week 8 part 1 Flashcards
Define Neurodevelopmental disorder
Group of the disorder in which the development of the CNS is disturbed
What can neurodevelopmental disorder include?
- Developmental brain dysfunction
2. manifest as neuropsychiatric problems or impaired motor function, learning, language or non-verbal communication.
What are examples of Neurodevelopmental disorder?
- Down syndrome
- Fragile X
- Rett Syndrome
- Autism spectrum disorders - social awareness and communication
- Other disorders which are classified as neurodevelopmental or as learning disability
What is the history of Autism?
First described by a Swiss psychiatrist, Paul Eugen Bleuler in 1912 to describe symptoms of schizophrenia
What did Hans Asperger describe?
Child psychology in 1938
Reported 4 boys, did not mix with their peer group
did not understand the meaning of terms ‘‘respect’’ and ‘‘polite’’
show unnatural stereotypic movement and habits
now called Asperger’s syndrome
What did Leo Kanner report . in 1943?
8 boys and 3 girls with ‘‘inability to form the usual biologically provided affective contact with people’’
What does autism affect?
1% of the population
Where is Autism detectable?
in children before the age of 3 years old
Where does autism occur in?
All countries, ethnic backgrounds and socioeconomic groups
When is significant changes in development noticed?
between 6 months and 1 years of life
what are some features of autism?
- baby does not turn when called by name
- unusual visual exploration
- lack of preference for people vs objects
- Repetitive use of objects (spinning)
What are the symptoms of 18 months of age?
- Do not automatically direct their attention to the person or object that is the focus of others people’s attention
- Fail to use pointing to direct attention of other people; fail to engage in ordinary make–up play
- signs of delayed and abnormal language development are evident
What is autism?
life-long but not progressive
What leads to marked improvements in behaviour with age?
Special educational programmes and support
What are the three common diagnostic features of ASD?
- Impaired social interaction
- Impaired verbal and non-verbal communication
- Restricted or circumscribed interests with stereotyped behaviours
What does Aspergers show?
Many features of autism
but have a high verbal ability and no delay in language acquisition
What does theory of mind refer to?
Ability to understand the desires, intentions and beliefs of others
skill that develops between 3 and 5 years of age in typically developing children
What is Sally Anne test used in?
Psychological research to investigate ‘‘Theory of Mind’’ in children with autism
who was Sally-Anne study conducted by?
Simon Baron-Cohen
What did Simon Baron-Cohen test?
theory of mind in 3 groups of children:
- Those with autism
- Those with Down’s syndrome
- Control group with no developmental disroder
What did study of Sally-Anne involve?
showing children a story involving two dolls called Sally and Anne
They were shown Sally putting her ball in a basket and leaving the room, while she was out of the room, Anne moved the ball from the basket to her box
When sally came back, the child was asked where Sally would look for her ball and if they had developed theory of mind
They would say in the basket because that there is where Sally left it and she did not know it has been moved
What was the result of the Sally-Anne study?
Most of the control group and most of the children with Down’s Syndrome gave the correct answer but only 20% of those with autism provided the right answer
What is the Genetic component in Autism?
- comes from studies of monozygotic twins
- shows 60-90% concordance of autism
- Dizygotic twins show 10-30% concordance when full autism spectrum is considered
What is ASD usually?
Result of mutations in many genes
What are genetic factors of Autism?
Mutations in genes which are involved in synaptogenesis and axon motility
leading to microstructureal, macrostructural and functional abnormalities in connectivity which is involved in sociomotional processing
What are Environemntal factors of Autism?
- Prenatal
- Perinatal
- Postnatal
All include possibility of viral infections
What do some of the genes associated with ASD involve?
- synaptic proteins
2. Cell adhesion scaffolding proteins that are necessary to organise synapses structurally
Microstructurally
Altered ration of short-to long diameter axons and disorganisation of cortical layers observed
Macrostructurally
MRI studies of brain vole
show cortical and subcortical grey matter overgrowth in early brain development
Functionally
Resting state FMRI
show a narrative of widespread global underconnectivity in socioemotional networks
Task-based FMRI
show decreased activation of networks involved in socioemotional processing
Electrophysiological studies
shows alteration in both resting state and stimulus induced oscillatory activities in patients with ASD
What are some examples of genes associated with Autism?
- SHANK3 - SH3 and multiple ankyrin repeat domain 3
- NRXN1 - Neurexin 1
- CNTN3 - Contactin 3
What gene is associated with Fragile X syndrome?
FMR1
What is neurodevelopmental Disorders and mRNA metabolism?
