Cultured Leptomeningeal Cells Secrete Cerebrospinal Fluid Proteins

: To extrapolate the function of the leptomeninges, we examined the profile of the proteins secreted from the cultured leptomeningeal cells prepared from 1–2‐day‐old rats. In sodium dodecyl sulfate‐polyacrylamide gel electrophoresis analysis of the medium conditioned with the cultured cells, 20–25 differentially distinctive protein bands were noted. Through several chromatographic procedures (Sephadex G‐75, Mono Q, and 7C8‐300), altogether 18 proteins were purified to homogeneity, and the partial amino acid sequence of each protein was determined. Homology search revealed that the major proteins included prostaglandin‐d‐synthase or β‐trace protein, insulin‐like growth factor (IGF)‐II, IGF‐binding protein‐2, apolipoprotein E, β2‐microglobulin, cystatin C, transferrin, peptidyl‐prolyl cis‐trans isomerase or cyclophilin C, secreted protein acidic and rich in cysteine, ubiquitin, lysozyme C, extracellular superoxide dismutase, and collagen α‐1 (III). Most of these proteins are known to be the major brain‐derived protein constituents of CSF and are thought to play important roles in certain biological events in the brain. Considering the morphological features, the present findings suggest the importance of the leptomeninges as an origin of such proteins in CSF.