| Popis: |
Aquaporins (AQPs) are water channel proteins which function to increase plasma membrane water permeability in secretory and absorptive cells in response to osmotic gradients. In the lung, AQP1 and AQP5 are expressed at the site of gas exchange. Water movement through the air space-capillary barrier in the distal lung is facilitated by AQP1 in the capillary endothelium and AQP5 in the alveolar epithelium. The overall goal of this thesis was to examine the regulation of distal lung AQPs. First, the regulation of AQP1 and AQP5 expression in the lung was examined under conditions of aberrant fluid handling induced through intratracheal infection of mice with adenovirus. The expression of AQP1 and AQP5 mRNA and protein were significantly decreased in the lungs after adenovirus infection. Immunohistochemical analysis demonstrated that the decreases in AQP1 and AQP5 expression were not localized to regions of overt inflammation but were found throughout the lung. Decreased AQP1 and AQP5 levels during adenoviral infection suggest a role for AQP1 and AQP5 in the abnormal fluid fluxes detected during pulmonary inflammation. The mechanisms underlying this decrease in AQP levels are therefore of considerable interest. We next examined the possible regulation of AQP5 by the proinflammatory cytokine tumor necrosis factor alpha (TNF-α). Treatment of murine lung epithelial (MLE-12) cells in culture with TNF-α resulted in a concentration- and time-dependent decrease in AQP5 mRNA and protein expression. Activation of the p55 TNF-α receptor (TNFR1) with an agonist antibody was sufficient to cause decreased AQP5 expression, demonstrating that the TNF-α effect is mediated through TNFR1. Inhibition of nuclear factor κB (NF-κB) translocation to the nucleus blocked the effect of TNF-α on AQP5 expression, indicating activation of NF-κB is required, while inhibition of extracellular signal-regulated (ERK) or p38 MAP kinases had no effect. These data show that TNF-α decreases AQP5 mRNA and protein expression, and that the molecular pathway for this effect involves TNFR1 and activated NF-κB. The ability of inflammatory cytokines to decrease aquaporin expression may help explain the connection between inflammation and edema and contribute to the development of novel treatments for diseases such as asthma. |
