Data Sheet 1_GABAergic neurons are a key cell type in a Drosophila model of PARK14/PLA2G6-associated neurodegeneration.docx

The causes of sporadic Parkinson’s Disease (PD) are still unclear, despite its prevalence. By contrast, inherited parkinsonian disorders have a clear genetic basis and have been studied intensively in laboratory organisms, including Drosophila melanogaster. Because inherited parkinsonian disorders clinically resemble sporadic PD, it has been suggested that they may share an underlying etiology. Loss of function mutations in the gene PLA2G6 give rise to inherited neurodegenerative diseases including autosomal recessive early onset parkinsonism (PARK14). Using RNAi to deplete the Drosophila PLA2G6 homolog iPLA2-VIA, we asked whether subsets of neurons, identified by their neurotransmitter usage, were more susceptible to loss of this gene. To model movement disorders connected with PLA2G6-associated neurodegeneration, we used the well-established climbing assay. Our results demonstrated that loss of iPLA2-VIA in GABAergic neurons alone strongly affected locomotor ability in aged flies, similar to pan-neuronal knockdown. Depletion of iPLA2-VIA in both dopaminergic and serotonergic neurons weakly affected locomotor ability as well. Depletion in other neuronal subsets did not disrupt locomotion. Furthermore, reintroducing wild-type iPLA2-VIA into only the dopaminergic neurons of fly knockouts improved climbing performance slightly, while reintroduction into GABAergic neurons rescued climbing performance strikingly, as well as lifespan. Although much research on this gene has focused on the dopaminergic neurons, whose degeneration leads to clinical parkinsonism, our results highlight the importance of GABAergic neurons to PLA2G6-associated neurodegeneration. Because sporadic PD is not thought to impact most GABAergic neurons directly, our data support the idea that sporadic PD and PARK14 have distinct etiologies despite overlapping clinical presentations.

尽管散发性帕金森病（sporadic Parkinson’s Disease, PD）患病率较高，但其具体致病原因仍未明确。与之相对，遗传性帕金森综合征具有明确的遗传基础，且已在包括黑腹果蝇（Drosophila melanogaster）在内的模式生物中得到深入研究。由于遗传性帕金森综合征的临床表现与散发性PD高度相似，有假说认为二者可能共享潜在的致病机制。PLA2G6基因的功能丧失突变可引发多种遗传性神经退行性疾病，其中常染色体隐性早发性帕金森综合征（PARK14）便是典型代表。本研究借助RNA干扰（RNA interference, RNAi）技术敲低果蝇体内的PLA2G6同源基因iPLA2-VIA，旨在探究以神经递质类型划分的各类神经元亚群，是否对该基因的缺失更为敏感。为模拟PLA2G6相关神经退行性疾病引发的运动障碍，我们采用了成熟经典的攀爬实验范式。实验结果显示，仅在γ-氨基丁酸能神经元（GABAergic neurons）中敲低iPLA2-VIA，即可显著损伤老龄果蝇的运动能力，其效果与全神经元敲低相当。同时在多巴胺能神经元（dopaminergic neurons）与5-羟色胺能神经元（serotonergic neurons）中敲低iPLA2-VIA，也会对运动能力产生轻度影响；而在其他神经元亚群中进行基因敲低，则不会破坏果蝇的运动功能。进一步的挽救实验表明，仅在多巴胺能神经元中重新表达野生型iPLA2-VIA，仅能轻度改善果蝇敲除模型的攀爬能力；而在γ-氨基丁酸能神经元中恢复该基因的表达，则可显著修复其攀爬能力，并同时延长其寿命。尽管此前针对该基因的研究多聚焦于多巴胺能神经元——其变性可引发临床帕金森综合征——本研究结果凸显了γ-氨基丁酸能神经元在PLA2G6相关神经退行性疾病中的关键作用。由于目前认为散发性PD并不会直接累及多数γ-氨基丁酸能神经元，本研究数据支持“尽管散发性PD与PARK14存在临床表现上的重叠，但二者的致病机制并不相同”这一观点。