Scientists Transform Skin Cells into Functioning Liver Cells

Joint Gladstone-UCSF study highlights novel reprogramming method; offers new hope for treating liver failure

Sunday, 23 February 2014

The power of regenerative medicine now allows scientists to transform skin cells into cells that closely resemble heart cells, pancreas cells and even neurons. However, a method to generate cells that are fully mature — a crucial prerequisite for life-saving therapies — has proven far more difficult. But now, scientists at the Gladstone Institutes and the University of California, San Francisco (UCSF), have made an important breakthrough: they have discovered a way to transform skin cells into mature, fully functioning liver cells that flourish on their own, even after being transplanted into laboratory animals modified to mimic liver failure.

In previous studies on liver-cell reprogramming, scientists had difficulty getting stem cell-derived liver cells to survive once being transplanted into existing liver tissue. But the Gladstone-UCSF team figured out a way to solve this problem. Writing in the latest issue of the journal Nature, researchers in the laboratories of Gladstone Senior Investigator Sheng Ding, PhD, and UCSF Associate Professor Holger Willenbring, MD, PhD, reveal a new cellular reprogramming method that transforms human skin cells into liver cells that are virtually indistinguishable from the cells that make up native liver tissue.

These results offer new hope for the millions of people suffering from, or at risk of developing, liver failure — an increasingly common condition that results in progressive and irreversible loss of liver function. At present, the only option is a costly liver transplant. So, scientists have long looked to stem cell technology as a potential alternative. But thus far they have come up largely empty-handed.

"Earlier studies tried to reprogram skin cells back into a pluripotent, stem cell-like state in order to then grow liver cells," explained Dr. Ding, one of the paper's senior authors, who is also a professor of pharmaceutical chemistry at UCSF, with which Gladstone is affiliated.

"However, generating these so-called induced pluripotent stem cells, or iPS cells, and then transforming them into liver cells wasn't always resulting in complete transformation. So we thought that, rather than taking these skin cells all the way back to a pluripotent, stem cell-like state, perhaps we could take them to an intermediate phase."

This research, which was performed jointly at the Roddenberry Center for Stem Cell Research at Gladstone and the Broad Center of Regeneration Medicine and Stem Cell Research at UCSF, involved using a 'cocktail' of reprogramming genes and chemical compounds to transform human skin cells into cells that resembled the endoderm. Endoderm cells are cells that eventually mature into many of the body's major organs — including the liver.

"Instead of taking the skin cells back to the beginning, we took them only part way, creating endoderm-like cells," added Gladstone and CIRM Postdoctoral Scholar Saiyong Zhu, PhD, one of the paper's lead authors.

"This step allowed us to generate a large reservoir of cells that could more readily be coaxed into becoming liver cells."

Next, the researchers discovered a set of genes and compounds that can transform these cells into functioning liver cells. And after just a few weeks, the team began to notice a transformation.

"The cells began to take on the shape of liver cells, and even started to perform regular liver-cell functions," said UCSF Postdoctoral Scholar Milad Rezvani, MD, the paper's other lead author.

"They weren't fully mature cells yet — but they were on their way."

Now that the team was encouraged by these initial results in a dish, they wanted to see what would happen in an actual liver. So, they transplanted these early-stage liver cells into the livers of mice. Over a period of nine months, the team monitored cell function and growth by measuring levels of liver-specific proteins and genes.

Two months post-transplantation, the team noticed a boost in human liver protein levels in the mice, an indication that the transplanted cells were becoming mature, functional liver cells. Nine months later, cell growth had shown no signs of slowing down. These results indicate that the researchers have found the factors required to successfully regenerate liver tissue.

"Many questions remain, but the fact that these cells can fully mature and grow for months post-transplantation is extremely promising," added Dr. Willenbring, associate director of the UCSF Liver Center and the paper's other senior author.

"In the future, our technique could serve as an alternative for liver-failure patients who don't require full-organ replacement, or who don't have access to a transplant due to limited donor organ availability."

Source: Gladstone Institutes 

Contact: Anne Holden 

Reference:

Mouse liver repopulation with hepatocytes generated from human fibroblasts

Saiyong Zhu, Milad Rezvani, Jack Harbell, Aras N. Mattis, Alan R. Wolfe, Leslie Z. Benet, Holger Willenbring & Sheng Ding

Nature 23 February 2014, doi:10.1038/nature13020

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A Step Closer to Artificial Liver

A Step Closer to Artificial Liver

Monday, 03 June 2013

Prometheus, the mythological figure who stole fire from the gods, was punished for this theft by being bound to a rock. Each day, an eagle swept down and fed on his liver, which then grew back to be eaten again the next day.

Modern scientists know there is a grain of truth to the tale, says MIT engineer Sangeeta Bhatia: The liver can indeed regenerate itself if part of it is removed. However, researchers trying to exploit that ability in hopes of producing artificial liver tissue for transplantation have repeatedly been stymied: Mature liver cells, known as hepatocytes, quickly lose their normal function when removed from the body.

"It's a paradox because we know liver cells are capable of growing, but somehow we can't get them to grow" outside the body, says Bhatia, the John and Dorothy Wilson Professor of Health Sciences and Technology and Electrical Engineering and Computer Science at MIT, a senior associate member of the Broad Institute and a member of MIT's Koch Institute for Integrative Cancer Research and Institute for Medical Engineering and Science.

