Abstract 1084 Preserving Bioenergetics through Mitochondrial Calcium Homeostasis in Alzheimer's Disease

Background: In Alzheimer's disease (AD), the intricate balance of mitochondrial calcium (mCa2+) plays a crucial role in regulating cellular bioenergetics. Physiologically, mCa2+ uptake stimulates dehydrogenases and enhances bioenergetic processes. However, in AD, sustained high intracellular calcium (iCa2+) levels overload mitochondria, leading to metabolic disruption, protease activation, and excessive reactive oxygen species (ROS) generation, ultimately resulting in cellular demise. Recent research, including our own investigations, has shed light on the significant role of mCa2+ overload in the pathogenesis of AD. Consequently, modulating mCa2+ signaling emerges as a pivotal strategy to slow AD progression, making it a promising therapeutic target. Mere inhibition of mCa2+ uptake to prevent overload through the main pore-forming subunit MCU levels may not be sufficient, as fine-tuned mCa2+ flux is necessary to prevent overload while maintaining essential bioenergetics. Novel approaches are needed to effectively regulate mCa2+ homeostasis in AD and provide potential therapeutic solutions. Methods. In this study, we sought to unravel a novel molecular regulatory mechanism that could limit mCa2+ overload in AD while preserving vital bioenergetics and preventing cell death. To achieve this, we focused on investigating the role of Mitochondrial Calcium Uniporter Beta (MCUB), a paralog of MCU known to act as a negative regulator of mCa2+ uptake. Our research involved the examination of MCUB expression using AD patient samples, AD mice models, and cell lines. Specifically, we utilized a neuroblastoma cell line stably expressing the human Swedish mutant amyloid precursor protein (N2a/APPswe) and overexpressed MCUB through adenovirus encoding. We then studied mitochondrial alterations, including Ca2+ handling, ROS generation, permeability transition pore activation, oxidative phosphorylation (OxPHOS), ATP levels and cell death in these cell lines. Results. Our study revealed significant reductions in MCUB expression in frontal cortex samples of non-familial AD patients, 5xFAD and AppSAA-KI mice, and APPswe cell lines, suggesting a link to mCa2+ dysregulation in AD. Further investigations in N2a/APPswe neurons showed severe impairments in mCa2+ handling, redox balance, and bioenergetics in AD cells. However, rescuing MCUB via adenoviral expression led to enhanced clearance of pathogenic mCa2+, improved OxPHOS, and prevented ROS accumulation and cell death. Conclusions and future directions. Our data suggest that MCUB modulation has the therapeutic potential to preserve bioenergetics and limit cell death in AD. Future studies will investigate the effects of neuronal-specific MCUB knockouts and overexpression in 5xFAD mouse models to explore MCUB's impact on metabolism, mCa2+ dynamics, cognitive functions and AD phenotype in vivo. This research is supported by National Institute on Aging grant numbers R00AG065445, Wake Forest Alzheimer's Disease Research Center- REC and development grant (P30 AG072947), and Wake Startup Fund to PJ