NIH Awards $4.8M Grant to Project Investigating the Role of ApoE4 Gene Variant in Alzheimer’s

The National Institutes of Health (NIH) has awarded a $4.8-million grant to support a project designed to discover how the ApoE4 gene variant, a known genetic risk factor for late-onset Alzheimer’s disease, induces neurodegeneration.

The apolipoprotein E (ApoE) proteins encoded by the APOE gene help in the repair of nerve cells (neurons) upon damage caused by aging or a stroke, among others. The three forms of ApoE proteins are ApoE2, ApoE3, and ApoE4, each encoded by a different APOE allele (different versions of the same gene).

ApoE2 is the rarest form and is considered neuroprotective, while ApoE3 is the most common form. ApoE4 is found in approximately 25% of the human population and in two-thirds of those with Alzheimer’s.

Despite being similar, ApoE3 and ApoE4 have different shapes. The structure of ApoE4 increases the likelihood that it’ll break down into smaller toxic fragments inside neurons. Scientists believe these toxic fragments may change key processes taking place inside neurons, culminating in their death.

“ApoE4 dramatically rewires cellular pathways in neurons and impairs their function,” Robert Mahley, MD, PhD, a senior researcher at Gladstone Institutes, and the project’s lead researcher, said in a press release. “Our goal is to understand how this rewiring occurs and identify potential new treatment strategies to negate the detrimental effects.”

More specifically, the researchers want to delve further into the molecular mechanisms by which ApoE4 causes toxicity in Alzheimer’s.

“Our work suggests that these ApoE4 fragments are toxic to neurons and cause sweeping changes to the collection of proteins expressed within a neuron,” Mahley said. “We suspect that their toxicity may underlie much of the neurodegeneration seen in Alzheimer’s disease.”

To achieve their goal, they will first use a technique, called affinity purification mass spectrometry (AP-MS), to identify which proteins interact directly with ApoE4 fragments. This work will be done in mouse-derived neuronal cells, which are similar to human neurons.

“AP-MS is an important first step because it will allow us to define physical interactions between proteins that may underlie the functional deficits observed in neurons that express ApoE4,” said Danielle Swaney, PhD, director of the Gladstone Mass Spectrometry Facility, who is collaborating with Manley on the project.

In addition to AP-MS, the team will also use other advanced protein analysis techniques to investigate the cellular processes that are deregulated in human neurons producing ApoE4 derived from human-induced pluripotent stem cells (hiPSCs). Of note, hiPSCs are fully matured cells that are reprogrammed back to a stem cell state, where they are able to grow into any type of cell.

“We are quite excited to be involved in this project,” Nevan Krogan, PhD, a senior investigator at Gladstones and expert on protein-protein interactions who is also involved in the project. “My lab has successfully applied AP-MS and other cutting-edge proteomic and genetic techniques to many different diseases, and we now hope to enable a much deeper understanding of ApoE4.”

By combining AP-MS with other techniques, the investigators hope to identify key proteins that are altered in ApoE4-producing neurons when compared with ApoE3 neurons. Top candidate proteins will then be selected for further testing in human neurons derived from hiPSCs.

The researchers will also use the CRISPR gene-editing tool to activate or inhibit the genes coding for the identified proteins to see if they can reverse the effects of ApoE4 in human neurons. This will be followed by studies in mice.

“By the end of the project, we hope to narrow down our list to just a few target genes or proteins that protect or restore neuronal health when we activate or inhibit them in live mice with the ApoE4 gene,” Swaney said. “They could then be explored as potential targets for Alzheimer’s treatment in humans.”

The team already has some ideas about where their research might lead. Previous evidence suggests that ApoE4 affects mitochondria, the cell compartments responsible for producing energy, impairing their function. Therefore, targeting the mitochondria may help rescue ApoE4’s effects in Alzheimer’s. However, they noted that other therapeutic routes may also be possible.

“Anything could be a target at this point, but I’m particularly interested in the possibility of small-molecule drugs that could protect mitochondria from toxic ApoE4 fragments,” Mahley said.

“Ultimately, I think the treatment of Alzheimer’s disease will be similar to the treatment of high blood pressure, in that two, three, sometimes four drugs are needed to control the disorder,” he added. “So, we may need a mitochondrial protector, we may need a drug that will correct ApoE4’s shape so that it is more like ApoE3, and more.”