The tau protein is a key hallmark of Alzheimer?s disease and other tauopathies but its pathogenesis is not well understood. Targeting its toxicity and/or aggregates with antibodies is the leading therapeutic approach to slow the progression of these diseases. Here, we propose to clarify selective cellular vulnerability to tau pathology, and to develop single domain antibodies (sdAbs) to enhance pathogenic tau clearance. To realize these goals, three Specific Aims will be pursued: 1) To clarify cell-type specific vulnerability in Drosophila melanogaster tauopathy models. 2) To clarify in the fly tauopathy models the mechanisms of sdAb- mediated clearance of tau pathology, associated prevention of neurotoxicity, and tau-induced death. 3) Confirmation of key findings from Aims 1-2 in tauopathy mouse models and in human tauopathy neurons derived from induced pluripotent stem cells (iPSCs). We and others have shown GABAergic cell death and deficits in models and human tauopathy brains. Additionally, glutamatergic neurons have been reported to selectively accumulate tau aggregates. Both pathways are detrimental but possibly on a different timescale, and elucidation of the mechanisms involved may help develop tau therapies. We will determine in Drosophila tau models if GABAergic vs. glutamatergic neurons are more vulnerable to cell death vs. tau aggregation induced by tau expression in these cell subtypes individually, compared to global neuronal tau expression. We will then examine by genetic tools the roles of autophagy, lysosome or proteasome activity in tau sequestration or degradation. Additionally, astrocytic tau pathology occurs in all tauopathies, but its influence on functional impairments has not been well studied. We previously reported that an antibody fragment that targets tau suppresses tau-associated lethality and other phenotypes in Drosophila. For potentially more efficacious therapies, we developed anti-tau single domain antibody fragments (sdAbs) that are smaller, and should fold better for gene therapy, than conventional antibody fragments. Our preliminary data confirm their efficacy in a Drosophila tau model. We will determine whether secreted sdAbs still maintain anti-tau function, if their efficacy is cell-type related or requires CNS expression, and via which pathway these sdAbs promote tau clearance. Subsequently, we will seek to confirm the fly data in transgenic tauopathy mice and in iPSC-derived human tauopathy neurons. First, we will examine the temporal relationship between neurotoxicity, neuronal death and tau aggregation in GABAergic vs. glutamatergic neurons in the mice. Then, they will receive AAV gene therapy of the most efficacious sdAbs from the fly studies, followed by behavioral and brain analyses. An analogous approach will be conducted in the human neurons that have been differentiated into GABAergic and glutamatergic neurons. Together, these aims will provide valuable insights into cell-type specific vulnerability in tauopathies, and how tau pathology may be best targeted in future gene therapy trials.
The proposed project seeks to clarify selective cellular vulnerability in Alzheimer?s disease and related tauopathies, and to develop novel therapies to target pathological tau protein in these diseases. The studies should provide valuable insight into tau pathogenesis and are likely to identify clinical candidates to target pathological tau protein for therapy. Hence, this research is very relevant to public health.