BACKGROUND Metabolic dysfunction and neuroinflammation are increasingly implicated in Parkinson's disease (PD). The pentose phosphate pathway (PPP, a metabolic pathway parallel to glycolysis) converts glucose-6-phosphate into pentoses and generates ribose-5-phosphate and NADPH thereby governing anabolic biosynthesis and redox homeostasis. Brains and immune cells display high activity of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the PPP. A postmortem study reveals dysregulation of G6PD enzyme in brains of PD patients. However, spatial and temporal changes in activity/expression of G6PD in PD remain undetermined. More importantly, it is unclear how dysfunction of G6PD and the PPP affects neuroinflammation and neurodegeneration in PD. METHODS We examined expression/activity of G6PD and its association with microglial activation and dopaminergic neurodegeneration in multiple chronic PD models generated by an intranigral/intraperitoneal injection of LPS, daily subcutaneous injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) for 6 days, or transgenic expression of A53T α-synuclein. Primary microglia were transfected with G6PD siRNAs and treated with lipopolysaccharide (LPS) to examine effects of G6PD knockdown on microglial activation and death of co-cultured neurons. LPS alone or with G6PD inhibitor(s) was administrated to mouse substantia nigra or midbrain neuron-glia cultures. While histological and biochemical analyses were conducted to examine microglial activation and dopaminergic neurodegeneration in vitro and in vivo, rotarod behavior test was performed to evaluate locomotor impairment in mice. RESULTS Expression and activity of G6PD were elevated in LPS-treated midbrain neuron-glia cultures (an in vitro PD model) and the substantia nigra of four in vivo PD models. Such elevation was positively associated with microglial activation and dopaminergic neurodegeneration. Furthermore, inhibition of G6PD by 6-aminonicotinamide and dehydroepiandrosterone and knockdown of microglial G6PD attenuated LPS-elicited chronic dopaminergic neurodegeneration. Mechanistically, microglia with elevated G6PD activity/expression produced excessive NADPH and provided abundant substrate to over-activated NADPH oxidase (NOX2) leading to production of excessive reactive oxygen species (ROS). Knockdown and inhibition of G6PD ameliorated LPS-triggered production of ROS and activation of NF-кB thereby dampening microglial activation. CONCLUSIONS Our findings indicated that G6PD-mediated PPP dysfunction and neuroinflammation exacerbated each other mediating chronic dopaminergic neurodegeneration and locomotor impairment. Insight into metabolic-inflammatory interface suggests that G6PD and NOX2 are potential therapeutic targets for PD.

中文翻译：

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磷酸戊糖途径调节慢性神经炎症和多巴胺能神经变性。

背景技术代谢功能障碍和神经炎症越来越多地涉及帕金森氏病（PD）。磷酸戊糖途径（PPP，与糖酵解平行的代谢途径）可将6-磷酸葡萄糖转化为戊糖，并产生5-磷酸核糖和NADPH，从而控制合成代谢的生物合成和氧化还原稳态。脑和免疫细胞显示高活性的6-葡萄糖葡萄糖脱氢酶（G6PD），这是PPP的限速酶。一项验尸研究显示，PD患者大脑中的G6PD酶失调。然而，PD中G6PD的活动/表达的时空变化仍未确定。更重要的是，尚不清楚G6PD和PPP的功能障碍如何影响PD的神经炎症和神经变性。方法我们研究了腹膜内/腹膜内注射LPS，每天皮下注射1-甲基-4-苯基-1,2,3， 6天-四氢吡啶（MPTP）持续6天，或转基因表达A53Tα-突触核蛋白。用G6PD siRNA转染原发性小胶质细胞，并用脂多糖（LPS）处理，以检查G6PD敲低对共培养神经元小胶质细胞活化和死亡的影响。将LPS单独或与G6PD抑制剂一起施用给小鼠黑质或中脑神经胶质细胞培养物。虽然进行了组织学和生化分析以在体外和体内检查小胶质细胞的活化和多巴胺能神经退行性变，进行了轮转行为测试以评估小鼠的运动损伤。结果在经LPS处理的中脑神经元神经胶质细胞培养物（体外PD模型）和四种体内PD模型的黑质中，G6PD的表达和活性均升高。这种升高与小胶质细胞激活和多巴胺能神经退变正相关。此外，6-氨基烟酰胺和脱氢表雄酮对G6PD的抑制作用以及对小胶质细胞G6PD的抑制作用减弱了LPS引起的慢性多巴胺能神经变性。从机制上讲，具有提高的G6PD活性/表达的小胶质细胞产生过量的NADPH，并为过度活化的NADPH氧化酶（NOX2）提供了丰富的底物，从而导致产生过量的活性氧（ROS）。击倒和抑制G6PD改善了LPS触发的ROS产生和NF-кB的激活，从而抑制了小胶质细胞的激活。结论我们的研究结果表明，G6PD介导的PPP功能障碍和神经炎症相互加剧，介导了慢性多巴胺能神经退行性病变和运动功能障碍。对代谢-炎症界面的了解表明，G6PD和NOX2是PD的潜在治疗靶标。