Study on the immunopathogenesis of experimental Clostridium difficile colitis

Abstract

Clostridium difficile infection (CDI) is currently the leading cause of infectious diarrhea in hospitalized patients. The intense acute inflammatory response appears to be a major factor in causing colonic injury in CDI. An inability to mount a protective immune response to C. difficile appears to underlie susceptibility to recurrent infection. Gaps in our understanding of the immunopathogenesis of CDI present major challenges to the development of better preventive and therapeutic strategies against this problem. Thus, to overcome the resistance of wild-type mice to CDI, we translated our clinical findings to set up antibiotic-proton pump inhibitors (PPI)-associated clostridial colitis in wild-type C57BL/6 mice. We found that no significant signs of CDI were observed in the group without PPI treatment, whereas the group with PPI treatment exhibited diarrhea and signs of weakness. Further, CDI severity was confirmed by measuring clinical signs, such as weight loss, loss of stool consistency, decreased cecum weight, colonic pathology and increased bacterial load, which were shown to mimic CDI on human. Colon histology and the expression of innate immune-related genes were examined and found inflammation was increased, such as neutrophil infiltration, epithelial damage, and inflammatory cytokine genes were increased during CDI, especially after PPI treatment. In addition, the expression of peroxisome proliferator-activated receptor γ (PPARγ), a nuclear receptor prominently expressed in gut, and downstream CD36 was decreased in the colon. Alteration of PPARγ-regulated antimicrobial peptides (AMPs) and goblet cell secreted mucins were observed. PPARγ coactivator-1α (PGC-1α), which was responsible for mitochondrial biogenesis, was also down-regulated. Besides, we also found the expression of PPARγ-regulated Bcl-2 was decreased and apoptotic cells were increased during CDI. Therefore, we hypothesized that down regulation of PPARγ may influence innate immune protective ability, including antimicrobial peptide and mucins, and induce more apoptosis in colon that develop severe CDI. To prove it, we used a PPARγ agonist, Pioglitazone, to protect mice from C. difficile induced inflammation and disease progression through the activation of PPARγ. We monitored the effect of Pioglitazone on CDI by using of NF-κB-dependent luciferase mice. With Pioglitazone treatment, the NF-κB activation-mediated inflammation was decreased and disease progression, loss of ceacum weight, was reversed, implicating PPARγ-targeting therapeutic approaches may pave a way to ameliorate colitis symptoms of CDI.

Date of Award	2013
Original language	English
Supervisor	Pei-Jane Tsai (Supervisor)