Regionally different immunoreactivity for Smurf2 and pSmad2/3 in TDP-43-positive inclusions of amyotrophic lateral
M Nakamura1, S Kaneko1, R Wate1
1Department of Neurology, Kansai Medical University, OsakaDepartment of Neurology, Kyoto University Graduate School of Medicine, Kyoto, Japan.
Aims:
Smad ubiquitination regulatory factor-2 (Smurf2), an E3 ubiquitin ligase, can interact with Smad proteins and promote their ubiquitin-dependent degradation, thereby controlling the cellular levels of these signalling mediators. We previously reported that phosphorylated Smad2/3 (pSmad2/3) was sequestered in transactive response DNA-binding protein-43 (TDP-43) inclusions in the spinal cord of patients with amyotrophic lateral sclerosis (ALS). Recent biochemical and immunohistochemical studies on spinal cord and brain of ALS patients demonstrated that the composition of the TDP-43 inclusions is regionally distinct, suggesting different underlying pathogenic processes. We aimed to elucidate regional differences in pathomechanisms and composition of TDP-43 inclusions in relation to pSmad2/3 and Smurf2.
Methods:
The spinal cord and brain tissues of 13 sporadic ALS (SALS) patients were investigated using immunohistochemical analysis.
Results:
TDP-43-positive inclusions in lower motor neurones of SALS patients were immunopositive for Smurf2 and pSmad2/3. Multiple immunofluorescence staining for Smurf2, pSmad2/3, TDP-43 and ubiquitin revealed co-localization of these four proteins within the inclusions in lower motor neurones of SALS patients. Furthermore, the loss of nuclear pSmad2/3 immunoreactivity was observed in cells bearing TDP-43 inclusions. In contrast, TDP-43-positive inclusions in the extramotor neurones in the brain of SALS patients were noticeably negative for Smurf2 and pSmad2/3. In addition, pSmad2/3 immunoreactivity was preserved in the nuclei of inclusion-bearing cells.
Conclusions:
This regional difference in the expression of Smurf2 and pSmad2/3 within TDP-43-positive inclusions might be one of the pathomechanisms underlying the loss of lower motor neurones and comparatively spared cortical neurones seen in ALS.
Insights
Regional differences in Smurf2 and phosphorylated Smad2/3 (pSmad2/3) within transactive response DNA-binding protein-43 (TDP-43) inclusions may explain motor neuron loss in amyotrophic lateral sclerosis (ALS). This study investigated these inclusions in ALS patient tissues.
Area of Science:
- Neuroscience
- Cell Biology
- Pathology
Background:
- Smad ubiquitination regulatory factor-2 (Smurf2) regulates Smad protein levels.
- Phosphorylated Smad2/3 (pSmad2/3) is found in transactive response DNA-binding protein-43 (TDP-43) inclusions in ALS spinal cords.
- TDP-43 inclusion composition varies regionally in ALS patients, suggesting diverse pathomechanisms.
Purpose of the Study:
- To investigate regional differences in TDP-43 inclusion composition.
- To examine the relationship between TDP-43 inclusions, pSmad2/3, and Smurf2 in ALS.
- To elucidate pathomechanisms underlying motor neuron degeneration in ALS.
Main Methods:
- Immunohistochemical analysis of spinal cord and brain tissues from 13 sporadic ALS patients.
- Multiple immunofluorescence staining for Smurf2, pSmad2/3, TDP-43, and ubiquitin.
Main Results:
- TDP-43 inclusions in lower motor neurons contained Smurf2 and pSmad2/3, with co-localization of all four proteins.
- Loss of nuclear pSmad2/3 immunoreactivity occurred in motor neurons with TDP-43 inclusions.
- TDP-43 inclusions in extramotor neurons lacked Smurf2 and pSmad2/3, with preserved nuclear pSmad2/3.
Conclusions:
- Regional variations in Smurf2 and pSmad2/3 within TDP-43 inclusions are implicated in motor neuron loss in ALS.
- These differences may contribute to the distinct vulnerability of motor neurons versus cortical neurons in ALS pathogenesis.
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