Therapeutic potential of genetically modified human ES cells in an Alzheimer's disease model: Contribution of IGF-1
Alzheimer’s disease (AD) is a progressive and irreversible disease of the brain leading to deterioration of mental function and eventual morbidity and death. The major defining characteristic of AD brains is the excessive accumulation of amyloid plaques (composed of clumps of Abeta) outside of nerve cells and tangles (composed of clumps of tau) inside nerve cells. These lesions are toxic to nerve cells and likely explain the progressive degeneration seen in AD brains. Currently available treatments for AD provide only limited symptomatic relief and are unable to prevent, stop, or cure the disease. Even if next generation drugs prove to be more effective, they are unlikely to reverse the disease progression. Thus, it may be necessary to replace dead or dying nerve cells in order to reverse the course of the disease in many AD patients. The long-term objective of this proposal is to use genetically modified human embryonic stem cells (ESCs) as an inexhaustible source for replacing lost or damaged nerve cells, supplying the host brain with protection from further damage, and working against the underlying factors that promote amyloid and tangle lesions. Such objective ultimately may lead to a strategy for therapeutic intervention in AD patients who do not respond to available pharmacological treatments.
It is well known that mouse embryonic stem cells exhibit the remarkable ability to respond to damaged nerve cells and home in on these degenerative environments in brain. At present, the capacity of human embryonic stem cells (ESCs) to integrate into the diseased brain such as those with amyloid and tangle lesions is unknown. In this proposal, we will use a mouse model of AD that develops both amyloid plaques and tangles to test the idea that transplantation of ESCs might be beneficial in treating AD. Our hypothesis is that human ESCs possess the inherent capacity to home in and integrate into sites surrounding plaques and tangles, where nerve cell damage is occurring. In addition, we hypothesize that human ESCs genetically modified to produce a protective factor called IGF-1 will further enhance this capability, help host nerve cells from further damage, and block the accumulation of plaques and tangles. It is known that IGF-1 promotes ESCs to become nerve cells, protects nerve cells from damage by Abeta, and decreases the levels of Abeta in brain. Furthermore, IGF-1 levels are reduced in AD, and loss of IGF-1 promotes tangle-like lesions in mice. If the above hypotheses can be even partially demonstrated, the current proposal is expected significantly advance our long-term objective of applying genetically modified human ESCs as a therapeutic technology for AD patients who are refractory to available pharmacological treatments.
Alzheimer’s disease (AD) is an age-related debilitating disease of the brain characterized by progressive deterioration of mental function and accounts for more than 70% of all dementias of the brain. AD inflicts more than 465,000 residents in California alone and places substantial medical, social, psychological, and financial burden on the patients, their families, and social/medical institutions. The per capita cost of caring for an AD patient in California was estimated to be more than $65,000 per year in 1998. It was also projected at the time that the cost of caring for AD patients in California (in 1998 dollars) will be ~$25.9 billion in 2000, ~$47.5 billion in 2020, and ~$75.4 billion in 2040. During the same time period, the number of AD patients in California is projected to rise from ~395,000 in 2000 to ~1.2 million in 2040.
At present, no effective treatment is available for AD. First generation drugs can temporarily mask symptoms of the disease but rapidly lose effectiveness during the progression of AD. Even if next generation drugs prove to be more effective, they will only help to slow down the progression of AD but not reverse it. As such, it may be necessary use an alternate therapeutic strategy to replace dead or dying nerve cells, especially in patients that do not respond to available drugs. Human embryonic stem cells have emerged in recent years to hold enormous potential for cell replacement therapy for wide variety of neurological disorders, including AD.
As California continues to be at the forefront of new and innovative technologies, the passage of Proposition 71 to fund stem cell research further extends this spirit of innovation. The research proposed in this application attempts to generate genetically modified human embryonic stem cells capable of not only replacing lost nerve cells but also delivering protective factors that prevent further degeneration of existing nerve cells in an animal model of AD. Such kind of technological coupling between stem cell therapy and gene therapy poses therapeutic potential for application in AD where irreversible nerve cell damage cannot be treated with even the best of next generation drugs. If successful, this will also help to offset the enormous social and financial burden of caring for AD patients in California. Technologies and therapeutics derived from stem cell research funded by the California Institute for Regenerative Medicine (CIRM) are in part the contractual property of the state of California, and hence its residents. In the event that such intellectual property leads to commercialization or licensing down the line, a portion of the proceeds are contracted to enter the California state general fund, ensuring that all California residents benefit from potential successes of this research.