Mitochondrial Dysfunction in Alzheimer's Disease Is Driven By Excess ER-Calcium Release in Patient-Derived Neurons

Tight regulation of mitochondrial Ca2+ is essential for neuronal bioenergetics and cellular metabolism. Ca2+ transfer from ER-localized ryanodine receptors (RyR) and inositol triphosphate receptors (IP3R) to the mitochondria maintains a steady Ca2+ source that fuels oxidative phosphorylation and ATP production. In Alzheimers disease (AD), RyR-evoked Ca2+ release is markedly increased, contributing to synaptic deficits, protein mishandling, and memory impairment. Here, we demonstrate that dysregulated RyR-Ca2+ release directly compromises mitochondrial activity and is an early contributor to AD cellular pathology. We measured an array of mitochondrial functions using fluorescent biosensors and optical imaging in RyR2-expressing HEK cells and iPSC-derived neurons from familial AD and nonAD patients. In neurons from AD patients, resting mitochondrial Ca2+ levels were elevated alongside increased free radical production and higher caspase-3 activity relative to nonAD neurons. RyR-evoked Ca2+ release further potentiated pathogenic mitochondrial responses in AD neurons, with increased Ca2+ uptake and exaggerated membrane depolarization. Additionally, clearance of damaged mitochondria was impaired in AD neurons, demonstrating consequences from dysfunctional lysosomes. Notably, impairments to mitochondria in AD neurons were largely prevented with the RyR negative allosteric modulator, Ryanodex. These findings highlight how excess RyR-Ca2+ release broadly contributes to early cellular pathology in AD which includes a cascade of ER, lysosomal, and mitochondrial deficits culminating in neuronal decline and degeneration. Additionally, pharmacological suppression of RyR-Ca2+ release preserves mitochondrial, ER and lysosomal function, thus providing a novel and effective therapeutic. Significance StatementMitochondrial dysfunction plays a central role in the cellular pathogenesis of Alzheimers disease, yet the upstream mechanisms driving these deficits remain largely unknown. Here, in human neurons derived from Alzheimers patients, we reveal how early Ca2+ mishandling through the ER-localized ryanodine receptor (RyR) is sensed by the mitochondria and triggers a pathogenic metabolic cascade. Pharmacologically restoring Ca2+ homeostasis reversed these deficits, including the increased free radicals and defective mitophagy, and restored the nonAD phenotype. The findings reveal the early neuronal signaling mechanisms that affect ER Ca2+ handling, proteolysis, and mitochondrial activity, highlighting the potential role of the dysregulated RyR as a therapeutic target for AD using clinically relevant model systems.