Michael Sadek Shane P. Mitchell Priyanka Sinha Brianna Lundin Gokce Armagan Natalia Wieckiewicz Bradley T. Hyman Masato Maesako Florian Perrin ^* Oksana Berezovska ^*

• MassGeneral Institute for Neurodegenerative Disease, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, United States

Introduction: GLT-1, the major glutamate transporter in the brain, interacts with Presenilin 1 (PS1), the catalytic subunit of γ-secretase. This interaction is significantly reduced in sporadic Alzheimer's Disease (AD) brains, which may provide a link between amyloid pathology and glutamate dysregulation. With aging being a major risk factor for AD, it remains crucial to explore whether GLT-1/PS1 interaction changes during normal aging to better understand what occurs in pathological conditions. Methods: We investigated the age-associated changes in GLT-1 and PS1 expression (Western Blot), maturation (Native PAGE), and interaction (co-immunoprecipitation and fluorescence lifetime imaging microscopy) in the mouse cortex at 2, 8, and 22.5 months of age (mo). To elucidate the consequences of changes in GLT-1/PS1 interaction, we used a cellpermeable peptide to inhibit GLT-1/PS1 interaction in mouse primary neurons and evaluated GLT-1 cell surface expression (flow cytometry) and multimerization (Native PAGE). Results: We found that GLT-1 homo-multimer formation, PS1/γ-secretase complex formation, and GLT-1/PS1 interaction increase from 2mo to 8mo mice but are reduced in the 22.5mo mouse cortex. Inhibiting GLT-1/PS1 interaction in primary neurons enhanced GLT-1 cell surface delivery and homomultimerization. Conclusion: Therefore, we propose that reduction in GLT-1/PS1 interaction during normal aging could drive compensatory changes in GLT-1 maturation to counter the effects of glutamatergic dysregulation in the aged brain.