Bacteria hijack a neuro-immune axis in meninges to facilitate brain invasion

The meninges are densely innervated by nociceptive sensory neurons that mediate pain and headache. How pain and neuro-immune interactions impact meningeal host defenses is unclear. Bacterial meningitis causes life-threatening infections of the meninges and central nervous system (CNS), affecting over one million people a year. Here we find that Nav1.8+ neuron signaling to immune cells in the meninges via the neuropeptide calcitonin gene-related peptide (CGRP) exacerbates bacterial meningitis. Nociceptor ablation reduced meningeal and brain invasion by two bacterial pathogens: Streptococcus pneumoniae and Streptococcus agalactiae. S. pneumoniae activated nociceptors via Pneumolysin to release CGRP, which acts through its receptor RAMP1 on meningeal macrophages to inhibit chemokine expression, neutrophil recruitment and antimicrobial defenses. Macrophage-specific RAMP1 deficiency or blockade of RAMP1 signaling enhanced immune responses and bacterial clearance in meninges and brain. Therefore, targeting a neuro-immune axis in the meninges can enhance host defenses and may be a potential treatment for bacterial meningitis. For in vitro bulk RNA-seq experiments, there are 24 samples total, representing 4 biological replicates, two technical replicates, of 3 conditions at 1 time point. For in vivo scRNA-seq experiments, there are 40 samples total, representing 10 biological replicates of 4 conditions at 1 time point.

脑膜密集支配着介导疼痛与头痛的伤害感受性感觉神经元（nociceptive sensory neurons）。目前，疼痛及神经免疫相互作用如何影响脑膜宿主防御功能仍不明确。细菌性脑膜炎（bacterial meningitis）可引发脑膜与中枢神经系统（central nervous system，CNS）的致死性感染，每年影响超过百万人群。本研究发现，Nav1.8阳性神经元（Nav1.8+ neuron）通过神经肽降钙素基因相关肽（calcitonin gene-related peptide，CGRP）向脑膜内的免疫细胞传递信号，可加重细菌性脑膜炎。伤害感受神经元（nociceptor）的消融可减少两种细菌病原体——肺炎链球菌（Streptococcus pneumoniae）与无乳链球菌（Streptococcus agalactiae）对脑膜和大脑的侵袭。肺炎链球菌通过肺炎溶血素（Pneumolysin）激活伤害感受神经元并释放CGRP，CGRP通过脑膜巨噬细胞上的受体RAMP1抑制趋化因子表达、中性粒细胞招募及抗菌防御功能。巨噬细胞特异性RAMP1缺陷或阻断RAMP1信号通路可增强脑膜与大脑内的免疫应答及细菌清除能力。因此，靶向脑膜内的神经免疫轴可增强宿主防御功能，或可成为细菌性脑膜炎的潜在治疗手段。

体外批量RNA测序（bulk RNA-seq）实验共包含24个样本，对应1个时间点下3种实验条件，每种条件设4次生物学重复与2次技术重复。体内单细胞RNA测序（scRNA-seq）实验共包含40个样本，对应1个时间点下4种实验条件，每种条件设10次生物学重复。