...To elucidate the potential role of HDAC4 in the regulation of cellular senescence and skin aging, we established oxidative stress- and UV-induced cellular senescence models using primary human dermal fibroblasts (HDFs). RNA sequencing after overexpression or knockdown of HDAC4 in primary HDFs identified candidate molecular targets of HDAC4. Integrative analyses of our current and public mRNA expression profiles identified DNA damage-inducible transcript 4 (DDIT4) as a critical senescence-associated factor regulated by HDAC4. Indeed, DDIT4 and HDAC4 expressions were downregulated during oxidative stress- and UV-induced senescence. HDAC4 overexpression rescued the senescence-induced decrease in DDIT4 and senescence phenotype, which were prevented by DDIT4 knockdown. In addition, DDIT4 overexpression reversed changes in senescence-associated secretory phenotypes and aging-related genes, suggesting that DDIT4 mediates the reversal of cellular senescence via HDAC4. Collectively, our results identify DDIT4 as a promising target regulated by HDAC4 associated with cellular senescence and epigenetic skin aging.