Expression and Activity of Histone Deacetylases in Human Asthmatic Airways

Asthma is a chronic inflammatory disease that is characterized by increased expression of multiple inflammatory genes. Chromatin modification plays a critical role in the regulation of these genes. Acetyaltion of histones by histone acetyltransferases (HATs) is associated with increased gene transcription, whereas hypocetylation induced by histone deacetylases (HDACs) is associated with suppression of gene expression. We have examined the expression and activity of HATs and HDACs in bronchial biopsies from normal subjects and subjects with asthma. There was no difference in the site of HDAC1–HDAC6 expression between normal subjects and subjects with asthma, but subjects with asthma had reduced HDAC enzymatic activity and reduced HDAC1 and HDAC2 protein expression, as measured by Western blotting. In contrast, subjects with asthma treated with inhaled steroids were found to have greater HDAC activity than untreated subjects with asthma, although still lower than control subjects. In contrast, although there was no change in the site of HAT (CREB binding protein and p300/CREB binding protein–associated factor) expression, HAT activity was increased in subjects with asthma. HAT activity was reduced to control levels in subjects with asthma treated with inhaled steroids. The increase in HAT activity and reduced HDAC activity in asthma may underlie the increased expression of multiple inflammatory genes, and this is reversed, at least in part, by treatment with inhaled steroids.