Making tracks: microglia and the extracellular matrix.

Microglia are resident immune cells of the central nervous system (CNS) and critical regulators of neural homeostasis, mediating immune surveillance, synaptic remodeling, debris clearance, and inflammatory signaling. Emerging evidence highlights the extracellular matrix (ECM) as important to microglial behavior in both physiological and pathological contexts. The CNS ECM is a dynamic and bioactive scaffold composed of three primary compartments: interstitial matrix, basement membranes at neurovascular and neuroepithelial interfaces, and perineuronal nets (PNNs). Each compartment exhibits distinct molecular architectures, ranging from fibrillar collagens and glycoproteins in basement membranes to chondroitin sulfate proteoglycans and hyaluronan-rich structures in PNNs. In this review we examine how microglia engage with and reshape the ECM to dynamically respond to disruptions in homeostasis with aging and disease. We discuss the concept of the microglial-ECM "interactome", which may represent a molecular interface through which microglia sense, modify, and respond to their extracellular environment. This interactome enables microglia to enact fine-scale ECM remodeling during routine surveillance, as well as large-scale alterations under pathological conditions to help preserve function and motility. In aging and disease, dysregulation of the microglial-ECM interactome is characterized by aberrant mechanotransduction, elevated proteinase activity, remodeling of the ECM, and sustained pro-inflammatory cytokine release. These pathological changes compromise ECM integrity, challenge microglial activity, and contribute to progressive neurovascular and synaptic dysfunction. Deciphering the molecular mechanisms underpinning microglial-ECM interactions is essential for understanding region-specific vulnerability in neurodegeneration and may reveal new therapeutic targets for preserving ECM structure and countering CNS disorders.