Pro-inflammatory Cytokines Alter Tight Junction Structure/Function in Par-C10 Cells

Sjögren's syndrome (SS) is an autoimmune disorder characterized by inflammation and dysfunction of lacrimal and salivary glands, resulting in decreased tear and saliva secretion. Although levels of the pro-inflammatory cytokines tumor necrosis factor-α (TNFα) and interferon-γ (IFNg) are elevated in plasma and in salivary gland biopsies from patients with SS, little is known about the effects of cytokines on salivary gland epithelium, particularly with respect to the integrity of tight junctions (TJs). Objectives: To determine if pro-inflammatory cytokines alter TJ integrity in rat parotid gland Par-C10 cell monolayers. Methods: Trans-epithelial resistance (TER) was measured with an epithelial volt-ohmeter. Short-circuit current (Isc) was measured in Par-C10 cell monolayers using an Ussing chamber. Increases in the intracellular calcium concentration, [Ca²⁺]_i, were quantified in Par C-10 cells using Fura-2 fluorescence. Freeze-fracture electron microscopy was used to evaluate TJ morphology in Par-C10 cell monolayers. Western blot analysis was used to detect expression of TJ proteins in Par-C10 cells. Results: The SS-associated pro-inflammatory cytokines TNFα and IFNγ decreased TER and carbachol- and UTP-induced Isc in Par-C10 monolayers. However, carbachol- and UTP-induced increases in [Ca²⁺]_i were unaltered by TNFα and IFNγ. Additionally, TNFα and IFNγ treatment of Par-C10 monolayers for 48 h altered TJ morphology and decreased the expression of the TJ protein, claudin-1. Conclusion: TNFα and IFNγ alter TJ morphology and protein expression in Par-C10 monolayers, associated with decreases in the transepithelial resistance and carbachol- and UTP-induced Isc. These results suggest that chronic inflammation induced by cytokines in salivary glands of SS patients could affect secretory function by altering TJ integrity. Supported by NIH-NIDCR grants R01DE017591-01, R01DE07389-19, K08DE017633-01 and a Sjögren's Syndrome Foundation Research Grant.