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Transcriptome profiling of CCR2hi and CCR2lo osteoclast progenitor subpopulations associated with arthritis

As the existence of different osteoclast progenitor (OCP) subsets has been confirmed, their detailed characterization is required to understand the pathophysiology of increased osteoclast activity causing periarticular and systemic bone resorption in arthritis. We previously defined OCP subsets based on the level of CCR2 expression, as circulatory-like committed CCR2hi OCPs, substantially expanded in arthritis, and marrow-resident CCR2lo OCPs of immature phenotype and behavior. We sorted CCR2hi and CCR2lo OCPs of mice with collagen-induced arthritis (CIA) and control mice (n=4 for each group), and performed next-generation RNA sequencing. We confirmed a disparity between the transcriptomes of CCR2hi and CCR2lo OCP subsets, and identified pathway enrichment for osteoclast differentiation, chemokine and NOD-like receptor signaling in the CCR2hi OCP subset and ribosome biogenesis in eukaryotes and pyrimidine metabolism in the CCR2lo OCP subset. Genes associated with the osteoclastogenic pathway (Fcgr1, Socs3), and genes involved in cell adhesion and migration (F11r, CD38, Lrg1) were used to both identify the CCR2hi subset and distinguish CIA from control group, as validated by qPCR (n=6 for control, n=9 for CIA). The latter set positively correlated with arthritis clinical score and percentage of CCR2hi OCPs, indicating potential disease markers. Moreover, osteoclast pathway-identifying genes remained upregulated in committed preosteoclasts cultured for two days, suggesting their importance for enhanced osteoclastogenesis of CCR2hi OCPs in arthritis. Our approach identified differentially expressed genes that allow detection of distinct OCP subsets associated with arthritis and well as indicate possible therapeutic targets aimed to modulate progenitor migration, proliferation, differentiation or activity

RNA sequencing ; chemokine receptor ; flow cytometry ; gene expression ; mouse arthritis ; osteoclast differentiation ; osteoclast progenitor (OCP) ; qPCR

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