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2014 ; 289
(47
): 32703-16
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High glucose forces a positive feedback loop connecting Akt kinase and FoxO1
transcription factor to activate mTORC1 kinase for mesangial cell hypertrophy and
matrix protein expression
#MMPMID25288788
Das F
; Ghosh-Choudhury N
; Dey N
; Bera A
; Mariappan MM
; Kasinath BS
; Ghosh Choudhury G
J Biol Chem
2014[Nov]; 289
(47
): 32703-16
PMID25288788
show ga
High glucose-induced Akt acts as a signaling hub for mesangial cell hypertrophy
and matrix expansion, which are recognized as cardinal signatures for the
development of diabetic nephropathy. How mesangial cells sustain the activated
state of Akt is not clearly understood. Here we show Akt-dependent
phosphorylation of the transcription factor FoxO1 by high glucose.
Phosphorylation-deficient, constitutively active FoxO1 inhibited the high
glucose-induced phosphorylation of Akt to suppress the
phosphorylation/inactivation of PRAS40 and mTORC1 activity. In contrast, dominant
negative FoxO1 increased the phosphorylation of Akt, resulting in increased
mTORC1 activity similar to high glucose treatment. Notably, FoxO1 regulates high
glucose-induced protein synthesis, hypertrophy, and expression of fibronectin and
PAI-1. High glucose paves the way for complications of diabetic nephropathy
through the production of reactive oxygen species (ROS). We considered whether
the FoxO1 target antioxidant enzyme catalase contributes to sustained activation
of Akt. High glucose-inactivated FoxO1 decreases the expression of catalase to
increase the production of ROS. Moreover, we show that catalase blocks high
glucose-stimulated Akt phosphorylation to attenuate the inactivation of FoxO1 and
PRAS40, resulting in the inhibition of mTORC1 and mesangial cell hypertrophy and
fibronectin and PAI-1 expression. Finally, using kidney cortices from type 1
diabetic OVE26 mice, we show that increased FoxO1 phosphorylation is associated
with decreased catalase expression and increased fibronectin and PAI-1
expression. Together, our results provide the first evidence for the presence of
a positive feedback loop for the sustained activation of Akt involving
inactivated FoxO1 and a decrease in catalase expression, leading to increased ROS
and mesangial cell hypertrophy and matrix protein expression.
|Adaptor Proteins, Signal Transducing/metabolism
[MESH]
|Animals
[MESH]
|Catalase/genetics/metabolism
[MESH]
|Cell Size/drug effects
[MESH]
|Cells, Cultured
[MESH]
|Diabetes Mellitus, Type 1/genetics/metabolism/pathology
[MESH]