EphB Receptors: Novel Pro-Synaptic Therapeutic Targets for Alzheimer’s Disease

Summary

Alzheimer’s disease (AD) slowly progresses as more and more synapses in the brain are destroyed. This first causes a gradual decline in memories and eventually, inevitably, it leads to dementia and death. EphB receptors [for erythropoietin-producing human hepatocellular B receptors] are important proteins for synapse function and health, as they hold hands with the NMDA [N-methyl-D-aspartate] receptor protein to help our brains store memories. EphB also has the unfortunate ability to hold hands with plaque-forming amyloid-beta (Aβ) peptides made to ever increasing levels in Alzheimer’s disease, and this rise in Aβ targets EphB for degradation, resulting in a reduction in synapses and memories. Using novel high-throughput screens of small drug-like chemical libraries for compounds that disrupt the ability of EphB to bind with Aβ, I aim to discover a new class of medicines that will halt the destruction of synapses and avert memory loss with direct implication for the prevention of AD. 

Project Details

We aim to discover new drug-like chemicals that will prevent amyloid-beta (Aβ) peptides from binding to synaptic EphB receptors and will promote pro-synaptic interactions between EphB and NMDA receptors.

As Alzheimer’s disease (AD) slowly progresses more and more synapses in the brain are destroyed. This causes a gradual decline in memories that inevitably leads to dementia and death. EphB receptors are important proteins for synapse function and health as they hold hands (ie, form protein-protein binding interactions) with the NMDA [N-methyl-D-aspartate] receptor protein to help our brains make and store memories. EphB receptors also have the unfortunate ability to bind and hold hands with plaque-forming Aβ peptides made to ever increasing levels in AD. This in turn targets EphB for degradation, resulting in a gradual reduction in its ability to interact with the NMDA receptor and help promote synaptic health.

Using novel high-throughput screens of small drug-like chemical libraries for compounds that disrupt the ability of EphB to bind with Aβ, we hope to identify a new class of medicines that will halt the destruction of synapses and avert memory loss with direct implication for the prevention and treatment of AD.

In Aim 1, we will use a highly sensitive chemiluminescent protein-protein interaction assay (AlphaScreen) to measure the EphB-Aβ protein-protein interaction. We will use AlphaScreen to search for small chemical compounds that will antagonize/block the the EphB-Aβ interaction using high throughput methods. A high throughput screening facility available here at UT Southwestern has a large library of >200,000 small, drug-like organic molecules. We will search this library of drug-like compounds to identify those that disrupt/antagonize the EphB-Aβ interaction, as measured by the ability of a compound to reduce the chemiluminescent signal. In this Aim we hope to identify a small number of hit compounds from the library that exhibit ability to antagonize the EphB-Aβ interaction.

In Aim 2, we will conduct additional biochemical tests of selected “cherry-picked” inhibitory compounds identified in Aim 1. The biochemical experiments here will help us eliminate weak and/or non-specific hits in order to whittle down the number of inhibitory compounds to only those that exhibit the strongest ability to disrupt/antagonize the EphB-Aβ interaction.

In Aim 3, we will carry out cell-based studies of selected compounds. Using cell-based protein interaction assays, we will determine how well the selected lead compounds antagonize the EphB-Aβ interaction in a cell physiological context. With the use of cell-based assays, we will further assess whether these lead compounds can promote the pro-synaptic EphB-NMDA receptor association. The major benchmark here would be the identification of compounds that antagonize the ability of EphB receptors to bind to Aβ while at the same time promote the pro-synaptic EphB-Aβ receptor interaction.

We believe this research is highly significant to our search for a treatment for AD-associated memory loss. EphB receptors are well documented to be a major player in the formation and functioning of synapses. They form key protein-protein interactions with a number of other synaptic proteins to promote synapse health, most notably binding tightly to the NMDA receptor ion channel, which is central for synaptic plasticity and long-term potentiation (LTP). The physical protein-protein interaction of the EphB receptor with the NMDA receptor is thought to help keep the NMDA receptor localized to the synapse. Like buying a house, location, location, location is important; without EphB receptors the NMDA receptor becomes mislocalized away from its normal synaptic neighborhood, and this is not good. The direct connection of EphB receptors to AD was made when they were found to also form a protein-protein interaction with Aβ peptides. The binding of EphB to Aβ targets the EphB molecules for degradation. This is also not good as the Aβ-induced degradation of EphB receptors will likely affect synapse function due to resulting abnormal localization and/or activity of synaptic proteins like the NMDA receptor. We believe our sensitive and sophisticated chemiluminescent protein-protein interaction assay to measure the EphB-Aβ protein-protein interaction and to screen for novel drug-like chemicals that disrupt this interaction is a highly innovative way to search for new compounds that might promote synapse health. If successful, this work could help identify a new class of drugs that may ultimately be used to treat/prevent AD. It is further envisioned that such compounds may have general utility for treatment of other diseases of the synapses, and perhaps even help prevent memory loss associated with the normal aging brain.