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Compensatory Motor Neuron Response to Chromatolysis in the Murine hSOD1(G93A) Model of Amyotrophic Lateral Sclerosis.

Riancho J, Ruiz-Soto M, Villagrá NT, Berciano J, Berciano MT, Lafarga M - Front Cell Neurosci (2014)

Bottom Line: Collectively, the perinuclear reorganization of protein synthesis machinery, the predominant euchromatin architecture, and the active nucleolar transcription could represent compensatory mechanisms in ALS motor neurons in response to the disturbance of ER proteostasis.In this scenario, epigenetic activation of chromatin and nucleolar transcription could have important therapeutic implications for neuroprotection in ALS and other neurodegenerative diseases.Although histone deacetylase inhibitors are currently used as therapeutic agents, we raise the untapped potential of the nucleolar transcription of ribosomal genes as an exciting new target for the therapy of some neurodegenerative diseases.

View Article: PubMed Central - PubMed

Affiliation: Service of Neurology, University Hospital Marqués de Valdecilla, Instituto de Investigación Valdecilla (IDIVAL), University of Cantabria , Santander , Spain.

ABSTRACT
We investigated neuronal self-defense mechanisms in a murine model of amyotrophic lateral sclerosis (ALS), the transgenic hSOD1(G93A), during both the asymptomatic and symptomatic stages. This is an experimental model of endoplasmic reticulum (ER) stress with severe chromatolysis. As a compensatory response to translation inhibition, chromatolytic neurons tended to reorganize the protein synthesis machinery at the perinuclear region, preferentially at nuclear infolding domains enriched in nuclear pores. This organization could facilitate nucleo-cytoplasmic traffic of RNAs and proteins at translation sites. By electron microscopy analysis, we observed that the active euchromatin pattern and the reticulated nucleolar configuration of control motor neurons were preserved in ALS chromatolytic neurons. Moreover the 5'-fluorouridine (5'-FU) transcription assay, at the ultrastructural level, revealed high incorporation of the RNA precursor 5'-FU into nascent RNA. Immunogold particles of 5'-FU incorporation were distributed throughout the euchromatin and on the dense fibrillar component of the nucleolus in both control and ALS motor neurons. The high rate of rRNA transcription in ALS motor neurons could maintain ribosome biogenesis under conditions of severe dysfunction of proteostasis. Collectively, the perinuclear reorganization of protein synthesis machinery, the predominant euchromatin architecture, and the active nucleolar transcription could represent compensatory mechanisms in ALS motor neurons in response to the disturbance of ER proteostasis. In this scenario, epigenetic activation of chromatin and nucleolar transcription could have important therapeutic implications for neuroprotection in ALS and other neurodegenerative diseases. Although histone deacetylase inhibitors are currently used as therapeutic agents, we raise the untapped potential of the nucleolar transcription of ribosomal genes as an exciting new target for the therapy of some neurodegenerative diseases.

No MeSH data available.


