成纤维细胞生长因子(FGF)-21是一种重要的肝脏内分泌调节因子,用于葡萄糖和甘油三酸酯的代谢以及骨重塑。以前,FGF家族中的某些肽已经显示出调节穿过肠上皮的钙吸收。由于FGF21受体,即,FGF受体-1在肠上皮细胞中大量表达,FGF21有可能对肠道产生直接作用.在这里,开发了以多克水平大规模生产重组FGF21,以最大程度地减少不同批次之间的差异.在口服葡萄糖耐量试验中,发现重组FGF21可降低高脂饮食小鼠的血浆葡萄糖水平。在Ussing室中应用放射性示踪剂45Ca的一系列实验表明,FGF21增强了低剂量1,25-二羟基维生素D3[10nM1,25(OH)2D3]对跨肠上皮样Caco-2单层的跨上皮钙转运的刺激作用。FGF21+1,25(OH)2D3也降低了跨上皮阻力,但对上皮电位差或短路电流无影响。此外,1,25(OH)2D3单独上调主要根尖钙通道的Caco-2mRNA表达,即,瞬时受体电位香草素亚家族成员6(TRPV6),FGF21和1,25(OH)2D3的组合进一步升高,这与FGF21处理的小鼠肠细胞中TRPV6蛋白表达上调一致。然而,FGF21对电压门控钙通道1.3,calbindin-D9k的mRNA表达没有影响,质膜Ca2+-ATPase1b,claudin-12或claudin-15.总之,FGF21确实通过增强1,25(OH)2D3增强的钙转运对肠上皮细胞发挥直接作用,推测通过上调TRPV6表达。
Fibroblast growth factor (FGF)-21 is a salient liver-derived endocrine regulator for metabolism of glucose and triglyceride as well as bone remodeling. Previously, certain peptides in the FGF family have been shown to modulate calcium absorption across the intestinal epithelia. Since FGF21 receptor, i.e., FGF receptor-1, is abundantly expressed in the enterocytes, there was a possibility that FGF21 might exert direct actions on the intestine. Herein, a large-scale production of recombinant FGF21 at the multi-gram level was developed in order to minimize variations among various batches. In the oral glucose tolerance test, recombinant FGF21 was found to reduce plasma glucose levels in mice fed high-fat diet. A series of experiments applying radioactive tracer 45Ca in Ussing chamber showed that FGF21 potentiated the stimulatory effect of low-dose 1,25-dihydroxyvitamin D3 [10 nM 1,25(OH)2D3] on the transepithelial calcium transport across intestinal epithelium-like Caco-2 monolayer. FGF21 + 1,25(OH)2D3 also decreased transepithelial resistance, but had no effect on epithelial potential difference or short-circuit current. Furthermore, 1,25(OH)2D3 alone upregulated the Caco-2 mRNA expression of the major apical calcium channels, i.e., transient receptor potential vanilloid subfamily member 6 (TRPV6), which was further elevated by a combination of FGF21 and 1,25(OH)2D3, consistent with the upregulated TRPV6 protein expression in enterocytes of FGF21-treated mice. However, FGF21 was without effects on the mRNA expression of voltage-gated calcium channel 1.3, calbindin-D9k, plasma membrane Ca2+-ATPase 1b, claudin-12 or claudin-15. In conclusion, FGF21 did exert a direct action on the intestinal epithelial cells by potentiating the 1,25(OH)2D3-enhanced calcium transport, presumably through the upregulation of TRPV6 expression.