• Complex and delicate process; depends on tight regulation of gene expression
- Once the genes are transcribed theres a lot of processing that happens in the neurons especially, in the nervous system the amount of post-transcriptional processing of messengers is massive, alternative splicing is the largest within the whole organism so all of this needs to be controlled precisely during development
What does the spatial and temporal regulation of gene expression during development lead to?
Establishment of properly connected neuronal networks
What are early stages of brain development highly susceptoble to?
small changes in MRNA stability and translation
What are the regulatory process important for transcriptome regulation and protein synthesis?
- mRNA nuclear export
- Splicing
- Nonsense-mediated decay
- Translation
Why is localization of mRNA in neurons important?
morphologically specialized cells with long processes
When is mRNA not translated immediately?
As it exists the nucleus but is rather stored and transported to the right location to access terminals and dendrites and then is translated in a signal dependent manner
What is important in neurodevelopmental and neurodegenerative disorders?
- when the gene is transcribed
2. The processing of RNA e.g. protein translation and degradation
What is the synaptic changes, LTP and LTD, in response to activity important for?
Experience-dependent memory formation
What is De-novo protein synthesis fundamental for?
supporting LTP/LTD
Required for new memory formation
where have mutations associated with ASD/ID identified in?
Genes encoding regulators of protein synthesis
What are examples of gene encoding regulators of protein synthesis?
- FMR1
- TSC1 + 2
- Ras-MAPK pathway
- mTOR pathway
What does animal model studies suggest?
protein synthesis downstream of group I metabotropic glutamate receptors (mGluR1/5) is often disrupted, preventing LTD
what is protein degradation via ubiquitin proteasome system (UPS) important for?
- synaptic function
2. plasticity
What UPS gene is frequently mutated in ASD/ID?
- Ubiquitin ligase E3/Ube3a
What regulates synaptic UPS activity?
- NMDARs
2. AMPARs
What could contribute to ASD/ID?
Balance between protein synthesis and degradation
What is an example of ASD?
Fragile X syndrome
What is Fragile X syndrome?
most frequently inherited mental retardation disorder (esp in males)
Both sexes can be affected
What are the symptoms of ASD?
- severe mental retardation
2. Delayed verbal development and ‘‘austic-like behaviour’’
Where does Fragile X syndrome have abnormality in?
FMR1 gnes
How many repeats of CGG trinucleotides do fragile X syndrome have, what about affected?
- normal = 6-50 repeats
2. Affected = ca. 200 repeats
What is mechanism of Fragile X syndrome?
- early studies - synaptic protein synthesis is stimulated by activation of Group 1 metabotropic glutamate receptors e.g. mGluR1 and mGluR5
- consequence: protein synthesis is LTD of synaptic strngh
What could correct some of the pathology of FXS?
antagonism of group 1 mGluRs
What is FMRP?
RNA-binding protein, enriched in synapses which represses protein synthesis
What happens in active translation of FMRP?
mRNAs are translated into protein by translocating ribosomes (40S and 60S subunits are shown in light blue) that assemble at the start codon (AUG) and dissociate at the stop codon (for example, UAG)
What happens in Repressed translation by FMRP?
FMRP inhibits ribosomal translocation on specific mRNAs in a complex consisting of target mRNA and several stacked or condensed ribosomes. As the stoichiometry of FMRP to ribosomes to target mRNAs is not known, a minimum of one FMRP molecule (red sphere) is depicted in the stalled complex, recognizing the possibility that additional FMRP molecules (illustrated by transparent red spheres) may exist in the stalled complex.
What happens in translational repression restored by antibiotics?
minocycline-repressed translation. Minocycline, a tetracycline analog (orange spheres), and many other small molecules inhibit translation by interfering with ribosomal translocation in different ways. Because of the similarity in proposed action between FMRP and such small molecules, it is possible that they might partially replace FMRP functions lost in FXS and be therapeutically beneficial.
How is increased protein synthesis observed in mice with MFRP KO?
overactive Akt and mTOR activity
Where is LTD observed and what is it dependent on?
- Hippocampus of FMRP KO mice
2. Dependent on metabotropic Glutamate receptors activation (mGluR) and requires protein synthesis
What is currently in clinical trials to help alleviate some of the symptoms of FXS?
Antibiotic minocycline helps stall protein synthesis similar to FMRP
What is increased in the mouse model of FXS?
density of dendritic spines
What is LTD?
