Spinal Cord Damage and Repair

Question 1

SCI statistics

Answer 1

affects ~27mil worldwide
change in demographics (more elderly SCI patients)
burden to healthcare (£1 bil UK/ ASIA A $2.3 mil)
no cure
lose sensory/motor function below injury site causing defects in thermoregulation/defecation

Question 2

Spinal cord anatomy

Answer 2

C8/T12/L5/S5/1Coccygeal
cervical division - neck (least protected area of SC)/arms/hands/speech&swallow
thoracic division - muscles
lumbar division - leg/foot
sacral - bladder/bowel
no cognitive decline

Question 3

SCI symptoms

Answer 3

paralysis (paraplegia-L/T, tetraplegia, quadriplegia-C)
loss of movement/muscle function/loss of sensation
loss of bladder/bowel control
sexual dysfunction
secondary dysfunction: bladder infection/lung infection/pressure sores/pain/spasticity/depression/social exclusion

Question 4

what is the aim of therapies

Answer 4

therapies which promote neuroplasticity/regeneration means patients can breathe without a ventilator/have hand movements etc

Question 5

recent advances

Answer 5

epidural spinal stimulation combined with high intensity rehabilitative training

Question 6

caveats of regeneration

Answer 6

neuromodulation does not equal regeneration (no tissue repair)
better recovery in SCI patients with most remaining residual function (ASIA C/D)
regeneration which promotes growth can promote recovery, SC is more open to rehabilitation protocols

Question 7

2 approaches for tissue repair/neuroplasticity

Answer 7

1) regenerative therapies which enhance poor regenerative response of the CNS neurons (cellular transplanation-NSC/OPC/OEC/Schwann, PTEN/KLF7 regeneration gene overexpression, transcriptome screening/bioinformatics which discover regulators of axon regenerators (cama2d2)

2) regeneration which modifies the growth-inhibitory environment (targetting scar-ECM around scar/enzyme therapies/inhibit CSPGR signalling/CSPG synthesis/fibrotic scar, targetting myelin associated inhibitors- anti-Nogo antibodies, Nogo R inhibition)

Question 8

PNS response to injury

Answer 8

-good regenerative ability
-less abundant myelin inhibitors
-rapid wallerian degeneration (myelin debris is cleared from the distal stump by schwann cells and macrophages)
-no glial scar at injury site
-abundant growth factors (upregulated during injury)
-minimal secondary damage (responsible for non-resolving pathology/lack of regeneration)

Question 9

CNS response to injury

Answer 9

-poor regenerative capacity (no long distance regeneration, some neurons grow in adulthood)
-myelin inhibitors present (Nogo/MAG/netrin-1/sema4d/ephrinB3)
-slow wallerian degeneration(incomplete myelin debris clearance)
-glial scar in days, inhibits regeneration, high density of CSPGs
-no GF expression in temporal/spatial gradients
-extensive secondary damage (tissue destruction)

Question 10

neuropathology of SCI

Answer 10

immediate: bleeding/axon injury
hours: necrosis/neutrophil invasion/macrophage B+T cell activation/cytokine release
days: wallerian degeneration/apoptosis/demyelination/debris/ECM scarring/ongoing inflammation
weeks/months: muscle atrophy/ongoing cell death/cyst/cavities/axons die back

Question 11

2 classes of CNS growth inhibitors

Answer 11

scar-associated inhibitors
CNS myelin-associated inhibitors

Question 12

adult rat model of contusion injury

Answer 12

force-defined impactor device to create spinal contusion injury/loss of SC neurons (NeuN) GFAP (astrocyte)
classical pathology: cystic cavitation/predominant grey matter degeneration/WM spared rim/wallerian degeneration/focal demyelination/scar

causes: permanent sensory/motor/autonomic impairment/walk despite damage

Question 13

SCI targets for repair

Answer 13

prevent secondary injury (acute hrs)
repair damage (chronic)
maximise function in spared tissue (acute & chronic)

