Metabolic reprogramming of macrophages instigates CCL21-induced arthritis

Abstract

This study was designed to delineate the functional significance of CCL21 in metabolic reprogramming in experimental arthritis and differentiated rheumatoid arthritis (RA) macrophages (MΦs). To characterize the influence of CCL21 on immunometabolism, its mechanism of action was elucidated by dysregulating glucose uptake in preclinical arthritis and RA MΦs. In CCL21 arthritic joints, the glycolytic intermediates hypoxia-inducible factor 1α (HIF1α), cMYC and GLUT1 were overexpressed compared with oxidative regulators estrogen-related receptor γ and peroxisome proliferator-activated receptor gamma coactivator 1 (PGC1)-α. Interestingly, 2-deoxy-D-glucose (2-DG) therapy mitigated CCL21-induced arthritis by restraining the number of joint F4/80⁺ iNOS⁺ MΦs without impacting F4/80⁺ Arginase⁺ MΦs. Similar to the preclinical findings, blockade of glycolysis negated CCL21-polarized CD14⁺ CD86⁺ GLUT⁺ MΦ frequency; however, CD14⁺ CD206⁺ GLUT⁺ MΦs were not implicated in this process. In CCL21-induced arthritis and differentiated RA MΦs, the inflammatory imprint was uniquely intercepted by 2-DG via interleukin-6 (IL-6) downregulation. Despite the more expansive inflammatory response of CCL21 in the arthritic joints relative to the differentiated RA MΦs, 2-DG was ineffective in joint tumor necrosis factor-α, IL-1β, CCL2 and CCL5 enrichment. By contrast, disruption of glycolysis markedly impaired CCL21-induced HIF1α and cMYC signaling in arthritic mice. Notably, in RA MΦs, glycolysis interception was directed toward dysregulating CCL21-enhanced HIF1α transcription. Nonetheless, in concurrence with the diminished IL-6 levels, CCL21 differentiation of CD14⁺ CD86⁺ GLUT1⁺ MΦs was reversed by glycolysis and HIIF1α inhibition. Moreover, in the CCL21 experimental arthritis or differentiated RA MΦs, the malfunctioning metabolic machinery was accompanied by impaired oxidative phosphorylation because of reduced PGC1α or peroxisome proliferator-activated receptor-γ expression. CCL21 reconfigures naïve myeloid cells into glycolytic RA CD14⁺ CD86⁺ GLUT⁺ IL-6^high HIF1α^high MΦs. Therefore, inhibiting the CCL21/CCR7 pathway may provide a promising therapeutic strategy.

Keywords: CCL21-induced arthritis; CD14+CD86+GLUT+ macrophages; Glycolysis; Rheumatoid arthritis.