Bone fractures may result in delayed union (DU) or non-union (NU) in some patients. Evidence suggests that the skewing of the immune system toward the proinflammatory type is a contributing factor. Because B cells were previously found to infiltrate the fracture healing site at abundant levels, we examined the regulatory B cells (Bregs) in DU/NU patients. In bone fracture patients with normal healing, the frequency of interleukin (IL)-10-expressing B cells was significantly upregulated in the early healing process (6 weeks post-surgery) and was downregulated later on (18 weeks post-surgery), whereas in DU/NU patients, the early upregulation of IL-10-expressing B cells was missing. The majority of IL-10-expressing B cells were concentrated in the IgM CD27 fraction in both controls and patients. IgM CD27 B cells effectively suppressed interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), and IL-2 expression from CD4 T cells, as well as IFN-γ and TNF-α expression from CD8 T cells. The IgM CD27 B cell-mediated suppression was restricted to the sample from the early healing time point in controls, as the IgM CD27 B cells from normal healing patients later on or from DU/NU patients did not present significant regulatory function. In addition, culturing of CD4 CD25 Tregs with IgM CD27 B cells from controls at early healing time point resulted in higher Foxp3 expression, a function absent in controls at later time point, or in DU/NU patients. In conclusion, our results support a role of B cell-mediated regulation early during the bone healing process.

Mesenchymal stem cells (MSCs) have several features that make them an attractive option for potentiating cartilage repair. Synovium-derived (SMSCs) have been recently recognized as an excellent source. SRY-related HMG-box (Sox) family plays an important role in the proliferation and differentiation of SMSCs. However, the role of Sox4 in human SMSCs remains elusive. In the present study, we investigated the role of Sox4 in SMSCs through gain-of-function studies and found that Sox4 promoted cell proliferation and chondrogenesis. Furthermore, Sox4 could directly bind to the promoter of long noncoding RNA DANCR and increased its expression. Finally, knockdown of DANCR could reverse the stimulative effect of Sox4 on the proliferation and chondrogenesis of SMSCs. Taken together, our data highlights the pivotal role of Sox4 in the proliferation and differentiation of SMSCs.

Aseptic loosening secondary to periprosthetic inflammatory osteolysis results from the biological response to wear particles and is a leading cause of arthroplasty failure. The origin of this inflammatory response remains unclear. We aim to validate the definite link between endoplasmic reticulum (ER) stress and particle-induced inflammatory signaling pathways in periprosthetic osteolysis. We examine the histopathologic changes of osteolysis and the expression of specific biomarkers for ER-stress-mediated inflammatory signaling pathways (IRE1α, GRP78/Bip, c-Fos, NF-κB, ROS and Ca2+). Moreover, pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) and osteoclastogenic molecules (VEGF, OPG, RANKL and M-CSF) were assessed in clinical interface membranes and murine periosteum tissues. We found wear particles to be capable of inducing ER stress in macrophages within clinical osteolytic interface membranes and murine osteolytic periosteum tissues and to be associated with the inflammatory response and osteoclastogenesis. Blocking ER stress with sodium 4-phenylbutyrate (4-PBA) results in a dramatic amelioration of particle-induced osteolysis and a significant reduction of ER-stress intensity. Simultaneously, this ER-stress blocker also lessens inflammatory cell infiltration, diminishes the capability of osteoclastogenesis and reduces the inflammatory response by lowering IRE1α, GRP78/Bip, c-Fos, NF-κB, ROS and Ca2+ levels. Thus, ER stress plays an important role in particle-induced inflammatory osteolysis and osteoclastogenic reactions. The pharmacological targeting of ER-stress-mediated inflammatory signaling pathways might be an appealing approach for alleviating or preventing particle-induced osteolysis in at-risk patients.