ketoglutarate-dependent enzyme that catalyzes the oxidation of methylated cytosine to 5’-hydroxymethyl cytosine (5hmC). 5hmC is a stable epigenetic mark that can either activate or repress gene expression in a cell- and loci-dependent manner. Recently Tet-2 was identified as a genetic susceptibility locus in MS. TET2 loss-of-function mutations are abundant in a variety of cancers characterized by aberrant myeloid proliferation, differentiation, and activation. Since myeloid cells play a critical role in the pathogenesis of Multiple sclerosis (MS) and the animal model experimental autoimmune encephalitis (EAE), we hypothesized that Tet-2 reduction or inactivation in myeloid cells promotes susceptibility to autoimmune demyelinating disease.
Objectives
To measure the expression of Tet2 and 5hmC in CNS-infiltrating myeloid cells during the development of adoptively transferred EAE, and to assess the impact of Tet2 deficiency on the clinical course.
Methods
EAE was induced via adoptive transfer of Th17-polarized, myelin oligodendrocyte glycoprotein (MOG)-specific CD4+ T cells in WT and Tet2+/- mice. CNS mononuclear cells and splenocytes were analyzed via flow cytometry and transcriptomics.
Results
Tet2, 5hmC content, and markers of Tet2 activity, were reduced in CNS-infiltrating monocytes, macrophages and monocyte derived dendritic cells at the peak of EAE compared with their splenic counterparts. Tet2+/- mice experienced an exacerbated clinical course of Th17-mediated EAE compared to Tet2+/+ mice. The increase in disease severity was associated with hyperactivation of CNS myeloid cells. Ongoing studies in our laboratory are examining the effects of a myeloid-specific TET2 deletion on neuroinflammation and CNS damage during EAE using a Cre/lox genetic system.
Conclusions
Our data suggest that downregulation of TET2 expression and activity during EAE enhances neuroinflammation, CNS damage and neurological disability. This study elucidates a novel mechanism of myeloid cell regulation during CNS autoimmune disease. Disease modifying therapies that prevent Tet2 downregulation in myeloid cells may be beneficial in individuals with MS and related disorders who do not respond to lymphocyte targeting agents.