Interactiunea neuro-gliala in modelarea conectomului neuronal neuron-glie_Ana... · 2015-05-07 ·...
Transcript of Interactiunea neuro-gliala in modelarea conectomului neuronal neuron-glie_Ana... · 2015-05-07 ·...
Astrocytes marked with calcein-AM (green) in a cerebellar
granule cells culture, after oxygen-glucose deprivation.
Dr. Ana-Maria Zagrean Neuronal Cell Culture Lab
Interactiunea neuro-gliala
in modelarea
conectomului neuronal
Conf. univ. Ana-Maria Zagrean [email protected]
• Sistem nervos (SN): totalitatea celulelor din SN si a
conexiunilor dintre ele - morfologice, functionale
(electrice/metabolice), chimice si fizice…
• SN: cea mai mare diversitate celulara,
• SN: cea mai mare diveristate a conexiuilor/tipurilor de
semnalizare intercelulare…
If ‘‘the connectome’’ represents a complete map of
anatomical and functional connectivity in the brain, it
should also include glia!
Neuron, Aprilie 2015
White Matter Connections Obtained with MRI Tractography From: Gigandet X, Hagmann P, Kurant M, Cammoun L, Meuli R, et al. (2008) Estimating the Confidence Level of White Matter Connections Obtained with MRI Tractography. PLoS ONE 3(12): e4006. doi:10.1371/journal.pone.0004006
Connectomics - Human Connectome Project
http://www.neuroscienceblueprint.nih.gov/connectome/index.htm
Charting neural connections is unlikely to deliver understanding perception,
consciousness, how the brain produces memories
BRAIN project risk to failure – it should consider that although the human brain
contains roughly 100 billion neurons, it contains billions more glia, non-electrical
brain cells, residing outside the neuronal 'connectome'.
Dismissed as connective tissue when they were first described in the mid-1800s, glia
have long been neglected in the quest to understand neuronal signalling.
‘Connectomica’ in sistemul nervos: mai mult
decat o problema de conexiune interneuronala….
20% din debitul cardiac Conexiuni interneuronale
Semnalizare electrica…
…glial trees have exactly the same level of detail and importance as neural trees,
yet they are ignored in the aspirations of the connectomists.
…grey matter might be imagined more like an astrocytic christmas tree farm
superimposed on a neural rainforest.
Risks of science… Myths in Neurosciences:
Past and Present!
The prejudice that the relation between
neuroglial fibers and neuronal cells is
similar to the relation between connective
tissue and muscle or gland cells, that is, a
passive weft for merely filling and support
(and in the best case, a gangue for taking
nutritive juices), constitutes the main
obstacle that the researcher needs to
remove to get a rational concept about
the activity of the neuroglia.
S Ramon y Cajal
Nobel Price in Medicine 1906
Discoverer of the neuron
(Blocks of brain soaked in silver nitrate)
Past…
• Research is revealing that glia can sense neuronal activity and control it,
operate in diverse mental processes, as formation of memories.
• Glial cells have a central role in brain injury and disease, they are even at the
root of various disorders — such as schizophrenia and Alzheimer's —
previously presumed to be exclusively neuronal.
• Yet… the word 'glia' was not stated in any of the announcements of the
BRAIN Initiative, nor written anywhere in the 'white papers' published in
2012 and 2013 in prominent journals outlining the ambitious plan
• … urgent need for the community of neuroscientists behind the
initiative to expand its thinking!
Present…
Cellular diversity of the brain
• Human brain ~100 billion neurons and several times as many
non-neuronal cells – the glial cells.
• Nervous system has a greater range of distinct cell types than
any other organ system, categorized by
– morphology,
– molecular identity,
– physiological activity
Glial Cells – Non-neuronal Cells • Make up about 90% of the cells in the nervous system but 20%-
50% of the volume, depending on the nervous system region.
• Cannot generate or transmit nerve signals, but involved in
information processing.
• Responsible for the physical and metabolic support of the neurons,
but not only…
Types of Non-neuronal Cells
Four types associated with CNS:
-Astrocytes, oligodendrocytes,
microglia, and ependymal cells
Two types associated with the
peripheral nervous system
-Satellite cells and Schwann cells.
