In chronic obstructive pulmonary diseases, a profound loss of HDAC2 has been reported, which may mediate the upregulation of inflammatory genes and lower responses to steroids.38 In Parkinson's disease, hyperacetylation of H3 or H4 are the key findings in dopaminergic neurons, which may promote neuronal apoptosis.20 Nickels et al.39,40 showed that HDAC3 and 4 participate in retinal ganglion cell apoptosis in experimental models of glaucoma. Here, HDAC2 is linked to chronic obstructive pulmonary disease.