Ohlsson Lena, Hjelte Lena, Hühn Michael, Scholte Bob J, Wilke Martina, Flodström-Tullberg Malin, Nilsson Ake
Department of Clinical Sciences, Medicine (Gastroenterology and Nutrition), Lund University Hospital, Lund, Sweden.
J Pediatr Gastroenterol Nutr. 2008 Nov;47(5):547-54. doi: 10.1097/MPG.0b013e3181826daf.
The intestinal brush border enzymes alkaline sphingomyelinase (alk-SMase) and neutral ceramidase (CDase) digest milk sphingomyelin in suckling neonates. In addition, alk-SMase, CDase, and acid sphingomyelinase (acid-SMase) have been implicated in sphingolipid signaling, which exhibits abnormalities in cystic fibrosis (CF). In this study, we tested the hypothesis that the expression of these enzymes is different in CF.
We used mice with F508del (Cftr) mutation, a CF mouse model with well-characterized intestinal pathology. Enzyme activities were measured using radiolabeled sphingolipid substrates incubated with tissue homogenates from different organs and intestinal contents of wild-type mice, homozygous, and heterozygous F508del mice.
No difference was found in levels of CDase and alk-SMase in the small intestinal mucosa or in their longitudinal distribution. Acid-SMase activity was significantly lower in the mucosa of the distal half of the small intestine of F508del compared with wild-type mice. Despite a lower body weight of F508del mice, length and weight of the small intestine and weight per centimeter of colon were larger than in wild-type. Neutral CDase and alk-SMase activities in lungs were lower than in the gut, whereas acid-SMase activity was comparable in both organs. CDase activity in the spleen was significantly higher in F508del than in wild-type mice.
Alk-SMase and neutral CDase are normally expressed in F508del CF mice, whereas activity of acid-SMase in the distal small intestine is decreased. We found no differences in activity of these enzymes in lungs in this mouse model.
肠道刷状缘酶碱性鞘磷脂酶（alk-SMase）和中性神经酰胺酶（CDase）可消化哺乳新生儿的乳鞘磷脂。此外，alk-SMase、CDase和酸性鞘磷脂酶（acid-SMase）参与鞘脂信号传导，而该信号传导在囊性纤维化（CF）中存在异常。在本研究中，我们检验了CF中这些酶的表达存在差异这一假设。
我们使用了具有F508del（Cftr）突变的小鼠，这是一种具有特征明确的肠道病理学特征的CF小鼠模型。使用与来自不同器官的组织匀浆以及野生型小鼠、纯合和杂合F508del小鼠的肠内容物一起孵育的放射性标记鞘脂底物来测量酶活性。
在小肠黏膜中，CDase和alk-SMase的水平及其纵向分布均未发现差异。与野生型小鼠相比，F508del小鼠小肠后半段黏膜中的酸性鞘磷脂酶活性显著降低。尽管F508del小鼠体重较低，但其小肠长度和重量以及结肠每厘米重量均大于野生型小鼠。肺中的中性CDase和alk-SMase活性低于肠道，而酸性鞘磷脂酶活性在两个器官中相当。F508del小鼠脾脏中的CDase活性显著高于野生型小鼠。
alk-SMase和中性CDase在F508del CF小鼠中正常表达，而远端小肠中酸性鞘磷脂酶的活性降低。在该小鼠模型中，我们未发现这些酶在肺中的活性存在差异。
