Neuroscience and Mental Health Research Institute, Cardiff University, Cardiff, Wales, UK.
Institute of Pharmacology and Toxicology, University of Zurich-Vetsuisse, Zurich, Switzerland.
Mol Psychiatry. 2021 Jun;26(6):2025-2037. doi: 10.1038/s41380-020-0745-1. Epub 2020 May 12.
The mitochondrial protein, translocator protein (TSPO), is a widely used biomarker of neuroinflammation, but its non-selective cellular expression pattern implies roles beyond inflammatory processes. In the present study, we investigated whether neuronal activity modifies TSPO levels in the adult central nervous system. First, we used single-cell RNA sequencing to generate a cellular landscape of basal TSPO gene expression in the hippocampus of adult (12 weeks old) C57BL6/N mice, followed by confocal laser scanning microscopy to verify TSPO protein in neuronal and non-neuronal cell populations. We then quantified TSPO mRNA and protein levels after stimulating neuronal activity with distinct stimuli, including designer receptors exclusively activated by designer drugs (DREADDs), exposure to a novel environment and acute treatment with the psychostimulant drug, amphetamine. Single-cell RNA sequencing demonstrated a non-selective and multi-cellular gene expression pattern of TSPO at basal conditions in the adult mouse hippocampus. Confocal laser scanning microscopy confirmed that TSPO protein is present in neuronal and non-neuronal (astrocytes, microglia, vascular endothelial cells) cells of cortical (medial prefrontal cortex) and subcortical (hippocampus) brain regions. Stimulating neuronal activity through chemogenetic (DREADDs), physiological (novel environment exposure) or psychopharmacological (amphetamine treatment) approaches led to consistent increases in TSPO gene and protein levels in neurons, but not in microglia or astrocytes. Taken together, our findings show that neuronal activity has the potential to modify TSPO levels in the adult central nervous system. These findings challenge the general assumption that altered TSPO expression or binding unequivocally mirrors ongoing neuroinflammation and emphasize the need to consider non-inflammatory interpretations in some physiological or pathological contexts.
线粒体蛋白，转位蛋白（TSPO），是一种广泛用于神经炎症的生物标志物，但它的非选择性细胞表达模式暗示了其在炎症过程之外的作用。在本研究中，我们研究了神经元活动是否会改变成年中枢神经系统中 TSPO 的水平。首先，我们使用单细胞 RNA 测序生成了成年（12 周龄）C57BL6/N 小鼠海马体中 TSPO 基因基础表达的细胞图谱，然后使用共聚焦激光扫描显微镜验证了神经元和非神经元细胞群中的 TSPO 蛋白。接着，我们用不同的刺激物刺激神经元活动，包括设计受体专门激活药物（DREADD）、暴露于新环境和急性治疗精神兴奋剂安非他命，来量化 TSPO mRNA 和蛋白水平。单细胞 RNA 测序表明，在成年小鼠海马体中，TSPO 在基础条件下表现出非选择性和多细胞的基因表达模式。共聚焦激光扫描显微镜证实 TSPO 蛋白存在于皮质（前额叶皮质内侧）和皮质下（海马体）脑区的神经元和非神经元（星形胶质细胞、小胶质细胞、血管内皮细胞）细胞中。通过化学遗传（DREADD）、生理（新环境暴露）或精神药理学（安非他命治疗）方法刺激神经元活动，导致神经元中 TSPO 基因和蛋白水平持续增加，但小胶质细胞或星形胶质细胞中没有增加。总之，我们的发现表明，神经元活动有可能改变成年中枢神经系统中的 TSPO 水平。这些发现挑战了改变的 TSPO 表达或结合明确反映持续神经炎症的一般假设，并强调在某些生理或病理情况下需要考虑非炎症性解释。
