molecular adaptations to exercise Flashcards
mitochondria
endosymbiotic theory- he idea that the mitochondrion evolved from a bacterial progenitor via symbiosis within an essentially eukaryotic host cell
- mitochondria have their own mtDNA and ribosomoes
- can generate energy through TCA cycle and ETC
- ETC has 4 complexes- NADH dehydrogenase, succinate dehydrogenase, cytochrome C reductase and cytochrome c oxidase
mitochondrial biogenesis
growth and division of pre existing mitochondria (cant make it de novo)
increased mtDNA
increased mitochondrial proteins + enzymes- some derived from mtDNA (37 genes) and some from nuclear DNA
increased numbers of mitochondria
mitochondrial biogenesis + endurance exercise
mitochondria provide ATP which muscle and heart can use for muscle contraction
icnrease in the abundance of mitochondria/mitochondrial proteins (ETC) provides more capacity for ATP synthesis and fuel for the muscle
using mitochondria for ATP synthesis is more efficient as it uses oxygen
positive correlations exist between mitochondrial abundance and vo2 max + exercise performance
regulating mitochondrial biogenesis
PGC1a was first detected in brown adipose tissue and was inducable upon cold exposure
- brown adipose- thermogenic + main function is in heat generation
- an increase in pgc1a expression correlated with an increase in mitochondrial proteins eg atp synthase, coxII and IV
- overexpression of pgc1a in white adipocytes increased the expression of mitochondrial proteins + mtDNA
- suggesting pgc1a plays a causative role in regulating mitochondrial biogenesis
PGC1a in skeletal muscle
overexpression (generating a tissue that has more of a particular protein) of PGC1a in muscle cells grown in vitro
with the overexpression- there is a clear increase in number of mitochondria
PGC1a and exercise
studies show that pgc1a is a key regulator of mitochondrial biogenesis in skeletal muscle in response to exercise
- 4 weeks endurance running in mice
- control vs MKO (no pgc1a)
- in MKO, dont see the same increase in the mitochondrial protein as seen in control mice
what is pgc1a
trancriptional coactivator
transcription factor (TF)- either activators- switch on transcription
or repressors- switch off transcription by helping or hindering rna poly access the gene of interest
transcriptional coactivators- bind to transcription factors- activate and assist it in helping rna poly bind and acess dna- further helping it switch the gene on
TFs + pgc1a
pg1a coactivates a number of transcription factors
nuclear respiratory factors- assist in the trasncription of mitochondrial genes
- NRF1 and 2 are TF for nuclear encoded mitochondrial genes such as ATP synthase, COXIV and cytochrome C
- they are also TF for mitochondrial transcription factor A (TFAM)
myocyte enhancer factor 2
- MEF2 is a TF for genes involved in glucose homeostasis such as GLUT4 and PGC1a
TFAM- moves out of the nucleus, into the mitochondria, acts as a TF in mitochondria, transcirbed the mitogenes + stimulates genes encoded in mtDNA
regulation of pgc1a
PGC1a is a crucial regulator of mitochondrial biogenesis
master regulator
levels of pgc1a are increased after exercise
endurance exercise adaptation
2 potential biochemical signals were postulated to lead to increased mitochondrial biogenesis
1. Ca2+ is released from SR to trigger muscle contraction, excess free ca2+ can bind to Ca2+ sensitive proteins and lead to adaptation
2. atp/adp/amp- pertubations in the energy state of the muscle could trigger adaptation
amp kinase
kinases- proteins that act as enzymes, assist in adding a phosphate group to another protein
is activated when amp:atp ratio increases in the cell–> when there is more amp than atp
adenylate kinase reaction occurs in very intense exercise condtions (energy crisis) - which increases amount of amp in the cell, switching on amp kinase
therefore amp kinase is a cellular energy sensor
exercise and AMPk- study
study
1. low intensity- 55% vo2 max for 90 mins
2. high intensity- 75% vo2 max for 55 mins
followed by 90% vo2 max for 5 mins
equal energy expenditure
- exercise in high intensity condition stimulates ampk activity
- exercise in low intensity- ampk activity doesnt go up as much
ampk + mitochondrial biogenesis
lots of proteine and genes are also altered during exercise - how do we know ampk is responsible for mitochondrial biogenesis
- pharmalogical activation of AMPK- chronically turn on AMPk
- genetically deleting AMPk- chronically turning ampk off
pharmacological activation
study
4 weeks of intravenous AICAR in rats
