title: Lactation-Induced Changes in the Volume of Osteocyte Lacunar-Canalicular Space Alter Mechanical Properties in Cortical Bone Tissue.
abstract: Osteocytes can remove and remodel small amounts of their surrounding bone matrix through osteocytic osteolysis, which results in increased volume occupied by lacunar and canalicular space (LCS). It is well established that cortical bone stiffness and strength are strongly and inversely correlated with vascular porosity, but whether changes in LCS volume caused by osteocytic osteolysis are large enough to affect bone mechanical properties is not known. In the current studies we tested the hypotheses that (1) lactation and postlactation recovery in mice alter the elastic modulus of bone tissue, and (2) such local changes in mechanical properties are related predominantly to alterations in lacunar and canalicular volume rather than bone matrix composition. Mechanical testing was performed using microindentation to measure modulus in regions containing solely osteocytes and no vascular porosity. Lactation caused a significant (∼13%) reduction in bone tissue-level elastic modulus (p < 0.001). After 1 week postweaning (recovery), bone modulus levels returned to control levels and did not change further after 4 weeks of recovery. LCS porosity tracked inversely with changes in cortical bone modulus. Lacunar and canalicular void space increased 7% and 15% with lactation, respectively (p < 0.05), then returned to control levels at 1 week after weaning. Neither bone mineralization (assessed by high-resolution backscattered scanning electron microscopy) nor mineral/matrix ratio or crystallinity (assessed by Raman microspectroscopy) changed with lactation. Thus, changes in bone mechanical properties induced by lactation and recovery appear to depend predominantly on changes in osteocyte LCS dimensions. Moreover, this study demonstrates that tissue-level cortical bone mechanical properties are rapidly and reversibly modulated by osteocytes in response to physiological challenge. These data point to a hitherto unappreciated role for osteocytes in modulating and maintaining local bone mechanical properties. © 2016 American Society for Bone and Mineral Research.
authors.affiliation: Department of Biomedical Engineering, City College of New York, New York, NY, USA.
authors.forename: Serra
authors.initials: S
authors.lastname: Kaya
authors.affiliation: Department of Biomedical Engineering, City College of New York, New York, NY, USA.
authors.forename: Jelena
authors.initials: J
authors.lastname: Basta-Pljakic
authors.affiliation: Department of Biomedical Engineering, City College of New York, New York, NY, USA.
authors.forename: Zeynep
authors.initials: Z
authors.lastname: Seref-Ferlengez
authors.affiliation: Department of Biomedical Engineering, City College of New York, New York, NY, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Majeska
authors.affiliation: Department of Biomedical Engineering, City College of New York, New York, NY, USA.
authors.forename: Luis
authors.initials: L
authors.lastname: Cardoso
authors.affiliation: Department of Biomaterials, New York University College of Dentistry, New York, NY, USA.
authors.forename: Timothy G
authors.initials: TG
authors.lastname: Bromage
authors.affiliation: Department of Chemistry, Rutgers University, Newark, NJ, USA.
authors.forename: Qihong
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Rutgers University, Newark, NJ, USA.
authors.forename: Carol R
authors.initials: CR
authors.lastname: Flach
authors.affiliation: Department of Chemistry, Rutgers University, Newark, NJ, USA.
authors.forename: Richard
authors.initials: R
authors.lastname: Mendelsohn
authors.affiliation: Department of Basic Science, New York University College of Dentistry, New York, NY, USA.
authors.forename: Shoshana
authors.initials: S
authors.lastname: Yakar
authors.affiliation: Department of Biomedical Engineering, City College of New York, New York, NY, USA.
authors.forename: Susannah P
authors.initials: SP
authors.lastname: Fritton
authors.affiliation: Department of Biomedical Engineering, City College of New York, New York, NY, USA.
authors.forename: Mitchell B
authors.initials: MB
authors.lastname: Schaffler
mesh_terms: D000818:Animals; D015519:Bone Density / Q000502:physiology*; D001842:Bone and Bones / Q000166:cytology / Q000378:metabolism*; D048429:Cell Size; D055119:Elastic Modulus; D005260:Female; D007774:Lactation / Q000502:physiology*; D051379:Mice; D010011:Osteocytes / Q000166:cytology / Q000378:metabolism*; D010014:Osteolysis / Q000378:metabolism*
keywords: LACTATION; LACUNAR-CANALICULAR SPACE; MECHANICAL PROPERTIES; OSTEOCYTE; OSTEOCYTIC OSTEOLYSIS; POROSITY