Osteocyte calcium signals encode strain magnitude and loading frequency in vivo

Karl J. Lewis, Dorra Frikha-Benayed, Joyce Louie, Samuel Stephen, David C. Spray, Mia M. Thi, Zeynep Seref-Ferlengez, Robert J. Majeska, Sheldon Weinbaum, Mitchell B. Schaffler

Research output: Contribution to journalArticle

24 Scopus citations

Abstract

Osteocytes are considered to be the major mechanosensory cells of bone, but how osteocytes in vivo process, perceive, and respond to mechanical loading remains poorly understood. Intracellular calcium (Ca2+) signaling resulting from mechanical stimulation has been widely studied in osteocytes in vitro and in bone explants, but has yet to be examined in vivo. This is achieved herein by using a three-point bending device which is capable of delivering well-defined mechanical loads to metatarsal bones of living mice while simultaneously monitoring the intracellular Ca2+ responses of individual osteocytes by using a genetically encoded fluorescent Ca2+ indicator. Osteocyte responses are imaged by using multiphoton fluorescence microscopy. We investigated the in vivo responses of osteocytes to strains ranging from 250 to 3,000 µ and frequencies from 0.5 to 2 Hz, which are characteristic of physiological conditions reported for bone. At all loading frequencies examined, the number of responding osteocytes increased strongly with applied strain magnitude. However, Ca2+ intensity within responding osteocytes did not change significantly with physiological loading magnitudes. Our studies offer a glimpse into how these critical bone cells respond to mechanical load in vivo, as well as provide a technique to determine how the cells encode magnitude and frequency of loading.

Original languageEnglish (US)
Pages (from-to)11775-11780
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume114
Issue number44
DOIs
StatePublished - Oct 31 2017

Keywords

  • Bone
  • Calcium signaling
  • In vivo loading
  • Mechanotransduction
  • Osteocytes

ASJC Scopus subject areas

  • General

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