Gastroenterology and Nutrition Laboratory, Biomedical Center B11, Lund University, S-221 84 Lund, Sweden.
J Lipid Res. 2011 Apr;52(4):771-81. doi: 10.1194/jlr.M012880. Epub 2010 Dec 21.
Alkaline sphingomyelinase (alk-SMase) hydrolyses sphingomyelin (SM) to ceramide in the gut. To evaluate the physiological importance of the enzyme, we generated alk-SMase knockout (KO) mice by the Cre-recombinase-Locus of X-over P1(Cre-LoxP) system and studied SM digestion. Both wild-type (WT) and KO mice were fed ³H-palmitic acid labeled SM together with milk SM by gavage. The lipids in intestinal content, intestinal tissues, serum, and liver were analyzed by TLC. In KO mice, nondigested ³H-SM in the intestinal content increased by 6-fold and the formation of ³H-ceramide decreased markedly, resulting in 98% reduction of ³H-ceramide/³H-SM ratio 1 h after gavage. The absorbed ³H-palmitic acid portion was decreased by 95%. After 3 h, a small increase in ³H-ceramide was identified in distal intestine in KO mice. In feces, ³H-SM was increased by 243% and ceramide decreased by 74% in the KO mice. The KO mice also showed significantly decreased radioactivity in liver and serum. Furthermore, alkaline phosphatase activity in the mucosa was reduced by 50% and histological comparison of two female littermates preliminarily suggested mucosal hypertrophy in KO mice. This study provides definite proof for crucial roles of alk-SMase in SM digestion and points to possible roles in regulating mucosal growth and alkaline phosphatase function.
碱性鞘磷脂酶 (alk-SMase) 在肠道中将鞘磷脂 (SM) 水解为神经酰胺。为了评估该酶的生理重要性，我们通过 Cre 重组酶 - X 染色体上的交叉位点 1（Cre-LoxP）系统生成了 alk-SMase 敲除 (KO) 小鼠，并研究了 SM 的消化。将 ³H-棕榈酸标记的 SM 和牛奶 SM 通过灌胃给予野生型 (WT) 和 KO 小鼠。通过 TLC 分析肠道内容物、肠道组织、血清和肝脏中的脂质。在 KO 小鼠中，肠道内容物中未消化的 ³H-SM 增加了 6 倍，³H-神经酰胺的形成明显减少，导致灌胃 1 小时后 ³H-神经酰胺/³H-SM 比值降低 98%。吸收的 ³H-棕榈酸部分减少了 95%。3 小时后，在 KO 小鼠的远端肠道中发现 ³H-神经酰胺略有增加。在粪便中，KO 小鼠的 ³H-SM 增加了 243%，神经酰胺减少了 74%。KO 小鼠的肝脏和血清中的放射性也显著降低。此外，黏膜中的碱性磷酸酶活性降低了 50%，对两名雌性同窝仔鼠的组织学比较初步表明 KO 小鼠的黏膜肥大。这项研究为 alk-SMase 在 SM 消化中的关键作用提供了明确的证据，并指出其在调节黏膜生长和碱性磷酸酶功能方面可能具有作用。