GluR5 dependent and requires protein synthesis
What is lost in FXS?
depencency of GluR5
What is mGluR5 theory?
the defects observed in FXS arise due to aberrant mGluR signalling and high protein synthesis
What does reduction of mGluR5 in mouse model rescue?
dendritic morphology in FXS mice as well as lowering hippocampal LTD and elevated protein synthesis and some observed behavioural phenotypes
What is CTEP?
selective inhibitor of mGluR5 to young FXS mice
What does administration of CTEP do?
alleviates many of the symptoms of FXS – potentially a useful pharmacological compound and it reverses the effects way after the normal development has occurred within the CNS.
What did they employ to see which proteins are up-regulated within mice in experimental approach?
- Cell type specific translating Ribosome affinity purification (TRAP)
- RNA sequencing
What did they identify?
121 differentially translating mRNAs in CA1 pyramidal Neurons of the Fmr1-/y hippocampus
What is the most significantly changed gene category?
Muscarinic acetylcholine receptor (mAChR) signalling pathway
what does Chrm4 mRNA encode?
muscarinic subtype M4
significantly overexpressed in Fmr1-/y hippocampus
What did enhancement of M4 correct?
pathological changes in Fmr1 -/y brain
- normalised protein synthesis
- Elevated GluR-LTD
- Reduced the incidence of audiogenic seizures in these mices
What was the experimental strategy?
Transgenic mice expressing GFP-tagged ribosomal subunit L10 in CA1 hippocampal cell population Affinity isolate GFP-L10 ribosomes Isolate bound mRNAs Sequence and validate translating mRNAs
What was the findings?
They found few FMRP target mRNAs in the CA1-TRAP
Those identified were downregulated rather than upregulated!
Examination of Fmr1-/y CA1-TRAP encoded proteins for similarity to
Those encoded by FMRP targets
Sorting of identified transcripts by function (protein clans)
Found that 6/8 enriched transcripts are enriched in the FMRP target list
Majority of translating mRNAs are functionally similar to FMRP targets
What is M4?
- Gi/o/Gs-CAMP coupled signalling receptor
- It is highly expressed in Hippocampus
- Its protein levels are elevated in Fmr1-/y mice
What reduces level of m4?
Blocking glutamate with MTEP compound
What did they test the effect of M4 antaogonism on?
Excessive protein synthesis
phenotype observed in Fmr1 -/y mice
What were Hippocampal slices exposed to?
selective M4 antagonist PD102807
What was used to measure protein synthesis rates?
35S-methionine/cysteine
How is protein synthesis increased?
Antagonising m4
What reduced protein synthesis rates?
Enhancing M4 function by positive allosteric modulator PAM - VU0152100
What reduced protein synthesis?
enhancing m4 function with PAM
How did they induce LTD?
S-DHPG to activate mGlu1/5
What did stimulation of M4 correct?
Exaggerated mGluR LTD
What could be a protective mechanism?
M4 over translation
M4 PAM corrects Audiogenic Seizures (AGS)
Test whether M4 activation helps alleviate some of the behavioural
abnormalities observed in Fmr1-/y mice
- Injected WT or Fmr1-/y mice with VU0152100 or vehicle
Animals are habituated to the testing arena and then exposed to a loud
(>120dB) alarm for 2 minutes
Score for seizure occurrence and severity
Found that injection of VU0152100 reduces the incidence of AGS
(from 71% to 10%)
What is audogenic seizures?
test which is often applied to rodents – rodent placed in an arena and they get use to arena for time, then a very loud sound is presented for 2 mins – normal mice might shrink but they don’t run, but the mutant mice get seizures of different severity
In normal conditions downstream of metabotropic glutamate receptor activation
there is a control of protein synthesis which is normally controlled by the presence of FMRP
What has M4 PAM been proposed as ?
Treatment for schizophrenia and Alzheimer’s disease
What does Rodent studies using M4 PAM demonstrate?
pro-cognitive effects
What is important to address
not all excessively translated mRNAs in FX are contributing to pathological changes.
What may help alleviate activity of over translation and LTD?
enhance activity of m4
What is Rett syndrome?
X linked disorder affects girls (1 in 10000)
What are the symptoms of Rett Syndrome?
- Autistic like behaviour
- Loss of speech
- Motor coordination problems
- Loss of purposeful hand use
- Scoliosis
- Seizues
- Microencephaly
- Mental disabilities
What are the causes of Rett Syndrome?
- mutations in the mECP2 protein
What is MECP2?
methyl cytosine-binding protein 2
What does MECP2 recognise?
methylated CpG’s on the DNA
Binds these motifs and regulates gene transcription in this way
What are implicated in some of the pathology?
- Translational control
2. Global transcriptional control
