Influence of vitamin D3 deficiency and 1,25 dihydroxyvitamin D3 on de novo insulin biosynthesis in the islets of the rat endocrine pancreas
Influence of vitamin D3 deficiency and 1,25 dihydroxyvitamin D3 on de novo insulin biosynthesis in the islets of the rat endocrine pancreas
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DOI：
10.1677/joe.0.1600087
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发表时间：
1999-01-01
影响因子：
4
通讯作者：
Faure-Dussert, A
中科院分区：
文献类型：
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作者：
Bourlon, PM;Billaudel, B;Faure-Dussert, A
由于已知1,25二羟基维生素D-3 (1,25（OH)(2)D-3）可以激活多种组织中多种蛋白质的生物合成，因此我们进行了实验，比较体外1,25(OH)(2)D-3对4周维生素D-3缺乏大鼠和正常大鼠朗格汉氏胰岛胰岛素分泌和生物合成的影响。胰岛在不同浓度的1,25(OH)(2)D-3 (10(-12) M)（在对照中无活性）至10(-6)M的诱导期后孵育或灌注6小时。实验在未标记的氨基酸混合物中进行，以促进蛋白质合成。在葡萄糖刺激过程中加入氚化酪氨酸作为示踪剂。新合成的蛋白质用[H-3]酪氨酸标记，用酸醇法提取，并用适用于低分子量蛋白质的凝胶色谱法分离。即使在氨基酸混合物存在的情况下，胰岛对16.7 mM葡萄糖的胰岛素反应也因维生素D-3缺乏而降低，并因1,25(OH)(2)D-3而改善。这种有益的效果并不发生在基础条件下，而只发生在葡萄糖刺激期间，并且在胰岛素释放的两个阶段都观察到。此外，这些作用在5 × 10(-4) M环己亚胺（一种蛋白质生物合成抑制剂）存在下消失。维生素d -3缺乏大鼠的胰岛显示出新生生物合成蛋白和[H-3]酪氨酸标记的胰岛素和胰岛素原组分的数量普遍减少。1,25(OH)(2)D-3诱导6小时显著提高了新生生物合成蛋白的数量，特别是在2小时葡萄糖刺激下新合成的胰岛素。计算新合成的原胰岛素样物质转化为胰岛素的速率为[H-3]胰岛素/[H-3]原胰岛素样物质的比值，为1,25(OH)(2)D-3诱导的剂量依赖性增加提供了证据，可能超过正常胰岛的水平。这些数据支持了这样的假设，即1,25(OH)(2)D-3在体外不仅促进了β细胞的生物合成能力——在16.7 mm的葡萄糖刺激下，通过胰岛蛋白生物合成的全局激活，β细胞的生物合成能力得到了高度诱导——而且还加速了胰岛素原向胰岛素的转化。
Because 1,25 dihydroxyvitamin D-3 (1,25(OH)(2)D-3) is known to activate the biosynthesis of numerous proteins in various tissues, experiments were undertaken to compare the influence of 1,25(OH)(2)D-3 in vitro on both the secretion and biosynthesis of insulin in islets of Langerhans from both 4-week vitamin D-3-deficient rats and normal rats. Islets were either incubated or perifused after a 6-h induction period in the presence of various concentrations of 1,25(OH)(2)D-3 from 10(-12) M, which was inactive in controls, to 10(-6) M. Experiments were performed in the presence of a non-labelled amino acid mixture, to favour protein synthesis. Tritiated tyrosine was added as tracer during glucose stimulation. The newly synthesised proteins, labelled with [H-3]tyrosine, were extracted by an acid-alcohol method and separated by gel chromatography adapted for low-molecular-weight proteins. Even in the presence of the amino acid mixture, the insulin response of the islets to 16.7 mM glucose was decreased by vitamin D-3 deficiency and improved by 1,25(OH)(2)D-3. This beneficial effect did not occur in basal conditions, but only during glucose stimulation, and was observed in both phases of insulin release. Moreover, these effects disappeared in the presence of 5 x 10(-4) M cycloheximide, a protein biosynthesis inhibitor. Islets from vitamin D-3-deficient rats exhibited a general decrease in the amount of ne nova biosynthesised proteins and of [H-3]tyrosine-labelled insulin and proinsulin fractions. A 6-h period of 1,25(OH)(2)D-3 induction significantly improved the amount of ne novo biosynthesised proteins, and particularly of newly synthesised insulin in response to a 2-h glucose stimulation. Calculation of the rate of conversion of newly synthesised proinsulin-like material to insulin as the [H-3]insulin/[H-3]proinsulin-like material ratio provided evidence for a dose-dependent increase, induced by 1,25(OH)(2)D-3 that could exceed that of normal islets. These data support the hypothesis that 1,25(OH)(2)D-3 in vitro not only facilitated the biosynthetic capacity of the beta cell - which was highly induced during a 16.7-mM glucose stimulation, via a global activation of islets protein biosynthesis - but also produced an acceleration of the conversion of proinsulin to insulin.