Estrogen Deficiency Attenuates Fluid Flow-Induced [Ca 2+] i Oscillations and Mechanoresponsiveness of MLO-Y4 Osteocytes

FASEB J. 2017 Jul;31(7):3027-3039. doi: 10.1096/fj.201601280R. Epub 2017 Mar 31.

Abstract

It has been proposed that estrogen regulates the mechanosensitivity of osteocytes; however, the effects of estrogen deficiency that arises during postmenopausal osteoporosis on mechanical stimulation-induced calcium signaling in osteocytes remain elusive. Here, we pretreated MLO-Y4 osteocytes with 10 nM E2 for 2, 3 and 5 d, then simulated postmenopausal conditions either by estrogen withdrawal (EW) from culture medium, or by inhibiting the estrogen receptor by using fulvestrant and estrogen (FE; ICI 182,780) in vitro We investigated [Ca2+]i oscillations and mechanobiologic responses of osteocytes (EW and FE) that were exposed to oscillatory fluid flow (OFF; 1 Pa, 0.5 Hz). We demonstrated that estrogen treatment enhanced OFF-induced [Ca2+]i oscillations and that this effect was abrogated both by FE and EW. Moreover, osteocytes in both estrogen-depleted groups (EW and FE) had reduced levels of NO and prostaglandin E2 release, down-regulated dentin matrix protein-1, sclerostin, osteopontin, osteocalcin, and alkaline phosphatase mRNA expression, and reduced F-actin fiber formation after OFF stimulation compared with estrogen-treated cells. We propose a link between estrogen deficiency and alterations in [Ca2+]i-mediated mechanosensitivity of osteocytes, which ultimately alter osteocyte function and differentiation.-Deepak, V., Kayastha, P., McNamara, L. M. Estrogen deficiency attenuates fluid flow-induced [Ca2+]i oscillations and mechanoresponsiveness of MLO-Y4 osteocytes.

Keywords: E2; fluid shear stress; mechanobiology; menopause; osteoporosis.

MeSH terms

  • Actins / physiology
  • Animals
  • Biomarkers
  • Biomechanical Phenomena
  • Calcium Signaling / physiology*
  • Cell Line
  • Estradiol / analogs & derivatives
  • Estradiol / pharmacology
  • Estrogens / administration & dosage
  • Estrogens / pharmacology*
  • Fulvestrant
  • Gene Expression Regulation / drug effects
  • Gene Expression Regulation / physiology
  • Mice
  • Osteocytes / drug effects
  • Osteocytes / metabolism*
  • Stress, Mechanical*
  • Up-Regulation

Substances

  • Actins
  • Biomarkers
  • Estrogens
  • Fulvestrant
  • Estradiol