Mitochondria‑endoplasmic reticulum contact site nexus: Molecular integration, disease pathogenesis and therapeutic opportunities (Review)

Mitochondria‑endoplasmic reticulum contact sites (MERCs) are dynamic, nanoscale membrane domains that serve as crucial signaling hubs for inter‑organellar communication. These specialized interfaces are maintained by a complex network composed of tethering, promoter, and disruptor proteins and coordinate a wide range of cellular processes, such as calcium and zinc ion homeostasis, lipid biosynthesis and transfer, redox signaling, mitochondrial dynamics (fission, fusion and mitophagy), autophagy, apoptosis, inflammation and cellular senescence. Accordingly, the structural and functional integrity of MERCs is vital for cellular adaptation and survival. Nevertheless, MERC plasticity is often impaired in various human pathologies. Alterations in MERC composition, abundance, or function are regarded as pathogenic mechanisms in neurodegenerative diseases, metabolic disorders, cardiovascular conditions, cancer and orthopedic diseases. Common manifestations of MERC dysfunction include disrupted ion signaling, bioenergetic failure, excessive oxidative stress, and impaired organelle quality control. Therefore, targeted modulation of MERCs represents a promising therapeutic avenue. However, translating this potential into clinical practice faces considerable challenges. This is because MERC function is dynamic, context‑dependent and dualistic; both excessive and deficient coupling can drive pathology. Future progress hinges on deciphering the precise regulatory codes that govern MERC assembly, developing tools for real‑time, high‑resolution in vivo analysis, and designing innovative, cell‑type‑specific interventions that normalize rather than simply inhibit or enhance MERC function. A multidisciplinary approach integrating spatial proteomics, super‑resolution imaging, and advanced disease modeling is warranted for unlocking the full diagnostic and therapeutic potential of these organelle contact sites.