mitochondrial dynamics Flashcards
what can enlarged mt indicate?
disease
why are mt dynamics important for cell survival?
- allows localisation to oxygen rich areas of the cell
- redistribution of mt for cell division
- mt cant be made, have to be inherited
- important for accommodating cell growth
- long tubular network more efficient for ATP generation so can generate ATP in oxygen poor areas of the cell
what are mitofusins involved in?
OMM fusion
what dynamin proteins are involved in IMM fusion?
Opa1/Mgm1
what dynamin proteins are involved in fission?
Drp1/dnm1
what experiments allowed to conclusion that mitofusins are essential for fusion?
ts mutant screens of fzo1 in yeast. male flies that lacked fzo couldn’t under fusion so were sterile.
what mammalian mitofusin is essential?
mfn1 and 2
phenotype of mice lacking mfns?
cells have fragmented mt, die due to placental defects
what disease is associated with mfn2 mutations?
charot marie tooth type 2a
what is the conserved structure of mfns?
4 heptad repeats, 1 GTPase domain and 2 transmembrane domains
phenotype at restrictive temp for ts mgm1 mutants?
decrease in mt fusion and more deformed mt
what mediates cell death?
decrease in short or long isoforms of post transcriptionally alternatively spliced opa1
what else is opa1 involved in?
maintance of cristae structure
what is MOM permebalision regulated by?
abundance of various apoptotic and anti-apoptotic proteins eg BCL-2
what changes causes apoptosis?
downregulation of fis1 and drp1 enhances fusion so inhibits apoptosis
key steps in mt fusion
1 docking and tethering by mitofusins
2 GTP hydrolysis to fuse OMM
3 tethering and fusion of IMM via mgm1 and opa1
what do mutations in fission proteins cause?
large nets of mt
dnm1/drp1 dimerise with other copies of the protein and form a curved structure, what do they do?
they pinch off mt using energy from GTP hydrolysis
what does dnm1 deletion cause?
networks of mt- unopposed fusion
what does a fzo1 mutation cause?
unopposed fission- results in punctate mt
what are the key steps in mt fission?
1 fis1 recruits drp1
2 oiligomerisation of multiple drp1 molecules to form a scission machinery
3. GTP hydrolysis fuels membrane scission
how may regulation of fusion/ fission occur?
protein stability, protein cleavage, protein conformation via binding of other proteins, phosphorylation, localisation via association with binding partners
what mechanisms regulate fission proteins?
drp1 regulated by phosphorylation, or by ubiquitination or through action of PKC/cyclin B/ PKA
what mechanisms regulate fusion proteins?
proteolysis, fzo1 degraded by ubiquitination, mgm1/opa1 undergoes proteolytic cleavage
what triggers mitophagy?
changes in mt membrane potential
steps in mitophagy
damaged/defective mt tagged with specific kinases and ubiquitin ligases (PARKIN), mt fusion disabled, mt destroyed by proteasome
why is mitophagy important?
allows defective mt to be removed
morphology of aging cells
large mt, low ATP production, loss of cristae structure due to loss of mt dynamics and impaired autophagy
what is a prerequisite to mitophagy?
fragmentation
what happens to nucleoids if fission decreases?
nuceloids cluster together and lose even distribution throughout the network
where are lots of nuceloids localised to?
fission sites- dont know if nucleoids dictate fission sites or nucleoids move to sites
what is ERMES?
