| Summary: | 碩士 === 東海大學 === 食品科學系 === 97 === Microglia, resident immune cells in the central nervous system (CNS), respond to extracellular insults by releasing diversity of pro-inflammatory mediators such as nitric oxide (NO), tumor necrosis factor (TNF-alpha), interleukin 1beta(IL-1beta), and IL-6, leading to the initiation and promotion of inflammation. Evidence indicates that over-activated microglia and the associated pro-inflammatory mediators cause neural cell damage and contribute to several neurological disorders such as Alzheimer’s disease. Luteolin, a flavonoid compound, exhibits anti-oxidative, anti-neoplastic, anti-allerigc, and anti-inflammatory effects. Study suggests the neuroprotective effect of luteolin and proposes an anti-inflammatory mechanism. While the anti-inflammatory action is well demonstrated in the peripheral system, the role and potential action mechanisms of luteolin against inflammation in the CNS are largely unclear. The study was aimed to elicit the potential anti-inflammatory effect and mechanisms of luteolin against inflammatory responses in BV2 microglia cell lines after lipopolysaccharide (LPS)/interferon (IFN-gamma) stimulation. LPS/IFN-gamma stimulation caused BV2 cells elevating several pro-inflammatory mediators biosynthesis and releasing such as TNF-, iNOS, IL-6, and cyclooxygenase-2. Non-toxic level of luteolin reduced LPS/IFN-gamma-induced pro-inflammatory mediator production at the level of mRNA and protein. That is, the anti-inflammatory effect of luteolin is mediated by transcriptional regulation. Generally, intracellular signaling molecules such as ERK, JNK, p38, Akt, Jak family members, and Src could transduce extracellular signals to induce gene expression particularly pro-inflammatory genes through the modulation of transcription factors. Transcription factors such as NF-kappaB, IRF, and STAT are commonly downstream effectors of these signaling pathways. The inhibition of ERK, JNK, p38, Akt, and Jak activity by pharmacological inhibitors attenuated LPS/IFN-gamma-induced pro-inflammatory mediator production. LPS/IFN-gamma stimulation increased ERK, JNK, p38, Akt, Jak1, Jak2, Tyk2, and Src activity in BV2 cells, as evidenced by the elevated protein phosphorylation. Luteolin decreased ERK, JNK, p38, Akt, and Src but not Jak1, Jak2, and Tyk2 activity in LPS/IFN-gamma-treated cells. LPS/IFN-gamma stimulation caused IkappaB-alpha phosphorylation and triggered p50, p65, and RelB NF-kappaB subunit nuclear accumulation, indicating an activation of NF-kappaB. Luteolin attenuated LPS/IFN-gamma-induced IkappaB-alpha phosphorylation and p65 and RelB nuclear accumulation leading to a resolution of NF-kappaB activation. LPS/IFN-gamma increased IRF-1 protein expression resulting in activation and the increased IRF-1 expression was attenuated by luteolin. LPS/IFN-gamma stimulated STAT-1 and STAT-3 activity through the increased protein phosphorylation. Luteolin reduced LPS/IFN-gamma-induced STAT-1 and STAT-3 phosphorylation. Although luteolin had little effect on Jak family protein activity, another STAT upstream activator Src was inactivated in LPS/IFN-gamma stimulated cells by luteolin. Besides, luteolin increased SOCS3 protein expression, a negative regulator of STAT activation. Taken together, our experimental findings indicate that the anti-inflammatory effects of luteolin in microglia cells could be mediated by the down-regulation of ERK, JNK, p38, Akt, Src signaling molecules and NF-kappaB, IRF-1, STAT-1, and STAT-3 transcription factors.
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