The Effects of Alanine on Glucose Metabolism in Rainbow Trout: Integration of Glucose Fluxes and Molecular Evidence

• Main Author: Jubouri, Mais
• Other Authors: Weber, Jean-Michel
• Format: Others
• Language: en
• Published: Université d'Ottawa / University of Ottawa 2020
• Subjects: Glucose fluxes; Glycolysis; Gluconeogenesis; AMPK signaling; Alanine; Rainbow trout
• Online Access: http://hdl.handle.net/10393/41586; http://dx.doi.org/10.20381/ruor-25808

This thesis investigates the effects of alanine on rainbow trout’s glucose metabolism at the organismal and molecular levels. Rainbow trout is an important aquaculture species that belongs to the salmonid family. As a carnivorous fish, the requirement of protein/amino acids in trout’s diet is high. In contrast, rainbow trout are poor utilizers of carbohydrates. One prevalent hypothesis suggests that high levels of dietary amino acids could indeed contribute to the poor utilization of carbohydrates in this species. In mammals, there is evidence supporting the importance of alanine as a gluconeogenic precursor. However, a recent study found that alanine stimulates hepatic AMP-activated protein kinase (AMPK) to lower circulating glucose levels in mice. Alanine levels are high in all tissues in rainbow trout. The role of alanine in gluconeogenesis is less clear in trout and there is no evidence, to our knowledge, regarding its effects on glucose kinetics. Therefore, the main goal of the study was to investigate the impact of the continuous infusion of exogenous alanine for 4h on glucose fluxes and to identify potential mechanisms in tissues that could interpret the observed changes in glucose fluxes in vivo. Glucose turnover, appearance and disposal, Rt, Ra and Rd, respectively, were measured to determine the impact of alanine on glucose fluxes. The expression and/or activity of key genes in glucose transport, utilization and gluconeogenesis were assessed in liver and muscle. An additional goal was to assess whether alanine activates AMPK in trout. The levels of phosphorylated AMPK and other signaling proteins known to interact with the latter were quantified. Results show that alanine reduced plasma glucose levels and inhibited Ra and Rd glucose, consistent with previously observed effects of insulin in rainbow trout. The reduction in the expression of a paralogue of glut4, a key gene in glucose transport, and the activity of hexokinase (HK), a key enzyme in glucose utilization, in muscle can partially explain the observed reduction in Rd glucose. Together, these results suggest that glucose was not a preferred substrate under conditions of increased alanine availability and that alanine was probably oxidized to provide energy. Alanine failed to activate AMPK in trout, contrary to mammalian findings. However, it increased AKT (also known as protein kinase B) phosphorylation in muscle, similar to the effect of insulin in trout. In conclusion, my results suggest that alanine mediated at least some of the observed effects by stimulating insulin secretion given the similarities between the effects of exogenous alanine and insulin in rainbow trout as discussed above. Future studies are warranted to investigate the hypothesis that alanine is an insulin secretagogue in rainbow trout.