L17 and 18 - Neurotrophins

Question 1

What are Neurotrophic factors (NF)?

Answer 1

Proteins which promote growth, differentiation and survival in NS

Question 2

T/F: NF are not very potent

Answer 2

F- extremely potent

Question 3

Viktor Hamburger - what did he find?

Answer 3

Showed in chick embryos that removing a limb bud = sensory and motor neuron loss, transplanting a limb bud = increased motor survival

Initially Hamburger thought that the extra limb was recruiting undifferentiated neurons into motor neurons,

Question 4

Rita Levi-Montalcini

Answer 4

Showed in rodent embryos that using anti-NGF antibodies could prevent development of symp NS and using purified NGF increases numbers of symp nerves.

Question 5

Neurotrophic hypothesis

Answer 5

Growing axons compete for limiting amounts of target-derived trophic factors (these travel retrograde from axon to cell body) and axons that fail to receive sufficient trophic support die by apoptosis.

Question 6

What do cultures prepared from embryonic neurons need to be supplemented with?

Answer 6

Specific NF which corresponds with requirement for NF in vivo (what we use for the dish is what is used in the animal)

Question 7

There is only one exogenous stimuli that will increase levels of neural stem cells (more BDNF produced) in our brain

Answer 7

Exercise

Question 8

Couples in early romantic relationship (0-6 months) have twice as much ___ in their blood

Answer 8

NGF

Question 9

BDNF is produced in the brain but also produced in?

Answer 9

Muscle

Question 10

NGF - Promotes? Related to?

Answer 10

Protein dimer with cysteine bridges that promotes survival of symp, sensory neurons and cholinergic neurons

Related to TGFBeta and PDGF

Question 11

BDNF - Promotes? Related to?

Answer 11

Promotes survival or sensory, motor and dopaminergic neurons

Related in sequence to NGF

Question 12

NT-3 - Cloned on basis of homology between? Promotes?

Answer 12

Cloned on basis of homology between NGF and BDNF promotes survival of type 1A proprioceptive sensory neurons and various central populations

Question 13

!3 Sources of neurotrophins

Answer 13

Target-derived

• NGF in targets of symp neurons
• BDNF in muscle

Paracrine sources
-BDNF upregulated in Schwann cells after axonal lesion

Autocrine
-BDNF in DRG (dorsal root ganglion) neurons promote DRG neuronal survival

Question 14

2 types of neurotrophin receptors

Answer 14

TRK family of receptor tyrosine kinases

p75

Question 15

!p75 - binds to? homologous to? KO leads to?

Answer 15

• Binds all NTs with low affinity (Kd = 10^-9 M)
• Homologous to CD40 and TNF receptor
• Role in apoptosis (p75 knockout leads to loss of sympathetic and sensory neurons BUT increased basal forebrain cholinergic neurons due to UNREGULATED cell death)

Question 16

!p75 signalling pathways under investigation are

Answer 16

ceramide
JNK (phosphrylates c-jun)
NFkB

Question 17

p75 of trk family involved in myelination? What inhibits myelination?

Answer 17

BDNF + p75 promotes myelination

NT3 + Trk C inhibits myelination

Question 18

CNTF - related to? promotes?

Answer 18

A monomeric 4-helix bundle cytokine related to interleukin 6 (IL-6), leukaemia inhibitory factor (LIF) and oncostatin M (OSM)

Promotes survival of motor, ciliary and symp neurons

Question 19

How is the CNTF receptor different to the trk receptors?

Answer 19

Cytokine-like - No intrinsic tyrosine kinase domain but recruits intracellular tyrosine kinases (JAK/TYK) upon ligand binding by using
NOT in neuronal targets but in Schwann cells
NOT release but acts as a lesion factor - CNTF knockout produces slow neurodegen

Question 20

!BDNF - what two types of loops does it have? What mimetic peptides have been derived out of the two different loops?

Answer 20

Loop 2 mimetics that are trkB ligands (loop 2 dimeric peptides act as trkB agonists and are potent)

Loop 4 mimetics which are p75 ligands )loop 4 monomers aka dPAKKR are p75 modulators with drug-like properties: stable, light, crosses cell membrane, promotes peri myelination in vitro and in vivo)

Question 21

!The BDNF Loop 2 mimetic - is it a monomeric monocyclic (circular) or linear peptide? amide or cysteine linkage works better? bicyclic or tricyclic? Full or partial agonist? How is it flexible?

Answer 21

Circular, amide, tricyclic, partial agonist, flexible as if the loops face diff direction it becomes an antagonist

Question 22

a) What does dPAKKR (loop 4 monomers - Lys-lys-Arg-Ala-dPro = linker) promote?
b) What does it work independently of?
c) Is it stable in plasma?
d) Can it cross cell membranes?
e) low or high molecular weight

Answer 22

a) Neuronal survival and peripheral myelination (better effect compared to BDNF) in vitro AND in vivo where linker and p75 motif are both important for it’s activity
b) trkB - which is strange as it is suppose to be a peptide made from BDNF and BDNF does bind to trkB, BOTH phosphorylate MAP kinase though
c) Yes - this is important because they we can use it as a drug
d) Yes- same reason as c
e) Low - same reason as c and d

Question 23

Increased or decreased BDNF in schizophrenic brain?

Answer 23

Increased

Question 24

Increased or decreased NGF in injury, inflammation and chronic pain?

Answer 24

Increased as NGF sensitizes pain receptor TRPV1 and causes mast cell activation and increased sub P release from nociceptive neurons

Question 25

Tanezumab

Answer 25

Anti-NGF monocolonal antibody in phase 2 trials for back pain and osteoarthritis