Michael G. Kaplitt, MD/PhD - US grants

DESCRIPTION (provided by applicant): The PTEN anti-oncogene is among the most frequently mutated genes in malignant brain tumors. Normally, PTEN is a lipid phosphatase which blocks malignant phenotypes primarily by inhibiting the PI3 Kinase/AKT pathways, but PTEN can also act as a protein phosphatase. PTEN is expressed in brain late in development, and neuronal expression continues throughout adult life. Although loss of PTEN can cause neuronal hyperplasia, little is known about the role of PTEN in neuronal development or in normal neurons. Pathways influenced by PTEN suggest that this anti-oncogene may increase neuronal sensitivity to toxicity and/or degenerative processes, which is supported by our preliminary data. This proposal will first determine whether PTEN can modulate sensitivity of cultured neuron-like cells to toxins used in models of Alzheimer's disease and Parkinson's disease. While studying this hypothesis, we have unexpectedly found that PTEN blocks NGF signaling in PC12 cells, and this appears to be at least partially due to inhibition of expression of trkA and p75 NGF receptors at the protein and mRNA levels. DNA microarray then revealed that PTEN can inhibit expression of several genes, including tyrosine hydroxylase and GTP cyclohydrolase 1. Since this may also have implications for neuronal function and for Parkinson's disease, the second Aim of this proposal will also explore the mechanism by which PTEN inhibits expression of these genes. The final Aim of this proposal will explore the effect of age and neurotoxins used in models of neurodegenerative disorders on PTEN levels and function to determine the biological relevance of data generated from the first two Aims. These studies and my development as an independent clinical scientist will be significantly advanced by Dr. M. Flint Beal, who will serve as my sponsor and who is a leading expert in neuronal degeneration in PD and AD. Additional mentoring by Dr. Eric Holland, a leading expert on anti-oncogene signal transduction, will also add significantly to my scientific growth and will also help me to realize many of the Specific Aims of this proposal. The environment at Cornell and the strong support of my institution will permit me to focus upon these studies with minimal distractions. My scientific background is substantial, and this will facilitate realization of the goal of this project. This plan outlined in this award will, however, enhance previously underserved aspects of my education while focusing on an important scientific question, in order to promote a successful transition to scientific independence.

DESCRIPTION (provided by applicant): The PTEN anti-oncogene is among the most frequently mutated genes in malignant brain tumors. Normally, PTEN is a lipid phosphatase which blocks malignant phenotypes primarily by inhibiting the PI3 Kinase/AKT pathways, but PTEN can also act as a protein phosphatase. PTEN is expressed in brain late in development, and neuronal expression continues throughout adult life. Although loss of PTEN can cause neuronal hyperplasia, little is known about the role of PTEN in neuronal development or in normal neurons. Pathways influenced by PTEN suggest that this anti-oncogene may increase neuronal sensitivity to toxicity and/or degenerative processes, which is supported by our preliminary data. This proposal will first determine whether PTEN can modulate sensitivity of cultured neuron-like cells to toxins used in models of Alzheimer's disease and Parkinson's disease. While studying this hypothesis, we have unexpectedly found that PTEN blocks NGF signaling in PC12 cells, and this appears to be at least partially due to inhibition of expression of trkA and p75 NGF receptors at the protein and mRNA levels. DNA microarray then revealed that PTEN can inhibit expression of several genes, including tyrosine hydroxylase and GTP cyclohydrolase 1. Since this may also have implications for neuronal function and for Parkinson's disease, the second Aim of this proposal will also explore the mechanism by which PTEN inhibits expression of these genes. The final Aim of this proposal will explore the effect of age and neurotoxins used in models of neurodegenerative disorders on PTEN levels and function to determine the biological relevance of data generated from the first two Aims. These studies and my development as an independent clinical scientist will be significantly advanced by Dr. M. Flint Beal, who will serve as my sponsor and who is a leading expert in neuronal degeneration in PD and AD. Additional mentoring by Dr. Eric Holland, a leading expert on anti-oncogene signal transduction, will also add significantly to my scientific growth and will also help me to realize many of the Specific Aims of this proposal. The environment at Cornell and the strong support of my institution will permit me to focus upon these studies with minimal distractions. My scientific background is substantial, and this will facilitate realization of the goal of this project. This plan outlined in this award will, however, enhance previously underserved aspects of my education while focusing on an important scientific question, in order to promote a successful transition to scientific independence.

