Cells more representative of the US and world populations could lead to more accurate research and safer, more effective therapies
An international team of scientists led by researchers at The Scripps Research Institute has developed a straightforward technique to determine the ethnic origin of stem cells.
The Scripps Research scientists initiated the study—published in the January 2010 edition of the prestigious journal Nature Methods—because the availability of genetically diverse cell lines for cell replacement therapy and drug development could have important medical consequences. Research has shown that discordance between the ethnic origin of organ donors and recipients can influence medical outcomes for tissue transplantation, and that the safety and effectiveness of specific drugs can vary widely depending on ethnic background.
The team's analysis of a variety of human embryonic stem cell lines currently in use in research laboratories around the world found that these cells originated largely from Caucasian and East Asian populations, with little representation from populations originating in Africa. In response to these results, the scientists used skin cells from an individual of West African Yoruba heritage to create a new stem cell line, the first to carry the genetic profile of this ethnic group.
"Ethnic origin is a critical piece of information that should come with every cell line," said Scripps Research Professor Jeanne Loring, Ph.D., who is senior author of the paper. "Everyone who works with stem cells should be doing this kind of analysis."
"Knowing that a big push in the future is using these lines in the clinic and in drug development, there's a need to have an ethnically diverse population of cells," added Louise Laurent, M.D., Ph.D., assistant professor at the University of California, San Diego (UCSD) and research associate at Scripps Research, who is first author of the paper with Caroline Nievergelt, Ph.D., also an assistant professor at UCSD.
Greater diversity in cell samples would set the stage for more broadly relevant research by labs in academia and industry, more robust results on the safety and efficacy of potential therapies, and more successful tissue transplants.
The Promise of Stem Cells
Normally, cells develop from stem cells into a myriad of increasingly more specialized cell types during early development and throughout a lifetime. In humans and other mammals, these developmental events are usually irreversible. This means that when tissues are damaged or cells are lost, the body has limited means by which to replenish them.
Having a source of stem cells would be useful in many medical situations because these cells are "pluripotent," having the ability to become any of the body's cell types. Pluripotent stem cells would potentially provide physicians with the ability to replace or repair damaged tissues throughout the body. For example, pluripotent stem cells could be differentiated into the damaged cell type and transplanted.
Much research on pluripotent stem cells to date has been conducted on human embryonic stem cells, which are harvested from discarded embryos (those created but not used for the purposes of in vitro fertilization, a technique to help couples conceive). However, recently another source of pluripotent stem cells has come onto the scene. These cells—called induced pluripotent stem cells—are created by taking a sample of skin cells or another type of differentiated cell and using chemicals and molecular biology techniques to coax them back into a pluripotent state.
The current analysis included 47 human embryonic stem cell lines collected from labs located around the world—including Korea, Australia, and Finland. The analysis also included five induced pluripotent stem cell lines.
Ancestors Forgotten and Remembered
To determine the ethnic origins of the stem cell lines and to link them to genetic "signatures" that might affect medical outcomes, the scientists drew on previous research from the International HapMap Project, published in the journal Nature in 2003. This research linked single-letter alterations in the genetic code—known as single nucleotide polymorphisms, or SNPs—with people of known ethnic origins. This data provided a way to identify the ethnic heritage of a donor of any cell.
Laurent noted that simply asking cell donors about their ethnic heritage does not provide accurate data. "There's often an ancestor from a different area who a person doesn't know about," she said.
The technology used for the new study, known as SNP genotyping, uses microarrays, which are easily available, inexpensive, and relatively straight forward for scientists to use.
When the Scripps Research scientists applied the technique to the embryonic stem cell lines, they found that Caucasians were especially well represented among the samples, followed by East Asians. Cells of some mixed heritage were also common. Notably lacking from the samples were cell lines representing African heritage.
In addition, the authors found that the country in which a cell line was generated did not necessarily predict the ethnicity of the donor.
In creating a new pluripotent stem cell line from an individual with a West African Yoruba background, the scientists generated a line that contains distinct genetic markers for disease risk and drug metabolism.
"There's not a lot of value in making a new pluripotent stem cell line now unless it has something new to offer," said Loring. "I think that increasing ethnicity and genetic diversity is an important reason for generating new lines."
