RESUMO
The effects of Zinc(Zn)-deficiency on the function and differentiation of osteoblasts and osteoclasts were investigated in vivo using rats, which were fed a Zn-adequate (control) or Zn-free diet (ZD) or pair-fed a Zn-adequate diet (PF) for 3 weeks. Levels of Zn, insulin, insulin-like growth factor I (IGF-I), and osteoclacin in serum and the activities and numbers of osteoblasts and osteoclasts in bone decreased in ZD rats compared with the control and PF rats. The frequency analyses showed that the precursors of osteoblasts and osteoclasts decreased in bone marrow of ZD, but not PF, rats. The expression of receptor for activation of NF-κB (RANK) decreased with the Zn-deficiency, although RANK ligand, osteoprotegerin, macrophage colony-stimulating factor, and c-fms levels were unaltered. The protein level of a transcription factor MITF, but not PU.1, decreased. The expression of Runx2 decreased associated with the decrease in ß-catenin protein and the suppression of glycogen synthase kinase 3ß (GSK3ß) inhibition and Akt activation. The gene expression of the insulin receptor, IGF-I and the IGF-I receptor was decreased with a reduced level of transcription factor SP-1. These results suggested that a deficiency of Zn decreased osteoclastogenesis associated with the reduced expression of RANK through a decrease in MITF protein, and osteoblastogenesis associated with the reduced expression of Runx2 through the inhibition of Wnt/ß-catenin signaling via the suppression of GSK3ß inhibition and Akt activation preceded by the reduced level of SP-1 protein.
Assuntos
Subunidade alfa 1 de Fator de Ligação ao Core/metabolismo , Osteoblastos/metabolismo , Osteoclastos/metabolismo , Receptor Ativador de Fator Nuclear kappa-B/metabolismo , Zinco/deficiência , Fosfatase Ácida/metabolismo , Animais , Biomarcadores/metabolismo , Células da Medula Óssea/citologia , Células da Medula Óssea/metabolismo , Osso e Ossos/metabolismo , Diferenciação Celular/genética , Subunidade alfa 1 de Fator de Ligação ao Core/genética , Feminino , Fêmur/citologia , Fêmur/enzimologia , Isoenzimas/metabolismo , Osteogênese/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos , Ratos Wistar , Receptor de Insulina/genética , Receptor de Insulina/metabolismo , Coloração e Rotulagem , Fosfatase Ácida Resistente a Tartarato , Fatores de Transcrição/metabolismo , Zinco/metabolismoRESUMO
Insulin-dependent diabetes mellitus (IDDM) is known to be associated with an increased risk of osteopenia. However, the cellular and molecular mechanisms for IDDM-induced alterations of the bone are not well understood. The effects of IDDM on bone metabolism were investigated using rats rendered diabetic by an injection of streptozotocin (STZ). After 4 weeks, the diabetic rats exhibited bone loss, low levels of osteocalcin, insulin-like growth factor-I (IGF-I) and bone alkaline phosphatase (ALP) activity with normal levels of bone tartrate-resistant acid phosphatase (TRAP) and cathepsin K activity, and urinary excretion of deoxypyridinoline (Dpd). Histological analysis showed a decrease in the number of osteoblasts with a normal number of osteoclasts in the metaphysis of the proximal tibia. The decreased expression of ALP, osteoclacin and collagen mRNA was associated with a decrease in the expression of runt-related transcription factor 2 (Runx2), Osterix and distal-less homeobox 5 (Dlx5) and an unaltered expression of bone morphogenic protein-2 (BMP2). The protein levels of Runx2, phosphorylated glycogen synthase kinase 3ß (GSK3ß), active ß-catenin and ß-catenin decreased. The activation of Akt was inhibited. The mRNA and protein levels of sclerosteosis (Sost) and Dickkopf 1 (Dkk1), inhibitors of Wnt signaling, increased. The mRNA expression of IGF-I and the IGF-I receptor (IGF-IR) was suppressed. These changes observed in the bone of diabetic rats were reversed by treatment with insulin, but not by normalization of the circulating IGF-I levels by treatment with IGF-I. These results suggest that insulin-deficiency in IDDM decreases osteoblastogenesis associated with inhibition of Wnt signaling through the increased expression of Sost and Dkk1 and the inhibition of Akt activation.
