The p85α Subunit of Class I_A Phosphatidylinositol 3-Kinase Regulates the Expression of Multiple Genes Involved in Osteoclast Maturation and Migration

Abstract

Intracellular signals involved in the maturation and function of osteoclasts are poorly understood. Here, we demonstrate that osteoclasts express multiple regulatory subunits of class I A phosphatidylinositol 3-kinase (PI3-K) although the expression of the full-length form of p85␣ is most abundant. In vivo, deficiency of p85␣ results in a significantly greater number of trabeculae and significantly lower spacing between trabeculae as well as increased bone mass in both males and females compared to their sex-matched wild-type controls. Consistently, p85␣؊/؊ osteoclast progenitors show impaired growth and differentiation, which is associated with reduced activation of Akt and mitogen-activated protein kinase extracellular signal-regulated kinase 1 (Erk1)/Erk2 in vitro. Furthermore, a significant reduction in the ability of p85␣ ؊/؊ osteoclasts to adhere to as well as to migrate via integrin ␣v␤3 was observed, which was associated with reduced bone resorption. Microarray as well as quantitative real-time PCR analysis of p85␣؊/؊ osteoclasts revealed a significant reduction in the expression of several genes associated with the maturation and migration of osteoclasts, including microphathalmia-associated transcription factor, tartrate-resistant acid phosphatase, cathepsin K, and ␤3 integrin. Restoring the expression of the full-length form of p85␣ but not the version with a deletion of the Src homology-3 domain restored the maturation of p85␣ ؊/؊ osteoclasts to wild-type levels. These results highlight the importance of the full-length version of the p85␣ subunit of class I A PI3-K in controlling multiple aspects of osteoclast functions.Osteoclasts (OCs) are derived from precursors of monocyte/ macrophage lineage, whose growth and maturation are mainly dependent on two osteoblast/stromal cell-derived cytokines, including macrophage colony stimulating factor (M-CSF) and receptor activator of NF-B ligand (RANKL) (22,30,35,63). The critical role for these two cytokines in OC growth and differentiation has been further illustrated by studying mice lacking the expression of 64). These mice show severe osteopetrosis and lack mature OCs. M-CSF and RANKL regulate OC progenitor (OCp) growth and function in part by regulating the expression of several OC genes, including tartrate-resistant acid phosphatase (TRAP), cathepsin K, calcitonin receptor, and integrin ␤3 (15, 29). Stimulation of OC precursors by RANKL and M-CSF results in the activation of a number of signaling molecules, including Gab2, Grb2, Vav, Src homology-2 (SH2)-containing inositol-5-

Caffeic acid 3,4-dihydroxy-phenethyl ester suppresses receptor activator of NF-κB ligand–induced osteoclastogenesis and prevents ovariectomy-induced bone loss through inhibition of mitogen-activated protein kinase/activator protein 1 and Ca2+–nuclear factor of activated T-cells cytoplasmic 1 signaling pathways

“…Moreover, genetic and pharmacological evidence shows that PI3K can regulate the activation of MAPKs induced by RANKL. (16,41) In our results, CADPE suppressed the phosphorylation of MAPKs. Furthermore, CADPE inhibited AP-1/c-Fos nuclear translocation and activity.…”

Important roles of PI3Kγ in osteoclastogenesis and bone homeostasis

“…On the other hand, the PI3Kγ pathway does not seem to contribute significantly to osteoclast precursor proliferation (Fig. 6D), in which the M-CSF-PI3K pathway had an important role (30). These results together suggest that the PI3Kγ pathway may not be a rate-limiting step in proliferation regulation.…”

Class IA phosphatidylinositol 3-kinase regulates osteoclastic bone resorption through protein kinase B–mediated vesicle transport

“…In addition, PI3K activity is enhanced in mice lacking only p85a compared with wild-type mice, possibly because of higher p50a/p55a expression. (41) A recent report by Munugalavadla and colleagues (42) described a bone phenotype in mice lacking only p85a, but as mentioned above, this strain is not a model of PI3K loss-of-function, and therefore does not provide information on the role of class IA PI3K in osteoclasts.…”