Despite extensive efforts and investment, there is no cure for Alzheimer disease (AD) or effective treatment to slow progression of this devastating disorder. One potential therapeutic strategy is to promote degradation of amyloid beta (A?), whose accumulation in the brain is associated with and may be integral to the disease process. We have recently obtained strong evidence that the lysosomal protease tripeptidyl peptidase 1 (TPP1) plays an important role in degradation of A? fibrils. We hypothesize that increasing activity of TPP1 will promote degradation of A?, slowing or preventing its accumulation in the brain with subsequent therapeutic benefits for AD. We will test this hypothesis using two complementary approaches in the J20 mouse, a transgenic AD model that overproduces human A? and exhibits age-dependent plaque accumulation and cognitive deficits. First, in a genetic proof-of-principle study, we will cross the J20 mouse with our newly created transgenic mouse that constitutively overexpresses mouse TPP1 (~10-fold higher activity than endogenous levels). Second, we will use a peptide-mediated method to deliver recombinant human TPP1 protein from the bloodstream across the blood-brain barrier into the brain of the J20 mouse. Treatment groups and controls will each contain 30 animals with equal numbers of males and females. For both Aims, we will employ identical approaches to evaluate the effect of elevated TPP1 activity on the AD phenotype. At the age of seven months, we will analyze treated mice and controls using the Morris water maze, novel object recognition and fear conditioning assays. At eight months, the mice will be euthanized and levels of soluble and insoluble A? measured in brain extracts by ELISA and plaque measured in cortex and hippocampus by immunohistochemistry. If TPP1 augmentation has a positive effect on AD phenotype in the J20 mouse, this would provide a strong rationale to explore this further with the long-term goal of developing an effective therapy for AD. Additional studies in laboratory animals would be required prior to initiation of trials in humans. Looking forward, it is worth noting that targeting protein-based drugs across the blood-brain and/or cerebrospinal fluid-brain barrier continues to be a major obstacle for the development of biologic therapeutics for AD and other neurological disorders. However, in the case of TPP1, delivery of recombinant protein to the brain by intracerebroventricular administration has been approved by both the Federal Drug Administration and the European Medicines Agency for treatment of a neurodegenerative lysosomal storage disease. A similar delivery method should be feasible for AD and may allow repurposing of an existing drug.
There is no cure or treatment to effectively slow Alzheimer disease progression but one potential therapeutic strategy is to promote degradation of amyloid beta, whose accumulation in cells of the brain is associated with and may trigger disease. In preliminary studies, we have identified a cellular protease, tripeptidyl peptidase 1 (TPP1) that can degrade amyloid beta and we propose to determine whether elevated TPP1 in an Alzheimer disease mouse model increases amyloid beta degradation and improves disease phenotype. A positive outcome will provide the basis for future studies to optimize TPP1 augmentation as a therapeutic approach and in the long-term, to evaluate potential clinical utility for treatment of Alzheimer disease.
