Inflammatory processes and elevated osteoclast activity chaperon atrophic non-union establishment in a murine model

Johannes M Wagner,Björn Behr,Sonja V Schmidt,Mehran Dadras,Felix Reinkemeier,Marius Drysch,Mustafa Becerikli,Marcus Lehnhardt,Stephanie Dittfeld,Julika Huber,Christoph Wallner,Henriette Jaurich

doi:10.1186/s12967-019-02171-4

Johannes M Wagner, Björn Behr + Show 10 more

Open Access

https://doi.org/10.1186/s12967-019-02171-4

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Abstract

BackgroundDelayed bone healing, especially in long bones poses one of the biggest problems in orthopeadic and reconstructive surgery and causes tremendous costs every year. There is a need for exploring the causes in order to find an adequate therapy. Earlier investigations of human scaphoid non-union revealed an elevated osteoclast activity, accompanied by upregulated levels of TGF-beta and RANKL. Interestingly, scaphoid non-union seemed to be well vascularized.MethodsIn the current study, we used a murine femur-defect model to study atrophic non unions over a time-course of 10 weeks. Different time points were chosen, to gather insights into the dynamic processes of non-union establishment.ResultsHistological analyses as well as western blots and qRT-PCR indicated enhanced osteoclast activity throughout the observation period, paralleled by elevated levels of TGF-beta, TNF-alpha, MMP9, MMP13 and RANKL, especially during the early phases of non-union establishment. Interestingly, elevated levels of these mediators decreased markedly over a period of 10 weeks, as inflammatory reaction during non-union establishment seemed to wear out. To our surprise, osteoblastogenesis seemed to be unaffected during early stages of non-union establishment.ConclusionTaken together, we gained first insights into the establishment process of atrophic non unions, in which inflammatory processes accompanied by highly elevated osteoclast activity seem to play a leading role.

Highlights

Delayed bone healing, especially in long bones poses one of the biggest problems in orthopeadic and reconstructive surgery and causes tremendous costs every year
Osteoblast and osteoclast function during non‐union establishment Our primary interest investigating the reasons for non-union establishment was to evaluate osteoblast and osteoclast function and reveal dysregulated bone homeostasis of formation and resorption
Levels of transforming growth factor β (TGF-β), tumor necrosis factor α (TNF-α), matrix metallopeptidase 9 (MMP9) and MMP13 showed to be increased after 1 and 5 weeks in non-union group validated in qRT PCR and Western Blot (Figs. 2 and 3)

Summary

Introduction

Especially in long bones poses one of the biggest problems in orthopeadic and reconstructive surgery and causes tremendous costs every year. An avascular fracture site was contemplated to be causative for atrophic non-union establishment [9, 10]. This hypothesis was maintained by different authors, who could demonstrate impaired fracture healing by virtue of inhibiting angiogenesis during fracture healing in animal models [11,12,13]. Stimulation of angiogenesis could improve impaired fracture healing [14,15,16] In contrast to these findings, other authors showed that atrophic nonunions seem to be well vascularized [17,18,19,20]. Summarized, the exact role of angiogenesis in atrophic non-union establishment is still subject to debate

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