(Press-News.org) PHILADELPHIA — During embryonic development, animals generate many different types of cells, each with a distinct function and identity.
"Although the identities of these cells remain stable under normal conditions, some cells can be persuaded to take on new identities, through reprogramming," says Ben Stanger, MD, PhD, assistant professor of Medicine in the Division of Gastroenterology at the Perelman School of Medicine, University of Pennsylvania.
Researchers have been able to reprogram cells experimentally, but few have shown that cells can change their identities under normal physiological conditions in the body, particularly in mammals.
In the cover article of this month's issue of Genes and Development, Stanger, PhD candidate Kilangsungla Yanger, Yiwei Zong, PhD, and their colleagues, did just that in the liver of a mouse. Stanger is also an investigator in the Abramson Family Cancer Research Institute and the Department of Cell and Developmental Biology.
The adult liver contains two major cell types – hepatocytes and biliary cells – that differ dramatically in appearance and function. Hepatocytes are the main cell type in the liver, where they synthesize proteins and other macromolecules, and detoxify toxic substances. Biliary cells, on the other hand, line the bile ducts, which carry bile from the liver to the small intestine to help digest fats.
Using a sensitive method to tag and track how cells develop and differentiate, the researchers found that conditional expression of an activated Notch1 gene converted hepatocytes into biliary cells. Notch is an important receptor for relaying signals to tell cells how to develop.
What's more, after the researchers injured liver cells with a variety of toxins to stimulate wound healing, they found that over two to three weeks hepatocytes activated a biliary cell program on their own, acquiring the shape and function of biliary cells. These changes were dependent on the activation of endogenous Notch signaling.
"This is direct evidence that cells can be converted from one mature cell type to another in a live animal, as part of a normal response to injury," says Stanger. "We think that augmenting pre-existing cell reprogramming relationships may be another way to engineer cells for the treatment of diseases in which there are not enough bile ducts, such as cholestasis."
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Other co-authors are Lara Maggs, Suzanne Shapira, Ravi Maddipati, Nicole Aiello and Rebecca G. Wells, all from Penn, and Linda Greenbaum, from the Jefferson University School of Medicine.
The research was funded by Public Health Services grants (DK083355, DK 090306) and the Pew Charitable Trusts.
Penn Medicine is one of the world's leading academic medical centers, dedicated to the related missions of medical education, biomedical research, and excellence in patient care. Penn Medicine consists of the Raymond and Ruth Perelman School of Medicine at the University of Pennsylvania (founded in 1765 as the nation's first medical school) and the University of Pennsylvania Health System, which together form a $4.3 billion enterprise.
The Perelman School of Medicine has been ranked among the top five medical schools in the United States for the past 16 years, according to U.S. News & World Report's survey of research-oriented medical schools. The School is consistently among the nation's top recipients of funding from the National Institutes of Health, with $398 million awarded in the 2012 fiscal year.
The University of Pennsylvania Health System's patient care facilities include: The Hospital of the University of Pennsylvania -- recognized as one of the nation's top "Honor Roll" hospitals by U.S. News & World Report; Penn Presbyterian Medical Center; and Pennsylvania Hospital -- the nation's first hospital, founded in 1751. Penn Medicine also includes additional patient care facilities and services throughout the Philadelphia region.
Penn Medicine is committed to improving lives and health through a variety of community-based programs and activities. In fiscal year 2012, Penn Medicine provided $827 million to benefit our community.
Cell reprogramming during liver regeneration
2013-03-28
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