The Big Five Functional Levels of Vascular Calcification.

Vascular calcification is often described either as passive deposition of calcium-phosphate crystals or as an active osteogenic process. Neither view alone explains how mineral formation begins, progresses and becomes self-sustaining within the vascular wall. Here, we organize the main mechanisms of vascular calcification into five functional levels according to their predominant causal role. Level I defines mineral permissiveness through calcium-phosphate pressure and extracellular mineralization inhibitors. Level II determines how nascent mineral is packaged, nucleated and retained through calciprotein particles, extracellular vesicles and extracellular matrix remodeling. Level III describes the cellular response, including vascular smooth muscle cell plasticity, BMP-WNT signaling and endothelial-to-mesenchymal transition. Level IV comprises inflammatory, oxidative, mitochondrial, senescent and epigenetic-metabolic mechanisms that amplify and stabilize calcification-prone states. Level V determines whether cellular stress can still be contained or progresses to proteostatic failure and regulated cell death. These levels are functionally coupled rather than sequential: mineral can alter cellular phenotype, while cellular dysfunction feeds back to weaken mineral inhibition and generate new nucleation surfaces. This framework places failure of mineral containment, rather than any single signaling pathway, at the center of vascular calcification and provides a basis for considering causal order and therapeutic timing across different disease settings.