Atorvastatin inhibits insulin synthesis by inhibiting the Ras/Raf/ERK/CREB pathway in INS-1 cells.
BACKGROUND
Type 2 diabetes has become a global epidemic disease. Atorvastatin has become a cornerstone in the prevention and treatment of atherosclerosis. However, increasing evidence showed that statins can dose-dependently increase the risk of diabetes mellitus. The mechanism is not clear.


OBJECTIVE
The Ras complex pathway (Ras/Raf/extracellular signal-regulated kinase [ERK]/cAMP response element-binding protein [CREB]) is the major pathway that regulates the gene transcription. Except for the inhibition of cholesterol synthesis by inhibiting the 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-COA) reductase, statins can also downregulate the phosphorylation of a series of downstream substrates including the key proteins of the Ras complex pathway, therefore may inhibit the insulin syntheses in pancreatic beta cells. In our study, we investigated the inhibitory effect and the underlying mechanism of atorvastatin on insulin synthesis in rat islets.


METHODS
Islets were isolated from Wistar rats and cultured in Roswell Park Memorial Institute (RPMI)-1640 medium. The insulin content in the medium was measured by radioimmunoassay before and after the treatment of 50 μM atorvastatin. Effect of atorvastatin on the expression of insulin message Ribonucleic acid (mRNA) in pancreatic islet beta cells was also detected using quantitative real-time polymerase chain reaction. Western blotting was used to explore the possible role of the Ras complex pathway (Ras/Raf/ERK/CREB) in atorvastatin-inhibited insulin synthesis. The effects of atorvastatin on the binding of nuclear transcription factor p-CREB with CRE in INS-1 cells were examined via chromatin immunoprecipitation assay.


RESULTS
Compared with the control group, the insulin level decreased by 27.1% at 24 hours after atorvastatin treatment. Atorvastatin inhibited insulin synthesis by decreasing insulin mRNA expression of pancreatic islet beta cells. The activities of Ras, Raf-1, and p-CREB in the Ras complex pathway were inhibited by 50 μM atorvastatin in INS-1 cells in vitro. Moreover, 50 μM atorvastatin reduced the binding of p-CREB with deoxyribonucleic acid (DNA) in INS-1 cells in vitro.


CONCLUSIONS
Atorvastatin inhibits insulin synthesis in beta cells by inhibiting the activation of the Ras complex pathway.
aDepartment of Nephrology, 2011 Collaborative Innovation Center of Tianjin for Medical Epigenetics, Key Laboratory of Hormones and Development (Ministry of Health), Tianjin Key Laboratory of Metabolic Diseases, Tianjin Metabolic Diseases Hospital & Tianjin Institute of Endocrinology, Tianjin Medical University, Tianjin, China bDepartment of Endocrinology cDepartment of Neurosurgery, The Affiliated Hospital of Weifang Medical College, Weifang, Shandong 261031, China.
Hongxi
H
Sun
Yu
Y
Li
Bei
B
Sun
Ningning
N
Hou
Juhong
J
Yang
Miaoyan
M
Zheng
Jie
J
Xu
Jingyu
J
Wang
Yi
Y
Zhang
Xianwei
X
Zeng
Chunyan
C
Shan
Bai
B
Chang
Liming
L
Chen
Baocheng
B
Chang
D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology*; D000069059:Atorvastatin / Q000494:pharmacology*; D015153:Blotting, Western; D050882:CREB-Binding Protein / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D007328:Insulin / Q000096:biosynthesis*; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D049488:Phosphatidylethanolamine Binding Protein / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D060888:Real-Time Polymerase Chain Reaction; D018631:ras Proteins / Q000378:metabolism
D000924:Anticholesteremic Agents; D007328:Insulin; C550693:PEBP1 protein, rat; D049488:Phosphatidylethanolamine Binding Protein; D000069059:Atorvastatin; D050882:CREB-Binding Protein; C494365:Crebbp protein, rat; D048049:Extracellular Signal-Regulated MAP Kinases; D018631:ras Proteins
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