Background/Purpose: Increasing studies indicate that immune deregulation occurs prior to symptom in Rheumatoid arthritis (RA). Hematopoietic stem cell (HSC) gives rise to multipotent progenitors differentiating to lymphoid and myeloid immune cells. The turbulence of HSC development, precisely regulated by bone niche markers, may be the radical factor causing immune deregulation during RA progression. Gut microbiome (GM) is reported to implicate into RA and specific bacteria are known to influence immune cells and HSC¡¯s development. However, whether GM alteration is causation or consequence of RA is still unclear. In this study, we test whether GM affects RA development via regulating HSC¡¯s development in BM at the early stage of arthritis.

Methods: Collagen induced arthritis (CIA) in mice was applied in this study. HSC, common lymphoid progenitor (CLP) and common myeloid progenitor (CMP) in bone marrow were stained with Lineage, Sca-1, c-kit and CD127 cell surface markers and detected by flow cytometry on day 14 after the first immunization. Total numbers of stem cells and progenitors were monitored using beads. Stools were collected and the composition of the intestinal bacterial flora was detected by 16S rRNA sequencing. RT-PCR analysis was used to detect the genes expression of bone niche marker including CXCL12, CXCL4 and SCF.

Results: The percentages of hematopoietic stem cell (LSK, Lin^–Sca-1⁺c-Kit⁺) and CLP was not altered in CIA mice, whereas the total number of LSK was significantly increased compared with control mice. In contrast, the frequency and number of CMP were significantly enhanced in CIA mice (Fig 1A and B). The gene expressions of SCF, CXCL12 and CXCR4 in CIA mice were significantly lower than that of control. Additionally, the gut microbial communities in cecum of CIA mice was remarkably altered at the species and family level (Fig 2A and B). Analyses of the microbiota at the family level indicated an increase of Bacteroidales, Prevotellaceae, Corynebacteriaceae and a decrease of Lactobacillaceae and Bifidobacteriaceae (Fig 2C-D). Interestingly, Prevotellaceae was positively correlated with both LSK and CMP count. Corynebacteriaceae also showed highly positive correlation with LSK, CMP and CLP count. In contrast, Bifidobacteriaceae was negatively correlated with LSK count. No significant correlation was found between Bacteroidales/ Lactobacillaceae and HSC and progenitors (Fig 2E).

Conclusion: The increase of HSC count and its differentiation toward CMP occurs in bone marrow at the early stage of CIA mice, which is closely associated with GM alteration.

Fig 1

Fig 2