Activation of transforming growth factor-β/Smad signaling reduces aggregate formation of mislocalized TAR DNA-binding protein-43.
BACKGROUND
TAR DNA-binding protein of 43 kDa (TDP-43) is naturally located in the nucleus and has been identified as the major component of cytoplasmic ubiquitinated inclusions in patients with amyotrophic lateral sclerosis (ALS). We have reported that TDP-43 and phosphorylated Smad2 (pSmad2), an intracellular mediator protein of transforming growth factor-β (TGFβ) signaling, are co-localized within cytoplasmic inclusions in the anterior horn cells of sporadic ALS patients.


OBJECTIVE
To investigate the possible pathophysiological linkage between pathologic cytoplasmic inclusions containing TDP-43 and TGFβ/Smad signaling.


METHODS
We replicated cytoplasmic aggregates of TDP-43 in HEK293T cells by transfecting the cells with a nuclear localization signal deletion mutant of TDP-43 and inhibiting proteasome activity, and assessed the effect of TGFβ/Smad signaling on the cytoplasmic aggregate formation.


RESULTS
The aggregates contained ubiquitinated, phosphorylated, and fragmented TDP-43, consistent with the essential features of the human pathology. Moreover, the aggregates were co-localized with pSmad2 under continuous TGFβ stimulation. Overexpression of Smad2 reduced the amount of cytoplasmic aggregates in HEK293T cells, and TGFβ stimulation augmented this reduction effect in a dose-dependent manner.


CONCLUSIONS
Activation of the TGFβ/Smad signaling system is protective against aggregate formation of cytoplasmically mislocalized TDP-43 and may be a potential therapeutic approach to delay progression of ALS.
Department of Neurology, Kansai Medical University, Osaka, Japan.
Masataka
M
Nakamura
Satoshi
S
Kaneko
Hidefumi
H
Ito
Shiwen
S
Jiang
Kengo
K
Fujita
Reika
R
Wate
Satoshi
S
Nakano
Jun-ichi
J
Fujisawa
Hirofumi
H
Kusaka
D000690:Amyotrophic Lateral Sclerosis / Q000378:metabolism; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D019913:Nuclear Localization Signals / Q000378:metabolism; D010766:Phosphorylation / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D051899:Smad2 Protein / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism
D004268:DNA-Binding Proteins; D019913:Nuclear Localization Signals; C497782:SMAD2 protein, human; D051899:Smad2 Protein; D016212:Transforming Growth Factor beta