Azithromycin alleviates the severity of rheumatoid arthritis by targeting the unfolded protein response component of glucose-regulated protein 78 (GRP78)

Background and purpose: Azithromycin is a macrolide antibiotic with anti-inflammatory properties. We aim to substantiate the treatment potential of azithromycin in rheumatoid arthritis.

Experimental approach: Gene expression profiles were collected by RNA sequencing and the effects of azithromycin were assessed by in vitro and in vivo assays on the effects of azithromycin-mediated blockade of glucose-regulated protein 78 (GRP78). Anti-inflammatory activity of azithromycin was measured in fibroblast-like synoviocytes from rheumatoid arthritis patients and in collagen-induced arthritis in DBA/1 mice. Characterization of the binding of azithromycin to GRP78 was performed using drug affinity responsive target stability, proteomics and cellular thermal shift assays. Azithromycin-mediated inhibition of GRP78 and its relationship to its anti-arthritic activity was assessed.

Key results: Azithromycin reduced proinflammatory factor production, cell migration, invasion and chemoattraction and enhanced apoptosis, reducing the deleterious inflammatory response of rheumatoid arthritis fibroblast-like synoviocytes in vitro. Azithromycin ameliorated the severity of collagen-induced arthritis lesions as efficiently as the TNFα inhibitor etanercept. Transcriptional analyses suggested that azithromycin treatment impairs signalling cascades associated with cholesterol and lipid biosynthesis. GRP78 was identified as a novel target of azithromycin. Azithromycin-mediated activation of the unfolded protein response via the inhibition of GRP78 activity is required not only for inducing the expression of C/EBP-homologous protein (ChOP) but also for the activating sterol-regulatory element binding protein (SREBP) and its targeted genes involved in cholesterol and lipid biosynthetic processes. Furthermore, deletion of GRP78 abolished the anti-arthritic activity of azithromycin.

Conclusion and implications: These findings indicate that azithromycin can used to treat rheumatoid arthritis.