Metformin enhances insulin signalling in insulin-dependent and-independent pathways in insulin resistant muscle cells.
1 Metformin lowers blood glucose levels in type 2 diabetic patients. To evaluate the insulin sensitizing action of metformin on skeletal muscle cells, we have used C2C12 skeletal muscle cells differentiated in chronic presence or absence of insulin. 2 Metformin was added during the last 24 h of differentiation of the C2C12 myotubes. Insulin-stimulated tyrosine phosphorylation of insulin receptor (IR) and insulin receptor substrate-1 (IRS-1) was determined. 3 Chronic insulin treatment resulted in 60 and 40% reduction in insulin-stimulated tyrosine phosphorylation of IR and IRS-1, respectively. Treatment with metformin was able to increase the tyrosine phosphorylation of IR and IRS-1 by 100 and 90% respectively. 4 Chronic insulin treatment drastically reduced (45%) insulin-stimulated phosphatidyl inositol 3-kinase (PI 3-kinase) activity. Metformin treatment restored PI 3-kinase activity in insulin-resistant myotubes. 5 Insulin-stimulated glucose uptake was impaired in chronically insulin-treated myotubes. Metformin increased basal glucose uptake to significant levels (P<0.05), but metformin did not increase insulin-stimulated glucose transport. 6 All the three mitogen-activated protein kinases (MAPK) were activated by insulin in sensitive myotubes. The activation of p38 MAPK was impaired in resistant myotubes, while ERK and JNK were unaffected. Treatment with metformin enhanced the basal activation levels of p38 in both sensitive and resistant myotubes, but insulin did not further stimulate p38 activation in metformin treated cells. 7 Treatment of cells with p38 inhibitor, SB203580, blocked insulin- and metformin-stimulated glucose uptake as well as p38 activation. 8 Since the effect of metformin on glucose uptake corresponded to p38 MAPK activation, this suggests the potential role p38 in glucose uptake. 9 These data demonstrate the direct insulin sensitizing action of metformin on skeletal muscle cells.
Kumar
Naresh
N
Signal Transduction Research Laboratory, Department of Biotechnology, National Institute of Pharmaceutical Education and Research, Punjab, India.
Dey
Chinmoy S
CS
D000818:Animals; D002478:Cells, Cultured; D003847:Deoxyglucose / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007093:Imidazoles / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance; D008687:Metformin / Q000494:pharmacology*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011725:Pyridines / Q000494:pharmacology; D011972:Receptor, Insulin / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014443:Tyrosine / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases
D007004:Hypoglycemic Agents; D007093:Imidazoles; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010750:Phosphoproteins; D011725:Pyridines; D014443:Tyrosine; D008687:Metformin; D003847:Deoxyglucose; D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580