NEU 490 Quiz 1 Flashcards
Microglia – The sentinel of the central nervous system
Sentinel:
Microglial Functions in the Adult Brain Sick:
Role in healthy CNS:
Sentinel: constantly surveying for injury or insult like inflammation or infection - act as a first line in defense and clean up debris
Sick Functions:
- Myeloid phagocyte(to eat up debris or damaged tissue)
- Only innate immune cell of the NS in the CNS
- 5-12% of all cells in CNS are variable densities
- Immune defense and CNS maintenance
Role in healthy CNS:
- Development of CNS
- Connectivity
- CNS homeostasis throughout life
- Synaptic Plasticity
- Monitoring neuronal activity
- More than just diseased state
Location in the CNS
what % of CNS glia population?
how dispersed?
occupy what territory?
what happens after pathological event?
what happens during transformation?
have the capacity for what?
can have local what? can recruit who?
- Constitutes 20% of total CNS glia population, on average 10,000 microglia per mm3
- In the mature brain, they are found almost evenly dispersed throughout the CNS - Resident immune cell and play role of multiple peripheral immune cell
- Each cell seems to occupy a defined territory so don’t overlap
- After a pathological event (injury or invasion of pathogens), these cells undergo a transformation
- Transformed cells acquire amoeboid shape
- Have the capacity to migrate(microglia can move towards threat), proliferate, and phagocytose
- Can have some local proliferation and recruit circulating macrophages → insert into network of microglia
Our CNS Immune Cell
network of surveillance cells is called? responds to?
who is first line of defense?
what kind of cells? what do they release?
Pro- and anti-inflammatory?
- Network of surveillance cells - sentinel
respond to slightest alteration (pathogen/invasion/damage) in their environment - Resident immune cells – first line of defense in CNS
- Antigen-presenting cells(present to T-cells and eat up debris), phagocytose debris, communicate with nearby neurons. Perform fixes of several peripheral innate immune cells, Release cytokines and ATP
- Pro- and anti-inflammatory – distinct morphology depending on activation state. Can be beneficial for
—- Beneficial to repair
—- Inflammation → brings in more immune cells
—- Phagocytose(is the process by which a cell uses its plasma membrane to engulf a large particle)
what is synapse pruning?
What are some potential reasons for synapse pruning, during development and adulthood?
During development: synaptic pruning - getting rid of inactive synapse
In adults: maintenance of neural circuits, modification of connections – conserve energy (use it or lose it) depletion of microglia significantly reducing plus myelination
Microglial contributions to adult brain function include:
Adjusting neuronal firing rates to optimize network properties - sculpt activity like nitric oxide
Producing neuromodulatory factors that support synaptic plasticity and learning - creation of new synapses and pro growth factors
Responding to inflammation, disease states, or injury, in both protective and deleterious ways - improve recovery or impede recovery and reduce positive outcomes
Additional functions in synapse remodeling, neuronal function, supporting myelination, vasculogenesis(vascular formation and facilitate optimal vascular complexity), and BBB permeability(BBB integrating when active impairment of BB fix hyperpermeability and aberrant infiltration)
Microglia constitute _________________ percent of all cells in the brain and ________________ percent of the glia population
5-12%, 20%
What are some of the functions of microglia in the developing nervous system?
synaptic pruning, synapse remodeling, neuronal function, supporting myelination, vasculogenesis, and BB permeability
True or false: Depletion of microglia leads to increased vascular branching and complexity
False
Origin Of Microglia? YK? BBB start?
Microglia are of myeloid origin, arising from yolk sac (YS) primitive macrophages, which persist in the CNS into adulthood.
Primitive macrophages exit the yolk sac blood islands at the onset of circulation and colonize the neuroepithelium from E9.5 to give rise to microglia.
BBB stars at 13 days and isolate developing brain from hematopoiesis
Numbers increases throughout the first two postnatal weeks via in situ proliferation
Embryonic microglia expand and colonize? Until full adulthood?
During inflammation - for example bone marrow?
Microglia reside?
Embryonic microglia expand and colonize the whole CNS until adulthood, and locally proliferate, particularly during inflammatory conditions.
Until full adulthood maintain via local proliferation and during steady state
During inflammation - for example bone marrow, transplant recruitment of monocytes and other bone marrow derived progenitors that can supplement microglia population to some extent
- We do not understand yet whether these cells persist and become integrated in the microglial network, or are a temporary addition to the endogenous population.
Microglia reside in the brain throughout life, and maintain their numbers through a process of self-renewal
Which of the following are ways you can attempt to differentiate between a microglia and a macrophage?
Examine morphology shape/size, determine location of cell, follow them throughout development to determine source
Discovery of Microglia who?
Pio del Rio-Hortega - Father of modern microglia biology in early 1900’s - Student of Cajal
Microglial Structural Diversity – reflecting brain area populated
Microglial Activation States
Old View VS New View
microglial activation is?
