Proteomic analysis of human leptomeningeal matrisome identifies changes in Alzheimer's disease

The leptomeninges (arachnoid and pia) are the inner layers of the meninges that envelope the brain. They define the borders of the subarachnoid space (SAS) where cerebrospinal fluid (CSF) circulates. Leptomeninges act as the barrier tissue and contribute to fluid exchange and immune function of the brain. These processes are identified as key factors in the development of neurodegenerative diseases. The extracellular matrix (ECM) is a critical structural component of leptomeninges. However, it remains insufficiently characterized in health and disease. Here, we performed complete proteomic profiling of ECM proteins (matrisome) of human leptomeninges from individuals with Alzheimers disease (AD) and cognitively normal controls (CN) using sequential biochemical fractionation coupled with mass spectrometry. We resolved leptomeningeal matrisome based on the biochemical properties reflected by the protein solubility. This approach identified 211 ECM proteins in human leptomeninges and revealed disease-associated shifts in leptomeningeal solubility consistent with altered matrix organization and signaling. We found that ECM-linked regulators and secreted factors extracellular sulfatase SULF2, antithrombin-III (SERPINC1), secreted frizzled-related protein 3 (sFRP3) and integrin beta-5 (ITGB5), which is a receptor for fibronectin, were differentially expressed in AD leptomeninges based on the disease status. Seven ECM proteins were identified only in AD samples, and two ECM proteins in CN samples. Pathway enrichment implicated TGF-{beta} and Wnt-related signaling and coagulation as critical for leptomeningeal function. Our findings provide the first comprehensive proteomic characterization of the human leptomeningeal matrisome and establish a biochemical framework for investigating how meningeal matrix remodeling contributes to AD.