Parkinson's Disease Flashcards
Name the 3 main categories of PD symptoms
Premotor
Motor
Postmotor
Name the premotor symptoms of PD
Depression
Loss of olfaction
REM sleep disorder
Name the motor symptoms of PD
Bradykinesia
Rigidity
Resting tremor
Masked face
Name the postmotor symptoms of PD
Dementia
Visual hallucinations
What are the two main pathologies seen in PD?
Progressive loss of DAergic neurons in SNpc
Lewy bodies in remaining SN neurons
What are the 2 main treatment types for PD currently?
Deep brain stimulation
Drugs
Which drugs are currently used to treat PD?
L-Dopa
MAOB/COMT inhibitors
DA agonists
Through which brain areas do LBs spread?
Brainstem -> midbrain via SN -> cerebral cortex
Where in the periphery can LBs be found in PD?
Enteric neurons
Vagus nerve
Autonomic ganglia
What is the main component of LBs?
Alpha-synuclein
What is incidental LB disease?
LBs mainly in brainstem
Mild DAergic neuronal loss
Clinically normal
Diagnosed postmortem - could be presymptomatic PD
What are the 3 main types of PD risk factors?
Increased age
Environment
Genetics
Name 5 genes that increase familial PD risk
SNCA Parkin PINK1 LRRK2 GBA
Name 2 environmental factors that increase PD disease risk
Living near metal alloy industries
Well water drinking
Name 2 environmental factors that decrease PD disease risk
Smoking
Coffee drinking
What is the effect of MPTP?
Destroys SN DAergic neurons
Causes permanent Parkinsonian symptoms
What is the physiological function of alpha-synuclein?
Unknown
What is the effect of alpha-synuclein KO in mice?
Fairly normal
Altered DA release
Some neuronal dysfunction
Name an autosomal dominant cause of PD
SNCA
What is the effect of an SNCA locus duplication?
3 copies of gene - increased alpha-syn
PD development in 40s
What is the effect of an SNCA locus triplication?
4 copies of gene - greatly increased alpha-syn
PD development in 30s
What are the steps of alpha-synuclein aggregation?
Soluble monomer (normal/B-sheet-rich) Soluble oligomer (normal/B-sheet-rich) Protofibril Fibril LB (inclusion/aggregate)
Which alpha-synuclein species are thought to be toxic?
Soluble oligomers
Protofibrils
What is the effect of transplanting foetal tissue into PD patients and what could explain this?
LBs form in graft
Could be LB transmission - could be host environment causes dysfunction in graft causing alpha-syn aggregation
What are the structures of the normal and mutant alpha-synuclein monomers?
Normal - alpha-helices
Mutant - beta-sheets
What is permissive templating?
Exposing normal alpha-syn to misfolded B-sheet alpha-syn decreases energy required for normal protein unfolding
Increases chance of refolding
Increases chance of aggregate formation
Name 3 ways in which alpha-syn can be transferred between cells
Exosomes
Free in solution
Tunneling nanotubes
What is the effect of DA on alpha-synuclein?
Causes protofibril formation
How does MPTP cause parkinsonism?
Uncharged - crosses BBB
Metabolised to MPP+ - substrate for DAT - uptake into DAergic neurons
Opposite charge to -ve mito matrix - crosses mito membrane
Inhibits complex I function
Decreases ATP production, increases ROS (oxi stress)
DAergic neuron death
How does alpha-synuclein interact with lysosome functioning?
Alpha-syn degraded by chaperone-mediated autophagy
Alpha-syn aggregates removed by macroautophagy
How is mitochondrial function altered in idiopathic PD patients?
Decreased complex I activity
In SN tissue, platelet mitochondria
Which mitochondrial ageing phenomenon is further increased in PD SN neurons?
Higher mtDNA levels with deletion
How is the sensitivity of DAergic SN neurons to mitochondrial respiratory chain toxins altered in PD and why might this be?
Increased
Could be due to oxidative stress
Could be due to defective degradation of damaged mitos - due to autophagy/lysosome defects
What is the overall role of parkin and PINK1?
Prevent fusion back of damaged mitos fragmented by fission
Why might DAergic neurons be so vulnerable to mitochondrial dysfunction in PD?
High spontaneous burst/pacemaking activity - high energy demands
High Ca2+ fluxes - more vulnerable to Ca2+ dysregulation
How might alpha-synuclein affect mito function?
Inhibit mitochondrial respiratory chain - possibly complex I
What are the 4 main methods of alpha-synuclein degradation?
Ubiquitin proteasome system
Macroautophagy
Chaperone-mediated autophagy
Mitophagy
What does the ubiquitin proteasome system involve?
Unfolded protein tagged with ubiquitin
Sent to proteasome for degradation
What does macroautophagy involve?
Autophagosomes (double-membrane vesicles) form around proteins
Fuse with lysosomes
What does chaperone-mediated autophagy involve?
Unfolded protein associates with chaperone complex
Sent to lysosome for degradation
What does mitophagy involve?
Only degradation method for misfolded alpha-syn
Whole mitochondrial engulfed by autophagosomes
Fuse with lysosomes
How is UPS functioning altered in PD?
Decreased proteasomal activity in SN
Are proteins in LBs ubiquitinated in PD?
Yes
How is macroautophagy functioning altered in PD?
Fewer lysosomes in SN
More autophagosomes in SN
How is CMA functioning altered in PD?
Decreased CMA protein levels
How does VPS35 affect PD risk?
Autosomal dominant cause
What is the physiological function of VPS35?
Component of retromer complex
Retromer enables retrograde transfer of MPR from endosome back to trans-Golgi network
What is the role of the mannose-6-phosphate receptor (MPR)?
