Protein Synthesis in Postischemic Rat Brain: A Two-Dimensional Electrophoretic Analysis

Abstract

This study examined the pattern of protein synthesis in the neocortex, caudate–putamen, and the hippocampus following transient forebrain ischemia in rats. The animal model of temporary ischemia used in this study causes permanent damage to vulnerable neurons with a time course of injury that varies from hours (caudate nucleus) to days (hippocampus). To examine the spectrum of proteins synthesized in these regions at 3 and 18 h after recirculation, cerebral proteins were pulse-labeled in vivo by an intravenous injection of [³⁵S]methionine. Newly synthesized (³⁵S-labeled) and constitutive (unlabeled) proteins were analyzed by two-dimensional gel electrophoresis and fluorography. In all three brain regions, specific proteins underwent preferential synthesis (M_r∼27,000, ∼65,000, ∼70,000, ∼110,000), while others showed decreased synthesis (neuron-specific enolase, α- and β-tubulin). There was an early (3 h post ischemia) induction of the M_r∼70,000 mammalian “stress” protein; at 18 h post ischemia, its synthesis remained high in the hippocampus but was diminished in the neocortex and had largely subsided in the caudate–putamen. All regions at 18 h showed increased synthesis of an M_r∼50,000 protein, tentatively identified as glial fibrillary acidic protein. The results show that temporary forebrain ischemia induces changes in protein synthesis that include features similar to those observed in other eukaryotic cells subjected to injurious stress. These postischemic changes in protein synthesis are qualitatively similar in all brain regions examined despite regional differences in the severity of subsequent neuronal damage. The persistent synthesis of the M_r∼70,000 stress protein in the hippocampus, however, may reflect continued metabolic injury long after the ischemic episode has passed.