Pretreatment with alendronate augments lipid A-induced IFN-β production via upregulation of cGAS expression

Alendronate (ALN), a nitrogen-containing bisphosphonate (NBP), augments proinflammatory cytokine production by mouse macrophage-like cells incubated with ligands of Toll-like receptor (TLR) 2 and TLR4. The present study investigated whether ALN augments the production of interferon (IFN)-β, which has anti-viral activity.

Mouse macrophage-like J774.1 cells were pretreated with or without ALN and then incubated with or without lipid A, a TLR4 ligand. Levels of secreted mouse IFN-β were measured by enzyme-linked immunosorbent assay (ELISA). Expression of interferon regulatory factor (IRF)-5, cyclic GMP-AMP synthase (cGAS), stimulator of interferon genes (STING), retinoic acid-inducible gene-I (RIG-I), downstream of kinase (DOK) 3, caspase-11, Nur77, laminB1, and β-actin was analyzed by Western blot analysis. Cell viability was evaluated by measuring the reduction of 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) to formazan by living cells.

Pretreatment with ALN significantly augmented lipid A-induced IFN-β production and nuclear IRF-5 expression in J774.1 cells. In addition, treatment with ALN upregulated the expression of cGAS, RIG-I, and DOK3. Pretreatment of J774.1 cells with RU.521, a cGAS inhibitor, inhibited ALN-augmented IFN-β production, IRF-5 activation, and caspase-11 expression. Similar results were shown in the pretreatment of cells with another inhibitor, G140. RIG012, a RIG-I antagonist, also suppressed ALN-augmented lipid A-induced IFN-β production. Furthermore, pretreatment with ALN significantly upregulated lipid A-induced Nur77 expression, which was also inhibited by RU.521.

These results suggest that pretreatment with ALN augments lipid A-induced IFN-β production by J774.1 cells via the upregulation of cGAS expression.