P1‐216: LYSOSOME‐AUTOPHAGOSOME DEFECTS MEDIATE PROTEINOPATHY AND SYNAPTIC PATHOPHYSIOLOGY IN EARLY STAGES OF ALZHEIMER'S DISEASE

Vacuolar H+-ATPase (V-ATPase proton pump) regulates the acidic environment required for intracellular organelle functions, such as lysosomes and synaptic vesicles. The V-ATPase maintains an acidic pH in lysosomes essential for autophagy, a catabolic pathway to degrade cellular proteins. Synaptic vesicles require an acidic environment for neurotransmitter uptake and synthesis. In Alzheimer's disease (AD), V-ATPase disruption can lead to abnormal β-amyloid and tau accumulation, and deficient synaptic vesicle stores. A candidate mechanism concurrent with V-ATPase defects Ca dyshomeostasis, which alters the ion exchange and thus pH within these organelles. We hypothesize that altered Ca signaling disrupts V-ATPase ion exchange and instigates AD pathology. Immunohistochemistry in fixed brain slices was used to determine expression of V-ATPase subunits (V1B2, V0a1), lysosomes (Lamp1), pre-synaptic vesicles (synaptophysin), and mature autophagosomes (LC3B) in 3-month old 3xTg-AD mice and non-transgenic (NTg) controls with or without a 30-day Ryanodex treatment (NAM of RyR; 10mg/kg). Induced human neurons (iN) transformed from AD patient fibroblasts were used to measure β-amyloid and hyperphosphorylated tau levels after 500nM bafilomycin (V-ATPase inhibitor) treatment. Lysosomal pH upon RyR stimulation with caffeine (20mM) was measured in RyR-overexpressing HEK cells and iN using Lysosensor. V-ATPase, lysosome, and pre-synaptic vesicle markers are diminished in brains of 3xTg-AD mice relative to NTg, whereas LC3B expression is increased. These phenotypes were restored to NTg levels after Ryanodex treatment in 3xTg-AD mice. Additionally, increased aberrant RyR-Ca signaling alkalizes lysosomes and increases expression of β-amyloid and hyperphosphorylated tau. V-ATPase, lysosome, and pre-synaptic vesicle markers are diminished in brains of 3xTg-AD mice relative to NTg, whereas LC3B expression is increased. These phenotypes were restored to NTg levels after Ryanodex treatment in 3xTg-AD mice. Additionally, increased aberrant RyR-Ca signaling alkalizes lysosomes and increases expression of β-amyloid and hyperphosphorylated tau.