Intracellular Signaling Regulated by Activated α2-Macroglobulin: Expanding Beyond Its Protease Inhibitory Role

Alpha-2-macroglobulin (α2M) is a conserved plasma glycoprotein traditionally known for its broad-spectrum protease inhibitory activity. However, emerging evidence indicates that its activated form, α2M*, generated via proteolytic cleavage or nucleophilic attack, functions as a versatile signaling ligand. By engaging specific cell-surface receptors, most notably low-density lipoprotein receptor-related protein 1 (LRP1) and glucose-regulated protein 78 (GRP78), α2M* orchestrates a diverse array of intracellular programs, including the PI3K/Akt/mTOR, MAPK/ERK, and JAK/STAT cascades, as well as mechanosensitive YAP/TAZ signaling. These pathways collectively govern fundamental cellular processes such as proliferation, metabolic reprogramming, cytoskeletal remodeling, and inflammatory adaptation across various cell types, including macrophages, cardiomyocytes, and malignant cells. Altogether, this review synthesizes current knowledge on α2M activation, structural transitions, receptor interactions, and downstream signaling, highlighting the expanding functional landscape of α2M* as a potent regulator of intracellular communication with implications for physiology and disease.