Tu1997 A Novel In Vivo Method to Measure Gastrointestinal Transit in Mice

Abstract

INTRODUCTION The intestine is a significant site of gluconeogenesis, with high expression of glucose 6 phosphatase. Abnormal forms of glycogen, including polyglucosan bodies, occur in the muscularis propria in a subset of patients with gastrointestinal motility disorders. Little is known, however, of the distribution of glycogen metabolic enzymes and related proteins in normal gastrointestinal tract, or effects of deficiencies of these proteins on the bowel. METHODS Key enzymes in glycogen metabolism, including glycogen synthase (GS), glycogen branching enzyme (GBE), malin and laforin were examined in stomach, ileum and colon of two mouse strains and in normal human bowel using immunohistochemistry with semiquantitiative analysis of epithelium, muscle, submucosal and myenteric plexus, validated by western blotting and positive and negative controls. The pathological effects of GBE, laforin and malin gene knockout on mouse gastrointestinal tract were also studied. RESULTS GS was present at high levels in the smooth muscle of muscularis propria, GBE in the majority of large ganglion cells of the submucosal and myenteric plexuses, and laforin and malin in submucosal ganglia. Analysis of human bowel showed no significant regional differences in the distribution of GBE, laforin and malin, GS was more prominent in the muscularis propria of the small intestine, compared with stomach and colon. GBE knockout produced a progressive severe myopathy with numerous polyglucosan bodies and vacuolation. Polyglucosan bodies were also present in both laforin and malin knockout models, but with a less severe phenotype than that seen in the GBE knockout, and were not seen in controls. CONCLUSION The distribution of glycogen metabolic proteins in the bowel wall of mouse and man shows a specific neuromuscular distribution for each pathway component. Defects in glycogen metabolism in mouse knockout models reproduce histological features of polyglucosan body myopathy in human digestive motility disorders.