AB0066 Human multipotential stromal cells express low surface levels of pro-inflammatory cytokine receptors in bone healing defects
Authors: JJ El-Jawhari, G Kleftouris, YM El-sherbiny, R West, E Jones, PV Giannoudis
Journal: Annals of the Rheumatic Diseases (2017)

<h3>Background</h3> Osteoimmunology is an evolving field where the multipotential stromal cells (MSCs) can be considered as an important player linking immune response with bone generation. A group of pro-inflammatory cytokines including IFN-γ, TNF-α, IL-17 and IL-1, has been proven to have a licensing effect on MSCs promoting the immunomodulatory activities of MSCs (1). Importantly, these cytokines can regulate the osteogenic differentiation capability of MSCs and in particular, IL-1 and IL-17 can enhance the MSC osteogenesis as shown in previous in vitro studies (2,3). However, little is known about the role of these cytokine-MSC interactions in the bone-related diseases in humans. <h3>Objectives</h3> The main focus of this study was to assess if the immune-dependent licensing process of MSCs could be involved in defective bone regeneration. <h3>Methods</h3> We used samples of bone marrow aspirates (n=15) from two groups of traumatic bone fracture patients; normal union and non-union. Bone marrow MSCs were analyzed for the surface expression of the receptors of the pro-inflammatory licensing cytokines using flowcytometry-optimized panels. Additionally, a comparison of the cytokine effect on the proliferation of cultured MSCs was compared between normal union and non-union groups using the cell proliferation XTT test. <h3>Results</h3> Interestingly, there were significant lower expression levels of IL-1 receptors 1 and 3 (IL-1R1 and IL-1R3) on non-union MSCs compared to normal-union MSCs (p=0.0478 and p=0.0113 respectively). Furthermore, the surface levels of TNF-αR1 (CD120a) were significantly lesser on non-union MSCs (p=0.0119). There was a clear trend of reduced expression of IL-17 receptors (CD217) on the surface of non-union MSCs, but it was not statistically significant compared to normal-union (p=0.0726). The XTT data showed a significant less proliferation index for IL-1-treated non-union MSCs compared to normal-union MSCs (p=0.0446). Also, a consistent trend of lower proliferation index of non-union MSCs was detected when these cells were treated by IFN-γ, TNF-α or IL-17. <h3>Conclusions</h3> Together, the lower levels of the pro-inflammatory cytokine receptors indicated a possible mechanism for a defective response of non-union MSCs to the inflammatory signals (particularly IL-1). Further understating of the impact of immune-MSC interactions on human bone healing and regeneration will help to develop new therapies for musculoskeletal diseases involving osteolytic lesions. <h3>References</h3> Mesenchymal stromal cell 9licensing9: a multistep process. Krampera M. Leukemia. 2011 Sep;25(9):1408–14. Interleukin-1β induces differentiation of human mesenchymal stem cells into osteoblasts via the Wnt-5a/receptor tyrosine kinase-like orphan receptor 2 pathways. Sonomoto K, Yamaoka K, Oshita K, Fukuyo S, Zhang X, Nakano K, Okada Y, Tanaka Y. Arthritis Rheum. 2012 Oct;64(10):3355–63. Proinflammatory T cells and IL-17 stimulate osteoblast differentiation. Croes M, Öner FC, van Neerven D, Sabir E, Kruyt MC, Blokhuis TJ, Dhert WJ, Alblas J. Bone. 2016 Mar; 84:262–70. <h3>Acknowledgements</h3> This project (no. S-16–132E) was supported by the AO Foundation. <h3>Disclosure of Interest</h3> None declared