Tao Ma - US grants

DESCRIPTION (provided by applicant): Lack of mechanistic understanding hampers our search for solid therapeutic targets on Alzheimer's disease (AD), the most common form of dementia in the elderly and one of the leading causes of death across all ages. Current disease modifying strategies based on the Amyloid beta (Abeta) hypothesis, such as Abeta antibody immunotherapy, have met with limited success. Meanwhile, the downstream signaling pathways of Abeta as well as Abeta-independent mechanisms are being actively pursued as potential targets for AD therapy. One such potential mechanism is via regulation on the AMP-activated protein kinase (AMPK), a central cellular energy sensor and signaling transducer integrating a number of signaling pathways implicated in synaptic plasticity, learning and memory. Moreover, AMPK activity is stimulated during oxidative stress which is known to play a role in AD pathogenesis. The goal of this project is to understand the role of AMPK in AD pathophysiology and to develop therapeutics that can reverse impairments due to AMPK dysregulation. Driven by the preliminary data, the central hypothesis is that restoring normal AMPK activity will improve multiple aspects of pathophysiology in APP/PS1 AD model mice. Four specific aims are formulated to test this hypothesis as described in the following. The first two aims are to be performed during the mentored phase (K99): Aim 1 is to determine how AMPK signaling is regulated in AD model mice and whether aberrant AD-related autophagy can be rescued by restoring AMPK activity; Aim 2 is to determine whether pharmacologically inhibition of AMPK activity reverse synaptic plasticity impairments and memory deficits displayed by AD model mice. And with this information in hand, I will then move on to the other two aims to be achieved during the independent phase (R00): Aim 3 is to determine whether genetic reduction of AMPK activity prevents synaptic and behavioral defects in AD model mice; and Aim 4 is to determine the AD-related cellular and molecular abnormalities that are corrected in APP/PS1/AMPK¿2(+/-) double mutant mice. Findings derived from this project will potentially provide important insights into identification of novel therapeutic targets for AD and other related cognitive syndromes such as frontotemporal lobe dementia. Furthermore, the research project and career development components of this K99/R00 application will provide critical training for the applicant to become a successful independent investigator who can integrate these knowledge and techniques to improve our understanding of neurodegenerative diseases.

Project Summary/Abstract The basic molecular mechanisms associated with Alzheimer?s disease (AD) remain a critical knowledge gap that prevents identification of effective therapeutic targets and diagnostic/prognostic biomarkers. The current proposal will address this gap by studying the role of signaling pathways associated with AMP-activated protein kinase (AMPK) isoforms in AD. AMPK functions as a central cellular energy sensor to maintain energy homeostasis. Moreover, AMPK is a nexus to incorporate multiple signaling pathways for de novo protein synthesis (mRNA translation). Importantly, both disruptions in energy homeostasis and impairments in de novo protein synthesis are implicated in cognitive syndromes associated with neurodegenerative diseases, including AD. The kinase catalytic subunit of AMPK exists in two isoforms in brain: ?1 and ?2, and their roles in synaptic plasticity and memory are unknown. We generated brain- and isoform-specific conditional AMPK?1 and ?2 knockout mice (AMPK?1 cKO and AMPK?2 cKO), and performed behavioral, electrophysiology, imaging, and biochemical tests to characterize isoform-specific phenotypes. Driven by our preliminary data, our central hypothesis is that disruption of AMPK isoform homeostasis represents a key molecular mechanism underlying AD-associated impairments of synaptic plasticity and memory defects. Three specific aims are formulated to test the hypothesis. Aim 1 seeks to identify isoform-specific roles of AMPK in hippocampal synaptic plasticity and memory formation. Aim 2 is designed to determine AMPK isoform-specific regulation of synaptic failure and memory impairment in Tg19959 AD mouse model. Aim 3 is designed to elucidate AMPK isoform-specific effects on de novo protein synthesis and brain A? pathology in Tg19959 AD mouse model. The project proposes in-depth analyses using multiple state-of-art methods in neuroscience and AD, including mouse genetics, synaptic electrophysiology, confocal imaging, and behavioral tests. Moreover, novel methods to measure de novo protein synthesis combined with mass spectrometry/proteomics approach will be applied to reveal identities of proteins in AD brains whose synthesis is dysregulated because of abnormal signaling due to disruption of AMPK isoform homeostasis. This multidisciplinary approach will enable us to identify detailed cellular/molecular mechanisms associated with aberrant AMPK signaling in AD pathogenesis, providing insights into novel therapeutic targets and diagnostic biomarkers for AD and other dementia syndromes.

The basic cellular/molecular signaling mechanisms underlying Alzheimer?s disease (AD) pathophysiology are not well understood; this gap in knowledge is hampering our ability to find any effective therapies. Accumulating evidence indicates impaired synaptic function as a key event in AD pathogenesis. However, the molecular mechanisms underlying AD-associated synaptic dysfunction/failure remain elusive. We recently reported hyperphosphorylation of mRNA translational factor eukaryotic elongation factor 2 (eEF2) in AD brains. Phosphorylation of eEF2 by its (only known) kinase eEF2K results in repression of de novo protein synthesis, which is essential for long-lasting forms of synaptic plasticity and memory. Driven by the preliminary data, the central hypothesis to be tested in this application is that restoration of the capacity for de novo protein synthesis, via inhibition of eEF2K and thus eEF2 phosphorylation, will alleviate AD-associated synaptic failure and memory impairments. Three specific aims have been designed to test this hypothesis. Aim 1 seeks to determine whether restoration of normal eEF2 phosphorylation, via suppressing eEF2K activity, can rescue AD-associated impairments in hippocampal long-term synaptic plasticity. Aim 2 is to determine whether inhibition of eEF2K activity improves learning and memory deficits in AD mouse model. Aim 3 is to determine whether AD-associated impairments of de novo protein synthesis can be mitigated by inhibiting eEF2 kinase activity. The project proposes in-depth analyses using multiple state-of-art methods in neuroscience, including synaptic electrophysiology, confocal imaging, mouse genetics, and behavioral tests. We will also employ two new types of non-radioactive methods to assess de novo protein synthesis in brain slices: surface sensing of translation (SUnSET) and bioorthogonal noncanonical amino acid tagging (BONCAT). These novel methods will be combined with mass spectrometry/proteomics approach to reveal identities of proteins in AD brains whose synthesis is dysregulated because of abnormal eEF2K/eEF2 signaling. Findings from this project will contribute important data regarding the cellular/molecular signaling mechanisms underlying AD pathogenesis. Future studies will build on the results from this project and our other research findings on AD-related protein synthesis dysregulation to inform eventual development of novel diagnostic markers and better therapeutic strategies for AD-related cognitive syndromes, for which no effective treatments exist.