ER-mitochondria encounter structure complex associates with mt fission sites and is present at 60% of division sites
mutation rate in mtDNA
10% higher than in nucelar, can be up to 50%- vicious cycle
why are mtDNA mutations so frequent?
close proximity to ROS generation site
what does defects in fission/ fusion machinery result in?
reduced mtDNA content, increased rate of mtDNA mutation
what happens if you form a heteroplasmic cybrid from mutants?
can get complementation to restore oxphos activity
how can you repair mtDNA mutations?
use WT genome to complement the mutant DNA
what is the morphology of mt during G1/S phase?
more fusion and elongation of network for efficientm ATP production
morphology of mt during mitosis?
more fission to distribute the mt to daughter cells
morphology during interphase
tubular then fragment after
what is essential for fission in mitosis?
phosphorylation of S585 of Drp1 by ckd1/cyclin BMPF
what do mt move along?
actin cables
name for movement towards mother
retrograde transport
name for movement towards bud
anterograde
where to more motile, fitter mt go?
to the bud
what to mt in their bud have
fewer ROS
during cell division what happens to mt
they are anchored at one of the poles
what happens to PINK1 in healthy mt?
internalised and degraded
what is PINK1
a serine threonine kinase
what happens to PINK1 in defective kinases?
remains on surface and recruits PARKIN, this ubiquitinates mt proteins and is destroyed by mitophagy
what is PARKIn
an E3 ubiquitin ligase
how does fusion repair low functioning mt?
by intra organellar complementation
what binds to unfolded proteins to stabilise them
chaperones
what degrades damaged mt proteins
proteases
what happens when there is too much fission?
compromised mtDNA integrity and biogenesis. results in ETC issues and decreased membrane potential
what happens when there is too much fusion?
get englarged mt, decrease in mitophagy and biogenesis resulting in accumulation of damaged mt and increased oxidative stress. ETC issues and decreased membrane potential
what decreases with age?
biogenesis capacity and autophagy
what mediates biogenesis?
PGC1-alpha, stimulates TF activity and Mfn2 expression.
what do T2DM and obese people have?
decreased mfn2 and PGC1alpha levels
what does mutant Htt in HD cause?
abnormal calcium signallingand mt membrane potential. may colocalise with drp1 at fission sites and affect fusion and fission
pathogenesity of PD?
degeneration of dopaminergic neurons in substantia niagra. decreased complex I activity there.
how is mt involved in parkinsons
oxidative stress, mt dynamics and decreased mitophagy. mutations in PARKIN, PINK1 and mtDNA. mt cant keep itself healthy so results in decreased oxphos activity
symptoms of autosomal dominant optic atrophy
ataxia, deafness, degradation of optic nerve
how are mt involved in DOA
mtDNA depletion, Opa1 mutations, decreased oxphos- affects complex I
what is involved in CMT2A- peripheral heriditary neuropathy
mfn2 mutations, mainly in the GTPase domain. defects in mt motility. decreased oxphos and mtDNA depletion
older yeast have higher levels of what protein?
drp1
what morphology to older cells tend to have?
fragmented
what can not occur in absence of opa1?
inner membrane fusion, but outer membrane fusion still occurs
what does DOA alleles disrupt?
opa1 function, resulting in fragmented mt and loss of fusion activity
what happens in zebrafish that lack mfn2?
fusion failure. leads to adult onset motor dysfunction like CMT2A. progressive motor defects in swimming and altered mt distribution along axons due to defects in retrograde transport
why is the mt abnormally distributes in cmt2a patients?
defects in retrograde transport
what does overexpression of PINK1 cause in dopmine neurons?
induced mt clustering due to excessive fission
what is the epistatic order of the pathway controlling mt fission?
pink1, fis1, drp1
PINK1 interacts with what protein?
drp1, maybe other fission/ fusion proteins eg drp1
what do HD patients have higher and lower levels of?
higher levels of fission proteins drp1, fis1 and CypD. lower levels of mfn1,mfn2 and opa1
how may mutant htt cause damage?
generate oxidative conditions
what activity is decreased in HD patients?
cox1 and cytb
deletion of dnm1 results in what?
increased replicative lifespan and increased resistance to apoptosis
deletion of mgm1 does what?
decreases replicative lifespan- no fusion, decreased mitophagy
simultaneous impairment of both fission and fusion proteins does what?
cause mtDNA instability
