Norepinephrine Spares Adipose Tissue in Ovine Fetuses Complicated with Placental Insufficiency

Abstract

Placental insufficiency (PI) causes hypoxemia and hypoglycemia, which elevates norepinephrine (NE) concentrations throughout the final third of gestation, leading to intrauterine growth restriction (IUGR). The conditions causing IUGR also disrupt fetal adipose tissue, which is postulated to increases the risk of developing metabolic diseases. The sustained high NE concentrations lower adrenergic receptor β2 responsiveness in adipose tissue postnatally. Our objective was to characterize alterations in the perirenal adipose transcriptome and identify adrenergic programming responses from other conditions of IUGR. PI-IUGR was created with maternal hyperthermia during mid gestation. At 65% gestation, fetuses were randomly assigned to a sham (SH) or bilateral adrenal demedullation (AD) surgical procedure. Perirenal adipose tissue was collected from control (CON) and IUGR fetuses at 90% gestation. Physiological assessments were used to confirm AD. RNAseq (n=4/group) was performed on adipose mRNA to determine differentially expressed (DE) genes in adipose tissue among Control-Sham (CON-SH), IUGR-Sham (IUGR-SH), Control-AD (CON-AD) and IUGR-AD (IUGR-AD) groups. Three primary comparisons were analyzed to define IUGR specific genes and NE specific genes: CON-SH vs IUGR-SH, IUGR-SH vs IUGR-AD, and CON-AD vs IUGR-AD. Differentially expressed transcripts were modeled into functional pathways used to define genes of interest. Gene expression was confirmed with qPCR in an expanded cohort (n=7/group) and analyzed by ANOVA and post hoc LSD test. IUGR-AD had lower plasma NE concentrations than IUGR-SH fetuses despite being hypoxemic and hypoglycemic. IUGR-AD fetuses weighed more than IUGR-SH (2.2±0.3 vs 1.3±0.1kg, P<0.05). Perirenal adipose weight relative to body weight was greater in IUGR-SH fetuses compared to IUGR-AD and CON groups. The IUGR-SH adipose tissue also had a higher DNA content. RNAseq identified 593 DE genes in IUGR-SH compared to CON-SH, 297 DE genes in IUGR-SH compared to IUGR-AD, and 225 DE genes in CON-AD compared to IUGR-AD. Metabolism and PPAR signaling were enriched pathways in DE genes across comparisons. DE genes within enriched pathways were measured with qPCR and the majority of genes were increased in IUGR-SH compared to CON-SH. The expression of two metabolic regulators with a known role in adipose tissue, ADIRF and GLUT1, were decreased in IUGR-AD compared to IUGR-SH, indicating NE-dependent IUGR response. In conclusion, the adipose phenotype in intact IUGR fetuses indicated that there is higher relative adipose tissue mass due to hyperplasia. Furthermore, upregulation of ADIRF and GLUT1 expression may promote adipogenesis in response to NE.