Category Archives: Stem Cells

Researchers from the University of Minnesota's Lillehei Heart Institute have effectively treated muscular dystrophy in mice using human stem cells derived from a new process that for the first time makes the production of human muscle cells from stem cells efficient and effective.

The research, published today in Cell Stem Cell, outlines the strategy for the development of a rapidly dividing population of skeletal myogenic progenitor cells (muscle-forming cells) derived from induced pluripotent (iPS) cells. iPS cells have all of the potential of embryonic stem (ES) cells, but are derived by reprogramming skin cells. They can be patient-specific, which renders them unlikely to be rejected, and do not involve the destruction of embryos.

This is the first time that human stem cells have been shown to be effective in the treatment of muscular dystrophy.

According to U of M researchers who were also the first to use ES cells from mice to treat muscular dystrophy there has been a significant lag in translating studies using mouse stem cells into therapeutically relevant studies involving human stem cells. This lag has dramatically limited the development of cell therapies or clinical trials for human patients.

The latest research from the U of M provides the proof-of-principle for treating muscular dystrophy with human iPS cells, setting the stage for future human clinical trials.

"One of the biggest barriers to the development of cell-based therapies for neuromuscular disorders like muscular dystrophy has been obtaining sufficient muscle progenitor cells to produce a therapeutically effective response," said principal investigator Rita Perlingeiro, Ph.D., associate professor of medicine in the Medical School's Division of Cardiology. "Up until now, deriving engraftable skeletal muscle stem cells from human pluripotent stem cells hasn't been possible. Our results demonstrate that it is indeed possible and sets the stage for the development of a clinically meaningful treatment approach."

Upon transplantation into mice suffering from muscular dystrophy, human skeletal myogenic progenitor cells provided both extensive and long-term muscle regeneration which resulted in improved muscle function.

To achieve their results, U of M researchers genetically modified two well-characterized human iPS cell lines and an existing human ES cell line with the PAX7 gene. This allowed them to regulate levels of the Pax7 protein, which is essential for the regeneration of skeletal muscle tissue after damage. The researchers found this regulation could prompt nave ES and iPS cells to differentiate into muscle-forming cells.

Up until this point, researchers had struggled to make muscle efficiently from ES and iPS cells. PAX7 induced at exactly the right time helped determine the fate of human ES and iPS cells, pushing them into becoming human muscle progenitor cells.

Once Dr. Perlingeiro's team was able to pinpoint the optimal timing of differentiation, the cells were well suited to the regrowth needed to treat conditions such as muscular dystrophy. In fact, Pax7-induced muscle progenitors were far more effective than human myoblasts at improving muscle function. Myoblasts, which are cell cultures derived from adult muscle biopsies, had previously been tested in clinical trials for muscular dystrophy, however the myoblasts did not persist after transplantation.

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Researchers develop new muscular dystrophy treatment approach using human stem cells

ScienceDaily (May 3, 2012) Researchers have rejuvenated aged hematopoietic stem cells to be functionally younger, offering intriguing clues into how medicine might one day fend off some ailments of old age.

Scientists at Cincinnati Children's Hospital Medical Center and the Ulm University Medicine in Germany report their findings online May 3 in the journal Cell Stem Cell. The paper brings new perspective to what has been a life science controversy -- countering what used to be broad consensus that the aging of hematopoietic stem cells (HSCs) was locked in by nature and not reversible by therapeutic intervention.

HSCs are stem cells that originate in the bone marrow and generate all of the body's red and white blood cells and platelets. They are an essential support mechanism of blood cells and the immune system. As humans and other species age, HSCs become more numerous but less effective at regenerating blood cells and immune cells. This makes older people more susceptible to infections and disease, including leukemia.

Researchers in the current study determined a protein that regulates cell signaling -- Cdc42 -- also controls a molecular process that causes HSCs from mice to age. Pharmacologic inhibition of Cdc42 reversed HSC aging and restored function similar to that of younger stem cells, explained Hartmut Geiger, PhD, the study's principal investigator and a researcher in the Division of Experimental Hematology/Cancer Biology at Cincinnati Children's, and the Department of Dermatology and Allergic Diseases, Ulm University Medicine.

"Aging is interesting, in part because we still don't understand how we age," Geiger said. "Our findings suggest a novel and important role for Cdc42 and identify its activity as a target for ameliorating natural HSC aging. We know the aging of HSCs reduces in part the response of the immune system response in older people, which contributes to diseases such as anemia, and may be the cause of tissue attrition in certain systems of the body."

The findings are early and involve laboratory manipulation of mouse cells, so it remains to be seen what direct application they may have for humans. Still, the study expands what is known about the basic molecular and cellular mechanisms of aging -- a necessary step to one day designing rational approaches to aiding a healthy aging process.

