OASI Institute for Research and Care on Mental Retardation and Brain Aging, Neuropharmacology Section; Via Conte Ruggero 73, 94018 Troina (EN), Italy.
Mol Neurodegener. 2011 Jul 13;6:49. doi: 10.1186/1750-1326-6-49.
Dopamine-synthesizing (dopaminergic, DA) neurons in the ventral midbrain (VM) constitute a pivotal neuronal population controlling motor behaviors, cognitive and affective brain functions, which generation critically relies on the activation of Wingless-type MMTV integration site (Wnt)/β-catenin pathway in their progenitors. In Parkinson's disease, DA cell bodies within the substantia nigra pars compacta (SNpc) progressively degenerate, with causes and mechanisms poorly understood. Emerging evidence suggests that Wnt signaling via Frizzled (Fzd) receptors may play a role in different degenerative states, but little is known about Wnt signaling in the adult midbrain. Using in vitro and in vivo model systems of DA degeneration, along with functional studies in both intact and SN lesioned mice, we herein highlight an intrinsic Wnt1/Fzd-1/β-catenin tone critically contributing to the survival and protection of adult midbrain DA neurons.
In vitro experiments identifie Fzd-1 receptor expression at a mRNA and protein levels in dopamine transporter (DAT) expressing neurons, and demonstrate the ability of exogenous Wnt1 to exert robust neuroprotective effects against Caspase-3 activation, the loss of tyrosine hydroxylase-positive (TH+) neurons and [3H] dopamine uptake induced by different DA-specific insults, including serum and growth factor deprivation, 6-hydroxydopamine and MPTP/MPP+. Co-culture of DA neurons with midbrain astrocytes phenocopies Wnt1 neuroprotective effects, whereas RNA interference-mediated knockdown of Wnt1 in midbrain astrocytes markedly reduces astrocyte-induced TH+ neuroprotection. Likewise, silencing β-catenin mRNA or knocking down Fzd-1 receptor expression in mesencephalic neurons counteract astrocyte-induced TH+ neuroprotection. In vivo experiments document Fzd-1 co-localization with TH+ neurons within the intact SNpc and blockade of Fzd/β-catenin signaling by unilateral infusion of a Fzd/β-catenin antagonist within the SN induces reactive astrocytosis and acutely inhibits TH+ neuron survival in ipsilateral SNpc, an effect efficiently prevented by pharmacological activation of β-catenin signaling within the SNpc.
These results defining a novel Wnt1/Fzd-1/β-catenin astrocyte-DA autoprotective loop provide a new mechanistic inside into the regulation of pro-survival processes, with potentially relevant consequences for drug design or drug action in Parkinson's disease.
腹侧中脑（VM）中的多巴胺合成（多巴胺能，DA）神经元构成了控制运动行为、认知和情感脑功能的关键神经元群体，其产生严重依赖于其祖细胞中 Wingless 型 MMTV 整合位点（Wnt）/β-连环蛋白途径的激活。在帕金森病中，黑质致密部（SNpc）内的 DA 细胞体逐渐退化，但原因和机制尚不清楚。新出现的证据表明，通过 Frizzled（Fzd）受体的 Wnt 信号可能在不同的退行性状态中发挥作用，但关于成年中脑的 Wnt 信号知之甚少。本研究使用 DA 变性的体外和体内模型系统，以及在完整和 SN 损伤的小鼠中进行的功能研究，强调了内在的 Wnt1/Fzd-1/β-连环蛋白信号对成年中脑 DA 神经元的存活和保护具有重要作用。
体外实验鉴定了多巴胺转运蛋白（DAT）表达神经元中 Fzd-1 受体的 mRNA 和蛋白质表达，并证明外源性 Wnt1 能够对抗 Caspase-3 激活、酪氨酸羟化酶阳性（TH+）神经元的丧失和不同 DA 特异性损伤诱导的[3H]多巴胺摄取发挥强大的神经保护作用，包括血清和生长因子剥夺、6-羟多巴胺和 MPTP/MPP+。DA 神经元与中脑星形胶质细胞共培养可模拟 Wnt1 的神经保护作用，而用 RNA 干扰介导的中脑星形胶质细胞中 Wnt1 的敲低显著降低了星形胶质细胞诱导的 TH+神经保护作用。同样，沉默中脑神经元中的β-连环蛋白 mRNA 或敲低 Fzd-1 受体表达可拮抗星形胶质细胞诱导的 TH+神经保护作用。体内实验记录了 Fzd-1 与完整 SNpc 内的 TH+神经元的共定位，并且单侧 SNpc 内 Fzd/β-连环蛋白拮抗剂的阻断通过诱导反应性星形胶质细胞增生并急性抑制同侧 SNpc 内的 TH+神经元存活，这种作用可通过 SNpc 内β-连环蛋白信号的药理学激活有效地预防。
这些定义新的 Wnt1/Fzd-1/β-连环蛋白星形胶质细胞-DA 自保护环的结果为生存过程的调节提供了新的机制，并为帕金森病的药物设计或药物作用提供了潜在的相关影响。
