AMPK and AMP Sensors Flashcards
What is the point of metabolic research?
Better and more personalized treatments
Because T2D and obesity pandemic is getting worse
What are some flaws of current metabolic treatments?
Current treatments are efficacious but lack durability and have side effects
What groups of people is T2D difficult to treat?
Younger people
Ethnic minorities
What are two fuels in non-muscle stores?
Liver glycogen»_space;> plasma glucose
Adipose tissue triacylglycerol»_space;> plasma fatty acids
What fuels are available to muscle (in fit, healthy males)
There are intramuscular stores of glycogen and triacylglycerol
Both of which get converted into ATP by the mitochondria
How are fatty acids broken down in mitochondria during exercise?
In muscle cell, FA need to enter mitochondria = inner mitochondrial membrane is impermeable to fatty acids, so they require a transport mechanism.
Fatty acids are first activated in the cytoplasm by acyl-CoA synthetase = attaching to Coenzyme A (CoA) to form fatty acyl-CoA.
Fatty acyl-CoA = transported into the mitochondria with the help of a carrier protein called the carnitine shuttle.
This shuttle involves:
Carnitine palmitoyltransferase I (CPT1), which converts fatty acyl-CoA to acylcarnitine, allowing it to pass through the outer mitochondrial membrane.
Once inside the mitochondria, CPT2 on the inner membrane converts the acylcarnitine back to fatty acyl-CoA.
What is the cartinine shuttle and its function?
Fatty acyl-CoA = transported into the mitochondria with the help of a carrier protein called the carnitine shuttle.
This shuttle involves:
Carnitine palmitoyltransferase I (CPT1), which converts fatty acyl-CoA to acylcarnitine, allowing it to pass through the outer mitochondrial membrane.
Once inside the mitochondria, CPT2 on the inner membrane converts the acylcarnitine back to fatty acyl-CoA.
What is the correlation between mobilization and depletion of fuels?
Fuels that can be mobilized most rapidly are also the most short-lived
The larger the estimated maximum rate of ATP generated = shorter estimated time of complete depletion
What fuels have the highest estimated max rate of ATp generation (and thus quicker depletion time)
Muscle phosphocreatine
Muscle glycogen when converted to lactate
Muscle glygogen to CO2
Blood glucose to CO2
Blood fatty acids to CO2
Where is blood glucose mainly derived from?
Liver glycogen breakdown
Where is blood fatty acids mainly derived from ?
Adipose tissue triacylglycerol breakdown
What enzyme generates phosphocreatine?
Mitochondrial creatine kinase (mi-CK)
What is phosphocreatine generated from?
ATP by mitochondrial creatine kinase
Where does phosphocreatine diffuse to after being made in the mitochondria?
Diffuses to myofibril, where it is then converted to creatine and ATP by “muscle” isoform of creatine kinase (M-CK)
Once ATP is hydrolysed for muscle contraction = creatine diffuses back to mitochondria
What is the role of phosphocreatine?
Energy carrier
Transports energy (ATP) from the site of production (mitochondria) to side of consumption (myofibril)
What exercise does phosphocreatine help with?
Sustain intense, brief contractions
From rest to about 50% maximum intensity what fuels are mainly used?
Fatty acids and triacylglycerol
Fats are an abundant, rich store of energy
Why at higher intensities of exercise does fuel usage shift to glucose and glycogen?
Because amount of ATP generated per molecule of oxygen used is higher for glucose htan fatty acids
At higher exercise intensities = rate of oxygen delivery to muscle becomes LIMITING FACTOR
At higher exercise intensities, what are the rate limiting factors?
Rate of oxygen supply
Rate of glucose uptake
So breakdown of glycogen IN MUSCLE is important
Where are the two carnitine:palmitoyl-CoA transferases found?
CPT1 = outside inner mitochondrial membrane
CPT2 = inside inner mitochondrial membrane
What inhibits CPT1?
Malonyl-CoA
What happens to malonyl-CoA during exericse?
Malonyl-CoA decreases in muscle during exercise
Could explain the increase in fat oxidation
Because malonyl-CoA normally inhibits CPT1 causing reduced fatty acid oxidation
How is malonyl-CoA made?
actyl-CoA > malonyl-CoA > fatty acids
Acetyl-CoA carboxylase exists as 2 converts step 1
Fatty acid synthase converts step 2
What is the function of ACC1 and ACC2?
ACC2 = associated with mitochondria (where FA oxidation takes place)
Malonyl-CoA produced by ACC2 = mainly used to regulate FA oxidation (rather than FA synthesis)
Where does FA oxidation take place?
