PROJECT SUMMARY/ABSTRACT Reactive astrocytes and astrogliosis are one of the earliest pathological markers associated with Alzheimer’s Disease (AD) development, appearing months before amyloid-beta A plaques, Tau neurofibrillary tangles, and cognitive deficits. However, underlying mechanisms and whether modulating astrocyte function can attenuate prevent AD progression remain under studied. Recent findings from our lab show that reactive astrocytes upregulated Na+/H+ exchanger 1 (NHE1) protein activity, a proton extrusion ion transporter in pH homeostasis, in mouse models of stroke and vascular dementia. Both pharmacological inhibition and transgenic knockout of astrocytic NHE1 protein significantly attenuated astrogliosis and neurodegeneration in these studies. In this application, our preliminary study with AD comorbidity post-mortem human brain tissues reveals significantly increased cell counts of NHE1+ and GFAP+ reactive astrocytes in cortical regions, compared to control specimens. Using APP/PS1dE9 AD mouse model, we also detected increased NHE1 protein expression in hippocampus at 8-10-month-old AD mice than wild-type (WT) mice. These preliminary findings led me to hypothesize that abnormal astrocytic NHE1 activation contributes to astrogliosis and AD pathogenesis, and that NHE1 inhibition may be effective at mitigating AD-induced astrogliosis pathologies and cognitive decline. To test my hypothesis, I will first characterize the correlation between changes of NHE1 protein expression and activity and astrogliosis during AD development over a 4-8-month period using the APP/PS1dE9 AD mouse model (Aim 1). Secondly, I will test efficacy of pharmacological NHE1 inhibitor HOE642 in the APP/PS1E9 model or genetic deletion of astrocytic NHE1 in APP/PS1E9-NHE1 KO line to assess whether targeting NHE1 protein is effective at attenuating AD astrogliosis, neurodegeneration, A accumulation, and cognitive decline (Aim 2). Completion of this project will determine the potential of NHE1 as a possible therapeutic target for AD treatment. Through these research activities, I will acquire expertise in studying astrocyte morphological and transcriptional transformation and their roles in AD pathogenesis. Concentrating on non-neurocentric approaches in AD research in the enriched environment within the University of Pittsburgh’s ADRC, PIND, and Aging Institute will enhance my training and prepare me to develop innovative research throughout my career development as an independent neuroscientist.