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Summary

Impaired mitochondrial transport and morphology are involved in various neurodegenerative diseases. The presented protocol uses induced pluripotent stem cell-derived forebrain neurons to assess mitochondrial transport and morphology in hereditary spastic paraplegia. This protocol allows characterization of mitochondrial trafficking along axons and analysis of their morphology, which will facilitate the study of neurodegenerative disease.

Abstract

Neurons have intense demands for high energy in order to support their functions. Impaired mitochondrial transport along axons has been observed in human neurons, which may contribute to neurodegeneration in various disease states. Although it is challenging to examine mitochondrial dynamics in live human nerves, such paradigms are critical for studying the role of mitochondria in neurodegeneration. Described here is a protocol for analyzing mitochondrial transport and mitochondrial morphology in forebrain neuron axons derived from human induced pluripotent stem cells (iPSCs). The iPSCs are differentiated into telencephalic glutamatergic neurons using well-established methods. Mitochondria of the neurons are stained with MitoTracker CMXRos, and mitochondrial movement within the axons are captured using a live-cell imaging microscope equipped with an incubator for cell culture. Time-lapse images are analyzed using software with "MultiKymograph", "Bioformat importer", and "Macros" plugins. Kymographs of mitochondrial transport are generated, and average mitochondrial velocity in the anterograde and retrograde directions is read from the kymograph. Regarding mitochondrial morphology analysis, mitochondrial length, area, and aspect ratio are obtained using the ImageJ. In summary, this protocol allows characterization of mitochondrial trafficking along axons and analysis of their morphology to facilitate studies of neurodegenerative diseases.

Introduction

Mitochondrial motility and distribution play a vital role in fulfilling variable and specialized energetic demands in polarized neurons. Neurons can extend extremely long axons to connect with targets through the formation of synapses, which demand high levels of energy for Ca2+ buffering and ion currents. Transport of mitochondria from soma to axon is critical for supporting axonal and synaptic function of neurons. Spatially and temporally dynamic mitochondrial movement is conducted by fast axonal transport at rates of several micrometers per second1.

Specifically, motor or adaptor proteins, such as kines....

Protocol

1. Generation of telencephalic glutamatergic neurons from iPSCs

NOTE: The detailed protocol for maintaining iPSCs and their differentiation into telencephalic glutamatergic neurons are similar to those described previously18. Here, the critical process during the differentiation of human pluripotent stem cells is introduced and highlighted.

  1. Culture iPSCs on mouse embryonic fibroblast (MEF) feeders in human embryonic stem cell (hESC) medium supplemented with .......

Representative Results

Here, human iPSCs were differentiated into telencephalic glutamatergic neurons, which were characterized by immunostaining with Tbr1 and βIII tubulin markers (Figure 1A). To examine the axonal transport of mitochondria, these cells were stained with red fluorescent dye, and time-lapse imaging was performed. Since ImageJ is readily available and easier to obtain, mitochondrial transport was further analyzed with the "MultiKymograph" and "Macros" ImageJ pl.......

Discussion

This article describes a method to analyze mitochondrial transport and morphology in neuronal axons using red fluorescent dye and ImageJ software, both of which provide a unique platform to study axonal degeneration and mitochondrial morphology in neurodegenerative disease. There are several critical steps in the protocol, including staining of mitochondria, live cell imaging, and analyzing the images. In this method, a fluorescent dye was used to stain mitochondria. Since human iPSC-derived neurons are easily detached f.......

Acknowledgements

This work was supported by the Spastic Paraplegia Foundation, the Blazer Foundation and the NIH (R21NS109837).

....

Materials

NameCompanyCatalog NumberComments
Accutase Cell Detachment SolutionInnovative Cell TechnologiesAT104
Biosafety hoodThermo Scientific1300 SERIES A2
Bovine serum albumin (BSA)SigmaA-7906
Brain derived neurotrophic factor (BDNF)Peprotech450-02
CentrifugeThermo ScientificSorvall Legend X1R/ 75004261
CoverslipsChemiglass Life Sciences1760-012
Cyclic AMP (cAMP)Sigma-AldrichD0627
DispaseGibco17105-041
DorsomorphinSelleckchemS7146
Dulbecco's modified eagle medium with F12 nutrient mixture (DMEM/F12)Corning10-092-CV
FBSGibco16141-002
Fibroblast growth factor 2 (FGF2, bFGF)Peprotech100-18B
Geltrex LDEV-Free Reduced Growth Factor Basement Membrane MatrixGibcoA1413201
Gem21 NeuroPlex Serum-Free SupplementGemini400-160
Glass Bottom DishesMatTekP35G-0.170-14-C
9'' glass pipetesVWR14673-043
Glial derived neurotrophic factor (BDNF)Sigma-AldrichD0627
GlutaMAX-IGibco35050-061
HeparinSigmaH3149
Insulin growth factor 1 (IGF1)InvitrogenM7512
Knockout Serum ReplacerGibcoA31815
LamininSigmaL-6274
2-MercaptoethanolSigmaM3148-100ML
MitoTracker CMXRosInvitrogenM7512
Neurobasal mediumGibco21103-049
Non Essential Amino AcidsGibco11140-050
N2 NeuroPle Serum-Free SupplementGemini400-163
Olympus microscope IX83OlympusIX83-ZDC2
PBSCorning21-031-CV
Phase contrast microscopeOlympusCKX41/ IX2-SLP
6 well platesCorning353046
24 well platesCorning353047
Poly-L-ornithine hydrobromide (polyornithine))Sigma-AldrichP3655
SB431542Stemgent04-0010
Sterile 50ml Disposable Vacuum Filtration System 0.22 μm Millipore Express® Plus MembraneMilliporeSCGP00525
Stericup 500/1000 ml Durapore 0.22 μM PVDFMilliporeSCGVU10RE
Tbr1 antibody (1:2000)ChemiconAB9616
Trypsin inhibitorGibco17075029
50 ml tubesPhenixSS-PH50R
15 ml tubesPhenixSS-PH15R
T25 flasks (untreated)VWR10861-572
Plugins for softwares
Bio-formats Packagehttp://downloads.openmicroscopy.org/bio-formats/5.1.0/
Fiji softwarehttps://fiji.sc/
Kymograph Pluginhttps://www.embl.de/eamnet/html/body_kymograph.html
MultipleKymograph.classhttps://www.embl.de/eamnet/html/body_kymograph.html
MultipleOverlay.classhttps://www.embl.de/eamnet/html/body_kymograph.html
WalkingAverage.classhttps://www.embl.de/eamnet/html/body_kymograph.html
StackDifference.classhttps://www.embl.de/eamnet/html/body_kymograph.html
Straighten_.jarhttps://imagej.nih.gov/ij/plugins/straighten.html
tsp050706.txthttps://www.embl.de/eamnet/html/body_kymograph.html

References

  1. Brown, A. Axonal transport of membranous and nonmembranous cargoes: a unified perspective. Journal of Cell Biology. 160 (6), 817-821 (2003).
  2. Morris, R. L., Hollenbeck, P. J. Axonal....

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