Soluble alpha v beta 3-integrin ligands raise [Ca2+]i in rat osteoclasts and mouse-derived osteoclast-like cells

Abstract

We evaluated the possible involvement of intracellular Ca2+ concentration ([Ca2+]i) changes in the action of alpha v beta 3-ligands, known to regulate osteoclast function. Rat osteoclasts or mouse osteoclast-like cells, as examined by microfluorimetry and fura 2, showed a transient [Ca2+]i increase when perfused with (all 0.1 microM) vitronectin, osteopontin, polypeptide echistatin, fibronectin, and Arg-Gly-Asp-Asp and Arg-Gly-Asp-Ser peptides (10(-4) M) but not with laminin, collagen I, collagen IV, or [Ala24]echistatin, in which Ala was substituted for Arg in the Arg-Gly-Asp complex. The threshold for echistatin was 10 pM, the 50% effective concentration was 1 nM, and the median [Ca2+]i increase was 420 nM above the resting level (217 +/- 22 nM) at saturating concentration of 0.1 microM. Echistatin did not cause Mn2+ influx, and 10 microM nifedipine, 10 nM omega-conotoxin, 5 mM Ni2+, or Cd2+ did not prevent [Ca2+]i change. However, extracellular Ca2+ was needed for the [Ca2+]i increase, probably enabling ligand-integrin interaction. Polyclonal and monoclonal (LM609) antibody as well as depletion of [Ca2+]i stores with 5 microM thapsigargin and Ca(2+)-free medium abolished the [Ca2+]i increase, after restoring extracellular Ca2+. Furthermore, the LM609 antibody induced a Ca2+ signal in the presence or absence of extracellular Ca2+, suggesting that the alpha v beta 3-ligand interaction is mediated at least partially by Ca2+ mobilized from intracellular stores.

Osteopontin-deficient mice are resistant to ovariectomy-induced bone resorption

“…It is also produced by the cells in nonskeletal tissues and has been implicated in tumorigenesis (17,18). Substrate-bound OPN promotes attachment of osteoclasts (19,20), whereas soluble OPN can alter calcium levels in osteoclasts (21,22), suppress inducible nitric-oxide synthase induction in kidney cells, and macrophages and serve as a chemoattractant (17,18,23). These observations suggest that OPN may play a key role both in cell attachment and in controlling subsequent bone cell functions such as resorption.…”

Extensive Induction of Important Mediators of Fibrosis and Dystrophic Calcification in Desmin-Deficient Cardiomyopathy

“…55 The present cDNA array studies revealed increased ACE expression in the desmin-null hearts, which might contribute to osteopontin induction through angiotensin II. In turn, osteopontin could modulate calcium levels by different ways including calcium mobilization, 56,57 activation of Ca ϩϩ ATPase pump, 58 Ca ϩϩ binding, 59 and by modulating hydroxyapatite crystal growth. 38 Thus, abnormalities in mitochondria apart from cytochrome c-and caspase-related prodeath events, can initiate and maintain the Ca ϩϩ /osteopontin cycle described above, which could lead to the extensive calcification in desmin-null hearts.…”

A Glanzmann’s mutation in β3 integrin specifically impairs osteoclast function

“…Thus, signal transduction mediated by the β3 cytoplasmic tail is critical for integrin function in the osteoclast. Previous studies have demonstrated that binding of RGD-containing peptides to the integrin triggers various intracellular signals, including changes in intracellular calcium (24)(25)(26), and activation of c-src (8), PYK2 (9), p130cas (27), and PI3-kinase (28). Despite these observations, the structural components of the β3 cytoplasmic tail mediating osteoclast function have not been elucidated.…”