The glycosyltransferase EXTL2 promotes proteoglycan deposition and injurious neuroinflammation following demyelination

Annie Pu,Stephen Sawcer,Hiroshi Kitagawa,Khalil S Rawji,Manoj K Mishra,Yifei Dong,Claudia Silva,Samira Ghorbanigazar,V Wee Yong,Erin L Stephenson

doi:10.1186/s12974-020-01895-1

Abstract

BackgroundChondroitin sulfate proteoglycans (CSPGs) are potent inhibitors of axonal regrowth and remyelination. More recently, they have also been highlighted as a modulator of macrophage infiltration into the central nervous system in experimental autoimmune encephalomyelitis, an inflammatory model of multiple sclerosis.MethodsWe interrogated results from single nucleotide polymorphisms (SNPs) lying in or close to genes regulating CSPG metabolism in the summary results from two publicly available systematic studies of multiple sclerosis (MS) genetics. A demyelinating injury model in the spinal cord of exostosin-like 2 deficient (EXTL2-/-) mice was used to investigate the effects of dysregulation of EXTL2 on remyelination. Cell cultures of bone marrow-derived macrophages and primary oligodendrocyte precursor cells and neurons were supplemented with purified CSPGs or conditioned media to assess potential mechanisms of action.ResultsThe strongest evidence for genetic association was seen for SNPs mapping to the region containing the glycosyltransferase exostosin-like 2 (EXTL2), an enzyme that normally suppresses CSPG biosynthesis. Six of these SNPs showed genome-wide significant evidence for association in one of the studies with concordant and nominally significant effects in the second study. We then went on to show that a demyelinating injury to the spinal cord of EXTL2−/− mice resulted in excessive deposition of CSPGs in the lesion area. EXTL2−/− mice had exacerbated axonal damage and myelin disruption relative to wild-type mice, and increased representation of microglia/macrophages within lesions. In tissue culture, activated bone marrow-derived macrophages from EXTL2−/− mice overproduce tumor necrosis factor α (TNFα) and matrix metalloproteinases (MMPs).ConclusionsThese results emphasize CSPGs as a prominent modulator of neuroinflammation and they highlight CSPGs accumulating in lesions in promoting axonal injury.

Highlights

Chondroitin sulfate proteoglycans (CSPGs) are potent inhibitors of axonal regrowth and remyelination
Single nucleotide polymorphism (SNP) data mining from Multiple sclerosis (MS) databases implicates exostosin-like 2 (EXTL2) Ignoring pseudogenes, we identified 154 autosomal genes involved in the metabolism of CSPGs (Table 1)
All six of the SNPs mapping to the region containing the EXTL2 gene were confirmed as associated with genome-wide significance in the larger MS genome-wide association screen (GWAS) meta-analysis (IMSGC 2017 BioRxiv 143933) that involved a total of 14,802 cases and 26,703 controls, including those considered in the 2011 GWAS

Summary

Introduction

Chondroitin sulfate proteoglycans (CSPGs) are potent inhibitors of axonal regrowth and remyelination. They have been highlighted as a modulator of macrophage infiltration into the central nervous system in experimental autoimmune encephalomyelitis, an inflammatory model of multiple sclerosis. Previous reports have highlighted the deposition of chondroitin sulfate proteoglycans (CSPGs) at the borders of chronic active MS lesions [4]. Lectican CSPG members are versican, aggrecan, neurocan, and brevican. In demyelinating injury, they are locally upregulated by several cell types and deposited near the injury site [7,8,9,10,11,12,13]. CSPGs are potent inhibitors for regenerative processes such as axonal regeneration and remyelination [14,15,16,17]

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Discussion

Conclusion