Zebrafish model of in utero glucose exposure alters developmental programming that leads to life‐long metabolic consequences
Authors: Konadu Bridget D. , Cox Carol , Speed Joshua , Gibert Yann 
Published: May 2022

Background and Aim

One in ten pregnancies in the US, suffers from Gestational Diabetes Mellitus (GDM). Offspring born to mothers who have GDM have a higher risk of developing Obesity, Type 2 diabetes and Non‐alcoholic fatty liver disease later in life. Although in utero glucose exposure provides evidence for developmental programming leading to metabolic disorders in adults, the molecular mechanisms are still unclear. We aim to understand the mechanisms implicated in developmental programming and their associated adult outcomes in a well‐established zebrafish model of fetal hyperglycemia that mimics the metabolic disorders in human GDM.

Methods

We developed a zebrafish model of fetal hyperglycemia by exposing embryos to high glucose (4.5% w/v) during the last day of embryogenesis from 96 to 120 hours post fertilization. Glucose level was detected in embryos and larvae homogenates and in adult serum by glucometer. Body composition was determined in adults by EchoMRI, gene expression of glycolytic, lipogenic (Acetyl‐CoA Carboxylase (acca) and mitochondria biogenesis (Peroxisome proliferator‐activated receptor‐gamma coactivator [PGC‐1α/β) markers were quantified by RT‐qPCR and acca by western blot. Lipid accumulation was detected by Oil‐Red‐O staining (ORO) and quantified by spectrophotometry. Triglyceride and cholesterol levels (ELISA), adiposity (Nile red staining) and mitochondrion number (mitotracker staining) were also evaluated. We also assessed if co‐administration of metformin or ND646 (known inhibitors of acca) with glucose can attenuate fetal hyperglycemia‐mediated metabolic outcomes.

Results

Zebrafish embryos exposed to high glucose for 24 hrs are transiently hyperglycemic while normoglycemia is restored after glucose exposure. Larvae and adults with embryonic glucose exposure are normoglycemic. Embryos showed an upregulation of hexokinase and pyruvate Kinase expression when assessed at 120 hpf, but no change in expression was detected in larvae. Embryos exposed to glucose showed increased lipid accumulation by ORO staining (0.22 ±0.01 Vs 0.17±0.01) while larvae showed a 5‐fold increase in adiposity. Adult fish develop obesity characterized by increased BMI (0.83±26.34 Vs. 0.60± 33.89) kg/m2 and fat mass (12.07± 2.92 Vs 3.4± 0.4) g. Embryos showed increase in both acca mRNA expression (3‐folds) and activation (decreased phosphorylation). Interestingly, acca expression remained increased in larvae while glycemia was normal. Moreover, there was a significant increase in cholesterol (57.92± 0.7 Vs 34.8±1.01 µM) and triglyceride levels in glucose exposed embryos compared to controls (4.1± 0.75 Vs 0.98±0.27 µM). Our data in embryos revealed an increase in mitochondria number validated by an increase in the expression of PGC‐1α/β. Finally, ORO staining showed that embryonic lipid accumulation was decreased to normal levels, by metformin or ND646 exposure when co‐administered with glucose.

Conclusion and significance

Together our results show that embryonic glucose exposure alters developmental programming, including lipid homeostasis dysregulation that is persistent in larvae and adult. However, it can be rescued by pharmacological approaches.