| First Author | Xu H | Year | 2022 |
| Journal | J Biol Chem | Volume | 298 |
| Issue | 12 | Pages | 102708 |
| PubMed ID | 36402444 | Mgi Jnum | J:332155 |
| Mgi Id | MGI:7410114 | Doi | 10.1016/j.jbc.2022.102708 |
| Citation | Xu H, et al. (2022) Glucagon Changes Substrate Preference in Gluconeogenesis. J Biol Chem 298(12):102708 |
| abstractText | Fasting hyperglycemia in diabetes mellitus is caused by unregulated glucagon secretion that activates gluconeogenesis (GNG) and increases the use of pyruvate, lactate, amino acids, and glycerol. Studies of GNG in hepatocytes, however, tend to test a limited number of substrates at non-physiologic concentrations. Therefore, we treated cultured primary hepatocytes with three identical substrate mixtures of pyruvate/lactate, glutamine, and glycerol at serum fasting concentrations, where a different U-(13)C or 2-(13)C labeled substrate was substituted in each mix. In the absence of glucagon stimulation, 80% of glucose produced in primary hepatocytes incorporated either one or two (13)C-labeled glycerol molecules in a 1:1 ratio, reflecting the high overall activity of this pathway. In contrast, glucose produced from (13)C-labeled pyruvate/lactate or glutamine rarely incorporated two labeled molecules. While glucagon increased glycerol and pyruvate/lactate contribution to glucose carbon by 1.6- and 1.8-fold, respectively, glutamine contribution to glucose carbon was increased 6.4-fold in primary hepatocytes. To account for substrate (13)C carbon loss during metabolism, we also performed a metabolic flux analysis, which confirmed that the majority of glucose carbon produced by primary hepatocytes was from glycerol. In vivo studies using a PKA-activation mouse model that represents elevated glucagon activity confirmed that most circulating lactate carbons originated from glycerol, but very little glycerol was derived from lactate carbons, reflecting glycerol's importance as a carbon donor to GNG. Given diverse entry points for GNG substrates, hepatic glucagon action is unlikely to be due to a single mechanism. |
