Study on Clostridium difficile-induced inflammasome activation

Abstract

Clostridium difficile infection (CDI) is the major leading cause of nosocomial infection in hospitalized patients with long-term antibiotic treatment. An excessive host inflammatory response is believed to be the major mechanism in pathogenesis of C. difficile infection and various proinflammatory cytokines such as IL-1β are detected in patients with C. difficile infection. IL-1β is known to be processed by caspase-1, a cysteine protease regulated by a protein complex called inflammasome, which leads to a specialized form of cell death, pyroptosis. However, the precise mechanism of C. difficile induced- inflammasome activation is still controversial and unclear. Thus, the specific aim of this study is to assess the role of inflammasome and its detail mechanism during C. difficile infection. First, we found that caspase-1 dependent IL-1β production was induced by C. diffiicle in peritoneal macrophages, and increased in a dose- and time-dependently manner under aerobic condition. Moreover, intracellular toxigenic C. diffiicle is essential to P2X7–dependent inflammasome activation and subsequent caspase-1-dependent pyroptotic cell death leading to loss of membrane integrity and release of intracellular contents, such as LDH and HMGB1. Notably, we also observed bacteria were released from pyroptotic cells. In addition, the mRNA expression of pro-IL-1β and IL-1β production was significantly reduced in MyD88-/-, Tlr2-/- and Tlr2-/-/Tlr4-/- cells, whereas comparable in Tlr4-/- cells compared with wild-type cells. Finally, to investigate the role of inflammasome in vivo, we found that colonic inflammasome activation was also induced by CDI, and caspase-1 inhibition led to less intestinal inflammation and increased load of C. difficile. Taken together, our study suggested that MyD88-mediated TLR2 signaling was involved in pro-IL-1β production and intracellular toxigenic C. diffiicle induced following P2X7- dependent inflammasome activation and pyroptosis which may act as an important regulation in host defence during C. difficile infection.

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