The Bohn lab is interested in understanding and applying developmental mechanisms to generate novel approaches for neurodegenerative diseases. The present focus is on developing gene and stem cell therapies using rodent models of Parkinson’s disease and amyotrophic lateral sclerosis (ALS). Previous studies in the lab on the effects of the neurotrophic factor, glial cell line-derived (GDNF) in rat models of Parkinson’s disease are now being translated to clinical trials for patients afflicted with Parkinson’s disease. Current studies are focused on neuronal rejuvenating therapies using stem cells derived from bone marrow, gene silencing of a gene linked to hereditary forms of Parkinson’s disease and on therapeutic gene targeting of upper motoneurons for ALS.
Mesenchymal stem cell therapies for Parkinson’s disease
Parkinson’s disease is a prevalent movement disorder that debilitates over 1.5M individuals in the US. There is no cure for Parkinson’s and the effects of drugs that ameliorate clinical symptoms in early stages of the disease lose effectiveness as the disease progresses. The primary basis of Parkinsonian symptoms is the slow degeneration of nigrostriatal dopaminergic neurons. In addition to attempts to develop new drugs and surgical approaches, experimental strategies are focused on either replacing the dopamine neurons with stem cells or fetal dopamine neurons, or stimulating rejuvenation of damaged dopamine neurons with gene therapy. While each of these strategies has merit, to date, none has met with clear success in the clinic. We are working on a paradigm shift in thinking about how stem cells can be used to rejuvenate, rather than replace, the intrinsic DA neurons that are lost in Parkinson’s by harnessing the tropic effects of mesenchymal stem cells (MSC) derived from bone marrow. These cells are easily procured, they lack the ethical issues presented by other stem cell sources, and host immune responses leading to rejection or graft-vs-host disease could be precluded in the clinic through the use of patient-specific stem cells. In addition, cell approaches for Parkinson’s disease are usually focused on replacing dopamine neurons, thus presenting an extreme challenge not only in directing differentiation of the cells to the correct phenotype, but also of re-establishing the sophisticated circuitry of the nigrostriatal system. In our approach, the circuitry is already in place or partially in place, but is damaged and needs to be rejuvenated. The grafted cells do not need to be differentiated into dopamine neurons. MSC secrete an array of extracellular matrix molecules and factors with neurotrophic and neuroprotective activities, suggesting these cells may promote recovery of DA neurons better than delivery of a single neurotrophic factor, such as GDNF. Studies in progress in the Bohn laboratory are focused on using neuroprogenitors derived from genetically modified MSC to reinvigorate damaged nigrostriatal dopamine neurons and their striatal projections. This approach is in distinct contrast to other stem cell approaches being developed to replace dead or dying DA neurons and is supported by key observations from studies in our laboratory.
Small Interference RNA vectors and cell death genes
A small percentage of cases of Parkinson’s disease are linked to mutations in the gene alpha-synuclein. In addition, alpha-synuclein is known to aggregate in cells forming Lewy bodies. Lewy bodies are characteristic of both Parkinson’s disease and other neurodegenerative diseases called synucleinopathies, such as Dementia with Lewy Bodies (DLB). Our lab has generated viral vectors that express a small inhibitory double stranded RNA in cells that completely turns off expression of human alpha-synuclein. Various designs of silencing vectors have been made in the context of lentivirus and/or adeno-associated virus (AAV). These are being tested in vivo and in vitro for specificity of gene silencing and degree of neurotoxicity. In vivo studies are in progress in an alpha-synuclein dependent rat model of Parkinson’s disease to test the hypothesis that silencing alpha-synuclein gene expression in dopamine neurons will lead to protection of these neurons and dopaminergic function. In addition, viral vector mediated gene silencing is being applied to other genes that are up-regulated in endoplasmic reticulum (ER) stress induced neuronal cell death with the idea of using gene therapy to interfere directly with cell death pathways.
Gene therapy for ALS
Previous studies in the Bohn laboratory have shown that delivery of a neurotrophic factor gene to lower motoneurons in the spinal cord protects these neurons from cell death and ameliorates motor deficits in a mouse model of ALS. In studies being carried out in collaboration with Hande Ozdinler’s laboratory at Northwestern, gene therapy approaches are being developed to target upper motoneurons in mouse cortex. Various serotypes of adeno-associated viral vectors (AAV) are being tested for their ability to deliver therapeutic gene products to upper motoneurons following injection into the spinal cord. Studies are based on the capability of AAV to be retrogradely transported by axons. Identification of a highly tropic AAV serotype for upper motoneurons will lead to functional studies of gene delivery to these neurons in novel mouse models of ALS.