Id (inhibitors of DNA binding)屬於HLH(helix-loop-helix---胺基酸的二級結構)轉錄因子家族中的一員，是細胞分化的負調節者。近來研究報告指出Id不僅能調控細胞分化，也參與細胞增生的調控機制。當中樞神經系統受傷時小膠質細胞會被活化：遷移至受傷處進行細胞複製，並釋放前發炎因子。因此本實驗想探討Id1、Id2與Id3與小膠質細胞活化機制間的關係。
　　利用老鼠初級小膠質細胞與小鼠的細胞株-BV2，以LPS及FBS處理檢測Id的表現。結果發現FBS可誘導BV2細胞增生，並在轉錄層級調控Id的表現：Id mRNA及蛋白質的表現同時被FBS誘導而增加。另一方面，LPS處理也具有誘導初級小膠質細胞生長的能力，並伴隨此Id蛋白質表現量的上升。配合Id antisense轉殖抑制了Id蛋白質表現與小膠質細胞生長的結果，證明Id具有促進小膠質細胞增生的能力。
　　此外，LPS處理老鼠初級小膠質細胞與BV2細胞，皆可促進其TNF-α的分泌。此時Id在BV2細胞中表現降低，卻在初級小膠質細胞中上升。Id antisense轉殖可抑制BV2細胞TNF-α的分泌，但對初級小膠質細胞TNF-α的分泌並無明顯的影響。由此結果推測：Id與TNF-α的分泌並無直接關聯，但可透過調控細胞生長而影響。最後實驗也發現FBS與LPS可調控Id蛋白質在BV2細胞與初級小膠質細胞內的分佈，使其進入細胞核。總括來說，本實驗證實Id可受FBS及LPS誘導上升，進入細胞核並促進小膠質細胞的增生。

　　The central nerve system (CNS) injury leads to a complex response including neural cell death, astroglial/microglial activation, axonal degeneration, and demyelination. Microglia stay at the resting stage in normal CNS, and are activated in response to proinflammatory cytokines produced after CNS injury. The molecular mechanism responsible for microglial activation after CNS injury is still unclear. Inhibitors of DNA binding(Id), Id1-Id4 members, have been well known to act as positive regulators for cell proliferation. Previous studies have shown that Id1 and Id3 gene transcripts was upregulated in primary rat microglia treated with TNF-α. In the present study, we used BV2 cells, a mouse microglial cell line, and rat primary microglia to examine the expression of Id1-Id3 proteins. We found that Id1-Id3 transcripts and proteins were highly increased by serum in BV2 cells that were initially starved in serum-free medium for 48 h. The levels of Id1-Id3 transcripts and proteins were increased in a dose-dependent manner. Antisense transfection of Id2 and Id3 but not Id1 inhibited the poliferation of BV2 cells. Interestingly, Id1-3 were downregulated in BV2 cells treated with lipoposaccharide(LPS), which induces BV2 activation, but not their proliferation.
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