Metformin ameliorates insulin resistance in L6 rat skeletal muscle cells through upregulation of SIRT3.
BACKGROUND
SIRT3 is an important regulator in cell metabolism, and recent studies have shown that it may be involved in the pharmacological effects of metformin. However, the molecular mechanisms underlying this process are unclear.


METHODS
The effects of SIRT3 on the regulation of oxidative stress and insulin resistance in skeletal muscle were evaluated in vitro. Differentiated L6 skeletal muscle cells were treated with 750 µmol/L palmitic acid to induce insulin resistance. SIRT3 was knocked down and overexpressed in L6 cells. SIRT3, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65, c-Jun N-terminal kinase 1 (JNK1), and superoxide dismutase 2 (SOD2) were evaluated by Western blotting.


RESULTS
Over expression of SIRT3 increased glucose uptake and decreased ROS production in L6-IR cells as well as in L6 cells. Knock-down of SIRT3 induced increased production of ROS while decreased glucose uptake in both L6 and L6-IR cells, and these effects were reversed by N-acetyl-L-cysteine (NAC). Metformin increased the expression of SIRT3 (1.5-fold) and SOD2 (2-fold) while down regulating NF-κB p65 (1.5-fold) and JNK1 (1.5-fold). Knockdown of SIRT3 (P < 0.05) reversed the metformin-induced decreases in NF-κB p65 and JNK1 and the metformin-induced increase in SOD2 (P < 0.05).


CONCLUSIONS
Upregulated SIRT3 is involved in the pharmacological mechanism by which metformin promotes glucose uptake. Additionally, SIRT3 may function as an important regulator of oxidative stress and a new alternative approach for targeting insulin resistance-related diseases.
Department of Endocrinology, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China.
Yuping
Y
Song
Department of Endocrinology, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China.
Jingli
J
Shi
Department of Endocrinology, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China.
Ying
Y
Wu
Department of Endocrinology, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China.
Chong
C
Han
Department of Endocrinology, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China.
Junjie
J
Zou
Department of Endocrinology, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China.
Yongquan
Y
Shi
Department of Endocrinology, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China. Email: zmliu_cz@hotmail.com.
Zhimin
Z
Liu
D000818:Animals; D002460:Cell Line; D007333:Insulin Resistance / Q000502:physiology*; D008687:Metformin / Q000494:pharmacology*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects; D051381:Rats; D056566:Sirtuin 3 / Q000378:metabolism; D051996:Transcription Factor RelA / Q000378:metabolism
C498145:Rela protein, rat; D051996:Transcription Factor RelA; D008687:Metformin; D056566:Sirtuin 3