Mitochondrial matrix
What site on AMPK is phosphorylated to regulate it?
Thr 172
What does AMPK bind?
Binding of AMP to MAPK promotes phosphorylation of Thr172 by upstream kinase
What is the potential mechanism by which AMPK stimulates fat oxidation?
In resting muscle, fat oxidation is LOW because of inhibition by malonyl-CoA
Exercise activates AMPK due to increase in AMP:ATP ratio = ACC2 is inactivated so malonyl-CoA is decreased
Lell malonyl-CoA to inhibit CPT1 = increased fatty acid transport so increased fat oxidation
What is AICAR and what is it converted to?
AICAR = adenosine analogue
AMPK activator
Converted to ZMP (analogue of AMP)
How does AICAR activate AMPK?
AICAR converted to ZMP (analgoue of AMP)
ZMP is NOT a specific activator of AMPK
Regulates AMP-binding proteins
How does AICAR affect fatty acid oxidation?
Increases FA oxidation
Independently of AMPK in muscle
Dependently of AMPK in liver
Is AMPK requred for effect of AICAR on glucose uptake in muscle?
AMPK is required for AICAR-stimulated glucose uptake
BUT not needed for contraction-stimulated glucose uptake
NOR needed for fatty acid oxidation in muscle
What is the evidence AICAR increases FA oxidation independently of AMPK in MUSCLE?
What is the evidence AICAR increases FA oxidation dependently of AMPK in LIVER?
What is the role of glycogen phoshporylase?
Glycogen breakdown
What activated glycogen phosphorylase?
AMP
Increase in AMP:ATP ratio during muscle contraction
How is glycogen phoshporylase like AMPK?
AMP/ATP sensor
What is the role of phosphofructokinase?
Glycolytic enzyme also activated by rise in AMP:ATP
Thus stimulating glycolysis at the same time as glycogen breakdown
What two enzymes are activated by AMP and why is this important?
Glycogen phosphorylase and phosphofructokinase
Important in muscle when ATP is low that glycogen is broken down then glycosis occurs to produce ATP
What are the two forms of glycosegen phosphorylase?
AMP-sensitive b form
AMP-INSENSITIVE a form
What converts glycogen phoshporylase from a to b form?
Phophorylase KINASE
(Ca2+-dependent protein kinase)
How are muscle contraction and glycogen breakdown synchronized?
When Ca2+ is released for SR in response to stimulated motor nerves and is trigger for muscle control
PKA phosphorylates phosphorylase kinase = increasing its max activity and making it much more sensitive to Ca2+
Ca2+ activtes phoshporylase kinase converting glycogen phosphorylase to AMP-insensitive a form = meaning it can catalyze glycogen breakdown without needing high AMP levels
Glycogen breakdown can occur BEFORE ATP becomes depleted and AMP increases
What is PKA?
cAMP-dependent protein kinase
Increases phosphorylase kinase max activity and makes it more sensitive to Ca2+
Alloing more rapid and complete conversion of phosphorylated to AMP-independent a form under stressful/exercising conditions
What activates PKA?
Nor/adrenaline
Released during stress/exercise
What is the role of Fructose-1,6-bisphosphatase 1(FBP1)?
FBP1 is a rate-limiting enzyme in gluconeogenesis = the process of producing glucose
AMP sensitive
Is AMPK needed for AICAR to inhibit AGP in mice?
No
Why are FBP1-G27P-KI mice resistance to hypoglycaemic action of AICAR?***
https://pmc.ncbi.nlm.nih.gov/articles/PMC6207338/
What is the action of Metformin?
Restores insulin-like repression of HGP in liver by inhibition of gluconeogenesis
Metformin is a diabetes medication that lowers blood sugar levels by reducing glucose production in the liver and improving how the body uses insulin.
What is required for acute effect of Metformin on the liver?
FBP1
What is Salicylate and its mechanism of action?
Preclinical anti-diabetic agent
Inhibits mitochondria by acting as protonophore
Directly bind and activates AMPK
Is AMPK needed for action of Metformin & Salicylates in glucose reduction, FA oxidation and lipogenesis
AMPK NOT needed for action of metformin and salicylates on glucose
AMPK NEEDED for FA oxidation for action of both
AMPK required for Metformin action on lipogenesis
AMPK NOT required for Salicylate action on lipogenesis
What is FBP1 required for in Metformin action?
FBP1 required for acute action of Metformin on gluconeogenesis inhibition
