Professor, Department of Medicine (Gastroenterology & Liver Diseases)
Professor, Department of Cell Biology
Professor, Department of Pathology
Liver Stem/Progenitor Cells for Transplantation and Gene Therapy
Dr. David Shafritz’s research has focused on regulation of liver gene expression, cell growth control, liver regeneration and liver reconstitution through cell transplantation.
A number of years ago, Dr. Shafritz and fellow investigators developed a cell transplantation system to follow the proliferation, lineage fate and repopulation capacity of liver stem/progenitor cells, using a marker gene, dipeptidyl peptidase IV (DPPIV). This cell transplantation system has also been used to identify stem cells in the fetal liver that are bipotent, proliferate extensively for up to one year after their transplantation, differentiate into both hepatocyte and bile duct cells, form completely new liver lobules and replace 25-30% of hepatic mass in normal adult rats. He determined that liver replacement occurs by cell competition, a mechanism originally described in Drosophila during embryonic wing development. Dr. Shafritz is currently conducting laser capture microdissection studies in conjunction with microarray analysis to identify specific genes that regulate cell competition in liver repopulation, compared to those genes regulating cell competition in Drosophila.
Liver regenerative capacity decreases with aging, and Dr. Shafritz and fellow investigators have discovered that tissue levels of activin A increase progressively as the liver ages. Activin A induces expression of the cellular senescence gene, p15INK4b, in adult hepatocytes, whereas fetal liver stem/progenitor cells are resistant to activin A signaling because they lack expression of activin A receptors. This creates a tissue microenvironment in which there is increased cell competition between fetal liver stem/progenitor cells and host hepatoyctes, leading to augmented liver repopulation by fetal liver stem/progenitor cells in the aging liver. Finally, they have purified both rat and mouse FLSPC cells and by microarray analysis are defining unique genes expressed by these cells that control their proliferative potential.
Recent studies have established a mammalian counterpart of the Drosophila Hippo kinase phosphylation cascade that controls organ size and that hyperexpression of the effector gene in this pathway, Yap, in mouse liver causes hyperplasia. Dr. Shafritz’s laboratory has found that Yap, as well as several Yap target genes that effect cellular proliferation and apoptosis, are hyperexpressed in mouse and rat fetal liver stem/progenitor cells. They are currently conducting studies to introduce these genes into adult hepatocytes, using lentiviruses, to develop hepatocyte cell lines that can be expanded in culture and will effectively repopulate the normal adult liver.
In other studies, Dr. Shafritz has transplanted human cord blood stem cells into NOD/Scid mice with conversion of some of these cells into hepatocytes. He is also studying the ability of human and mouse embryonic stem (ES) cells to differentiate into hepatocytes and repopulate the liver and are planning to study liver repopulation by transplanted iPS cells. The long-range goal of these and other above studies is to identify methods to effectively repopulate the human liver with engineered hepatic-derived cells.
More Information About Dr. David Shafritz
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