Impaired Osteocyte Differentiation and Functional Expression of Sclerostin in Adolescent Idiopathic Scoliosis (AIS) in a 3D Culture Model - a New Novel Finding
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AbstractSummary
This is the first study to illustrate the impaired osteocytogenesis in AIS with an in vitro 3D model. The result highlighted that AIS expressed reduced representative osteocyte markers at mRNA and protein level during osteoblast to osteocyte differentiation process. Current investigation provided a novel mechanism might contribute
to the observed unique bone quality and bone metabolism profile in AIS.

Hypothesis
We hypothesized that the ultrastructural change of osteocytes and LCN in AIS might be attributed to the abnormal osteocytogenesi (differentiation process from osteoblasts to osteocytes). Design With an in vitro 3D culture model, we here compared the osteocytogenic potential of primary osteoblasts culture from AIS Vs controls.

Introduction
In Adolescent Idiopathic Scoliosis (AIS), low bone mineral density is one of the independent prognostic factors for curve progression. The underlying cause might be associated with altered bone turnover profile of AIS, including higher RANKL/OPG ratio, TRAP5b and bALP in serum. There is growing interest in the patho-physiological roles of osteocytes. We first reported ultrastructural change of osteocytes and lacuna-canalicular network (LCN) in AIS, which might contribute to the low BMD and deranged bone micro-structure.

Methods
In this case-control study, primary osteoblasts were isolated from trabecular iliac crest bone biopsies intraoperatively from AIS patients (n=6) and from control subjects (n=4). Total mRNA was isolated with Trizol. Osteoblast was embedded within 2mg/ml type I collagen gel which drived osteocytic differentiation. mRNA level of representative osteocytic markers was determined with qPCR. ELISA test was used to detect secretory sclerostin in conditioned medium.

Results
AIS bone biopsy expressed reduced DMP1 (p=0.017), FGF23 (p=0.014) and SOST (p=0.024). Osteocytogenic differentiation in the 3D culture model was confirmed with positive immunofluorescent staining of sclerostin (mature osteocytes marker) after 7 days of culture. AIS osteocytes culture had lower mRNA expression of SOST (p=0.021) and FGF23 (p=0.02). ELISA assay showed reduction of secreted sclerostin in 3D culture by 14.8 fold in AIS at day 7.

Conclusion
This is the first in vitro study demonstrating altered osteocytes activities in AIS, which might underlie the observed ultrastructural change of LCN in AIS. Further study is merited to investigate the molecular mechanism and clinical implications.
All Author(s) ListJ. Zhang, W. Y. W. Lee, H. X. Chen, E. M. S. Tam, G. C. W. Man, T. P. Lam, Y. Qiu, J. C. Y. Cheng
Name of Conference51st Annual Meeting of Scoliosis Research Society (SRS)
Start Date of Conference21/09/2016
End Date of Conference24/09/2016
Place of ConferencePrague, Czech Republic
Country/Region of ConferenceCzech Republic
Year2016
LanguagesEnglish-United Kingdom

Last updated on 2018-22-01 at 09:16