SUMMARY The bacterial CRISPR-Cas9 system has emerged as an effective tool for sequence-specific gene knockout through non-homologous end joining (NHEJ), but it remains inefficient for precise editing of genome sequences. Here we develop a reporter-based screening approach for high-throughput identification of chemical compounds that can modulate precise genome editing through homology-directed repair (HDR). Using our screening method, we have identified small molecules that can enhance CRISPR-mediated HDR efficiency, 3-fold for large fragment insertions and 9-fold for point mutations. Interestingly, we have also observed that a small molecule that inhibits HDR can enhance frame shift insertion and deletion (indel) mutations mediated by NHEJ. The identified small molecules function robustly in diverse cell types with minimal toxicity. The use of small molecules provides a simple and effective strategy to enhance precise genome engineering applications and facilitates the study of DNA repair mechanisms in mammalian cells.

Metabolism has been shown to integrate with epigenetics and transcription to modulate cell fate and function. Beyond meeting the bioenergetic and biosynthetic demands of T-cell differentiation, whether metabolism might control T-cell fate by an epigenetic mechanism is unclear. Here, through the discovery and mechanistic characterization of a small molecule, (aminooxy)acetic acid, that reprograms the differentiation of T helper 17 (T17) cells towards induced regulatory T (iT) cells, we show that increased transamination, mainly catalysed by GOT1, leads to increased levels of 2-hydroxyglutarate in differentiating T17 cells. The accumulation of 2-hydroxyglutarate resulted in hypermethylation of the Foxp3 gene locus and inhibited Foxp3 transcription, which is essential for fate determination towards T17 cells. Inhibition of the conversion of glutamate to α-ketoglutaric acid prevented the production of 2-hydroxyglutarate, reduced methylation of the Foxp3 gene locus, and increased Foxp3 expression. This consequently blocked the differentiation of T17 cells by antagonizing the function of transcription factor RORγt and promoted polarization into iT cells. Selective inhibition of GOT1 with (aminooxy)acetic acid ameliorated experimental autoimmune encephalomyelitis in a therapeutic mouse model by regulating the balance between T17 and iT cells. Targeting a glutamate-dependent metabolic pathway thus represents a new strategy for developing therapeutic agents against T17-mediated autoimmune diseases.

Summary It was recently shown that mouse fibroblasts could be reprogrammed into cells of a cardiac fate by forced expression of multiple transcription factors and microRNAs. To ultimately apply such reprogramming strategy for cell-based therapy or in vivo cardiac regeneration, reducing or eliminating the genetic manipulations by small molecules would be highly desirable. Here, we report the identification of a defined small-molecule cocktail that enables highly efficient conversion of mouse fibroblasts into cardiac cells with only one transcription factor, Oct4, without entering the pluripotent state. Small-molecule-induced cardiomyocytes spontaneously contract and exhibit a ventricular phenotype. Furthermore, such induced cardiomyocytes under our condition pass through a cardiac progenitor stage. This study lays the foundation for future pharmacological reprogramming approaches and provides a novel small-molecule condition to investigate the mechanisms underlying cardiac reprogramming process.

SUMMARY Stem cell-based approaches to cardiac regeneration are increasingly viable strategies for treating heart failure. Generating abundant and functional autologous cells for transplantation in such a setting, however, remains a significant challenge. Here, we isolated a cell population with extensive proliferation capacity and restricted cardiovascular differentiation potentials during cardiac transdifferentiation of mouse fibroblasts. These induced expandable cardiovascular progenitor cells (ieCPCs) proliferated extensively for more than 18 passages in chemically defined conditions, with 105 starting fibroblasts robustly producing 1016 ieCPCs. ieCPCs expressed cardiac signature genes and readily differentiated into functional cardiomyocytes (CMs), endothelial cells (ECs), and smooth muscle cells (SMCs) in vitro, even after long-term expansion. When transplanted into mouse hearts following myocardial infarction, ieCPCs spontaneously differentiated into CMs, ECs, and SMCs and improved cardiac function for up to 12 weeks after transplantation. Thus, ieCPCs are a powerful system to study cardiovascular specification and provide strategies for regenerative medicine in the heart.