RESUMEN
Mechanical stimulation and biological factors coordinately regulate bone development and regeneration; however, the underlying mechanisms are poorly understood. Microgravity induces bone loss, which may be partly related to the development of resistance to local cytokines, including insulin-like growth factor 1 (IGF-1). Here, we report the involvement of integrin αvß3 in microgravity-associated bone loss. An established OSE-3T3 cell model was stably transfected with a 6OSE2 (Osteoblast-Specific Element 2)-luciferase reporter and cultured under simulated microgravity (SMG) and hypergravity (HG) conditions in the presence or absence of IGF-1, the disintegrin echistatin, the phosphoinositide 3-kinase (PI3K) inhibitor LY294002, or combinations of these agents. Activity of core-binding factor α1 (Cbfa1), an essential transcription factor for osteoblastic differentiation and osteogenesis, was reflected by luciferase activity. Different gravity conditions affected the induction of IGF-1 and subsequent effects on Cbfa1 transcription activity. SMG and HG influenced the expression and activity of integrin αvß3 and phosphorylation level of p85. LY294002 inhibited the effects of HG or IGF-1 on Cbfa1 activity, indicating that HG and IGF-1 could increase Cbfa1 activity via PI3K signaling. Inhibition of integrin αvß3 by echistatin attenuated the induction of IGF-1 and thus its effect on Cbfa1 activity under normal and HG conditions. Co-immunoprecipitation demonstrated that integrin ß3 interacted with insulin receptor substrate 1, and that this interaction was decreased under SMG and increased under HG conditions. These results suggest that integrin αvß3 mediates the synergetic regulation of Cbfa1 transcription activity by gravity and IGF-1 via PI3K signaling.
Asunto(s)
Subunidad alfa 1 del Factor de Unión al Sitio Principal/metabolismo , Gravedad Alterada/efectos adversos , Factor I del Crecimiento Similar a la Insulina/metabolismo , Integrina alfaVbeta3/metabolismo , Fosfatidilinositol 3-Quinasas/metabolismo , Células 3T3 , Animales , Western Blotting , Remodelación Ósea/fisiología , Inmunoprecipitación , Ratones , ARN Interferente Pequeño , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transducción de Señal/efectos de los fármacos , Vuelo Espacial , Transfección , Ingravidez/efectos adversosRESUMEN
INTRODUCTION: Bone loss and subclinical diabeteslike are developed during long-term spaceflight. Recently, it was demonstrated that bone was able to regulate energy metabolism and testosterone synthesis via osteocalcin. The aim of this study was to determine whether serum osteocalcin level is associated with glycolipid metabolism or testosterone under the influence of microgravity with or without resistive vibration exercise (RVE). METHODS: A total of 14 healthy adult male volunteers (25-40 years) were randomly assigned to two groups (n = 7 each): control (CON) group and RVE group. Radioimmunoassay kits and ELISA kits were used for measurement of serum indices. RESULTS: During 60-day bed rest, serum osteocalcin of both groups increased at day 4 during bed rest. Serum OPG started decreasing and reached its lowest value at day 30 during bed rest. In control group, serum insulin increased at day 4 during bed rest. IGF-I did not change significantly during the entire period of bed rest. The serum glucose decline 10% and 14% in CON and RVE groups at day 4 during bed rest. Relatively, the same results as glucose were found in serum HDL and LDL for both groups. Leptin rose and became highest at day 60 during bed rest in both groups. The level of serum testosterone was declined in control group at day 4 during bed rest. Cortisol kept stable in both group during bed rest. By spearman correlation analysis, serum osteocalcin was significantly associated with serum insulin (P < 0·05), LDL (P < 0·01) and Leptin (P < 0·01). CONCLUSION: Our findings suggested that the mutual regulation may exist between skeletal and energy metabolism under simulated microgravity.