Cortical malformations Flashcards
Two main types fo cortical malformations
- abnormal neuronal and glial proliferation or differentiation
- abnormal cortical organisation
Abnormal types of neuronal and glial ploferiations (6)
- Tuberous sclerosis
- Focal cortical dysplasia
- Hemimegalencephaly
- Periventricular nodular heterotopia
- Lysencephaly
- Subcortical band heterotopia
Abnormal cortical organisation types (2) :
- polymicrogyria
- Schizencephaly
Types of mTORapthies (3):
- tuberous sclerosis
- focal cortical dysplasia
- hemimegalencephaly
What are mTORopathies?
neurological diseases caused by a mutation in the mTOR signalling pathway.
Two divisions of mTORopathies:
- mutations that produce DIFFUSE malformations of cortical development (MCD)
- mutations that produce FOCAL MCD
Pathological effects of mutations in the mTOR pathway (6)
- Turnover of proteins
- Lipid and glucose metabolism
- Cellular growth and proliferation
- Cytoskeleton organisation
- Ribosome biogenesis
- Autophagy.
Focal cortical dysplasia
caused by somatic OR mosaic mutations in the neuronal progenitors.
- 5-10% of epilepsy patients have FCD.
- 6.3 years is the mean age of onset.
- Most common structural brain lesion in children with drug-resistant epilepsy
- 38% of FC patients suffer recurring seizures after surgery resection.
FCD II
involves the loss of cortical lamination, blurred gray-white matter junction.
What pathological alterations does FCD II introduce into the cortical layers (6)
- Balloon cells – huge cells, highly spherical, no excitability or synaptic function.
- Activated microglia – indicates inflammation
- Hypertrophic pyramidal cells – neurofilaments, twice as big as healthy pyramidal cells.
- Dysmorphic neurons
- Excessive cellular gliosis – indicates inflammation
- Hypomyelination of white matter and indistinct grey-white matter boundaries
How many types of FCD?
Four
Hallmarks of FCD I
Small immature neurons and hypertrophic pyramidal cells.
Heterotopic neurons
Hallmarks of FCD III
abnormal cortical laminations.
Cellular and architectural abnormalities also seen present in type I and II.
Animal model characterisation of FCD II - 3 steops
- Face validity
- Predictive validity
- Construct validity
Four steps of face validity
- Histological assays
- Biomolecular assays
- EEG assays
- Behavioural assays
Cre/lox xystem
Cre/lox system: cre is a protein that is expressed in transgenic mice model or injected.
Main point – cre will recognise the sites and cut them – to cut out the gene and knock down the protein of interest. So, in this case knock down identified inhibitor mTOR – to hyperactive it.
Two systems for mouse model development
- In-utero electroporation
- cre/lox system
RHEB CA ANIMAL MODEL in FCD
- The RhebCA animal model shows a significant reduction of seizure frequency with rapamycin treatment > predictive validity
- The RhebCA animal model is generated by in-utero electroporation for targeting neuronal progenitors > construct validity
- The RhebCA animal model displays the histological and behavioural hallmarks of the disorder > face validity.
options for gene therapy for FCD II (2)
- Restore the physiological activity of the impaired signalling pathway
- Rescue protein levels impaired in FCD.
Pros (2) and cons (2) of restoring the physiological activity of the impaired signalling pathway - FCD-II
+ allows for easier fine-tuning of the therapeutic effect
+ the mutated gene can be specifically targetd
- the impaired pathway needs to be well-known
- the therapy effectiveness depends on the mutation
pros (2) and cons (2) of rescuing protein levels impaired in FCD
+ targets the direct cause of the symptoms
+ is effective independently of the causing mutation
- harder to predict the potential secondary effects
- compensatory mechanisms may affect long-term effectivity of the therapy.
Kv1.1 and excitability
reduces excitability of neurons – so it is probable that it is contributing to seizure occurrence in FCD.
Kv1.1 and mTOR
- In an active synapse – activation of NMDA receptors leads to activation of mTOR pathway > which in turn leads to synthesis of micro-interference RNA-129.
- miRNA-129 – target Kv1.1. mRNA – induces degradation of this mRNA and therefore the preventing the translation fo the Kv1.1 channel.
mTOR activation hinders expression Kv1.1 by degrading its mRNA. So need to design a plasmid that is carrying the KCNA1 gene (that encodes for Kv1.1) that doesn’t have the region where miRNA is binding.
Filamin A and gene therapy for FCD II
Filamin A inhibition reduces seizure activity in a mouse model of focal cortical malformations.
