The biochemical pathway mediating the proliferative response of bone cells to a mechanical stimulus.
Calvarial bone cells of rats were subjected to either a cyclic biaxial strain of 0.17 per cent (1700 microstrain) or a hydrostatic pressure of 2.5, five, or ten pounds per square inch (17.2, 34.5, or sixty-nine kilopascals). The frequency was held constant at one hertz for both types of mechanical stimulation. When cultured bone cells that had been subjected to a cyclic biaxial strain for two hours were harvested twenty-two hours later, it was found that the level of prostaglandin E2 had increased significantly (p < 0.01) as had cellular proliferation (p < 0.01), as indicated by the incorporation of [3H]-thymidine. The addition to the medium of indomethacin, an inhibitor of prostaglandin synthesis, at a ten-micromolar concentration significantly inhibited (p < 0.01) the increase in prostaglandin E2 synthesis but had no effect on the strain-induced increase in cellular proliferation, as indicated by the incorporation of [3H]-thymidine. Twenty-four hours after exposure to the same cyclic biaxial strain for thirty seconds, other cultured bone cells showed a significant increase in the level of cytoskeletal calmodulin (p < 0.05) and in the DNA content (p < 0.05). N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide (W-7), a calmodulin antagonist, was added to the medium at a one-micromolar concentration, which had been shown to have no effect on the increase in the DNA content of control cells; W-7 completely blocked the increase in the level of cytoskeletal calmodulin and in the DNA content in the cells that were subjected to a cyclic biaxial strain. The bone cells subjected to a hydrostatic pressure showed a dose-dependent increase in the concentration of cytosolic Ca2+, as measured with Fura 2-AM, a fluorescent indicator of intracellular calcium. With a pressure of ten pounds per square inch (sixty-nine kilopascals), the increase in the concentration of cytosolic Ca2+ was nearly eight times greater than that at 2.5 pounds per square inch (17.2 kilopascals) (126 +/- 15.2 compared with 16 +/- 8.0 nanomolar, mean and standard deviation). The addition to the medium of neomycin, an inhibitor of the inositol phosphate cascade, at a ten-millimolar concentration completely blocked the increase in the concentration of cytosolic Ca2+ in these cells; this concentration of neomycin had been shown to have no effect on proliferation in control bone cells. There was also a dose-dependent relationship between the duration of the stimulus and the cellular proliferation. Remarkably, one cycle of pressure at ten pounds per square inch (sixty-nine kilopascals) and a frequency of approximately one hertz produced a 57 per cent increase in the incorporation of [3H]-thymidine at twenty-four hours (p < 0.001). From these findings, we hypothesized that the inositol phosphate cascade-cytosolic Ca(2+)-cytoskeletal calmodulin system plays a dominant role in the signal transduction of a mechanical stimulus into increased proliferation of bone cells, at least under the conditions reported here.
Brighton
C T
CT
Department of Orthopaedic Surgery, University of Pennsylvania School of Medicine, Philadelphia 19104, USA.
Fisher
J R
JR
Levine
S E
SE
Corsetti
J R
JR
Reilly
T
T
Landsman
A S
AS
Williams
J L
JL
Thibault
L E
LE
D000818:Animals; D001842:Bone and Bones / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D002118:Calcium / Q000032:analysis / Q000378:metabolism; D002147:Calmodulin / Q000032:analysis / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D002455:Cell Division / Q000187:drug effects; D046508:Culture Techniques; D016861:Cyclooxygenase Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004247:DNA / Q000032:analysis / Q000096:biosynthesis; D015232:Dinoprostone / Q000032:analysis / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D006874:Hydrostatic Pressure; D007213:Indomethacin / Q000008:administration & dosage / Q000494:pharmacology; D007295:Inositol Phosphates / Q000037:antagonists & inhibitors; D009355:Neomycin / Q000494:pharmacology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D012886:Skull; D013314:Stress, Mechanical; D013449:Sulfonamides / Q000008:administration & dosage / Q000494:pharmacology; D013936:Thymidine / Q000378:metabolism; D013997:Time Factors; D014316:Tritium
D002147:Calmodulin; D016861:Cyclooxygenase Inhibitors; D005456:Fluorescent Dyes; D007295:Inositol Phosphates; D011500:Protein Synthesis Inhibitors; D013449:Sulfonamides; D014316:Tritium; C049925:fura-2-am; C017967:W 7; D004247:DNA; D009355:Neomycin; D015232:Dinoprostone; D002118:Calcium; D016257:Fura-2; D013936:Thymidine; D007213:Indomethacin