Related Experiment Videos
Rapamycin partially prevents insulin resistance induced by chronic insulin treatment
Cathleen E Berg1, Brian E Lavan, Cristina M Rondinone
1Metabolic Diseases Research, Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, IL 60064, USA.
Abstract:
Chronic insulin exposure induces serine/threonine phosphorylation and degradation of IRS-1 through a rapamycin-sensitive pathway, which results in a down-regulation of insulin action. In this study, to investigate whether rapamycin (an mTOR inhibitor) could prevent insulin resistance induced by hyperinsulinemia, 3T3-L1 adipocytes were incubated chronically in the presence of insulin with or without the addition of rapamycin. Subsequently, the cells were washed and re-stimulated acutely with insulin. Chronic insulin stimulation caused a reduction of GLUT-4 and IRS-1 proteins with a correlated decrease in acute insulin-induced PKB and MAPK phosphorylations as well as a reduction in insulin-stimulated glucose transport. Rapamycin prevented the reduction of IRS-1 protein levels and insulin-induced PKB Ser-473 phosphorylation with a partial normalization of insulin-induced glucose transport. In contrast, rapamycin had no effect on the decrease in insulin-induced MAPK phosphorylation or GLUT-4 protein levels. These results suggest that chronic insulin exposure leads to a down-regulation of PKB and MAPK pathways through different mechanisms in adipocytes.
Insights
Rapamycin prevents insulin resistance by maintaining IRS-1 protein levels and improving insulin signaling in adipocytes. This suggests distinct mechanisms regulate insulin-induced pathways during chronic insulin exposure.
Area of Science:
- Cell Biology
- Metabolism
- Endocrinology
Background:
- Chronic hyperinsulinemia can lead to insulin resistance.
- Insulin receptor substrate-1 (IRS-1) degradation is implicated in insulin resistance.
- The mechanistic target of rapamycin (mTOR) pathway's role in insulin resistance is under investigation.
Purpose of the Study:
- To determine if rapamycin, an mTOR inhibitor, can prevent insulin resistance induced by chronic insulin exposure in 3T3-L1 adipocytes.
- To elucidate the specific effects of rapamycin on key insulin signaling proteins and glucose transport.
Main Methods:
- 3T3-L1 adipocytes were chronically exposed to insulin with or without rapamycin.
- Cells were subsequently washed and acutely re-stimulated with insulin.
- Levels of GLUT-4, IRS-1, and phosphorylation of PKB and MAPK were assessed.
- Insulin-stimulated glucose transport was measured.
Main Results:
- Chronic insulin exposure reduced GLUT-4 and IRS-1 protein levels, decreased PKB and MAPK phosphorylation, and impaired glucose transport.
- Rapamycin treatment prevented IRS-1 reduction and partially restored PKB Ser-473 phosphorylation and glucose transport.
- Rapamycin did not affect MAPK phosphorylation or GLUT-4 levels.
Conclusions:
- Chronic insulin exposure down-regulates insulin action through distinct mechanisms affecting PKB and MAPK pathways in adipocytes.
- Rapamycin partially ameliorates insulin resistance by preserving IRS-1 and modulating PKB signaling.
- These findings highlight potential therapeutic targets for managing insulin resistance.