PROJECT SUMMARY Idiopathic pulmonary fibrosis (IPF) is an age related fatal disease with unknown etiology. Its incidence increases with age, environmental effects is important. Epigenetic changes, including DNA methylation and histone modifications, are major causes of age-related diseases. Environmental stressors and aging contribute to histone modifications. Epigenetic modifications are potentially reversible. We and others have established that epigenetic mechanisms participate in the pathogenesis of IPF. Aging may potentiate the susceptibility to environmental stress by modulating pro-fibrotic cellular phenotypes in IPF. However, studies of epigenetic regulation, in particular histone modifications and their related cellular phenotypes in the aging lung and in IPF are lacking. Chromatin structure, which is affected by histone modifications, is an important determinant of the cell phenotype. The active histone mark H4K16Ac epigenetically regulates gene expression. Our preliminary data demonstrated the dysregulation of this histone modification in IPF fibroblasts. We hypothesize that age-related histone modifications, in particular H4K16Ac, mediates fibrotic cell phenotype, promotes senescence and induced apoptosis resistant lung fibroblasts that leads to persistent fibrosis in aging. Targeting this histone modification will alter pro-fibrotic cell phenotypes and promote resolution of fibrosis. Our specific aims are: (1) Determine mechanisms that regulate H4K16Ac in persistent lung fibrosis associated with aging. (2) Determine the role of H4K16Ac in regulating pro-fibrotic phenotypes in fibrotic lung fibroblasts. (3) Determine the efficacy of targeting H416Ac in an aging mice model of persistent lung fibrosis. The proposed studies will define the role of age-related histone modification H4K16Ac in the pathogenesis of IPF, and translate that knowledge to novel therapeutic interventions for pulmonary fibrosis.