Brain Flashcards
Cytokines/cytotoxic mediators in the brain come from where?
Activated microglia can release them, (ROS and nitrogen species) –> apoptosis and loss of OL precurosors, dysregulation (failing to myelinate axons)
What is the knowledge gap
Molecular mechanisms eliciting inflammation thru placenta-fetal-brain axis are unknown
Rat brain is considered as developed as human newborn how many days postnatal
P10-12
Neurogenesis is what and starts when in rat vs human
rat: G0 - 10
human: 0 - 12 weeks
STEP 1: Neurogenesis: This is the earliest step, where neural stem cells in the ventricular zone differentiate into neurons.
Astrocyte and OLs start to generate after..
the beginnning of neurogenesis, and gliogenesi continues postnatally in both humans and rats
Astrogenesis is what step and what is it?
3RD STEP
following neurogenesis, radial glial cells differentiate into astrocytes, which support neurons and maintain the brain’s environment.
Microglial invasion is what step and what is it?
SECOND
Support immune protection and help shape developing neural circuits
Come from progenitor cells in the yolk sac
Start colonising the rat brain slightly after G10 continue to peak postnatally
What marks the 3rd trimester?
Beginning of synaptogenesis, astrogenesis, myelination (20-40 weeks human, G20-P12 rats)
When do OLs start developing ?
OLs start developing prenatally, maturating from pre-OLs to immature OLs from mid-gestation to the end of gestation
When does myelination occur?
prenatally and postnatally in humans but occurs postnatally in rodents
What is myelination and what step?
4th
Myelination: Oligodendrocytes wrap axons in myelin to speed up electrical signaling. In humans, myelination
What are the mechanisms linking maternal and fetal responses to brain damage?
Increased proinflammatory cytokines in the brain:
1) activated microglia (critical in synaptic plasticity/myelination)/astrocytes
- activation of these = neuronal migration processes, neuronal death, damage surrounding axons etc
2) maturation and death of OLs
3) axonal loss or death of neurons, cytoskeletal damage, neurotoxicity
Innate immune molecules may alter directly or indirectly some neuronal processes
Overall, cerebral dysconnectivity associated with hypomyelination
The nature and severity of brain injuries depend on…
The timing, intensity and nature of inflammatory insult
First trimester insults associated with?
brain maldevelopments
Second trimester insults associated with?
periventricular WM injury (periventricular leukomalacia)
Third trimester insults?
cortical and deep grey matter damage
Altered myelination is partially due to what?
impaired OL maturation
Effect of IL1b on brain?
ACTIVATE astrocyte and microglia cells
(and then these release more cytokines)
directly (i.e. by neurotoxicity) or indirectly (i.e. by modulating axonal guidance proteins and synaptogenesis) inhibit cell proliferation and neurogenesis, cause neuronal death, delayed myelination and disrupt neuroglial fibre tract growth and synaptic connections, which can lead to permanent alterations of brain connectivity
Pillars of ASD?
- repetitive/stereotype behavior
- impairments in communication / social behavior
ASD affects how many children?
1/60
Among a cohort of ex-preterm ASD human subjects,
Brain development in utero explain
Week 3 - ectoderm thickens and forms neural plate –> neural groove
Week 4 - neural tube, (become the brain and spinal cord)
Week 8 - most structures in place, wweek 11 - has a similar shape to what it will be like at birth
Give examples of studies that have highlighted proinflammatory effect of androgen in the brain?
A study using finasteride (drug inhibits the formation of DHT) in a PPA-induced autism rat model. Neuroprotective effects, biochemical, histopathological, and behavioral analyses.
What are OLs?
Glial cells that support and maintain integrity of axons and neuronal connectivity within the central nervous system
Another study which shows protective effect of flutamide on OLs?
The study showed that flutamide prevented both the direct toxicity of testosterone and its ability to exacerbate excitotoxic damage induced by glutamate receptors in cultured oligodendrocytes
Is there a conflict in the literature of T effects on the brain - neuroprotective/ neurotoxic?
Yes, some studies indicate that T low levels being protective and high levels being detrimental.
In a study, blocking T conversion to estradiol did what?
Increased damage, estradiol as a neuroprotective factor against cerebral ischemia
What happens to plasma levels of LH and T after acute flutamide tx?
Increase, reduces negative feedback on HPA
In our study what is the effect of flutamide on hormonal balances?
More androgen = more conversion of A into E in brain tissue by aromatase
How does estradiol regulate OLs?
E delays the exit of OPC from the cell cycle, so in our model the inc of CC1+ OLs may have resulted from estradiol prolonging the cell cycle of OPCs, thereby increasing the pool of mature OLs in flut/gbs group
Why did GBS cause enlargement of LV?
