Resolution of TLR2-induced inflammation through manipulaton of metabolic pathways
McGarry T, Biniecka M, Cregan S, Veale DJ, Fearon U
Centre for Arthritis and Rheumatic Diseases, Dublin Academic Medical Centre and Conway Institute of Biomolecular and Biomedical Research, Dublin 4, Ireland
Toll-like receptors are innate immune receptors known to regulate infection and inflammation. However exciting new evidence is emerging to suggests they are also involved in regulation of impaired mitochondrial function and metabolism.
In this study we examine the effect of TLR2 on mitochondrial function, metabolic pathways and subsequent synovial inflammation in RA.
RA synovial explants and primary RA synovial fibroblasts (RASFC) were cultured with TLR2-ligand PAM3Cysk4 (1ug/ml). Expression of inflammasome components NLRP3 and pro/active forms of IL-1b, IL-18 and caspase-1 were quantified by Taqman PCR and ELISA. Mitochondrial and glucose metabolism gene arrays were quantified by Real-Time PCR. Alterations in the synovial mitochondrial genome was assessed using a Random Mutation Capture assay and mitochondrial structure by transmission electron microscopy. Reactive oxygen species (ROS), mitochondrial membrane potential (MMP) and mitochondrial mass (MM) were quantified using fluorescent probes and M2 isoform of pyruvate kinase (PKM2) by Real-time PCR/western blot. Finally we examined the effect of TLR2 in the presence of a glycolytic inhibitor 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen- 1-one (3PO)(10uM) on RASFC cytokine production, invasion and endothelial cell tube formation.
TLR2 activation significantly induced NLRP3, Caspase-1, IL-1β and IL-18 expression in RA explants ex-vivo (all p<0.05).
TLR2 activation promotes mitochondrial dysfunction, resulting in a metabolic shift to glycolysis, reprogramming of which resulted in resolution of TLR2-induced inflammation. These results show close interplay between TLR2 signalling and metabolism, further elucidation of these interaction may provide new insights to new therapeutic approaches.