904 Alterations in stem cell self-renewal in aged human epidermis

Abstract

Global regulation of gene expression is essential for appropriate epidermal stratification. One set of global regulators is the histone deacetylase (HDAC) family; HDACs repress transcription by removing acetyl groups from histones. HDAC inhibitors are used to treat cutaneous malignancies, but broadly inhibit all class I HDAC family members and have side effects. Delineating the activities of individual class I HDACs in the skin will be important for the development of improved therapeutics. To address this, we are using loss of function genetic analyses in mice. We find that epidermal deletion of Hdac3 during embryonic life results in failure to form a functional barrier and perinatal lethality; this phenotype is distinct from that caused by deletion of Hdac1/2 but partially overlaps with the effects of loss of the transcription factor KLF4, suggesting a possible interaction of HDAC3 and KLF4. Transcriptional profiling of Hdac3 and Klf4 embryonic mutant epidermis reveals statistically significant overlap in dysregulated genes, including epidermal differentiation and danger response genes. ChIP-seq experiments identify statistically significant overlap in sites bound by HDAC3 and KLF4, and proximity ligation assays reveal direct HDAC3/KLF4 interaction in suprabasal cells. In vitro data suggest that HDAC3 functions in a complex with NCoR/SMRT. To determine whether HDAC3 function is dependent on interaction with NCoR/SMRT in the epidermis in vivo, we have deleted the genes coding for these proteins. Ncor/Smrt double mutants recapitulate the epidermal barrier defect and gene expression changes observed in Hdac3 mutant epidermis. Intriguingly, total HDAC3 protein is severely decreased in Ncor/Smrt mutant epidermis, demonstrating that NCoR/SMRT function to stabilize HDAC3 in keratinocytes. Together, our data indicate that HDAC3 has distinct functions from HDAC1/2 and associates with KLF4 and NCoR/SMRT to repress gene expression in the developing epidermis.