Crucial role of alkaline sphingomyelinase in sphingomyelin digestion: a study on enzyme knockout mice

• DOI: 10.1194/jlr.m012880
• Publication Date: 2010-12-22T04:36:12Z
• Authors: Yao Zhang; Yajun Cheng; Gert H. Hansen; Lise-Lotte Niels-...; Frank Koentgen; Lena Ohlsson; Åke Nilsson; Rui-Dong Duan
• Keywords: Male; Mice, Knockout; 0301 basic medicine; 0303 health sciences; Genotype; NPP7; QD415-436; Alkaline Phosphatase; Biochemistry; Sphingomyelins; Mice; 03 medical and health sciences; Sphingomyelin Phosphodiesterase; Other Clinical Medicine; Intestine, Small; Animals; Female; hypertrophy; alkaline phosphatase

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.