Now, Bhatia and colleagues have taken a step toward that goal. In a paper appearing in the June 2 issue of Nature Chemical Biology, they have identified a dozen chemical compounds that can help liver cells not only maintain their normal function while grown in a lab dish, but also multiply to produce new tissue.

Cells grown this way could help researchers develop engineered tissue to treat many of the 500 million people suffering from chronic liver diseases such as hepatitis C, according to the researchers.

Lead author of the paper is Jing (Meghan) Shan, a graduate student in the Harvard-MIT Division of Health Sciences and Technology. Members of Bhatia's lab collaborated with researchers from the Broad Institute, Harvard Medical School and the University of Wisconsin.

Large-scale screen

Bhatia has previously developed a way to temporarily maintain normal liver-cell function after those cells are removed from the body, by precisely intermingling them with mouse fibroblast cells. For this study, funded by the National Institutes of Health and Howard Hughes Medical Institute, the research team adapted the system so that the liver cells could grow, in layers with the fibroblast cells, in small depressions in a lab dish. This allowed the researchers to perform large-scale, rapid studies of how 12,500 different chemicals affect liver-cell growth and function.

The liver has about 500 functions, divided into four general categories: drug detoxification, energy metabolism, protein synthesis and bile production. David Thomas, an associate researcher working with Todd Golub at the Broad Institute, measured expression levels of 83 liver enzymes representing some of the most finicky functions to maintain.

After screening thousands of liver cells from eight different tissue donors, the researchers identified 12 compounds that helped the cells maintain those functions, promoted liver cell division, or both.

MIT researchers have generated mature liver cells 

from induced pluripotent stem cells. In this image, 

the cell nuclei are stained blue. The green stain 

identifies liver cells, and the red stain identifies cells 

that are actively dividing. Image: Shan et al., Nature 

Chemical Biology, 2013.

Two of those compounds seemed to work especially well in cells from younger donors, so the researchers — including Robert Schwartz, an IMES postdoc, and Stephen Duncan, a professor of human and molecular genetics at the University of Wisconsin — also tested them in liver cells generated from induced pluripotent stem cells (iPSCs). Scientists have tried to create hepatocytes from iPSCs before, but such cells don't usually reach a fully mature state. However, when treated with those two compounds, the cells matured more completely.

Bhatia and her team wonder whether these compounds might launch a universal maturation program that could influence other types of cells as well. Other researchers are now testing them in a variety of cell types generated from iPSCs.

In future studies, the MIT team plans to embed the treated liver cells on polymer tissue scaffolds and implant them in mice, to test whether they could be used as replacement liver tissues. They are also pursuing the possibility of developing the compounds as drugs to help regenerate patients' own liver tissues, working with Trista North and Wolfram Goessling of Harvard Medical School.

Making connections

Bhatia and colleagues have also recently made progress toward solving another challenge of engineering liver tissue, which is getting the recipient's body to grow blood vessels to supply the new tissue with oxygen and nutrients. In a paper published in the Proceedings of the National Academy of Sciences in April, Bhatia and Christopher Chen, a professor at the University of Pennsylvania, showed that if preformed cords of endothelial cells are embedded into the tissue, they will rapidly grow into arrays of blood vessels after the tissue is implanted.

To achieve this, Kelly Stevens in the Bhatia lab worked with Peter Zandstra at the University of Toronto to design a new system that allows them to create 3-D engineered tissue and precisely control the placement of different cell types within the tissue. This approach, described in the journal Nature Communications in May, allows the engineered tissue to function better with the host tissue.

"Together, these papers offer a path forward to solve two of the longstanding challenges in liver tissue engineering — growing a large supply of liver cells outside the body and getting the tissues to graft to the transplant recipient," Bhatia says.

Source: Massachusetts Institute of Technology 

Contact: Anne Trafton, MIT News Office

Reference:

Identification of small molecules for human hepatocyte expansion and iPS differentiation

Jing Shan, Robert E Schwartz, Nathan T Ross, David J Logan, David Thomas, Stephen A Duncan, Trista E North, Wolfram Goessling, Anne E Carpenter & Sangeeta N Bhatia

Nature Chemical Biology, 02 June 2013, doi:10.1038/nchembio.1270

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Scientists First to Grow Liver Stem Cells in Culture

New mouse research raises hope that human liver stem cells can be grown, transplanted in a similar way

Monday, 25 February 2013

For decades scientists around the world have attempted to regenerate primary liver cells known as hepatocytes because of their numerous biomedical applications, including hepatitis research, drug metabolism and toxicity studies, as well as transplantation for cirrhosis and other chronic liver conditions. But no lab in the world has been successful in identifying and growing liver stem cells in culture – using any available technique – until now.

In the journal Nature, physician-scientists in the Papé Family Pediatric Research Institute at Oregon Health & Science University Doernbecher Children's Hospital, Portland, Ore., along with investigators at the Hubrecht Institute for Developmental Biology and Stem Cell Research, Utrecht, Netherlands, describe a new method through which they were able to infinitely expand liver stem cells from a mouse in a dish.

"This study raises the hope that the human equivalent of these mouse liver stem cells can be grown in a similar way and efficiently converted into functional liver cells," said Markus Grompe, M.D., study co-author, director of the Papé Family Pediatric Research Institute at OHSU Doernbecher Children's Hospital; and professor of paediatrics, and molecular and medical genetics in the OHSU School of Medicine.

