Background & aims: Accumulating evidence indicates that the peroxisome proliferator activated receptor (PPAR)-gamma is a major player in maintaining intestinal mucosa homeostasis, but whether PPAR-gamma is directly involved in probiotic-mediated effects and the molecular events involved in its activation are not known.
Methods: We investigated the role of PPAR-gamma in the immunomodulatory effects of Lactobacillus crispatus M247 on intestinal epithelial cells (IEC) and the role of probiotic-derived H(2)O(2) on PPAR-gamma activity.
Results: L crispatus M247 supplementation in mice significantly increased PPAR-gamma levels and transcriptional activity in the colonic mucosa. L crispatus M247 induced PPAR-gamma nuclear translocation and enhanced transcriptional activity in epithelial (CMT-93) cells, as demonstrated by the increased luciferase activity of a PPAR-gamma-responsive element, PPAR-gamma-responsive gene up-regulation, and reduced activity of an nuclear factor-kappaB-responsive element. Pharmacologic PPAR-gamma inhibition or silencing by small interfering RNA cancelled the L crispatus M247-mediated effects in CMT-93 cells. Because Lactobacillus strains producing little H(2)O(2) failed to activate PPAR-gamma, we investigated the role of L crispatus M247-derived H(2)O(2) in PPAR-gamma activation. L crispatus M247 induced a transient rise in intracellular H(2)O(2) and PPAR-gamma transcriptional activity was cancelled by antioxidant or H(2)O(2) scavenger. Toll-like receptor (TLR)-2 was not required for PPAR-gamma up-regulation mediated by L crispatus M247 in mice, although the protective effects of L crispatus M247 on dextran sodium sulfate-induced colitis were less pronounced in TLR-2(-/-) mice.
Conclusions: L crispatus M247 uses H(2)O(2) as a signal transducing molecule to induce PPAR-gamma activation in IEC, directly modulating epithelial cell responsiveness to inflammatory stimuli.