Transfers lysosomal enzymes from Golgi to endosomes - then lysosomes
What is the proposed pathological mechanism of VPS35 in PD?
Retromer defect - MPR not returned to Golgi
Incomplete transfer of lysosomal enzymes to lysosomes
Impaired protein degradation - alpha-syn accumulation
What is the physiological role of GBA1?
Encodes glucocerebrosidase - lysosomal enzyme
Catalyses glucocerebroside breakdown
What do recessive mutations in GBA1 cause and what does this disease involve?
Gauchers disease
Lysosomal storage dysfunction
What is the effect of a heterozygous recessive GBA1 mutation?
Increased PD risk
What is the proposed pathological mechanism of GBA1 in Gauchers disease?
Loss-of-function
Accumulation of glucocerebroside in lysosomes
Lysosome dysfunction - impairs mitophagy - impairs MRC activity
Induces unfolded protein response
What are the 2 possible mechanisms by which GBA1 mutation may lead to neuronal death in PD?
GBA1 misfolding in ER causes UPR - decreases translation - causes apoptosis
GBA1 misfolding in ER - targeted for degradation - decreases GBA1 in lysosome - increases glucocerebroside - causes lysosome dysfunction - decreases alpha-syn degradation
What is the physiological role of ATP13A2?
Transports Zn2+ into lysosome
What is the pathological role of ATP13A2?
Loss-of-function
Affects lysosomal function - impairs protein degradation
Which LRRK2 variant increases PD risk?
G2019S
What is the physiological role of LRRK2?
Unknown
Kinase
Linked to autophagy, microglial mobility, mito function
What is the pathological role of LRRK2 with a G2019S mutation?
Increased kinase activity
Effect unknown
What is the effect of a PINK1/parkin KO?
MRC defects
What is the physiological role of DJ-1?
Oxidative stress sensor
Translocated to mitos in response to oxi stress - antioxidant role - protective
What does mutant DJ-1 PD involve?
Abnormal symptoms - dystonia, psychiatric features
What is the pathological role of DJ-1?
Loss-of-function
No translocation to mitos in response to oxi stress - impairs defence against damage
What does oxidative damage modify?
Amino acids
DNA (inc. mtDNA)
Lipids
How has oxidative stress been linked to idiopathic PD?
Increased oxi stress
Mouse models deficient in the expression of which genes show increased oxi stress?
Parkin
PINK1
DJ-1
What are the 3 sources of ATP in the cell and which is the main source?
ETC - main source
Krebs cycle
Glycolysis
What is the effect of mito damage on mito membrane potential?
Depolarisation
Why is mito function particularly important in neurons?
Neurons have very little glycolysis - dependent on mitos for ATP
Many energy-demanding processes in neurons
How are ROS formed in the mitochondria?
Electron leak from ETC
Electrons react with free oxygen
What are the roles of antioxidant enzymes?
Decrease ROS number
Decrease ROS toxicity - by converting to different ROS
What are the 4 effects of age on mitos?
Decreased antioxidant levels
Decreased protein degradation
Increased mtDNA damage - by ROS
Electron leak decreases H+ gradient - decreases ATP production - decreases mito membrane potential - mPTP opening - cell death
What causes mPTP opening?
Increased mito Ca2+
Mito depolarisation
What is the effect of mPTP opening?
H+ efflux - loss of H+ gradient
Decreased ATP production
Cell death
What happens to fissioned mitos?
Fusion or mitophagy
What is the physiological role of PINK1?
Regulates mito Ca2+ efflux - via IMM Ca2+/Na+ exchanger
What is the effect of PINK1 deficiency?
Impairs Na+/Ca2+ exchanger in IMM
Increased mito Ca2+ - decreases buffering capacity
Increased cytosolic Ca2+ - decreases mPTP opening threshold
Increased NADPH oxidase activity - increased ROS
Opens mPTP
Cell death
How do excess fission and fusion affect synapses?
Decreased ATP at synapse
Which mitochondrial process are PINK1 and parkin involved in?
Mitophagy
Name 7 mechanisms of mitochondrial quality control
Mito chaperones Mito proteases Cytoplasmic UPS mtUPR Mitochondria derived vesicles (MDRs) Mitophagy Apoptosis
What is the role of mitochondrial chaperones?
Fold protein once inside mito
What is the role of mitochondrial proteases?
Break down improperly-folded proteins
What is the role of cytoplasmic UPS?
Ubiquitinates faulty proteins
What is the role of mtUPR?
Damaged mito protein causes signal to nucleus - increases transcription of chaperones and proteases
What are mitochondria derived vesicles (MDRs)?
Damaged proteins cluster - form vesicles budding off mitos
Fuse with lysosome - degraded
What type of parkin mutation increases PD risk?
Autosomal recessive
Loss-of-function
What is the role of parkin in mitophagy?
Recruited to damaged mitos
E3 ubiquitin ligase - tags proteins for degradation with ubiquitin
What type of PINK1 mutation increases PD risk?
Autosomal recessive
Loss-of-function
How do PINK1 and parkin cause mitophagy?
Mitochondrial depolarisation
PINK1 accumulates on OMM
Recruits parkin to mitos
PINK1 phosphorylates parkin and ubiquitin chains on mito membrane proteins (e.g. Mfn1/2)
Activates parkin - builds more ubiquitin chains on mito membrane proteins - amplifies signal
Marks mito for degradation by mitophagy
A mutation in which gene causes juvenile Parkinsonism with additional pyramidal signs?
Fbxo7
What is the role of Fbxo7?
Facilitates parkin-mediated Mfn1 ubiquitination
May recruit parkin to mitos
What is required for Fbxo7 translocation to mitos?
PINK1