Bidirectional Responses of Eight Neuroinflammation-Related Transcriptional Factors to 64 Flavonoids in Astrocytes with Transposable Insulated Signaling Pathway Reporters

Neuroinflammation is implicated in a variety of pathologies and is mechanistically linked to hyperactivation of glial cells in the central nervous system (CNS), predominantly in response to external stimuli. Multiple dietary factors were reported to alter neuroinflammation, but their actions on the relevant transcription factors in glia are not sufficiently understood. Here, an in vitro protocol employing cultured astroglial cells, which carry reporters of multiple signaling pathways associated with inflammation, was developed for screening environmental factors and synthetic drugs. Immortalized rat astrocyte line DI TNC1 was stably transfected with piggyBac transposon vectors containing a series of insulated reporters for the transcriptional activity of NF-κB, AP-1, signal transducer and activator of transcription 1 (STAT1), signal transducer and activator of transcription 3 (STAT3), aromatic hydrocarbon receptor (AhR), Nrf2, peroxisome proliferator-activated receptor γ (PPARγ), and HIF-1α, which is quantified via luciferase assay. Concatenated green fluorescent protein (GFP) expression was employed for simultaneous evaluation of cellular viability. Responses to a set of 64 natural and synthetic monomeric flavonoids representing six main structural classes (flavan-3-ols, flavanones, flavones, flavonols, isoflavones, and anthocyan(id)ins) were obtained at 10 and 50 μM concentrations. Except for HIF-1α, the activity of NF-κB and other transcription factors (TFs) in astrocytes was predominantly inhibited by flavan-3-ols and anthocyan(id)ins, while flavones and isoflavones generally activated these TFs. In addition, we obtained dose-response profiles for 11 flavonoids (apigenin, baicalein, catechin, cyanidin, epigallocatechin gallate, genistein, hesperetin, kaempferol, luteolin, naringenin, and quercetin) within the 1-100 μM range and in the presence of immune-stimulants and immune-suppressors. The flavonoid concentration profiles for TF-activation reveal biphasic response curves from the astrocytes. Apart from epigallocatechin gallate (EGCG), flavonoids failed to inhibit the NF-κB activation by proinflammatory agents [lipopolysaccharide (LPS), cytokines], but most of the tested polyphenols synergized with STAT3 inhibitors (stattic, ruxolitinib) against the activation of this TF in the astrocytes. We conclude that transposable insulated reporters of transcriptional activation represent a convenient neurochemistry tool in screening for activators/inhibitors of signaling pathways.

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