The activation states of microglia are hotly contested. For many years it was thought that they primarily existed in two different states – M1, or pro-inflammatory, or M2, or anti-inflammatory.
New research has thrown that categorization into question.
New understanding and state-dependent microglial activation
Old View: rigid, dichotomic categorization - m2 vs m1, resting vs activated, ramified vs ameboid, anti vs pro inflammatory
New View: based on coexistence of multiple states - proteomic, metabolomic, transcriptomic, morphological, epigenetic
Ramified (Resting) Microglia - More accurately BLANK
Ramified are highly?
What type of cell body?
Important for?
Mobility?
Ramified (Resting) Microglia - More accurately surveillance
- smaller cell bodies and constantly moving at 360 degree to assess the area
Ramified microglia are highly branched with multiple primary and secondary processes
Small somata (cell bodies) and fine ramifications
Extend far away from cell body long and branched
Surveillance microglia – important for maintaining homeostasis
Processes constantly moving - located close to neurons and other glia, Ramified microglia have fine processes capable of moving around
Ramified (Resting) Microglia
“Resting” while working
Pinocytosis?
First line?
Assessing?
DAMP/PAMP?
Pinocytosis: sipping away at the ECF → taking up small amounts of extracellular fluid as samples to see what is going on nearby as the first line of defense
- extracellular fluid to see if damage or anything being released to survey environment
First line of defense, so constant surveilling is important → prompt response to threats
Assessing neuronal activity, potential insults, or injury
Have receptors for neurotransmitters, have DAMP (damage associated molecular patterns - things released by damaged cells) receptors, have PAMP receptors (pathogen associated molecular patterns like bacteria, virus, and fungi)
Activated Microglia (mobile)
Change shape and size in response to? Become?
Migration toward?
Primary goal?
Factors?
Phagocytes?
Busy hypertrophic and release cytokines and growth factors and try to repair and not reach cell death
Change shape and size in response to threats – become large and bushy → hypertrophic
- In response to changes in extracellular environment (pH, ions, DAMPS and PAMPS)
- In response to loss of calcium signals - microglia have intracellular calcium
Directional migration toward site of injury - movement of microglia
Primary goal: repair and recruitment
Neurotrophic factors (growth factors) and pro- inflammatory cytokines (recruit other cells)
We are not phagocytes yet bc it is still trying to repair not at a lost cause
Reactive Microglia
What shape/ other name?
Phagocytic?
1,2,3?
Ameboid shaped - small round fat
Reactive circles and engulf or eat up any dead tissue and will not release cytokines bc past the point of no return
Phagocytic: ingestion of particulate matter from the ECF - taken to intracellular compartments of microglia to destroy
- Development: Synaptic stripping or pruning - change in morphology even though this is normal - change in morphology aids in change in function
- Damage: Clearance of debris (pieces of dead cells or pathogens)
- Disease: Participant or Proponent(is phagocytosis a good thing? Sometimes for example Alzheimer’s?) - Pieces of dead cells or pathogens
Microglia that are round and have little to no processes are BLANK, ones that are large and bushy are BLANK, and ones with small cell bodies and thin longer branched processes are BLANK.
Reactive/Ameboid
Activated/Hypertrophied
Resting/Ramified
Ramified:
Ameboid:
Ball-and-chain:
Hyper-ramified:
Bulbous tips:
Honeycomb:
Jellyfish:
Trains of rods:
Ramified: Highly branched, Multiple primary and secondary processes, Surveillance
Ameboid: Highly rounded, Phagocytose and migrate
Ball-and-chain: Tip if a ramified can phagocytose small amounts of material like synapses or apoptotic bodies,
Synaptic pruning converses energy
Hyper-ramified: Increased branching points, On our way to activated bushy state and cell body and process increase
Bulbous tips:
Important for ATP sensing, On ramified microglia
Honeycomb: Network, BBB leakage
Jellyfish: Honeycomb translation when lots of cell death
Trains of rods: Elongate soma, Attach in trains, Respond to injury
You are assessing microglial morphology in different pathological conditions. For each of the following situations, which activation state is the microglial cell in? (Use resting, activated, and reactive)
Cell appears rounded and fat
Cell releases pro-inflammatory cytokines
Cell is taking up extracellular fluid
Cell is bushy and large
Cell is phagocytosing dead cells
Cell’s processes are constantly moving around in 360-degrees
You damage tissue, see cells moving towards the source
Cell appears rounded and fat - reactive
Cell releases pro-inflammatory cytokines - activated
Cell is taking up extracellular fluid - resting, activated, and reactive
Cell is bushy and large - activated
Cell is phagocytosing dead cells - reactive
Cell’s processes are constantly moving around in 360-degrees - resting
You damage tissue, see cells moving towards the source - activated
What are some examples of DAMPs that neurons might release when damaged or dying?
