Title: The BMP2 variant L51P restores the osteogenic differentiation of human mesenchymal stromal cells in the presence of intervertebral disc cells

Authors: A Tekari, RD May, DA Frauchiger, SCW Chan, LM Benneker, B Gantenbein

Address: Tissue and Organ Mechanobiology, Institute for Surgical Technology and Biomechanics, Stauffacherstrasse 78, 3014 Bern, Switzerland

E-mail: Benjamin.Gantenbein at istb.unibe.ch

Key Words: Spinal fusion, intervertebral disc, stem cells, coculture, osteogenesis, bone morphogenetic proteins, antagonists of bone morphogenetic proteins, BMP2 variant L51P.

Publication date: February 23rd 2017

Abstract: Spinal fusion is hampered by the presence of remaining intervertebral disc (IVD) tissue and leads to spinal non-union. While the exact mechanism remains unknown, we hypothesise that factors preventing disc ossification, such as antagonists of the bone morphogenetic proteins (BMP), could be responsible for this process.
The objective of this study was to investigate spinal non-union using an in vitro human model with a focus on the BMP signalling components and to identify factors contributing to the incomplete and delayed ossification. Human bone marrow-derived mesenchymal stromal cells (MSC) were cocultured with IVD cells in the presence of L51P, a BMP2 variant with osteoinductive potential. The ossification of MSC was evaluated by quantitative reverse transcription polymerase chain reaction (qPCR), alkaline phosphatase (ALP) activity and alizarin red staining. Endogenous expression of major BMP antagonists, namely Gremlin (GREM1), Noggin (NOG) and Chordin (CHRD) was detected in IVD-derived cells, with abundance in nucleus pulposus cells. Osteogenesis of MSC was hindered by IVD cells as shown by reduced alizarin red staining, ALP activity and qPCR. L51P, added to the cocultures, restored mineralisation, blocking the activity of the BMP antagonists secreted by IVD cells.
It is possible that the BMP antagonists secreted by IVD cells are responsible for spinal non-unions. The inhibition of BMP antagonists with L51P may result in an efficient and more physiological osteoinduction rather than delivery of exogenous osteogenic factors. Therefore, L51P might represent an attractive therapeutic candidate for bone healing.

Article download: Pages 197-210 (PDF file)
DOI: 10.22203/eCM.v033a15