Keys for maturation of human embryonic stem cell derived hepatocytes may lie in over expression of hepatic maturation genes and epigenetics

The liver is the largest solid organ that performs many vital functions systemically for the body and contains about 13% of the blood at any given time. The vital functions of the liver are attributive to the combined and cooperative functions of the different cell types found within liver tissue. There are two main categories of cell types within the liver; parenchymal and nonparenchymal. Parenchymal cells, also known as hepatocytes, are the primary source of most of the liver's functions, but rely on neighboring and supportive nonparenchymal cells for regulation of their functions. Unfortunately, since hepatocytes are involved in so many vital functions, the systemic functions of the liver can be dramatically affected when hepatocytes become damaged or undergo apoptosis. For this reason, biological researchers have been looking for ways to replace hepatocyte populations as a means to restore the liver's functions. Many researchers, in turn, believe that human embryonic stem cells (hESC) may be the solution. Even though hESCs have shown promise for differentiating into hepatocytes, producing a mature enough population in vitro has been proven more difficult. While the exact molecular mechanisms of producing a fully mature population ofhepatocytes remain largely unknown, exogenous over expression of mature hepatic genes known as, liver emiched transcription factors (LETFs) through a viral vector delivery system may allow for a more mature and functional phenotype. Another insight into producing more mature hepatocytes may lie in studying epigenetic changes, such as changes in histone methylation patterns. The Jumonji C-domain-containing histone demethylase family is composed of 30 enzymes that are involved in changing histone methylation patterns and may have roles in the epigenetic changes and modifications found in mature hepatocytes. The current hepatocyte differentiation protocol successfully differentiated H9 hESC stem cell line to immature hepatocytes. Preliminary analysis of exogenous LETF gene expression has shown that certain over expressed genes delivered through adenoviral vectors such as, CCAAT/enhancer-binding protein beta (C/EBPB) and hepatocyte nuclear factor I homeobox A (HNFIA), have been shown to increase expression of genes responsible for contributing to mature hepatocyte functions. The investigation into the epigenetics ofhepatocyte derived hESCs has shown that certain Jumonji C-domaincontaining histone demethylase family members, such as MINA53, JHDM3 and HR, have a higher expression in conjunction with a higher secretion of albumin and lower secretion of alpha-fetoprotein. While all these findings are still relatively inconclusive, they provide a major insight for future research studies and goals. Future studies for over expression of genes through adenoviral vector delivery will include replication of initial analysis and functional metabolic activity tests. Future studies for Jumonji C-domain-containing histone demethylase family members will include investigating possible molecular pathways through PCR array analysis and knockout and rescuing procedures.