Cellular and molecular mechanisms of bone damage and repair in inflammatory arthritis

Puerarin improves graft bone defect through microRNA‑155‑3p‑mediated p53/TNF‑α/STAT1 signaling pathway

Bone graft defects may lead to dysfunction of bone regeneration and metabolic disorders of bone mesenchymal stem cells (BMSCs). Puerarin has demonstrated pharmacological activities in the treatment of human metabolic diseases. The purpose of the present study was to investigate the role of puerarin and to explore its possible protective mechanism of action in rats with bone grafts. A bone graft rat model was established using bone grafting surgery and the rats received puerarin or PBS. Reverse transcription‑quantitative PCR, western blot, TUNEL, immunofluorescence and immunohistochemistry assays were used to analyze the beneficial effects of puerarin on bone repair. The results demonstrated that puerarin effectively ameliorated pathological graft bone defects, decreased bone loss and apoptosis of BMSCs, promoted BMSC proliferation and differentiation, and increased bone mass and the parameters of bone formation in rats with bone grafts. Puerarin decreased the levels of pro‑inflammatory cytokines [tumor necrosis factor (TNF)‑α, interleukin (IL)‑1β, IL‑17A, IL‑6 and transforming growth factor (TGF)‑β1] and increased the levels of anti‑inflammatory cytokines (IL‑2 and IL‑10) in the serum compared with the PBS group. Puerarin treatment was associated with lower serum alanine transaminase, glutamic oxaloacetic transaminase, γ‑glutamyl transferase, alkaline phosphatase, direct bilirubin and total bilirubin levels compared with those in the PBS group in experimental rats. The expression of microRNA‑155‑3p (miR‑155‑3p) was upregulated, whereas that of p53, TNF‑α and signal transducer and activator of transcription (STAT)1 was downregulated in BMSC cultures of puerarin‑treated rats. In vitro assay demonstrated that knockdown of miR‑155‑3p increased p53, TNF‑α and STAT1 expression in BMSCs, and blocked puerarin‑regulated p53/TNF‑α/STAT1 signaling. Most importantly, miR‑155‑3p knockdown inhibited puerarin‑regulated apoptosis, proliferation and differentiation of BMSCs. Moreover, the results demonstrated that puerarin regulated vascular endothelial growth factor expression via the miR‑155‑3p signaling pathway. In conclusion, the results of the present study demonstrated that the upregulation of miR‑155‑3p induced by puerarin promoted BMSC differentiation and bone formation and increased bone mass in rats with bone grafts, thereby supporting the potential application of puerarin in the prevention of bone graft defects.

Bone marrow mesenchymal stem cells improve bone erosion in collagen-induced arthritis by inhibiting osteoclasia-related factors and differentiating into chondrocytes

Background

Rheumatoid arthritis (RA) is characterized by joint inflammation and damage to the cartilage and bone in collagen-induced arthritis (CIA). Mesenchymal stem cells (MSCs) can improve articular symptoms and reduce bone erosion in CIA rats; however, the underlying mechanism remains unknown. This study aimed to investigate the mechanism underlying MSC-induced improvement of bone destruction in CIA.

Methods

Wistar rats were divided into a normal group, CIA control group, MTX intervention group, and BMSC intervention group, each comprising 8 rats. Serum RANKL, OPG, and CXCL10 levels of all groups were determined via flow cytometry after 42 days of interventions. RANKL, OPG, TRAF6, CXCL10, and CXCR3 were detected on the synovial membrane via immunohistochemistry, and their relative mRNA levels were determined via RT-PCR analysis. BMSCs were labeled with GFP and administered to CIA rats via the tail vein. At different time points, the distribution of implanted GFP-MSCs in synovial tissues was observed using a fluorescence microscope, and the potential of GFP-MSCs to differentiate into chondrocytes was assessed via immunofluorescence analysis.

Results

BMSC transplantation improved joint inflammation and inhibited bone destruction in CIA rats. BMSCs inhibited the expression of serum CXCL10 and CXCL10 and CXCR3 expression at the synovial membrane. Moreover, protein and mRNA expression analyses revealed that BMSCs potentially regulated RANKL/OPG expression levels in the serum and synovial tissue. Upon implantation into CIA rats, GFP-MSCs were traced in the joints. GFP-positive cells were observed in the cartilage tissue from day 11 and until 42 days after transplantation. Anti-type II collagen/GFP double-positive cells were observed in the articular cartilage (especially damaged cartilage) upon immunofluorescence staining of anti-type II collagen.