One reason the research team focused on Cdc42 is that previous studies have reported elevated activity of the protein in various tissue types of older mice -- which have a natural life span of around two years. Also, elevated expression of Cdc42 has been found in immune system white blood cells in older humans.

In the current study, researchers found elevated activity of Cdc42 in the HSCs of older mice. They also were able to induce premature aging of HSCs in mice by genetically increasing Cdc42 activity in the cells. The aged cells lost structural organization and polarity, resulting in improper placement and spacing of components inside the cells. This disorganization contributed to the cells' decreased functional efficiency.

The researchers then analyzed HSCs from older mice to see if inhibition of Cdc42 would reverse the aging process. They used a specific dose (5uM) of a pharmacologic inhibitor of Cdc42, CASIN, to reduce the protein's activity in the cells -- processing them for 16 hours ex vivo in laboratory cultures. This improved structural organization, increased polarity and restored functionality in the older cells to levels found in young cells.

To test the rejuvenated cells, the researchers used a process known as serial competitive transplantation. This included extracting HSCs from young (2-4 months) and aged (20-26 months) mice and processing them in laboratory cultures. Young and rejuvenated cells were then engrafted into recipient mice. This allowed scientists to compare how well young and rejuvenated aged HSCs started to repopulate and transform into different types of blood cells. It also confirmed that HSCs rejuvenated by targeting Cdc42 do function similarly to young stem cells.

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Aged hematopoietic stem cells rejuvenated to be functionally younger

Public release date: 3-May-2012 [ | E-mail | Share ]

Contact: Mika Ono mikaono@scripps.edu 858-784-2052 Scripps Research Institute

LA JOLLA, CA May 3, 2012 A team led by scientists at The Scripps Research Institute and the University of California (UC) San Diego has discovered a new type of dynamic change in human stem cells.

Last year, this team reported recurrent changes in the genomes of human pluripotent stem cells as they are expanded in culture. The current report, which appears in the May 4, 2012 issue of the journal Cell Stem Cell, shows that these cells can also change their epigenomes, the patterns of DNA modifications that regulate the activity of specific genessometimes radically. These changes may influence the cells' abilities to serve as models of human disease and development.

"Our results show that human pluripotent stem cells change during expansion and differentiation in ways that are not easily detected, but that have important implications in using these cells for basic and clinical research," said team leader Louise Laurent, assistant professor in the UC San Diego School of Medicine.

Human pluripotent stem cells can give rise to virtually every type of cell in the body. Because of this remarkable quality, they hold huge potential for cell replacement therapies and drug development.

Many avenues of stem cell research focus on determining how genes are turned on and off during the course of normal development or at the onset of a disease transformation. It is widely accepted that gene activation and silencing play important roles in transforming all-purpose stem cells into the specific adult cell types that make up the specialized tissues of organs such as the heart and brain.

In the new study, Laurent and her collaborator, Professor Jeanne Loring of Scripps Research, and their colleagues focused on understanding gene silencing via DNA methylation, a process whereby bits of DNA are chemically marked with tags that prevent the genes from being expressed, effectively switching them off. Errors in gene silencing via DNA methylation are known contributors to serious developmental defects and cancer.

Specifically, the team assessed the state of both DNA methylation and gene expression in the most comprehensive set of human stem cell samples to date, comprised of more than 200 human pluripotent stem cell samples from more than 100 cell lines, along with 80 adult cell samples representing 17 distinct tissue types. The researchers used a new global DNA methylation array, developed in collaboration with Illumina, Inc, which detects the methylation state of 450,000 sites in the human genome. The results showed surprising changes in patterns of DNA methylation in the stem cells. Because of the unprecedented breadth of the study, the researchers were able to determine the frequency of different types of changes.

One of the anomalies highlighted by the study centers on X chromosomes. Since female cells contain two X chromosomes and males only one, one of the X chromosomes in females is normally silenced by DNA methylation through a process called X-chromosome inactivation (XCI). The new study demonstrated that a majority of female human pluripotent stem cells cultured in the lab lost their X chromosome inactivation over time, resulting in cells with two active X chromosomes.

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Study reveals dynamic changes in gene regulation in human stem cells

ScienceDaily (May 3, 2012) A team led by scientists at The Scripps Research Institute and the University of California (UC) San Diego has discovered a new type of dynamic change in human stem cells. Last year, this team reported recurrent changes in the genomes of human pluripotent stem cells as they are expanded in culture. The current report, which appears in the May 4, 2012 issue of the journal Cell Stem Cell, shows that these cells can also change their epigenomes, the patterns of DNA modifications that regulate the activity of specific genes -- sometimes radically. These changes may influence the cells' abilities to serve as models of human disease and development.

