Title: Neurotoxicity of Spermine Synthase-Deficiency and Polyamine Imbalance PI: R. Grace Zhai, PhD, University of Miami School of Medicine, Miami, FL Co-I: Rich Steet, PhD, Greenwood Genetic Center, Greenwood, SC Co-I: Luigi Boccuto, MD, Clemson University School of Nursing, Clemson, SC PROJECT SUMMARY Polyamines, namely spermidine, spermine, and their precursor putrescine are tightly regulated polycations essential for life. First indications linking polyamine metabolism and neurological disorders came from the observations of abnormal polyamine levels accompanying several brain injury conditions including ischemic brain damage and traumatic brain injury. The pivotal role of polyamine metabolism emerged with the mapping of causal mutation of Snyder-Robinson Intellectual Disability Syndrome (SRS, OMIM 309583) to spermine synthase (SMS), an enzyme that catalyzes the conversion of spermidine to spermine. Our work in the previous grant cycle (R01 NS109640) investigated the pathological consequence of polyamine imbalance in the nervous system in the context of SRS. We have established a Drosophila model for SRS to recapitulate several key features of SRS pathology, have uncovered altered redox state, dysregulated protein acetylation, and lysosomal dysfunction as primary neurotoxicity underlying SRS pathology, and most importantly, have identified phenylbutyrate (PBA) as a robust pharmacological suppressor of neurotoxicity in SRS in vivo models and in patient cells. Recently, we made the exciting discovery of the critical connection between polyamine metabolism and Tau aggregation-induced neurodegeneration. Specifically, we found that while complete loss of SMS causes SRS, partial loss of SMS (SMS+/-, carriers) showed resistance to Tau-induced neurodegeneration in Tauopathy models. This finding has two important implications: first, polyamines may regulate Tau aggregational toxicity; and second, progression of neurodegeneration in Tauopathy could be delayed by modulating polyamine metabolism. Our objectives for this renewal application are to establish the mechanistic link between polyamine metabolism and Tau/amyloid aggregational neurotoxicity, and identify neuroprotective strategies based on modulating polyamine metabolism using complementary model systems; 1) in vivo Drosophila models, 2) human fibroblasts cells from SRS patients (male, SMS-/y) and heterozygous carriers (female, SMS+/-), and 3) gene expression analyses of human Alzheimer’s Disease related dementia (ADRD) datasets. We hypothesize that modulating polyamine metabolism and shifting spermine/spermidine ratio enhances autophagic flux, regulates global acetylation landscape, facilitates the clearance of toxic Tau/amyloid oligomer species, and confers resistance to neurodegeneration in proteinopathy. We propose to define metabolic and cellular mechanisms underlying SMS+/- mediated neuroprotection against Tau/amyloid accumulation-induced neurodegeneration in vivo in Drosophila (Aim 1); ch...