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Patient-derived Nerve Cells Help Scientists Understand What Goes Wrong in Individuals with Inherited Syndrome that Includes Autism: For complex disorders like autism that are likely caused by multiple rare inherited changes to genes, scientists are unable to produce experimental animals that reflect the genetic complexity of humans, and therefore animal models are not useful. Autism researchers have found a way to increase their chances of understanding how genetic changes cause autism by studying individuals with Timothy syndrome. Individuals with Timothy syndrome suffer irregular heartbeat, hypoglycemia, and developmental delay, and more than 60% are diagnosed with autism spectrum disorder (ASD). The symptoms are caused by an inherited change to a single gene. Scientists reprogrammed skin cells from individuals who are affected and unaffected with Timothy syndrome into induced pluripotent stem cells (iPSCs). The iPSCs were then generated into nerve cells (neurons) for studies to identify differences between Timothy syndrome neurons (TS-neurons) and neurons from unaffected individuals. Numerous problems were identified with the TS-neurons. Cultures of TS-neurons generated fewer types of the specific nerve cells that are important for making connections between different brain regions as compared to cultures of neurons derived from unaffected individuals. TS-neurons have defects in firing action potentials, and in a cellular communication process called calcium signaling, and they make abnormally high amounts of certain neurotransmitters—brain chemicals used for communicating with other cells. The scientists identified a drug that can reverse the abnormal characteristics of the TS-neurons, providing hope of a future drug treatment for Timothy syndrome. This research sheds light on the molecular basis of Timothy syndrome, and how its effects on neurons may cause autism spectrum disorders. Nat Med 17:1657–62; laboratory of R. Dolmetsch (supported by NIH Pioneer Award). 2011 Nov 27.
Scientists Use Human Eggs to Reprogram Skin Cells and Generate Human Pluripotent Cells: Human somatic cell nuclear transfer (SCNT) has not yet been accomplished. SCNT involves combining an enucleated (nucleus removed) egg with the nucleus of a somatic cell (a body cell other than an egg or sperm) and stimulating the resulting embryo-like entity to divide. In humans, however, the embryo-like entity fails to reach the blastocyst stage, and so scientists are unable to derive human embryonic stem cells (hESCs) from it. Scientists in New York decided to add the somatic cell nucleus to a human egg and stimulate division without removing the egg’s nucleus. The resulting entity developed to the blastocyst stage, and the scientists derived pluripotent stem cells from it. This demonstrates that the human egg nucleus is able to reprogram the somatic cell nucleus to a pluripotent state. The new cells are triploid (contain 3 copies of the DNA, rather than the normal 2 copies) and so are unsuitable for transplantation therapy. Still, they will be a valuable resource for stem cell research. Scientists may now compare pluripotent stem cells made via this new technique with those generated via forced expression of reprogramming factors (called induced pluripotent stem cells, or iPSCs). Knowledge from these comparisons will help improve the efficiency of iPSC generation, thus advancing study of human cells for research and potential therapies. Nature 478:70–5; Laboratory of D. Egli (Funded by the New York Stem Cell Foundation). 2011 Oct 5.
The Ideal Control: Scientists Generate Genetically Defined Stem Cells to Study Parkinson's Disease in a Dish: Scientists are studying induced pluripotent stem cells (iPSCs) derived from individuals with diseases in order to learn how disease develops and how they might intervene to prevent or reverse the disease process. However, some diseases still pose a challenge for this type of study. For example, in some human diseases, one altered gene does not always cause the disease, and in others, the disease develops late in life. In these cases, scientists would like to compare a cell with the altered gene to a cell with a normal copy of the gene side by side. But subtle disease characteristics might show up only if the genetic background of the cells is carefully controlled. Now, scientists have used genetic engineering to generate two types of ideal control cells for comparison—other than the disease-causing gene, the cells are genetically identical. Beginning with skin cells from a patient with an inherited form of Parkinson's disease (PD), they generated PD- iPSCs. Next, they corrected the mutation in the PD-iPSCs. They coaxed both PD-iPSCs and corrected iPSCs to generate nerve cells. They can now study the characteristics of both disease-corrected and disease-carrying nerve cells from the same person. The scientists also used genetic engineering to generate two genetically-identical human embryonic stem cell (hESC) lines carrying mutations associated with two different forms of inherited PD, for comparison with the original wild type (normal) hESC cells. Using the new cell lines as tools, scientists can now make careful comparisons to learn how these mutations cause disease. This research also demonstrates the feasibility of correcting disease-causing mutations in human cells. Cell 146:318–31; laboratory of R. Jaenisch (NIH-supported). 2011 Jul 22.