Decrease of CC-1 oligodendrocytes in forebrain whtie matter = shrinkage of surrounding brain tissue due to a loss of mature OLs and subsequent demylination (Smaller bundles of axons and underdeveloped neuronal connections)
What is often used to treat cerebral edema by reducing inflammation?
glucocorticoids (adverse effects like brain atrophy)
What other effects on GBS could brain have?
Neuronal loss, cortical thickness,
Is there evidence of androgen contributing to vulnerability in females and how?
Yes by androgenization of females
Astrocytes in development ?
Derived from radial glial cells, beginning around E14 in rodents. from the subventricular zone of the lateral ventricles (also OLs)
Microglia in development?
Derived from yolk sac progenitors, migrating into the brain around E9
OLs in development
Derived from oligodendrocyte precursor cells (OPCs), starting around E14 and maturing postnatally.
Fronto-parietal tract
passes through EC
attention, working memory
Thalamo-corticla tract
passes through EC
sensory integration and processing
Amygdalo-hippocampal tract
passes through EC
social behaviors and emotion
is iba-1 for activated microglia? explain more
activated - amoeboid shape, thicker retracted processes
M1 - proinflammatory -> proinflammatory cytokines, ROS
M2 - anti inflammatoyr (a bit less amoeboid than M1, more branches) -> BDNF, IL10, TGFb, clear debris wound healing
why did cc-1 increase with flutamide?
LH and T plasma levels increase
flutamide, as an androgen receptor antagonist, reduces the negative feedback that testosterone and other androgens have on the hypothalamic-pituitary-gonadal axis
higher conversions of androgens into estrogens in brain tissues by aromatase
estradiol delays the exit of OPCs from the cell cycle
[37]. Thus, the observed increase in CC-1+ oligodendrocytes may result from estradiol’s role in prolonging the cell cycle of OPCs, thereby increasing the pool of mature oligodendrocytes in flutamide/GBS groups
what about LV , why. did it increase
The observed decrease in CC-1+ oligodendrocytes in the forebrain white matter likely resulted in the observed enlargement of lateral ventricles in GBS-infected groups
This increase in size may reflect the atrophy or shrinkage of surrounding brain tissue due to a loss of mature oligodendrocytes and subsequent dysmyelination
likely be a result of the underdevelopment of neuronal connections, resulting in smaller bundles of axons within the forebrain white matter
why was microglia not reduced in GBS induced ca?
previous studies in our lab noted a decreased in females in microglia but not males
in another stuyd, microglia depleted rats spent less time in open arms of EPM –> more anxiety, same as what our mdoel showed
GBS III showed dec microglia in CC
could have looked at microglial morphology, spacing, clustering as opposed to jsut density
what else are microglia importnat in?
neuronal migration, prenatal brain circuit shaping, myelination, synpatogenesis
During neurogenesis, microglia influence the survival, differentiation, and apoptosis of neuronal precursor cells through the secretion of brain-derived neurotrophic factor and neurotoxic factors
In postnatal development, microglia facilitate synaptic formation and maturation via synaptic pruning
The involvement of microglia in long-term synaptic plasticity serves as the foundation for learning and memory processes
which cell type produces myelin
schwann cell
why arent microglia activated in our model?
Time point matters - this is at P50, microglia could have already turned to a less active state, we could have missed earlier peaks
how can il1b inhibit neurogenesis
Directly: By damaging neurons through its toxic effects.
Indirectly: By disrupting critical developmental processes like axon growth and synapse formation.
why white matter?
axonal wiring anomalies inducing dysconnective/ dysfunctional brain networks7–12
Explain IL1ra study?
In such MIA models, anti-inflammatory interventions
54 using interleukin-1 (IL-1) blockade administered to the dam exerted placento- and
55 neuro-protective effects alleviating forebrain anomalies as well as ASD
manifestations5,6
Trial for preterm infants with brain injuries
what are the effects of GBS on neuron
neuronal apoptosis reported in our model of gbs CA at P5. neuronal cell differentiation, synaptic connectivity and neuronal survival
altering the WM connectivity via neuronal death, axonal degeneration
is there a sex diff in microglia ?
Sex differences in microglia number and function are evident early in the neonatal brain.
yes more activated in male in utero and less activated in male adulthood (Females mroe)
microglia what age they colonize in rats?
