Conclusion
Glucose availability regulates NNMT expression via an mTOR-dependent mechanism.
Methods
3T3-L1 adipocytes were cultured in media with varying glucose concentrations or activators and inhibitors of intracellular pathways. NNMT mRNA and protein levels were measured with quantitative polymerase chain reaction and Western blotting.
Results
Glucose deprivation of 3T3-L1 adipocytes induced a 2-fold increase in NNMT mRNA and protein expression. This effect was mimicked by inhibition of glucose transport with phloretin, and by inhibition of glycolysis with the phosphoglucose isomerase inhibitor 2-deoxyglucose. Conversely, inhibition of the pentose phosphate pathway did not affect NNMT expression. Pharmacological activation of the cellular energy sensor AMP-activated protein kinase (AMPK) and inhibition of the mammalian target of rapamycin (mTOR) pathway caused an increase in NNMT levels that was similar to the effect of glucose deprivation. Activation of mTOR with MHY1485 prevented the effect of glucose deprivation on NNMT expression. Furthermore, upregulation of NNMT levels depended on functional autophagy and protein translation.