Wallings Rebecca L, Gillett Drew A, Staley Hannah A, Mahn Savanna, Mark Julian, Neighbarger Noelle, Kordasiewicz Holly, Hirst Warren D, Tansey Malú Gámez
Department of Neuroscience, Center for Translational Research in Neurodegenerative Disease, College of Medicine, University of Florida, McKnight Brain Institute, Gainesville, FL, 32610, USA.
Current address: Department of Neurology, School of Medicine, Stark Neurosciences Research Institute, Indiana University, Indianapolis, IN, USA.
Mol Neurodegener. 2025 Apr 8;20(1):41. doi: 10.1186/s13024-025-00829-w.
GPNMB has been discussed as a potential therapeutic target in GRN-mediated neurodegeneration, based on the observed reproducible upregulation in FTD-GRN cerebrospinal fluid (CSF) and post-mortem brain. However, the functional impacts of up-regulated GPNMB are currently unknown, and it is currently unclear if targeting GPNMB will be protective or deleterious. Increases in GPNMB seen in FTD-GRN are reproduced in brains of aged Grn-deficient mice. Importantly, although brains of young Grn-deficient mice do not exhibit upregulated Gpnmb expression, peripheral immune cells of these mice exhibit increased Gpnmb expression as young as 5-to-6 months, suggesting the effects of Grn-deficiency in the periphery proceed those in the brain. Grn-deficiency is known to alter peripheral immune cell function, including impaired autophagy and altered cytokine secretion. GPNMB has potential effects on these processes, but has never been studied in peripheral immune cells of patients or preclinical models. Informing the functional significance of GPNMB upregulation in Grn-deficient states in myeloid cells has potential to inform GPNMB as a therapeutic candidate.
The effects of GPNMB knock-down via antisense oligonucleotide (ASO) were assessed in peripheral blood mononuclear cells (PBMCs) from 25 neurologically healthy controls (NHCs) and age- and sex-matched FTD-GRN patients, as well as peritoneal macrophages (pMacs) from progranulin-deficient (Grn -/-) and B6 mice. Lysosomal function, antigen presentation and MHC-II processing and recycling were assessed, as well as cytokine release and transcription.
ASO-mediated knock-down of GPNMB increased lysosomal burden and IL1β cytokine secretion in FTD-GRN carriers and NHCs monocytes. ASO-mediated knock-down of Gpnmb in Grn-deficient macrophages decreased lysosomal pan-cathepsin activity and protein degradation. In addition, ASO-mediated knock-down of Gpnmb increased MHC-II surface expression, which was driven by decreased MHC-II uptake and recycling, in macrophages from Grn-deficient females. Finally, ASO-mediated knock-down of Gpnmb dysregulated IFN -stimulated IL6 cytokine transcription and secretion by mouse macrophages due to the absence of regulatory actions of the Gpnmb extracellular fragment (ECF).
Our data herein reveal that GPNMB has a regulatory effect on multiple immune effector functions, including capping inflammation and immune responses in myeloid cells, potentially via secretion of its ECF. Therefore, in progranulin-deficient states, the marked upregulation in GPNMB transcript and protein may represent a compensatory mechanism to preserve lysosomal function in myeloid cells. These novel findings indicate that targeted depletion of GPNMB in FTD-GRN would not be a rational therapeutic strategy because it is likely to dysregulate important immune cell effector functions mediated by GPNMB. Specifically, our data indicate that therapeutic strategies inhibiting GPNMB levels and/or activity may worsen the effects of GRN deficiency.
基于在额颞叶痴呆-原颗粒蛋白（FTD-GRN）患者的脑脊液（CSF）及尸检大脑中观察到的可重复性上调现象，GPNMB已被视为GRN介导的神经退行性变中的一个潜在治疗靶点。然而，目前尚不清楚上调的GPNMB的功能影响，并且目前也不清楚靶向GPNMB是具有保护作用还是有害作用。FTD-GRN患者中GPNMB的增加在老年Grn基因缺陷小鼠的大脑中也有重现。重要的是，尽管年轻的Grn基因缺陷小鼠大脑中未表现出Gpnmb表达上调，但其外周免疫细胞在5至6个月大时就表现出Gpnmb表达增加，这表明外周Grn基因缺陷的影响先于大脑中的影响。已知Grn基因缺陷会改变外周免疫细胞功能，包括自噬受损和细胞因子分泌改变。GPNMB对这些过程可能有影响，但从未在患者或临床前模型的外周免疫细胞中进行过研究。了解GPNMB在Grn基因缺陷状态下在髓样细胞中的上调的功能意义，有可能为将GPNMB作为治疗候选药物提供依据。
通过反义寡核苷酸（ASO）敲低GPNMB的作用，在25名神经功能正常的对照者（NHC）以及年龄和性别匹配的FTD-GRN患者的外周血单核细胞（PBMC）中进行了评估，同时也在原颗粒蛋白缺陷（Grn -/-）小鼠和B6小鼠的腹腔巨噬细胞（pMac）中进行了评估。评估了溶酶体功能、抗原呈递以及MHC-II的加工和再循环，以及细胞因子释放和转录情况。
ASO介导的GPNMB敲低增加了FTD-GRN携带者和NHC单核细胞中的溶酶体负荷以及IL1β细胞因子分泌。ASO介导的Grn基因缺陷巨噬细胞中Gpnmb的敲低降低了溶酶体组织蛋白酶的总体活性和蛋白质降解。此外，ASO介导的Gpnmb敲低增加了Grn基因缺陷雌性小鼠巨噬细胞中MHC-II的表面表达，这是由MHC-II摄取和再循环减少所驱动的。最后，由于Gpnmb细胞外片段（ECF）缺乏调节作用，ASO介导的Gpnmb敲低使小鼠巨噬细胞中IFN刺激的IL6细胞因子转录和分泌失调。
我们在此的数据表明，GPNMB对多种免疫效应功能具有调节作用，包括可能通过其ECF的分泌来抑制髓样细胞中的炎症和免疫反应。因此，在原颗粒蛋白缺乏状态下，GPNMB转录本和蛋白的显著上调可能代表一种补偿机制，以维持髓样细胞中的溶酶体功能。这些新发现表明，在FTD-GRN中靶向清除GPNMB并非合理的治疗策略，因为这可能会使由GPNMB介导的重要免疫细胞效应功能失调。具体而言，我们的数据表明，抑制GPNMB水平和/或活性的治疗策略可能会使GRN缺乏的影响恶化。
