Nahum Duker, MD
Professor, Pathology and Laboratory Medicine
Assistant Professor, Fels Institute for Cancer Research and Molecular Biology
Department of Pathology and Laboratory Medicine
Fels Institute for Cancer Research and Molecular Biology
A paradigm for etiogenesis of neurodegenerative disorders has emerged which implicates unrepaired oxidative DNA damage in neuron cell death via apoptosis. Evidence indicates unrepaired DNA purine dimers to be the molecular link between intracerebral deposition of amyloid-ß protein [Aß] and neural cell loss in Alzheimer's disease. Aß reacts with the receptor for advanced glycation end products [RAGE], resulting in generation of free radicals; these result in oxidative DNA damages. The RAGE receptor is present on the surfaces of neural and endothelial cells. Over fifty such types of base damages have been described. Most are monomeric, but a number of DNA dimers formed between adjacent purines have been synthesized in my laboratory. One purine dimmer, 8-8-(2'-deoxyguanosyl)-2'-deoxyguanosine-5'-monophosphate, was used as a hapten for elicitation of rabbit anti-purine dimer antiserum. DNA oxidized by the Fenton reaction is bound by this antiserum. Therefore, induction and excision of DNA purine dimers can be immunologically assayed. Incubation of PC-12 cells, derived from the neural tumor pheochromocytoma, with Aß induces these purine dimers; these are subsequently removed from cellular DNA by the nucleotide excision repair pathway. There are nucleotide excision repair defects in xeroderma pigmentosum, a human disease that results in neurodegeneration, with evidence for such defects in familial Alzheimer's disease and Down's syndrome. To elucidate the Aß reaction with cells that result in DNA damage and possible apoptosis, a number of exploratory studies will be executed. These include devising of a set of Aß-sensitive fibroblasts from these diseases by inducing stable expression of the cloned human RAGE gene. The induction and excision of oxidized DNA bases, including 8-oxoguanine and but stressing purine dimers, resulting from Aß-induced, radiation-induced and chemical-induced oxidative DNA damages will be assayed in these cells. To abet the assay, stable lines of cells producing monoclonal anti-DNA-purine-dimer antibodies will be constructed. Modulation of proteins involved in excision-repair of these oxidative DNA damages during different phases of the cell cycle will be examined. The effects of induction and excision of these oxidized DNA moieties on initiation of apoptosis will be assayed, and the progress of apoptosis and its vital checkpoints explored. These in vitro studies will be extended in vivo by development of mouse strains with both increased Aß production and reduced DNA repair capacities. This will allow for testing of the paradigm linking Aß, the congophilic angiopathy (with deposits of amyloid in intracerebral blood vessels) of Alzheimer’s disease, oxidative DNA damage and repair, with neural cell losses that result in the clinical and pathological changes characteristic of Alzheimer's disease and other conditions. Therefore, these studies can result in elucidation of the roles of DNA intrastrand purine dimers in the etiogenesis of human neurodegenerative disorders.