Second Generation Gene Therapy for APOE4 Homozygous Individuals at High Risk for Alzheimer's Disease

Alzheimer’s disease (AD), a degenerative brain disease and the most common cause of dementia, currently affects 5.8 million Americans and 50 million people worldwide.

AD symptoms include progressive decline of cognitive and functional abilities and brain pathology, including extracellular beta-amyloid plaques, intracellular tau tangles, chronic inflammation, and brain atrophy.

The strongest genetic risk factor for susceptibility to late-onset AD concerns polymorphisms in the apolipoprotein E (APOE) allele.

APOE4 is found at high frequency in AD patients and homozygous inheritance is associated with a 14.5-fold increased risk of developing AD. In contrast, APOE2 decreases risk of AD development and delays onset of disease.

A previous study demonstrated that delivery of APOE2 directly to the CNS of AD murine models using an adeno-associated virus (AAV) vector could provide significant APOE2 expression and decrease the levels of soluble and insoluble amyloid-β peptide and amyloid burden.

However, even with APOE2 supplementation, the presence of APOE4 still constitutes an increased risk as APOE2/4 heterozygotes have a 2.6-fold increased risk of developing AD.

We propose to develop a second-generation AAV-based gene therapy to introduce expression of the protective APOE2 while simultaneously decreasing the levels of deleterious endogenous APOE4 in APOE4 homozygotes.

Our strategy is to encode artificial microRNAs (miRNA) targeting the endogenous APOE4 into the AAV expression cassette along with the cDNA for the human APOE2 gene (hAPOE2-mirAPOE4).

The AAV9 serotype capsid will be used to package the expression cassette because it mediates efficient transduction of astrocytes, the main producers of APOE, as well as microglia and neurons.

The established P301S/E4 AD mouse model that expresses mutant human tau and human APOE4 and has high phosphorylated tau burden, chronic inflammation, and extensive neurodegeneration will be used to assess therapy efficacy. To evaluate this second-generation strategy with AAV9-hAPOE2-mirAPOE4, we propose two specific aims: Aim 1.

Test an AAV construct to silence endogenous APOE4 expression and deliver the APOE2 coding sequence in vitro. Aim 2.

Determine if augmentation of APOE2 with reduction of endogenous APOE4 protects against tau pathology, neurodegeneration, and neuroinflammation in vivo.