Mitochondrial quality control & NDDs Flashcards
Describe the funcdemental mechnism that drives ATP in the mitochondria?
Oxidative phosphorylation across the Inner mitochondrial membrane. Utilising a proton gradient built up and driven through an ATP synthase to get ATP from ADP and phosphate- Large membrane potential to allow it to happen 180mv
what is Antimycin A and its effect?
Antimycin A Induces a Loss of Mitochondrial Membrane Potential. Aa is an inhibitor of complex III of the ETC.
What is FCP?
Uncoupler (uncopules respiration from phosphorylation) - dissapates a proton grient anywhere in the cell inclu the mitochondrial. Respiration occurs not but not fast
‘Uncouplers’ uncouple respiration from
phosphorylation – mitochondria still respire but make
no ATP. They sit in the inner mitochondrial membrane
and transport protons down their electrochemical
gradient, dissipating all proton gradients in the cell. In
mitochondria, they collapse the membrane potential.
Respiration is normally rate limited by the potential, as
the respiratory complexes pump protons ‘uphill’
against a proton gradient. If the concentration
gradient is dissipated by FCCP, mitochondria will be
depolarized and respiration will run at maximal
capacity
What is the action of oligomycin
Blocker for ATP synthase
Inhibits proton gradient building up less ATP produced- research this more
oligomycin inhibits the ATP synthase.
Normally the proton pump of the respiratory
chain is offset by proton flux back into
mitochondria through the ATPsynthase. If the
synthase is blocked, the chain will continue to
pump protons, increasing the membrane
potential until the free energy available
through substrate supply is no longer
sufficient to drive the pumps against the
proton electrochemical gradient and
respiration is suppressed. The difference
caused by oligomycin in cells reflects the
oxygen consumption required to balance the
proton flux through the ATPsynthase – i.e.
the respiratory activity needed to sustain ATP
turnover.
How is the orgnaisation of Mito related to function?
Mito looks different from other cell types.
Mito look different in microglia cell versus muscle cells. Why they differ is an active research question rn?
Why has imaging of Mito been limited and what have the advances been ?
Optical imaging was limited but recently
https://www.embopress.org/doi/full/10.15252/embj.2018101056
To overcome this limitation, we developed a novel approach for imaging the IMM at high spatiotemporal resolution in living cells, using the LSM880 with Airyscan as well as STED microscopy. Staining active mitochondria with various dyes, we verified that we can resolve cristae from IBM. We then used various ΔΨm‐dependent dyes to explore how the intricate architecture of the IMM relates to the most basic mitochondrial function—the ΔΨm generated by the electrochemical gradient of protons.
mtDNA
Long term regulation of mitochondrial function
- Biogenesis
- Mitophagy (mitochondrial autophagy)
- Fission
- Fusion
- Trafficking
Defects in all cause disease. Several represent potential
‘druggable’ targets, ie. suitable as therapeutic strategies.
PINK1- mitophagy
On the outer mito membrane
Depolarized mitochondria are tagged for mitophagy by retention of PINK1 on the OMM
Role of calcium signalling in driving energy production?
Contraction of muscle cells, for a heart beat, for CNS communication
Ca2+ regulates multiple metabolic processes
The transmission of calcium from cytosol
to mitochondrial matrix stimulates
oxidative phosphorylation, increases ATP
generation and helps balance energy
supply with demand.
What helps Ca2+ into and out of cell
a uniporter? recently disocvered
Mitochondrial Calcium uptake and MICU1 (slide 18)
There is a threshold for mito to really begin taking up calcium.
This is regulated by the MICU1-KD protein, when they did a knock down of this protein- the calcium uptake by mito was faster and harsher bypassing the threshold.
What is the significance of mitochondira portions within the cell?
Mito position near Calcium release sites like the ER.
The transfer of calcium to the mitochondria at
fertilisation drives increased ATP generation
example of caclium transfer.
Very important for calcium to oscillate its signalling furing fertilisation- if blocked embryo does not develop.
You can measure the ATP conc as the ca2+ signalling oscillates - you see ATP goes up when ca2+ active
Excessive mitochondrial calcium
accumulation – ‘calcium overload’
major trigger to cell death especially in
combination with an oxidative or
nitrosative stress.
-Involves the mitochondrial permeability transition pore (mPTP).
mPTP inhibitors
inhibitied by ATP, CsA, SfA
mPTP opened by
Opened by high Calcium, pro oxidants, high Pi
opening regulated by Cyclophilin D-CypD knockout mice show reduced infarct size on ischaemia reperfusion – but no protection to apoptotic stimuli.
mPTP opening is of major importance in defining………
mPTP opening is of major importance in defining cell
death in response to ischaemia and reperfusion in heart
brain and kidney (evidence is least ambiguous in heart) .
It represents an important potential therapeutic target,
and modulation by signalling pathways also recruits
protective mechanisms (preconditioning).
It does not seem to be involved in most models of
apoptotic cell death.
Why do cells die??
*Collapse of mitochondrial membrane potential means
no oxidative ATP generation. Mitochondria may even
consume ATP to maintain their potential and so hasten
ATP depletion. This leads to energetic collapse, run
down of ionic gradients and the cells will die.
*Release of pro-apoptotic factors – cytochrome c and
AIF, activation of caspases and progression to
apoptotic cell death in cells that maintain ATP supply
through glycolysis
Cyclophilin D and PTP may be important in AD
proposed amyloid binds to cyclophilin D in studies
Most causes of mitochondrial dysfunction lead to CNS dysfunction
Mitochondria may play a role as primary drivers of disease or as a step in a
cascade to cell injury through multiple mechanisms.
Most of the processes/mechanisms that we have so far discussed are in some
way implicated in CNS disease, often several operating in combination.
* Respiratory chain dysfunction
* Oxidative stress
* Dynamics – Trafficking, fission and fusion
* Impaired MitoQC – mitophagy or biogenesis
* Dysregulated Calcium signaling
* Initiation of cell death through cytochrome c release or PTP opening
* Activation of the cGAS – STING pathway
Several represent potential ‘druggable’ targets, ie. offering potential
therapeutic strategies.
what is the cGAS-STING pathway
https://www.nature.com/articles/s12276-023-00965-7#:~:text=Recent%20extensive%20studies%20have%20shown,activating%20the%20cGAS%2DSTING%20pathway.
mito dysfucntion leads to activation of cGAS-STING pathway
Recent extensive studies have shown that mtDNA is released under pathological conditions, such as oxidative stress, genotoxic stress, high levels of proinflammatory factors, viral infection, and mitochondrial dysfunction, subsequently activating the cGAS-STING pathway
Etiology of Vici syndrome
Multisystem disorder- very rare 150 cases
recessive mutation in EPG5 gene
Defective mitochondrial autophagy
Small subset of those with parkinsons have ths defect too.
They have increase mito calcium uptake so highly activated cGAS-STING pathway