In a previous Nature study, investigators at the Hubrecht Institute, led by Hans Clever, M.D, Ph.D., were the first to identify stem cells in the small intestine and colon by observing the expression of the adult stem cell marker Lgr5 and growth in response to a growth factor called Wnt. They also hypothesized that the unique expression pattern of Lgr5 could mark stem cells in other adult tissues, including the liver, an organ for which stem cell identification remained elusive.

In the current study, Grompe and colleagues in the Papé Family Pediatric Research Institute at OHSU Doernbecher used a modified version of the Clever method and discovered that Wnt-induced Lgr5 expression not only marks stem cell production in the liver, but it also defines a class of stem cells that become active when the liver is damaged.

The scientists were able to grow these liver stem cells exponentially in a dish – an accomplishment never before achieved – and then transplant them in a specially designed mouse model of liver disease, where they continued to grow and show a modest therapeutic effect.

"We were able to massively expand the liver cells and subsequently convert them to hepatocytes at a modest percentage. Going forward, we will enlist other growth factors and conditions to improve that percentage. Liver stem cell therapy for chronic liver disease in humans is coming," said Grompe.

Source: Oregon Health & Science University 

Contact: Tamara Hargens-Bradley

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Complexity of Human Genome Unravelled

ENCODE data describes function of human genome’s ‘dark matter’

Wednesday, 05 September 2012

The Human Genome Project produced an almost complete order of the 3 billion pairs of chemical letters in the DNA that embodies the human genetic code — but little about the way this blueprint works. Now, after a multi-year concerted effort by more than 440 researchers in 32 labs around the world, a more dynamic picture gives the first holistic view of how the human genome actually does its job.

During the new study, researchers linked more than 80 percent of the human genome sequence to a specific biological function and mapped more than 4 million regulatory regions where proteins specifically interact with the DNA. These findings represent a significant advance in understanding the precise and complex controls over the expression of genetic information within a cell. The findings bring into much sharper focus the continually active genome in which proteins routinely turn genes on and off using sites that are sometimes at great distances from the genes themselves. They also identify where chemical modifications of DNA influence gene expression and where various functional forms of RNA, a form of nucleic acid related to DNA, help regulate the whole system.

"During the early debates about the Human Genome Project, researchers had predicted that only a few percent of the human genome sequence encoded proteins, the workhorses of the cell, and that the rest was junk. We now know that this conclusion was wrong," said Eric D. Green, M.D., Ph.D., director of the National Human Genome Research Institute (NHGRI), a part of the National Institutes of Health.

"ENCODE has revealed that most of the human genome is involved in the complex molecular choreography required for converting genetic information into living cells and organisms."

NHGRI organized the research project producing these results; it is called the Encyclopedia of DNA Elements or ENCODE. Launched in 2003, ENCODE's goal of identifying all of the genome's functional elements seemed just as daunting as sequencing that first human genome. ENCODE was launched as a pilot project to develop the methods and strategies needed to produce results and did so by focusing on only 1 percent of the human genome. By 2007, NHGRI concluded that the technology had sufficiently evolved for a full-scale project, in which the institute invested approximately $123 million over five years. In addition, NHGRI devoted about $40 million to the ENCODE pilot project, plus approximately $125 million to ENCODE-related technology development and model organism research since 2003.

William Noble, professor of genome sciences and computer
science, in the data centre at the William H. Foege Building, 

University of Washington, Seattle, Washington. Noble, an 

expert on machine learning, and his team designed artificial 

intelligence programs to analyse ENCODE data. These 

computer programs can learn from experience, recognize 

patterns, and organize information into categories 

understandable to scientists. The centre houses systems for a 

wide variety of genetic research. The computer centre has the 

capacity to store and analyse a tremendous amount of data, 

the equivalent of a 670-page autobiography of each person on 

earth, uncompressed. The computing resources analyse over 

4 pentabytes of genomic data a year. Credit: Clare McLean, 

courtesy of University of Washington. 

The scale of the effort has been remarkable. Hundreds of researchers across the United States, United Kingdom, Spain, Singapore and Japan performed more than 1,600 sets of experiments on 147 types of tissue with technologies standardized across the consortium. The experiments relied on innovative uses of next-generation DNA sequencing technologies, which had only become available around five years ago, due in large part to advances enabled by NHGRI's DNA sequencing technology development program. In total, ENCODE generated more than 15 trillion bytes of raw data and consumed the equivalent of more than 300 years of computer time to analyse.

"We've come a long way," said Ewan Birney, Ph.D., of the European Bioinformatics Institute, in the United Kingdom, and lead analysis coordinator for the ENCODE project.

"By carefully piecing together a simply staggering variety of data, we've shown that the human genome is simply alive with switches, turning our genes on and off and controlling when and where proteins are produced. ENCODE has taken our knowledge of the genome to the next level, and all of that knowledge is being shared openly."

The ENCODE Consortium placed the resulting data sets as soon as they were verified for accuracy, prior to publication, in several databases that can be freely accessed by anyone on the Internet. These data sets can be accessed through the ENCODE project portal as well as at the University of California, Santa Cruz genome browser, the National Center for Biotechnology Information, and the European Bioinformatics Institute.

"The ENCODE catalogue is like Google Maps for the human genome," said Elise Feingold, Ph.D., an NHGRI program director who helped start the ENCODE Project.

