Week 8 Part 2 Flashcards
What is Retrograde signalling of cytokines to sensory neurons (A)
After injury, CNTF is released from Schwann cells, LIF synthesis is induced in Schwann cells
IL-6 synthesis is induced in neurons
IL-1 and tumour necrosis factor alpha released at site of injury
Retrograde signalling (B)
CNTF, LIF and IL-6 activate the gp130 receptor which recruits Janus kinases to phosphorylation STAT3. pSTAT3 dimerises and be imported into the nucleus
Retrograde signalling (C)
STAT3 dimers bind directly to specific sequences in DNA
Induce transcription of many genes related to inflammation and repair
What are other molecules released by Schwann cells?
Other cytokines
Growth factors
Enzymes
Chemokines
Other cytokines
IL-1alpha, IL-1beta, TNF alpha (tumour necrosis factor alpha)
Growth factors
GDNF NGF BDNF NT-3 TGF-beta
Enzymes
Metalloproteinase 9 (MMP9)
Chemokines
MCP-1
CCL2
CCL3
What 2 molecules are used for axon regeneration?
GAP-43
SPR1A
What does macrophages and Schwann cells produce?
Matrix metalloproteases that interrupt the blood-nerve barrier
What is released when the blood-nerve barrier is interrupted?
CGRP
Substance P
Bradykinin
Nitric oxide
- induct hyperaemia and swelling - promote the invasion of further monocytes and T lymphocytes
What is the role of CCL2 and CCL3?
Attract and guide monocytes to the lesion site
What is the role of macrophages and mast cells?
Release prostaglandin and cytokines
IL-1B, IL-6, IL-18, TNF and LIF
What does blood vessels have?
MCP-1
What do cells at injury site release?
Variety of cytokines
What does IL-10 from macrophages inhibit?
Fibroblasts and Schwann cells
What happens after nerve injury?
Expression of thousand of genes changes
What are regeneration associated transcription factors?
STAT3, ATF3, cJun, CREB, SOX11, SMAD1, KLF7, C/EBPdelta, p53
What are terminal RAGS?
GAP43 CAP23 Galanin PACAP Rac1 Cdc42 Arginase I CRMP2 GDNF BDNF
What does ATP released after injury trigger?
Neural responses to an injury
What does ATP release cause?
Peripheral cells to release cytokines
What is Calpain?
An intercellular Ca2+ dependent cysteine protease
How do neuronal bodies sense injury?
Rapid phase
Slow phase
Rapid phase
Injury-induced discharge of axonal potential and ions
Goes back to cell body
Slow phase
Conveyed by molecular motors
What is negative injury signals?
Interruption of normal supply of retrogradely transported trophic factors of negative regulators of neuronal growth from target
What is positive injury signals?
Retrograde transport of activated proteins at injury site
What does calcium wave lead to?
Molecular changes in the neuronal soma
What does sudden calcium change result in?
Body detecting there’s an injury
What is one of the molecules involved with calcium waves?
Histone deacetylase 5 with protein kinase
What does epigenetic change result in?
Histone acetylation
What does nuclear export of Histone deacetylase via protein kinase enhance?
Histone acetylation
Priming the chromatin for subsequent transcription events
What is a big player in peripheral axon regeneration?
Neurgulin
What does Neuregulin do?
Bind to receptor ERBB2 which is on the Schwann cells
It is released in the axons
What does axons have ?
TRKA receptors
What molecules are early injury signals?
IL-6 family Gp130 family Neuropoietic family Interleukin-6, IL-11, IL-27 Ciliary neurotrophic factor (CNTF) Leukaemia inhibitory factor (LIF) Cardiotrophin 1 (CT-1) Neuropoietin Cardiotrophin-like cytokines (CLC)
What does Neuropoietic cytokines activate?
JAK-STAT and MAPK pathway
What are signalling pathways of neuropoietic cytokines?
Jak
STAT3
SOCS
Jak
Janus-family tyrosine kinases
STAT3
Signal transducers and activators of transcription 3
SOCS
Suppressor of cytokine signalling
Where is CNTF highly expressed?
Schwann cells
Has no signal peptide - not secreted by conventional pathways
What is experimental evidence of earl injury signal?
- Phosphorylation and nuclear translocation of STAT3 was maximally induced within 12h post lesion in motoneurons of facial nucleus of wild type mice - maintained for 3 days
- In CNTF-deficient mouse, activation of STAT3 signalling was delayed by 10-12h
- Application of CNTF to transects nerve restored STAT3 activation in CNTF- deficient animals
Why is LIF important?
Increases the regeneration state of injured neurons
What are other transcription factors involved in injury induced responses?
ATF3
ATF3
Injury marker
Regeneration marker
Pain marker
What does the gene GAP-43 show?
Undergo axon growth
What gets travelled all the way up to the injury site because the gene is made in the cell body?