Conclusions

BMSCs improve bone destruction in CIA by inhibiting the CXCL10/CXCR3 chemotactic axis, regulating the RANKL/OPG ratio, and directly differentiating into chondrocytes.

Serum Heme Oxygenase-1 and BMP-7 Are Potential Biomarkers for Bone Metabolism in Patients with Rheumatoid Arthritis and Ankylosing Spondylitis

Backgrounds. Heme oxygenase-1 (HO-1) has been reported to play a regulatory role in osteoclastogenesis. Bone morphogenetic protein (BMP) pathways induce osteoblastic differentiation and bone remodeling. Aims. To identify serum levels of HO-1, BMP-7, and Runt related-transcription factor 2 (Runx2) in patients with rheumatoid arthritis (RA) and ankylosing spondylitis (AS) and to investigate the relationships between HO-1, BMP-7, Runx2, and other common biomarkers for bone metabolism. Results. Serum levels of HO-1 and BMP-7 were revealed to be significantly higher in patients with RA or AS than in healthy controls (p < 0.01). In RA group, HO-1 was positively correlated with BMP-7, Runx2, and tartrate-resistant acid phosphatase-5b (TRAP-5b) (p < 0.05, resp.), BMP-7 was positively correlated with Runx2 and TRAP-5b (p < 0.05, resp.), and Runx2 was negatively correlated with N-terminal midfragment of osteocalcin (NMID) (p < 0.05). In AS group, we observed identical correlation between HO-1 and BMP-7, but opposite correlations between BMP-7 and TRAP-5b and between Runx2 and NMID, when comparing with the RA cohort. Conclusion. Our findings suggest that HO-1 and BMP-7 are potential biomarkers for bone metabolism in patients with RA and AS. The different correlations between the bone markers point to distinct differences in bone remodeling pathways in the two types of arthritis.

Dental Follicle Cells Participate in Tooth Eruption via the RUNX2-MiR-31-SATB2 Loop

Cleidocranial dysplasia (CCD) is characterized by the runt-related transcription factor 2 (RUNX2) mutation, which results in delayed tooth eruption due to disturbed functions of dental follicle. Accumulating evidence has revealed a key regulatory circuit, including RUNX2, miR-31, and special AT-rich binding protein 2 (SATB2) acting in concert in mesenchymal stem cell homeostasis and functions. However, whether such a regulatory loop works in dental follicle cells (DFCs) remains unknown. Herein, we investigated the roles of RUNX2-miR-31-SATB2 in DFCs from patients with CCD (DFCs-CCD) to advance our understanding regarding physical tooth eruption. We identified a novel mutation on exon 5 (c.634T>G, p.T212P) in RUNX2 via exome sequencing in the CCD patient with typical clinical presentations. Compared with DFCs from healthy donors, DFCs-CCD displayed significantly lower osteogenic, osteoclast-inductive, and matrix-degrading capacities and had lower RUNX2 (a transcriptional inhibitor of miR-31), higher miR-31, and downregulated SATB2. Lower ratios of RANKL/OPG and RANKL/RANK, as well as decreased expression of matrix metalloproteinase 9 (MMP9) and matrix metalloproteinase 2 (MMP2), would lead to inactivation of osteoclasts and suppression of bone matrix remodeling in DFCs-CCD. Furthermore, the roles of the RUNX2-miR-31-SATB2 loop in DFCs-CCD were revealed by endogenous miR-31 knockdown, which resulted in increased SATB2 and RUNX2, as well as osteoclast-inductive and matrix degradation capacities. Conversely, SATB2, RUNX2, MMP9, MMP2, and osteoclast-inductive factors expression declined upon ectopic miR-31 overexpression in normal DFCs. Importantly, neonatal mice with in vivo siRUNX2 delivery exhibited less activated osteoclasts around dental follicles and delayed tooth eruption. Together, these results suggest that RUNX2 mutation/haploinsufficiency disturbs osteoclast-inductive signaling in DFCs, which may be responsible for delayed tooth eruption in CCD patients. Manipulation of the RUNX2-miR-31-SATB2 loop may be a potential way to facilitate tooth eruption in CCD patients.