Fig. 5

Propionate attenuates the cAMP-AMPK-TAK1 signaling axis for the activation of NF-κB. A and B. A549 (A) and H1299 (B) cells were treated with vehicle, HKLM, and poly(I:C) in the presence or absence of propionate, as indicated. The activation of AMPK, TAK1, and p65 was evaluated by pho-AMPK, pho-TAK1, and pho-p65 antibodies. Anti-p65 and anti-GAPDH were used as blot-loading controls. C and D. A549 and H1299 cells were treated with vehicle, HKLM, and poly(I:C) in the presence or absence of different concentrations of propionate, as indicated. The NF-κB luciferase reporter assay was performed. The results are presented as means ± standard deviation (SD, n = 3 independent experiments). ***P < 0.001; ^#P < 0.05, ^##P < 0.01, ^###P < 0.001, \(^{\blacklozenge \blacklozenge}\)P < 0.01, and \(^{\blacklozenge \blacklozenge \blacklozenge}\)P < 0.001 in HKLM or poly(I:C) vs. HKLM plus propionate or poly(I:C) plus propionate. E and F. A549 (E) and H1299 (F) cells were treated with vehicle, HKLM, and poly(I:C) in the presence or absence of propionate, as indicated. cAMP levels were measured. The results are presented as means ± standard deviation (SD, n = 3 independent experiments). **P < 0.01 and ***P < 0.001. ^#P < 0.05 and ^##P < 0.01 in HKLM or poly(I:C) vs. HKLM or poly(I:C) plus propionate. G-I. A549 and H1299 cells were treated with vehicle, HKLM, and poly(I:C) in the presence or absence of propionate, as indicated. The production of CCL2 (G), IL-6 (H), and MMP2 (I) cytokines was measured. The results are presented as means ± standard deviation (SD, n = 3 independent experiments). ***P < 0.001; ^#P < 0.05, ^##P < 0.01, \(^{\blacklozenge }\)P < 0.05, and \(^{\blacklozenge \blacklozenge}\)P < 0.01 in HKLM or poly(I:C) vs. HKLM plus propionate or poly(I:C) plus propionate. J. Schematic diagram of how propionate, as a ligand of FFAR2, inhibits the TLR-induced AMPK-TAK1 signaling axis for the activation of NF-κB by modulating cAMP levels