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Autophagy is involved in the reduction of myelinating Schwann cell cytoplasm during myelin maturation of the peripheral nerve.

Jang SY, Shin YK, Park SY, Park JY, Rha SH, Kim JK, Lee HJ, Park HT - PLoS ONE (2015)

Bottom Line: Inhibition of autophagy via Schwann cell-specific removal of ATG7, an essential molecule for macroautophagy, using a conditional knockout strategy, resulted in abnormally enlarged abaxonal cytoplasm in myelinating Schwann cells that contained a large number of ribosomes and an atypically expanded endoplasmic reticulum.Rapamycin-induced suppression of mTOR activity during the early postnatal period enhanced not only autophagy but also developmental reduction of myelinating Schwann cells cytoplasm in vivo.Together, our findings suggest that autophagy is a regulatory mechanism of Schwann cells structural plasticity during myelination.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Mitochondria Hub Regulation Center, Busan, Korea.

ABSTRACT
Peripheral nerve myelination involves dynamic changes in Schwann cell morphology and membrane structure. Recent studies have demonstrated that autophagy regulates organelle biogenesis and plasma membrane dynamics. In the present study, we investigated the role of autophagy in the development and differentiation of myelinating Schwann cells during sciatic nerve myelination. Electron microscopy and biochemical assays have shown that Schwann cells remove excess cytoplasmic organelles during myelination through macroautophagy. Inhibition of autophagy via Schwann cell-specific removal of ATG7, an essential molecule for macroautophagy, using a conditional knockout strategy, resulted in abnormally enlarged abaxonal cytoplasm in myelinating Schwann cells that contained a large number of ribosomes and an atypically expanded endoplasmic reticulum. Small fiber hypermyelination and minor anomalous peripheral nerve functions are observed in this mutant. Rapamycin-induced suppression of mTOR activity during the early postnatal period enhanced not only autophagy but also developmental reduction of myelinating Schwann cells cytoplasm in vivo. Together, our findings suggest that autophagy is a regulatory mechanism of Schwann cells structural plasticity during myelination.

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Changes of cytoplasmic area of mSCs during the postnatal period.A. A schematic drawing of mSCs showing the abaxonal cytoplasm outside of the compact myelin sheath. B. Representative EM images of sciatic nerves from wild-type mice showing the reduction of cytoplasmic area of mSCs during postnatal development. Asterisk; nucleus, double arrows; abaxonal cytoplasm. Note the developmental downregulation of abaxonal cytoplasm. C. Representative EM images of mSCs from mice of different ages. Arrowheads: lysosome. M: mitochondria. N: nucleus. Arrows demonstrate various morphologies of RER. C’. Enlarged image of a lysosome. D. Morphometric quantification of the abaxonal cytoplasmic area (n = 3 for each ages). E. The number of lysosomes in the perinuclear cytoplasm of mSCs from different ages was counted under EM, and the mean number of lysosomes per mSC is displayed (n = 3, mean±SEM).
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pone.0116624.g001: Changes of cytoplasmic area of mSCs during the postnatal period.A. A schematic drawing of mSCs showing the abaxonal cytoplasm outside of the compact myelin sheath. B. Representative EM images of sciatic nerves from wild-type mice showing the reduction of cytoplasmic area of mSCs during postnatal development. Asterisk; nucleus, double arrows; abaxonal cytoplasm. Note the developmental downregulation of abaxonal cytoplasm. C. Representative EM images of mSCs from mice of different ages. Arrowheads: lysosome. M: mitochondria. N: nucleus. Arrows demonstrate various morphologies of RER. C’. Enlarged image of a lysosome. D. Morphometric quantification of the abaxonal cytoplasmic area (n = 3 for each ages). E. The number of lysosomes in the perinuclear cytoplasm of mSCs from different ages was counted under EM, and the mean number of lysosomes per mSC is displayed (n = 3, mean±SEM).

Mentions: For electron microscopic analysis, captured EM images (×4000~5000) were analyzed using the ImageJ software (National Institute of Health, Bethesda). Abaxonal areas were demarcated and calculated by drawing a continuous line with the ImageJ software and mean areas were calculated from approximately 300~500 randomly selected myelinated SCs at each time point (n = 3). The number of lysosomes in the perinuclear cytoplasm of 70~100 mSCs that had nuclei visible in ultrathin sections was counted, using three animals in each age group. Lysosome was defined as a membrane-bound electron dense structure (0.2~0.5 μM in diameter, Fig. 1C’) which was distinguished from membrane-unbound less electron-dense lipid droplets. Quantitative analysis of the number of appositions in the mSCs was performed from 300~500 randomly selected myelinated SCs at P60 (n = 3). G ratios were determined by dividing the perimeter of the axon by that of the outset leaflet of the myelin sheath at P10 and P60. Approximately 170~200 round axons from two mice in each group were employed for the analysis. The morphometric analysis of Remak bundle development (the number of axons in a bundle) was determined from the same images used for g ratio analysis and approximately 130 Remak bundles from two animals (P60) in each group were pooled and analyzed.