Related in: MedlinePlus

(A–C) Nucleolar organization in motor neurons from control (C) and ALS (A,B) hSOD1G93A mice. (A) ALS chromatolytic neurons with nuclear eccentricity and a prominent nucleolus. Note the presence of interchromatin granule clusters (white asterisks) and a Cajal body (arrow). (B,C) In both control and ALS motor neurons, the nucleolus exhibits a typical reticulated configuration with numerous fibrillar centers surrounded by the dense fibrillar component and intercalated masses of the granular component. hChr: nucleolus-associated heterochromatin. (D,E) Transcription assay with a 45 min pulse of 5′-FU incorporation into nascent RNA. A similar pattern of 5′-FU incorporation is detected in nucleoli of both control and ALS motor neurons. Immunogold particles of 5′-FU incorporation in nucleolar transcription sites preferentially decorate the dense fibrillar component. Transcriptional activity is also detected throughout the euchromatin, while the transcriptionally silent heterochromatin (hChr) lacks of immunogold particles. (F,G) Detail of euchromatin regions from control and ALS motor neurons shows the localization of the extranucleolar transcription sites in perichromatin fibrils, which appear decorated with immunogold particles. (H) Some immunogold particles decorate newly synthesized RNA on polyribosomes accumulated at the perinuclear region, within a nuclear invagination, in a motor neuron from the hSOD1G93A mouse. Scale bars: A = 2 μm; B,C = 0.8 μm; D,E = 0.75 μm; F–H = 325 nm. (I) Morphometric analysis of the nucleolar diameter in mononucleolated motor neurons from control and hSOD1G93A mice. Data are mean ± SE from three independent experiments; *p < 0.05. At least 100 neurons per animal group were sampled. (J) Labeling density of gold particles detecting 5′-FU incorporation in euchromatin and nucleolar compartments. Data are mean ± SD (see additional information in Materials and Methods).
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Figure 5: (A–C) Nucleolar organization in motor neurons from control (C) and ALS (A,B) hSOD1G93A mice. (A) ALS chromatolytic neurons with nuclear eccentricity and a prominent nucleolus. Note the presence of interchromatin granule clusters (white asterisks) and a Cajal body (arrow). (B,C) In both control and ALS motor neurons, the nucleolus exhibits a typical reticulated configuration with numerous fibrillar centers surrounded by the dense fibrillar component and intercalated masses of the granular component. hChr: nucleolus-associated heterochromatin. (D,E) Transcription assay with a 45 min pulse of 5′-FU incorporation into nascent RNA. A similar pattern of 5′-FU incorporation is detected in nucleoli of both control and ALS motor neurons. Immunogold particles of 5′-FU incorporation in nucleolar transcription sites preferentially decorate the dense fibrillar component. Transcriptional activity is also detected throughout the euchromatin, while the transcriptionally silent heterochromatin (hChr) lacks of immunogold particles. (F,G) Detail of euchromatin regions from control and ALS motor neurons shows the localization of the extranucleolar transcription sites in perichromatin fibrils, which appear decorated with immunogold particles. (H) Some immunogold particles decorate newly synthesized RNA on polyribosomes accumulated at the perinuclear region, within a nuclear invagination, in a motor neuron from the hSOD1G93A mouse. Scale bars: A = 2 μm; B,C = 0.8 μm; D,E = 0.75 μm; F–H = 325 nm. (I) Morphometric analysis of the nucleolar diameter in mononucleolated motor neurons from control and hSOD1G93A mice. Data are mean ± SE from three independent experiments; *p < 0.05. At least 100 neurons per animal group were sampled. (J) Labeling density of gold particles detecting 5′-FU incorporation in euchromatin and nucleolar compartments. Data are mean ± SD (see additional information in Materials and Methods).

Mentions: Since ribosome biogenesis is an essential step to sustain protein synthesis activity, we analyzed the response of nucleolus to severe chromatolysis in motor neurons of the ALS transgenic SOD1 mice. Light microscopy cytochemical staining with propidium iodide clearly illustrated prominent nucleoli in motor neurons from both control and ALS mice (Figure 1). The morphometric determination of the nucleolar diameter demonstrated that the nucleolar size was preserved in motor neurons from ALS mice (Figure 5I).


Compensatory Motor Neuron Response to Chromatolysis in the Murine hSOD1(G93A) Model of Amyotrophic Lateral Sclerosis.

Riancho J, Ruiz-Soto M, Villagrá NT, Berciano J, Berciano MT, Lafarga M - Front Cell Neurosci (2014)

