Session Type: Abstract Submissions (ACR)
Rheumatoid arthritis (RA) is a systemic autoimmune disease that often leads to joint damage, a process mediated by an imbalance between bone resorption and bone formation. Additional evidence implicates the role of B cells in joint destruction including the presence of B cell aggregates in RA synovium and subchondral bone and the efficacy of B cell depletion therapy in halting radiographic progression. However, B cell effects on bone have been described as mediated via indirect influences on other immune cell such as T cells. Whether B cells directly affect bone homeostasis in RA is not known. In this study we investigated the effects of B cells on osteoclast (OC) and osteoblast (OB) functions in RA.
Isolated B cells from peripheral blood of healthy controls (HC) or RA patients were stimulated with α-CD40 and PMA for 96 h, and RANKL and TNF production was assessed by flow cytometry, ELISA, and qPCR. Stimulated and un-stimulated B cells were fixed then co-cultured with CD14+ monocytes isolated from HC along with M-CSF and sub-optimal levels of exogenous RANKL (10ng/ml). OC formation in vitrowas examined by TRAP staining. For OB differentiation assays, stimulated and un-stimulated B cells were co-cultured in Transwells with human mesenchymal stem cells (hMSCs) (Lonza, #PT-2501) for 24 h and the expression of OB transcription factor RUNX2 and Notch signaling molecules, Hes1 and Hey1 in hMSCs was detected by qPCR.
HC B cells stimulated with α -CD40 and PMA produce significant amounts of RANKL as compare to un-stimulated B cells (%RANKL+: 4.9±0.94 vs. 0.413±0.095, P<0.0001). Stimulated HC B cells promoted more OC formation than that of un-stimulated B cells (#OC/well: 66±8 vs. 4±1, P< 0.0001), which can be blocked by RANKL neutralizing antibody (#OC/well: 66±8 vs. 21±3, P<0.0001). Notably, stimulated RA B cells induced significantly more OC formation in comparison to HC B cells (using the same donor for OCP) (#OC/well: RA: 60±7 vs. HC: 12±7, P<0.001). In parallel, RA memory B cells expressed higher RANKL than memory B cells from HC (%RANKL+: 20.4±1.68 vs. 11.25±3.15, P<0.05). In addition to RANKL, stimulated B cells produce TNFα (91±11.6 pg/ml, n=4) a cytokine that we reported recently to inhibit OB differentiation of murine CD45- MSCs via up-regulating the Notch signaling pathway. In co-culture with hMSCs, stimulated RA B cells significantly reduced RUNX2 expression in hMSCs as compared to un-stimulated B cells (Runx2/actin: 0.21±0.01vs. 1±0.04 P=0.002, n=3), which was associated with increased levels of Hes1 and Hey1. In agreement with this finding, RA CD45- cells (MSC-enriched cells) isolated from peripheral blood have reduced expression of RUNX2 and increased expression of Hes1 and Hey1 compared to HC (n=11 for RA, n=14 for HC), suggesting abnormal OB function in vivo.
Our finding suggest that B cells play a critical role in promoting bone erosion in RA both by directly enhancing osteoclastogenesis and inhibiting osteoblast differentiation.
J. H. Anolik,
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/dual-role-for-b-cells-in-promoting-bone-erosion-in-rheumatoid-arthritis-via-effects-on-osteoclast-and-osteoblast-differentiation/