Urinary tract infections (UTIs) account for the second most common bacterial infections in man. Most ofthese infections are caused by E.coli which have a distinct mechanism for entry into the highlyimpregnable superficial epithelium of the bladder. While investigating molecular aspects of howuropathogenic E.coli (UPEC) enter bladder epithelial cells (BECs), we observed that infected BECshave a powerful and largely overlooked capacity to exocytose most of the infecting UPEC without lossof cellular viability. These observations point to a powerful capacity of BECs to sense intracellularbacteria and initiate bacterial expulsion activities. Using biochemical and molecular approaches, wehave identified a distinct mechanism in BECs that are capable of recognizing intracellular UPECinvolving the imunosurveillance molecule, Toll like Receptor (TLR)4. We have also identified severalkey mediators of bacterial exocytosis which include components of the exocyst complex a RabGTPase, Rab11 and the SNARE complex. Additionally, we have implicated cellular components in lipidraft compartments not traditionally associated in exocytic processes in the extrusion of bacteria throughthe plasma membrane. Studies to examine how these various signaling components and pathwaysintegrate and achieve bacterial expulsion could provide valuable clues on how to therapeuticallymaximize bacterial expulsion mechanisms in the bladder. In this proposal, we plan to confirm andextend these observation in the following specific Aims: (i) Elucidate the mechanism by which TLR4senses intravesicular E. coli in BECs. (ii) Investigate how exocyst complex and vesicular traffickingelements promote bacterial expulsion. (iii) Determine the contribution of SNARE complex to themembrane fusion and apical bacteria discharge. (iv) Identify components in cellular lipid raft fractionsinvolved in bacterial expulsion.
Recently we discovered that bladder epithelial cells have the innate unique capacity to expel infecting uropathogenic E.coli. We propose to examine how bladder epithelial cells sense intracellular E.coli and mediate bacterial expulsion without loss of cell viability. These studies are directed at an overlooked aspect of the host cell's innate immune response and could potentially lead to the development of novel strategies to combat urinary tract infections.
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