Downregulation of adipose glutathione S-transferase A4 leads to increased protein carbonylation, oxidative stress, and mitochondrial dysfunction.
OBJECTIVE
Peripheral insulin resistance is linked to an increase in reactive oxygen species (ROS), leading in part to the production of reactive lipid aldehydes that modify the side chains of protein amino acids in a reaction termed protein carbonylation. The primary enzymatic method for lipid aldehyde detoxification is via glutathione S-transferase A4 (GSTA4) dependent glutathionylation. The objective of this study was to evaluate the expression of GSTA4 and the role(s) of protein carbonylation in adipocyte function.


METHODS
GSTA4-silenced 3T3-L1 adipocytes and GSTA4-null mice were evaluated for metabolic processes, mitochondrial function, and reactive oxygen species production. GSTA4 expression in human obesity was evaluated using microarray analysis.


RESULTS
GSTA4 expression is selectively downregulated in adipose tissue of obese insulin-resistant C57BL/6J mice and in human obesity-linked insulin resistance. Tumor necrosis factor-alpha treatment of 3T3-L1 adipocytes decreased GSTA4 expression, and silencing GSTA4 mRNA in cultured adipocytes resulted in increased protein carbonylation, increased mitochondrial ROS, dysfunctional state 3 respiration, and altered glucose transport and lipolysis. Mitochondrial function in adipocytes of lean or obese GSTA4-null mice was significantly compromised compared with wild-type controls and was accompanied by an increase in superoxide anion.


CONCLUSIONS
These results indicate that downregulation of GSTA4 in adipose tissue leads to increased protein carbonylation, ROS production, and mitochondrial dysfunction and may contribute to the development of insulin resistance and type 2 diabetes.
Department of Biochemistry, Molecular Biology and Biophysics, The University of Minnesota, Minneapolis, Minnesota, USA.
Jessica M
JM
Curtis
Paul A
PA
Grimsrud
Wendy S
WS
Wright
Xin
X
Xu
Rocio E
RE
Foncea
David W
DW
Graham
Jonathan R
JR
Brestoff
Brian M
BM
Wiczer
Olga
O
Ilkayeva
Katherine
K
Cianflone
Deborah E
DE
Muoio
Edgar A
EA
Arriaga
David A
DA
Bernlohr
D041721:3T3-L1 Cells; D000818:Animals; D015536:Down-Regulation; D005982:Glutathione Transferase / Q000235:genetics / Q000502:physiology*; D006801:Humans; D007333:Insulin Resistance / Q000235:genetics / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008928:Mitochondria / Q000378:metabolism / Q000473:pathology*; D009765:Obesity / Q000201:enzymology / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis; D018384:Oxidative Stress / Q000235:genetics / Q000502:physiology*; D050050:Protein Carbonylation / Q000235:genetics / Q000502:physiology*
D005982:Glutathione Transferase; C041116:leukotriene-C4 synthase