Jiangsu KeyLaboratory of Neurodegeneration, Department of Pharmacology, Nanjing Medical University, 101 Longmian Avenue, Nanjing, Jiangsu 211166, China.
Department of Pharmacology, Nanjing University of Chinese Medicine, 138 Xianlin Avenue, Nanjing, Jiangsu 210023, China.
Brain Behav Immun. 2020 Nov;90:259-271. doi: 10.1016/j.bbi.2020.08.025. Epub 2020 Aug 27.
Activated astrocytes secrete inflammatory cytokines such as interleukin-1β (IL-1β) into the extracellular milieu, damaging surrounding neurons and involving in the pathogenesis of neurodegenerative diseases, such as Parkinson's disease (PD). Dopamine receptor D2 (Drd2) expresses both in neurons and astrocytes, and neuronal Drd2 is a significant target in therapy of PD. Our previous study reveals that astrocytic Drd2 exerts anti-inflammatory effect via non-classical β-arrestin2 signaling in PD model. Therefore, seeking new biased ligands of Drd2 with better efficacy and fewer side effects to treat PD is desirable and meaningful. In the present study, we evaluated the effects of UNC9995, a novel biased Drd2 agonist on astrocyte-derived neuroinflammation and dopaminergic (DA) neuron degenerationin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD. We showed that UNC9995 rescued the TH neurons loss and inhibited glial cells activation in mouse substantia nigra in a Drd2 dependent manner. Focusing on astrocytes, we found UNC9995 shows a relatively safe concentration range and significantly suppresses astrocytic NLRP3 inflammasome activation induced by lipopolysaccharide plus ATP. Further study revealed that the anti-inflammatory effect of UNC9995 is independent of Drd2 / Gα protein pathway. It activates β-arrestin2 by recruiting it to cell membrane. Critically, UNC9995 enhances β-arrestin2 interacting with NLRP3 to interfere inflammasome assembly, which consequently reduces IL-1β production. On the other hand, UNC9995 inhibits IL-1β-induced inflammatory pathway activation in DA neurons and rescues subsequent apoptosis via β-arrestin2 interacting with protein kinases, such as JNK and suppressing their phosphorylation. Furthermore, β-arrestin2 knockout abolishes the anti-inflammatory and neuroprotective effects of UNC9995 in PD mouse model, supporting that UNC9995 is a β-arrestin2-biased Drd2 agonist and revealing its novel function in PD treatment. Collectively, this work illustrates that Drd2 agonist UNC9995 prevents DA neuron degeneration in PD and provides a new strategy for developing the β-arrestin2-biased ligands in the therapy of NDDs.
活化的星形胶质细胞将炎症细胞因子如白细胞介素-1β（IL-1β）分泌到细胞外环境中，损害周围的神经元，并参与神经退行性疾病（如帕金森病）的发病机制。多巴胺受体 D2（Drd2）在神经元和星形胶质细胞中均有表达，神经元中的 Drd2 是治疗帕金森病的重要靶点。我们之前的研究表明，星形胶质细胞中的 Drd2 通过非经典的β-arrestin2 信号通路在帕金森病模型中发挥抗炎作用。因此，寻找新的具有更好疗效和更少副作用的 Drd2 偏倚配体来治疗帕金森病是可取的，也是有意义的。在本研究中，我们评估了 UNC9995 对 1-甲基-4-苯基-1,2,3,6-四氢吡啶（MPTP）诱导的帕金森病小鼠模型中星形胶质细胞源性神经炎症和多巴胺能（DA）神经元变性的影响。我们发现 UNC9995 以 Drd2 依赖的方式挽救了 TH 神经元的丢失，并抑制了小鼠黑质中的神经胶质细胞激活。我们专注于星形胶质细胞，发现 UNC9995 显示出相对安全的浓度范围，并显著抑制脂多糖加 ATP 诱导的星形胶质细胞 NLRP3 炎性小体激活。进一步的研究表明，UNC9995 的抗炎作用独立于 Drd2 / Gα 蛋白通路。它通过将其募集到细胞膜上来激活β-arrestin2。至关重要的是，UNC9995 增强了β-arrestin2 与 NLRP3 的相互作用，干扰炎性小体的组装，从而减少 IL-1β 的产生。另一方面，UNC9995 通过与蛋白激酶（如 JNK）相互作用抑制其磷酸化，抑制 IL-1β 诱导的 DA 神经元炎症通路激活，并挽救随后的细胞凋亡。此外，β-arrestin2 敲除消除了 UNC9995 在帕金森病小鼠模型中的抗炎和神经保护作用，支持 UNC9995 是一种β-arrestin2 偏向性 Drd2 激动剂，并揭示了其在帕金森病治疗中的新功能。总的来说，这项工作表明，Drd2 激动剂 UNC9995 可防止帕金森病中 DA 神经元变性，并为开发 NDD 治疗中的β-arrestin2 偏向性配体提供了新策略。
