Changes in the metabolism of glial fibrillary acid protein (GFAP) during chronic relapsing experimental allergic encephalomyelitis in the strain 13 guinea-pig

Abstract

Spinal cords were removed from strain 13 guinea pigs in various stages of chronic relapsing experimental allergic encephalomyelitis (CREAE). Levels of glial fibrillary acidic protein (GFAP) in cord extracts were determined by radioimmunoassay and protein synthesis was monitored by incubating tissue prisms with [(35)S]methionine. Analysis of cytoskeletal enriched preparations from these incubations by SDS-polyacrylamide electrophoresis and fluorography permitted evaluation of the metabolism of discrete polypeptides; the identity of a labelled band at 51,000 daltons as GFAP was confirmed by immunoprecipitation with a specific antibody. Total protein synthesis increased 4-fold during the acute phase of CREAE but fell to control values with clinical recovery, while over the same period GFAP synthesis increased by 6-7-fold and remained elevated in the post-acute phase at about 200% of control values. During this time there was no increase in the GFAP content of the cord indicating an increased turnover of this protein rather than net synthesis. In later stages of CREAE however, GFAP levels were raised, correlating with a further increase in the incorporation of precursor into GFAP, this being most pronounced in animals in clinical relapse.