Tollip, an early regulator of the acute inflammatory response in the substantia nigra.

Marie Humbert-Claude,F Legueux,D Duc,D Velin,D Dwir,L Thieren,M H Maillard,K Q Do,L Tenenbaum,J Sandström Von Tobel,F Monnet-Tschudi,C Begka

doi:10.1186/s12974-016-0766-5

Abstract

BackgroundTollip is a ubiquitously expressed protein, originally described as a modulator of the IL-1R/TLR-NF-κB signaling pathways. Although this property has been well characterized in peripheral cells, and despite some evidence of its expression in the central nervous system, the role of Tollip in neuroinflammation remains poorly understood. The present study sought to explore the implication of Tollip in inflammation in the substantia nigra pars compacta, the structure affected in Parkinson’s disease.MethodsWe first investigated Tollip distribution in the midbrain by immunohistochemistry. Then, we addressed TLR4-mediated response by intra-nigral injections of lipopolysaccharide (LPS), a TLR4 agonist, on inflammatory markers in Tollip knockout (KO) and wild-type (WT) mice.ResultsWe report an unexpectedly high Tollip immunostaining in dopaminergic neurons of the mice brain. Second, intra-nigral injection of LPS led to increased susceptibility to neuroinflammation in Tollip KO compared to Tollip WT mice. This was demonstrated by a significant increase of tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β), interleukin 6 (IL-6), and interferon gamma (IFN-γ) messenger RNA (mRNA) in the midbrain of Tollip KO mice upon LPS injection. Consistently, brain rAAV viral vector transduction with a nuclear factor kappa B (NF-κB)-inducible reporter gene confirmed increased NF-κB activation in Tollip KO mice. Lastly, Tollip KO mice displayed higher inducible NO synthase (iNOS) production, both at the messenger and protein level when compared to LPS-injected WT mice. Tollip deletion also aggravated LPS-induced oxidative and nitrosative damages, as indicated by an increase of 8-oxo-2′-deoxyguanosine and nitrotyrosine immunostaining, respectively.ConclusionsAltogether, these findings highlight a critical role of Tollip in the early phase of TLR4-mediated neuroinflammation. As brain inflammation is known to contribute to Parkinson’s disease, Tollip may be a potential target for neuroprotection.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-016-0766-5) contains supplementary material, which is available to authorized users.

Highlights

Toll-interacting protein (Tollip) is a ubiquitously expressed protein, originally described as a modulator of the IL-1R/Toll-like receptors (TLR)-Nuclear factor kappa B (NF-κB) signaling pathways
Tollip protein is highly expressed in dopaminergic neurons Unexpectedly, the percentage of Tollip-immunopositive cells relative to the DAPI-positive cells in the substantia nigra pars compacta (SNc) (32.0 ± 3.5%) was 10- and 2fold higher than those found respectively in the hippocampus (3.0 ± 0.6%) and the cortex (13.7 ± 0.9%) (Fig. 1a)
The results of our study show that Tollip deletion exacerbated inducible nitric oxide (NO) synthase (iNOS) production, protein nitration, and DNA oxidation induced by LPS injection in the substantia nigra, a structure affected in Parkinson’s disease (PD)

Summary

Introduction

Tollip is a ubiquitously expressed protein, originally described as a modulator of the IL-1R/TLR-NF-κB signaling pathways. Enzymes associated with oxidative (i.e., COX-1 and COX-2) and nitrosative stresses (i.e., iNOS) have been involved in neuronal vulnerability in PD [16, 17]. Due to their high iron content [18] and reduced glutathione levels [19], dopaminergic neurons are thought to be susceptible to reactive oxygen species released by activated microglia

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