Microglia Function

Question 1

What type of neurodegenerative and developmental disorders can microglia initiate

Answer 1

AD
PD
Autoimmune disease
MS
ASD
Schizophrenia

Question 2

What is the abundance of microglia in the CNS

Answer 2

5-12%

Question 3

Features of microglia

Answer 3

Highly motile, extend and retract to monitor environment (tiling)
Large regenerative capacity
Regionally diverse

Question 4

CNS macrophages

Answer 4

Microglia
Border associated macrophages (BAM)

Question 5

Development of microglia

Answer 5

Formed during haematopoiesis in the extra embryonic yolk sac
Microglia enter before BBB formation
Microglia cannot be replaced

Question 6

Microglia turnover rate

Answer 6

8-41 months
Long lived

Question 7

How can microglia be depleted

Answer 7

Small molecule inhibition
Genetic ablation

Question 8

Microglia specific genes

Answer 8

Cx3cr1
Tmen119
P2ry12
Sall1

Question 9

Microglia based therapy

Answer 9

Recovery of healthy functions
Eliminate ‘toxic’ microglia
Cross correction of lost enzymes

Question 10

Benefit of microglia based therapy

Answer 10

Formed from iPSCs and blood derived substitutes
Microglia replacement reverses ongoing disease progress and prevent progression

Question 11

Method to study microglia

Answer 11

Single cell technology (Dumas et al., 2021)

Question 12

What is AAV (adeno-associated virus)

Answer 12

Do not activate microglia
Cloned with cas9/sgRNA to knock down genes only in microglia
Cre ER/loxP system allows time dependent in/activation

Question 13

Why are AAV capsid proteins used

Answer 13

Traditional AAVs for gene therapy target neurons not microglia
Direct evolution forms AAV capsids (viral protein shell) which target microglia
Variants: AAV-cMG and AAV-MG deliver genes to microglia

Question 14

What determines microglia density and molecular state

Answer 14

Pyramidal neurons (somatosensory cortex)

Question 15

Main functions of embryonic and post natal microglia

Answer 15

Cell death and apoptosis (NGF/ROS/TNF)
Axon outgrowth and fasciculation (f: glutamatergic axons) (o: dopaminergic axons)
Cortical interneuron migration
Neuronal cell survival and oligodendrocytes
Synaptic spine formation and presynaptic pruning

Question 16

how do astrocytes and microglia optimise function (synapse formation and neuronal signalling)

Answer 16

microglia are ramified
surveilence motility
secretory
P2Y12high

Question 17

how do astrocytes and microglia optimise survival (physical barrier and engulf pathogen)

Answer 17

microglia are ameboid
highly phagocytic
directionally chemotactic
P2Y12low

Question 18

old view vs new view

Answer 18

old: rigid, dichromatic organisation

new: coexistence of multiple states

Question 19

when do microglia induce synapse formation

Answer 19

P8-10

Question 20

schafer et al., 2012

Answer 20

microglia prune synapses during circuit refinement
‘eat’ weak presynaptic terminals
more active synapses less likely to be targeted by microglia
complement system needed for microglial pruning (CR3)

Question 21

how do microglia influence connectivity in the visual system

Answer 21

immature with overlapping projections then mature with separate projections
in dLGN

Question 22

complement activation

Answer 22

start: expression and activation of C1q
major convergence at C3
C3 cleavage into opsonin (C3b and C3a)
opsonisation with C3b causes elimination of target structure by phagocytes

Question 23

how do microglia refine retinogeniculate projections

Answer 23

-competition between strong and weak synapses
-complement upregulated in RGCs by astrocyte signalling
-local activation of complement system causes deposition of C3b on weaker synapses (eat me) phagocytes by microglia expression C3 receptor
-C3b and CD47 is a dont eat me signal for stronger synapses

Question 24

what is the punishment model of synaptic stabilisation

Answer 24

weaker synapses fail to establish a protective molecular signal
microglia engulf via phagocytosis

Question 25

how do microglia promote synaptic formation

Answer 25

actin accumulation precedes filopodia formation

Question 26

how do microglia control neural circuits involved in sex specific behaviours

Answer 26

brain masculisation
epigenetic supression in brain feminisation

Question 27

how does sexual identity influence microglia development

Answer 27

males and females have distinct transcriptomic signature of microglia

Question 28

sex differences in psychiatric disorders

Answer 28

ASD 4-5x higher in males
ADHD 2-3x higher in males

Question 29

early life programming of sex differences

Answer 29

activation of sex specific circuits for mating
modulation of social and emotional behaviour
changes in cognitive learning strategies

Question 30

rodent critical window

Answer 30

onset of gonadal steroid production in males during birth
no steroidogenesis in females
expression of chromatin modifying enzymes and DNA methylases

Question 31

how do males have social play

Answer 31

adolescent social play correlates to D1r expression
D1r receptor removed by microglia in males (less social play)
if C3+ D1r synapses and C3R+ receptor microglia abolished (social play is maintained)

Question 32

how does negative feedback occur via microglia

Badimon et al., 2020

Answer 32

ATP released by active synapses and associated with astrocytes
ATP converted to AMP then adenosine (ADO) by microglia

ADO suppresses pre and post synaptic neuronal excitability by reducing cAMP cia A1r receptor

Question 33

what do inhibitory interneurons and microglia inhibit

Answer 33

active neurons

Question 34

role of GABA receptive microglia prune inhibitory synapses

Answer 34

engulf inhibitory synapses
different behavioural changes in female and less engulfment in male GABA B2 receptor KO

Question 35

how do microglia enable plasticity

Answer 35

microglia endowed with IL-33 receptor upregulates/secretes enzymes degrading ECM