Nervous System Ageing LT1 Flashcards
What is the role of afferent neruones?
Receive and transmit information from environment TO the CNS
Sensory nerves and sensory ganglia
What is the role of efferent neurones?
Transmit information generated in CNS to the PERIPHERY
Autonomic ganglion and motor nerves
What is the difference between a nerve and ganglia?
Ganglion is a collection of cell bodies of neurons outside the CNS
Nerves are the axons of neurons that may be afferents carrying sensations or efferents carrying motor commands.
What are the cellular components of the central nervous system?
Neuron & myelin sheath
Oligodendrocyte & Polydendrocyte
Astroglia & Microglia
What is the role of an oligodendrocyte?
Oligodendrocytes are a type of glial cell in the CNS
Their primary function is to produce and maintain the myelin sheath
What is the role of astroglia?
One of their primary roles is to provide structural support to neurons, helping to maintain the integrity of the brain’s architecture.
Astrocytes also regulate the extracellular environment by maintaining ion balance, particularly potassium ions, and removing excess neurotransmitters, such as glutamate, from the synaptic cleft
Astrocytes are also involved in metabolic support, supplying glucose and lactate to neurons and facilitating energy metabolism. During injury or disease, they can become reactive, leading to the release of inflammatory molecules and contributing to neuroinflammation.
What is the role of microglia?
Microglia are the primary immune cells of the CNS = maintains brain health
Have highly motile processes, allowing them to respond quickly to changes in their surroundings
Microglia are involved in synaptic pruning, a process crucial for normal brain development and function
What are the parts of a neurone?
Dendrite = input signal
Cell body = integration
Presynaptic axon terminal = output signal
Post-synaptic dendrite = input of the next neurone
What are the 4 glial cells found in CNS and 2 glial cells found in PNS?
Ependymal cells
Astrocytes
Microglia
Oligodendrocytes
PNS = Schwann cells and Satellite cells
What is the role of ependymal cells, and where are they found??
Lines the chambers in our brain that secretes CSF
Generates cerebrospinal fluid (CSF)
When we age, what cognitive domains are most affected, and which are least affected?
Lose long-term memory and working memory
Keep vocabulary
Don’t deteriorate equally
What are the two frameworks to account for cognitive decline?
Unitary factor = one factor causes the difference between normal ageing and dementia
Multiple factor = distinct factors target different brain systems
What are two distinct factors that cause memory decline in ageing?
Disruption of executive function that influences memory
Decline in long term memory = declarative memory
How can a decline in executive function influence memory?
Because remembering often relies on controlled processing
What do we see primarily in the frontal cortex of ageing patients?
White matter hyperintensities
What happens to Alzheimer’s patients, which impacts their memory?
Medial temporal atrophy
Hippocampal shape deformation (atrophy)
How does gene KO procedure occur in mice?
Targeting vector designed with gene
Targeting vector is introduced into embryonic stem (ES) cells via electroporation. Vector needs integrate into the ES cell genome through homologous recombination
Selection of KO cells with chosen marker
Successful KO cell injected into blastocyst and implanted in foster mother mouse
Chimeric mice are born and typically have a mix of cells with the knockout gene and normal cells. These chimeras are then bred with normal mice to produce offspring. The goal is to obtain mice that inherit the knockout gene
What is the difference between Cre recombinase and Flp recombinase?
Flp originates from yeast and recognizes FRT (FLP Recognition Target) sites.
Can be used together = dual recombinase strategy
What is the Neo cassette used for?
Selection marker
Confers resistance to neomycin or related antibiotics
After the targeting vector integrates into the genome, cells can be cultured in the presence of the antibiotic. Only those cells that have successfully integrated the Neo cassette will survive and proliferate, allowing researchers to isolate and expand the modified cells.
What is the need for temporal control of site-specific recombinase activity?
The goal of adding temporal control to SSR activity to enable the induction of genetic changes late in embryogenesis and/or in adult tissues (as opposed to at the onset of recombinase expression)
What are OPCs?
They are Oligodendrocyte precusor cells
OPCs generate mature myelinating oligodendrocytes
What is NG2 also known as?
CSPG2
What are the roles of NG2 and PDGFRalpha?***
What happens when OPCs commit to becoming oligodendrocytes?
NG2 expression is turned off when OPCs commit to becoming oligodendrocytes
What are the stages that precede mature oligodendrocytes?
Neural stem cell
Polydendrocyte (OPC)
Premyelinating oligodendrocyte
Myelinating oligodendrocyte (mature)
What is white matter and grey matter?
White = composed mainly of myelinated axons. Myelin sheath facilitates faster communication between different brain regions and between the brain and spinal cord. White matter is found in the deeper areas of the brain and surrounds the grey matter in the spinal cord.
Grey = primarily consists of neuronal cell bodies, dendrites, and unmyelinated axons. It is involved in processing and transmitting information and is found in the brain’s cortex and the inner regions of the spinal cord.
Wht is mGFP used to label?
Newly formed myelin sheaths in mature and middle aged mice
4-6months = mature
13-17months = middle-aged
What are the possible reasons for myelin declines at 18months?
Myelin degeneration
Inefficient myelin renewal
What is the stability of pre-existing myelin sheaths in mature adult mice?
