Mechanism of Prion Protein Absorption from Digestive Tract in Calves

虽然有研究表明，异常的朊蛋白从肠黏膜被吸收并感染许多牛海绵状脑病（BSE）动物，但其具体机制尚不清楚。本研究采用翻转袋法和Ussing室法，研究了用辣根过氧化物酶（HRP）代替异常朊蛋白在兔、羊和荷斯坦犊牛十二指肠、空肠、回肠和结肠等分离节段的吸收及其机制。我们还通过免疫化学方法和扫描电镜观察了Peyer’s patches中M细胞的形态学特征。1)犊牛的十二指肠、空肠和回肠中HRP的吸收高于结肠，13周龄时HRP的吸收高于4周龄。2)家兔回肠对HRP的吸收倾向大于结肠，并与年龄、肠道、H^+梯度和Na^+/K^+- atp酶活性有关。3)犊牛6周龄时空肠和回肠对HRP的吸收高于15周龄，且培养基pH从7.4降至5.4显著降低了HRP的吸收。阿米洛利的加入也显著增加，但瓦巴因没有。4)在犊牛空肠上皮中，随着瘤胃功能的发展，M细胞增加了细胞数量，促进了细胞分化，加快了对大分子的吸收能力。这些发现有力地表明，在断奶后，异常朊蛋白的吸收可能发生在小肠，主要是回肠。

Although it has been suggested that abnormal Prion proteins are absorbed from the intestinal mucosa and infect many animal species with bovine spongiform encephalopathy (BSE), the detailed mechanisms remain clarified. The aim of the present study was to investigate Horseradish peroxidase (HRP) absorption, in which HRP was used instead of abnormal Prion proteins, and its mechanism in isolated segments of the duodenum, jejunum, ileum and colon from rabbits, sheep and Holstein calves by the methods with everted sacks and the Ussing chamber. We also observed morphological features of M cells in Peyer's patches by the immunochemical method and SEM.1)In calves, the HRP absorption was greater in the duodenum, jejunum and ileum than in the colon, and also was greater at the age of 13 weeks than at 4 weeks.2)In rabbits, the HRP absorption showed a tendency to be greater in the ileum than in the colon, and was dependent on aging, the intestine, H^+ gradient and Na^+/K^+-ATPase activities.3)In calves, the HRP absorption in the jejunum and ileum was greater at the age of 6 weeks than of 15 weeks, and was significantly decreased by the reduction of the medium pH from 7.4 to 5.4. It was also significantly increased by an addition of amiloride but not by ouabain.4)In the calf jejunal epithelium, it was indicated that M cells increase the cell number and promote the differentiation as the ruminal function develops, and accelerate the ability for absorption of higher molecules.These findings strongly suggest the possibility that the absorption of abnormal Prion proteins occur at the small intestine, mainly the ileum, after weaning.