[unreadable] DESCRIPTION (provided by applicant): Huntington's disease (HD) is devastating hereditary neurodegenerative disorder characterized by a severe movement disorder, mood and emotional disturbances, and cognitive decline before premature death. It is caused by a CAG repeat expansion in the gene encoding huntingtin (htt), but the mechanism whereby mutant htt (mhtt) ultimately induces selective neurodegeneration is still unknown. There is substantial evidence from multiple HD models that mhtt induces apoptotic cell death processes and mitochondrial dysfunction. XIAP is a potent inhibitor of apoptosis and thus represents an attractive target for neuroprotection in Huntington's disease. The goal of this proposal is to determine the potential therapeutic utility of a novel gene delivery approach, using an AAV-vector approach to deliver the gene encoding XIAP to the major site of neurodegeneration in Huntington's disease, the neostriatum. The proposed experiments in genetic mouse models of Huntington's disease arise from the observations that (i) we have found that XIAP has neuroprotective actions against mhtt- induced toxicity in vitro, (ii) that this effect is potentially mediated by inhibitory actions against Smac/DIABLO or Omi, rather than caspase inhibition, (iii) that our adeno-associated viral (AAV) vector delivery system results in widespread gene expression within the striatum, and (iv) pilot experiments suggest that XIAP gene delivery improves phenotype in a mouse model of Huntington's disease. Specifically, we will examine whether an AAV gene therapy approach to deliver the anti-apoptotic agent XIAP to striatal neurons improves outcome and reduces neurodegeneration in animal models of Huntington's disease, by examining AAV-dXIAP's effects in the N171-82Q "fragment" mouse model of Huntington's disease, and in a second "full length" HD model, YAC-128 HD mice. We will also elucidate whether XIAP'S neuroprotective anti-apoptotic actions are due to inhibition of Smac/DIABLO or Omi/HtrA2, rather than direct effects on caspases in HD mice. We will generate AAV vectors carrying dXlAP with point mutations either disabling its ability to bind to Smac/DIABLO-Omi, or caspases, and examine their effects on HD pathobiology in an HD mouse model. The outcomes of these studies will provide a substantial foundation for larger studies to determine cell damage pathways underlying HD pathogenesis, and to develop an effective gene-delivery approach for the treatment of Huntington's disease. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by principal investigator): Huntington's disease (HD) is a autosomal dominant neurodegenerative disorder which is normally fatal and untreatable and results in a severe movement disorder, cognitive and neuropsychiatric abnormalities. HD is caused by a pathological expansion of polyglutamine repeats in the Huntingtin gene (mhtt), resulting in the eventual loss predominantly of striatal medium spiny neurons although dysfunction and/or degeneration of other brain regions can occur as well. While the mechanism of mhtt-induced neurodegeneration remains unknown, apoptosis (programmed cell death) has emerged as a potential mediator in a variety of prior studies. X-linked inhibitor of apoptosis (XIAP) is the most potent member of a family of apoptosis inhibitor proteins, which is known to bind to and block the function of effectors of apoptosis including caspases and mitochondrial cell death proteins Smac and Omi. We have long used the adeno-associated virus (AAV) vector as a gene transfer agent for neurodegenerative diseases and have recently reported the use of AAV in the first human trial of gene therapy for Parkinson's disease. Based upon this, we received a pilot application R21 NS055003 to examine the potential of AAV-XIAP gene therapy in the striatum as a novel therapy for HD. We have now demonstrated that intrastriatal AAV-XIAP can reverse motor dysfunction in both the N171-82Q and YAC128 transgenic mouse models of HD. The normally shortened lifespan of N171 mice were also significantly extended by 20% while statistically complete prevention of neurodegeneration was demonstrated in the normal lifespan YAC128 mice. While this pilot data along with cell culture studies strongly supports the potential of AAV-XIAP as a potential gene therapy agent, here we propose to address several important remaining questions which have significance for both understanding the pathogenesis of HD