What's the science?
All cells in the body produce proteins, and certain tissues synthesize these proteins and recycle them (to produce new ones) faster than others. Skeletal muscle is an example of one tissue that recycles proteins quickly, at a rate of 1-2% per day. Historically, we have assumed that the brain does not regenerate itself as much as other tissues. This week in Brain, Smeets and colleagues report that brain protein turnover is much higher than previously assumed.
How did they do it?
Six participants that were scheduled to undergo surgery for drug-resistant temporal lobe epilepsy were recruited. Amino acids are the precursors to proteins. Patients were given continuous intravenous infusion (before and during surgery) of an amino acid called phenylalanine, which was radiolabeled with a stable isotope. Blood and tissue samples from the cortex and hippocampus were taken, as well as from two muscle tissues throughout the surgery. These tissue samples were examined for the incorporation of phenylalanine into tissue protein. They then calculated protein synthesis rates based on phenylalanine enrichment in the tissue, and also identified what type of proteins are present in brain tissue.
What did they find?
Tissue phenylalanine enrichments were found in muscle tissue and brain tissue; however, they were higher in brain tissue, indicating that protein synthesis rates were 3-4 times higher in brain tissue compared to skeletal muscle tissue. Protein synthesis rates were higher in the cortex compared to the hippocampus. They were able to identify 1192 different proteins in brain tissue, and the most abundant form of proteins were cytoskeletal proteins (proteins that make up the structure of the neuron).
What's the impact?
This is the first study to report protein synthesis rates in the living human brain. It is well established that skeletal muscle tissue regenerates itself rapidly in order to adapt to repeated use. Until now we didn’t know that brain tissue regenerates at an even higher rate than skeletal muscle. This rapid tissue regeneration could underlie the ability of the brain to adapt and remodel itself throughout life.
J. S. J. Smeets et al., Brain tissue plasticity: protein synthesis rates of the human brain. Brain. (2018). Access the original publication here.