Neural stem cell (NSC) transplantation is an emerging technique with immense promise for the treatment of disorders of the peripheral (PNS) and central nervous system (CNS). More recently, our laboratory has begun investigating the use of NSC as a viable therapeutic strategy for disorders of gastrointestinal motility. Using a strategy of transplanting CNS-derived NSC (CNS-NSC) in mice with a genetic deletion of the neuronal nitric oxide synthase (nNOS) enzyme, we have shown that CNS-NSC can successfully engraft and differentiate into nNOS expressing neurons, can restore nitrergic relaxation and "rescue" gastric function (emptying) in these mice. We have also shown that intrinsic apoptotic signaling is more important in determining the survival of transplanted NSC than the host immune response. The results of these experiments have generated considerable confidence in the viability of this strategy as a potential therapy. Further validation of this approach will require a greater knowledge of the mechanisms responsible for differentiation and survival of NSC in the gut. In this regard, we have initially focused on the most well characterized pathway responsible for the normal development of the enteric nervous system, glial derived neurotrophic factor or GDNF, and its cognate receptor, RET. Our preliminary data, using CNS-NSC transfected with a constitutively active RET mutant (RET/PTC2) suggest that activation of this pathway results in greater proliferation, survival and neuronal differentiation of NSC. Our overall hypothesis is that activation of RET is sufficient to improve the survival and differentiation of CNS-NSC after transplantation into the gut and that this can be an effective therapeutic strategy to replace enteric nervous system function. To test this hypothesis, we will pursue the following specific aims using NSC isolated from the CNS (CNS-NSC) and the gut (ENS-NSC):
Specific Aim 1 : To use an inducible, constitutively active RET/PTC2 gene construct to determine the duration of RET activation required for an optimal outcome after transplantation.
Specific Aim 2 : To determine if RET-activation can produce a similar phenotype in either CNS or ENS derived NSC.
Specific Aim 3 : To determine if RET-activated CNS and ENS-derived NSC can effectively restore enteric neuronal function in clinically relevant models of disease such as Hirschsprung's disease and inflammatory neuropathies. Our long-term objective is to develop neuronal transplantation as a treatment for human diseases of the enteric nervous system. To establish the optimal source of stem cells (adults versus embryonic;CNS versus ENS etc.) currently remains an elusive goal and will need several more years of work by many laboratories across the world. By establishing a permissive and necessary role of RET, the proposed studies will provide the critical groundwork for the therapeutic use of neuronal precursors from a variety of sources.
Disorders of gastrointestinal motility are common and pose a significant burden of disease on our society.These disorders results from disturbances in the function of the nerves and muscle responsible for orderly movement within the digestive tract and result in symptoms such as severe constipation, intestinal obstruction, nausea and vomiting from delayed gastric emptying or difficulty in swallowing. Several of these conditions are caused by loss or abnormal function of gastrointestinal nerves and cannot be treated satisfactorily by drugs alone. An ideal strategy for these disorders is to restore nerve function by transplanting neural stem cells. It is the purpose of this proposal to study this approach experimentally and determine the biological factors that can optimize the use of neural stem cells for the treatment and perhaps cure of these diseases.
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