- Scientists Take Advantage of Molecular Memory to Generate Insulin-producing Cells from Human Induced Pluripotent Stem Cells: Scientists hope to use induced pluripotent stem cells (iPSCs) to generate cells to replace those lost or damaged by diseases such as diabetes. Individuals with diabetes can't regulate their blood sugar because their bodies don't make enough insulin, or their bodies don't respond to insulin properly. Restoring insulin-producing ability (and thus blood sugar regulation) is a major therapeutic goal. Scientists are trying to use stem cells to generate human pancreatic beta cells – the insulin-producing cells of the pancreas. Prior research suggests that even after reprogramming, iPSCs "remember" their original identities. Israeli researchers hypothesized that iPSCs generated from beta cells might also retain a molecular memory that could be exploited to generate more beta cells. They compared gene expression patterns in 3 cell types: non-beta-cell derived human iPSCs, beta-cell-derived human iPSCs (BiPSCs), and human embryonic stem cells (hESCs). Their data suggest that BiPSCs maintain an open chromosome structure (i.e., genes more likely to be expressed) in areas of the chromosome that contain genes most important for beta cell function. These important beta cell-specific regions of the chromosome were not open in either non-beta-cell-derived iPSCs or in hESCs. Next, the scientists differentiated BiPSCs and hESCs into beta cells, transplanted them into diabetic mice, and evaluated the abilities of each to regulate blood sugar. Their results suggest that BiPSC-derived beta cells matured faster after transplantation and produced higher levels of insulin than beta cells produced from hESCs. These data support previous studies' conclusions that reprogrammed cells retain an epigenetic memory of their former cell type, and suggest that scientists may be able to take advantage of this memory to generate cells for replacement therapies. Cell Stem Cell 9:17–23; Laboratory of N. Benvenisty (Supported by Israel and the JDRF). 2011 July 8.
Induced Pluripotent Stem Cells Rejected in Mice: Scientists hoped that replacement tissues derived from induced pluripotent stem cells (iPSCs) generated from adult skin cells would avoid rejection after transplantation into the original skin cell donor. This potential gave iPSCs a proposed advantage over tissues derived from human embryonic stem cells. Ironically, a mouse study now demonstrates that iPSCs generated from an individual mouse are rejected even by that same mouse, while unrelated mouse ESCs are tolerated. This scenario differs from an actual transplant, because the stem cells, and not differentiated cells, were transplanted into the mice. Nonetheless, this study highlights a potential safety concern for clinical applications of iPSC-derived cells. The authors suggest that changes in gene expression during the cells' reprogramming to iPSCs may attract attack from the recipient’s immune system. Nature 474: 212–216; laboratory of Y. Xu. (NIH and CIRM-supported). 2011 June 09.
- Scientists are generating Induced Pluripotent Stem Cells (iPSCs) from individuals with a disease, and using these cells to learn more about causes and possible treatments for the diseases.
- Telomere shortening and loss of self-renewal in dyskeratosis congenita induced pluripotent stem cells. Individuals who inherit dyskeratosis congenita (DC) have characteristic abnormally-shaped fingernails and toenails, a lacy rash on the face and chest, and white patches in the mouth. They also have an increased risk of developing several life-threatening conditions, including bone marrow failure, leukemia, and pulmonary fibrosis. Although patient-derived iPSCs offer hope for disease modeling, it is unclear whether the iPSCs will mirror the faulty biochemical characteristics of the patients from which they were derived. NIH-funded scientists generated iPSCs from individuals with several different forms of inherited DC, and determined that the iPSCs demonstrate the same faulty biochemistry found in the original patient cells, and that the severity of the cellular errors correlates with the patients’ disease severity. This makes patient-derived iPSCs a valid model to study DC, and to screen possible treatments. Nature [Epub ahead of print]; laboratories of S.E. Artandi and R.A. Reijo Pera. (NIH-supported). 2011 May 22.
- Modelling schizophrenia using human induced pluripotent stem cells. Schizophrenia is a chronic, severe, and disabling brain disorder that affects about 1% of Americans. Scientists generated iPSCs from individuals with schizophrenia (SCZD-iPSCs), and then differentiated these SCZD- iPSCs into nerve cells, or neurons. They compared properties of iPSC-derived neurons from individuals with and without schizophrenia to try to identify how schizophrenia affects brain function. Neurons generated from SCZD-iPSCS demonstrated differences in gene expression and cell-cell communications. When treated with an antipsychotic drug (loxapine), the neurons derived from SCZD-iPSCS behaved more like iPSC-derived neurons of individuals without schizophrenia. Nature 473:221–5; laboratory of F. Gage. (CIRM-supported). 2011 May 12.
