Epithelial inducible nitric oxide synthase causes bacterial translocation by impairment of enterocytic tight junctions via intracellular signals of Rho-associated kinase and protein kinase C zeta*

Abstract

Epithelial inducible nitric oxide synthase activates two distinct signals, protein kinase C ζ and Rho-associated kinase, to disrupt tight junctions leading to bacterial influx.

Commensal bacterial internalization by epithelial cells: An alternative portal for gut leakiness

“…Bacterial endocytosis by epithelial cells was observed after 6 h of obstruction, whereas TJ damage was seen only after 24 h. 15,29,57 The TJ damage in gut tissues after 24 h of obstruction was evidenced by occludin cleavage, ZO-1 destruction, and increased tissue conductance and macromolecular permeability. 15,29,57 Interestingly, continuous epithelial lining on villus surface with no sign of cell death was found at both time points, ruling out loss of cell viability as a cause of bacterial transcellular passage. Normal crypt/villus ratio was observed after 6 h in comparison to villus blunting without crypt hyperplasia after 24 h, suggesting cell sloughing on villus tip may partly contribute to TJ damage at the later time point.…”

“…[73][74][75] Although the innate immune response as an early warning system is aiming for bacterial elimination, excessive inflammatory and oxidative/nitrosative stress may act as double-edged swords and result in bystander damage to intestinal barrier integrity. Death-dependent TJ disruption or cell death-independent signaling for TJ impairment have been documented in intestinal epithelial cells following exposure to ROS and NO, [27][28][29] as well as IFNg, TNFa, and IL-1b. 21,22,26 We and others demonstrated that bacterial endocytosis by epithelial cells preceded TJ damage under inflammatory stress in a doseand time-dependent manner.…”

“…21,22,26 We and others demonstrated that bacterial endocytosis by epithelial cells preceded TJ damage under inflammatory stress in a doseand time-dependent manner. 15,29,38,57 Therefore, we suspect that bacterial entry through intermicrovillous lipid rafts may trigger activation of intracellular NLRs by the sensing of endosomally derived bacterial structural components (unrelated to virulence factors). The NLRmediated immune responses may adversely cause aggravated inflammatory and oxidative stress, leading to secondary TJ damage in epithelial cells (Fig.…”

“…Numerous studies using epithelial cell lines in vitro have shown that the proinflammatory cytokines, e.g., IFNg, TNFa, and IL-1b, cause TJ disruption without affecting cell viability, 21,22,26 whereas free radicals induce cell death-dependent or -independent TJ disruption. [27][28][29] …”

“…As many previously established models, such as chemically induced colitis and pathogen infection, are confounded by co-existing transcellular and paracellular bacterial influx, we attempted to overcome this limitation by developing novel animal models that displayed transcellular passage of bacteria without TJ disruption. Two models with enteric bacterial dysbiosis (changes in numbers or composition of gut microbiota) were established, including bowel obstruction 15,29,57 and infection with antibiotic-resistant enterobacteria. 16 The bowel obstruction model induced commensal bacterial overgrowth after loop ligation in the distal small intestine.…”