What are TWO examples of receptors on microglia activated by DAMPs or PAMPs, and what is the consequence of their activation?
What are some examples of DAMPs that neurons might release when damaged or dying? - mtDNA, histones, heat shock proteins
What are TWO examples of receptors on microglia activated by DAMPs or PAMPs, and what is the consequence of their activation? - toll like receptors (TLRs), pattern recognition receptors (PRT)
Microglia During Development - Helper of Neuronal Development
Phagocytosis of apoptotic neurons?
Microglia induce programmed cell death?
Triggered via?
Mice lacking microglia can still?
Phagocytosis of apoptotic neurons:
- About half of the neurons that are created during development undergo apoptosis and microglia induce apoptosis triggering superoxide ions
- Over 50% of neurons undergo apoptosis before adulthood → in regions where microglia are closely situated
Microglia induce programmed cell death - Superoxide ions → oxidative stress to induce apoptosis
- Triggered via CD11b and immune receptors during microglia-neuron interaction
- Possible other cells types can pick up slack
Mice lacking microglia can still remove apoptotic neurons, suggesting involvement of other cells
Trophic support of developing neurons does what?
Essential for?
Secretion of?
Secrete?
Neurotrophins are those factors that keep?
Trophic support(things that help neurons differentiate, grow, and survive) of developing neurons
Essential for survival and development of cortical layer V neurons → mice without microglia have thinner layers of cortex (the thicker layer of cortex is allows for more complexity and communication)
- Help control the size of neural precursor pools – affects cortical thickness
Secretion of growth factors
Secrete neurotrophins to induce programmed cell death → sculpting circuits
Neurotrophins are those factors that keep neurons alive and induce cell death
Neuronal Circuit Development uses the BLANK?
Blood vessels used for?
In which tissue? Begins which day?
Microglia connect sprouting blood vessels, promoting?
Depletion or absence of microglia leads to?
Guidance of developing vasculature (needed to have oxygen, nutrients, and then waste taken away)
During CNS development, blood vessels extent into the neuroectoderm to provide nutrients(glucose) and oxygen
Development of blood vessels used and routed in CNS tissue. Begins around 10 days post-conception in mice – coincides with microglial entry into neuroectoderm - blood vessels enter here to provide energy to keep the blood alive like connecting vasculature is something microglia does
Microglia connect sprouting blood vessels, promoting vessel branching
Depletion or absence of microglia leads to reduced vascular growth, branching, and density
Microglia make direct contact with?
help modulate neuronal activity bc have?
Engulf and remove less active?
Depletion or absence of microglia lead to impaired?
Microglia make direct contact with pre- and postsynaptic structures → PSK-95 synaptic protein, microglia touching PSD-95 structures
Prolong their contact with active synapses, help modulate neuronal activity → can sense activity because have receptors for things released by neurons
Engulf and remove less active synapses, help contribute to plasticity – called synaptic pruning. Microglia synaptic pruning influenced by neuronal activity – complement( apart of innate immune system) system plays a role
Depletion or absence of microglia lead to impaired circuit formation which can lead to a decrease of complexity of synapses
For each of these ages during development on the right, what do you think microglia are helping with most at each of these stages?
1 month:
6 months:
2 years - now have all connection:
15 years (not shown):
1 month: Vascularization is the process of growing blood vessels into a tissue or organ to improve the supply of nutrients and oxygen, trophic support (to get increased number of neurons for stuff like cortical thickness)
6 months: refinement of synapses to expand cortex and increase connection and growth factor
2 years - now have all connection: pruning(get rid of any aberrant connections), induced apoptosis
15 years (not shown): maintenance of connections → maturation of circuits - immune surveillance - once have all neurons all about maintenance of the ones you want and removal the old ones you don’t want
Developing (wiring and pattering) VS
Adult (maintenance and surveying)
Developing (wiring and pattering): guidance of sprouting vessels, neurotrophic factors(growth factors), induction of apoptosis in neuronal subsets, phagocytosis of apoptotic neurons, synaptic pruning for circuit formation/maturation
Adult (maintenance and surveying): maintenance for nerve health and survivance, synaptic pruning for circuit formation/maturation, control of adult neurogenesis
Chronic Pain - Microglia are activated in the BLANK and which side?
Microglia are activated in the spinal cord in a number of experimental models of pain - mostly ipsilateral and not contralateral - large increase in number and change in morphology/shape with increase in concentration of different markers
Microglial activation in the spinal cord following peripheral nerve injury
Spared nerve injury is a model of chronic pain caused by?
Leads to which side pain?
increase of microglial activation throughout the white and gray matter of the spinal cord, with largest increase in the BLANK and severed axons have BLANK
Mechanisms of Microglial participation in central sensitization, which is?
