Energy Metabolism in the Brain II Flashcards
What is the main function of astrocytes? (1)
regulating synapse – ‘’tri-partite synapse’’
Aqp4 info (4)
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
Astrocyte protein shuttling egs (4)
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
Astrocyte transporters- neurotransmitters (1)
neurotransmitters transporter: uptake mechanism to clear from synaptic cleft into the intracellular space
Astrocytes + neuron - glutamine + glutamate synthesis steps (6)
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
Linking the Glutamate-glutamine cycle (2)
neuron energy cycle - TCA cycle makes glutamate that is used
astroglial energy cycle = TCA cycle makes glutamine
Astrocyte’s release of chemicals (4)
- 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
Astrocyte to Neuron Lactate Shuttle info (3)
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
Capillary to Astrocyte to Neuron Lactate Shuttle steps (8)
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)
what’s interesting about glycogen + astrocytes? (2)
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.
Astrocyte lactate - signalling steps (3)
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
Energy metabolism is coupled with ATP facts (5)
- 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
purines vs pyrimidines + astrocytes (4)
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
Purinergic signalling steps - ATP (5)
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
What does P2X do? (1)
influx/efflux of Na+, Ca2+ or K+
What does P2Y do? (1)
when there are changes to Ca2+, cAMP (up or down)
What does P1 do? (1)
also coupled to cAMP (up or down)
Astrocyte-derived ATP drives breathing facts + results (3 +2)
- 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
Purinergic receptors in dementia - experiment (4)
- 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
P2X7R activation increases inflammation - how? (3)
- key cytokine: IL1-beta
-P2X7 basically causes NLRP3 inflammasome activation
= cytokine release + pyroptosis (DAMP)
= inflammation
ATP – mediated microglial chemotaxis (5)
- 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
Traumatic Brain Injury (TBI) (3)
*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
ATP-P2X7R axis in neurodegeneration (2)
image
modest stimuli:
= ca2+ influx, ATP production etc (cytoprotective function)
excessive stimuli:
= ROS, Ca2+ overload + microglial activation (toxic function)
What’s the importance of Studying Brain Metabolism? (4)
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
Measuring oxidative metabolism - then vs now(4)
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)
Deuterium metabolic imaging (DMI) (3)
uses deuterium to trace + visualise metabolic pathways within the human
replaces H+ in molecules = allows tracking
-glycolysis + TCA etc
- uses in cancers etc.
In vitro studies - ways (5)
- Primary cultures
- Co-cultures
- Brain slices
- Synaptosomes
- Isolated mitochondria
- latest technique = seahorse
In vivo Imaging Studies (5)
*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)
