Alzheimer's disease (AD) is now feared more than cancer among the elderly, yet we still do not understand the mechanisms of neuronal cell death in AD well enough to know which pathways to target for therapy. Notably, rare cases of familial AD (FAD) cause a more aggressive clinical course than more common cases of sporadic AD (SAD), suggesting that studying FAD cases may inform SAD pathophysiology. However, no one has ever studied this possibility on a molecular level with single neuron resolution. To this end, we used laser capture microdissection to harvest individual pre-tangle bearing frontal cortex layer III neurons from presenilin-1 (PS1)- linked FAD cases and SAD cases, as well as nave, unlabeled neurons from aged control cases. We then used custom microarrays to compare gene expression profiles within each neuron. The most remarkable observation from this study was that FAD and SAD neurons displayed ~40-70% increases in the expression of several chaperones (e.g., DNAJA3/HSP40) and proteases (e.g., CLPP) that function in the mitochondrial unfolded protein response (mtUPR), a critical pathway for maintaining mitochondrial proteostasis that helps the cell counter mitochondrial stress. Moreover, we found evidence for mtUPR gene activation in pre-tangle bearing layer III neurons harvested from cases of amnestic mild cognitive impairment (aMCI), a putative prodromal stage of AD. These novel pilot data suggested that mitochondrial proteostatic stress is an early event in FAD and SAD and that the mtUPR is activated as a neuroprotective mechanism. However, when we induced mitochondrial proteostatic stress in human hNT neurons, these cells first displayed an up-regulation of mtUPR genes and then, paradoxically, underwent cell death. This response was highly reminiscent of the endoplasmic reticulum UPR, where sustained activation shifts a normally protective pathway to an apoptotic one. Additional in vitro studies showed that mtUPR+ neurons exhibited signs of mitochondrial fission, lysosomal accrual, and mitophagy prior to cell death. Given that one of the prominent theories in the field is that lysosomal/autophagy abnormalities contribute to neurodegeneration in both FAD and SAD, these findings suggest that mtUPR dysfunction in vulnerable neurons acts upstream of lysosomal perturbations to trigger a feed-forward cell death cascade. To test this novel hypothesis, we propose to expand upon our molecular profiling studies to show that neuronal mtUPR activation precedes lysosomal/autophagy activation during the progression of AD. We will then use mitochondrial proteostatic stressors +/- pharmacological interventions in human neuronal cultures to dissect the mechanistic role of mtUPR activation in mitochondrial fission, lysosomal dysfunction and cell death. Altogether, this proposal will establish chronic mtUPR activation as a pivotal early event in familial and sporadic AD and build the knowledge scaffold necessary to model and target this pathway as a disease modifying therapeutic.

Public Health Relevance

Alzheimer's disease (AD) research has become increasingly focused on the earliest neurodegenerative changes involved in disease pathogenesis. This proposal expounds upon our compelling human tissue and in vitro pilot data to test that mitochondrial proteostatic stress and chronic activation of the mitochondrial unfolded protein response (mtUPR) triggers mitochondrial fission, mitophagy, and cell death in familial and sporadic AD. Results from these studies will significantly impact our understanding of the upstream pathways mediating selective neuronal vulnerability in AD and identify new targets for therapy.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Exploratory/Developmental Grants (R21)
Project #
5R21AG053581-02
Application #
9352743
Study Section
Neural Oxidative Metabolism and Death Study Section (NOMD)
Program Officer
Yang, Austin Jyan-Yu
Project Start
2016-09-15
Project End
2019-05-31
Budget Start
2017-07-01
Budget End
2019-05-31
Support Year
2
Fiscal Year
2017
Total Cost
Indirect Cost
Name
Michigan State University
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
193247145
City
East Lansing
State
MI
Country
United States
Zip Code
48824
Tiernan, Chelsea T; Ginsberg, Stephen D; He, Bin et al. (2018) Pretangle pathology within cholinergic nucleus basalis neurons coincides with neurotrophic and neurotransmitter receptor gene dysregulation during the progression of Alzheimer's disease. Neurobiol Dis 117:125-136
McKay, Erin; Counts, Scott E (2017) Multi-Infarct Dementia: A Historical Perspective. Dement Geriatr Cogn Dis Extra 7:160-171
Sorrentino, Vincenzo; Romani, Mario; Mouchiroud, Laurent et al. (2017) Enhancing mitochondrial proteostasis reduces amyloid-? proteotoxicity. Nature 552:187-193
Beck, John S; Mufson, Elliott J; Counts, Scott E (2016) Evidence for Mitochondrial UPR Gene Activation in Familial and Sporadic Alzheimer's Disease. Curr Alzheimer Res 13:610-4
Counts, Scott E; He, Bin; Prout, John G et al. (2016) Cerebrospinal Fluid proNGF: A Putative Biomarker for Early Alzheimer's Disease. Curr Alzheimer Res 13:800-8