Microglia are activated by increased neuronal activity at the synapse on?
Activated microglia can in turn activate other BLANK in a BLANK fashion
Spared nerve injury is a model of chronic pain caused by severing two of three branches of the sciatic nerve → common peroneal nerve is spared
Leads to ipsilateral chronic pain → same side as injury
Ipsilateral increase of microglial activation throughout the white and gray matter of the spinal cord, with largest increase in the dorsal horn → immediately after injury neurons with severed axons have excitotoxicity, microglia have all things like receptors where stuff will be released by damaged neurons like DAMPS
nerve pain due to tissue damage – increased excitation of dorsal horn neurons happens though things like LTP (enhanced synaptic strength) and disinhibition
Microglia are activated by increased neuronal activity at the synapse on second-order dorsal horn neurons
Activated microglia can in turn activate other microglia in a paracrine fashion → release stuff like proinflammatory cytokines
Additionally, microglia can release things that can directly activate second-order neurons in the dorsal horn → second order are sending pain sensation info to brain - ATP and cytokines release ATP that activate neurons
P2X4 (ATP receptors - located on microglia and neurons) receptors induced in spinal microglia gate BLANK
Allodynia?
Spinal injection of activated microglia induces BLANK BLANK
Mechanisms of Microglial participation in central sensitization: what is the loop?
Proinflammatory cytokines: produced predominantly by?
P2X4 (ATP receptors - located on microglia and neurons) receptors induced in spinal microglia gate mechanical allodynia after nerve injury
Nerve injury - P2X4R increase on ipsilateral side
Allodynia - Normally non-painful is painful in allodynia - can suppress allodynia when inhibit P2X4 activity
Spinal injection of activated microglia induces mechanical hypersensitivity
Mechanisms of Microglial participation in central sensitization: Excitatory loop after injury
- PG = prosti landons (can activate neurons and are the target of NSAIDS like advil)
- Nitric oxide can induce -NO = oxidative stress - which can lead to apoptosis
- Microglia worsening pain after injury
Proinflammatory cytokines: produced predominantly by activated macrophages and are involved in the up-regulation of inflammatory reactions. There is abundant evidence that certain pro-inflammatory cytokines such as IL-1β, IL-6, and TNF-α are involved in the process of pathological pain.
Stroke: face dropping, arm weakness, speech difficulty
There are Two Types of Stroke: Ischemic Stroke VS Hemorrhagic Stroke
reperfusion injury means?
Global ischemia?
Ischemic Stroke: Blood vessel block - brain deprived of blood
(~80% of all strokes)
Clots can form in the body and travel to the brain
Any tissue supplied by that blood vessel is starved of oxygen and nutrients
Hemorrhagic Stroke: Bursting of blood vessel - bleeding in brain
(~20% of all strokes)
Pressure build up of blood that starve brain area
reperfusion injury means lack of oxygen which can cause brain death and have a 3hr window
Global ischemia
Overall anoxia(absence of oxygen) which leads to global ischemia
How can you selectively reduce the presence of microglia?
-Knockout/knockdown
- Mac-1 saporin
-Drive expression of TK in microglia and macrophages using CD11b promoter
Are Microglia/Macrophages Important for Ischemic Injury or Repair? If knockdown microglia and then induce stroke
Result
Conclusion
Knockout(never have microglia then no neuronal circuits - distributing NS development) or knockdown mouse? Not the best option, bc NS won’t develop properly
Mac-1 saporin - is a cell detergent and breaks up fat of cell walls membrane - Mac binds selectivity to microglia - selectively kill microglia
Drive expression of TK in microglia and macrophages using CD11b promoter.
Ganciclovir activates TK and kills cells - inducible knockdown
Are Microglia/Macrophages Important for Ischemic Injury or Repair? If knockdown microglia and then induce stroke:
Result: Loss of microglia/macrophages worsens ischemic stroke
Conclusion: Microglia/macrophage activation limits injury after stroke
Deleterious and induce chronic pain but useful in stroke
Microglia have a neuroprotective role in stroke, and a neurotoxic role in pain conditions. Which of the following could possibly be occurring in microglia during neuroprotection?
a. Release of interleukin-10 (IL-10)
b. Activation of the NfkB pathway
c. Release of Tumor Necrosis Factor alpha (TNF-alpha)
d. Upregulation of Interferon Regulatory Factor 4 (IRF4) expression
e. Clearing up debris from damaged cells
a. Release of interleukin-10 (IL-10) anti inflammatory cytokines
b. Activation of the NfkB pathway - proinflammation active in chronic pain and deleterious to recovery
c. Release of Tumor Necrosis Factor alpha (TNF-alpha) - proinflammatory and needed in pain so not protective
d. Upregulation of Interferon Regulatory Factor 4 (IRF4) expression - following stroke important for salvaging neurons
e. Clearing up debris from damaged cells
