1 PATHWAYS AND CELLULAR FUNCTIONS INFLUENCED BY INSULIN TREATMENT DURING OOCYTE MATURATION – A TRANSCRIPTOME STUDY OF IN VITRO-PRODUCED BOVINE DAY 8 BLASTOCYSTS

Abstract

Insulin as a key metabolic hormone has crucial functions in metabolic regulation in all mammals. Deviation of its physiological concentration occurs in metabolic disorders as obesity and diabetes in humans or negative energy balance and overfeeding in the cow. As these metabolic disorders are strongly correlated with reproductive disturbances, we investigated the effect of insulin during oocyte maturation on gene expression of bovine Day 8 blastocysts (BC8) by transcriptome analysis. Abattoir-derived oocytes (n = 882) were divided into 3 groups and in vitro matured for 22 h by adding insulin (H: High 10 µg mL^–1; L: Low 0.1 µg mL^–1 and Z: Zero, control). This was followed by standard in vitro production (IVP) and evaluation of developmental rates up to blastocyst stage. BC8 (n = 120) were pooled in groups of 10 and total RNA was extracted by parallel gDNA and total RNA-extraction (AllPrepDNA/RNA micro kit, cat no. 80284, Qiagen®, Valencia, CA, USA) for analyses of the transcriptome. All samples (4 biological replicates/group) resulted in RIN-values >7.5. RNA amplification, cDNA synthesis, purification, and labelling were performed and 825 ng of Cy3- and Cy5-labelled linearly amplified aRNA was hybridized on the Agilent-manufactured EmbryoGENE-slides in a 2-colour dye swap design. An empirical Bayes moderated t-test was applied to search for the differentially expressed transcripts (DET) between control and insulin-treated groups, using the ‘limma’ package in R (www.r-project.org). The DET were defined as having a 1.5-fold change difference between treatment and control and P < 0.05. Pathways and molecular functions influenced by insulin treatment were analysed by using Ingenuity Pathway Analysis (IPA; Ingenuity® Systems, www.ingenuity.com). As a global pattern, insulin treatment induced an up-regulation of genes. In total, 202 DET in the H and 142 DET in the L group were found where 104 DET were common in both insulin groups. Fifteen selected candidate genes chosen for qPCR validation and 12 (80%) showed similar expression patterns as the microarray data. DET relevant for following cellular functions were found in H: Cell Cycle, Cellular Compromise, Lipid Metabolism, Molecular Transport, Small Molecule Biochemistry respective L: Cell Morphology, Cellular Growth and Proliferation, Cell Cycle, Carbohydrate Metabolism and Cellular Assembly and Organization. The top canonical pathways influenced were Epithelial Adherens Junction Signalling and Remodelling, Germ Cell Sertoli Cell Junction Signalling and NRF2-mediated Oxidative Stress Response. Correlatively, blastocyst rates on Day 8 were significantly lower in H and L v. Z (P < 0.05). The transcriptome data could explain the mechanisms behind the impaired development, as genes involved in cellular growth and energy metabolism in Day 8 blastocysts were affected. The fact that transcripts related to NRF2-mediated oxidative stress response and lipid metabolism are up-regulated suggests that insulin induces dysregulation of cellular functions and energy metabolism leading to impaired embryo developmental potential.

Funded by FORMAS.