Ca2+ regulates fluid shear-induced cytoskeletal reorganization and gene expression in osteoblasts

Neal X. Chen, Kimberly D. Ryder, Fredrick M. Pavalko, Charles H. Turner, David B. Burr, Jinya Qiu, Randall L. Duncan

Research output: Contribution to journalArticle

243 Scopus citations

Abstract

Osteoblasts subjected to fluid shear increase the expression of the early response gene, c-fos, and the inducible isoform of cyclooxygenase, COX- 2, two proteins linked to the anabolic response of bone to mechanical stimulation, in vivo. These increases in gene expression are dependent on shear-induced actin stress fiber formation. Here, we demonstrate that MC3T3- E1 osteoblast-like cells respond to shear with a rapid increase in intracellular Ca2+ concentration ([Ca2+](i)) that we postulate is important to subsequent cellular responses to shear. To test this hypothesis, MC3T3-E1 cells were grown on glass slides coated with fibronectin and subjected to laminar fluid flow (12 dyn/cm2). Before application of shear, cells were treated with two Ca2+ channel inhibitors or various blockers of intracellular Ca2+ release for 0.5-1 h. Although gadolinium, a mechanosensitive channel blocker, significantly reduced the [Ca2+](i) response, neither gadolinium nor nifedipine, an L-type channel Ca2+ channel blocker, were able to block shear-induced stress fiber formation and increase in c-fos and COX-2 in MC3T3-E1 cells. However, 1,2-bis(2-aminophenoxy)ethane- N,N,N',N'-tetraacetic acid-AM, an intracellular Ca2+ chelator, or thapsigargin, which empties intracellular Ca2+ stores, completely inhibited stress fiber formation and c-fos/COX-2 production in sheared osteoblasts. Neomycin or U-73122 inhibition of phospholipase C, which mediates D-myo- inositol 1,4,5-trisphosphate (IP3)-induced intracellular Ca2+ release, also completely suppressed actin reorganization and c-fos/COX-2 production. Pretreatment of MC3T3-E1 cells with U-73343, the inactive isoform of U-73122, did not inhibit these shear-induced responses. These results suggest that IP3-mediated intracellular Ca2+ release is required for modulating flow- induced responses in MC3T3-E1 cells.

Original languageEnglish (US)
Pages (from-to)C989-C997
JournalAmerican Journal of Physiology - Cell Physiology
Volume278
Issue number5 47-5
StatePublished - Jun 22 2000

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Keywords

  • Actin cytoskeleton
  • Cyclooxygenase- 2
  • Intracellular calcium, c-fos
  • Phospholipase C

ASJC Scopus subject areas

  • Clinical Biochemistry
  • Cell Biology
  • Physiology
  • Physiology (medical)

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