Interleukin-4 inhibits bone resorption and acutely increases cytosolic Ca2+ in murine osteoclasts.
Interleukin-4 (IL-4) is an immune cytokine recently shown to inhibit bone resorption. To determine whether IL-4 directly acts on osteoclasts, we have analyzed its effect on cytosolic calcium concentration [Ca2+]i and bone resorptive function of murine osteoclastic cells generated from bone marrow/stromal cell co-cultures. IL-4 exposure induced an immediate and sustained increase in [Ca2+]i that remained elevated for at least 10 min. This IL-4 effect was dose-dependent, with the maximal effect (209 +/- 15% of baseline, n = 16) at 200 units/ml and an apparent ED0.5 of 60 units/ml. The IL-4-induced [Ca2+]i rise required extracellular Ca2+ influx, since the response was prevented by LaCl3, and voltage-gated Ca2+ channel blockers, although the IL-4 effect was more sensitive to nicardipine and nifedipine than to diltiazem. Depolarization by high extracellular K+ concentration also raised [Ca2+]i, and, under these conditions, osteoclasts failed to respond to IL-4. On the other hand, when intracellular Ca2+ stores were depleted by thapsigargin, IL-4 still induced an increase in [Ca2+]i, although smaller in amplitude and transient. Calcitonin also produced [Ca2+]i increases in osteoclasts, yet it only slightly desensitized these cells to IL-4. Furthermore, IL-4 was much less effective on osteoclasts pretreated (5-10 min) with either forskolin or 8-bromo-cAMP. Both IL-4 and calcitonin were effective even when [Ca2+]i had been increased by exposure to high extracellular Ca2+. Finally, IL-4 dose dependently inhibited the bone-resorptive activity of mature osteoclasts. Therefore, IL-4 signal transduction in osteoclasts involves a rapid and sustained elevation of [Ca2+]i mediated by a voltage-dependent Ca2+ influx, in combination with Ca2+ release from intracellular stores. Modulation of osteoclast [Ca2+]i represents a potential mechanism by which IL-4 inhibits bone resorption.
Bizzarri
C
C
Consorzio Biolaq., L'Aquila, Italy.
Shioi
A
A
Teitelbaum
S L
SL
Ohara
J
J
Harwalkar
V A
VA
Erdmann
J M
JM
Lacey
D L
DL
Civitelli
R
R
D000818:Animals; D001692:Biological Transport; D001862:Bone Resorption / Q000517:prevention & control*; D002116:Calcitonin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism*; D015847:Interleukin-4 / Q000494:pharmacology*; D015640:Ion Channel Gating; D051379:Mice; D010010:Osteoclasts / Q000378:metabolism*
D015220:Calcium Channels; D015847:Interleukin-4; D002116:Calcitonin; D002118:Calcium