Th116 - SPP1+ Macrophages Are Pro-inflammatory and Pro-glycolytic in Rheumatoid Arthritis

Abstract Text:

Aim: Osteopontin/secreted phosphoprotein 1 (SPP1) plays an important role in inflammation and osteoclastogenesis. We previously identified enrichment of SPP1+ synovial-tissue macrophages (STMs) in rheumatoid arthritis (RA) compared to healthy control (HC), correlating with clinical parameters with distinct glycolytic signatures.

Methods: Blood obtained from HC and RA donors, CD14+ monocytes isolated, and differentiated either in the presence of M-CSF (50ng/ml) or Ca2+(2.5 mM) for 7 days to derive M0 or SPP1-expressing macrophages respectively. Inflammatory and metabolic outputs measured by RT-PCR, ELISA and Seahorse-XFE technology.

Results: SPP1-expressing macrophages display increased gene expression of SPP1 and secrete osteopontin in high concentrations compared to M0, an effect that is greater in SPP1-expressing macrophages derived from RA patients compared to HC. SPP1-expressing macrophages also display increased gene expression of key pro-inflammatory mediators IL-6, TNFa, IL-1B and IL-8 and glycolytic genes HIF1a and HK2 compared to M0. Importantly this effect is more pronounced in RA vs HC indicating priming in the RA periphery. Mounting evidence indicates that altered metabolic pathways play a crucial role in directing cellular functions. To assess the metabolic mechanisms that underpin SPP1+ macrophage function we utilized the seahorse analyzer. SPP1-expressing macrophages display decreased baseline oxidative phosphorylation and maximal respiratory capacity compared to HC/RA M0 while concomitantly skewing the ECAR/OCR ratio in favor of glycolysis indicating that SPP1-expressing RA macrophages rely heavily on glycolysis.

Conclusions: This study demonstrates that RA SPP1-expressing macrophages are metabolically re-programmed for sustained induction of pro-inflammatory responses. This may represent a potential pathway for therapeutic targeting early in disease.