Production of ammonium by Helicobacter pylori mediates occludin processing and disruption of tight junctions in Caco-2 cells

Abstract

Tight junctions, paracellular permeability barriers that define epithelial cell polarity, play an essential role in transepithelial transport, cell-cell adhesion and lymphocyte transmigration. They are also important for the maintenance of innate immune defence and intestinal antigen uptake. Ammonium (NH 4 + ) is elevated in the gastric aspirates of Helicobacter pylori-infected patients and has been implicated in the disruption of tight-junction functional integrity and the induction of gastric mucosal damage during H. pylori infection. The precise mechanism of the effect of ammonium and the molecular targets of ammonium in host tissue are not yet identified. To study the effects of ammonium on epithelial tight junctions, the human colon carcinoma cell line Caco-2 was cultured on permeable supports and the transepithelial resistance (TER) was measured at different time intervals following exposure to ammonium salts or H. pylori-derived ammonium. A biphasic response to treatment with ammonium was found. Acute exposure to ammonium salts or NH 3 /NH 4 + derived from urea metabolism by wild-type H. pylori resulted in a 20-30 % decrease in TER. After 24 h, the NH 4 Cl-treated cells showed a partial recovery of TER. In contrast, the control culture, or cultures that were exposed to supernatants derived from urease-deficient H. pylori, showed no significant decrease in TER. Occludin-specific immunoblots revealed the expression of a low-molecular-weight form of occludin of 42 kDa upon NH 3 /NH 4 + exposure. The results indicate that modulation of tight-junction function by H. pylori is ammonium-dependent and linked to the accumulation of a low-molecular-weight and detergent-soluble form of occludin.

Innate Immunity in the Female Reproductive Tract: Role of Sex Hormones in Regulating Uterine Epithelial Cell Protection Against Pathogens

“…Treatments with pathogenic microbes typically have deleterious effects on barrier integrity. Helicobacter pylori, a major cause of ulcers, decreased TER and barrier function in human intestinal epithelial cell lines [36,37]. Similar effects were observed with polarized epithelial cell monolayers treated with rotavirus [38], Salmonella enterica [39], and enteropathogenic Escherichia coli [40].…”

Transcellular Passage of Neisseria meningitidis across a Polarized Respiratory Epithelium

“…There is a distinction between pathogens that utilize a transcellular route to cross epithelial cell monolayers (19) and bacteria that cross by a paracellular route after destruction of cells of the layer or disruption of tight junctions (1,10,18,34,35,40,55,59,68). There is conflicting evidence about the route that the meningococcus takes to traverse the epithelial cell barrier in the nasopharynx.…”

Toxoplasma gondiiInfection Promotes Epithelial Barrier Dysfunction of Caco-2 Cells

“…[30][31][32] TJs act as a semipermeable barrier (or gate) to the paracellular transport of ions, solutes, and water, as well as cells, and are considered to function as a fence that divides apical and basolateral domains of plasma membranes. 33 Several proteins, such as occludin, claudins, and ZOs, are associated and maintain the structure of the TJ.…”