Epigenetic Enzymes, Age, and Ancestry Regulate the Efficiency of Human iPSC Reprogramming

Epigenetic enzymes regulate higher-order chromatin architecture and cell-type specific gene expression. The ATPase BRG1 and the SWI/SNF chromatin remodeling complex are epigenetic enzymes that regulate chromatin accessibility during steady and transitional cell states. Experiments in mice show that the loss of BRG1 inhibits cellular reprogramming, while studies using human cells demonstrate that the overexpression of BRG1 enhances reprogramming. We hypothesized that the variation of SWI/SNF subunit expression in the human population would contribute to variability in the efficiency of induced pluripotent stem cells (iPSC) reprogramming. To examine the impact of an individual's sex, ancestry, and age on iPSC reprogramming, we created a novel sex and ancestry balanced cohort of 240 iPSC lines derived from human dermal fibroblasts (DF) from 80 heathy donors. We methodically assessed the reprogramming efficiency of each DF line and then quantified the individual and demographic-specific variations in SWI/SNF chromatin remodeling proteins and mRNA expression. We identified BRG1, BAF155, and BAF60a expression as strongly correlating with iPSC reprogramming efficiency. Additionally, we discovered that high efficiency iPSC reprograming is negatively correlated with donor age, positively correlated with African American descent, and uncorrelated with donor sex. These results show the variations in chromatin remodeling protein expression have a strong impact on iPSC reprogramming. Additionally, our cohort is unique in its large size, diversity, and focus on healthy donors. Consequently, this cohort can be a vital tool for researchers seeking to validate observational results from human population studies and perform detailed mechanistic studies in a controlled cell culture environment. Stem Cells 2018;36:1697-1708.