Human BRD2 impedes pluripotency reprogramming mainly by suppressing lipogenesis

Induction of pluripotent stem cells (iPSCs) from human somatic cells encounters extensive and significant molecular barriers. Our understanding of the reprogramming barriers remains limited. Lipids are the fundamental cellular building blocks, energy sources, nutrition, signaling molecules, and components for protein lipidation. The roles of lipids and lipogenesis in reprogramming are unknown. Here, we proved that BRD2 is a major molecular barrier to human iPSC (HiPSC) reprogramming. Human pluripotent stem cells (hPSCs) displayed a much weaker transcriptional program in matrisome compared to that of the reprogramming starting cells. BRD2 legitimately reprogrammed a set of matrisome and the related genes from the higher somatic to the weaker pluripotent states. BRD2 also suppressed expression of genes in lipogenesis and lipid metabolism in the reprogramming cells. The two rate-limiting enzymes of lipogeneses, SCD and HMGCR, enhanced iPSC reprogramming while chemical inhibition of HMGCR abrogates reprogramming. Critically, the supplementation of lipids rescues BRD2 suppression of reprogramming. ET tail of BRD2 suppresses reprogramming and the transcriptional programs of lipogenesis and lipid metabolism, but positively regulates gene expression of matrisome and the related genes. These discoveries advance our molecular understanding of HiPSC reprogramming, matrisome, and lipogenesis, and improve HiPSC technology. Overall design: We conducted RNA-seq on human fibroblast cells under reprogramming in different conditions. This research focused on different BRD2 conditions including overexpression, shRNA knockdown, CRISPR KO, ET tail deletion, and luciferase shRNA controls. The starting cells for reprogramming is humana BJ fibroblasts. RNA was extracted at early stage of reprogramming (48 hours and 72 hours post transduction). ChIP-seq of BJ fibroblasts transduced with lentiviral vector preparations of shRNA/sgRNA targeting BRD2 gene. Scrambled vector was used as control for shRNA knockdown. For gene disruption, BJ fibroblasts with a dox-inducible Cas9 construct was used. *************************************************************** The table below lists GEO accessions reused/reanalyzed for this study. ***************************************************************