Chronic exposure to TNF-alpha increases airway mucus gene expression in vivo.

Abstract

Hypersecretion of mucus plays an important role in the pathogenesis and severity of asthma. The primary proteins in mucus are mucin glycoproteins; MUC-5AC is the primary airway mucin gene. The calcium chloride-activated channel gene hCLCA1 (gob-5 in the mouse) has been suggested to increase MUC-5AC gene expression, and both are increased in asthmatic patients and murine models. TNF-alpha increases the expression of these genes in vitro but has not been investigated in vivo. We sought to determine whether TNF-alpha increases gene expression of gob-5 and MUC-5AC and induces mucus cell metaplasia in vivo. Naive BALB/c mice received 50 ng of recombinant murine TNF-alpha (rmTNF-alpha) intratracheally daily for 1, 2, or 3 weeks; another group received the same dose of intratracheal rmTNF-alpha daily for 3 weeks and then alternate-day treatment for 3 additional weeks (total of 6 weeks). AKR mice received 50 ng of rmTNF-alpha intratracheally for 3 or 6 weeks daily. Naive nontreated mice were used as control animals. Airway gene products for gob-5 and MUC-5AC were determined by means of real-time PCR. Lung tissue sections were stained with periodic acid-Schiff/Alcian blue to assess mucus cell metaplasia. rmTNF-alpha significantly increased gene expression of airway gob-5 and MUC-5AC after 2 weeks in the BALB/c mice. There was noticeable mucus staining in all mice treated for at least 3 weeks with TNF-alpha and in 80% of the mice receiving 2 weeks of treatment. After 3 weeks of treatment, the AKR mice also showed increased gob-5 expression. This study demonstrates for the first time that TNF-alpha alone in vivo is sufficient to increase airway mucus gene expression in 2 murine strains.