The data generated by the study—which Loring describes as the foundation of a new database of human pluripotent stem cell genetic information—will be available for other researchers to access for studies on specific genes, stem cell transplantation, and other topics.
In addition to Loring, Laurent, and Nievergelt, authors of the Nature Methods paper, "Restricted Ethnic Diversity in Human Embryonic Stem Cells," are: Candace Lynch and Eyitayo Fakunle of Scripps Reserach; Julie Harness of the University of California, Irvine; Uli Schmidt of Sydney IVF (Australia); Vasiliy Galat of Northwestern University Feinberg School of Medicine; Andrew Laslett of Commonwealth Scientific and Industrial Research Organisation Molecular and Health Technologies, Australian Stem Cell Centre, and Monash University; Timo Otonkoski of Biomedicum Stem Cell Center and Children's Hospital, University of Helsinki (Finland); Hans Keirstead of the University of California, Irvine; Andrew Schork of UCSD; and Hyun-Sook Park of Modern Cell and Tissue Technologies, Inc. (Korea). For more information, see http://www.nature.com/nmeth/journal/v7/n1/index.html .
The research was funded by grants from the California Institute for Regenerative Medicine, the National Institutes of Health, and the Bill and Melinda Gates Foundation.
At the request of the House Committee on Energy and Commerce as part of an investigation into preventable medical errors, the Institute of Medicine (IOM) has issued a report recommending further restrictions regarding duty hours for resident physicians and other actions to reduce resident fatigue and ensure patient safety, according to an article published in the January issue of the Journal of the American College of Radiology (JACR).
In 2003, the Accreditation Council for Graduate Medical Education (ACGME) set duty hour limits across all medical specialties nationally in order to promote safe patient care and resident well-being. The increasing acuity and intensity of medical care in teaching institutions and the scientific evidence of the negative effect of sleep deprivation on performance were cited as reasons for the new duty hour requirements.
"Compliance with the current Accreditation Council for Graduate Medical Education duty hour requirements is assessed by an anonymous annual resident survey in addition to periodic site visits," said Martha B. Mainiero, MD, lead author of the article. "When a survey indicates that a significant number of residents work beyond duty hour limits, the ACGME will perform an immediate site visit of the program as well as a focused review of the institution," said Mainiero. Data from resident surveys since the institution of the common duty hour requirements show that each year there are fewer residents who report working beyond duty hour limits.
The new IOM recommendations focus more on reducing fatigue related errors by assuring that residents get regular opportunities for sleep each day than by reducing the maximum weekly work hours. The current ACGME duty hour requirements state that residents must not work more than 80 hours per week averaged over 4 weeks, and must be provided 1 day in 7 free from all educational and clinical responsibilities, averaged over 4 weeks.
"The radiology community supports the current ACGME requirements but recognizes that there has been inadequate study of the outcomes of the current duty hour regulations and that there continues to be issues with compliance with those regulations. Therefore, we feel these issues should be addressed with more rigorous monitoring of duty hours before implementing new duty hour requirements," said Mainiero.
"The ACGME is currently reviewing the IOM's recommendations but will have little choice but to take further action in this area," said Mainiero.
The January issue of JACR is an important resource for radiology and nuclear medicine professionals as well as students seeking clinical and educational improvement.
For more information about JACR, please visit www.jacr.org.
The master regulator of muscle differentiation, MyoD, functions early in myogenesis to help stem cells proliferate in response to muscle injury, according to researchers at Case Western Reserve University. The study appears online Jan. 4 in the Journal of Cell Biology (www.jcb.org).
MyoD is a transcription factor that activates muscle-specific genes as myoblast precursors differentiate and fuse to form mature muscle fibers. But MyoD is also expressed at an earlier stage of myogenesis when quiescent stem cells rapidly expand in number to generate the myoblasts needed to repair tissue damage. The transcription factor's function in this proliferative phase is unknown.
