Mitochondrial function adaptation to physical activity

Question 1

Where does energy come from?

Answer 1

o Energy as heat
 Heat is the process of energy transfer between two bodies (Thermodynamics)
o 1 calorie: heat required to raise 1 gram of water by 1oC Diets consist of kcal (1 kcal = 1000 cals)
o SI units: Joules 1 joule: energy used to move 1 kg 1 m by a force of 1 N 1 kcal = 4.184 kJ
o Organismal: kcals per gram nutrient Protein – 4 Carbohydrate – 4 Fat – 9 Alcohol – 7
o Cellular: Hydrolysis of ATP ATP ….ADP + Pi Yields ~ 7.3 kcal/mole (36.8-50 in vivo?)

Question 2

What is ATP?

Answer 2

o Energy “currency”
 Others exist
o Phosphorylation
 ADP + Pi …. ATP

Question 3

Why is energy required?

Answer 3

In general, “active” processes (e.g. work) require energy
 Organismal/tissue level: Muscle use (Heart beat) Brain function Respiration Digestion Excretion
 Cellular level: Active transport Cell division Molecular/cellular movement Production of biomolecules

Question 4

Where does the ATP that powers contraction come from?

Answer 4

o ATP (<4s)- anaerobic
o Phospho-creatine (<10s)- anaerobic (Phosphocreatine + ADP creatine + ATP)
o Glycolysis (<1.5m)- anaerobic
o Oxidative phosphorylation (>1.5m)- aerobic

Question 5

What is Glycolysis?

Answer 5

One of the major pathways for fuel metabolism
 Proteins, glycogen & Triacylglycerols are built up from and broken down to smaller units: AA, G6P and FA
 Oxidation of these fuels yields metabolic energy (ATP)
 Pyruvate (result of glucose and AA degradation) and acetyl-CoA are major branch points in metabolic pathways

Question 6

What is Oxidative Phosphorylation?

Answer 6

o The transfer of electrons are transferred from organic compounds through a series of electron carriers to O2 or other inorganic or organic molecules (via oxidization)
o The sequence of electron carriers is often called the electron transport chain or the respiratory chain
o The transfer of electrons from one carrier to the next generates energy which is used to make ATP from ADP by chemiosmosis
o The reactions are coupled oxidation and reduction reactions (redox)

Question 7

What is Chemiosmosis?

Answer 7

o A proton concentration gradient serves as the energy reservoir for driving ATP formation
o This gradient is established across the mitochondrial inner membrane space

Question 8

How is pyruvate turned in Acetyl-CoA?

Answer 8

o Transported into mitochondria
o Oxidatively decarboxylated to acetyl-CoA
o Pyruvate dehydrogenase (enzyme complex- 3 enzymes multiple copies)
 Irreversible reaction
 Multiple components involved in the reaction
o This reaction mainly takes place in tissues with high oxidative capacity e.g. cardiac

Question 9

What if we block Oxidative Phosphorylation?

Answer 9

o Inhibitors of complex I: Halothane (anesthetic) Rotenone (pesticide)
o Inhibitors of complex III: Antimycin A (fish poison) Stobilurins (pesticides) Atovaquone (anti-malarial)
o Mutations in complex III are documented
o Inhibitors of complex IV (cytochrome c): Cyanide, Sulphide, Azide, Carbon monoxide
o Inhibitors of ATP synthase: Oligomycin

Question 10

What happens to the Acetyl-CoA?

Answer 10

o Acetyl-CoA goes into the Tricaboxylic Acid Cycle (TCA) Acetyl-CoA is also the link to fat and protein metabolism
o TCA cycle is also known as the Krebs and/or citric acid cycle

Question 11

What if we insert additional proton channels into the membrane?

Answer 11

o This is called uncoupling and is seen in:
 Fish “heater” cells
 Brown fat (important in newborns- non shivering thermogenesis)
o Normally, complete oxidation of glucose (to CO2 and H2O) is efficient with 45% of energy from glucose lost as heat, this % increases with uncoupling
o Heat production is facilitated by:
 High mitochondrial content Uncoupling proteins

Question 12

What is the TCA cycle?

Answer 12

For every 1 glucose (2 acetyl CoA) the cycle generates: 
	4 CO2 
	6 NADH 
	2 FADH2 
	2 ATP

Question 13

What are these cofactors and where do they come from?

Answer 13

o	NAD+ Nicotinamide adenine dinucleotide
	B3 Niacin
o	FAD Flavin adenine dinucleotide
	B2 Riboflavin
o	FMN Flavin mononucleotide

Question 14

What happens to the pyruvate?

Answer 14

o It is used for anaerobic respiration (common in bacteria/microbes)
o Normally O2 needed to regenerate NAD+ (Glyceraldehyde-3-phosphate→1,3-bisphosphoglycerate req.NAD+ )
o However, pyruvate reduced to lactate can regenerate NAD+ via Lactate dehydrogenase
o Lactate is normally used (in people) by:
 Liver- to generate glucose via gluconeogenesis
 Muscle (including cardiac) – to provide pyruvate for TCA

Question 15

What would a Niacin deficiency do/cause?

