Diverse Cell Types Establish a Pathogenic Immune Environment in Peripheral Neuropathy [bulk RNA-seq]

Neuroinflammation plays a complex and context-dependent role in many neurodegenerative diseases. We identified a key pathogenic function of macrophages in a mouse model of a rare human congenital neuropathy in which SARM1, the central executioner of axon degeneration, is activated by hypomorphic mutations in the axon survival factor NMNAT2. Macrophage depletion blocked and reversed neuropathic phenotypes in this sarmopathy model, revealing SARM1-dependent neuroimmune mechanisms as key drivers of disease pathogenesis. In this study, we investigated the impact of chronic subacute SARM1 activation on the peripheral nerve milieu using single cell/nucleus RNA-sequencing (sc/snRNA-seq). Our analyses reveal an expansion of immune cells (macrophages and T lymphocytes) and repair Schwann cells, as well as significant transcriptional alterations to a wide range of nerve-resident cell types. Notably, endoneurial fibroblasts show increased expression of chemokines (Ccl9, Cxcl5) and complement components (C3, C4b, C6) in response to chronic SARM1 activation, indicating enhanced immune cell recruitment and immune response regulation by non-immune nerve-resident cells. Analysis of CD45+ immune cells in sciatic nerves revealed an expansion of an Il1b+ macrophage subpopulation with increased expression of markers associated with phagocytosis and T cell activation/proliferation. We also found a significant increase in T cells in sarmopathic nerves. Remarkably, T cell depletion rescued motor phenotypes in the sarmopathy model. These findings delineate the significant changes chronic SARM1 activation induces in peripheral nerves and highlights the potential of immunomodulatory therapies for SARM1-dependent peripheral neurodegenerative disease. Overall design: - Bulk RNA sequencing of WT and Nmnat2 V98M/R232Q;SARM1 KO mouse sciatic nerves at 2-3-month

神经炎症在多种神经退行性疾病中发挥着复杂且依赖于具体情境的作用。我们在一种罕见人类先天性周围神经病的小鼠模型中，鉴定出巨噬细胞的关键致病功能；该模型中，作为轴突变性核心执行因子的SARM1（SARM1），可因轴突存活因子NMNAT2（NMNAT2）发生功能减退突变而被激活。在该SARM1病（sarmopathy）模型中，巨噬细胞耗竭可阻断并逆转神经病变表型，揭示了依赖SARM1的神经免疫机制是疾病发病机制的关键驱动因素。本研究采用单细胞/单细胞核RNA测序（single cell/nucleus RNA-sequencing，sc/snRNA-seq）技术，探究了慢性亚急性SARM1激活对周围神经微环境的影响。分析结果显示，免疫细胞（巨噬细胞与T淋巴细胞）及修复型雪旺细胞出现扩增，同时多种神经驻留细胞类型发生显著的转录组改变。值得注意的是，在慢性SARM1激活的刺激下，内膜成纤维细胞的趋化因子（Ccl9、Cxcl5）与补体成分（C3、C4b、C6）表达上调，表明非免疫性神经驻留细胞可增强免疫细胞招募与免疫应答调控。对坐骨神经中CD45阳性免疫细胞的分析显示，Il1b阳性巨噬细胞亚群出现扩增，其与吞噬作用及T细胞活化/增殖相关的标志物表达上调。我们还在SARM1病模型小鼠的坐骨神经中发现T细胞数量显著增加。值得注意的是，T细胞耗竭可挽救该SARM1病模型中的运动功能表型。本研究阐明了慢性SARM1激活诱导周围神经发生的显著改变，并凸显了免疫调节疗法用于治疗依赖SARM1的周围神经退行性疾病的潜力。实验设计：- 对2-3月龄野生型（Wild Type，WT）以及Nmnat2 V98M/R232Q;SARM1基因敲除（SARM1 KO）小鼠的坐骨神经进行批量RNA测序。