HNF4A Regulates the Formation of Hepatic Progenitor Cells from Human iPSC-Derived Endoderm by Facilitating Efficient Recruitment of RNA Pol II.

Elucidating the molecular basis of cell differentiation will advance our understanding of organ development and disease. We have previously established a protocol that efficiently produces cells with hepatocyte characteristics from human induced pluripotent stem cells. We previously used this cell differentiation model to identify the transcription factor hepatocyte nuclear factor 4 α (HNF4A) as being essential during the transition of the endoderm to a hepatic fate. Here, we sought to define the molecular mechanisms through which HNF4A controls this process. By combining HNF4A chromatin immunoprecipitation (ChIP) followed by high-throughput DNA sequencing (ChIP-seq) analyses at the onset of hepatic progenitor cell formation with transcriptome data collected during early stages of differentiation, we identified genes whose expression is directly dependent upon HNF4A. By examining the dynamic changes that occur at the promoters of these HNF4A targets we reveal that HNF4A is essential for recruitment of RNA polymerase (RNA pol) II to genes that are characteristically expressed as the hepatic progenitors differentiate from the endoderm.

A Drug Screen using Human iPSC-Derived Hepatocyte-like Cells Reveals Cardiac Glycosides as a Potential Treatment for Hypercholesterolemia.

Efforts to identify pharmaceuticals to treat heritable metabolic liver diseases have been hampered by the lack of models. However, cells with hepatocyte characteristics can be produced from induced pluripotent stem cells (iPSCs). Here, we have used hepatocyte-like cells generated from homozygous familial hypercholesterolemia (hoFH) iPSCs to identify drugs that can potentially be repurposed to lower serum LDL-C. We found that cardiac glycosides reduce the production of apolipoprotein B (apoB) from human hepatocytes in culture and the serum of avatar mice harboring humanized livers. The drugs act by increasing the turnover of apoB protein. Analyses of patient medical records revealed that the treatment of patients with cardiac glycosides reduced serum LDL-C levels. These studies highlight the effectiveness of using iPSCs to screen for potential treatments for inborn errors of hepatic metabolism and suggest that cardiac glycosides could provide an approach for reducing hepatocyte production of apoB and treating hypercholesterolemia.

Parvovirus b19 DNA CpG dinucleotide methylation and epigenetic regulation of viral expression.

CpG DNA methylation is one of the main epigenetic modifications playing a role in the control of gene expression. For DNA viruses whose genome has the ability to integrate in the host genome or to maintain as a latent episome, a correlation has been found between the extent of DNA methylation and viral quiescence. No information is available for Parvovirus B19, a human pathogenic virus, which is capable of both lytic and persistent infections. Within Parvovirus B19 genome, the inverted terminal regions display all the characteristic signatures of a genomic CpG island; therefore we hypothesised a role of CpG dinucleotide methylation in the regulation of viral genome expression.The analysis of CpG dinucleotide methylation of Parvovirus B19 DNA was carried out by an aptly designed quantitative real-time PCR assay on bisulfite-modified DNA. The effects of CpG methylation on the regulation of viral genome expression were first investigated by transfection of either unmethylated or in vitro methylated viral DNA in a model cell line, showing that methylation of viral DNA was correlated to lower expression levels of the viral genome. Then, in the course of in vitro infections in different cellular environments, it was observed that absence of viral expression and genome replication were both correlated to increasing levels of CpG methylation of viral DNA. Finally, the presence of CpG methylation was documented in viral DNA present in bioptic samples, indicating the occurrence and a possible role of this epigenetic modification in the course of natural infections.The presence of an epigenetic level of regulation of viral genome expression, possibly correlated to the silencing of the viral genome and contributing to the maintenance of the virus in tissues, can be relevant to the balance and outcome of the different types of infection associated to Parvovirus B19.

Evidence of human bocavirus viremia in healthy blood donors.

Human bocavirus DNA was detected by means of a quantitative, real-time polymerase chain reaction at low levels in the 5.51% of sera obtained from healthy blood donors, suggesting that viral detection in blood is not necessarily associated with disease status.