脂多醣為格蘭氏陰性菌（gram-negative bacteria）外層細胞壁上的一種內毒素（endotoxin），其會引起中樞神經系統發炎。脂多醣能活化中樞神經系統中的微神經膠細胞（microglia）使其釋放出促發炎或抗發炎物質，例如：細胞激素、化學激活激素、前列腺素等發炎相關物質，這些由細胞釋放的物質大部份為蛋白質，並且可能會進入腦脊髓液中。之前有文獻報導過，某些腦脊髓液中的蛋白質被認為來自於大腦並且由中樞神經系統之細胞所釋放出。因此鑑定腦脊髓液之蛋白質體對於瞭解中樞神經系統的狀況具有參考價值。本研究的目的為，藉由腦室注射脂多醣的方式引發老鼠中樞神經系統發炎，配合利用液相層析串聯式質譜儀分析中樞神經系統發炎之老鼠其腦脊髓液蛋白質體的變化。依據免疫組織化學染色的結果，發現施予老鼠脂多醣後第五天最能代表中樞神經系統發炎情況，並且以此時間點為抽取老鼠腦脊髓液之取樣時間點。在液相層析串聯式質譜儀中，有237段胜肽片段（186個蛋白質）被鑑定到。在186個蛋白質中，根據Swiss-Prot網站資料庫搜尋，有37個蛋白質為存在於中樞神經系統組織（包含：腦、腦下垂體及腦脊髓液）中。本研究以液相層析四極棒飛行時間質譜儀（LC-Q-TOF-MS）來測量上述這186個蛋白質對於處理脂多醣後所產生的表現量差異分析。實驗結果發現18個蛋白質其表現量在實驗組與對照組間具有統計上明顯差異（p-value<0.05，以Wilcoxon rank-sum test進行統計, N = 6）；其中，有16個蛋白質在實驗組中表現量增加，另外兩個蛋白質則是表現量降低。在這18個蛋白質中，有9個蛋白質，Shen-dan、PRP18 pre-mRNA processing factor 18 homolog、L-fucose kinase short variant、calcium activated chloride channel、complement C3、CYP2J9（cytochrome P450, family 2, subfamily J, polypeptide 9）、platelet-activating factor acetylhydrolase（PAF-AHs）、phosphatidylinositol-4-phosphate 5-kinase（type II, beta）、serine/threonine-protein kinase MARK2，為Swiss-Prot網站資料庫搜尋或先前有文獻報導存在於中樞神經系統中。已知complement C3會參與中樞神經系統發炎過程；之前有學者將脂多醣注射於老鼠體內發現PAF-Ahs在一些器官（如：肝臟、脾臟及肺臟）中表現量增加。MARK2為一種serine/threonine-protein kinase，它能磷酸化蛋白質tau；tau為一種神經的微細小管聯繫性蛋白質(neuronal microtubule-associated protein)，在阿茲海默症(Alzheimer's disease)中可以觀察到異常之磷酸化tau及其聚集的情形。本研究在腦脊髓液中發現到有差異的蛋白質可能參與脂多醣引發中樞神經系統發炎。

Lipopolysaccharide (LPS) is a constituent on the outer membrane of gram-negative bacteria and induces the inflammation in the central nervous system (CNS). LPS is known to activate microglia to release pro- or anti-inflammatory cytokines, chemokines, prostaglandins, and nitric oxide. Most of these inflammatory molecules are proteins which may enter into the cerebrospinal fluid (CSF). It has been reported that certain CSF proteins are brain-derived and released by some of the CNS cells (e.g., astrocytes and neurons). Characterization of CSF proteome has the potential merit for understanding of certain biological events in the CNS. The objective of this study was to investigate the changes of rat CSF proteome in response to LPS-induced CNS inflammation using intracerebroventricular LPS administration and liquid chromatography tandem mass spectrometry (LC-MS/MS) proteomics analysis. CSF samples were obtained 5 days after administration when CNS inflammation was confirmed by immunohistochemistry (IHC). LC-MS/MS analysis identified 237 unique peptides, corresponding to 186 proteins. According to annotations in the Swiss-Prot database, 37 proteins, among 186 proteins identified, are known to be found in CNS tissues, including brain, pituitary gland, and CSF. Differential analysis was performed using liquid chromatography quadrupole-time-of-flight mass spectrometry (LC-Q-TOF-MS) to measure the relative changes of these 186 proteins in response to LPS treatment. It was found that the levels of 16 proteins increased with LPS-induced inflammation, while only 2 proteins decreased (p-value < 0.05, Wilcoxon rank-sum test, N = 6). Among them, Shen-dan, PRP18 pre-mRNA processing factor 18 homolog, L-fucose kinase short variant, calcium activated chloride channel, complement C3, CYP2J9 (cytochrome P450, family 2, subfamily J, polypeptide 9), platelet-activating factor acetylhydrolase (PAF-Ahs), phosphatidylinositol-4-phosphate 5-kinase (type II, beta) and serine/threonine-protein kinase MARK2, were known to present in the CNS according to annotations in the Swiss-Prot database and limited literature search. Complement C3 is known to involve with the CNS inflammatory processes. Platelet-activating factor acetylhydrolase (PAF-Ahs) has been reported to increase in organs, such as liver, spleen, and lung, after systemic injection of LPS to rat. Microtubule affinity regulating kinase 2 (MARK2) is a serine/threonine-protein kinase and has the ability to phosphorylate tau protein, a neuronal microtubule-associated protein. The abnormal phosphorylation and aggregation of tau are hallmarks of Alzheimer’s disease. The differential proteomics profiling of CSF has revealed several proteins that are potentially involved with LPS-induced CNS inflammation.

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