"Simply by selecting the magnification in Google Maps, you can see countries, states, cities, streets, even individual intersections, and by selecting different features, you can get directions, see street names and photos, and get information about traffic and even weather. The ENCODE maps allow researchers to inspect the chromosomes, genes, functional elements and individual nucleotides in the human genome in much the same way."

The coordinated publication set includes one main integrative paper and five related papers in the journal Nature; 18 papers in Genome Research; and six papers in Genome Biology. The ENCODE data are so complex that the three journals have developed a pioneering way to present the information in an integrated form that they call threads.

"Because ENCODE has generated so much data, we, together with the ENCODE Consortium, have introduced a new way to enable researchers to navigate through the data," said Magdalena Skipper, Ph.D., senior editor at Nature, which produced the freely available publishing platform on the Internet.

Since the same topics were addressed in different ways in different papers, the new website will allow anyone to follow a topic through all of the papers in the ENCODE publication set by clicking on the relevant thread at the Nature ENCODE explorer page. For example, thread number one compiles figures, tables, and text relevant to genetic variation and disease from several papers and displays them all on one page. ENCODE scientists believe this will illuminate many biological themes emerging from the analyses.

In addition to the threaded papers, six review articles are being published in the Journal of Biological Chemistry and two related papers in Science and one in Cell.

The ENCODE data are rapidly becoming a fundamental resource for researchers to help understand human biology and disease. More than 100 papers using ENCODE data have been published by investigators who were not part of the ENCODE Project, but who have used the data in disease research. For example, many regions of the human genome that do not contain protein-coding genes have been associated with disease. Instead, the disease-linked genetic changes appear to occur in vast tracts of sequence between genes where ENCODE has identified many regulatory sites. Further study will be needed to understand how specific variants in these genomic areas contribute to disease.

"We were surprised that disease-linked genetic variants are not in protein-coding regions," said Mike Pazin, Ph.D., an NHGRI program director working on ENCODE.

"We expect to find that many genetic changes causing a disorder are within regulatory regions, or switches, that affect how much protein is produced or when the protein is produced, rather than affecting the structure of the protein itself. The medical condition will occur because the gene is aberrantly turned on or turned off or abnormal amounts of the protein are made. Far from being junk DNA, this regulatory DNA clearly makes important contributions to human health and disease."

Identifying regulatory regions will also help researchers explain why different types of cells have different properties. For example why do muscle cells generate force while liver cells break down food? Scientists know that muscle cells turn on some genes that only work in muscle, but it has not been previously possible to examine the regulatory elements that control that process. ENCODE has laid a foundation for these kinds of studies by examining more than 140 of the hundreds of cell types found in the human body and identifying many of the cell type-specific control elements.

Despite the enormity of the dataset described in this historic collection of publications, it does not comprehensively describe all of the functional genomic elements in all of the different types of cells in the human body. NHGRI plans to invest in additional ENCODE-related research for at least another four years. During the next phase, ENCODE will increase the depth of the catalog with respect to the types of functional elements and cell types studied. It will also develop new tools for more sophisticated analyses of the data.

Source: National Human Genome Research Institute

Contact: Omar McCrimmon 

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Gallbladder Shown as Potential Stem Cell Source for Regenerative Liver and Metabolic Disease

Gallbladder Shown as Potential Stem Cell Source for Regenerative Liver and Metabolic Disease

Thursday, 19 April 2012

A new study presented today at the International Liver Congress™ 2012 indicates the potential for gallbladder tissue (which is routinely discarded from organ donors and surgical interventions) to be a highly available candidate source for multipotential stem cells.

Biliary tree stem/progenitor cells (BTSCs) have previously been identified in the glands of normal adult human extrahepatic bile ducts and been shown to generate in vitro and in vivo mature cells of the hepato-biliary and pancreatic endocrine lineages.

The study found both normal and pathological gallbladders contained easily isolable cells with the phenotype and biological properties of BTSCs. Interestingly, in an animal model, these cells were able to repopulate the injured liver and to improve synthetic functions.

These data open novel perspectives for the collection and use of multipotent stem cells in regenerative therapies of liver, bile duct, and pancreatic diseases including diabetes.

Source: European Association for the Study of the Liver

Contact: Travis Taylor

Reference:

Gallbladder is a highly available source of stem cells with multiple endodermic mature gates potentiality
Carpino G et al.
Abstract presented at the International Liver Congress^TM 2012
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Predicting the Fate of Personalized Cells Next Step toward New Therapies

Predicting the Fate of Personalized Cells Next Step toward New Therapies
Thursday, 19 May 2011


Kenneth S. Zaret, PhD.

Discovering the step-by-step details of the path embryonic cells take to develop into their final tissue type is the clinical goal of many stem cell biologists. To that end Kenneth S. Zaret, PhD, of Cell and Developmental Biology at the Perelman School of Medicine at the University of Pennsylvania, and associate director of the Penn Institute for Regenerative Medicine, and Cheng-Ran Xu, PhD, a postdoctoral researcher in the Zaret laboratory, looked at immature cells called progenitors and found a way to potentially predict their fate. They base this on how the protein spools around which DNA winds — called histones — are marked by other proteins. This study appeared this week in Science.
In the past, researchers grew progenitor cells and waited to see what they differentiated into. Now, they aim to use this marker system, outside of a cell's DNA and genes, to predict the eventual fate. This extra-DNA system of gene expression control is called epigenetics.

