PPARG and microRNA-146 in mucosal immune responses to C. difficile

Clostridium difficile is typically a harmless anaerobic bacterium but recently it has re-emerged as a facultative pathogen that can cause nosocomial diarrhea, colitis and even death. Peroxisome proliferator-activated receptor (PPAR) gamma has been implicated in the prevention of inflammation in autoimmune and infectious diseases; however, its role in the immunoregulatory mechanisms modulating host responses to C. difficile remains largely unknown. To characterize the role of PPAR gamma in C. difficile-associated disease (CDAD), immunity and gut pathology, we used a mouse model of C. difficile infection in wild-type and T cell-specific PPAR gamma null mice. The loss of PPAR gamma in T cells increased disease activity and colonic inflammatory lesions following C. difficile infection. Colonic expression of IL-17 was upregulated and IL-10 downregulated in colons of T cell-specific PPAR gamma null mice. Also, both the loss of PPAR gamma in T cells and C. difficile infection favored Th17 responses in spleen and colonic lamina propria of mice with CDAD. MicroRNA (miRNA)-sequencing analysis and RT-PCR validation indicated that miR-146b was significantly overexpressed in colons of C. difficile-infected mice. We next developed a computational model that predicts the upregulation of miR-146b, downregulation of the PPAR gamma co-activator NCOA4, and PPAR gamma, leading to upregulation of IL-17. Treatment of C. difficile-infected mice with the PPAR gamma agonist pioglitazone ameliorated colitis and suppressed pro-inflammatory gene expression. In conclusion, our data indicates that miRNA-146b and PPAR gamma may be implicated in the regulation of Th17 responses and colitis in C. difficile-infected mice.