巴金森氏症是由於中腦黑質區多巴胺神經元的退化，使動作功能逐漸喪失的神經退化性疾病，其致病機制到目前還不清楚。多巴胺神經元對微小膠細胞的活化具高敏感性，也就是小膠細胞活化後所釋放的發炎相關物質，對多巴胺神經元具有很高的毒性。因此中腦黑質區小膠細胞的活化，被認為是導致該區多巴胺神經元退化的原因之一。根據流行病學的統計，男性患有巴金森氏症的比例約是女性的兩倍。所以我們假設性別會影響老化或是發炎因子所引起的小膠細胞活化程度，進而導致不同程度的多巴胺神經死亡。為了驗證這個假設，我們以三、六、九、十二個月大的公鼠與母鼠為研究模式，以免疫組織化學染色法觀察黑質區中小膠細胞活化程度，和多巴胺神經元的數目。結果顯示，公鼠與母鼠的小膠細胞活化，和多巴胺神經元的數目，皆會受到老化的影響；但是對公鼠的影響明顯大於母鼠。以LPS誘發之小膠細胞活化與多巴胺神經元死亡之程度，也是公鼠比母鼠嚴重。我們接著假設此差異可能是因為卵巢分泌了一些因子，可以抗發炎和保護神經。因此，我們在母鼠兩個月大時進行卵巢切除，並在一個月後接受腹腔注射LPS。結果顯示，卵巢切除後的母鼠，小膠細胞活化與多巴胺神經元死亡之程度，明顯大於未切除卵巢之母鼠。我們進一步假設此保護是源自於卵巢所分泌的雌激素。因此，我們在中年母鼠卵巢切除後三個月內，給予為期一個月或三個月的雌激素補充。結果發現，雌激素會降低卵巢切除後，老化所導致之小膠細胞活化和多巴胺神經元死亡；而三個月的補充效果優於一個月。在細胞培養的實驗中，我們發現雌激素前處理30分鐘後，可以透過抑制Toll-like receptor 4 及其訊息傳遞路徑，有效抑制LPS所誘發之小膠細胞活化。總結本研究我們發現，雖然無論是公鼠或母鼠，老化皆會導致小膠細胞活化和多巴胺神經元數目下降，但是這個現象在母鼠比公鼠和緩。此性別差異與母鼠卵巢所分泌的雌激素抑制小膠細胞的活化有關。雌激素或可被用來延緩巴金森氏症的發生與病情之惡化。

Parkinson’s disease (PD) is a progressive neurodegenerative disease characterized by the loss of dopaminergic (DA) neurons in the substantia nigra (SN). The mechanisms responsible for the loss of DA neurons in PD are poorly understood. Because DA neurons are highly susceptible to microglial activation and pro-inflammatory cytotoxic factors, it has been suggested that microglia activation predisposes DA neuron degeneration. Epidemiological studies reveal that both incidence and prevalence of PD are 1.5–2 times higher in men than in women. Thus, we hypothesize that different sex has differential effects on aging and inflammation-induced microglia activation, which then cause different levels of DA neuron death. To test this hypothesis, brains of male and female mice at the ages of 3-, 6-, 9- and 12-month-old were harvested to investigate DA neuron loss and microglia activation in the SN. Our data showed that although the degrees of microglia activation and DA neuron loss in the SN were increased with age in both genders, these phenomena were more pronounced in the male mice. Furthermore, the degrees of microglia activation and DA neuron loss in the SN induced by peripheral LPS injection were more severe in the young male mice than that of young female mice. We then hypothesize that ovarian hormones are capable of affecting the activation of microglia and survival of DA neurons. To examine this hypothesis, female mice were subjected to bilateral ovariectomy (OVX) at two months of age followed by a LPS injection one month later. OVX eliminated the female-associated protection against LPS-induced microglia activation and DA neuron loss. Given mice that received OVX at 6-month-old with 17-β estradiol (E2) for 3 months (from 6 to 9 months of age) or 1 month (from 8 to 9 months of age), the microglia activation and DA neuron loss were partially inhibited with stronger effects evident in the 3 month supplement group. Furthermore, 30 min pre-exposure of BV2 cells, a macrophage/microglia cell line, with E2 effectively inhibited the LPS-induced microglia activation via the Toll-like receptor 4 signaling pathways. In conclusion, although DA neuron loss and microglia activation in the SN are evident in both male and female C57BL/6 mice during aging, these changes are less dramatic in the female mice. The E2-induced inhibition of microglia activation may partially explain this gender differences. E2 supplement may be used to delay the onset or slow down the development of PD.

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