Answer 15

o If you can’t make Niacin (you can from Tryptophan) then you wouldn’t be able to run glycolysis, TCA cycle, or oxidative phosphorylation well.
o Reduced Niacin: “slow metabolism” reduced cold tolerance (can’t produce heat).
 Is this see in people with malabsorption? (elderly, alcoholics, patients with diarrhea)
o Massively reduced/absent Niacin: Death, Dementia (why?), Dermatitis (photosensitivity, not fully understood why), and Diarrhea (all mucus membranes poorly maintained)

Question 16

If lactate can normally be used in muscle why is there a problem with lactate being produced?

Answer 16

High levels of lactate in blood reduce blood pH, seen in:
	Pyruvate dehydrogenase deficiency (the enzyme that takes pyruvate to Acetyl-CoA) 
	Physical exercise 
	Severe lung disease 
	High altitude 
	Drowning 
	Severe anaemia 
	Carbon monoxide poisoning
	Cyanide poisoning 
	Alcohol intoxication

Question 17

Biochemical Adaptations in Muscle: EFFECTS OF EXERCISE ON MITOCHONDRIAL OXYGEN UPTAKE AND RESPIRATORY ENZYME ACTIVITY IN SKELETAL MUSCLE* (Holloszy, 1967)

Answer 17

Mitochondria from muscles of the exercised animals exhibited a high level of respiratory control and tightly coupled oxidative phosphorylation. Thus, the increase in electron transport capacity was associated with a concomitant rise in the capacity to produce adenosine triphosphate. This adaptation may partially account for the increase in aerobic work capacity that occurs with regularly performed, prolonged exercise.

Question 18

Repeated transient mRNA bursts precede increases in transcriptional and mitochondrial proteins during training in human skeletal muscle (Perry et al., 2010)

Answer 18

This investigation revealed numerous rapid mRNA and protein expression responses to repeated high‐intensity interval training sessions with a temporal precision that has not been reported previously. Our findings demonstrated the occurrence of repeated, transient increases in mRNA to produce sustained increases in the content of transcription and metabolic proteins as previously proposed (Williams & Neufer, 1996; Booth & Neufer, 2006). The mRNA response to exercise was attenuated as the muscle adapted to the exercise challenge, even as the training intensity increased. Nevertheless, we found that increases in mitochondrial proteins occurred within five days and following three sessions of high‐intensity interval training. Furthermore, the rapid increase in β‐HAD mRNA (4 h post‐session 1) suggests the initial increases in mRNA for certain mitochondrial proteins can occur without an initial increase in the protein content of the PGC‐1 and PPAR isoforms, and NRF‐2 and Tfam. However, the rapid increase in PGC‐1 and PPAR isoform protein contents and NRF‐2 within three exercise sessions may accelerate the adaptive response to subsequent exercise bouts. This may be especially true for PGC‐1α and PPARα, which increased after one session but before the initial increase in mitochondrial proteins. Finally, the increase in MFN‐1 supported the greater degree of fusion that occurs during training whereas the increases in Fis‐1 and DRP‐1 suggested fission was also required for expanding and/or re‐modelling the morphology of the mitochondrial reticulum. These observations reveal a dynamic temporal sequence of molecular (mRNA and protein expression) and potential morphological events during the early periods of exercise training in human skeletal muscle that has not been apparent previously. These unique responses raise the intriguing possibility that the contribution of each transcription protein in mediating mitochondrial biogenesis may be time dependent.

Question 19

Exercise intensity-dependent regulation of peroxisome proliferator-activated receptor γ coactivator-1α mRNA abundance is associated with differential activation of upstream signalling kinases in human skeletal muscle (Egan et al., 2010)

Answer 19

In conclusion, a single bout of exercise at high intensity resulted in a greater elevation of PGC‐1α mRNA abundance during recovery compared to isocaloric low intensity exercise. We propose that this response was mediated by intensity‐dependent regulation of ATF‐2 and class IIa HDAC activity, and downstream of activation of the established contraction‐induced signalling kinases AMPK and CaMKII, but independent of the activation of p38 MAPK, which was similarly activated by both intensities. Furthermore, CREB phosphorylation may prolong the activation of PGC‐1α transcription in the hours after exercise.

Question 20

Adult Expression of PGC-1α and β in Skeletal Muscle is Not Required for Endurance Exercise-Induced Enhancement of Exercise Capacity (Ballmann et al., 2016)

Answer 20

In summary, the current study demonstrates that exercise training-induced increased exercise capacity does not require PGC-1α and PGC-1β in skeletal muscle. Exercise is still the best known intervention for the treatment of many conditions, and many of these benefits have been attributed to PGC-1 function. Therefore, identifying these PGC-1-independent pathways will be extremely important in understanding the molecular mechanisms that contribute to the benefits of exercise.