Muscle and Exercise Lecture 3.3 - Role of nutrition, energy and amino acid sensing in the control of muscle protein turnover

Question 1

Does protein synthesis increase with protein intake?

Answer 1

Yes, but is capped at 25g. Very small difference between ie 50g and 25g.

Question 2

How much protein is needed to maximally stimulate protein synthesis?

Answer 2

~25g.

Question 3

How many hours after eating protein does protein synthesis remain high?

Answer 3

~2h before decreasing to baseline.

Question 4

Does amino acid infusion increase protein synthesis?

Answer 4

Yes, very rapidly, but is short-lived.

Question 5

Do essential amino acids stimulate protein synthesis via mTOR (mTORC1)? How can this be tested? What happened to mTORC2?

Answer 5

Yes they do, by using rapamycin. mTORC1 was inhibited, and protein intake had no effect on protein synthesis.
mTORC2 wasn’t inhibited.

Question 6

What are the main downstream targets of mTORC1?

Answer 6

4EBP1 and S6K (S6 too).

Question 7

Which amino acids are known to stimulate mTOR?

Answer 7

Leucine and arginine.

Question 8

How does mTOR sense amino acid concentrations? How can this be tested?

Answer 8

Infuse different amino acids.
Plasma amino acid, muscle amino acid concentration and muscle synthesis levels taken.
Correlation between amino acid level and protein synthesis.

Question 9

Does extracellular amino acid availabiltiy regulate protein turnover?

Answer 9

Yes.

Question 10

Do amino acid transporters act as receptors?

Answer 10

Yes, they can link directly to mTOR.

Question 11

What must mTOR do to activate?

Answer 11

Translocate to the lysosome.

Question 12

What does protein ingestion do to expression levels of amino acid transporters?

Answer 12

Changes their expression levels.

Question 13

What is needed for mTOR to activate?

Answer 13

Amino acids are needed for it to bind to a lysosome to activate.

Question 14

Name an enzyme that catalyses mTOR binding to a lysosome.

Answer 14

Leucyl tRNA synthase

LTS, needs activation by leucine.

Question 15

Does Isoleucyl tTNA synthase bind to mTOR?

Answer 15

No.

Question 16

What helps recruit leucine transporters to lysosomes?

Answer 16

Laptm4b.

Question 17

How does leucine stimulate muscle protein synthesis?

Answer 17

It stimulates it via mTORC1.

Question 18

How does arginine stimulate muscle protein synthesis?

Answer 18

It has an amide group which can be used to make NO, a vasodilator, which increases amino acid flow, indirectly increasing protein synthesis.

Question 19

What is anabolic resistance?

Answer 19

Less response (lower protein synthesis levels) to exercise in old people vs young.

Question 20

Goes additional leucine/amino acids stop anabolic resistance?

Answer 20

It doesn’t help increase protein synthesis any further.

Question 21

What else, aside from age causes anabolic response?

Answer 21

Cancer cachexia, who dont increase protein synthesis in response to food.

Question 22

Does protein synthesis increase in response to food in cancer cachexia?

Answer 22

No.

Question 23

How can you normalise anabolic resistance?

Answer 23

Controlling the inflammatory response.

Question 24

Do carbohydrates affect anabolic resistance?

Answer 24

No effect.

Question 25

Are carbohydrates needed for optimal recovery post exercise?

Answer 25

No.

Question 26

What will combining glucose and fructose do to carbohydrate oxidation and glycogen usage?

Answer 26

It will increase carbohydrate oxidation and reduce muscle glycogen storage/usage, improving performance.