"We were surprised that there's a difference in the epigenetic marks in the process for liver versus pancreas before the cell-fate 'decision' is made." says Zaret.

"This suggests that we could manipulate the marks to influence fate or look at marks to better guess the fate of cells early in the differentiation process."

"How cells become committed to particular fates is a fundamental question in developmental biology," said Susan Haynes, PhD, program director in the Division of Genetics and Developmental Biology at the National Institutes of Health, which funds this line of research.

"This work provides important new insights into the early steps of this process and suggests new approaches for controlling stem-cell fate in regenerative medicine therapies."

A Guiding Path
How the developing embryo starts to apportion different functions to different cell types is a key question for developmental biology and regenerative medicine. Guidance along the correct path is provided by regulatory proteins that attach to chromosomes, marking part of the genome to be turned on or off. But first the two meters of tightly coiled DNA inside the nucleus of every cell must be loosened a bit. Regulatory proteins help with this, exposing a small domain near the target gene.

Earliest cells that form the liver (blue)

emerging from progenitor cells (yellow)

in the early embryo (green). Credit: Ken

Zaret, PhD, Perelman School of Medicine

at the University of Pennsylvania.

Chemical signals from neighbouring cells in the embryo tell early progenitor cells to activate genes encoding proteins. These, in turn, guide the cells to become liver or pancreas cells, in the case of Zaret's work. Over several years, his lab has unveiled a network of the common signals in the mouse embryo that govern development of these specific cell types.

Zaret likens the complexity of this system to the 26-letter alphabet being able to encode Shakespeare or a menu at a restaurant. Many investigators are now trying to broadly reprogram cells into desired cell fates for potential therapeutic uses.

The researchers had previously shown that a particular growth factor that attaches to the cell surface, gives a specific chemical signal for cell-type fate, promoting development along the liver-cell path and suppressing development along the pancreas-cell path. Liver and pancreas cells originate from a common progenitor cell type.

Zaret's group figured out which enzymes — called histone acetyl transferases or methyl transferases (that add methyl groups or acetyl groups to histones) are relevant to the pancreas arm of the liver-pancreas fate decision. They used mice in which they knocked out the function for one enzyme type versus the other to induce the development of fewer liver cells and more pancreas cells.

The transferases mark genes for liver and pancreas fates differently before a cell moves into the next intermediate type along the way to becoming a mature liver or pancreas cell.

Investigators want to make embryonic stem cells for liver or pancreatic beta cells for therapies and research. To do this, they mimic the embryonic developmental steps to proceed from an embryonic stem cell to a mature cell, but have no way of knowing if they are on the right track. The hope is that the findings from this study can be applied to assess the epigenetic state of intermediate progenitor cells.

"By better understanding how a cell is normally programmed we will eventually be able to properly reprogram other cells," notes Zaret. In the near term, the team also aims to generate liver and pancreas cells for research and to screen drugs that repair defects or facilitate cell growth.

With regenerated cells, researchers hope to one day fill the acute shortage in pancreatic and liver tissue available for transplantation in cases of type I diabetes and acute liver failure.

Source: University of Pennsylvania School of Medicine
Contact: Karen Kreeger

Reference:
Chromatin “Prepattern” and Histone Modifiers in a Fate Choice for Liver and Pancreas
Cheng-Ran Xu, Philip A. Cole, David J. Meyers, Jay Kormish, Sharon Dent, and Kenneth S. Zaret
Science 20 May 2011, Vol. 332 no. 6032 pp. 963-966, DOI: 10.1126/science.1202845
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Adult Stem Cells Take Root in Livers and Repair Damage

Adult Stem Cells Take Root in Livers and Repair Damage
Thursday, 12 May 2011

Johns Hopkins researchers have demonstrated that human liver cells derived from adult cells coaxed into an embryonic state can engraft and begin regenerating liver tissue in mice with chronic liver damage.

These are regenerative liver cells eight

weeks after transplantation. Credit:

Yoon-Young Jang.

The work, published in the May 11 issue of the journal Science Translational Medicine, suggests that liver cells derived from so-called "induced-pluripotent stem cells (iPSCs)" could one day be used as an alternative to liver transplant in patients with serious liver diseases, bypassing long waiting lists for organs and concerns about immune system rejection of donated tissue.

"Our findings provide a foundation for producing functional liver cells for patients who suffer liver diseases and are in need of transplantation," says Yoon-Young Jang, M.D., Ph.D., assistant professor of oncology at the Johns Hopkins Kimmel Cancer Center.

"iPSC-derived liver cells not only can be generated in large amounts, but also can be tailored to each patient, preventing immune-rejection problems associated with liver transplants from unmatched donors or embryonic stem cells."

iPSCs are made from adult cells that have been genetically reprogrammed to revert to an embryonic stem cell-like state, with the ability to transform into different cell types. Human iPSCs can be generated from various tissues, including skin, blood and liver cells.

Although the liver can regenerate in the body, end-stage liver failure caused by diseases like cirrhosis and cancers eventually destroy the liver's regenerative ability, Jang says. Currently, the only option for those patients is to receive a liver organ or liver cell transplant, a supply problem given the severe shortage of donor liver tissue for transplantation. In addition, mature liver cells and adult liver stem cells are difficult to isolate or grow in the laboratory, she says. By contrast, iPSCs can be made from a tiny amount of many kinds of tissue; and the embryonic stem-like iPSCs can grow in laboratory cultures indefinitely.

