Muscle and Exercise Lecture 3.3 - Role of nutrition, energy and amino acid sensing in the control of muscle protein turnover Flashcards
Does protein synthesis increase with protein intake?
Yes, but is capped at 25g. Very small difference between ie 50g and 25g.
How much protein is needed to maximally stimulate protein synthesis?
~25g.
How many hours after eating protein does protein synthesis remain high?
~2h before decreasing to baseline.
Does amino acid infusion increase protein synthesis?
Yes, very rapidly, but is short-lived.
Do essential amino acids stimulate protein synthesis via mTOR (mTORC1)? How can this be tested? What happened to mTORC2?
Yes they do, by using rapamycin. mTORC1 was inhibited, and protein intake had no effect on protein synthesis.
mTORC2 wasn’t inhibited.
What are the main downstream targets of mTORC1?
4EBP1 and S6K (S6 too).
Which amino acids are known to stimulate mTOR?
Leucine and arginine.
How does mTOR sense amino acid concentrations? How can this be tested?
Infuse different amino acids.
Plasma amino acid, muscle amino acid concentration and muscle synthesis levels taken.
Correlation between amino acid level and protein synthesis.
Does extracellular amino acid availabiltiy regulate protein turnover?
Yes.
Do amino acid transporters act as receptors?
Yes, they can link directly to mTOR.
What must mTOR do to activate?
Translocate to the lysosome.
What does protein ingestion do to expression levels of amino acid transporters?
Changes their expression levels.
What is needed for mTOR to activate?
Amino acids are needed for it to bind to a lysosome to activate.
Name an enzyme that catalyses mTOR binding to a lysosome.
Leucyl tRNA synthase
LTS, needs activation by leucine.
Does Isoleucyl tTNA synthase bind to mTOR?
No.
What helps recruit leucine transporters to lysosomes?
Laptm4b.
How does leucine stimulate muscle protein synthesis?
It stimulates it via mTORC1.
How does arginine stimulate muscle protein synthesis?
It has an amide group which can be used to make NO, a vasodilator, which increases amino acid flow, indirectly increasing protein synthesis.
What is anabolic resistance?
Less response (lower protein synthesis levels) to exercise in old people vs young.
Goes additional leucine/amino acids stop anabolic resistance?
It doesn’t help increase protein synthesis any further.
What else, aside from age causes anabolic response?
Cancer cachexia, who dont increase protein synthesis in response to food.
Does protein synthesis increase in response to food in cancer cachexia?
No.
How can you normalise anabolic resistance?
Controlling the inflammatory response.
Do carbohydrates affect anabolic resistance?
No effect.