Autophagy is involved in the reduction of myelinating Schwann cell cytoplasm during myelin maturation of the peripheral nerve.

Jang SY, Shin YK, Park SY, Park JY, Rha SH, Kim JK, Lee HJ, Park HT - PLoS ONE (2015)

Changes of cytoplasmic area of mSCs during the postnatal period.A. A schematic drawing of mSCs showing the abaxonal cytoplasm outside of the compact myelin sheath. B. Representative EM images of sciatic nerves from wild-type mice showing the reduction of cytoplasmic area of mSCs during postnatal development. Asterisk; nucleus, double arrows; abaxonal cytoplasm. Note the developmental downregulation of abaxonal cytoplasm. C. Representative EM images of mSCs from mice of different ages. Arrowheads: lysosome. M: mitochondria. N: nucleus. Arrows demonstrate various morphologies of RER. C’. Enlarged image of a lysosome. D. Morphometric quantification of the abaxonal cytoplasmic area (n = 3 for each ages). E. The number of lysosomes in the perinuclear cytoplasm of mSCs from different ages was counted under EM, and the mean number of lysosomes per mSC is displayed (n = 3, mean±SEM).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4291222&req=5

pone.0116624.g001: Changes of cytoplasmic area of mSCs during the postnatal period.A. A schematic drawing of mSCs showing the abaxonal cytoplasm outside of the compact myelin sheath. B. Representative EM images of sciatic nerves from wild-type mice showing the reduction of cytoplasmic area of mSCs during postnatal development. Asterisk; nucleus, double arrows; abaxonal cytoplasm. Note the developmental downregulation of abaxonal cytoplasm. C. Representative EM images of mSCs from mice of different ages. Arrowheads: lysosome. M: mitochondria. N: nucleus. Arrows demonstrate various morphologies of RER. C’. Enlarged image of a lysosome. D. Morphometric quantification of the abaxonal cytoplasmic area (n = 3 for each ages). E. The number of lysosomes in the perinuclear cytoplasm of mSCs from different ages was counted under EM, and the mean number of lysosomes per mSC is displayed (n = 3, mean±SEM).
Mentions: For electron microscopic analysis, captured EM images (×4000~5000) were analyzed using the ImageJ software (National Institute of Health, Bethesda). Abaxonal areas were demarcated and calculated by drawing a continuous line with the ImageJ software and mean areas were calculated from approximately 300~500 randomly selected myelinated SCs at each time point (n = 3). The number of lysosomes in the perinuclear cytoplasm of 70~100 mSCs that had nuclei visible in ultrathin sections was counted, using three animals in each age group. Lysosome was defined as a membrane-bound electron dense structure (0.2~0.5 μM in diameter, Fig. 1C’) which was distinguished from membrane-unbound less electron-dense lipid droplets. Quantitative analysis of the number of appositions in the mSCs was performed from 300~500 randomly selected myelinated SCs at P60 (n = 3). G ratios were determined by dividing the perimeter of the axon by that of the outset leaflet of the myelin sheath at P10 and P60. Approximately 170~200 round axons from two mice in each group were employed for the analysis. The morphometric analysis of Remak bundle development (the number of axons in a bundle) was determined from the same images used for g ratio analysis and approximately 130 Remak bundles from two animals (P60) in each group were pooled and analyzed.

Bottom Line: Inhibition of autophagy via Schwann cell-specific removal of ATG7, an essential molecule for macroautophagy, using a conditional knockout strategy, resulted in abnormally enlarged abaxonal cytoplasm in myelinating Schwann cells that contained a large number of ribosomes and an atypically expanded endoplasmic reticulum.Rapamycin-induced suppression of mTOR activity during the early postnatal period enhanced not only autophagy but also developmental reduction of myelinating Schwann cells cytoplasm in vivo.Together, our findings suggest that autophagy is a regulatory mechanism of Schwann cells structural plasticity during myelination.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Mitochondria Hub Regulation Center, Busan, Korea.

ABSTRACT
Peripheral nerve myelination involves dynamic changes in Schwann cell morphology and membrane structure. Recent studies have demonstrated that autophagy regulates organelle biogenesis and plasma membrane dynamics. In the present study, we investigated the role of autophagy in the development and differentiation of myelinating Schwann cells during sciatic nerve myelination. Electron microscopy and biochemical assays have shown that Schwann cells remove excess cytoplasmic organelles during myelination through macroautophagy. Inhibition of autophagy via Schwann cell-specific removal of ATG7, an essential molecule for macroautophagy, using a conditional knockout strategy, resulted in abnormally enlarged abaxonal cytoplasm in myelinating Schwann cells that contained a large number of ribosomes and an atypically expanded endoplasmic reticulum. Small fiber hypermyelination and minor anomalous peripheral nerve functions are observed in this mutant. Rapamycin-induced suppression of mTOR activity during the early postnatal period enhanced not only autophagy but also developmental reduction of myelinating Schwann cells cytoplasm in vivo. Together, our findings suggest that autophagy is a regulatory mechanism of Schwann cells structural plasticity during myelination.

Show MeSH
Related in: MedlinePlus