For the study, Jang and colleagues generated human iPSCs from a variety of adult human cells, including liver cells, fibroblasts (connective tissue cells), bone marrow stem cells and skin cells. They found that though the iPSCs overall were molecularly similar to each other and to embryonic stem cells, they retained a distinct molecular "signature" inherited from the cell of origin.

Next, they chemically induced the iPSCs to differentiate first into immature and then more mature liver cell types. Regardless of their origin, the different iPSC lines all showed the same ability to develop into liver cells.

Using mice with humanlike liver cirrhosis, the researchers then injected the animals either with 2 million human iPSC-derived liver cells or with normal human liver cells. They discovered that the iPSC-derived liver cells engrafted to the mouse liver with an efficiency of eight to 15 percent, a rate similar to the engraftment rate for adult human liver cells at 11 percent.

Researchers also found the engrafted iPSCs worked well. The scientists detected proteins normally secreted by adult human liver cells, including albumin, alpha-1-antitrypsin, transferrin and fibrinogen, in the blood of mice transplanted with human iPSC-derived liver cells.

Additional studies will need to be completed before clinical trials can begin, Jang says. One concern has been the potential for embryonic stem cells or iPSCs to cause tumours, though no tumours formed in any of the transplanted mice during the seven months they were studied (equating to more than 30 years in a human life). The scientists also plan to evaluate the impact of molecular memory that may linger in iPSCs for other type of cellular fate changes.

Source: Johns Hopkins Medical Institutions
Contact: Vanessa Wasta
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Researchers Engineer Miniature Human Livers in the Lab

Researchers Engineer Miniature Human Livers in the Lab
Sunday, 31 October 2010

Researchers at the Institute for Regenerative Medicine at Wake Forest University Baptist Medical Center have reached an early, but important, milestone in the quest to grow replacement livers in the lab. They are the first to use human liver cells to successfully engineer miniature livers that function – at least in a laboratory setting – like human livers. The next step is to see if the livers will continue to function after transplantation in an animal model.

The ultimate goal of the research, which will be presented Sunday at the annual meeting of the American Association for the Study of Liver Diseases in Boston, is to provide a solution to the shortage of donor livers available for patients who need transplants. Laboratory-engineered livers could also be used to test the safety of new drugs.

"We are excited about the possibilities this research represents, but must stress that we're at an early stage and many technical hurdles must be overcome before it could benefit patients," said Shay Soker, Ph.D., professor of regenerative medicine and project director.

"Not only must we learn how to grow billions of liver cells at one time in order to engineer livers large enough for patients, but we must determine whether these organs are safe to use in patients."

Pedro Baptista, PharmD, Ph.D., lead author on the study, said the project is the first time that human liver cells have been used to engineer livers in the lab.

"Our hope is that once these organs are transplanted, they will maintain and gain function as they continue to develop," he said.

To engineer the organs, the scientists used animal livers that were treated with a mild detergent to remove all cells (a process called de-cellularization), leaving only the collagen "skeleton" or support structure. They then replaced the original cells with two types of human cells: immature liver cells known as progenitors, and endothelial cells that line blood vessels.

The cells were introduced into the liver skeleton through a large vessel that feeds a system of smaller vessels in the liver. This network of vessels remains intact after the de-cellularization process. The liver was next placed in a bioreactor, special equipment that provides a constant flow of nutrients and oxygen throughout the organ.

After a week in the bioreactor system, the scientists documented the progressive formation of human liver tissue, as well as liver-associated function. They observed widespread cell growth inside the bioengineered organ.

The ability to engineer a liver with animal cells had been demonstrated previously. However, the possibility of generating a functional human liver was still in question.

The researchers said the current study suggests a new approach to whole-organ bioengineering that might prove to be critical not only for treating liver disease, but for growing organs such as the kidney and pancreas. Scientists at the Wake Forest Institute for Regenerative Medicine are working on these projects, as well as many other tissues and organs, and also working to develop cell therapies to restore organ function.

Bioengineered livers could also be useful for evaluating the safety of new drugs.

"This would more closely mimic drug metabolism in the human liver, something that can be difficult to reproduce in animal models," said Baptista.

Source: Wake Forest University Baptist Medical Center
Contact: Karen Richardson
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ZenMaster

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Liver Cells Created from Patients' Skin Cells

Research paves way for new liver disease research and possibly cell-based therapy
Thursday, 26 August 2010

By creating diseased liver cells from a small sample of human skin, scientists have for the first time shown that stem cells can be used to model a diverse range of inherited disorders. The University of Cambridge researchers' findings, which will hopefully lead to new treatments for those suffering from liver diseases, were published today in The Journal of Clinical Investigation.

Because liver cells (hepatocytes) cannot be grown in the laboratory, researching liver disorders is extremely difficult. However, today's new research, which was funded by the Wellcome Trust and the Medical Research Council (MRC), demonstrates how to create diseased liver-like cells from patients suffering from a variety of liver disorders.

By replicating the organ's cells, researchers can not only investigate exactly what is happening in a diseased cell, they can also test the effectiveness of new therapies to treat these conditions. It is hoped that their discovery will lead to tailored treatments for specific individuals and eventually cell-based therapy - when cells from patients with genetic diseases are 'cured' and transplanted back. Additionally, as the process could be used to model cells from other parts of the body, their findings could have implications for conditions affecting other organs.