(A–C) Nucleolar organization in motor neurons from control (C) and ALS (A,B) hSOD1G93A mice. (A) ALS chromatolytic neurons with nuclear eccentricity and a prominent nucleolus. Note the presence of interchromatin granule clusters (white asterisks) and a Cajal body (arrow). (B,C) In both control and ALS motor neurons, the nucleolus exhibits a typical reticulated configuration with numerous fibrillar centers surrounded by the dense fibrillar component and intercalated masses of the granular component. hChr: nucleolus-associated heterochromatin. (D,E) Transcription assay with a 45 min pulse of 5′-FU incorporation into nascent RNA. A similar pattern of 5′-FU incorporation is detected in nucleoli of both control and ALS motor neurons. Immunogold particles of 5′-FU incorporation in nucleolar transcription sites preferentially decorate the dense fibrillar component. Transcriptional activity is also detected throughout the euchromatin, while the transcriptionally silent heterochromatin (hChr) lacks of immunogold particles. (F,G) Detail of euchromatin regions from control and ALS motor neurons shows the localization of the extranucleolar transcription sites in perichromatin fibrils, which appear decorated with immunogold particles. (H) Some immunogold particles decorate newly synthesized RNA on polyribosomes accumulated at the perinuclear region, within a nuclear invagination, in a motor neuron from the hSOD1G93A mouse. Scale bars: A = 2 μm; B,C = 0.8 μm; D,E = 0.75 μm; F–H = 325 nm. (I) Morphometric analysis of the nucleolar diameter in mononucleolated motor neurons from control and hSOD1G93A mice. Data are mean ± SE from three independent experiments; *p < 0.05. At least 100 neurons per animal group were sampled. (J) Labeling density of gold particles detecting 5′-FU incorporation in euchromatin and nucleolar compartments. Data are mean ± SD (see additional information in Materials and Methods).
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Figure 5: (A–C) Nucleolar organization in motor neurons from control (C) and ALS (A,B) hSOD1G93A mice. (A) ALS chromatolytic neurons with nuclear eccentricity and a prominent nucleolus. Note the presence of interchromatin granule clusters (white asterisks) and a Cajal body (arrow). (B,C) In both control and ALS motor neurons, the nucleolus exhibits a typical reticulated configuration with numerous fibrillar centers surrounded by the dense fibrillar component and intercalated masses of the granular component. hChr: nucleolus-associated heterochromatin. (D,E) Transcription assay with a 45 min pulse of 5′-FU incorporation into nascent RNA. A similar pattern of 5′-FU incorporation is detected in nucleoli of both control and ALS motor neurons. Immunogold particles of 5′-FU incorporation in nucleolar transcription sites preferentially decorate the dense fibrillar component. Transcriptional activity is also detected throughout the euchromatin, while the transcriptionally silent heterochromatin (hChr) lacks of immunogold particles. (F,G) Detail of euchromatin regions from control and ALS motor neurons shows the localization of the extranucleolar transcription sites in perichromatin fibrils, which appear decorated with immunogold particles. (H) Some immunogold particles decorate newly synthesized RNA on polyribosomes accumulated at the perinuclear region, within a nuclear invagination, in a motor neuron from the hSOD1G93A mouse. Scale bars: A = 2 μm; B,C = 0.8 μm; D,E = 0.75 μm; F–H = 325 nm. (I) Morphometric analysis of the nucleolar diameter in mononucleolated motor neurons from control and hSOD1G93A mice. Data are mean ± SE from three independent experiments; *p < 0.05. At least 100 neurons per animal group were sampled. (J) Labeling density of gold particles detecting 5′-FU incorporation in euchromatin and nucleolar compartments. Data are mean ± SD (see additional information in Materials and Methods).
Mentions: Since ribosome biogenesis is an essential step to sustain protein synthesis activity, we analyzed the response of nucleolus to severe chromatolysis in motor neurons of the ALS transgenic SOD1 mice. Light microscopy cytochemical staining with propidium iodide clearly illustrated prominent nucleoli in motor neurons from both control and ALS mice (Figure 1). The morphometric determination of the nucleolar diameter demonstrated that the nucleolar size was preserved in motor neurons from ALS mice (Figure 5I).

Bottom Line: Collectively, the perinuclear reorganization of protein synthesis machinery, the predominant euchromatin architecture, and the active nucleolar transcription could represent compensatory mechanisms in ALS motor neurons in response to the disturbance of ER proteostasis.In this scenario, epigenetic activation of chromatin and nucleolar transcription could have important therapeutic implications for neuroprotection in ALS and other neurodegenerative diseases.Although histone deacetylase inhibitors are currently used as therapeutic agents, we raise the untapped potential of the nucleolar transcription of ribosomal genes as an exciting new target for the therapy of some neurodegenerative diseases.

View Article: PubMed Central - PubMed

Affiliation: Service of Neurology, University Hospital Marqués de Valdecilla, Instituto de Investigación Valdecilla (IDIVAL), University of Cantabria , Santander , Spain.

ABSTRACT
We investigated neuronal self-defense mechanisms in a murine model of amyotrophic lateral sclerosis (ALS), the transgenic hSOD1(G93A), during both the asymptomatic and symptomatic stages. This is an experimental model of endoplasmic reticulum (ER) stress with severe chromatolysis. As a compensatory response to translation inhibition, chromatolytic neurons tended to reorganize the protein synthesis machinery at the perinuclear region, preferentially at nuclear infolding domains enriched in nuclear pores. This organization could facilitate nucleo-cytoplasmic traffic of RNAs and proteins at translation sites. By electron microscopy analysis, we observed that the active euchromatin pattern and the reticulated nucleolar configuration of control motor neurons were preserved in ALS chromatolytic neurons. Moreover the 5'-fluorouridine (5'-FU) transcription assay, at the ultrastructural level, revealed high incorporation of the RNA precursor 5'-FU into nascent RNA. Immunogold particles of 5'-FU incorporation were distributed throughout the euchromatin and on the dense fibrillar component of the nucleolus in both control and ALS motor neurons. The high rate of rRNA transcription in ALS motor neurons could maintain ribosome biogenesis under conditions of severe dysfunction of proteostasis. Collectively, the perinuclear reorganization of protein synthesis machinery, the predominant euchromatin architecture, and the active nucleolar transcription could represent compensatory mechanisms in ALS motor neurons in response to the disturbance of ER proteostasis. In this scenario, epigenetic activation of chromatin and nucleolar transcription could have important therapeutic implications for neuroprotection in ALS and other neurodegenerative diseases. Although histone deacetylase inhibitors are currently used as therapeutic agents, we raise the untapped potential of the nucleolar transcription of ribosomal genes as an exciting new target for the therapy of some neurodegenerative diseases.

No MeSH data available.


Related in: MedlinePlus