TLR4 Facilitates Translocation of Bacteria across Renal Collecting Duct Cells

Abstract

Uropathogenic Escherichia coli (UPEC) are the most frequent causes of urinary tract infections and pyelonephritis. Renal medullary collecting duct (MCD) cells are the intrarenal site to which UPEC strains prefer to adhere and initiate an inflammatory response, but the ability of UPEC strains to translocate across impermeant MCD cells has not been demonstrated definitively. Here, several UPEC strains adhered to the apical surface and translocated across confluent murine inner MCD cells grown on filters. UPEC strains expressing cytolytic and vacuolating cytotoxins disrupted the integrity of cell layers, whereas noncytolytic UPEC strains passed through the cell layers without altering tight junctions. Apical-to-basal transcellular translocation was dramatically reduced after extinction of Toll-like receptor 4 (TLR4) and the lipid raft marker caveolin-1 by small interfering RNA. Furthermore, disruption of lipid raft integrity by filipin III and methyl-␤-cyclodextrin significantly reduced both the transcellular translocation of UPEC across murine inner MCD cell layers and the stimulation of proinflammatory mediators. Bacterial translocation was also significantly reduced in primary cultures of TLR4-deficient mouse MCD cells compared with MCD cells from wild-type mice. Benzyl alcohol, an anesthetic that enhances membrane fluidity, favored the recruitment of caveolin-1 in lipid rafts and increased the translocation of UPEC across cultured TLR4-deficient MCD cells. These findings demonstrate that the transcellular translocation of UPEC strains across impermeant layers of MCD cells may occur through lipid rafts via a TLR4-facilitated process.

High molecular weight hyaluronic acid: a two‐pronged protectant against infection of the urogenital tract?

“…Cells challenged with UPEC resulted in bacteria being localised to the tight junctions of the urothelium, which over 24 h resulted in a weakened, disrupted epithelial barrier concomitant with UTI pathology. These data endorsed previous observations,39, 40, 41 and supported an UPEC infection mechanism involving manipulation of the paracellular pathway. Tight junction investigation in primary urothelial cells has shown that claudin 3, ZO‐1 and ZO‐1α + are important for the correct functionality of tight junctions in urothelia,42, 43 with the loss of ZO‐1 associated with UPEC infection of bladder epithelia39 and a potential UPEC target.…”

Les cellules du tubule collecteur rénal, régulateurs de la réponse immunitaire au cours des pyélonéphrites

“…L'activation cellulaire dépendante de TLR4 est associée à un recrutement membranaire de la cavéoline 1 des radeaux lipidiques (4) et à une augmentation de la fluidité membranaire (5) favorisant la translocation apicale-basale des bacté-ries vers l'interstitium. MIP-2 : macrophage inflammatory protein-2 ; MCP-1 : macrophage chemotactic protein-1 ; RANTES : regulated on activation normal T-cell expressed and secreted ; TNF : tumor necrosis factor (d'après [15]). …”

“…L'identification des cellules intercalaires comme sites d'adhésion des UPEC et d'initiation de la réponse inflammatoire qui en résulte a conduit à rechercher si les E. coli sont capables de traverser l'épithélium étanche du tubule collecteur rénale. Utilisant plusieurs souches d'UPEC exprimant différents facteurs de virulence, nous avons proposé deux mécanismes d'invasion bactérienne, paracellulaire et transcellulaire [15]. La souche d'UPEC CFT073 exprimant les cytotoxines cytolytiques et vacuolisantes sat (secreted vacuolating cytotoxin) et hlyA (alpha-hemolysin) altère l'inté-grité de l'épithélium (ce qui se traduit par un effondrement de la résistance transépithéliale) et permet le passage paracellulaire des bactéries.…”

“…Deux autres souches d'UPEC (HT7, HT91), n'exprimant pas les facteurs de virulence sat et hlyA, peuvent franchir l'épithélium tubulaire rénal sans altérer l'intégrité des jonctions serrées. Dans ce cas, la translocation transcellulaire des bactéries s'effectue par un mécanisme d'activation cellulaire dépendant de TLR4, induisant le recrutement de radeaux lipidiques à la membrane plasmique, favorisant ainsi le passage transcellulaire des bactéries [15]. La Figure 1 résume les deux mécanismes de passage paracellulaire et transcellulaire des UPEC au travers de l'épithélium du tubule collecteur rénal.…”

Strengths and Limitations of Model Systems for the Study of Urinary Tract Infections and Related Pathologies

“…UPEC-associated adhesins that have been implicated in the formation of biofilms include type 1 pili, F1C pili, S pili, and F9 fimbriae as well as the adhesive autotransporter proteins Ag43, UpaG, UpaB, and UpaH (63)(64)(65)(66)(67)(68)(69)(70). Flagella and thin aggregative amyloid fibers known as curli can also promote biofilm formation by UPEC (63,64,67,70 (80,81). Following entry into host bladder cells, most UPEC cells face one of three fates: (i) they can be quickly returned back to the extracellular environment (82,83), (ii) they can enter into a nonreplicating quiescent state (83)(84)(85), or (iii) they can multiply, forming large intracellular bacterial communities (IBCs) (83,86,87).…”