Abstract - Wendy Aquino Nunez

Modeling Early Tau Aggregation and Neurodegeneration Using Caenorhabditis elegans

Wendy Aquino Nunez and Brian D. Ackley

Department of Molecular Biosciences, University of Kansas, Lawrence, KS

Alzheimer’s Disease and Alzheimer’s Disease-Related Disorders (AD/ADRD) are tauopathies. In disease, the microtubule-associated protein tau is found to be aggregated in areas of the brain that exhibit high levels of neuronal and synaptic degeneration. Most animal models of tauopathies have focused on neuronal degeneration as a phenotype because it is an obvious endpoint. However, we have generated new C. elegans tauopathy models that exhibit neuronal and organismal phenotypes in the absence of cell death. For example, cell-specific expression of a disease-relevant tau variant (P301L), or a synthetic tau variant that spontaneously aggregates (3PO), causes an age-dependent progressive loss of GABAergic synapses without neuronal degeneration. These models can help us to understand tau-induced phenotypes prior to cell death. Tauopathies can be caused by mutations in the tau gene (MAPT), but these are rare, especially in AD. Recent work has found considerable structural heterogeneity in tau aggregates isolated from AD and ADRD brains. This has been confirmed by in vitro polymerization experiments, where different molecules that can induce tau to aggregate result in unique structural polymers. Compounds that can prevent (or in some cases reverse) tau aggregation exhibit activity in specific ways. That is, aggregation inhibitors that are effective against heparin-initiated polymers are not effective against polymers formed in response to arachidonic acid, and vice versa. The simplest interpretation of these results is that there are multiple potential initiating events that can result in AD-like disorders. We need to better understand the factors that initiate disease, how those factors induce different “strains” of tauopathies, and what interventions are likely to be effective in each case. Ideally, we would like to be able to do this early in disease progression, prior to significant dementia. To do that, we are expressing GFP-tagged tau proteins throughout the nervous system. We find that discreet differences between tau variants can be measured using GFP. For example, wild-type tau-GFP appears smooth and filamentous and localizes to axons and cell bodies. The aggregation prone 3POtau-GFP is punctate in axons with extensive inclusions of GFP in cell bodies, that increase in an age-dependent manner. Thus, we can use these differences to identify factors that induce wild-type tau to aggregate in vivo. We exposed wild-type tau expressing animals to heat of stress, and looked for changes in tau-GFP intensity, localization, and appearance. We found that heat shock causes changes in tau-GFP. Rather than being entirely filamentous, there are now slight inclusions of GFP develop in the axonal tracts and cells bodies. In addition, the ratio of GFP intensity of heat-shocked vs. non-heat-shocked animals almost doubled on day1. However, GFP intensity continuously decreases with time, which might indicate that the nematodes’ heat-shock protein response is targeting and eliminating aggregated tau. Developing an in vivo model for early tau polymerization can enhance our understanding of the cellular and molecular steps that lead to neurodegeneration.