AICAR- tricks the cell into thinking it is an energy crisis as it will think it is getting lots of AMP
AICAR activates AMPk in myslce
- study shows that mitochondrial enzyme activity will increase in aicar conditions
this data supports the role of ampk in mitochondrial biogenesis
deletion of ampk
4 weeks of aicar in mice
gene manipulation data supports the role of AMPk in mitochondrial biogenesis- in this study the mice have deletion of AMPK
in wild type all of the different enzymes increase when the mice are given AICAR
in the muce that dont have ampk, they dont benefit from aicar, showing that aicar is stimulating ampk
AMPK + glucose metab
in the presence of AICAR, glucose uptake, increases, suggesting that ampk is involved in glucose uptake
control- perfused with glucose but no aicar
4 weeks of aicar increased the number of glut4 in the cell- allowing the cell to uptake more glucose
AMPK + PGC1a
study:
AMPK is able to switch on pgc1a
in KO there is no increase in pgc1a
if a cell has no pgc1a, you cannot get more of it when you switch on ampk (same with glut4 and cytochdrome c)
ampk has no effect on transcription when pgc1a protein is knocked out of muscle cells
tells us that ampk must either directly or indirectly effect pgc1a in order to exert its potent effects on mithcondrial biogenesis
purpose of AMPK
ampk regulated cellular metabolism in 2 ways
1. increases cellular functions which may generate energy eg glucose uptake (glut4) and mitochondrial biogenesis
2. reduces cellular processes which cost energy- such as mTOR signalling, protein synthesis and ribosomal biogenesis
very high ampk can dampen mTOR signalling to try and prevent the energy costly functions
ampk and pgc1a
study
wild type- with AMPK
mdKO- without AMPK
mice lacking AMPK have a reduced PGC1a transcriptional response to exercise
still some response which suggests there might be other signals regulating pgc1a gene expression
calcium and muscle contraction
AP arrives at motor neuron
depolarisation
release ACL from neuron through synaptic cleft
binds to sarcolemma
causes wave of depolarisation along sarcolemma, into t tubules
at the t tubules, wave of depolarisation in ryanoidine in SR
SR is storage site for Ca+
Ca+ stimulates muscle contraction
calcium + its effects
manipulating calcium influxes in vivo is hard due to lots of confounding variables
ca2+ ionophore- binds calcium from extracellular spce and imports it into muscle cell
with ca+ ionophore- increase of cyt c, suggesting that ca2+ may be important in making more mitochondria
EGTA- Ca2+ chelator
chelating agent is a compound that vinds to an ion + reduces the free levels of it
brings calcium into the cell and binds to it- acts as an inhibitor
with EGTA- reduces levels of mitochondrial genes- COXI and cit synthase
caffiene and pgc1a
caffiene triggers the activation of a protein kinase called calcium calmodulin kinase II
camkII is required for calcium induced mitochondrial biogenesis (through pgc1a)
caffiene is important in switching on mitochondrial biogenesis through pgc1a- signals through another protein kinase- triggers camkII
exercise + camkII
calcium mediates its effects on mitochondrial biogensis through camkII
exercise increases camkII
pgc1a is required for mitocndrial biogensis
caMK control and HDAC
histone deacetylase 4 (HDAC4) is an inhibitor of MEF2 TF
it is therefore normally localised to the nucleus of a cell (ihibits transcription factors)
camk causes hdac4 to move to the cytosol - if it is no longer in the nucleus, it cant inhibit the transcription factors
MFE2 can function as a transcription factor- stimulates pgc1a
in normal conditions- HDAC4 is localised to the nucleus but where CAMKII has been overexpressed, the HDAC4 has moved out of the nucleus and into the cytosol
some evidence shows that camk can also phosphorylate ampk, leading to phosphortylation of pgc1a
p38 map kinase
camk can also phosphorylate p38 mapk
p38mapk can phosphorylate pgc1a whcih can move to the nucleus when this occurs
study
- knock out of p38 mapk
- loss of p38 prevents exercise induced increases in mitochondrial protein abundance
- loss of p38 prevents pgc1a mRNA induction after exercise
- without p38- prevents pgc1a and mitochondrial biogenesis
p3
conclusions
- Mitochondrial biogenesis is a well characterised adaptation to endurance exercise
- It is controlled by the transcriptional co activator PGC1a – master regulartor
- In turn, PGC1a activity and mRNA levels are regulated by the protein kinases AMPK. P38 MAPK and CaMKII
- These kinases are induced by biochemical signals in the cell under conditions of exercise stress