Microglia initially colonize the brain early in development (embryonic day (E) 9-10 in rodents). During this time and into the postnatal weeks, microglia have an important role in forming neural circuits by initiating synapse formation, pruning aberrant synapses, and phagocytosing naturally dying cells.
what’s so imp about microglia?
function may affect WM connectivity and perturb NDD process such as OL maturation
in development: During this time and into the postnatal weeks, microglia have an important role in forming neural circuits by initiating synapse formation, pruning aberrant synapses, and phagocytosing naturally dying cells.
why didnt you see activation of microglia?
outcome of functional damage of microglia, p50 - dont remain activated until that day
explain microglia and damp
Microglia and macrophages detect dead and dying cells via released “find-me” signals such as high-mobility group box protein 1 (HMGB1) and the presence of “eat-me” signals such as phosphatidylserine on the outer leaflet of cell membranes. (23) (released by dying cells, or microglia themselves)
HMGB1 translocates from the nucleus to the cytosol and is released extracellularly. (25,28) When located extracellularly, HMGB1 acts as a damage-associated molecular pattern (DAMP), also called an alarmin, where it mediates neuroinflammatory responses in stroke
Toll-like receptors (TLRs), triggering the translocation and activation of nuclear factor kappa B (NF-κB) to the nucleus to induce gene expression and subsequent proinflammatory cytokine
what did other studies look atin our lab ?
MBP analyses were focused on that specific distance from the Bregma based on previously published results in addition to MRI findings of enlarged lateral ventricles in GBS-exposed versus control males
what have they found in ASD in humans?
. A meta-analyses of region of interest (ROI) brain volumes showed larger total brain (TBV), intracranial (ICV), cerebral hemispheres, cerebellum, and caudate volumes as well as smaller corpus callosum volumes in ASD subjects compared to healthy control
explain how dysonnectivity is associated with ASD?
Hence, microglial activation by pro-inflammatory cytokines can damage neurons and glial cells, leading to WM injuries or interferences with synaptic connections, and brain dysconnectivity. Astrogliosis and microglial activation can alter neuronal migration processes, induce neuronal death, stop oligodendrocyte maturation, damage surrounding axons and/or trigger a loss of synaptic connections, leading to cerebral dysconnectivity associated with hypomyelination (Figure
why is the white matter vulenrable to inflammatory insults near end of gestation? esp since myelination occurs postnatally in rats?
Ongoing Myelination Process: While myelination begins postnatally, the precursor cells (oligodendrocyte progenitor cells) are still present and actively developing at the end of gestation. These immature oligodendrocytes are more susceptible to damage from inflammation
Blood-Brain Barrier Development: The blood-brain barrier (BBB) in rats, like in humans, is still immature at the end of gestation. An underdeveloped BBB allows immune cells and inflammatory cytokines to cross into the brain more easily, making the white matter more vulnerable to inflammation.
why was it thought that inflammatory insults cause the fetall BBB to become more permeable?
cytokines interacting with tight junction proteins
activated microglia release MMPs degrade extracellulr matrix/ tight junction proteins
enzymes repsonsible for degredation of extracellular matrix (matrix metalloproteinases)
but why is it in our case that the fetal BBB becomes leass m
an increase in claudin 5 expressin found in brains post mortem ASD, BBB is important in delivery of neurotrophic faactors from placenta to brain - ensure proper development of the brain connectome - defects in these factors are linked to ASD
can exosomes pass the BBB? how?
transytosis
radiolabeled exosomes. The exosomes are labeled with 125I using the chloramine-T method. After labeling, they are purified using an Illustra NAP-5 column and characterized. In the subsequent experiment, the radiolabeled exosomes are injected into the mice through the jugular vein, and samples are collected from the brain and serum to assess exosome uptake at various time points. The radioactivity in these samples is measured to evaluate the levels of exosomes in different tissues.
in summary - dysregulated IR –> alter white matter connectivity in the brain how?
neuronal death, axonal degeneration, OL defects, impairing microglia (which are critical cells invovled in plasticity, myelination), loss of synaptic connections,
how do cytokines cause nueronal death?
activated microglia and astrocyte can produce cytokines –> can release ROS
cytokines can lead to an imblanace in glutamate signaling –> excitotoxicity
mitochondrial dysfunction, activation of apoptotic pathways/cell death pathways
cytokines can also disrupt the BBB
why we see this effect on BBB becoming less permeable in GBS?
Such drop
187 of permeability of BBB might interfere with the systemic transfer from the placenta to
188 the brain of key neurotrophic factors – such as the insulin-like growth factor 1 –
189 involved in the development of the brain connectome whose defects are present in
ASD22
following release of cytokines in placenta and fetal bloodstream, neurotoxic effects on fetal brain…? how
elevating glutamate production - excitotoxicity (by elevating glutamate production), inducing neuronal necrosis, activation on gligal necroptosis/apoptosi, death of OLs – myelination and diffuse white matter brain injuries
why would microglia be reduced?
they are imp in synaptogenesis - Hence, this decreased density of microglial cells in GBS-exposed rats might affect some neurodevelopmental key processes such as postnatal synaptic pruning, failing to remove or promote effective synapses (Pierre et al., 2017). Moreover, the reduced number of microglial cells might affect OL functions, by affecting the production of MBP component, forming the myelin sheath along with proteolipid protein
what else do we see in ASD brains?
altered neuronal and axonal netwroks
microglia effect what
WM connectivity and synaptic plasticity, and may perturb neurodevelopmental processes such as pre-OL maturation
