Pathological extracellular matrix changes in decellularized normal appearing gray matter and subpial multiple sclerosis lesions

Multiple sclerosis (MS) is a chronic CNS disease characterized by demyelinated lesions. Gray matter lesions (GMLs) are associated with neurodegeneration and clinical disability, and normal appearing gray matter (NAGM) also shows neuropathology. The extracellular matrix (ECM) supports neuronal health, with perineuronal nets (PNNs) regulating synaptic stability. Microglia remodel the ECM by secreting matrix metalloproteinases, while ECM composition affects microglia behavior. We examined ECM composition in decellularized human control gray matter, NAGM and GML slices and investigated its effects on microglia. Label-free quantitative mass spectrometry of decellularized control gray matter and NAGM revealed differential abundances in PNN ECM components and condition-specific synaptic and basement membrane ECM components. ECM composition was similar between decellularized GMLs and perilesional gray matter. Microglia introduced to decellularized NAGM and GML slices lost IBA1 expression in half the cells, while some remaining IBA1+ microglia acquired proinflammatory marker inducible nitric oxide synthase (iNOS). These findings suggest ECM alterations in NAGM influencing microglial characteristics potentially contributing to MS pathology.