Adenosine monophosphate-activated protein kinase activator inhibits activation of fibroblast-like synoviocytes but promotes hyaluronan and proteoglycan link protein 1 secretion

Abstract Objectives: To determine whether any correlation exists between disease activity and AMPK levels in rheumatoid arthritis (RA) patients and investigate the effects of AMPK activator treatment on RA fibroblast-like synoviocytes (RA-FLS).Methods: Serum AMPK-α1, p-AMPK-α1, TNF-α and IL-17 levels between osteoarthritis (OA) and RA patients having different disease activities were compared by ELISA. Differentially expressed genes (DEGs) between RA and OA synovium from NCBI GEO Profiles (accession numbers: GSE1202112, GSE55235, GSE5545713) were identified and the genes intersecting in all the three datasets were selected for enrichment analysis. Immunohistochemical staining was done with synovium obtained from OA and RA patients for p-AMPK-α1. AMPK gene expression in synovium was semi-quantified by RT-qPCR. RNA sequencing of FLS was performed and DEGs were selected for KEGG enrichment analysis. AMPK activator, metformin, treated RA-FLS were tested for proliferation and migration by MTT and scratch test, respectively. Expression of IL-6, AMPK-α1, PKA-α, RAPTOR, mTOR, HAPLN1, RUNX1 and RUNX2 genes were determined by qPCR. Phosphorylated AMPK-α1 and HAPLN1 levels were determined by an automated electrophoresis-western blot analysis method.Results: In RA sera, a positive correlation between p-AMPK-α1 levels and DAS28 (r = 0.270, 95%CI: 0.142-0.492, p < 0.0001) as well as CRP levels (r = 0.259, 95%CI: 0.009-0.478, p < 0.05) was found. Similarly, a positive correlation was observed between AMPK-α1 and TNF-α levels (r = 0.460, 95% CI: 0.241-0.640, p = 0.0002). DEGs between OA and RA synovium from NCBI GEO profiles and our RNA sequencing data suggested activation of metabolic pathways specific to RA-FLS. AMPK-α1 was highly expressed in the synovium of RA but not OA patients. Metformin at higher concentrations inhibited RA-FLS proliferation in a dose dependant manner, however, at lower concentrations it has an opposite effect. On the other hand, AMPK inhibitor, dorsmophin, promoted the proliferation of RA-FLS significantly. Interestingly, both metformin and dorsmophin substantially inhibited the migration of RA-FLS. In FLS, relative expression level of IL-6 mRNA was significantly decreased after metformin treatment, while the expression of AMPK-α1, PKA-α and HAPLN1 genes were significantly increased. Western blot analysis confirmed increased expression of p-AMPK-α1 and HAPLN1 genes in the metformin treated FLS.Conclusions: Inflammatory stress in RA synovium leads to an increase in AMPK levels, possibly as a protective mechanism. AMPK activator but not metformin per se could be a potential therapeutic for RA by promoting HAPLN1 secretion to protect the joints.