Effects of transfection with adiponectin cDNA on glycogen synthesis and glucose oxidation in myotubes of skeletal muscle cell strain C2C12

Miao ZHANG; Fangping LI; Chuan YANG; Yan QIAN; Dan LIU; Zuzhi FU

ABSTRACT

BACKGROUND:

Adiponectin possess functions of lowering blood glucose and blood lipids, and improve insulin sensitivity. But, controversy results about the effect of adiponectin on skeletal muscle have been reported.

OBJECTIVE:

To study the effects of eukaryon expressed adiponectin on the glycogen synthesis and glucose oxidation in skeletal muscle cell strain C2C12 myotubes by transfecting plasmids carrying mouse adiponectin.

DESIGN:

A controlled experiment.

SETTING:

The Second Affiliated Hospital of Sun Yat-sen University.MATERIALS PcDNA3.0 plasmid with mouse adiponectin cDNA, pcDNA3.0-mad (generously presented from Dr. Gong,University of Maryland), C2C12 cell strain (purchased from ATCC, GRL-1722), DMEM high glucose (Gibco), MEM (Hyclone), fetal bovine serum (Hanagzhou Sijiqing), equine serum (Hyclone), lipofectamine 2000 (Invitrogene), G418 (Gibco), rabbit anti-mouse adiponectin IgG (ACRP303-A, Alpha Diagnostic International), chemiluminescence kit (ECL+PLUS,Amersham), SABC instant immunohistochemistry kit (Boster), D-[U-14C] glucose (specific activity 9.25-13.32 GBq/mmol,NEC), scintillation fluid POP, POPOP (SIGMA), liquid scintillation counter (LS3801, Beckman, USA).

METHODS:

This study was carried out in the Central Laboratory of the Second Affiliated Hospital of Sun Yat-sen University from March to August, 2003. ① After extraction of plasmid, double digest with Xho Ⅰ and Xba Ⅰ and identification with HindⅢ digest were carried out. ② Plasmid pcDNA3.0-mad and pcDNA3.0 blank vector were transfected using liposome to C2C12 cells, and the stably transfected cells were screened by 500 mg/L G418 for 3 weeks, G418 resistant C2C12 cells were thereafter harvested, therefore stable transfected pcDNA3.0-mad and pcDNA 3.0 C2C12 cell strains were established.③ Adiponectin protein expression was determined by Western blot analysis and immunohistochemistry. ④ Glucose oxidation and glycogen synthesis detections were divided into control, vector and pcDNA3.0-mad (mad)group. Each group was further divided into 4 subgroups with 0, 0.5, 5 and 100 nmol/L insulin (n =6), respectively. Detection of glucose oxidation and glycogen synthesis was carried out with 14C-labeled glucose by counting radioactivity of 14CO2 or 14C labeled glycogen with scintillation, respectively.MAIN OUTCOME

MEASURES:

Changes of glycogen synthesis and glucose oxidation in skeletal muscle cell strain C2C12myotubes.

RESULTS:

① Results of plasmid transfection and restrict digest After plasmid extraction, double digest with Xba Ⅰ and Xho Ⅰ was carried out along with HindⅢ digest identification.Digest fragments were in accordance with expectation.Length of adiponectin cDNA fragment was 781 bp, plasmid fragment was 5 446 bp, adiponectin cDNA was inserted between digest sites (Xho Ⅰ and Xba Ⅰ ) of eukaryotic expression vector pcDNA3.0. ② Plasmid transfection of C2C12 cell and positive clone screening On the 10th day of G418 media culture screening after transfection, most C2C12 cells died.Positive clone appeared at the 2nd week. G418 resistant C2C12 colonies were harvested at the 3rd week. ③ Western blot and immunohistochemical identifications Both confirmed that adipoenctin gene was stably transfected into cells in the Mad group, with successful adipoenctin expression. ④ Effect of stably transfected adiponectin gene to myocyte glucose metabolismThe myocyte glycogen synthesis and glucose oxidation increased along with the increasing of insulin concentration. The linear regression analyses of measured myocyte glucose oxidation amount showed that the regression coefficients of the control group, blank vector group and mad group were 23.34, 2;3.23 and 26.06 respectively. This result indicated that in C2C12 cell stably transfected with adiponectin gene, when insulin concentration increased, the acceleration rate of glucose oxidation increasing was higher than other 2 groups. However, no significant difference could be observed in glycogen synthesis and glucose oxidation of C2C12 cells under basic status without insulin stimulus and treatment status with different insulin concentrations between control group, blank vector group and mad group (P＞ 0.05).

CONCLUSION:

① We have successfully established stably adiponectin gene transfected C2C12 cell strain with adiponectin protein expression ability. ② Transfection with adiponectin cDNA had no significant effect on the glucose oxidation and glycogen synthesis of C2C12 myotubes.③ The glucose oxidation and glycogen synthesis of C2C12 myotubes increased with the increasing of insulin concentration. ④ Adipoenctin may coordinate with insulin in improving myocyte glucose oxidation and increasing myocyte glucose uptake.