axoplasmic flow in axons - mechanisms and applications in clinical neurology

Axoplasmic transport

Road Map for the Session

• Introduction and need for this discussion• Historical aspects and the pioneers• Characterization of the types of axoplasmic flow• The molecular “motors”• Integration of concepts• Clinical utilization of the information – pathogenesis• Clinical utilization of the information – therapeutics

• Further reading

The Neuron

• Largest and longest cells of body (107 rbc)

All proteins have to come from the soma

“Axoplasmic flow”

• Conveyor Belt

• Passive Transport

• Gravity dependent



• Further reading

Pioneering Work

• Concept of Axoplasmic Flow

• Simple, elegant experiment

• Rat Sciatic Nerve

Initial Response

Jordi Floch, Founder AAN –

“Thank God! What do you think the

nervous system is, a plumbing system ?”



• Further reading

Advent of electron microscopy

• Late 1960’s

• Characterization of Sub cellular structure of Neuron

• Absence of Golgi apparatus, RER and centromere from Axon

• Presence of cytoskeletal proteins, vesicles, neurofilaments and neurotubules in axon

Classification of Axonal Flow

• Slow Transport– Antegrade, 0.1 to 4 mm/day

Requires ATP/Mg2+ as fuel for the motor



• Fast Transport– Antegrade at up to 400 mm/day

Horse Radish Peroxidase Concentration



• Fast Transport– Antegrade at up to 400 mm/day– Retrograde at 40-400 mm/day

Slow Axonal Transport

Slow Axonal Transport: ~1-4 mm/day

Delivery of cytosolic and cytoskeletal proteins to the nerve terminal:

Microtubules, Neurofilaments, Enzymes

The Cytoskeletons of Neurons and Glia(and all eukaryotic cells!)

Microtubules (Tubulin)- Tubulins, MAPs, Motors: Kinesins and Dyneins

Microfilaments (Actin)-Actins, Actin Monomer Binding Proteins, Capping Proteins, Gelsolin Family, Crosslinking and Bundling Proteins, Tropomyosin, Motors: Myosin

Intermediate Filaments- Superfamily of 5 classes:Types I and II: Keratins, Type III: GFAP, Vimentin, Desmin, Peripherin, Type IV: NF Triplet,Internexin, Nestin, Type V: Nucelar Laminins

Fast Axonal Transport

The Substrate

• Microfilaments

• Microtubules

• The Package

• ATP !!!

Subunit: tubulinMW: ~50 kD, - és -tubulin -> heterodimer1 bound GTP or GDP;

Microtubules

Microtubules

Intermediate filaments

Polymerisation of IF

protofilamentum

filamentum

http://www.sciencemag.org/content/vol279/issue5350/images/large/se0486221001.jpeg

Requires ATP/Mg2+ as fuel for the motor



• Further reading

Kinesins

Kinesins

Kinesins are a large family of proteins with diverse structures. Mammalian cells have at least 40 different kinesin genes.

The best studied is referred to as conventional kinesin, kinesin I, or simply kinesin.

Some are referred to as kinesin-related proteins (KRPs).

Kinesin I has a structure analogous to but distinct from that of myosin.

There are 2 copies each of a heavy chain and a light chain.

stalk domain

N-terminal heavy chain motor

domains (heads)

Kinesin I

hinge light chains

C-terminal tail domains

cargo vesicle

kinesin

micro

tubule

scaffolding protein

receptor

Single kinesin moving a bead

Kinesin superfamily proteins (KIFs) bind to cargoes through adaptor or scaffolding protein complexes.

Kinesin superfamily proteins (KIFs) and cargoes for axonal and dendritic

transport.

Molecular motors: from one motor many tails to one motor many tales. Lawrence S.B. Goldstein Trends in Cell Biology, 2001, 11:12:477-482

Rafts and cytoskeletal proteins as new cargoes

Walking along the microtubules

Single Headed Kinesin…

cargo vesicle

kinesin

mic

rotu

bule

scaffolding protein

receptor

inactive kinesin

Kinesin Inactivation

So, how does it all work together?

Fast Axonal Transport: 100-400 mm/day Purpose: Transport organelles such as mitochondira and vesicles

carrying SV and plasma membrane proteins to the nerve terminal.

Also retrograde movement of vesicles containing neurotrophic factors back to the cell body.

Dyneins

The dynein microtubule motor.Biochim Biophys Acta. 2000. 1496:60-75.



• Further reading

Summary for axoplasmic transport

• Necessity• Types• Kinesins• Dyenins

• Summation

• Need for this information !!!



• Further reading

•

• Axonopathy and transport deficits early in the pathogenesis of

Alzheimer's disease. Stokin GB, Lillo C, Falzone TL, Brusch RG, Rockenstein E, Mount SL, Raman R, Davies P, Masliah E, Williams DS, Goldstein LS Science 2005 Feb 25; 307(5713):1282-8

• Selective vulnerability and pruning of phasic motoneuron axons in motoneuron disease alleviated by CNTF.Pun S, Santos AF, Saxena S, Xu L, Caroni PNat Neurosci

2006 Mar 9(3):408-19

• Charcot-Marie-Tooth disease type 2A caused by mutation in a

microtubule motor KIF1Bbeta.Zhao C, Takita J, Tanaka Y, Setou M, Nakagawa T, Takeda S, Yang HW, Terada S, Nakata T, Takei Y, Saito M, Tsuji S, Hayashi Y, Hirokawa NCell 2001 Jun 1 105(5):587-97

• 1-Methyl-4-phenylpyridinium induces synaptic dysfunction through a pathway involving caspase and PKCdelta enzymatic activities. Proc Natl Acad Sci U S A. 2007 Feb

13;104(7):2437-41 – Model for neurodegenration

• Jones LG, Prins J, Park S, Walton JP, Luebke AE, Lurie DI.

• Lead exposure during development results in increased neurofilament phosphorylation, neuritic beading, and temporal processing deficits within the murine auditory brainstem.

• J Comp Neurol. 2008 Feb 20;506(6):1003-17.

• Pan T, Kondo S, Le W, Jankovic J.

•The role of autophagy-lysosome pathway in neurodegeneration associated with Parkinson's disease.

• Brain. 2008 Jan 10; [Epub ahead of print]

• Inflammation, demyelization,neurodegeneration, and neuroprotection in the pathogenesis of

mutliple sclerosis. Peterson, Lisa K., Fujinami, Robert S.

• Journal Neuroimmunology 184 (2007): 37-44

•Sodium channels and multiple sclerosis: Role in symptom production,

damage and therapy. Smith, Kenneth J.

• Brain Pathology 2007 Apr;17(2):230-42.

•Proteomic analysis of rat cortical neurons after fluoxetine (FLUX) treatment

• Long-Term Impairment of Anterograde Axonal Transport Along Fiber Projections Originating in the Rostral Raphe Nuclei After Treatment With Fenfluramine or Methylenedioxymethamphetamine (MDMA)

Is it only bad news ?



• Further reading

axoplasmic flow in axons - mechanisms and applications in clinical neurology

Health & Medicine

axoplasmic transport

slow axonal transport

fast axonal transport

information therapeutics

mmday fast transport

types of axoplasmic

transport organelles

dendritic transport