- 學位論文
分枝桿菌索狀因子類似物TDB對微膠質細胞引起發炎及 極化反應之分子機制探討
Molecular mechanism of mycobacterial cord factor analogue trehalose-6,6’-dibehenate (TDB) on inflammation and M1/M2 polarization in microglia
摘要
Microglia are the resident macrophage of the central nervous system (CNS), have been increasingly recognized as a contributing factor to neuroinflammation and neurodegeneration. Recently, the tuberculosis vaccine bacillus Calmette-Guerin (BCG) has been reported to exert neuroprotective effects against several neurodegenerative disorders. Trehalose-6,6’-dibehenate (TDB) is a synthetic analog of trehalose-6,6’-dimycolate (TDM, also known as the mycobacterial cord factor), and is a new adjuvant currently in phase I clinical trials for tuberculosis subunit vaccine. Both TDM and TDB can activate macrophages and dendritic cells through binding to C-type lectin receptor Mincle; however, its action mechanism in microglia and their relationship with neuroinflammation are still unknown. In this study, we found that TDB inhibited LPS-induced M1 microglial polarization in primary microglia and BV-2 cells. However, TDB itself had no effects on IKK, p38, JNK activity or cytokine expression. In contrast, TDB activated ERK1/2 through PLC-γ1/PKC signaling, and in turn decreased LPS-induced NF-κB nuclear translocation. Furthermore, TDB-induced AMPK activation via PLC-γ1/calcium/CaMKKβ-dependent pathway, and thereby enhanced M2 gene expressions. Moreover, TDB-mediated M2 gene expressions in LPS-stimulated BV-2 cells was prevented by AMPK siRNA, indicating that AMPK activation participates in TDB-mediated M2 polarization of microglia. In addition, TDB induced a metabolic shift in LPS-activated cells towards higher oxygen consumption rate (OCR) and lower extracellular acidification rate (ECAR). On the other hand, this pattern was reversed upon inhibition of AMPK in LPS-stimulated cells, which markedly reduced OCR but increased ECAR. Interestingly, knocking out Mincle did not alter the anti-inflammatory and M2 polarization effects of TDB in microglia. Conditional media from LPS-stimulated microglial cells can induce in vitro neurotoxicity, and this action was attenuated by TDB. Using a mouse neuroinflammation model, we found that TDB suppressed LPS-induced M1 microglial activation and sickness behavior, but promoted M2 microglial polarization in both WT and Mincle-/- mice. Taken together, our results suggest that TDB can act independently of Mincle to inhibit LPS-induced inflammatory response through PLC-γ1/PKC/ERK signaling, and promote M2 microglial polarization and mitochondrial bioenergetics via PLC-γ1/calcium/CaMKKβ/AMPK pathway. Thus, TDB may be a promising therapeutic agent for treating neuroinflammatory diseases.
並列摘要
Microglia are the resident macrophage of the central nervous system (CNS), have been increasingly recognized as a contributing factor to neuroinflammation and neurodegeneration. Recently, the tuberculosis vaccine bacillus Calmette-Guerin (BCG) has been reported to exert neuroprotective effects against several neurodegenerative disorders. Trehalose-6,6’-dibehenate (TDB) is a synthetic analog of trehalose-6,6’-dimycolate (TDM, also known as the mycobacterial cord factor), and is a new adjuvant currently in phase I clinical trials for tuberculosis subunit vaccine. Both TDM and TDB can activate macrophages and dendritic cells through binding to C-type lectin receptor Mincle; however, its action mechanism in microglia and their relationship with neuroinflammation are still unknown. In this study, we found that TDB inhibited LPS-induced M1 microglial polarization in primary microglia and BV-2 cells. However, TDB itself had no effects on IKK, p38, JNK activity or cytokine expression. In contrast, TDB activated ERK1/2 through PLC-γ1/PKC signaling, and in turn decreased LPS-induced NF-κB nuclear translocation. Furthermore, TDB-induced AMPK activation via PLC-γ1/calcium/CaMKKβ-dependent pathway, and thereby enhanced M2 gene expressions. Moreover, TDB-mediated M2 gene expressions in LPS-stimulated BV-2 cells was prevented by AMPK siRNA, indicating that AMPK activation participates in TDB-mediated M2 polarization of microglia. In addition, TDB induced a metabolic shift in LPS-activated cells towards higher oxygen consumption rate (OCR) and lower extracellular acidification rate (ECAR). On the other hand, this pattern was reversed upon inhibition of AMPK in LPS-stimulated cells, which markedly reduced OCR but increased ECAR. Interestingly, knocking out Mincle did not alter the anti-inflammatory and M2 polarization effects of TDB in microglia. Conditional media from LPS-stimulated microglial cells can induce in vitro neurotoxicity, and this action was attenuated by TDB. Using a mouse neuroinflammation model, we found that TDB suppressed LPS-induced M1 microglial activation and sickness behavior, but promoted M2 microglial polarization in both WT and Mincle-/- mice. Taken together, our results suggest that TDB can act independently of Mincle to inhibit LPS-induced inflammatory response through PLC-γ1/PKC/ERK signaling, and promote M2 microglial polarization and mitochondrial bioenergetics via PLC-γ1/calcium/CaMKKβ/AMPK pathway. Thus, TDB may be a promising therapeutic agent for treating neuroinflammatory diseases.
參考文獻
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