BT1: a novel fluorescent probe to detect pathological tau in human AD retina.

Background: Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by cognitive deficits and memory decline. The aggregations of misfolded and hyperphosphorylated tau protein are hallmarks of AD, which lead to neurofibrillary tangles (NFTs). Neurodegenerative changes in the brain associated with AD are accompanied by structural changes in the retina, such as optic nerve degeneration and reduced thickness of retinal layers. Moreover, the retina is a readily accessible neural tissue, making it an ideal target for studying biomarkers of neurodegenerative diseases. In add, numerous studies have shown the presence of tau aggregates in both AD mouse models and postmortem samples of AD patients’ retina. Effective therapies and preventive measures are still lacking in Alzheimer’s research, likely due to the absence of early detection methods and the inability to monitor disease progression before the onset of significant behavioral symptoms. To this purpose, we have developed tau protein-specific fluorescent labels, such as BT1, capable of detecting pathological forms of tau protein. We test the ability of BT1-probe to detect neurofibrillary tangles, a key marker of tauopathies, in human induced pluripotent stem cell (iPSC)-derived 2D and 3D retinal cultures and in postmortem samples of AD retina patients. Method: We generated retinal cultures from two isogenic human iPSC lines: WT (control) and a tau mutant with a MAPT-related intronic mutation, as a model of tau pathology. Both 2D and 3D retinal cultures, as well as retinal samples from AD patients, were treated with the BT1 probe. Then, we performed immunofluorescence analysis using different antibodies, each targeting specific forms of the tau protein. Result: The results show an increased co-localization between the BT1 signal and pathological tau forms into the tested models. Our findings highlight the high specificity of the BT1 probe in detecting phosphorylated and oligomeric tau in hiPSC-derived retinal neurons, retinal organoids, and postmortem AD retina samples. Conclusion: These results suggest that the BT1 fluorescent ligand is capable of effectively identifying pathological forms of the tau protein, offering a promising tool for monitoring tau tangles in retinal tissues and introducing a novel diagnostic approach for the early detection of Alzheimer’s disease.