2021 Volume No 41 – pages 558-575
Title: Prenatal muscle forces are necessary for vertebral segmentation and disc structure, but not for
notochord involution in mice |
Authors: A Levillain, S Ahmed, D-M Kaimaki, S Schuler, S Barros, D Labonte, JC Iatridis, NC Nowlan |
Address: Department of Bioengineering, Imperial College London, London SW72AZ, UK. |
E-mail: n.nowlan at imperial.ac.uk |
Abstract: Embryonic muscle forces are necessary for normal vertebral development and spinal curvature, but their
involvement in intervertebral disc (IVD) development remains unclear. The aim of the current study was
to determine how muscle contractions affect (1) notochord involution and vertebral segmentation, and (2)
IVD development including the mechanical properties and morphology, as well as collagen fibre alignment
in the annulus fibrosus. Muscular dysgenesis (mdg) mice were harvested at three prenatal stages: at Theiler
Stage (TS)22 when notochord involution starts, at TS24 when involution is complete, and at TS27 when the
IVD is formed. Vertebral and IVD development were characterised using histology, immunofluorescence,
and indentation testing. The results revealed that notochord involution and vertebral segmentation occurred
independently of muscle contractions between TS22 and TS24. However, in the absence of muscle contractions,
we found vertebral fusion in the cervical region at TS27, along with (i) a displacement of the nucleus pulposus
towards the dorsal side, (ii) a disruption of the structural arrangement of collagen in the annulus fibrosus,
and (iii) an increase in viscous behaviour of the annulus fibrosus. These findings emphasise the important
role of mechanical forces during IVD development, and demonstrate a critical role of muscle loading during
development to enable proper annulus fibrosus formation. They further suggest a need for mechanical loading
in the creation of fibre-reinforced tissue engineering replacement IVDs as a therapy for IVD degeneration. |
Key Words: Intervertebral disc – development, spine – biomechanics, notochord, muscular dysgenesis,
embryo, paralysis, ECM – collagens.
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Publication date: May 22nd 2021 |
Article download: Pages
558-575 (PDF file) |
