Research Overview

1. ApoE effects on Neuroinflammation and Synapse Viability

2. APOE and AD in vivo: EFAD mice

3. Mechanistic AD Biomarkers

4. AD therapeutics

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LaDu Lab Research Overview

Our research investigates the causes of AD and other neurodegenerative processes by focusing on the structure/function interactions between the human isoforms of apolipoprotein E (apoE) and amyloid-β peptide (Aβ).

A naturally occurring isoform of the APOE gene, apoE4, increases lifetime risk for AD 60-fold compared to the more common apoE3. Aβ, particularly oligomeric aggregates (oAβ), is considered a major cause of AD. Our overall hypothesis is that apoE4 and oAβ act synergistically to compromise neuronal viability. We utilize an integrated approach to address the complexity of apoE/Aβ interactions, including biochemical, molecular biology, and cell biology methods using in vitro, ex vivo, and in vivo models. Our goal is to develop oAβ and apoE/Aβ complex as "mechanistic biomarkers" and therapeutic targets as both are significant prior to neuronal damage.

Several of our most important initial contributions to the field demonstrated the critical dependence of the source and preparation of apoE and Aβ on experimental outcomes, particularly apoE/Aβ complex formation. For instance, unlipidated apoE4 binds Aβ with a higher affinity than apoE3. However, lipidated apoE3, not apoE4, binds Aβ and inhibits Aβ-induced neurotoxicity and inflammation. We developed protocols for preparations of oligomeric and fibrillar Aβ42. Oligomeric Aβ42 (oAβ42) is significantly more neurotoxic and neuroinflammatory than fibrillar assemblies and acts synergistically with apoE4 to reduce neuronal viability in vitro.

To move our research in vivo required both novel readouts for specific species of Aβ and a tractable in vivo model. To that end, we generated a new Aβ-specific antibody MOAB-2, that allowed for the development of quantitative, novel ELISAs to measure the levels and stability of apoE/Aβ complex and oAβ levels, both adaptable for high throughput analysis. To generate a tractable in vivo model, EFAD transgenic mice (E2FAD, E3FAD, and E4FAD) were made by introducing human APOE into 5xFAD mice, an Aβ-transgenic mouse line that specifically over-produces human Aβ42. In EFAD mice, Aβ deposition was delayed ~4 months, though generally greater in E4FAD mice. Intraneuronal Aβ accumulation was not apoE isoform-specific.

However, in E4FAD mice total apoE levels were lower and total Aβ levels were higher. In the soluble fraction of E4FAD mice, Aβ42 and oAβ levels were higher and apoE4/Aβ complex levels were lower than E2FAD or E3FAD evidence that apoE/Aβ levels isoform-specifically modulate soluble oAβ clearance. Thus, apoE isoforms differentially regulate Aβ speciation, an effect potentially modulated by apoE/Aβ complex formation.

The next step in our research was to evaluate the interactions between Aβ and apoE in human samples. In human synaptosomes and CSF, levels of soluble apoE/Aβ are lower and oAβ are higher in AD patients compared to controls, and with APOE4 compared to APOE3 in the AD cohort. These results suggest that soluble levels of apoE/Aβ isoforms-specially modulate oAβ clearance and that apoE/Aβ and oAβ represent "mechanistic biomarkers". Having validated the novel readouts for apoE interactions with Aβ in the EFAD mice and human control and AD patients, we are now using these reagents and transgenic mice for preclinical testing of both apoE-based and other potential AD therapeutics.