Glucose Transporter Expression and Regulation Following a Fast in the Ruby-throated Hummingbird,Archilochus colubris

Abstract

statement: Hummingbird ingest nectar rich in glucose and fructose. When fasted, 14 tissue capacity for circulating glucose import declines while remaining elevated for fructose. 15This may underlie maintenance of high blood glucose and rapid depletion of blood fructose. 16Abstract 17 Hummingbirds subsist almost exclusively on nectar sugar and face extreme challenges 18 blood sugar regulation. Transmembrane sugar transport is mediated by facilitative glucose 19 transporters (GLUTs) and the capacity for sugar transport is dependent on both the activity of 20GLUTs and their localisation to the plasma membrane (PM). In this study, we determined the 21 relative protein abundance in whole-tissue (WT) homogenates and PM fractions via immunoblot 22 List of Abbreviations39 AIC Akaike Information Criterion 40 AICc Akaike Information Criterion for small sample sizes 41 ANOVA Analysis of Variance 42 APS Ammonium Persulfate 43 cDNA Complementary Deoxyribonucleic Acid 44 CO 2 Carbon Dioxide 45 DTT Dithiothreitol 46 f exo Proportion of expired CO 2 fuelled by oxidation of exogenous sugar 47 GAPDH Glyceraldehyde-3-Phosphate Dehydrogenase 48 GLUT Glucose Transporter 49 HEK293T Homo sapiens Embryonic Kidney cell line with Mutant SV40 large T antigen 50 HRP Horseradish Peroxidase 51 LC MRM/MS Liquid Chromatography Multiple Reaction Monitoring Mass 52 Spectrometry 53 LMM Linear Mixed-effects Model 54 mM Millimolar 55 mRNA Messenger Ribonucleic Acid 56 MW Molecular Weight 57

Genomic insights into metabolic flux in ruby-throated hummingbirds

“…SLC2A2 , encoding the GLUT2 protein which has a high K m , plays a stronger role in enteric (Karasov 2017) and hepatic (Mueckler and Thorens 2013) sugar transport, resulting in the expected higher expression we observe in liver over muscle samples. Interestingly, chicken SLC2A1 and SLC2A3 share sequence homologies of ~80% and ~70% respectively with human GLUTs, but other isoforms such as SLC2A2 and SLC2A5 only share ~65% and ~64% sequence homology (Ali et al 2020). A comparison of SLC2A2 sequences to 20 bird species reveals the loss of an N -linked glycosylation site in four of the 20 species (Workman et al 2018).…”

“…Another key regulator of blood glucose homeostasis is glucokinase ( GCK ), in mammals this enzyme has a high K m and is the glucose sensor not only for regulation of insulin release by pancreatic β-cells, but also for key organs that contribute to glucose homeostasis, such as the liver (Matschinsky and Wilson 2019; Peter et al 2011). However, birds do not express GLUT4, the insulin sensitive glucose transporter, and the ruby-throated hummingbird in particular maintains the highest blood glucose concentration known amongst vertebrates (Ali et al 2020; Beuchat and Chong 1998). Our transcriptome assembly did not identify GCK in the assembled hummingbird transcriptome and we did not identify any GCK sequence in any of the ruby-throated hummingbird RNA-seq reads.…”