Majority of myelin sheaths generated before 3 months = stable over the next 10 months
What is the role of tamoxifen in recombination?
In genetic studies, tamoxifen is used to induce recombination in mouse models utilizing the Cre/LoxP system. It activates a modified Cre recombinase (CreERT2) by binding to it, allowing the enzyme to function. This activated Cre recognizes loxP sites flanking a target gene, leading to its excision or modification. This approach enables precise control over when and where genetic changes occur, facilitating the study of gene functions at specific developmental stages or in particular tissues. Tamoxifen thus plays a key role in enabling controlled and reversible genetic manipulations in research.
What is the hippocampus crucial for?
Memory storage
What is Olig2 and its function in OPCs?
An important transcription factor in regulating the differentiation of OPCs
What happens when Olig2 is deleted?
Decrease in new myelin formation and myelin sheaths
Does not change number of mature oligodendrocytes and microglia in brain
What does Clemastine treatment do?
Enhance myelination and preserve spatial memory capacity in water maze test
What other function do oligodendrocytes provide other than myelination?
Provide metabolic support for neurones
What are the roles of astrocytes?
Provide trophic support for neurons
Promote formation and function of synapses, Prune synapses by phagocytosis
Fulfil a range of other homeostatic maintenance functions
How are A1 and A2 reactive astroyctes induced?
Injection of LPS causes brain inflammation = A1
Middle cerebral artery occlusion to induce ischemia = A2
What effects on the brain do A1 and A2 types have?
A1s highly up-regulate many classical complement cascade genes previously shown to be destructive to synapses, so we postulated that A1s might be harmful
In contrast, A2s up-regulated many neurotrophic factors and we thus postulated that A2s are protective. Consistent with this latter possibility, previous studies have provided evidence that reactive astrocytes induced by ischemia promote CNS recovery and repair
Can A1 reactive astrocytes be produced without microglia?
No
In KO mice that don’t have microglia, A1s were not induced after LPS injection
Can astrocytes in culture respond to LPS?
No
Rodent astrocytes lack receptors and downstream signaling components required for LPS-activation (TLR4 and MYD88)
What cytokines induced a PARTIAL A1 phenotype?
Astrocytes were cultured with all three cytokines (IL-1a, TNFa, C1q), astrocytes exhibited an A1 phenotype nearly identical to the A1 phenotype induced by LPS in vivo.
All three of these cytokines are highly expressed specifically by microglia13,15, again suggesting a critical role for microglia in inducing A1 reactive astrocytes.
How did they use coculture to confirm microglia induced A1 reactive astrocytes and which cytokines?
- Control microglia conditioned media
- LPS-activated microglia conditioned medium
Only (2) strongly induced A1
Levels of Il-1α, TNFα and C1q were all significantly elevated after microglial activation.
Il-1β secretion also increased in LPS-activated MCM, but was unable to induce expression of A1 transcripts
How did they ensure no other factors induced A1?
Used neutralizing antibodies against IL-1a, TNFa and C1q
Does cessation of Il-1α, TNFα, and C1q signaling enable A1 reactive astrocytes in vitro to revert back to resting astrocytes or is the A1 phenotype stable?
To find out, we removed all three cytokines from A1 cultures, and added neutralizing antibodies to all three to make sure they were fully inhibited. After 7 days, we assessed levels of A1 transcripts and found the A1 phenotype remained.
Could genetic deficiency of Il-1α, TNFα, or C1q be sufficient to prevent A1 astrocyte reactivity in vivo?
First we checked if single knock mice (Il-1α−/−, TNFα−/−, or C1q−/−) were still able to produce neuroinflammatory reactive microglia following systemic LPS injection
Each knock-out mouse had significantly decreased A1 astrocyte reactivity
Additionally, we looked at double (Il-1α−/−TNFα−/−) and triple knock-out mice (Il-1α−/−TNFα−/−C1q−/−) and saw decreases in A1 reactivity, with triple knock-out animals having no response following systemic LPS injection
Microglia from these same knock-out mice still upregulate inflammatory mediators in response to LPS injection, but simply fail to release A1 initiators
Taken together our data show that microglia-derived Il-1α, TNFα, and C1q work together to mediate A1 reactive astrocytes.
A1 reactive astrocytes lose many normal astrocyte functions, what are these functions?
A1 produce fewer synapses that have weaker postsynaptic excitatory currents
A1 lose phagocytotic capacity
A1 induce death of neurones and oligodendrocytes
What effect do A1 deficiencies in phagocytosis have?
Deficiencies in phagocytosis of both synaptosomes and myelin debris in culture
This deficiency can also influence efficiency of synaptic pruning in vivo, and suggest that A1s may well lose the capacity to clear myelin debris in vivo, an important area for future investigation
What effect do A1 have on OPCs?
Not toxic but A1s were able to slow their differentiation and division
How do A1s induce death of neurones and oligodendrocytes?
A1s secrete a soluble toxin that rapidly kills a subset of CNS neurons and mature oligodendrocytes, but not other CNS cell types
What was found out about C3-positive A1 in human disease?
Complement component C3 is not expressed in A2 so good marker to track A1
A1-like reactive astrocytes are present in most major neurodegenerative diseases, where they are likely to help to drive neurodegeneration.
