Nakamura H, Tashiro M, Asaumi H, Nomiyama Y, Kaku M, Watanabe S, Miyamoto T, Otsuki M
Third Department of Internal Medicine, University of Occupational and Environmental Health, Japan, School of Medicine, 1-1 Iseigaoka, Yahatanishi-ku Kitakyushu 807-8555, Japan.
Gut. 2008 Jun;57(6):788-98. doi: 10.1136/gut.2007.119370.
Smad6 is implicated in the inhibition of bone morphogenetic protein signalling. However, the function of Smad6 in the pancreas remains obscure.
To elucidate the unknown function of Smad6, we developed transgenic mice selectively expressing Smad6 in pancreatic acinar cells using a plasmid construct coding rat elastase 1 enhancer/promoter.
Smad6 transgenic mice had no specific distinguishing phenotype such as body weight, pancreatic wet weight and concentrations of pancreatic protein. However, Smad6 transgenic mice reacted to hyperstimulation by caerulein injection or a diet containing 0.5% ethionine. Maximal amylase release stimulated by CCK-8 was significantly decreased in Smad6 transgenic mice acini, and trypsin activities in transgenic mice acini were significantly increased after stimulation of CCK-8. There was no difference in effect of CCK-8 stimulation on the subsequent increase in intracellular free Ca2+ concentration (Ca2+) between wild-type and transgenic mice acini. These findings suggest that reduced pancreatic enzyme secretion was caused by the disorder of its downstream signal transduction pathways in acinar cells. The amino acid sequence at the N-terminus of Smad6 was similar to that of synaptosome-associated protein (SNAP) 25 interacting protein, which plays an important role in regulating exocytosis of pancreatic enzymes in acinar cells. Pancreatic SNAP25 protein levels in transgenic mice were decreased after caerulein-induced pancreatitis.
These results suggest that elevated expression of Smad6 inhibits normal function of SNAP25-interacting protein and SNAP25, reduces amylase secretion in acinar cells, and increases the susceptibility of acinar cells to the onset of pancreatitis.
Smad6参与抑制骨形态发生蛋白信号传导。然而，Smad6在胰腺中的功能仍不清楚。
为阐明Smad6的未知功能，我们使用编码大鼠弹性蛋白酶1增强子/启动子的质粒构建体，培育出在胰腺腺泡细胞中选择性表达Smad6的转基因小鼠。
Smad6转基因小鼠没有如体重、胰腺湿重和胰腺蛋白浓度等特定的显著表型。然而，Smad6转基因小鼠对蛙皮素注射或含0.5%乙硫氨酸的饮食引起的过度刺激有反应。在Smad6转基因小鼠腺泡中，CCK-8刺激引起的最大淀粉酶释放显著降低，CCK-8刺激后转基因小鼠腺泡中的胰蛋白酶活性显著增加。野生型和转基因小鼠腺泡之间，CCK-8刺激对随后细胞内游离Ca2+浓度（[Ca2+]i）增加的影响没有差异。这些发现表明，胰腺酶分泌减少是由腺泡细胞中其下游信号转导通路紊乱所致。Smad6 N端的氨基酸序列与突触体相关蛋白（SNAP）25相互作用蛋白相似，后者在调节腺泡细胞中胰腺酶的胞吐作用中起重要作用。蛙皮素诱导的胰腺炎后，转基因小鼠胰腺中的SNAP25蛋白水平降低。
这些结果表明，Smad6表达升高会抑制SNAP25相互作用蛋白和SNAP25的正常功能，减少腺泡细胞中淀粉酶的分泌，并增加腺泡细胞对胰腺炎发病的易感性。
