Abstract
Purpose :
Several studies report a role for apigenin in inhibiting microglia activation; however, the molecular mechanism associated with this activity remains unknown. Here, we examined apigenin-mediated inhibition of the expression of proinflammatory genes in activated microglia by analyzing microRNAs (miRNAs), particularly miR-155, which regulate inflammatory cytokines and thereby contribute to microglia-activation phenotypes. Additionally, we investigated the role of Ets2, a transcriptional activator of primary miR-155 (pri-miR-155).
Methods :
The microglia cell line BV2 was incubated with various concentrations of apigenin for 2 h prior to lipopolysaccharide (LPS) stimulation, followed by collection at 24 h and assessment of the expression of proinflammatory genes [interleukin-1β (il1b), C-C motif chemokine ligand 2 (ccl2), C-X-C motif chemokine 10 (cxcl10), tumor necrosis factor-α, and colony stimulating factor 1 (csf1)] and miRNAs (miR-155, miR-125b, and miR-146a). Similar experiments were undertaken to determine the effect of apigenin on Ets2 and pri-miR-155 levels at various time points following LPS stimulation.
Results :
Apigenin at 10 µM strongly suppressed il1b, ccl2, cxcl10, and csf1 by 6.7-, 3.6-, 9.1-, and 2.4-fold, respectively, relative to levels observed following treatment with LPS alone, with these suppressive effects occurring in a concentration-dependent manner. Additionally, analysis of miR-155, miR-125b, and miR-146a revealed that apigenin treatment attenuated their expression by 2.9-, 2.0-, and 1.8-fold, respectively. Moreover, Ets2 levels were attenuated 1.5-3.7 fold by apigenin treatment at early time points (from 3-6 h), followed by a decline in this effect over time, whereas pri-miR-155 levels were suppressed from 6 h by 2.1 fold, with this effect lasting up to 24 h (1.7 fold).
Conclusions :
These results demonstrate that apigenin inhibited proinflammatory cytokine expression by regulating multiple miRNAs and represent the first findings suggesting that apigenin modulates miR-155 through the Ets2 pathway. Further investigations are required to elucidate the apigenin-specific molecular mechanism in order to promote its development for microglia-targeted treatment or prevention of retinal degenerative diseases.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.