- Genetic correction and analysis of induced pluripotent stem cells from a patient with gyrate atrophy. Gyrate atrophy is an inherited disorder characterized by progressive vision loss. People with this disorder continually lose cells (atrophy) in the retina, which is the specialized light-sensitive tissue that lines the back of the eye, and in a nearby tissue layer called the choroid. Since scientists know which gene mutation causes this disorder, they derived iPSCs from a patient and attempted to correct the mutation. Next, they compared the original patient-derived iPSCs to the gene-corrected iPSCs to determine if the prolonged culture period used to achieve gene correction caused additional mutations in the cells. Although the process of generating patient-derived iPSCs caused numerous mutations, they determined that the correction of the genetic defect in those iPSCs did not cause new mutations. PNAS 108: 6537–42; laboratory of J. Thomson. (NIH-supported). 2011 April 19.
- Using induced pluripotent stem cells to investigate cardiac phenotypes in Timothy syndrome. Timothy syndrome is a rare disorder that affects many parts of the body including the heart, digits (fingers and toes), and the nervous system. Individuals with Timothy syndrome suffer from a heart condition called long QT syndrome, which causes the heart muscle to take longer than usual to recharge between beats. This abnormality in the heart's electrical system can cause irregular heartbeats (arrhythmia), which can lead to sudden death. NIH-funded scientists generated iPSCs from individuals with Timothy syndrome, and differentiated the iPSCs into heart cells, or cardiomyocytes. By performing tests on the iPSC-derived cardiomyocytes, they were able to identify the molecular basis for long QT syndrome. Next, they tested drugs on the cardiomyocytes and identified one, roscovitine, which seemed to correct the arrhythmia. Nature 471:230–4; laboratory of R. Dolmetsch. (NIH-supported: NIH Director's Pioneer Award to R. Dolmetsch). 2011 March 10 .
- Discovery of Lung Stem Cells May Herald New Treatments: NIH-supported scientists have found stem cells in the human lung capable of forming different parts of the lung, including blood vessels. NEJM 364(19); laboratory of P. Anversa. 2011 May 12.
- Exploring Different Methods to Make Induced Pluripotent Stem Cells: Certain aspects of the original induced pluripotent stem cell (iPSC) reprogramming technique are not suited for possible clinical applications. See "Safer Reprogramming of Human Cells." Scientists continue to develop improved methods for generating iPSCs.
- Use of miRNA: Scientists identified microRNA (miRNA) that was highly expressed in embryonic stem cells, and tested its ability to reprogram non-embryonic mouse and human fibroblasts. The miRNA reprogrammed non-embryonic cells without the use of any viruses, or any of the traditional reprogramming factors (Oct4/Sox2/ Klf4/Myc, or OSKM) and was two orders of magnitude more efficient than the OSKM methods. Cell Stem Cell 8: 376–388; laboratories of J. A. Epstein and E.E. Morrisey (NIH-supported). 2011 April 8.
- Beginning with Cells that are Amenable to Reprogramming: Characteristics of certain cell types, when used as starting material, are likely to make them more amenable to being reprogrammed into iPSCs. Scientists determined that epigenetic and gene expression in cord blood and adult mononuclear (blood) cells were closest to iPSCs and hESCs. They reprogrammed these two cell types using a non-integrating vector (does not insert itself into the DNA of the cells) carrying 5 reprogramming factors. The technique takes less time than reprogramming other cell types, such as fibroblasts (<10 days vs. 4+weeks), and they were unable to detect any leftover vector in the resulting iPSCs. Cell Res. 21: 518–529; laboratory of Linzhao Cheng (NIH-supported). 2011 March.
- How to Make More Stem Cells: Scientists know that stem cells are found in small quantities and in particular locations within many (if not all) organs of the human body. Although these resident stem cells are able to replace cells of the organ following normal wear and tear, they do not seem able to repair or correct more severe organ damage—like that caused by disease or severe injury. Scientists hypothesize that the limited number of adult stem cells and their limited ability to make more copies of themselves (a process known as self-renewal) may be at fault. They tried to overcome this problem by isolating human neural stem cells and forcing them to self-renew. To do this, they infected the neural stem cells with a virus carrying v-myc, a factor known to be important for self-renewal. V-myc was combined with a tetracycline regulation system, so as to activate self-renewal of the cells only when the drug tetracycline was added to the culture system. The scientists used this system to generate large numbers of neural stem cells. Next, the human neural stem cells were transplanted into a mouse model of human stroke.
The study reports three important observations after the transplant:
- self-renewal stopped because there was no longer any tetracycline in the system,
- some of the transplanted cells survived, migrated to the area of injury, and differentiated into neurons and glia, and
- the mice demonstrated improvement of stroke symptoms.
The authors propose this new system as a means of generating large numbers of therapeutic cells for a particular organ. Proc Natl Acad Sci U S A. 108:4876–81; Laboratories of S.U. Kim and E. Snyder (Not NIH-supported). 2011 March 22.