Biallelic loss of SPG11 function constitutes the most frequent cause of complicated autosomal recessive hereditary spastic paraplegia (HSP) with thin corpus callosum, resulting in progressive multisystem neurodegeneration. While the impact of neuroinflammation is an emerging and potentially treatable aspect in neurodegenerative diseases and leukodystrophies, the role of immune cells in SPG11–HSP patients is unknown. Here, we performed a comprehensive immunological characterization of SPG11–HSP, including examination of three human postmortem brain donations, immunophenotyping of patients’ peripheral blood cells and patient-specific induced pluripotent stem cell-derived microglia-like cells (iMGL). We delineate a previously unknown role of innate immunity in SPG11–HSP. Neuropathological analysis of SPG11–HSP patient brain tissue revealed profound microgliosis in areas of neurodegeneration, downregulation of homeostatic microglial markers and cell-intrinsic accumulation of lipids and lipofuscin in IBA1⁺ cells. In a larger cohort of SPG11–HSP patients, the ratio of peripheral classical and intermediate monocytes was increased, along with increased serum levels of IL-6 that correlated with disease severity. Stimulation of patient-specific iMGLs with IFNγ led to increased phagocytic activity compared to control iMGL as well as increased upregulation and release of proinflammatory cytokines and chemokines, such as CXCL10. On a molecular basis, we identified increased STAT1 phosphorylation as mechanism connecting IFNγ-mediated immune hyperactivation and SPG11 loss of function. STAT1 expression was increased both in human postmortem brain tissue and in an Spg11^–/– mouse model. Application of an STAT1 inhibitor decreased CXCL10 production in SPG11 iMGL and rescued their toxic effect on SPG11 neurons. Our data establish neuroinflammation as a novel disease mechanism in SPG11–HSP patients and constitute the first description of myeloid cell/ microglia activation in human SPG11–HSP. IFNγ/ STAT1-mediated neurotoxic effects of hyperreactive microglia upon SPG11 loss of function indicate that immunomodulation strategies may slow down disease progression.

SPG11功能的双等位基因丧失是导致胼胝体薄的复杂常染色体隐性遗传性痉挛性截瘫（HSP）的最常见原因，导致进行性多系统神经变性。虽然神经炎症的影响是神经退行性疾病和脑白质营养不良中一个新兴的、潜在可治疗的方面，但免疫细胞在 SPG11-HSP 患者中的作用尚不清楚。在这里，我们对 SPG11-HSP 进行了全面的免疫学表征，包括对三个人类死后大脑捐赠的检查、患者外周血细胞和患者特异性诱导多能干细胞衍生的小胶质细胞样细胞 (iMGL) 的免疫表型分析。我们描述了先天免疫在 SPG11-HSP 中先前未知的作用。 SPG11-HSP 患者脑组织的神经病理学分析显示，神经变性区域存在严重的小胶质细胞增生、稳态小胶质细胞标记物的下调以及 IBA1 ⁺细胞中脂质和脂褐素的细胞内在积累。在较大的 SPG11-HSP 患者队列中，外周经典单核细胞和中间单核细胞的比例增加，并且与疾病严重程度相关的血清 IL-6 水平增加。与对照 iMGL 相比，用 IFNγ 刺激患者特异性 iMGL 会导致吞噬细胞活性增加，并增加促炎细胞因子和趋化因子（例如 CXCL10）的上调和释放。在分子基础上，我们发现 STAT1 磷酸化增加是 IFNγ 介导的免疫过度激活与SPG11功能丧失之间的机制。 STAT1 表达在人类死后脑组织和Spg11 ^–/–小鼠模型中均有所增加。 STAT1抑制剂的应用减少了SPG11 iMGL中CXCL10的产生，并挽救了它们对SPG11神经元的毒性作用。我们的数据将神经炎症确立为 SPG11-HSP 患者的一种新疾病机制，并首次描述了人类 SPG11-HSP 中骨髓细胞/小胶质细胞的激活。SPG11功能丧失后，高反应性小胶质细胞的 IFNγ/STAT1 介导的神经毒性作用表明，免疫调节策略可能会减缓疾病进展。