Cardiac fibrosis increases with age. Fibroblast activation plays an essential role in cardiac fibrosis. Histone modifications are involved in various chromatin-dependent processes. Attenuation of the histone H3 trimethylation on lysine 27 demethylase UTX by RNA interference or heterozygous mutation extends lifespan in worm. The

Silencing of UTX attenuates aging-associated cardiac fibrosis via blocking cardiac fibroblasts-to-myofibroblasts transdifferentiation and consequently attenuates aging-associated cardiac dysfunction and cardiac fibrosis.

Middle-aged mice (15 months old) were used and started to receive adeno-associated virus-scrambled-small hairpin RNA and adeno-associated virus-UTX-small hairpin RNA every 3 months from 15 months to 21 months, respectively. The mice were euthanized at 24 months of age (length of the study).

Adeno-associated virus-UTX-small hairpin RNA delivery significantly attenu-ated aging-associated increase in blood pressure, especially in diastolic blood pressure, indicating silencing of UTX rescued aging-associated cardiac dysfunction. Aging-associated cardiac fibrosis is characterized by fibroblast activation and abundant extracellular matrix deposition, including collagen deposition and alpha smooth muscle actin activation. Silencing of UTX abolished collagen deposition and alpha smooth muscle actin activation, decreased serum transforming growth factor β, blocked cardiac fibro blast s-to- myofi brobl asts trans-differentiation by elevation of cardiac resident mature fibroblast markers, TCF21, and platelet-derived growth factor receptor alpha, which are important proteins for maintaining cardiac fibroblast physiological function. In the mechanistic study, adeno-associated virus-UTX-small hairpin RNA blocked transforming growth factor β-induced cardiac fibro blast s-to- myofi brobl asts trans-differentiation in isolated fibroblasts from 24-month-old mouse heart. The same results demonstrated as the in vivo study. Conclusions: Silencing of UTX attenuates aging-associated cardiac fibrosis via blocking cardiac fibroblasts-to-myofibroblasts transdifferentiation and consequently attenuates aging-associated cardiac dysfunction and cardiac fibrosis.