Biphasic and dosage-dependent regulation of osteoclastogenesis by -catenin.
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abstract
Wnt/-catenin signaling is a critical regulator of skeletal physiology. However, previous studies have mainly focused on its roles in osteoblasts, while its specific function in osteoclasts is unknown. This is a clinically important question because neutralizing antibodies against Wnt antagonists are promising new drugs for bone diseases. Here, we show that in osteoclastogenesis, -catenin is induced during the macrophage colony-stimulating factor (M-CSF)-mediated quiescence-to-proliferation switch but suppressed during the RANKL-mediated proliferation-to-differentiation switch. Genetically, -catenin deletion blocks osteoclast precursor proliferation, while -catenin constitutive activation sustains proliferation but prevents osteoclast differentiation, both causing osteopetrosis. In contrast, -catenin heterozygosity enhances osteoclast differentiation, causing osteoporosis. Biochemically, Wnt activation attenuates whereas Wnt inhibition stimulates osteoclastogenesis. Mechanistically, -catenin activation increases GATA2/Evi1 expression but abolishes RANKL-induced c-Jun phosphorylation. Therefore, -catenin exerts a pivotal biphasic and dosage-dependent regulation of osteoclastogenesis. Importantly, these findings suggest that Wnt activation is a more effective treatment for skeletal fragility than previously recognized that confers dual anabolic and anti-catabolic benefits.
