Neuronal Regeneration and Neural Stem Cells Flashcards
What is the ability to regenerate determined by?
the availability of neurotrophic factors and the presence of an intrinsic growth program
What is the ability to regenerate countered by?
the presence of growth inhibitors in the glial scar and myelin
What happens after SCI?
many cells die immediately as well as progressively
What happens after penetrating injury?
cells from the PNS often invade the injury site to form a connective tissue scar that incorporates astrocytes, progenitor cells and microglia
What happens during the early stages of injury?
myelin-associated inhibitors from intact oligodendrocytes and myelin debris can restrict axon regrowth
What does the recruitment of inflammatory cells and reactive astrocytes over time lead to?
the formation of a glial scar, often accompanied by a fluid-filled cyst
What is the scarring process associated with?
the increased release of chondroitin sulphate proteoglycans, which can further limit regeneration
What is Nogo-A?
a neurite growth inhibitor that plays a role both in the restriction of axonal regeneration after injury and in structural plasticity in the CNS of higher vertebrates
What are the 3 types of factor that regulate neurite outgrowth?
- permissive e.g. ECM-associated, CAMs, neurotrophic factors
- inhibitory e.g. Nogo
- guiding e.g. ephrins, Slits
What are the 2 main molecular inhibitors of the adult CNS glial environment?
- CSPGs associated with reactive astrocytes from the glial scar
- myelin-associated inhibitors from intact oligodendrocytes and myelin debris
What does signalling from the Nogo-66 receptor do?
affect the actin cytoskeleton through activation of RhoA
What does a reduction of myelin-associated inhibitors do?
enhance regeneration
What does the end of severed nerve in the extracellular space between cells in a wounded spinal cord do?
form a growth cone which explores the territory by constantly forming and retracting filopodia
What does the extracellular space between cells in a wounded spinal cord contain?
- CSPG molecules, which have a backbone and many side branches that block the way
- special cell-membrane-anchored proteins that actively stop growing nerve fibres
What does the bacterial enzyme ChABC do?
prune the side chains of CSPGs, clearing the way for growing nerve fibres and promote regeneration of corticospinal tract axons
What does intrathecal treatment with ChABC degraded CS-GAG at the injury site do?
- upregulate a regeneration-associated protein in injured neurons
- promote regeneration of both ascending sensory projections and descending corticospinal tract axons
What do embryonic neurons have for regeneration?
a cell-intrinsic program leading to axonal elongation
What is the intrinsic growth capacity of adult CNS and PNS neurons respectively?
- CNS = limited
- PNS = high
What does a conditioning lesion do?
protect axons from degeneration after a second injury
What is the DRG neuron model for CNS axonal regeneration?
- young DRG CNS axons could regenerate, but adult ones could not
- regeneration of the CNS branch of the DRG neuron could be enhanced by a conditioning lesion to the PNS branch
- cAMP could mimic the effects of a conditioning lesion, overcoming even the inhibitory effects of myelin-associated inhibitors
What is the relationship between cAMP levels and regenerative ability?
decreased cAMP levels = decreased ability
What does neurotrophin treatment do?
elevate cAMP levels
What is PTEN?
a tumour suppressor phosphatase whose deletion enhances axonal regeneration
What does PTEN act as?
a brake for the mTORC1 pathway, which promotes potent CNS axon regeneration
What does mTOR activation do?
promote the synthesis of the raw materials for axon extension
What do PI3K and GSK-3 do?
enhance axonal transport and cytoskeleton assembly in the axon terminal
What does axotomy trigger?
the translation of importin β1 and vimentin mRNAs
What is axotomy?
the cutting or severing of an axon
What does vimentin do?
link pERK to the importin–dynein complex so that the injury signal is retrogradely transported to the cell body
What is required for the axonal localisation of β-actin and GAP-43 mRNAs that are translated after injury?
zipcode binding protein 1 (ZBP1)
What do intracellular signalling molecules do after CNS injury?
regulate the ability of the neuron to regenerate its damaged axon through the lesion environment
What does C3 transferase do after CNS injury?
inhibit RhoA to promote axon extension and cell survival
What does bpV do after CNS injury?
inhibit PTEN to promote neuroprotection
What does rolipram do after CNS injury?
inhibit phosphodiesterase 4 (PDE4) to stabilise cAMP and promote axon extension
What do MT stabilisers do after CNS injury?
reduce fibrotic scarring and promote axon extension
What does ChABC do after CNS injury?
digest GAG chains, relieving CSPG-dependent growth inhibition
What do Nogo extracellular peptides do after CNS injury?
compete for NgR binding to neutralise inhibitory signalling through NgR
How can stem cells be used in CNS repair?
- endogenous adult neurogenesis
- transplantation-based therapy
What is the source of stem cells for endogenous adult neurogenesis?
adult neurogenic regions e.g. SVZ and DG
What is the source of stem cells for transplantation-based therapy?
allogenic autologous
What must the neurons from neurogenic zones do during endogenous adult neurogenesis?
survive and differentiate/mature into site-specific functional neurons, and form appropriate axonal and dendritic connections
Where can stem/progenitor cells be collected?
- the inner cell mass layer of the mature blastocyst
- the brain, spinal cord, olfactory system or umbilical cord of the foetus
- the brain, spinal cord, olfactory system, bone marrow or blood of the adult
Which cells can be used for autologous transplantation?
- olfactory system cells
- umbilical cord blood cells
- haematopoietic stem cells
- bone marrow stromal cells
What is possible treatment for acute damage e.g. SCI?
- peripheral nerve grafts
- schwann cells
- olfactory ensheathing cells
- activated macrophages
- embryonic/foetal spinal cord tissues
- stem cells
What is possible treatment for neurodegenerative diseases e.g. PD?
- embryonic/foetal striatal tissues
- stem cells
- dopaminergic neurons derived from the above
What are embryonic stem cells the best in terms of?
generating specific neuron subtypes
Which neuron subtypes can embryonic stem cells generate?
- motor neurons that can populate the embryonic spinal cord, extend axons and form synapses
- grafted cells that become TH positive neurons
What happens when human neural stem cells were used in CNS repair?
most transplanted cells assumed an astrocytic fate
What may transplantation therapy require?
stringent checks for tumorigenic potential (even with the use of pre-differentiated cells)
What are the advantages of bone marrow stromal mesenchymal cells in CNS repair?
- autologous, patient specific source
- little ethical concern
What are the disadvantages of bone marrow stromal mesenchymal cells in CNS repair?
capacity for neuronal/glia differentiation not yet clearly defined
What can BMSCs form?
neurospheres that can morphologically differentiate into neuron-like cells which expressed neuronal markers and some electrophysiological properties
How do iPSCs facilitate research into brain disorders?
through the generation of brain organoids
What are the 8 main strategies of CNS repair?
- growth conduits
- helper cells
- endogenous adult neurogenesis
- stem cell replacement therapy
- reduced inflammation and environment hostility
- reduce myelin-associated inhibition
- enhanced intrinsic regenerative growth capacity
- exogenous neurotrophic help