The team found that MyoD bound to the promoter of CDC6, a gene that initiates DNA replication, suggesting that MyoD might activate Cdc6 expression in muscle stem cells to promote their reentry into the cell cycle and rapid proliferation. Indeed, Cdc6 was expressed shortly after MyoD in stimulated muscle progenitors, and knocking down MyoD reduced Cdc6 production and slowed cells' entry into S phase. MyoD works in conjunction with transcription factors from the E2F family. E2F3a activated the CDC6 promoter with MyoD, but was replaced by the repressive family member E2F4 as myoblasts began to differentiate.
Senior author Nikki Harter now wants to investigate how the transcription factors cooperate to control Cdc6 expres-sion—initial results suggest that MyoD recruits E2F3a to the promoter region. The researchers also propose that a related protein, Myf5, might control Cdc6 transcription in MyoD's absence, acting as a backup mechanism to ensure that muscle stem cells expand to repair tissue damage.
New epigenetic study in the FASEB Journal shows a link between maternal diet and brain development in gestating mice
Finally, an excuse for pregnant women to eat bacon and eggs
New epigenetic study in the FASEB Journal shows a link between maternal diet and brain development in gestating mice
If you're pregnant and looking for an excuse to eat bacon and eggs, now you've got one: a new research study published in the January 2010 print issue of the FASEB Journal (http://www.fasebj.org) by a team of University of North Carolina researchers shows that choline plays a critical role in helping fetal brains develop regions associated with memory. Choline is found in meats, including pork, as well as chicken eggs.
"Our study in mice indicates that the diet of a pregnant mother, especially choline in that diet, can change the epigenetic switches that control brain development in the fetus" said Steven Zeisel, the senior scientist involved in the work and a senior member of the FASEB Journal's editorial board. "Understanding more about how diet modifies our genes could be very important for assuring optimal development."
Zeisel and colleagues made this discovery by feeding two groups of pregnant mice different diets during the window of time when a fetus develops its hippocampus, that part of the brain responsible for memory. The first group received no choline while the other received choline (1.1g/Kg). The group that received no choline had changes in epigenetic marks on the proteins (histones) that wrap genes in cells responsible for the creation of new brain cells (neural progenitor cells). Then, by isolating these cells from the developing brains and growing them in cell culture, the scientists determined the expression of genes for two proteins that regulate neuronal cell creation and maturation. These two proteins (G9a and Calb1) were changed in the brains of fetuses whose mothers were fed low choline diets.
"We may never be able to call bacon a health food with a straight face, but the emerging field of epigenetics is already making us rethink those things that we consider healthful and unhealthful," said Gerald Weissmann, MD, Editor-in-Chief of the FASEB Journal. "This is yet another example showing that good prenatal nutrition is vitally important throughout a child's entire lifetime."
The Agricultural Research Service's Nutrient Data Laboratory makes a database available to the public in an effort to help them get healthful amounts of choline in their diets. The database provides researchers and consumers with the means to estimate daily choline intake from consumption of more than 400 different foods and can be accessed at http://www.ars.usda.gov/main/site_main.htm?modecode=12-35-45-00. The Agricultural Research Service says that "experts suggest that an adequate choline intake is 425 milligrams a day for women and 550 milligrams a day for men. Top sources of choline include meat, nuts, and eggs."
Receive monthly highlights from the FASEB Journal by e-mail. Sign up at http://www.faseb.org/fasebjournalreaders.htm. The FASEB Journal (http://www.fasebj.org) is published by the Federation of the American Societies for Experimental Biology (FASEB). The journal has been recognized by the Special Libraries Association as one of the top 100 most influential biomedical journals of the past century and is the most cited biology journal worldwide according to the Institute for Scientific Information. FASEB comprises 22 nonprofit societies with more than 80,000 members, making it the largest coalition of biomedical research associations in the United States. FASEB advances health and welfare by promoting progress and education in biological and biomedical sciences through service to its member societies and collaborative advocacy.
Details: Mihai G. Mehedint, Mihai D. Niculescu, Corneliu N. Craciunescu, and Steven H. Zeisel. Choline deficiency alters global histone methylation and epigenetic marking at the Re1 site of the calbindin 1 gene. FASEB J. 2010 24: 184-195. http://www.fasebj.org/cgi/content/abstract/24/1/184