GAP-43 and CAP23
What does two sequential injections of ATP significantly promote?
Sensory axon regeneration in spinal cord
What are demyelination pathways?
JIP
Calpain
What is JIP?
JNK-interacting protein of scaffold protein
Mediate JNK signaling by aggregating specific components of MAPK cafe to form functional JNK signaling module
What is calpain?
Intracellular Ca2+ dependent cysteine protease
What gene is involved in WLDs?
NMNAT1
Where is NMNAT1 located?
Nuclei
Also expressed in axonal cytoplasm
Organelle: mitochondria
What are factors controlling early Schwann cell development and myelination?
NRG1 B1 integrity’s Claw paw Laminin P75 NTR TGF beta BRN2 Krox20/ NAB 1/2 NRG1 OCT6
What does different types of neuregulin carry?
Epidermal growth factor (EGF) domain
5 matured forms are soluble
What is matured type III ?
Membrane bound protein
Interact with receptors in Schwann cells
What is ErbB proteins?
Type 1 transmembrane receptor tyrosine kinase
What does Neuregulin 1 (NRG1) stimulate?
ErbB to dimerize
What does ERB2 have?
Active kinase domain
ErbB3
Binds to NRG1 but has an impaired tyrosine kinase domain
ErbB4
Homodimers can bind to NRG1 and become activated
What does NRG-III tell Schwann cells?
Myelinate axons
What does injury have?
Growth cone
For axons to grow back again it needs to have growth cone
What does growth cones have?
Microtubules which go all the way back to the cell body
Have actin surrounding
Fingers Filopodia
What does P domain contain?
Unipolar actin filament bundles embedded in a less polar actin network
Contains: lamellipodia and filopodia
What is T domain?
Thin interface between P and C domain
Where is C domain located?
Centre of growth cone nearest the axon
Composed of microtubules and contains numerous organelles and vesicles
What does membrane rupture lead to?
Elevation of the free intra-axonal ca2+
What are the process of axon growth?
Protrusion
Engorgement
Consolidation
What is protrusion?
Rapid extension of filopodia and thIn lamellar protrusion
extension are primarily composed of bundled and mesh-like F-actin networks
What is Engorgement?
Microtubules invade protrusion bringing membranous vesicles and organelles
What is consolidation?
F-actin depolymerises in the neck of growth cone and membrane to shrink around the bundle of microtubules to form a cylindrical axon shaft
What does calcium wave lead to?
Molecular changes in the neuronal soma
What is calcium wave?
Sudden change in calcium that results in cell body detecting there’s injury
What is one molecule that’s involved in calcium wave?
Histone deacetylase 5 with protein kinase Cm
What does epigenetic change result in?
Histone acetylation
What does nuclear export of Histone deacetylase 5 via protein kinase activation lead to?
Enhancing Histone acetylation
Pruning the chromatin for subsequent transcription events
Molecular changes in the neuronal soma?
Calcium ion flux into the axons
Released from internal stores
Generate calcium waves
Spread to soma and trigger gene expression
What happens when there is damage to the axons?
Schwann cell axon interaction
What is a key player in peripheral axon regeneration?
Neuregulin
What is the role of Neuregulin?
Bind to its receptor ERBB2 (on Schwann cells)
Released in axons when injured
What does axons have?
TRKA receptors
What molecules are early injury signals?
IL-6 family Gp130 family Neuropoietic family IL-6, IL-11 and IL-27 Ciliary neurotrophic factor (CNTF) Leukaemia inhibitory factor (LIF) Cardiotrophin 1 (CT-1) Neuropoietin Cardiotrophin-like cytokine (CLC)
Signalling pathways of neuropoietic cytokines
Shown through IL-6 receptor
JAK: Janus-family tyrosine kinases
STAT3: signal transducers and activators of transcription 3
SOCS: suppressor of cytokine signalling
What is another pathway for regeneration?
PI3 kinase AKT pathway
What is CNTF?
Early injury signal
Highly expressed in adult Schwann cells
Has no signal peptide - not secreted by conventional pathways
Can be released instantly after Schwann cell damage
What is experimental evidence for CNTF?
- Phosphorylation and nuclear translocation of STAT3 was maximally induces within 12h post lesion in motoneurons of facial nucleus of WT mice and maintained for at least 3 days
- In CNTF- deficient mouse, activation of STAT3 signalling was delayed by 10-12h
What is CNTF neuroprotective for?
Motoneurons
Sensory neurons
Retinal ganglion neurons
Where is LIF mRNA levels increased?
Both proximal and distal stumps soon after PNI
What is LIF important for?
Increasing the regeneration state of injured neurons
What is bi-directional relationship between axons and Schwann cells during neural repair?
- Axons are re-myelinated
- Schwann cell begin re-myelination
- Schwann cells ensheath the axons
- As Schwann cells re-contact axons they proliferate
