Smad3 signaling is indicated to regulate microglia activity. Parkinson’s disease (PD) neurodegeneration is shown to be associated with aging and neuroinflammation. However, it remains unclear about the relationship among Smad3 signaling, aging, neuroinflammation, and PD. Rats were treated with SIS3 (a specific inhibitor of Smad3, intranigal injection) and/or lipopolysaccharide (intraperitoneal injection). We investigated the effect of SIS3 and lipopolysaccharide and their mechanism of action on motor behavior and nigrostriatal dopaminergic system in the rats. Furthermore, we explored the effect of SIS3 and LPS and their potential signaling mechanism of action on inflammatory response by using primary microglial cultures. Finally, we investigated the relationship among aging, Smad3 signaling, and neuroinflammation using animals of different ages. Both SIS3 and lipopolysaccharide induced significant behavior deficits and nigrostriatal dopaminergic neurodegeneration in the rats compared with the vehicle-treated (control) rats. Significantly increased behavior deficits and nigrostriatal dopaminergic neurodegeneration were observed in the rats co-treated with SIS3 and lipopolysaccharide compared with the rats treated with vehicle, SIS3, or lipopolysaccharide. Furthermore, both SIS3 and lipopolysaccharide induced significant microglia activation and proinflammatory factor (IL-1β, IL-6, iNOS, and ROS) level increase in the SN of rats compared with the control rats. Significantly enhanced microglial inflammatory response was observed in the rats co-treated with SIS3 and lipopolysaccharide compared with the other three groups. For our in vitro study, both SIS3 and lipopolysaccharide induced significant proinflammatory factor level increase in primary microglia cultures compared with the control cultures. Significantly increased inflammatory response was observed in the cultures co-treated with SIS3 and lipopolysaccharide compared with the other three groups. MAPK (ERK/p38) contributed to microglial inflammatory response induced by co-treatment with SIS3 and lipopolysaccharide. Interestingly, there was decrease in Smad3 and pSmad3 expression (protein) and enhancement of neuroinflammation in the mouse SN with aging. Proinflammatory factor levels were significantly inversely correlated with Smad3 and pSmad3 expression. Our study strongly indicates the involvement of SN Smad3 signaling deficiency in aging and PD neurodegeneration and provides a novel molecular mechanism underlying the participation of aging in PD and helps to elucidate the mechanisms for the combined effect of multiple factors in PD.

中文翻译：

---

黑质 Smad3 信号缺陷：与衰老和帕金森病的相关性以及小胶质细胞、促炎因子和 MAPK 的作用

Smad3 信号转导用于调节小胶质细胞活性。帕金森病 (PD) 神经变性被证明与衰老和神经炎症有关。然而，Smad3 信号传导、衰老、神经炎症和 PD 之间的关系仍不清楚。大鼠用SIS3（Smad3的特异性抑制剂，黑腹注射）和/或脂多糖（腹腔注射）治疗。我们研究了 SIS3 和脂多糖的作用及其对大鼠运动行为和黑质纹状体多巴胺能系统的作用机制。此外，我们通过使用原代小胶质细胞培养物探索了 SIS3 和 LPS 的影响及其对炎症反应的潜在信号传导机制。最后，我们使用不同年龄的动物研究了衰老、Smad3 信号传导和神经炎症之间的关系。与载体处理的（对照）大鼠相比，SIS3 和脂多糖均在大鼠中诱导了显着的行为缺陷和黑质纹状体多巴胺能神经变性。与用载体、SIS3 或脂多糖治疗的大鼠相比，在用 SIS3 和脂多糖共同治疗的大鼠中观察到显着增加的行为缺陷和黑质纹状体多巴胺能神经变性。此外，与对照大鼠相比，SIS3 和脂多糖均诱导大鼠 SN 中显着的小胶质细胞活化和促炎因子（IL-1β、IL-6、iNOS 和 ROS）水平增加。与其他三组相比，在 SIS3 和脂多糖共同治疗的大鼠中观察到显着增强的小胶质细胞炎症反应。对于我们的体外研究，与对照培养物相比，SIS3 和脂多糖均诱导原代小胶质细胞培养物中促炎因子水平显着增加。与其他三组相比，在用 SIS3 和脂多糖共同处理的培养物中观察到显着增加的炎症反应。MAPK (ERK/p38) 有助于由 SIS3 和脂多糖共同处理诱导的小胶质细胞炎症反应。有趣的是，随着衰老，小鼠 SN 中 Smad3 和 pSmad3 的表达（蛋白质）降低，神经炎症增强。促炎因子水平与 Smad3 和 pSmad3 表达显着负相关。