Connecting Immune Cell Infiltration to the Multitasking Microglia Response and TNF Receptor 2 Induction in the Multiple Sclerosis Brain.

Caterina Veroni,Corrado Fagnani,Cristina Agresti,Francesca Aloisi,Barbara Rosicarelli,Barbara Serafini

doi:10.3389/fncel.2020.00190

Caterina Veroni, Corrado Fagnani + Show 4 more

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https://doi.org/10.3389/fncel.2020.00190

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Abstract

Signaling from central nervous system (CNS)-infiltrating lymphocytes and macrophages is critical to activate microglia and cause tissue damage in multiple sclerosis (MS). We combined laser microdissection with high-throughput real time RT-PCR to investigate separately the CNS exogenous and endogenous inflammatory components in postmortem brain tissue of progressive MS cases. A previous analysis of immune infiltrates isolated from the white matter (WM) and the meninges revealed predominant expression of genes involved in antiviral and cytotoxic immunity, including IFNγ and TNF. Here, we assessed the expression of 71 genes linked to IFN and TNF signaling and microglia/macrophage activation in the parenchyma surrounding perivascular cuffs at different stages of WM lesion evolution and in gray matter (GM) lesions underlying meningeal infiltrates. WM and GM from non-neurological subjects were used as controls. Transcriptional changes in the WM indicate activation of a classical IFNγ-induced macrophage defense response already in the normal-appearing WM, amplification of detrimental (proinflammatory/pro-oxidant) and protective (anti-inflammatory/anti-oxidant) responses in actively demyelinating WM lesions and persistence of these dual features at the border of chronic active WM lesions. Transcriptional changes in chronic subpial GM lesions indicate skewing toward a proinflammatory microglia phenotype. TNF receptor 2 (TNFR2) mediating TNF neuroprotective functions was one of the genes upregulated in the MS WM. Using immunohistochemistry we show that TNFR2 is highly expressed in activated microglia in the normal-appearing WM, at the border of chronic active WM lesions, and in foamy macrophages in actively demyelinating WM and GM lesions. In lysolecithin-treated mouse cerebellar slices, a model of demyelination and remyelination, TNFR2 RNA and soluble protein increased immediately after toxin-induced demyelination along with transcripts for microglia/macrophage-derived pro- and anti-inflammatory cytokines. TNFR2 and IL10 RNA and soluble TNFR2 protein remained elevated during remyelination. Furthermore, myelin basic protein expression was increased after selective activation of TNFR2 with an agonistic antibody. This study highlights the key role of cytotoxic adaptive immunity in driving detrimental microglia activation and the concomitant healing response. It also shows that TNFR2 is an early marker of microglia activation and promotes myelin synthesis, suggesting that microglial TNFR2 activation can be exploited therapeutically to stimulate CNS repair.

Highlights

Multiple sclerosis (MS) is the most common chronic inflammatory disease of the central nervous system (CNS) affecting young adults and causing progressive deterioration of motor, sensory, and cognitive functions
Serial brain sections for laser capture microdissection (LCM) and subsequent RNA analysis were cut from 18 tissue blocks of 10 progressive MS cases (Table 1) that were selected for presence of substantial immune infiltrates in the white matter (WM) and meninges and for good RNA quality (RIN ≥ 6, as detailed in Veroni et al, 2018)
The WM areas surrounding medium to large size perivascular cuffs included: (i) normal-appearing WM (NAWM) (n = 14) characterized by apparently normal myelin and activated microglia (Figures 1A–C), possibly evolving into actively demyelinating lesions; (ii) active WM lesions characterized by myelin breakdown and presence of foamy macrophages throughout the lesion area (n = 13) (Figures 1D–G); these lesions usually evolve into chronic active lesions; (iii) the edge of chronic active WM lesions, denominated mixed active/inactive WM lesions (Kuhlmann et al, 2017), defined as the rim of activated microglia/macrophages surrounding the demyelinated, inactive lesion core (n = 8) (Figures 1H–J)

Summary

Introduction

Multiple sclerosis (MS) is the most common chronic inflammatory disease of the central nervous system (CNS) affecting young adults and causing progressive deterioration of motor, sensory, and cognitive functions. To date, it remains unclear whether it is self or non-self-antigens that stimulate the CNS-targeted immune response. Blood-derived lymphocytes, including CD4+ T helper cells, CD8+ cytotoxic T cells, B cells and, to a lesser extent, myeloid cells, accumulate predominantly in the connectival spaces of the CNS: the venous perivascular spaces in the white matter (WM) and more rarely in the gray matter (GM) (Lassmann, 2019), and the subarachnoid space of the meninges where ectopic lymphoid-like structures can develop (Serafini et al, 2004). Microglia activation can contribute to both the pathological features of MS lesions and the healing response attenuating inflammation and promoting functional recovery (Butovsky and Weiner, 2018; Li and Barres, 2018)

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