"Our results show that human pluripotent stem cells change during expansion and differentiation in ways that are not easily detected, but that have important implications in using these cells for basic and clinical research," said team leader Louise Laurent, assistant professor in the UC San Diego School of Medicine.

Human pluripotent stem cells can give rise to virtually every type of cell in the body. Because of this remarkable quality, they hold huge potential for cell replacement therapies and drug development.

Many avenues of stem cell research focus on determining how genes are turned on and off during the course of normal development or at the onset of a disease transformation. It is widely accepted that gene activation and silencing play important roles in transforming all-purpose stem cells into the specific adult cell types that make up the specialized tissues of organs such as the heart and brain.

In the new study, Laurent and her collaborator, Professor Jeanne Loring of Scripps Research, and their colleagues focused on understanding gene silencing via DNA methylation, a process whereby bits of DNA are chemically marked with tags that prevent the genes from being expressed, effectively switching them off. Errors in gene silencing via DNA methylation are known contributors to serious developmental defects and cancer.

Specifically, the team assessed the state of both DNA methylation and gene expression in the most comprehensive set of human stem cell samples to date, composed of more than 200 human pluripotent stem cell samples from more than 100 cell lines, along with 80 adult cell samples representing 17 distinct tissue types. The researchers used a new global DNA methylation array, developed in collaboration with Illumina, Inc, which detects the methylation state of 450,000 sites in the human genome. The results showed surprising changes in patterns of DNA methylation in the stem cells. Because of the unprecedented breadth of the study, the researchers were able to determine the frequency of different types of changes.

One of the anomalies highlighted by the study centers on X chromosomes. Since female cells contain two X chromosomes and males only one, one of the X chromosomes in females is normally silenced by DNA methylation through a process called X-chromosome inactivation (XCI). The new study demonstrated that a majority of female human pluripotent stem cells cultured in the lab lost their X chromosome inactivation over time, resulting in cells with two active X chromosomes.

This phenomenon could affect stem cell-based models of diseases caused by mutations of the X chromosome, such as Lesch-Nyhan disease, the researchers note. These cell-based models require that only the diseased copy of an X-linked gene be expressed, with the normal copy of the gene in females silenced via XCI. As the originally inactive X chromosome becomes active, the normal copy of the gene is expressed, changing the phenotype of the cells from diseased to normal.

"If an X chromosome that was assumed to be inactive is actually active, scientists may find that their cells perplexingly change from mutant to normal over time in culture," Loring said.

Another epigenomic aberration noted in pluripotent cells was in imprinted genes. Human cells contain two copies of most genes: one inherited from the mother and one from the father. In most cases, both the maternal and paternal copies of a gene are expressed equally. This is not the case, however, for imprinted genes, some of which are only expressed from the paternal chromosomes and others expressed only from the maternal chromosomes. This parent-of-origin specific gene expression involves silencing of one of the copies of the gene. Abnormalities in this selective silencing of genes can lead to serious developmental diseases.

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Dynamic changes in gene regulation in human stem cells revealed

ScienceDaily (May 4, 2012) Researchers from the University of Minnesota's Lillehei Heart Institute have effectively treated muscular dystrophy in mice using human stem cells derived from a new process that -- for the first time -- makes the production of human muscle cells from stem cells efficient and effective.

The research, published May 4 in Cell Stem Cell, outlines the strategy for the development of a rapidly dividing population of skeletal myogenic progenitor cells (muscle-forming cells) derived from induced pluripotent (iPS) cells. iPS cells have all of the potential of embryonic stem (ES) cells, but are derived by reprogramming skin cells. They can be patient-specific, which renders them unlikely to be rejected, and do not involve the destruction of embryos.

This is the first time that human stem cells have been shown to be effective in the treatment of muscular dystrophy.

According to U of M researchers -- who were also the first to use ES cells from mice to treat muscular dystrophy -- there has been a significant lag in translating studies using mouse stem cells into therapeutically relevant studies involving human stem cells. This lag has dramatically limited the development of cell therapies or clinical trials for human patients.

The latest research from the U of M provides the proof-of-principle for treating muscular dystrophy with human iPS cells, setting the stage for future human clinical trials.

"One of the biggest barriers to the development of cell-based therapies for neuromuscular disorders like muscular dystrophy has been obtaining sufficient muscle progenitor cells to produce a therapeutically effective response," said principal investigator Rita Perlingeiro, Ph.D., associate professor of medicine in the Medical School's Division of Cardiology. "Up until now, deriving engraftable skeletal muscle stem cells from human pluripotent stem cells hasn't been possible. Our results demonstrate that it is indeed possible and sets the stage for the development of a clinically meaningful treatment approach."

Upon transplantation into mice suffering from muscular dystrophy, human skeletal myogenic progenitor cells provided both extensive and long-term muscle regeneration which resulted in improved muscle function.

