Energy Metabolism in the Brain II

Question 1

What is the main function of astrocytes? (1)

Answer 1

regulating synapse – ‘’tri-partite synapse’’

Question 2

Aqp4 info (4)

Answer 2

water channel -> capable of taking up K+ ions

located at end of astrocytes -> directly connect to the blood vessels

role: maintaining fluid balance in the brain
- periods of fluid swelling = life threatening

Question 3

Astrocyte protein shuttling egs (4)

Answer 3

image:

• H+ pump: removes H+
• NHE1 (Na/H exchanger): Na+ enters and H+ leaves
• protein shuttle: has MCT1/4 to remove H+ and Lac-
• bicarbonate transporter -NBCe1 adds/removes HCO3- and Na+ AND PROTONS

Question 4

Astrocyte transporters- neurotransmitters (1)

Answer 4

neurotransmitters transporter: uptake mechanism to clear from synaptic cleft into the intracellular space

Question 5

Astrocytes + neuron - glutamine + glutamate synthesis steps (6)

Answer 5

astro:
1) glutamate released from pre-synaptic cell into cleft in neuron
2) uptaken by EAAT transporters by astro
3) converted to glutamine (also made via TCA cycle + conversion in astro.)
4) pr-cursor released from astro to neuron to make glutamate

neuron:
5) glutamine -> Glutamate via glutaminase
6) released and acts on post-synpatic membrane

Question 6

Linking the Glutamate-glutamine cycle (2)

Answer 6

neuron energy cycle - TCA cycle makes glutamate that is used

astroglial energy cycle = TCA cycle makes glutamine

Question 7

Astrocyte’s release of chemicals (4)

Answer 7

• uptake GABA from pre-synaptic cleft via GABA transporter1 + 2
• release:
  Glutamate
  Purines (ATP) -> main source of energy released but used as glial neurotransmitter instead of fuel!!!!
  GABA
  D-serine
  GFs (BDNF)
  Cytokines (TNFα)
• release other things at nodes of Ranvier via ca2+ dependent process

Question 8

Astrocyte to Neuron Lactate Shuttle info (3)

Answer 8

image
capillary -> astrocyte -> <-> <- neuron

• capillary positioned well to take up blood + gap b/w cap + astrocyte is key as the cell can detect changes in glucose
• neuron is positioned to take up metabolites

Question 9

Capillary to Astrocyte to Neuron Lactate Shuttle steps (8)

Answer 9

cap:
1) glucose transported via 2 glut r’s to astrocyte ( + leaves capillary normally too via GLUT)

astro:
2) glucose undergoes glycolysis + glycogenesis
3) makes pyruvate (ADP -> ATP)
4) pyruvate -> lactate (LDH5)
5) lactate via MCT1/4 leaves + enters neuron via MCT2
also (H+ + HCO3- <-> CO2) + NBCe1 (Na+)

neuron:
6) lactate -> pyruvate via LDH1
7) pyruvate in TCA -> CO2
8) CO2 in b/w + into astro
(also has glucose entering norm via glut)

Question 10

what’s interesting about glycogen + astrocytes? (2)

Answer 10

astrocytes are the only cells in the brain to store glucose as glycogen (which undergoes glycolysis to produce lactate and then glucose) as a result of neural activation.

Question 11

Astrocyte lactate - signalling steps (3)

Answer 11

astrocyte lactate acts as a signalling molecule
eg in ischaemia

1) external stimuli -> lactate released by astrocytes
2) = increased firing rate of noradrenergic neurons
3) released of neurotransmitters

Question 12

Energy metabolism is coupled with ATP facts (5)

Answer 12

• Glucose metabolism provides the fuel
• 95% glucose used in production of ATP
• Astrocytes = arguably the main source for the physiologically released ATP in the CNS
• Decreased ATP affect proper synaptic functioning
• Astrocytes = also central for energy consumption, neurotransmitter release and reactive oxygen species (ROS) production in the nervous

Question 13

purines vs pyrimidines + astrocytes (4)

Answer 13

Purines and pyrimidines = fundamental elements for storage + transfer of energy in cells (release ATP to communicate)

• Astroglial ATP activate purinoceptors on neurons, microglia, oligodendrocytes + blood vessels
• P2X are ligand gated
• P2Y is G-protein couple

Question 14

Purinergic signalling steps - ATP (5)

