W11 - Molecular and cellular responses to endurance exercise Flashcards
What are the 2 potential biochemical signals were postulated to lead to mitochondrial biogenesis?
- Ca2+ - Ca2+ is released from the SR to trigger muscle contraction. Excess free Ca2+ can bind to Ca2+ sensitive proteins and lead to adaptation(can act as a signalling molecule for mitochondrial biogenesis)
- ATP/ADP/AMP – perturbations in the energy state of the muscle could trigger adaptation(acts as a signalling trigger for the increase in mitochondria of the cell)
Describe AMPK:
AMP kinase(causes the phosphorylation of a downstream protein)
Activated when AMP:ATP ratio increases in the cell - causes activation of AMPK
Therefore a cellular energy sensor
ATP is hydrolysed to create ADP and Pi for free energy
AMP is phosphorylated in high intensity exercise in muscle cells
Describe the Adenylate kinase reaction:
Adenylate kinase reaction - to maintain high intensity exercise, uses 2 ADP (4 phosphate groups) to resynthesise an ATP molecule, the left over phosphate creates AMP
- Causes an elevation of AMP in muscle cell and decrease of ATP in muscle
- Increases ratio of AMP:ATP = switches on the AMP kinase of the cell - an energy sensor for the cell, energy deficit switches AMPK on
What can be shown by muscle biopsies during exercise about AMPK?
- Muscle biopsies at each state, biochemical assay to measure AMPK activity
- Low intensity - not much AMPK activity, and no change during exercise. - addition of AMP into assay causes increase in AMPK
- AMP switches on AMPK
- High intensity - immediately after exercise AMPK is activated
What is the pharmacological activation of AMPK?
- turns on AMPK chronically using a drug
- Drug inhibits creatine kinase reaction, used chronically will reduce ATP in the cell
- Switches on AMPK activity, intendent of exercise
- Tricks the cell to think it is in an energy crisis, to switch on AMPK
- Increase in mitochondrial enzyme when AICAR is used, suggesting mitochondrial biogenesis
What is the relationship between AMPK and glucose metabolism?
What does hexokinase do?
- Glucose uptake into the muscle increases with AICAR treatment
- Infusing the muscle with glucose increases glucose uptake
- AICAR increases glucose uptake into the muscle cell as well as switching on AMPK
Hexokinase adds a phosphate group to glucose - 1st step in glycolysis
- Increased abundance in GLUT4, letting more glucose into the muscle
How does AMPK exert its affects?
- Exercise increase the AMP/ADP :ATP ratio, switching on AMPK
- Kinase - phosphorylates target proteins (PGC1α, in sarcoplasm) - reffered to as the master regulator of mitochondrial biogenesis
- When phosphorylated will translocate to the nucleus, PGC1α a transcriptional co-activator - binding to transcription factors(binds to section of DNA) and cause them to bind and increase the transcription of a gene
- Transcription factors: Tfam, NRF-1, MEF2, these bind to DNA causing genes to be increased –> e.g.: cytochrome c, MEF2 e.g.: GLUT 4 and PGC1α
- PGC1α = Feedforward mechanism to regulate itself
- Drives glucose metabolism in the cell
What is PCG1-α?
How is this regulated?
a master regulator of mitochondrial biogenesis
- When phosphorylated will translocate to the nucleus, PGC1α a transcriptional co-activator - binding to transcription factors(binds to section of DNA) and cause them to bind and increase the transcription of a gene
- After exercise there is a massive increase in PCG1α, AMPK is regulating the expression of PGC1α
What are the 2 ways that AMPK regulates cellular metabolism?
- Increase cellular functions which may generate energy e.g. glucose uptake and mitochondrial biogenesis
- AMPK tries to increase the function of the cell so that it has the mechanisms to cope with the stress placed on it
- Reduce cellular processes which cost energy
- Protein synthesis is highly costly in energy, which could be compromised by AMPK to preserve energy
How does exercise stimulate the release of calcium into the sarcoplasm?
Calcium in the muscle - is released for the sarcoplasmic reticulum(from store of calcium) - into sarcoplasm, which forms muscle contractions - releasing calcium from sarcoplasmic reticulum into sarcoplasm
Action potential causes release of acetyl to depolarise the muscle
- can lead to mitochondrial biogenesis
Why is calcium important in mitochondrial biogenesis?
- Calcium chelator - Binds to calcium in the muscle cell reducing the amount of calcium available in the muscle(inhibitor)
- Calcium availability to the muscle regulates mitochondrial biogenesis
- Caffeine will cause calcium to be released from the sarcoplasmic reticulum, creating a big increase in PGC1α
- If we increase calcium availability allows for mitochondrial biogenesis, inhibiting the availability prevents mitochondrial biogenesis
what is parvalbumin?
What happens when there is a lot of it?
- binds to calcium and shuttles it back to the SR after contraction
More parvalbumin - less calcium availability, decreases SDH activity (which is a marker of mitochondrial biogenesis)
How does calcium exert its effects?
- SR is depolarised by exercise, causing it to release calcium - this binds to actin-myosin crossbridge cycle for muscle contraction
- Ca2+ binds to protein called calmodulin –> a calcium sensor for the cell, senses amount of calcium in the sarcoplasm
- Calcium calmodulin complex causes calmodulin do undergo a confirmational change = calmodulin binds to protein(calmodulin kinase II)
- calmodulin kinase II - autophosphorylation(phosphorylates itself) can work independent to the amount of calcium in the cell
- calmodulin kinase II stays phosphorylated after Ca2+ is shuttled back to SR
- MEF2 in basal conditions is inhibited by HDAF4, calmodulin kinase II phosphorylated HDAC4 moves away from MEF2 to allow it to make more mitochondria, acting as a transcription factor
- calmodulin kinase II phosphorylates AMPK as well to feed into the AMPK signalling pathway
Why is CaMKII important in mitochondrial biogenesis?
how can caffeine affect mitochondrial biogenesis?
what is the role of CAMKII?
CAMKII is heavily involved in the mitochondrial biogenesis response to calcium
caffeine causes an increase in calcium release from the RR
KN93 is an inhibitor of calmodulin kinase II (CAMKII)
