Dietary Methionine Restriction Enhances Tight Junction Barrier Functions in Rat Colon but Not Rat Ileum

Dietary methionine restriction (MR) (an 80% reduction of methionine level) has been shown previously to improve tight junctional barrier function in both LLC-PK1 renal epithelial cells (Skrovanek et al., 2008) and rat colonic epithelium (Ramalingam et al., 2010). We investigated to see if this phenomenon also holds in a structurally and functionally distinct gastrointestinal tissue, rat ileum. Rat plasma methionine level started to decrease as early as 1 week on experimental diet and reached a constant level (~20% decrease) from 2 weeks onwards up to 9 weeks. Despite the change in plasma methionine level, we were not able to detect any differences in ileal transepithelial resistance, or paracellular mannitol as well as lactulose transepithelial fluxes between the control and MR groups. Western blot analysis of ileal mucosal scrapes revealed no statistically significant changes in protein abundance of the tight junctional proteins occludin, claudin-1, 2, 3, 4, 5, or 7. Although a prominent improvement was observed on barrier function (and tight junction composition) in rat distal colon following MR, no significant epithelial tight junctional changes were detected in rat distal ileum. Our data suggest that MR may have different effects on TJ composition and barrier function depending on epithelial tissue location and function.