Answer 14

1) astrocytes release small amount of ATP as signal

2) ATP activate purinoceptors (P2X + P2Y)

3) ATP degraded (take off p group) -> ADP via CD39

4) ADP degraded (remove p group) -> AMP via CD39

5) AMP takes off last p group -> adenosine via CD73

Question 15

What does P2X do? (1)

Answer 15

influx/efflux of Na+, Ca2+ or K+

Question 16

What does P2Y do? (1)

Answer 16

when there are changes to Ca2+, cAMP (up or down)

Question 17

What does P1 do? (1)

Answer 17

also coupled to cAMP (up or down)

Question 18

Astrocyte-derived ATP drives breathing facts + results (3 +2)

Answer 18

• Reductions in pH, caused by high CO2 causes astrocytic ATP release
• Biosensor
• Increases calcium in astrocytes in the brain stem seen via ca2+ spike
• can block via Apyrase = ATP degrading enzyme -> no calcium spike here

=> suggesting that ATP release from astrocytes in response to a decrease in pH = neuronal activation

=> activating astrocytes optogenetically - can conclude that astrocyte derived ATP release drives neighbouring neurons to drive breathing

Question 19

Purinergic receptors in dementia - experiment (4)

Answer 19

• Isolated microglia from human brain
• Measured P2X7 receptor (most common in Alzheimer’s)
• P2X7 activated by high ATP concentrations
• Permeable to Na+, Ca2+ and K+ = sig depol

-adding amyloid beta to microglia = drives sig increase in P2X7

Question 20

P2X7R activation increases inflammation - how? (3)

Answer 20

• key cytokine: IL1-beta

-P2X7 basically causes NLRP3 inflammasome activation
= cytokine release + pyroptosis (DAMP)
= inflammation

Question 21

ATP – mediated microglial chemotaxis (5)

Answer 21

• Patch pipette contains ATP = attracts microglia
• Lysosomes contain ATP
• ATP is a key DAMP
• Lysosomal Membrane Protein 1
• ATP induces lysosome secretion – seen via LAMP1 staining = more ATP
  = ATP induced ATP release

Question 22

Traumatic Brain Injury (TBI) (3)

Answer 22

*Increased attention to TBI as a possible cause of chronic traumatic encephalopathy (CTE)

*Linked to Alzheimer’s, Parkinson’s + Motor neuron Disease

*Repeated head injuries has received a lot of media attention in recent years

Question 23

ATP-P2X7R axis in neurodegeneration (2)

Answer 23

image
modest stimuli:
= ca2+ influx, ATP production etc (cytoprotective function)

excessive stimuli:
= ROS, Ca2+ overload + microglial activation (toxic function)

Question 24

What’s the importance of Studying Brain Metabolism? (4)

Answer 24

Understanding of energy supply for brain function

• Understanding of disease processes and potential treatment
• Appreciate the complexity of brain development and plasticity
• Highlights new areas for diagnostic and therapeutic targets

Question 25

Measuring oxidative metabolism - then vs now(4)

Answer 25

Traditionally, studies have focused on the net uptake of oxygen and glucose, measured through the arteriovenous difference of O2 content
- CMR = CBF(A−V)
Where cerebral metabolic rate (CMR) + cerebral blood flow (CBF)

now:
* Direct measure of oxygen consumption – Positron emission tomography (PET) or polarography,
- Radiotracers such as 18 F-2-deoxyglucose (FDG) (Sokoloff’s method)

• The blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI)

Question 26

Deuterium metabolic imaging (DMI) (3)

Answer 26

uses deuterium to trace + visualise metabolic pathways within the human

replaces H+ in molecules = allows tracking

-glycolysis + TCA etc
- uses in cancers etc.

Question 27

In vitro studies - ways (5)

Answer 27

• Primary cultures
• Co-cultures
• Brain slices
• Synaptosomes
• Isolated mitochondria
• latest technique = seahorse

Question 28

In vivo Imaging Studies (5)

Answer 28

*Nuclear magnetic resonance spectroscopycarbon-13 (Carbon-13 NMR spectroscopy) -> non-invasive : looks at glutamate + pyruvate TCA cycle

*Optogenetics

*In vivo microdialysis - invasive (real-time) - TBI application

*Near-Infrared Spectroscopy (NIRS) - blood o2 etc.

*Magnetic Resonance Spectroscopy (MRS)