Histone Acetylation Regulates Intracellular pH

Differences in global levels of histone acetylation occur in normal and cancer cells although the reason why cells regulate these levels has been unclear Here we demonstrate a role for histone acetylation in regulating intracellular pH (pH(i)) As pH(i) decreases histones are globally deacetylated by histone deacetylases (HDACs) and the released acetate anions are coexported with protons out of the cell by monocarboxylate transporters (MCTs) preventing further reductions in pH(i) Conversely global histone acetylation increases as pH(i) rises such as when resting cells are induced to proliferate Inhibition of HDACs or MCTs decreases acetate export and lowers pH(i) particularly compromising pH(i) maintenance in acidic environments Global deacetylation at low pH is reflected at a genomic level by decreased abundance and extensive redistribution of acetylation throughout the genome Thus acetylation of chromatin functions as a rheostat to regulate pH(i) with important implications for mechanism of action and therapeutic use of HDAC inhibitor

Enrichment of Pluripotent Stem Cell-Derived Hepatocyte-Like Cells by Ammonia Treatment

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) are potential resources for the regeneration of defective organs, including the liver. However, some obstacles must be overcome before this becomes reality. Undifferentiated cells that remain following differentiation have teratoma-forming potential. Additionally, practical applications require a large quantity of differentiated cells, so the differentiation process must be economical. Here we describe a DNA microarray-based global analysis of the gene expression profiles of differentiating human pluripotent stem cells. We identified differences and commonalities among six human pluripotent stem cell lines: the hESCs KhES1, KhES2, KhES3, and H1, and the iPSCs 201B7 and 243G1. Embryoid bodies (EBs) formed without requiring supplementation with inducing factors. EBs also expressed some liver-specific metabolic genes including the ammonia-metabolizing enzymes glutamine synthetase and carbamoyl-phosphate synthase 1. Real-time PCR analysis revealed hepatocyte-like differentiation of EBs treated with ammonia in Lanford medium. Analysis of DNA microarray data suggested that hepatocyte-like cells were the most abundant population in ammonia-treated cells. Furthermore, expression levels of undifferentiated pluripotent stem cell markers were drastically reduced, suggesting a reduced teratoma-forming capacity. These results indicate that treatment of EBs with ammonia in Lanford medium may be an effective inducer of hepatic differentiation in absence of expensive inducing factors

Identification of small molecules for human hepatocyte expansion and iPS differentiation

Cell-based therapies hold the potential to alleviate the growing burden of liver diseases. Such therapies require human hepatocytes, which, within the stromal context of the liver, are capable of many rounds of replication. However, this ability is lost ex vivo, and human hepatocyte sourcing has limited many fields of research for decades. Here we developed a high-throughput screening platform for primary human hepatocytes to identify small molecules in two different classes that can be used to generate renewable sources of functional human hepatocytes. The first class induced functional proliferation of primary human hepatocytes in vitro. The second class enhanced hepatocyte functions and promoted the differentiation of induced pluripotent stem cell–derived hepatocytes toward a more mature phenotype than what was previously obtainable. The identification of these small molecules can help address a major challenge affecting many facets of liver research and may lead to the development of new therapeutics for liver diseases. Chronic liver disease affects more than 500 million people worldwide 1. Most treatments are palliative; the only therapy shown to directly alter outcome and prevent mortality is organ transplantation, but its utility is limited by a persistent shortage of donor organs 2. Cell-based therapies, such as cell transplantation, engineered hepatocellular tissue constructs and bioartificial live