Zebrafish model of Gestational Diabetes

Abstract

One in seven births in the US are affected by Gestational Diabetes Mellitus (GDM). In addition to the acute risk of death and complications for the fetus, GDM exposure in utero leads to an increase in the development of cardiovascular diseases, obesity, insulin resistance, type 2 diabetes and metabolic syndrome later in life. In utero fetal exposure to hyperglycemia leads to Non‐Alcoholic Fatty Liver Disease (NAFLD) in adulthood, later in life, characterized by increased lipid droplets in hepatocytes. Although the consequences of GDM in infants have been documented, the cellular, molecular and physiological mechanisms underlying the link between fetal hyperglycemia and metabolic consequences later in life is poorly understood. We recently developed a model of fetal hyperglycemia in zebrafish embryo, by exposure of zebrafish embryos to high glucose (4.5% or 5% w/v) for 24 hours. Glucose level was detected in the fish homogenate by glucometer. Body composition was detected by EcoMRI. Gene expression of glycolytic and lipogenic markers (Glucokinase, Hexokinase, Pyruvate Kinase, Acetyl CoA Carboxylase, Fatty Acid Synthase) was quantified by RT‐qPCR. Adiposity was assessed by Nile red staining and liver lipid droplet accumulation was performed to evaluate NAFLD. Additionally, the enzymes involved in Triglyceride and Cholesterol synthesis (Acetyl‐CoA and Malonyl‐CoA) were assessed by ELISA. Our data demonstrate that zebrafish embryos exposed to high glucose and raised to adulthood under normal glycemic conditions (normal fish diet) have significant increase in body mass index (826.6±26.34 Vs. 598.8± 33.89) g/m2and fat mass (12.07± 2.92 Vs 3.4± 0.4) g, develop obesity (by size), have increased adiposity and develop NAFLD, however these adults are normoglycemic. At the cellular and molecular level, our results show a differential increase in glycolytic and lipogenic gene expression. Moreover, there was significant increases in Acetyl‐CoA (2.5‐fold) and Malonyl‐CoA (1.4‐fold) levels that was associated with increased cholesterol (57.92± 0.7 Vs 34.8±1.01) uM and Triglyceride (4.1± 0.75 Vs 0.98±0.27) levels in embryos exposed to high glucose compared to control group. Together our results show that fetal exposure to glucose leads to metabolic consequences later in life including obesity and NAFLD under normal diet. We also concluded from our results that fetal hyperglycemia increases glycolysis and lipogenesis. Moreover, our project demonstrates that the zebrafish is an excellent system to model fetal hyperglycemia by focusing on direct glucose exposure of the embryo without the need of modifying the glucose levels of the mother. Experiments utilizing both genetic and pharmacological approaches are in progress to investigate if the molecular changes observed during fetal life under glucose exposure are persistent in the adults.