Spatiotemporal Ca²⁺ Nanodomain Remodeling at MERCS Regulates Mitochondrial Proteostasis

Mitochondrial calcium fluxes serve as pivotal regulators of optimal organellar function and cellular viability, yet the spatiotemporal regulation of nanodomain Ca²⁺ transients at mitochondria-ER contact sites (MERCS) and their integration into adaptive mitochondrial stress signaling remain unresolved. In this study, we employed custom-built high temporal-spatial resolution GI/3D-SIM imaging techniques to achieve nanoscale resolution of calcium transients. We identify that MERCS-localized calcium oscillations gate retrograde stress signaling. Mechanistically, we demonstrate that augmented mitochondria-associated ER membrane (MAMs) connectivity unexpectedly attenuated global mitochondrial Ca²⁺ efflux, which triggering ATF5 shuttling-mediated transcriptional licensing and calcium-sensitive epigenetic reprogramming that synergistically activating stress-resilience programs. Quantitative protein expression and transcriptome analyses confirm that CsA-mediated calcium retention mimics MAMs induction preserves mitochondrial integrity and protecting cells from apoptosis in Aβ1-42-challenged neurons through synchronized UPRmt activation. Our findings reveal a novel mechanism by which MERCS decode proteotoxic stress into transcriptional and epigenetic adaptations, offering therapeutic potential for neurodegenerative diseases.