as well as specifically translating AAV-XIAP into a clinical gene therapy agent. Aim 1 will further address the breadth and mechanism of AAV-XIAP-mediated neuro protection. Since death was used as an endpoint for the pilot N171 study, histological analysis was not performed so we will determine the effect of AAV-XIAP on neuropathology in this line just prior to death. We will also use XIAP point mutants lacking certain specific functions to explore potential mechanisms of XIAP-mediated neuro protection in order to better define pathways which may be targeted for novel neuro protective therapeutics in HD. In both N171 and YAC128 models, motor function was improved to wild-type levels prior to the reported age at which neuro degeneration normally ensues. This suggests an improvement in neuronal dysfunction by XIAP distinct from neuro protective effects. Aim 2 will use both striatal slices and a novel transgenic HD mouse to determine the effect of XIAP on dopamine receptor signaling in HD striatal neurons. Finally, aim 3 will address certain remaining questions which would inform a potential human clinical trial of AAV-XIAP for HD. This study should help develop AAV-XIAP into a human therapeutic and provide novel information to develop drugs to reverse neuronal dysfunction and/or loss in HD.

Project Summary In this collaborative and interdisciplinary application, we propose to develop further a novel non-invasive method for cell regulation (NICR) that is suitable for preclinical proof of concept studies. This technology potentially could be used to treat neurologic diseases and provide a less invasive alternative to deep brain stimulation (DBS) or optogenetics. We thus propose to refine the technology and develop a prototype device to test the use of NICR for the treatment of symptoms of Parkinson's Disease (PD) in mice. Cell activity is controlled by two components; the iron binding ferritin protein that spontaneously forms 5 nm iron nanoparticles and TRPV1, a temperature and mechano-sensitive channel. By tethering ferritin to TRPV1, one can gate the channel with radiofrequency (RF) (which heat or induce mechanical motion of ferritin) or a magnet (which induces motion). The method has been shown to be capable of controlling neural activity in vitro and in vivo, the latter by increasing neural firing. In addition, we have introduced a mutation into TRPV1 that converts it into a chloride channel, and the use of the mutant channel makes it possible to inhibit neural activity using electromagnetic waves (e.g., RF). Because the system is genetically encoded, one can regulate the activity of cells into which the two protein components of the system have been delivered by recombinant Adeno- Associated Virus (AAV) strains. AAV has been used in numerous human studies including patients with PD. Thus NICR could provide a less invasive alternative to implanted electrodes (DBS) or implanted light devices (optogenetics) for the modulation of neural activity (deep brain stimulation) and also be used to simultaneously control several different nodes in a neural circuit. In this application, we propose a set of preclinical proof-of-concept studies for the treatment of PD including: 1) refinement of the technology to improve its efficiency and to create suitable AAV strains to ameliorate the symptoms of PD. We also propose to increase the sensitivity of the system by using channels that can be gated with lower field strength and by identifying variants of ferritin with enhanced sensitivity to an electromagnetic field; 2) development of a prototype device that would create local electromagnetic fields of suitable strength with the aim of enabling the use of the method in routine laboratory settings and ultimately as a portable/wearable device; 3) testing the ability of the improved method and suitable instrumentation to alleviate the symptoms of PD in mice; and 4) creating knockin mice with cre dependent expression of the constructs to assess the safety of long term TRPV1 and ferritin expression. The validation of this technology could also lead to its use for the treatment of other diseases at sites within and outside the nervous system to either increase or decrease cell activity or regulate protein production. Finally, the further development of NICR could impact basic research by allowing the non-invasive activation or inhibition of cells by simply mating genetically modified mice and exposing them to RF or magnetic fields.