title: Significant deterioration in nanomechanical quality occurs through incomplete extrafibrillar mineralization in rachitic bone: evidence from in-situ synchrotron X-ray scattering and backscattered electron imaging.
abstract: Bone diseases such as rickets and osteoporosis cause significant reduction in bone quantity and quality, which leads to mechanical abnormalities. However, the precise ultrastructural mechanism by which altered bone quality affects mechanical properties is not clearly understood. Here we demonstrate the functional link between altered bone quality (reduced mineralization) and abnormal fibrillar-level mechanics using a novel, real-time synchrotron X-ray nanomechanical imaging method to study a mouse model with rickets due to reduced extrafibrillar mineralization. A previously unreported N-ethyl-N-nitrosourea (ENU) mouse model for hypophosphatemic rickets (Hpr), as a result of missense Trp314Arg mutation of the phosphate regulating gene with homologies to endopeptidase on the X chromosome (Phex) and with features consistent with X-linked hypophosphatemic rickets (XLHR) in man, was investigated using in situ synchrotron small angle X-ray scattering to measure real-time changes in axial periodicity of the nanoscale mineralized fibrils in bone during tensile loading. These determine nanomechanical parameters including fibril elastic modulus and maximum fibril strain. Mineral content was estimated using backscattered electron imaging. A significant reduction of effective fibril modulus and enhancement of maximum fibril strain was found in Hpr mice. Effective fibril modulus and maximum fibril strain in the elastic region increased consistently with age in Hpr and wild-type mice. However, the mean mineral content was ∼21% lower in Hpr mice and was more heterogeneous in its distribution. Our results are consistent with a nanostructural mechanism in which incompletely mineralized fibrils show greater extensibility and lower stiffness, leading to macroscopic outcomes such as greater bone flexibility. Our study demonstrates the value of in situ X-ray nanomechanical imaging in linking the alterations in bone nanostructure to nanoscale mechanical deterioration in a metabolic bone disease.
authors.affiliation: School of Engineering and Material Sciences, Queen Mary University of London, London, UK.
authors.forename: Angelo
authors.initials: A
authors.lastname: Karunaratne
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Esapa
authors.forename: Jennifer
authors.initials: J
authors.lastname: Hiller
authors.forename: Alan
authors.initials: A
authors.lastname: Boyde
authors.forename: Rosie
authors.initials: R
authors.lastname: Head
authors.forename: J H Duncan
authors.initials: JH
authors.lastname: Bassett
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Terrill
authors.forename: Graham R
authors.initials: GR
authors.lastname: Williams
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Brown
authors.forename: Peter I
authors.initials: PI
authors.lastname: Croucher
authors.forename: Steve D M
authors.initials: SD
authors.lastname: Brown
authors.forename: Roger D
authors.initials: RD
authors.lastname: Cox
authors.forename: Asa H
authors.initials: AH
authors.lastname: Barber
authors.forename: Rajesh V
authors.initials: RV
authors.lastname: Thakker
authors.forename: Himadri S
authors.initials: HS
authors.lastname: Gupta
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology; D001842:Bone and Bones / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000648:ultrastructure*; D002113:Calcification, Physiologic / Q000502:physiology*; D004583:Electrons; D005038:Ethylnitrosourea; D053098:Familial Hypophosphatemic Rickets / Q000473:pathology / Q000503:physiopathology*; D005260:Female; D040181:Genetic Diseases, X-Linked; D005838:Genotype; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D020125:Mutation, Missense / Q000235:genetics; D049329:Nanostructures / Q000648:ultrastructure*; D053402:PHEX Phosphate Regulating Neutral Endopeptidase / Q000737:chemistry / Q000235:genetics; D010641:Phenotype; D011859:Radiography; D053838:Scattering, Small Angle; D013314:Stress, Mechanical; D017356:Synchrotrons; D013718:Tensile Strength / Q000502:physiology; D014965:X-Rays
chemical_list: D053402:PHEX Phosphate Regulating Neutral Endopeptidase; D005038:Ethylnitrosourea