Background/Purpose:  Axial spondyloarthritis (AxSpA) is an immune–mediated inflammatory disease involving the spine and sacroiliac joint. AxSpA is characterized by vertebral trabecular bone loss and progressive bone formation in the spine. To date, the root cause of osteoproliferation and aberrant bone formation is unknown. Therefore, we evaluated, (i) whether bone progenitor cells (mesenchymal cells (MSCs) and osteoblasts (OBs)) derived from AxSpA patients (P) exhibit differences in their capacity to form mineralizing osteoblasts in comparison to healthy controls (HC), and (ii) whether inflammatory cytokines alter osteoblastogenesis and gene expression patterns in MCSs.

Methods:  We used MSCs derived from induced pluripotent stem cells (iPSCs) generated from P and HC skin fibroblasts. MSCs from 3 HC and 5 P were differentiated into mineralizing osteoblasts. The influence of cytokines (combination of IFNγ/TNFα and IL-1β) and the IL-1 receptor anatgonist (IL-ra) on MSCs and osteoblastogenesis was examined. The degree of osteoblast calcification was measured by alizarin red stain. Cell numbers were determined by DAPI staining. Whole transcriptome expression profiles were established for MSCs with and without cytokine treatments by using RNA-seq and Nanostring. (3 HC and 4P). Standard approaches and statistical methods were used to analyze the data.

Results:  On average, OBs derived from P (n=5) exhibited a 1.4 fold higher mineralization capacity compared to OBs from HC (n=3) (p<0.05; Mann Whitney test). Interestingly, in all tested P IL-1α (n= 4) or IL-1β (n=3) mRNA levels were enriched compared to HC up to 5 fold (p<0.05). Stimulation with IFNγ & TNFα induced IL-1α and IL-1β up to 20-fold and COX2 up to 15-fold. Incubation of P and HC MSC lines with IL-1β for 24h induced IL-1β, IL-1α and COX2 expression 5,10-20, and 3-5 fold (p<0.05), respectively. Treatment of MSCs for 48h with IL-1β before differentiation, led to a 25% increase of OB numbers and the degree of mineralization was up 2.5 fold (p<0.05). This effect was prevented by IL-1ra, which inhibited base line mineralization by 15%.

Conclusion: The results suggest that, under certain conditions, IL-1 can enhance proliferation of bone progenitors and osteoblast mineralization by auto- or paracrine mechanisms. Interestingly, exogenous IL-1β induced IL-1α, IL1β, and COX2 in MSCs correlated with increased proliferation and mineralization of OB. Since COX2 is crucial for the synthesis of prostaglandin E2 (PGE2) which can mediate aberrant ossification through β-catenin stabilization, we will evaluate whether PGE2 and β-catenin are increased in patient cell lines in future studies.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/elevated-il-1-expression-levels-in-mesenchymal-stem-cells-derived-from-spondyloarthitis-patients-might-be-linked-to-increased-osteoblast-mineralization/