Peroxisome Proliferator-Activated Receptor-δ Deficiency in Microglia Results in Exacerbated Axonal Injury and Tissue Loss in Experimental Autoimmune Encephalomyelitis

Ellinore R Doroshenko; Paulina C Drohomyrecky; Annette Gower; Heather Whetstone; Lindsay S Cahill; Milan Ganguly; Shoshana Spring; Tae Joon Yi; John G Sled; Shannon E Dunn

doi:10.3389/fimmu.2021.570425

Peroxisome Proliferator-Activated Receptor-δ Deficiency in Microglia Results in Exacerbated Axonal Injury and Tissue Loss in Experimental Autoimmune Encephalomyelitis

Front Immunol. 2021 Feb 26:12:570425. doi: 10.3389/fimmu.2021.570425. eCollection 2021.

Authors

Ellinore R Doroshenko¹, Paulina C Drohomyrecky¹, Annette Gower², Heather Whetstone³, Lindsay S Cahill⁴, Milan Ganguly⁵, Shoshana Spring⁴, Tae Joon Yi^{1

2}, John G Sled^{4

6}, Shannon E Dunn^{1

2

7}

Affiliations

¹ Department of Immunology, University of Toronto, Toronto, ON, Canada.
² Keenan Research Centre for Biomedical Science of St. Michael's Hospital, Toronto, ON, Canada.
³ Peter Gilgan Centre for Research and Learning, Hospital for Sick Children, Toronto, ON, Canada.
⁴ Mouse Imaging Centre, The Hospital for Sick Children, Toronto, ON, Canada.
⁵ Histology Core, The Centre for Phenogenomics, Toronto, ON, Canada.
⁶ Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada.
⁷ Women's College Research Institute, Women's College Hospital, Toronto, ON, Canada.

Abstract

Peroxisome proliferator-activated receptor (PPAR)-δ is a nuclear receptor that functions to maintain metabolic homeostasis, regulate cell growth, and limit the development of excessive inflammation during immune responses. Previously, we reported that PPAR-δ-deficient mice develop a more severe clinical course of experimental autoimmune encephalomyelitis (EAE); however, it was difficult to delineate the role that microglia played in this disease phenotype since PPAR-δ-deficient mice exhibited a number of immune defects that enhanced CNS inflammation upstream of microglia activation. Here, we specifically investigated the role of PPAR-δ in microglia during EAE by using mice where excision of a floxed Ppard allele was driven by expression of a tamoxifen (TAM)-inducible CX3C chemokine receptor 1 promoter-Cre recombinase transgene (Cx3cr1^CreERT2: Ppard^fl/fl). We observed that by 30 days of TAM treatment, Cx3cr1^CreERT2: Ppard^fl/fl mice exhibited Cre-mediated deletion primarily in microglia and this was accompanied by efficient knockdown of Ppard expression in these cells. Upon induction of EAE, TAM-treated Cx3cr1^CreERT2: Ppard^fl/fl mice presented with an exacerbated course of disease compared to TAM-treated Ppard^fl/fl controls. Histopathological and magnetic resonance (MR) studies on the spinal cord and brains of EAE mice revealed increased Iba-1 immunoreactivity, axonal injury and CNS tissue loss in the TAM-treated Cx3cr1^CreERT2: Ppard^fl/fl group compared to controls. In early EAE, a time when clinical scores and the infiltration of CD45⁺ leukocytes was equivalent between Cx3cr1^CreERT2: Ppard^fl/fl and Ppard^fl/fl mice, Ppard-deficient microglia exhibited a more reactive phenotype as evidenced by a shorter maximum process length and lower expression of genes associated with a homeostatic microglia gene signature. In addition, Ppard-deficient microglia exhibited increased expression of genes associated with reactive oxygen species generation, phagocytosis and lipid clearance, M2-activation, and promotion of inflammation. Our results therefore suggest that PPAR-δ has an important role in microglia in limiting bystander tissue damage during neuroinflammation.

Keywords: axon injury; experimental autoimmune encephalomyelitis; microglia; neuroinflammation; peroxisome proliferator-activated receptor.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Axons / metabolism*
Axons / pathology
Cells, Cultured
Disease Models, Animal
Disease Susceptibility
Encephalomyelitis, Autoimmune, Experimental / diagnosis
Encephalomyelitis, Autoimmune, Experimental / etiology*
Encephalomyelitis, Autoimmune, Experimental / metabolism*
Lymphocyte Activation / immunology
Magnetic Resonance Imaging
Mice
Mice, Knockout
Microglia / immunology*
Microglia / metabolism*
Microglia / pathology
PPAR delta / deficiency*
Severity of Illness Index
T-Lymphocytes / immunology
T-Lymphocytes / metabolism

Substances

PPAR delta