Dr Ludovic Vallier of the MRC Centre for Stem Cell Biology and Regenerative Medicine, University of Cambridge, principal investigator of the research, said:

"Our work represents an important step towards delivering the clinical promises of stem cells. However, more work remains to be done and our group is dedicated to achieving this ultimate goal by increasing the knowledge necessary for the development of new therapies."

In the UK, liver disease is the fifth largest cause of death after cardiovascular, cancer, stroke, and respiratory diseases. Over the past 30 years mortality from liver disease in young and middle-aged people has increased over six times, with the number of individuals dying from the disease increasing at a rate of 8-10 per cent every year.

By 2012, the UK is expected to have the highest liver disease death rates in Europe and, without action to tackle the disease, it could overtake stroke and coronary heart disease as the leading cause of death within the next 10-20 years. In the United States, it accounts for approximately 25,000 deaths a year.

For their research, the scientists took skin biopsies from seven patients who suffered from a variety of inherited liver diseases and three healthy individuals (the control group). They then reprogrammed cells from the skin samples back into stem cells. These stem cells were then used to generate liver cells, which mimicked a broad range of liver diseases - the first time patient-specific liver diseases have been modelled using stem cells - and to create 'healthy' liver cells from the control group. Importantly, the three diseases the scientists modelled covered a diverse range of pathological mechanisms, thereby demonstrating the potential application of their research on a wide variety of disorders.

Dr Tamir Rashid of the Laboratory for Regenerative Medicine, University of Cambridge, lead author of the paper, said:

"We know that given the shortage of donor liver organs alternative strategies must urgently be sought. Our study improves the possibility that such alternatives will be found - either using new drugs or a cell-based therapeutic approach."

Professor Mark Thursz, a specialist in liver disease and Professor of Hepatology at Imperial College (who was not affiliated with the study), commented on the importance of the research:

"Liver disease is the fifth most common cause of mortality in many developed countries and unlike the other leading causes of death, the rate of liver related mortality is increasing.”

"The development of patient specific liver cell lines from stem cells is a significant advance in the battle against liver diseases. This technology holds promise in the short term by providing new tools to explore the biology of liver diseases and in the long term as a potential source of liver cells for patients with liver failure."

Source: University of Cambridge
Contact: Genevieve Maul

Reference:
Modeling inherited metabolic disorders of the liver using human induced pluripotent stem cells
S. Tamir Rashid, Sebastien Corbineau, Nick Hannan, Stefan J. Marciniak, Elena Miranda, Graeme Alexander, Isabel Huang-Doran, Julian Griffin, Lars Ahrlund-Richter, Jeremy Skepper, Robert Semple, Anne Weber, David A. Lomas, Ludovic Vallier
J Clin Invest. doi:10.1172/JCI43122
.........


ZenMaster

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For more on stem cells and cloning, go to CellNEWS at
http://cellnews-blog.blogspot.com/

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Liver Cells Grown from Patients' Skin Cells

Treatment of liver diseases possible Wednesday, 14 October 2009 Scientists at The Medical College of Wisconsin in Milwaukee have successfully produced liver cells from patients' skin cells opening the possibility of treating a wide range of diseases that affect liver function. The study was led by Stephen A. Duncan, D. Phil., Marcus Professor in Human and Molecular Genetics, and professor of cell biology, neurobiology and anatomy, along with postdoctoral fellow Karim Si-Tayeb, Ph.D., and graduate student Ms. Fallon Noto. "This is a crucial step forward towards developing therapies that can potentially replace the need for scarce liver transplants, currently the only treatment for most advanced liver disease," says Dr. Duncan. Liver disease is the fourth leading cause of death among middle aged adults in the United States. Loss of liver function can be caused by several factors, including genetic mutations, infections with hepatitis viruses, by excessive alcohol consumption, or chronic use of some prescription drugs. When liver function goes awry it can result in a wide variety of disorders including diabetes and atherosclerosis and in many cases is fatal. The Medical College research team generated patient–specific liver cells by first repeating the work of James Thomson and colleagues at University of Wisconsin-Madison who showed that skin cells can be reprogrammed to become cells that resemble embryonic stem cells. They then tricked the skin–derived pluripotent stem cells into forming liver cells by mimicking the normal processes through which liver cells are made during embryonic development. Pluripotent stem cells are so named because of their capacity to develop into any one of eh more than 200 cell types in the human body. At the end of this process, the researchers found that they were able to very easily produce large numbers of relatively pure liver cells in laboratory culture dishes. "We were excited to discover that the liver cells produced from human skin cells were able to perform many of the activities associated with healthy adult liver function and that the cells could be injected into mouse livers where they integrated and were capable of making human liver proteins," says Dr. Duncan. Several studies have shown that liver cells generated from embryonic stem cells could potentially be used for therapy. However, the possible use of such cells is limited by ethical considerations associated with the generation of embryonic stem cells from preimplantation embryos and the fact that embryonic stem cells do not have the same genetic make-up as the patient. Although the investigations are still at an early stage the researchers believe that the reprogrammed skin cells could be used to investigate and potentially treat metabolic liver disease. The liver may be particularly suitable for stem-cell based therapies because it has a remarkable capacity to regenerate. It is interesting to note that the regenerative nature of the liver was referenced in the ancient Greek tale of Prometheus. When Prometheus was caught stealing the gift of fire from Zeus, he was punished by having his liver eaten daily by an eagle. This provided the eagle with an everlasting meal because each night the liver of Prometheus would re-grow. The liver is a central regulator of the body's metabolism and is responsible for controlling sugar and cholesterol levels, secretion of a variety of hormones, production of blood clotting factors, and has an essential role in preventing toxins from damaging other organs in the body. It is possible that in the future a small piece of skin from a patient with loss of liver function could be used to produce healthy liver cells, replacing the diseased liver with normal tissue. Recently, the National Institutes of Health's National Institute of Diabetes and Digestive and Kidney Diseases through the American Recovery and Reinvestment Act have provided the MCW researchers, in collaboration with Markus Grompe, M.D., at the Oregon Health and Science University, a $1 million research grant to pursue the possibility of using reprogrammed skin cells to study and treat metabolic liver disease. Using this support, as well as donations from individuals throughout Milwaukee, the Medial College researchers are currently producing reprogrammed cells from patients suffering from diabetes, hyperlipidemia, and hypercholesterolemia in an effort to identify new treatments for these diseases. ......... ZenMaster

