Parkinson’s disease (PD) is a neurodegenerative disease characterized by intraneuronal Lewy Body (LB) aggregates composed of misfolded alpha-synuclein (α-syn). The spread of misfolded α-syn follows a typical pattern: starting in the olfactory bulb (OB) and the gut, this pathology is followed by the progressive invasion of misfolded α-syn to the posterior part of the brain. It is unknown whether the administration of human mutant alpha-synuclein (hm-α-syn, a human mutation which occurs in familial PD) into the OB of rats would trigger similar α-syn propagation and subsequently cause pathological changes in broader brain fields associated to PD and establish an animal model of prodromal PD. hm-α-syn was overexpressed in the OB of rats with an AAV injection. Then motor and non-motor symptoms of the SD rats were tested in different behavioral tasks following the AAV injection. In follow-up studies, pathological mechanisms of α-syn spread were explored at the histological, biochemical and micro-structure levels. The experimental results indicated that hm-α-syn was overexpressed in the OB 3 weeks after the AAV injection. 1) overexpression of the Hm-α-syn in the OB by the AAV injection could transfer to wider adjacent fields beyond the monosynaptic scope. 2) The number of tyrosine hydroxylase positive cells body and fibers was decreased in the substantia nigra (SN) 12 weeks after AAV injection. This was consistent with decreased levels of the DA neurotransmitter. Importantly, behavioral dysfunctions were found that included olfactory impairment after 3 weeks, motor ability impairment and decreased muscular coordination on a rotarod 6 weeks after the AAV injection.3) The morphological level studies found that the Golgi staining revealed the number of neuronal branches and synapses in the OB, prefrontal cortex (PFC), hippocampus (Hip) and striatum caudate putamen (CPU) were decreased. 4) phosphorylated α-syn, at Ser-129 (pSer129), was found to be increased in hm-α-syn injected animals in comparison to controls that overexpressed GFP alone, which was also found in the most of LB stained by the thioflavine S (ThS) in the SN field. 5) A marker of autophagy (LC3B) was increased in serval fields, which was colacolizated with a marker of apoptosis in the SN field. These results demonstrate that expression of exogenous mutant α-syn in the OB induces pathological changes in the sensitive brain fields by transferring pathogenic α-syn to adjacent fields. This method may be useful for establishing an animal model of prodromal PD.

中文翻译：

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嗅球中α-突触核蛋白过度表达引发帕金森病的前驱症状和病理学

帕金森病 (PD) 是一种神经退行性疾病，其特征是神经元内路易体 (LB) 聚集体由错误折叠的 α-突触核蛋白 (α-syn) 组成。错误折叠的 α-syn 的传播遵循典型的模式：从嗅球 (OB) 和肠道开始，这种病理学随后是错误折叠的 α-syn 逐渐侵入大脑后部。目前尚不清楚将人类突变体 α-突触核蛋白（hm-α-syn，一种发生在家族性 PD 中的人类突变）注射到大鼠的 OB 中是否会引发类似的 α-syn 传播，并随后导致更广泛的脑区发生病理变化。建立PD前驱期动物模型。hm-α-syn 在注射 AAV 的大鼠 OB 中过度表达。然后在注射 AAV 后在不同的行为任务中测试 SD 大鼠的运动和非运动症状。后续研究从组织学、生化和微观结构水平探讨了α-syn扩散的病理机制。实验结果表明，注射AAV后3周，hm-α-syn在OB中过度表达。1）通过AAV注射在OB中过度表达Hm-α-syn可以转移到单突触范围之外更广泛的邻近区域。2)注射AAV后12周，黑质(SN)中酪氨酸羟化酶阳性细胞体和纤维的数量减少。这与 DA 神经递质水平下降一致。重要的是，三周后发现了行为功能障碍，包括嗅觉障碍，AAV 注射后 6 周，运动能力受损，旋转棒上的肌肉协调性下降。3) 形态学水平研究发现，高尔基染色显示 OB、前额皮质 (PFC)、海马 (Hip) 中神经元分支和突触的数量和纹状体尾状壳核（CPU）减少。4) 与单独过表达 GFP 的对照相比，在注射 hm-α-syn 的动物中发现 Ser-129 (pSer129) 磷酸化 α-syn 增加，这在大多数硫黄素染色的 LB 中也发现SN 字段中的 S (ThS)。5)自噬标记物(LC3B)在多个区域中增加，其与SN区域中的凋亡标记物共生。这些结果表明，OB 中外源突变体 α-syn 的表达通过将致病性 α-syn 转移到邻近区域，诱导敏感脑区发生病理变化。该方法可能有助于建立前驱 PD 动物模型。