Metformin prevents glucotoxicity by alleviating oxidative and ER stress-induced CD36 expression in pancreatic beta cells.
Cluster determinant 36 (CD36), a fatty acid transporter, was reported to have a pivotal role in glucotoxicity-induced beta cell dysfunction. However, little is known about how glucotoxicity influences CD36 expression, and it is unknown whether this action can be counteracted by metformin. In the present study, we showed that metformin counteracts glucotoxicity by alleviating oxidative and endoplasmic reticulum (ER) stress-induced CD36 expression.



We used primary rat islets as well as INS-1 cells for 72h to 24h with 30mM glucose, respectively. Thapsigargin was used as strong ER stressor, and Sulfo-N-succinimidyl oleate (SSO) and RNA interference were chosen for CD36 inhibition. Free fatty acid uptake was measured by radioisotope tracing technique.



Exposure of isolated rat islets to high glucose (HG) for 3days decreased insulin and pancreatic duodenal homeobox1 (Pdx1) mRNA expression, with the suppression of glucose-stimulated insulin secretion (GSIS) along with elevation of reactive oxygen species (ROS) levels. Incubation with metformin restored insulin and Pdx1 mRNA expression with significant improvements in GSIS and decrease in ROS production. HG exposure in INS-1 cells increased free fatty acid uptake via induction of CD36 along with impaired insulin and Pdx1 mRNA expression. Moreover, thapsigargin also increased the induction of CD36 expression. Metformin blocked HG- and thapsigargin-induced CD36 expression. In addition, the simultaneous inhibition of intracellular ROS production by metformin or CD36 activation by SSO or CD36 siRNA significantly decreased the apoptotic response in HG-treated INS-1 cells.



In conclusion, metformin conferred protection against HG-induced apoptosis of pancreatic beta cells, largely by interfering with ROS production, and inhibited the CD36-mediated free fatty acid influx. This report provides evidence that the inhibition of CD36 may have potential therapeutic effects against hyperglycemia-induced beta cell damage in diabetes.
Department of Internal Medicine, Yeungnam University College of Medicine, Daegu, Republic of Korea.
Jun Sung
JS
Moon
Institute of Medical Science, Yeungnam University College of Medicine, Daegu, Republic of Korea.
Udayakumar
U
Karunakaran
Institute of Medical Science, Yeungnam University College of Medicine, Daegu, Republic of Korea.
Suma
S
Elumalai
Department of Internal Medicine, Kyungpook National University School of Medicine, Daegu.
In-Kyu
IK
Lee
Department of Internal Medicine, Yeungnam University College of Medicine, Daegu, Republic of Korea.
Hyoung Woo
HW
Lee
Department of Physiology, Yeungnam University College of Medicine, Daegu, Republic of Korea.
Yong-Woon
YW
Kim
Department of Internal Medicine, Yeungnam University College of Medicine, Daegu, Republic of Korea; Institute of Medical Science, Yeungnam University College of Medicine, Daegu, Republic of Korea. Electronic address: kcwon@med.yu.ac.kr.
Kyu Chang
KC
Won
D000818:Animals; D018955:CD36 Antigens / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D019610:Cytoprotection / Q000187:drug effects / Q000235:genetics; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects* / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects; D005947:Glucose / Q000633:toxicity*; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism; D008687:Metformin / Q000494:pharmacology*; D018384:Oxidative Stress / Q000187:drug effects* / Q000235:genetics; D061251:Primary Cell Culture; D051381:Rats
D018955:CD36 Antigens; D008687:Metformin; D005947:Glucose
Beta cells; CD36; Diabetes; Glucotoxicity; Metformin; Oxidative stress