Apical splenic nerve electrical stimulation discloses an anti-inflammatory pathway relying on adrenergic and nicotinic receptors in myeloid cells

Mélanie Guyot,Thomas Simon,Clara Panzolini,Franck Ceppo,Douglas Daoudlarian,Emilie Murris,Eric Macia,Sophie Abélanet,Arun Sridhar,Margriet J Vervoordeldonk,Nicolas Glaichenhaus,Philippe Blancou

doi:10.1016/j.bbi.2019.03.015

Abstract

The autonomic nervous system innervates all lymphoid tissues including the spleen therefore providing a link between the central nervous system and the immune system. The only known mechanism of neural inhibition of inflammation in the spleen relies on the production of norepinephrine by splenic catecholaminergic fibers which binds to β2-adrenergic receptors (β 2-ARs) of CD4+ T cells. These CD4+ T cells trigger the release of acetylcholine that inhibits the secretion of inflammatory cytokines by macrophages through α7 nicotinic acetylcholine receptor (α7nAchRs) signaling. While the vagal anti-inflammatory pathway has been extensively studied in rodents, it remains to be determined whether it coexists with other neural pathways. Here, we have found that three nerve branches project to the spleen in mice. While two of these nerves are associated with an artery and contain catecholaminergic fibers, the third is located at the apex of the spleen and contain both catecholaminergic and cholinergic fibers. We found that electrical stimulation of the apical nerve, but not the arterial nerves, inhibited inflammation independently of lymphocytes. In striking contrast to the anti-inflammatory pathway mechanism described so far, we also found that the inhibition of inflammation by apical nerve electrical stimulation relied on signaling by both β 2-ARs and α7nAchRs in myeloid cells, with these two signaling pathways acting in parallel. Most importantly, apical splenic nerve electrical stimulation mitigated clinical symptoms in a mouse model of rheumatoid arthritis further providing the proof-of-concept that such an approach could be beneficial in patients with Immune-mediated inflammatory diseases.

Highlights

The autonomic nervous system innervates lymphoid tissues, providing an important link between the central nervous system and the immune system
Only apical nerve stimulation induced the release of acetylcholine spleen (21.8 ± 3.1 μg/mg unstimulated; 38.8 ± 4.9 ng/mg for the arterial nerve; 73.4 ± 11.9 ng/mg for the apical nerve) in lymphocyte-deficient mice (Rag1-/-) (Fig. 1f) further suggesting that cholinergic fibers, and not T cells, were the source of acetylcholine in these experiments
Because apical nerve stimulation was as efficient as vagus nerve stimulation (VNS) at inhibiting LPS-induced TNF production, we investigated whether apical splenic nerve could inhibit collagen-induced arthritis (CIA) in arthritis-prone

Summary

Introduction

The autonomic nervous system innervates lymphoid tissues, providing an important link between the central nervous system and the immune system. While previous studies have revealed direct autonomic innervation of parenchymal tissue in the thymus, bone marrow, spleen, lymph nodes, and gutassociated lymphoid tissues[1], the anatomical and functional characterization of the nerves that project to these lymphoid organs remain incomplete from an anatomical and functional point of view. This is the case for the spleen which is the largest secondary lymphoid organ in the body and the main source of pro-inflammatory cytokines in systemic inflammatory diseases[2]. Experimental studies in rodents have shown that sympathetic nerve terminals in the spleen are able to store and release norepinephrine in response to stimulation[8,9], and that the splenic norepinephrine content dramatically decreased following chemical[10] or surgical[11] sympathectomy

Methods

Results

Conclusion