Chronic mTOR inhibition by rapamycin induces muscle insulin resistance despite weight loss in rats.
OBJECTIVE
mTOR inhibitors are currently used as immunosuppressants in transplanted patients and as promising anti-cancer agents. However, new-onset diabetes is a frequent complication occurring in patients treated with mTOR inhibitors such as rapamycin (Sirolimus). Here, we investigated the mechanisms associated with the diabetogenic effects of chronic Sirolimus administration in rats and in in vitro cell cultures.


METHODS
Sirolimus was administered to rats fed either a standard or high-fat diet for 21 days. Metabolic parameters were measured in vivo and in ex vivo tissues. Insulin sensitivity was assessed by glucose tolerance tests and euglycaemic hyperinsulinaemic clamps. Rapamycin effects on glucose metabolism and insulin signalling were further evaluated in cultured myotubes.


RESULTS
Sirolimus induced a decrease in food intake and concomitant weight loss. It also induced specific fat mass loss that was independent of changes in food intake. Despite these beneficial effects, Sirolimus-treated rats were glucose intolerant, hyperinsulinaemic and hyperglycaemic, but not hyperlipidaemic. The euglycaemic hyperinsulinaemic clamp measurements showed skeletal muscle is a major site of Sirolimus-induced insulin resistance. At the molecular level, long-term Sirolimus administration attenuated glucose uptake and metabolism in skeletal muscle by preventing full insulin-induced Akt activation and altering the expression and translocation of glucose transporters to the plasma membrane. In rats fed a high-fat diet, these metabolic defects were exacerbated, although Sirolimus-treated animals were protected from diet-induced obesity.


CONCLUSIONS
Taken together, our data demonstrate that the diabetogenic effect of chronic rapamycin administration is due to an impaired insulin action on glucose metabolism in skeletal muscles.
Department of Internal Medicine, University of Geneva, Geneva, Switzerland.
N
N
Deblon
L
L
Bourgoin
C
C
Veyrat-Durebex
M
M
Peyrou
M
M
Vinciguerra
A
A
Caillon
C
C
Maeder
M
M
Fournier
X
X
Montet
F
F
Rohner-Jeanrenaud
M
M
Foti
D000273:Adipose Tissue / Q000187:drug effects; D000818:Animals; D002478:Cells, Cultured; D059305:Diet, High-Fat / Q000009:adverse effects; D005234:Fatty Liver / Q000517:prevention & control; D005947:Glucose / Q000378:metabolism; D015309:Glucose Clamp Technique; D018149:Glucose Intolerance / Q000139:chemically induced; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D007166:Immunosuppressive Agents / Q000633:toxicity*; D007328:Insulin / Q000378:metabolism; D007333:Insulin Resistance; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000633:toxicity*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015431:Weight Loss / Q000187:drug effects
D051275:Glucose Transporter Type 4; D007166:Immunosuppressive Agents; D007328:Insulin; C495694:Slc2a4 protein, rat; C546845:mTOR protein, rat; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D005947:Glucose; D020123:Sirolimus