hES Differentiation in Lesch Nyhan Disease
PUBLIC ABSTRACT. A number of human neurodegenerative disease are caused by degeneration or abnormal expression of vital signaling systems in the brain. Because some of these disorders result from complex interactions of many genes with still inadequately-defined environmental factors, some of our most powerful current methods of genetic analysis cannot be easily applied to understand how these diseases develop. However, one human disorder of the dopamine system results from the action of a single abnormal gene, making it an ideal model for studying how a single defective gene can do so much damage to one of the brain’s most important signaling systems. Lesch Nyhan Disease (LND) is a devastating metabolic and neurological disease of children that results from abnormalities in a single gene, HPRT, that regulates the production of purines – building blocks of DNA and RNA and vital elements of information flow in the brain. Children with this disease demonstrate mental retardation, uncontrollable movements, kidney damage and, most disturbingly, a bizarre and completely untreatable involuntary self-mutilatory behavior in which the children bite and amputate their finger tips, the corners of their mouth, etc. We do not understand at all the ways in which a body-wide defect in purine metabolism causes the abnormalities in brain dopamine function. We have long experience in studying the genetic mechanisms of this disorder, largely by characterizing the affected brain regions in a HPRT-deficient mouse model of the disease. We have found that nerve cells isolated from affected brain have reduced levels of dopamine and are unable to take up dopamine from their environment, just as occurs in human LND patients. We have interpreted that finding to suggest that HPRT deficiency probably leads to the dopamine deficit by affecting the expression of other genes whose role is to direct the normal development of the dopamine neurotransmitter system in and between brain neurons. We have approached that possibility by testing the levels of expression of virtually all 30,000 genes in affected HPRT-deficient mouse brain and by examining the proteins present in normal and HPRT-deficient tissue (proteomic analysis). We have discovered that a small number of genes are expressed abnormally in HPRT-deficient tissue and that some of the protein products of those genes are present in unusual forms or amounts. We are now working to determine the functional significance of these changes. We infer from these results that HPRT deficiency may cause a defect in the mechanisms by which human embryonic stem cells generate and differentiate into dopamine neurons and possibly other cells in the brain. We therefore wish to search for differences in the ways in which the genes of normal and HPRT-deficient human ES cells are expressed and how those differences may affect the proteins found in affected ES cells as they differentiate into dopamine neurons in culture.
BENEFIT TO CALIFORNIA. Through the establishment of the California Institute of Regenerative Medicine, the State of California has taken a major step to fill a great gap in biomedical research funding in the United States in the area of stem cell biology. At the present time, investigators in the United States are seriously hampered by insufficient and restricted federal funding for human stem cell research and cannot pursue some of the most promising basic and clinical research directions in this vital new area of biomedicine. The present proposal describes studies intended to understand the ways in which human embryonic stem cells develop into the brain neurons involved in vital brain neurotransmitter systems that cause some of our society’s most troublesome neurological diseases. Hundred of thousands of people in California suffer from degenerative neurological disease and related movement disorders, producing enormous harm to the well being and productivity of our society and constituting a huge financial burden on the State of California. If our studies with a crucial model disease are fruitful, the improved knowledge of the dopamine pathways in health and disease may help to improve the lives of many people in our State and country. In addition, the boost provided by these kinds of studies to the academic research environment in California can make the biomedical effort in this State even more vibrant than it is now, particularly in neurosciences, a field in which California is already a world leader. Furthermore, knowledge derived from these studies also has the potential for wide application in existing and new commercial settings, thereby catalyzing the biotechnology and pharmaceutical efforts in California and strengthening their intellectual property base.