Astrocytes (red) and immature oligodendrocytes (green), types of glial
cell, intertwine with neurons (blue) from the brain's hippocampus. Nature 501, 25–27 (05 September 2013)
All major glial cell types in the brain - oligodendrocytes, microglia and astrocytes -
communicate with each other and with neurons by using chemical neurotransmitters
and gap junctions, channels that permit the direct transfer between cells of ions and
small molecules.
Neuropil - any area in the nervous system composed of mostly
unmyelinated axons, dendrites and glial cell processes that forms a
synaptically dense region containing a relatively low number of cell bodies.
Hippocampus
Glial Cell Functions:
Structural support, “glue”
Metabolic support (lactate shuttle)
Insulation (oligocytes)
Destroy pathogens, remove debris (microcytes)
In devolopment, guide axons
Release gliotransmitters (ex glut, ATP)
Regulate extracellular environment
Clear transmitters from synapse, ion homeostasis
K+ uptake vs. spatial buffering
Oligodendrocytes (green)
• Form myelin electrical insulation, increasing conduction velocity by at least
50 times.
• Provide vital metabolic support for axons (purple).
Orthmann-Murphy, J. L. et al. J. Neurosci. 2007;27:13949-13957
Myelin, oligodendrocyts and network of intercellular channels
between astrocytes (A) and oligodendrocytes (O)
Microglia (green)
•Highly motile and responsive to nervous-system injury and infection.
•Monitor electrical activity in neurons and prune synaptic connections (red).
•Involved in almost all nervous-system diseases and in certain psychiatric conditions.
Microglia - 10-15% of all cells found within the brain
- the immune cells/resident macrophages of the brain and spinal cord (main
form of active immune defense in the central nervous
system, constantly scavenging the CNS for damaged neurons and
infectious agents and decreasing inflammation).
- release substances that stimulate repair.
- prune back synapses and rewire neural connections in a healthy brain
• ‘Synaptic pruning’ vs. apoptoza
• Pruning = indepartarea sinapsei inactive cu pastrarea
axonului si reorientarea catre alte sinapse, functionale
• Apoptoza=moarte celulara programata
• Scop:
-pastrarea preferentiala a sinapselor neuronale incluse
in retele functionale
-indepartarea neuronilor lezati/degenerati
-modelare functionala/plasticitate a sinapselor in scopul
imbunatatirii si/sau diversificarii functiei
Microglia
Astrocytes (red and green) influence nervous-system communication
and plasticity
•Primarily responsible for homeostasis of the central nervous system.
•Ensheath synapses, regulate neuronal excitability and synaptic
transmission.
•Respond to injury by secreting extracellular matrix proteins.
•Implicated in neurogenesis, cell migration, many neurological and
psychiatric disorders.
- Produce growth factors regulate morphology, proliferation, differentiation
or survival of neurons and glial cells
- Role in regulation of synaptic function. Volume transmission.
Neuron-glia connection. Network signalling - Can also undergo remodeling (Plasticity); astrogliosis in injury, neurodegeneration. - The fine distal processes are interposed between all neuronal elements. - Create a kind of synaptic island defined by its ensheathing processes.
-Processing information …
-Through perivascular processes astrocytes contribute to blood-brain barrier
and form "glymphatic" drainage system of the CNS.
-supplier of glutamine (neurotransmitters precursor).
-contribute to neuropathologies through mounting complex defensive
programme generally known as reactive astrogliosis.
Astocytes
Neurons alone provide only a partial explanation for complex cognitive processes,
formation of memories.
The complex branching structure of glial cells, integrating information from spatially
distinct parts of the brain and their relatively slow chemical (as opposed to
electrical) signalling in fact make them better suited than neurons to certain
cognitive processes.
Why are astrocytes important?
Different spatial and temporal
scales for neuronal and glial
activity…
Astrocytes marked with calcein-AM (green) in a cerebellar
granule cells culture, after oxygen-glucose deprivation.
