Characterization of polysomes purified from human postmortem brain tissues

To assess their suitability for studies of translational regulation of gene expression, cytosolic polyribosomes (polysomes) were purified from human postmortem frontal cortex and cerebellum. Human polysomes from 11 individual brains of various ages, postmortem intervals and agonal states were compared to polysomes purified from rat whole brains for yield, size and translational activity. Similar yields (mean +/- SD: 1.65 +/- 0.4 A(260) units/g tissue) of frontal cortical polysomes were obtained from the various human brain frontal cortices independent of age, postmortem interval and agonal state. The yields from the young rat brains were 2.5-fold greater. Polysomes containing up to 6 ribosomes per mRNA molecule were reproducibly purified from the human tissue whereas the rat polysomes were larger, containing 15-20 ribosomes per message. The human polysomes were less translationally efficient than rat (means +/- SD: 730 +/- 170 x 10(3) vs 5800 +/- 700 x 10 (3) dpm [ (35)S]methionine/A (260)unit ) which is consistent with the larger sizes of the rat polysomes and the inability of the human polysomal mRNA to reinitiate in the assay. Neither polysome sizes nor translational efficiency were dependent on age, postmortem interval and agonal state. However, the relative rates of elongation by total rat and human polysome populations were similar. The rat and human polysomes synthesized polypeptides of similar size ranges which indicates that similarly sized mRNAs were associated with the polysomes. Thus, utilizing the described methodology, intact and translationally active polysomes have been reproducibly isolated from various human postmortem brain tissues. The polysomes may be used to investigate translational control of gene expression in the human brain during normal and neuropathological conditions.