Glial pathology and retinal neurotoxicity in the anterior visual pathway in experimental autoimmune encephalomyelitis

Jing Jin,Kyle Martin,Matthew D Smith,Valina L Dawson,Ted M Dawson,Calvin J Kersbergen,Katharine Whartenby,Peter A Calabresi,Tae-In Kam,Donald J Zack,Mayuri Viswanathan

doi:10.1186/s40478-019-0767-6

Abstract

The animal model experimental autoimmune encephalomyelitis (EAE) has been used extensively in the past to test mechanisms that target peripheral immune cells for treatment of multiple sclerosis (MS). While there have been some notable successes in relapsing MS, the development of therapies for progressive multiple sclerosis (MS) has been hampered by lack of an appropriate animal model. Further, the mechanisms underlying CNS inflammation and neuronal injury remain incompletely elucidated. It is known that the MOG 35–55 EAE mouse model does not have insidious behavioral progression as occurs in people with MS, but there is significant neuronal and axonal injury in EAE, as a result of the inflammation. In the present study, we describe the time course of glial activation and retinal neurodegeneration in the EAE model, and highlight the utility of studying the anterior visual pathway for modeling mechanisms of neuronal injury that may recapitulate critical aspects of the pathology described in people with MS following optic neuritis and subclinical optic neuropathy. We show that A1 neurotoxic astrocytes are prevalent in optic nerve tissue and retina, and are associated with subsequent RGC loss in the most commonly used form of the EAE model induced by MOG 35–55 peptide in C57/B6 mice. We developed a semi-automatic method to quantify retinal ganglion cells (RGC) and show that RGCs remain intact at peak EAE (PID 16) but are significantly reduced in late EAE (PID 42). Postsynaptic proteins and neurites were also compromised in the retina of late EAE mice. The retinal pathology manifests weeks after the microglial and astrocyte activation, which were prominent in optic nerve tissues at PID 16. Microglia expressed iNOS and had increased gene expression of C1q, TNF-α, and IL-1α. Astrocytes expressed high levels of complement component 3 and other genes associated with A1 neurotoxic astrocytes. Our data suggest that EAE can be used to study the pathobiology of optic neuropathy and to examine the preclinical neuroprotective effects of drugs that target activation of neurotoxic A1 astrocytes.

Highlights

The mechanisms underlying neurodegeneration remain incompletely defined for most progressive neurological diseases, including multiple sclerosis (MS)
In a mouse EAE model induced with myelinoligodendrocyte glycoprotein peptide 35–55 (MOG35–55), we found significant retinal ganglion cell (RGC) loss in the retina of late EAE mice, post-immunization day (PID) 42, but not in early EAE (PID 16)
Discussion we show that A1 neurotoxic phenotype astrocytes are prevalent in optic nerve tissue and retina, and are associated with subsequent RGC loss, in the most commonly used form of the EAE model induced by Myelinoligodendrocyte glycoprotein (MOG) 35–55 peptide in C57/B6 mice

Summary

Introduction

The mechanisms underlying neurodegeneration remain incompletely defined for most progressive neurological diseases, including multiple sclerosis (MS). The roles of microglia and astroglia have long been studied in MS and related animal models, and recently transcriptomic profiling of glia has allowed for more specific target identification for neuroprotection [5, 6, 13, 17, 21, 40]. We and others have previously shown that in EAE there is extensive loss of axons in the spinal cord following an acute wave of immune cell infiltration into the CNS [18, 53]. The anterior visual pathway affords the opportunity to quantify pathology in the optic nerve, another primary location of immune cell infiltration in EAE, as well as in the retina to assess retinal ganglion cell (RGC) loss and local microglia and astroglia responses [14, 15, 23, 34, 46, 47]. Immunohistological staining further confirmed that in the optic nerve astrocytes were skewed to the neurotoxic subtype, which expressed high levels of complement component 3 (C3) and a neurotoxic astrocyte marker, immunoproteasome subunit beta type-8 (PSMB8)

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Discussion

Conclusion