Dr. Ana-Maria Zagrean Neuronal Cell Culture Lab
Premises for
neuron - glial cell - cerebral capillary unit
- Nervous system function ↔ cellular energetic status ↔
aerobic metabolism ↔ blood perfusion
- Brain vulnerability to hypoxia/ischemia
brain receives 15%-20% from CO
O2 brain consume – 20% from the whole body
consume (250 ml O2/min)
glucose brain consume – 25% from the whole body
Brain Vulnerability
• Aerobic metabolism:
-95% of brain ATP derive from cerebral oxidative
phosphorilation
-No energy stores in the brain (low glycogen…)
• Facts - blockage of cerebral blood flow results in:
- loss of consciousness in 10-20 sec
- irreversible cerebral changes in 3-5 min
The Magistretti Hypothesis
• Astrocytes anaerobically metabolize glucose to lactate
• Neurons aerobically metabolize lactate/pyruvate
Magistretti (2000) Brain Research 886:108
Physiological coupling of brain metabolism and neuronal activity:
Glutamate-induced glycolysis in astrocytes
phosphoglucokinase
As Neural activity there is an Energy requirement
To solve this…
Astrocytic uptake of Glutamate leads to> ADP leads to> Glycolysis within Astrocytic endfeet which finally leads to > Lactate delivered to neuron
Physiological changes linking neural and vascular responses
http://www.scholarpedia.org/article/Neurovascular_coupling
Typical CBF
response to
brief neural
activation.
(CBF)
BBB & Neurovascular coupling
• The human brain contains on the order of 100 million
capillaries containing a surface area of 12 m2.
• Nearly every neuron in the brain has its own capillary, with
an average distance from capillary to neuron of 8–20 µm
Neurovascular coupling
The no. of astrocytes increases with an increase in
brain size:
The glia/neurons ratio
- in the rat cerebral cortex ~0.4,
- in the human cerebelar cortex ~1.65.
Increased complexity of astroglia in humans –
throught size & complex process arborization
Neuroglia in neurovascular coupling
one human protoplasmic astrocyte contacts and integrates ~2 million synapses
residing in its territorial domain, whereas rodent astrocytes cover ~20,000–120,000
synaptic contacts.
Astrocytes form a barrier around the blood vessels in the brain (astrocyte
end feet contributes to the blood-brain barrier formation and function).
Blood Brain Barrier functions
• BBB = structural and functional barrier which impedes and regulates the influx of most compounds from blood to brain
• BBB formed by – brain microvascular endothelial cells
– astrocyte end feet
– pericytes
• BBB is essential for normal function of CNS – Regulates passage of molecules in and out of brain to maintain
neural environment.
– Responsible for metabolic activities such as the metabolism of L-dopa to regulate its concentration in the brain.
Neuroglia in neurovascular coupling
- an important glial function - isolation of the nervous tissue from the rest
of the body by the blood–brain barrier (BBB)
- The barrier function of the cerebral endothlial cells is under astrocytic
control.
• Provides biochemical support for cerebral endothelial cells*
• Influence of morphogenesis and organization of vessel wall
• Factors released by astrocytes involved in postnatal maturation of BBB
• Direct contact between endothelial cells and astrocytes necessary to generate BBB
• Co-regulate function by
- secretion of soluble cytokines
- Ca2+ dependent signals triggered by intracellular IP-3 consecutive to ATP binding on P2Y receptors
- gap junction dependent pathways form a syncytium able to propagate signals (as Ca waves) for large distances
Astrocyte end feet
Blood brain barrier selectivity
• Free permeability (passive diffusion):
– small molecules: H2O, O2, CO2, NH3, ethanol
– lipid soluble molecules: steroid hormones
• Carrier mediated transport (apical-basal polarity):
– glucose: GLUT-1 (insulin independent)
– amino acids
– nucleosides, nucleobases
• Pinocytosis
• Aquaporin-4 is the main channel through which water
enters and leaves the CNS
• Physical blockage to paracellular diffusion (ions, peptides,
immune cells)
– astrocytes do not fire action potentials, but are Ca2+-excitable!