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For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/ and http://www.geocities.com/giantfideli/index.html

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Artificial Liver for Drug Tests

Artificial Liver for Drug Tests Thursday, 25 June 2009 If you have hay fever, headaches or a cold, it's only a short way to the nearest chemist. The drugs, on the other hand, can take eight to ten years to develop. Until now animal experiments have been an essential step, yet they continue to raise ethical issues. "Our artificial organ systems are aimed at offering an alternative to animal experiments," says Professor Heike Mertsching of the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart. "Particularly as humans and animals have different metabolisms. 30 per cent of all side effects come to light in clinical trials." The test system, which Professor Mertsching has developed jointly with Dr. Johanna Schanz, should in future give pharmaceutical companies greater security and shorten the path to new drugs. Both researchers received the "Human-centered Technology" prize for their work. "The special feature, in our liver model for example, is a functioning system of blood vessels," says Dr. Schanz. "This creates a natural environment for cells." Traditional models do not have this, and the cells become inactive. "We don't build artificial blood vessels for this, but use existing ones – from a piece of pig's intestine." All of the pig cells are removed, but the blood vessels are preserved. Human cells are then seeded onto this structure – hepatocytes, which, as in the body, are responsible for transforming and breaking down drugs, and endothelial cells, which act as a barrier between blood and tissue cells. In order to simulate blood and circulation, the researchers put the model into a computer-controlled bioreactor with flexible tube pump, developed by the IGB. This enables the nutrient solution to be fed in and carried away in the same way as in veins and arteries in humans. "The cells were active for up to three weeks," says Dr. Schanz. "This time was sufficient to analyze and evaluate the functions. A longer period of activity is possible, however." The researchers established that the cells work in a similar way to those in the body. They detoxify, break down drugs and build up proteins. These are important pre-conditions for drug tests or transplants, as the effect of a substance can change when transformed or broken down – many drugs are only metabolized into their therapeutic active form in the liver, while others can develop poisonous substances. The researchers have demonstrated the basic possibilities for use of the tissue models – liver, skin, intestine and windpipe. At the moment, the test system is being examined. Within two years it could provide a safer alternative to animal experiments. ......... ZenMaster

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For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/ and http://www.geocities.com/giantfideli/index.html

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A New Method for Bone-marrow-derived Liver Stem Cells Isolation

Researchers designed a culture system to isolate, proliferate and differentiate liver stem cells directly from bone marrow cells. Thursday, 16 April 2009 Great interest has been aroused in the identification and isolation of liver stem cells from bone marrow cells. Several subsets of bone marrow cells have been found to have the potential to differentiate into hepatocytes, however, sorting based on immunological methods is difficult because of the complicated surface markers of the stem cells; furthermore, no report of successful passage has been published. A research article to be published on April 7, 2009 in the World Journal of Gastroenterology addresses this question. The research team led by Dr. Yun-Feng Cai and his colleagues from the Affiliated Foshan Hospital and the Second Affiliated Hospital of Sun Yat-sen University established a carefully designed culture system to isolate, proliferate and differentiate liver stem cells directly from bone marrow cells, and they were able to achieve six passages of the stem cells. The results suggest that BDLSCs can be purified and passaged (proliferated). The selecting culture system that contains cholestatic serum can purify BDLSCs directly from bone marrow cells, which provides an easy method to separate stem cells, by avoiding complicated immunological manipulation. The successful passage of the stem cells further verifies the proliferating ability of the cells, although the passage is limited, and further research will provide more experience. In this study, the authors used their original method to retrieve the cells, which are possibly BDLSCs. Then, they used fluorescence-activated cell sorting to determine the cells' characteristics before and after differentiation. This is an interesting and potentially important study, which suggests that bone-marrow-derived cells can be stimulated to expand and then differentiate into hepatocyte-like cells, which can possibly be used to treat liver disease. Reference: Passage of bone marrow-derived liver stem cells with a proliferating culture system Yun-Feng Cai, Ji-Sheng Chen, Shu-Ying Su, Zuo-Jun Zhen, Huan-Wei Chen World J Gastroenterol 2009, 15(13): 1630-1635 ......... ZenMaster

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For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/ and http://www.geocities.com/giantfideli/index.html

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