title: Multiscale alterations in bone matrix quality increased fragility in steroid induced osteoporosis.
abstract: A serious adverse clinical effect of glucocorticoid steroid treatment is secondary osteoporosis, enhancing fracture risk in bone. This rapid increase in bone fracture risk is largely independent of bone loss (quantity), and must therefore arise from degradation of the quality of the bone matrix at the micro- and nanoscale. However, we lack an understanding of both the specific alterations in bone quality n steroid-induced osteoporosis as well as the mechanistic effects of these changes. Here we demonstrate alterations in the nanostructural parameters of the mineralized fibrillar collagen matrix, which affect bone quality, and develop a model linking these to increased fracture risk in glucocorticoid induced osteoporosis. Using a mouse model with an N-ethyl-N-nitrosourea (ENU)-induced corticotrophin releasing hormone promoter mutation (Crh(-120/+)) that developed hypercorticosteronaemia and osteoporosis, we utilized in situ mechanical testing with small angle X-ray diffraction, synchrotron micro-computed tomography and quantitative backscattered electron imaging to link altered nano- and microscale deformation mechanisms in the bone matrix to abnormal macroscopic mechanics. We measure the deformation of the mineralized collagen fibrils, and the nano-mechanical parameters including effective fibril modulus and fibril to tissue strain ratio. A significant reduction (51%) of fibril modulus was found in Crh(-120/+) mice. We also find a much larger fibril strain/tissue strain ratio in Crh(-120/+) mice (~1.5) compared to the wild-type mice (~0.5), indicative of a lowered mechanical competence at the nanoscale. Synchrotron microCT show a disruption of intracortical architecture, possibly linked to osteocytic osteolysis. These findings provide a clear quantitative demonstration of how bone quality changes increase macroscopic fragility in secondary osteoporosis.
authors.affiliation: Queen Mary University of London, School of Engineering and Material Science, Mile End Road, London E1 4NS, UK. Electronic address: a.karunaratne@imperial.ac.uk.
authors.forename: A
authors.initials: A
authors.lastname: Karunaratne
authors.affiliation: Queen Mary University of London, School of Engineering and Material Science, Mile End Road, London E1 4NS, UK. Electronic address: l.xi@qmul.ac.uk.
authors.forename: L
authors.initials: L
authors.lastname: Xi
authors.affiliation: MRC Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell, Harwell Science and Innovation Campus, OX11 0RD, UK. Electronic address: l.bentley@har.mrc.ac.uk.
authors.forename: L
authors.initials: L
authors.lastname: Bentley
authors.affiliation: Core Research Laboratories, The Natural History Museum, London SW7 5BD, UK. Electronic address: d.sykes@nhm.ac.uk.
authors.forename: D
authors.initials: D
authors.lastname: Sykes
authors.affiliation: Queen Mary University of London, Barts and the London School of Medicine and Dentistry, Institute of Dentistry, E1 2AD, UK. Electronic address: a.boyde@qmul.ac.uk.
authors.forename: A
authors.initials: A
authors.lastname: Boyde
authors.affiliation: MRC Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell, Harwell Science and Innovation Campus, OX11 0RD, UK; Academic Endocrine Unit, Nuffield Department of Clinical Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM), University of Oxford, Churchill Hospital, Headington, Oxford OX3 7JL, UK. Electronic address: c.esapa@har.mrc.ac.uk.
authors.forename: C T
authors.initials: CT
authors.lastname: Esapa
authors.affiliation: Diamond Light Source Ltd., Beamline I22, Diamond House, Harwell Science and Innovation Campus, Chilton, Didcot, Oxfordshire, OX11 0DE, UK; Department of Chemistry, University of Sheffield, Dainton Building, Brookhill, Sheffield S3 7HF, UK. Electronic address: nick.terrill@diamond.ac.uk.
authors.forename: N J
authors.initials: NJ
authors.lastname: Terrill
authors.affiliation: MRC Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell, Harwell Science and Innovation Campus, OX11 0RD, UK. Electronic address: s.brown@har.mrc.ac.uk.
authors.forename: S D M
authors.initials: SDM
authors.lastname: Brown
authors.affiliation: MRC Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell, Harwell Science and Innovation Campus, OX11 0RD, UK. Electronic address: r.cox@har.mrc.ac.uk.
authors.forename: R D
authors.initials: RD
authors.lastname: Cox
authors.affiliation: Academic Endocrine Unit, Nuffield Department of Clinical Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM), University of Oxford, Churchill Hospital, Headington, Oxford OX3 7JL, UK. Electronic address: rajesh.thakker@ndm.ox.ac.uk.
authors.forename: R V
authors.initials: RV
authors.lastname: Thakker
authors.affiliation: Queen Mary University of London, School of Engineering and Material Science, Mile End Road, London E1 4NS, UK. Electronic address: h.gupta@qmul.ac.uk.
authors.forename: H S
authors.initials: HS
authors.lastname: Gupta
mesh_terms: D000818:Animals; D001857:Bone Matrix / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology*; D005260:Female; D005269:Femur / Q000473:pathology / Q000503:physiopathology / Q000648:ultrastructure; D050723:Fractures, Bone / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D008810:Mice, Inbred C57BL; D010024:Osteoporosis / Q000139:chemically induced* / Q000000981:diagnostic imaging / Q000503:physiopathology*; D013256:Steroids / Q000009:adverse effects*; D017356:Synchrotrons; D013718:Tensile Strength; D055114:X-Ray Microtomography
chemical_list: D013256:Steroids
keywords: Glucocorticoid induced osteoporosis; In situ micro mechanical testing; Multiscale imaging; Nanoscale deformation mechanisms; Synchrotron small angle X-ray scattering