Question 14

glial scar

Answer 14

reactive glial cells surround the injury site and seal in the injury, prevent regeneration

adv: barrier which seals in injury (isolates damage and prevents further infection)/scar ECM contains growth promoting molecules (laminin) /molecules for glial limitans formation (if not properly formed, increases damage)

dis: prevents neuronal growth/physical barrier(dense gap junctions)/molecule barrier (ECM contains CSPG/Ephrin/Slit/Sema)

Question 15

Chondroitin sulphate proteoglycan (CSPG)

Answer 15

increased CSPGs in scar tissue after injury
limits regeneration and plasticity
sugar components (CS-GAGs) inhibit neuronal growth - chondroitinase breaks down CS-GAGs and promotes growth/neuroplasticity

Question 16

chondroitinase ABC (ChABC)

Answer 16

bacterial enzyme which degrades CS-GAGs (from core CSPG component)
ECM is more permissive
in-vitro neurite growth (Zuo et al., 1998) vs in vivo regeneration, increases neuroplasticity, immune modulation (decreased cavitation/cell death), used in combination therapies
degrades at 37 degrees Celsius

Question 17

best time for chondroitinase administration

Warren et al., 2018

Answer 17

acute (immediate) treatment: minimal respiratory recovery
chronic (1.5yrs after injury) activates phrenic MNs, 100% animals showed recovery
respiratory recovery via growth of serotonergic neurons

Question 18

cell based therapies

clinical trials

Answer 18

autologous human schwaan cell (ahSC) The Miami Porject
human neural stem cells (HuCNSSC) trasnplant
human embryonic stem cells (hESCs) derived oligodendrocyte progenitor cells (GRNOPC1)
G Raisman/Tabakow clinical study - olfactory bulbar cells+nerve grafts+intensive rehabilitation

Question 19

pharmacology

clinical trials

Answer 19

riluzole (sodium channel blocker/glutamate antagonist)
cethrin (rho/rockA inhibitor)
nogo-A antibodies

Question 20

7 therapeutic targets for improving secovery after SCI

Answer 20

limit secondary damage
tissue/cell transplants
removal of inhibitory molecules (CSPG)
regeneration though neuron-intrinsic mechanisms
resupply of trophic support
remyelination of demyelinated axons
rehabilitation for circuit remodelling

Question 21

modulation of scar inhibition

Answer 21

-indirect modification (MT stabilising antimitotic agents Taxol/Epothilone B suppreses fibrotic scarring - cancer)
-targetting biosynthesis of inhibitory ECM components (target CSPG sulfation, neutralising antibodies, synthetic sulfotransferase inhibitors,disrupt CSPG GAG chain assembly using XT-1)
**-inhibiting CSPG signalling (receptors: PTP sigma/LAR - use ISP to block interaction)

Question 22

PTEN/mTOR intracellular signalling

Answer 22

mTOR - activates protein translation and ribosome biogenesis via phosphorylation (of S6 ribosomal protein) increases protein synthesis and cell growth

AKT - phosphorylates substrates/role in cell proliferation/growth/glucose metabolism = survival promoting factor

PTEN deletion (desired) activates mTOR/RGC axon regeneration after optic nerve injury/corticospinal tract regeneration (Park et al., 2008)

Question 23

cell types transplanted in SCI experimental models

Answer 23

ESC
adult neural precursor cells
OPC
fibroblast
fetal tissue
glial restricted progenitor
bone marrow stromal cell
cells derived from pluripotent SC
olfactory tissue
peripheral nerve graft
biomaterials

Question 24

NSC transplation of SCI

Lui et al., 2012

Answer 24

method: 14 days post injury add to fibrin gel: GFs(BDNF/GDNF/a-TNF), calpain inhibitor, human/rat ESC - inject rats with complete spinal transection, fill ~2mm gap
results: after 7 wks, NSCs differentiated into neurons (~20% grafted cells), projected over multiple spinal segments (connects cervical and lumbar SC)
considerations: only minor effects/multiple tumours//uncontrolled growth in brain

Question 25

considerations for transplantation in SCI

Answer 25

poorly understood
few clinical trials despite >1000 patients
lots of data in private NOT public domain
small labs make big claims - not independently reproduced
risk of tumours and pain
low methodological quality for rodent data/ few primate studies