– astrocytes ‘listen’ to neurons (all major receptors present)
– astrocytes release neurotransmitter (Glutamate, ATP, …)
– astrocytes modulate neuronal excitability and synaptic transmission
Glial presence at synaptic level:
the tripartite synapse
Amzica, 2000
Synchronous Firing Groups:
Astrocytic regulation of neural networks
Neuron-glia connections
Synchronous Firing Groups – Astrocytic Regulation of Neural Networks
Neuro-glial connection – “calcium wave” in glial networks
Neuron-glia communication by volume transmission -
quadrupartite synapse
Neurons-to-neurons and neurons to glia communication by extrasynaptic “volume”
transmission, which is mediated by diffusion in the extracellular space (ECS) of the
CNS = the microenvironment of neurons and glial cells. Composition & size of ECS
change dynamically during neuronal activity and during pathological states.
ECS size, geometry, and composition, together with pre- and postsynaptic
terminals and glial processes, form the so-called “quadrupartite synpase”.
ECS diffusion parameters affect neuron-glia communication, ionic homeostasis and
the movement and/or accumulation of neuroactive substances in the brain plays an
important role in extrasynaptic transmission, transmitter spillover, cross-talk between
synapses, and in vigilance, sleep, depression, chronic pain, memory formation and
other plastic changes in the CNS.
Retraction of glial processes in rat supraoptic nucleus (SON) and consequences for diffusion and synaptic crosstalk. Reduced astrocytic coverage of SON neurons in lactating rats leads to deficient glutamate clearance, resulting in increased glutamate concentration in the ECS, increased crosstalk between synapses and increased activation of either presynaptic or postsynaptic receptors.
The role of astrocytes in Epilepsy
– In astrocytes from epileptic foci
mGluRs are overexpressed by a
factor of about 20 (rat models and
human) Ulas et al., Glia 30, 352 (2000), Tang and Lee, J.
Neurocytology, 30, 137 (2001),
Aronica et al. Europ.J. Neurosci., 12, 2333 (2000)
Increased Ca2+ spikes during epileptic
seizure Ong et al. J. Neurochem. 72, 1574 (1999)
– More spontaneous astrocytic
calcium spikes in epileptic foci
Tashiro et al., J. Neurobiol. 50, 45 (2002)
Higher abundance of mGluRs
Ca2+
Ca2+Ca2+
Ca2+ Ca2+Ca2+
Ca2+
Ca2+
Ca2+Ca2+
IP3
ATP, Glutamate
uptakeCa2+
leak
Endoplasmic
Reticulum
Abnormalities in glial biology contribute
to the pathology of schizophrenia.
• Neuregulins (NRG) are required for initial differentiation
of oligodendrocyte precursors and for their survival.
• A deficiency of glial growth factors, such as NRG,
predisposes to synaptic destabilization.
• It is clear that NRG signaling is required for the
stabilization of nerve-muscle synapses, and evidence for
NRG involvement in astrocyte biology might implicate
neuregulins in formation or stabilization of central
synapses.
In loc de concluzii…
• Celulele gliale influenteaza activitatea si conectivitatea neuronala,
structural si functional; rol in transmiterea sinaptica si non-sinaptica…
• Eliberare de gliotransmitatori
• Prezenta receptorilor neuromediatorilor locali…
• “Sinapsa neuro-gliala”
• Specificitatea transmiterii semnalului
• Semnalizarea prin unde de calciu…
• Formarea de retele prin conexiuni gap (50-100 conexiuni gap cu alte
astrocite)
• Viteza de conducere a semnalului/informatiei…
• Mielinizarea este dependenta de activitatea neuronala
• Interactiunea neuro-gliala in formarea conexiunilor interneuronale, local
si la distanta; plasticitate neuro-gliala, neurogeneza si neurodegenerare
• Cuplarea neurometabolica si neurovasculara…
• Drenajul “glimfatic”
• Alterari la nivel glial in boli ale sistemului nervos
• ….
“Conectomul glial”, glie a conectomului neuronal…