Biochemical studies of chick brain development and maturation: I. Alterations in the macromolecule content and cell-free protein synthesis

Neural Protein Synthesis during Aging: Effects on Plasticity and Memory

During aging, many experience a decline in cognitive function that includes memory loss. The encoding of long-term memories depends on new protein synthesis, and this is also reduced during aging. Thus, it is possible that changes in the regulation of protein synthesis contribute to the memory impairments observed in older animals. Several lines of evidence support this hypothesis. For instance, protein synthesis is required for a longer period following learning to establish long-term memory in aged rodents. Also, under some conditions, synaptic activity or pharmacological activation can induce de novo protein synthesis and lasting changes in synaptic transmission in aged, but not young, rodents; the opposite results can be observed in other conditions. These changes in plasticity likely play a role in manifesting the altered place field properties observed in awake and behaving aged rats. The collective evidence suggests a link between memory loss and the regulation of protein synthesis in senescence. In fact, pharmaceuticals that target the signaling pathways required for induction of protein synthesis have improved memory, synaptic plasticity, and place cell properties in aged animals. We suggest that a better understanding of the mechanisms that lead to different protein expression patterns in the neural circuits that change as a function of age will enable the development of more effective therapeutic treatments for memory loss.

A comparison of protein synthesis by liver parenchymal cells isolated from Fischer F344 rats of various ages

Rates of protein synthesis by intact liver parenchymal cells isolated from male Fischer F344 rats ranging in age from 2.5 to 30 months were determined by measuring the incorporation of [3H] valine into acid-insoluble material and the specific activity of the extracellular valine. The rate of protein synthesis decreased 44% from 2.5 to 18 months and then increased slightly (18%) from 18 to 30 months. There was no dramatic change in the types of proteins synthesized by isolated liver parenchymal cells isolated from 2- or 18-month-old rats as determined by SDS-polyacrylamide gel electrophoresis. The ribosomal-transit time by liver parenchymal cells isolated from 18-month-old rats was 60% higher than the ribosomal-transit time of liver parenchymal cells isolated from 4-month-old rats. The fidelity of protein synthesis by parenchymal cells isolated from 4- and 18-month old rats was compared by measuring the incorporation of p-fluorophenyl alanine (an analogue of phenylalanine) into acid-insoluble material. Although protein synthesis decreased significantly from 4 to 18 months, the fidelity of protein synthesis remained constant.

Biochemical studies of chick brain development and maturation: II. Alterations in the mechanisms of cell-free protein synthesis

The molecular mechanisms responsible for the decreased cell-free protein synthetic activity of chicken brain (cerebrum, cerebellum, and optic lobes) from the late embryonic stage to the adult stage were investigated. The changes in polyribosome content closely paralleled changes in cell-free protein synthetic activity; both increased during late embryonic development, reached a maximum around hatching,and thereafter decreased to the level found in the adult. Both cell sap and microsomal or ribosomal fractions from the adult brain tissue were less active in protein synthesis; however, the microsomal or ribosomal fractions contributed more to the decreased protein synthesis than did the cell sap. The lower activity of adult cell sap in protein synthesis was primarily due to a decreased activity in the aminoacylation of tRNA with no apparent change in the ability of the cell sap to catalyze the elongation of polyphenylalanine synthesis. Ribosomal particles (80 S) from adult and embryonic brain tissue had similar biological activities and fidelity in the translation of polyuridylic acid; however, the cell-free protein synthetic activity of the embryonic post-mitochondrial supernatant preparation was more sensitive to inhibitors of the initiation of protein synthesis (aurintricarboxylic acid and polyinosinic acid) than adult post-mitochondrial supernatant, indicating a decreased initiation capacity in adult brain post-mitochondrial supernatant compared to embryonic brain post-mitochondrial supernatant.