Increased GABA transport activity in rat calvarial osteoblasts cultured under hyperglycemic conditions
Increased GABA transport activity in rat calvarial osteoblasts cultured under hyperglycemic conditions
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DOI：
10.1248/bpb.29.297
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发表时间：
2006-02-01
影响因子：
2
通讯作者：
Yoneda, Y
中科院分区：
文献类型：
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作者：
Fujimori, S;Osawa, M;Yoneda, Y
一些独立的证据表明，高浓度的细胞外葡萄糖直接损害不同的成骨细胞功能，导致骨量明显减少，从而导致骨质疏松症，但其潜在的机制迄今尚未得到很好的阐明。我们之前已经证明了神经氨基酸γ -氨基丁酸（GABA）信号系统的功能表达，包括甜菜碱/GABA转运蛋白-1 (BGT-1)，在培养的大鼠颅骨成骨细胞中具有[H-3]GABA积累的温度、钠和氯化物依赖活性。因此，在本研究中，我们试图证明BGT-1异构体可能参与在高血糖条件下培养的大鼠颅骨成骨细胞矿化受损引起的骨功能障碍。与正常血糖（葡萄糖= 5.5 mM）和高渗（甘露醇=25.5-50.5mM）条件下培养7d的成骨细胞（DIV）中[H-3]GABA积累无显著变化。然而，在高血糖条件下培养14 DIV的成骨细胞中，与在正常血糖和高渗条件下培养的成骨细胞相比，[H-3]GABA积累显著增加。动力学分析表明，高血糖培养导致V-max值从正常血糖条件下的2.85 nmol/min/mg蛋白显著增加到高血糖条件下的4.17 nmol/min/mg蛋白，而K-m值未受影响。然而，实验高血糖对成骨细胞BGT-1亚型mRNA的表达无显著影响。这些结果表明，GABA转运系统可能至少在一定程度上通过与高血糖下成骨细胞基因表达不直接相关的机制在病理功能障碍和异常中发挥作用。
Several independent lines of evidence indicate the direct impairment by extracellular glucose at high concentrations of different osteoblastic functions with a marked decrease in bone mass toward osteoporosis, while the underlying mechanisms are not well clarified to date. We have previously demonstrated the functional expression of the neural amino acid gamma-aminobutyric acid (GABA) signaling system including betaine/GABA transporter-1 (BGT-1) with a temperature-, sodium- and chloride-dependent activity of [H-3]GABA accumulation in cultured rat calvarial osteoblasts. In this study, therefore, we attempted to demonstrate the possible involvement of BGT-1 isoform in bone dysfunctions due to impaired mineralization in rat calvarial osteoblasts cultured under hyperglycemic conditions. No significant change was seen in [H-3]GABA accumulation in osteolalasts cultured for 7d in vitro (DIV) under hyperglycemic conditions (glucose= 25.5-50.5 mM) compared to those cultured in normoglycemic (glucose= 5.5 mM) and hyperosmotic (mannitol=25.5-50.5mM) conditions. In osteoblasts cultured for 14 DIV under hyperglycemic conditions, however, [H-3]GABA accumulation was significantly increased compared to those cultured under normoglycemic and hyperosmotic conditions. Kinetic analysis revealed that hyperglycemic cultivation resulted in a significant increase in V-max values from 2.85 nmol/min/mg protein for normoglycemic conditions to 4.17 nmol/min/mg protein for hyperglycemic conditions without affecting K-m values. However, experimental hyperglycemia did not significantly affect the expression of mRNA for BGT-1 isoform by osteoblasts. These results suggest that GABA transport system may at least in part play a role in pathological malfunctions and abnormalities through a mechanism not directly related to gene expression in osteoblasts under hyperglycemia.