Raymond Scott Turner, MD, PhD - US grants

The neuronal adaptor protein X11alpha/mint-1 interacts with amyloid precursor protein (APP) to regulate its trafficking and processing in vitro. In transfected non-neuronal cells, X11alpha inhibits alpha- and gamma- but not beta- cleavage of APP. Because the phosphotyrosine binding (PTB) domain of X11alpha interacts specifically with the APP family, X11alpha appears to inhibit gamma-cleavage of APP specifically while sparing gamma-cleavage of Notch and other substrates of regulated intramembranous proteolysis. To determine the in vivo significance of these in vitro data, we will generate and characterize novel hX11alpha transgenic mice and X11alpha knockout mice and examine murine APP metabolism. Crosses of these mice to Tg2576 mice (transgenic for the Swedish mutation of hAPP, or hAPPswe) will probe the effects of XI la on hAPPswe metabolism and on the development of partial AD-like phenotypes in aging brain. A recent human genome-wide analysis revealed significant linkage of sporadic AD to single nucleotide polymorphisms (SNPs) on chromosome 9, perhaps including the X11alpha region. We will probe genetic linkage of SNPs in the X11alpha region to sporadic AD by using genomic DNA extracted from samples from AD subjects versus carefully-matched control subjects. The specific aims are to: 1) generate X11alpha knockout and hX11alpha transgenic mice and determine effects on murine APP metabolism in brain and in primary neuronal cultures, 2) cross X11alpha knockout and hX11alpha transgenic mice with Tg2576 mice to determine a) modulatory effects on hAPPswe metabolism in brain and in neuronal cultures, and b) development of AD-like phenotypes with aging, and 3) elucidate the SNPs and haplotypes within or adjacent to the X11alpha gene of AD cases and age-, gender-, and ApoE-matched controls to determine if there is a statistically significant link to sporadic AD. Specific aim 3 will study DNA samples obtained from the Pathology Core and from other ADRCs. These results will 1) inform the normal functions of X11alpha as well as APP and its derivatives in CNS neurons, 2) lay the groundwork for viral-vector based gene therapy of AD using either X11alpha or its PTB domain in hAPP transgenic mouse models, and 3) probe a potential genetic risk factor of sporadic AD.

DESCRIPTION (provided by applicant): Alzheimer's disease (AD) is a neurodegenerative affliction associated with memory dysfunction. Pathological mutations in familial AD patients have been identified in several genes, and transgenic mice carrying pathological genes have been generated. The generation of transgenic models of amyloidosis has significantly aided progress in the development of therapeutic approaches designed to lower brain amyloid beta (Abeta) load. One of these approaches is called "immunization". Immunologically provoked (or passively administered) antibodies against Abeta have been shown to enhance microglial phagocytosis and reduce Abeta load in the brains of transgenic mice. Significantly, immunization also reversed Abeta associated memory dysfunction. Concomitant with reduced CNS Abeta is the simultaneous observation by us and others that plasma Abeta levels are significantly elevated following immunization. As a result of this observation, we have devised a new methodology to alter brain Abeta load, which has proved to be effective in preliminary studies. In the human active immunization clinical trial, Abeta vaccine approach was terminated after severe brain inflammation was found approximately in 6% of patients. The cause of brain inflammatory side effects is not clear yet, but it is most likely due to immune modulation. Although the first clinical trial of vaccine therapy was terminated, follow up reports are encouraging. Sequestration approach does not modulate immune reaction;therefore, it therapy has higher flexibility in drug development, and drugs based on sequestration approaches have less side effects. In addition, plasma Abeta elevation is a possible biomarker when this approach translates to clinical use. In this study, we will investigate the mechanism of Abeta sequestration mechanism and identify optimal molecular property and drugable target for future development of pharmacological therapy.

DESCRIPTION (provided by applicant): Druggable regulators of nitric oxide production as new Alzheimer's disease therapeutics Summary: Nitrosative stress is a critical mediator of the onset and progression of Alzheimer's disease (AD): it precedes and is associated with neuritic dystrophy and dendritic spine loss, A¿/amyloid accumulation and deposition, cholinergic denervation and a memory loss phenotype in animal models of disease. Normally, nitric oxide (NO) is an important signaling molecule and the enzyme that produces it, nitric oxide synthase (NOS), regulates ApoE and its other protein partners via nitrosylation. Under pro-inflammatory conditions (e.g. AD), oxidative stress upregulates NOS. Excess NO combines with oxygen radicals forming the reactive nitrosylating species peroxynitrite, which in turn causes promiscuous dysregulation and indiscriminate damage. Because direct inhibition of NOS results in systemic toxicity, our unique strategy is to selectively reduce NO activity at sites of inflammation. This will be achieved by targeting Sigma- 1 receptors (S1R), because they become important regulators of NOS activity only under conditions of oxidative stress. Our hypothesis is that elevated brain NO levels can be lowered at inflammatory sites by drugs that promote S1R-mediated reductions in NOS activity. The path for discovery and proof-of-concept phases includes: A) synthesis of additional novel candidate molecules to impart the appropriate selectivity and drug-like characteristics to compounds that reduce NO levels and promote neuronal and/or glial cell survival in vitro under conditions of nitrosative stress; B) evaluate 1- of these leads in a transgenic mouse model of AD by measuring reductions in CNS A¿/amyloid burden, 3-nitrotyrosine levels and improvements in cognition. Novel high affinity S1R candidates (hits) have been identified in our preliminary work and now we seek to create leads with refined drug-like properties for testing our target and mechanism- based hypothesis for therapeutics designed to slow the progression of AD. PUBLIC HEALTH RELEVANCE: The objective is to discover and develop news drugs for the treatment of Alzheimer's disease, a leading cause of morbidity and mortality in the US.