Vitamin C-deficiency stimulates osteoclastogenesis with an increase in RANK expression

The effects of vitamin C (VC) on osteoclastogenesis were studied in vivo using ascorbate-requiring Osteogenic Disorder Shionogi (ODS) rats and in vitro using bone marrow-derived monocyte/macrophage cells (BMMs). The results confirmed previous findings of increases in the number of osteoclasts and in bone resorption at 2 and 3 weeks, but not 1 week, of VC-deficiency in ODS rats. The mRNA and protein levels of receptor activator nuclear factor kappaB (RANK) ligand and osteoprotegerin, and the mRNA level of macrophage-colony stimulating factor (M-CSF) in the proximal tibia of VC-deficient rats did not differ from those in VC-supplemented control rats. However, the mRNA levels of RANK, c-fos and c-jun were significantly increased at as early as 1 week of VC-deficiency. These results suggested that VC-deficiency stimulated osteoclastogenesis by increasing RANK expression. The osteoclastic differentiation of BMMs was suppressed in the presence of VC. The suppressed osteoclastogenesis was associated with decreased levels of RANK, c-fos and c-jun. The pretreatment of BMMs with VC or PD 98059, a specific inhibitor of extracellular signal regulated kinase (ERK)-activating MEK1, decreased the expression of RANK induced by M-CSF. VC inhibited the M-CSF-induced activation of ERK. These results suggested that VC-deficiency increased osteoclastogenesis by increasing RANK expression mediated through the activation of ERK.