Flashcards in Mitochondrial influences in motor disorders Deck (28):
What are examples of neurodegenerative disorders with motor symptoms?
- parkinson's disease
- Alzheimer's disease
- Huntington's disease
- Amyotrophic lateral sclerosis
- Charcot-marie-Tooth's disease
- Friedreich's ataxia
What are the pathologies and symptoms of HD?
striatal lesions caused by the loss neurones
involuntary choreiform movements
behavioural/cognitive impairments- irritable and demented
neuropsychiatric symptoms such as hallucinations
What is the life expectancy of HD patients?
premature death - die within 10 years of first symptoms occurring
What is the cause of HD?
caused by a polyglutamine expansion - CAG repeat in the huntingtin protein
it is a genetic hereditary disorder
What happens to HD patient's weight?
they show extreme weight loss even though they are eating a normal diet - they become emaciated- this indicates problems with metabolic processes indicating mitochondrial dysfunction
What changes have been demonstrated in HD patients?
changes in glucose metabolism in certain areas of the brain
- there is a loss of glucose uptake over time in the striatum (caudate nucleus and thalamus) and also in the cortex - determined by looking at the levels over time using different types of scans
the control patients didn't show reductions in glucose uptake
What was shown about glucose metabolism by covariance patterns?
it showed reduced glucose metabolism in the striatum- caudate nucleus and putamen and increased glucose metabolism in the occipital lobe of HD patients compared to controls
What was seen in patients that weren't yet showing symptoms of HD ?
there were already changes in glucose metabolism in the caudate, putamen and thalamus compared to controls indicating that these changes precede the symptoms of the disorder.
There were no changes in the motor cortex, globus pallidus or cerebellum
What does 1H NMR spectroscopy measure?
measures the appearance of molecules in the respiratory chain
What was shown by 1H NMR spectroscopy?
increased lactate suggesting anaerobic respiration
symptomatic/presymptomatic HD- suggests these changes are occurring before cell death occurs so may be the cause of cell death which then leads onto the symptoms
What processes appear to be affect in symptomatic/presymptomatic HD patients?
reduced oxidative phosphorylation
reduced TCA cycle
reduced complexes 2, 3 and 4
NO change in complex 1 activity like PD
What did yeast induced to express 103Q show ?
-demonstrated changes in the shape of their mitochondria over time - they look like they aggregate with huntingtin protein
-they demonstrate increased abnormal mitochondrial distribution in yeast overtime
- decreased cell respiration
-altered amount/function of complexes 2 and 3
- altered mitochondrial morphology/distribution
What was seen in the yeast expressing 25Q ?
this number of repeats isn't sufficient to cause HD
there was little overlap between the mitochondria and huntingtin protein
What did the HD mtDNA deletion 4977 show ?
There were accumulations of this mitochondrial DNA deletion in the temporal lobes of HD patients
using PCR there was no staining for deleted mutations in the control patients but there was substantial staining for deleted mutations in the HD patients
so there appear to be mtDNA deletions in HD patients
What are suggestions that mitochondria are involved in HD?
- mutant huntingtin localised to mitochondria which doesn't happen normally
- mitochondrial calcium handling is altered
- transcriptional dysregulation in HD
What are the early on effects that precede symptoms in HD?
- these are powerful indicators of importance
changes in mitochondrial function which can lead to the production of ROS
changes in respiration which can lead to activation of apoptotic processes
What are the symptoms of ALS?
degeneration of both upper and lower motoneurons causing flaccid paralysis of voluntary muscles
What are the different forms of ALS?
10% familial - 20% of these are caused by SOD1 mutations (2% of all cases)
What are the other mutations in ALS?
TDP-43 mutations (RNA transactivation response DNA binding protein 43)- it binds to DNA and alters transcription
TDP-43 accumulation (sporadic form)- indicates this binding protein is important in both forms
FUS/TLS mutations (fused in sarcoma/translocated in liposarcoma)
What did they do to look at the effects of human TDP-43 in mice?
they overexpressed it in different types of mice
- different mice demonstrated different degrees of expression relative to their endogenous expression of the protein
1) TAR4/4 - had highest expression
4) TAR6 - Lowest expression
What was seen in the mice models that demonstrated the high levels of expression of human TDP-43?
Demonstrated most drastic changes in limb movements - feet didn't hang down and toes didn't splay when held upside down- these effects occur earlier in those that expressed high levels of TDP-43
changes in their gait- smaller steps and they stumbled more
reductions in motor function
reductions in survival
-TAR4/4 all died after 30 days while TAR6/6 were able to live up to about 12 months
What was shown in transgenic mice with high levels of TDP43?
Higher levels of ubiquitin aggregates shown by increased ubiquitin staining
ubiquitin aggregates are close to the nucleus of cells
Changes in mitochondria are associated with the ubiquitin
What other changes were indicated in the transgenic TDP43 mice?
changes in the levels of mitofusin 1 - important for mitochondrial fusion - mutations in this gene cause changes in the structure of the mitochondria
there are also reduced number of mitochondria in the motor cortex in these mice
24 day old TDP43 transgenic mice have very reduced motor function- one even looked completely paralysed
What are the symptoms seen in sporadic ALS?
evidence which suggests mitochondrial dysfunction
- increased CSF levels of 8-hydroxy-2'- deoxyguanosine which is indicative of oxidative damage in the brain
- altered respiratory chain enzymes - these activities tend to be reduced
- CNS energy hypo metabolism in both the spinal cord and motor cortex
What changes were seen in SOD1 G93A ALS Tg mice?
- altered mitochondrial morphology
- then decreased mitochondrial respiration due to reduced function
- decreased oxygen consumption
- decreased mitochondrial calcium loading capacity
- decreased respiratory chain complex activities
- decreased ATP synthesis
ALL this is likely to cause degeneration of nerve cells
What changes were seen in SOD1 G37R neuronal cells?
morphological abnormalities of mitochondria
reduced acitvity in complex 1, 2 and 4
reduced mitochondrial membrane potential
decreased levels of cytosolic ATP
What happens in SOD1 mutants?
DIRECT mitochondrial interaction
- localisation in the mitochondria inter membrane space, matrix and outer mitochondria membrane - forms macroscopic aggreagtes of SOD1
compartmentalizes in the matrix
it has been suggested to be caused by failures in the folding of the protein but its not clear
damages the mitochondrial membrane so mitochondria can no longer function properly leading to decreased mmp, swelling, vacuole degeneration, impaired calcium and redox homeostasis, increased mitochondrial mediated apoptosis
binds to anti-apoptotic protein Bcl-2, therefore cause apoptosis