PROJECT 4 SUMMARY/ABSTRACT An astrocyte mechanism will be targeted with the goal of preventing a common subtype of dementia. Limbic- predominant age-related TDP-43 encephalopathy (LATE) and hippocampal sclerosis (HS) pathology are present at autopsy in approximately 25% of “Alzheimer’s-type dementia” cases. Notably, a specific ABCC9 gene variant is associated with increased risk of developing LATE+HS. ABCC9 encodes a protein that serves as a “metabolic sensor” linking brain hypoxia and stress to changes in intracellular calcium and blood flow. We hypothesize that dysregulation of ABCC9 in astrocytes causes or exacerbates LATE+HS via impaired cerebrovascular function, hypometabolism (with ionic dyshomeostasis), and neuronal hyperexcitability, aligning perfectly with themes of this P01. These astrocyte mechanisms can be targeted by a well-tolerated drug (nicorandil) that has been shown to be clinically safe and effective, with high potential public health impact. The research will be conducted with the following Specific Aims: Aim 1: Characterize ABCC9/SUR2 transcripts and proteins in human astrocytes. We will test the hypothesis that the ABCC9 genetic variant associated with LATE+HS risk is also associated with decreased ABCC9 expression in astrocytes. Astrocyte ABCC9 transcripts are mostly unknown. In human samples, we will evaluate the repertoire of mRNA transcripts and splicing in astrocytes. We will characterize ABCC9 gene expression with RNA-Seq data across cell types. In genotyped human brains from Core C (LATE+HS and controls), we will evaluate ABCC9 proteins immunohistochemically, and we will explore Sur2 expression in mouse models. Aim 2: Test the hypothesis that modulation of astrocytic ABCC9//KATP leads to improved neurovascular and metabolic function in LATE+HS model mice. The novel (TetR-TDP) mouse, an excellent animal model that has proven hippocampal cell loss, astrocytosis, TDP-43 proteinopathy, and memory impairment, will be used to test the impact of astrocyte specific ABCC9 upregulation on neurovascular function (multiphoton to look at neurovascular coupling and vessel leakiness; MRI to look at cerebral blood flow and other endpoints). The impact of astrocyte specific upregulation of SUR2B on brain metabolism will also be tested (glutamate uptake in astrocytes; Ca2+ dynamics [GCaMP]; and, MRS to characterize brain metabolites). Aim 3: Test the hypothesis that pharmacological modulation with nicorandil (a KATP channel agonist well-tolerated in oral preparations) leads to improved neuronal and astrocyte function and neurobehavioral assessment outcomes in TetR-TDP mice. These outcomes will include readouts of neurobehavioral parameters (RAWM and Y- maze) and other endpoints including electrophysiological assessments in astrocytes. Follow-up assessments will include detailed neuropathology (astrocytosis, HS, TDP-43 proteinopathy, and small vessel morphology). In summary, while studying the mechanisms of astrocyte metabolic and neuro...