title: The loss of activating transcription factor 4 (ATF4) reduces bone toughness and fracture toughness.
abstract: Even though age-related changes to bone tissue affecting fracture risk are well characterized, only a few matrix-related factors have been identified as important to maintaining fracture resistance. As a gene critical to osteoblast differentiation, activating transcription factor 4 (ATF4) is possibly one of these important factors. To test the hypothesis that the loss of ATF4 affects the fracture resistance of bone beyond bone mass and structure, we harvested bones from Atf4+/+ and Atf4-/- littermates at 8 and 20 weeks of age (n≥9 per group) for bone assessment across several length scales. From whole bone mechanical tests in bending, femurs from Atf4-/- mice were found to be brittle with reduced toughness and fracture toughness compared to femurs from Atf4+/+ mice. However, there were no differences in material strength and in tissue hardness, as determined by nanoindentation, between the genotypes, irrespective of age. Tissue mineral density of the cortex at the point of loading as determined by micro-computed tomography was also not significantly different. However, by analyzing local composition by Raman Spectroscopy (RS), bone tissue of Atf4-/- mice was found to have higher mineral to collagen ratio compared to wild-type tissue, primarily at 20 weeks of age. From RS analysis of intact femurs at 2 orthogonal orientations relative to the polarization axis of the laser, we also found that the organizational-sensitive peak ratio, ν1Phosphate per Amide I, changed to a greater extent upon bone rotation for Atf4-deficient tissue, implying bone matrix organization may contribute to the brittleness phenotype. Target genes of ATF4 activity are not only important to osteoblast differentiation but also in maintaining bone toughness and fracture toughness.
authors: Department of Veterans Affairs, Tennessee Valley Healthcare System, Nashville, TN 27212, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN 37232, USA.
authors: Alexander J
authors: AJ
authors: Makowski
authors: Department of Orthopaedic Surgery & Rehabilitation, Vanderbilt University Medical Center, Nashville, TN 37232, USA; Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
authors: Sasidhar
authors: S
authors: Uppuganti
authors: Department of Veterans Affairs, Tennessee Valley Healthcare System, Nashville, TN 27212, USA.
authors: Sandra A
authors: SA
authors: Wadeer
authors: Department of Orthopaedic Surgery & Rehabilitation, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
authors: Jack M
authors: JM
authors: Whitehead
authors: Department of Veterans Affairs, Tennessee Valley Healthcare System, Nashville, TN 27212, USA; Center for Bone Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
authors: Barbara J
authors: BJ
authors: Rowland
authors: Department of Orthopaedic Surgery & Rehabilitation, Vanderbilt University Medical Center, Nashville, TN 37232, USA; Center for Bone Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
authors: Mathilde
authors: M
authors: Granke
authors: Department of Biomedical Engineering, Vanderbilt University, Nashville, TN 37232, USA.
authors: Anita
authors: A
authors: Mahadevan-Jansen
authors: Center for Bone Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA; Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA; Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
authors: Xiangli
authors: X
authors: Yang
authors: Department of Veterans Affairs, Tennessee Valley Healthcare System, Nashville, TN 27212, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN 37232, USA; Department of Orthopaedic Surgery & Rehabilitation, Vanderbilt University Medical Center, Nashville, TN 37232, USA; Center for Bone Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA. Electronic address: jeffry.s.nyman@vanderbilt.edu.
authors: Jeffry S
authors: JS
authors: Nyman
mesh_terms: D051701:Activating Transcription Factor 4 / Q000172:deficiency* / Q000378:metabolism; D000818:Animals; D001857:Bone Matrix / Q000473:pathology; D001842:Bone and Bones / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology*; D002113:Calcification, Physiologic; D019245:Compressive Strength; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology; D050723:Fractures, Bone / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000503:physiopathology*; D017353:Gene Deletion; D016014:Linear Models; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology; D051379:Mice; D009928:Organ Specificity; D013997:Time Factors; D055114:X-Ray Microtomography
chemical_list: D051701:Activating Transcription Factor 4
keywords: Bone quality; Collagen; Fracture toughness; Micro-computed tomography; Raman