Role of salt inducible kinase 1 in high glucose-induced lipid accumulation in HepG2 cells and metformin intervention.
OBJECTIVE
To investigate the roles of salt inducible kinase (SIK1) in high glucose-induced triglyceride accumulation in human hepatoma HepG2 cells as well as in the molecular mechanism by which metformin, a drug to treat diabetes, suppresses high glucose-induced lipogenesis.


METHODS
A cell model for high glucose-induced hepatic steatosis was prepared by exposing HepG2 cells to high glucose (25mmol) in the absence or presence of metformin (0.5mmol). Intracellular triglycerides were visualized by Oil Red O and measured using a triglyceride assay kit. Cell viability was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method. SIK1 overexpression in HepG2 cells was achieved by transient transfection, and the mRNA and protein levels of SIK1 and lipogenic factors were measured using a reverse transcription-polymerase chain reaction and western blotting, respectively.


RESULTS
Lipid accumulation in HepG2 cells was obvious after treatment with high glucose for 24h. In response to high glucose, SIK1 expression was negatively correlated with that of lipogenic factors and lipid accumulation in HepG2 cells. We observed that overexpression of SIK1, or treatment with metformin, suppressed lipogenesis, even in high glucose conditions. Furthermore, treatment with metformin upregulated SIK1 mRNA and protein levels, as well as the active form of SIK1.


CONCLUSIONS
SIK1 plays a vital role in high glucose-induced lipid accumulation, and metformin suppresses lipogenesis via the induction and activation of SIK1.
Department of Endocrinology, Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, PR China.
Yue
Y
Zhang
Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University, Gifu, Japan.
Hiroshi
H
Takemori
Department of Endocrinology, Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, PR China.
Chang
C
Wang
Department of Endocrinology, Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, PR China.
JiaHui
J
Fu
Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, PR China.
MingWang
M
Xu
Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, PR China.
Liang
L
Xiong
Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, PR China.
NingXu
N
Li
Department of Traditional Chinese Medicine and Endocrinology, Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, PR China. Electronic address: wenxyoung@hust.edu.cn.
XiuYing
X
Wen
D005234:Fatty Liver / Q000139:chemically induced / Q000188:drug therapy* / Q000201:enzymology* / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D005947:Glucose / Q000009:adverse effects / Q000494:pharmacology; D056945:Hep G2 Cells; D006801:Humans; D050155:Lipogenesis / Q000187:drug effects*; D008687:Metformin / Q000494:pharmacology*; D008954:Models, Biological; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis* / Q000235:genetics
D008687:Metformin; D017346:Protein Serine-Threonine Kinases; C509080:SIK1 protein, human; D005947:Glucose
ACC1; FASN; HepG2 cells; High glucose; Lipogenesis; Metformin; SIK1; SREBP-1c