To achieve their results, U of M researchers genetically modified two well-characterized human iPS cell lines and an existing human ES cell line with the PAX7 gene. This allowed them to regulate levels of the Pax7 protein, which is essential for the regeneration of skeletal muscle tissue after damage. The researchers found this regulation could prompt nave ES and iPS cells to differentiate into muscle-forming cells.

Up until this point, researchers had struggled to make muscle efficiently from ES and iPS cells. PAX7 -- induced at exactly the right time -- helped determine the fate of human ES and iPS cells, pushing them into becoming human muscle progenitor cells.

Once Dr. Perlingeiro's team was able to pinpoint the optimal timing of differentiation, the cells were well suited to the regrowth needed to treat conditions such as muscular dystrophy. In fact, Pax7-induced muscle progenitors were far more effective than human myoblasts at improving muscle function. Myoblasts, which are cell cultures derived from adult muscle biopsies, had previously been tested in clinical trials for muscular dystrophy, however the myoblasts did not persist after transplantation.

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New muscular dystrophy treatment approach developed using human stem cells

Newswise HOUSTON Prostate cancer cells that defy treatment and display heightened tumor-generating capacity can be identified by levels of prostate specific antigen (PSA) expressed in the tumor cells, a research team led by scientists at The University of Texas MD Anderson Cancer Center reports in the May 3 edition of Cell Stem Cell.

Using a new technique, we were able for the first time to separate low-PSA and high-PSA prostate cancer cells. This led to the discovery of a low-PSA population of cancer stem cells that appears to be an important source of castration-resistant prostate cancer, said study senior author Dean Tang, Ph.D., professor in MD Andersons Department of Molecular Carcinogenesis.

Hormone therapy is used to block production of testosterone, which fuels prostate cancer growth, via either chemical or physical castration. Tumors eventually resist this approach.

In cell lines and mouse model experiments, the low-PSA cells resisted chemotherapy and thrived under hormone deprivation, the two main prostate cancer drug treatments , the researchers found.

Low-PSA cells were found to be both self-renewing and capable of differentiating into other prostate cancer cell types upon division, a hallmark of stem cells called asymmetric cell division.

Asymmetric cell division is the gold standard feature of normal stem cells, Tang said. Using time-lapse fluorescent microscopy, we were able to show asymmetric cell division by filming a low-PSA cell dividing into one high-PSA cell and one low-PSA cell.

Their findings point to the need to develop new therapeutics to target low-PSA prostate cancer cells that can be combined with hormone therapy to wipe out cancer cells and prevent recurrence.

Low-PSA tumors associated with advanced prostate cancer

Previous research by others indicated that low-PSA tumor cells are rare in early stage disease but become more abundant in advanced prostate cancer. And patients whose tumors were composed of more than 50 percent PSA-positive cells enjoyed longer survival.

This made Tang and colleagues wonder whether the two cell types fundamentally differ from each other and so play different roles in prostate cancer progression.

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Scientists Identify Prostate Cancer Stem Cells Among Low-PSA Cells

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THURSDAY, May 3 (HealthDay News) -- Researchers who found a way to rejuvenate aged blood-forming cells in mice say their achievement offers clues about how it may be possible to combat health problems associated with old age.

The study by scientists at Cincinnati Children's Hospital Medical Center and Ulm University Medicine in Germany appeared online May 3 in the journal Cell Stem Cell.

Hematopoietic (meaning "to make blood") stem cells, which originate in the bone marrow, produce all of the body's red and white blood cells and platelets. As people age, these cells increase in number but become but less effective at generating new blood cells and immune cells. This makes older people more susceptible to infections and diseases, including leukemia.

In laboratory experiments with mouse cells, the researchers found that a specific protein that regulates cell aging also controls a process that causes blood-making stem cells to age. Using drugs to inhibit the action of this protein (called Cdc42) reversed aging of the hematopoietic stem cells and restored their function to a level similar to that of younger stem cells.

It had been believed that the aging of hematopoietic stem cells was locked in by nature and could not be reversed by using drugs, according to a hospital news release.

"Our findings suggest a novel and important role for Cdc42, and identify its activity as a target for ameliorating natural [hematopoietic stem cell] aging," principal investigator Hartmut Geiger, of the University of Ulm, said in the release. "We know the aging of [these stem cells] reduces in part the response of the immune system response in older people, which contributes to diseases such as anemia and may be the cause of tissue attrition in certain systems of the body."

Researchers say the next step is to test a protein inhibitor in mice to see how hematopoietic stem cells and various tissues respond. The researchers also are gathering samples of human blood-making stem cells for future lab tests.

Although studies involving animals can be useful, they frequently fail to produce similar results in humans.

-- Robert Preidt

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Researchers Rejuvenate Blood-Forming Stem Cells in Mice