Increased IRS2 mRNA Expression in SGA Neonates: PCR Analysis of Insulin/IGF Signaling in Cord Blood

Abstract

Context:Hypoglycemia is the most common metabolic problem among small-for-gestational-age (SGA) neonates. However, the pathological mechanism and insulin/ insulin-like growth factor (IGF) signaling axis in neonates remain unknown.Objective:To determine the insulin/IGF axis in neonates, we analyzed the messenger RNA (mRNA) expression of insulin/IGF signaling in fetal umbilical cord blood.Setting:The Perinatal Medical Center of Tottori University Hospital.Participants:Fifty-two [42 appropriate-for-gestational-age (AGA) and 10 SGA] neonates.Interventions:Immediately collected cord blood was placed into a PAXgene Blood RNA Tube. Total RNA from the blood was purified using reagents provided in the PAXgene Blood RNA Kit within 4 days, and reverse transcription polymerase chain reaction (PCR) was performed.Main Outcome Measure:Quantitative real-time PCR analysis was applied to evaluate the mRNA expression of insulin receptor (INSR), IGF-I receptor (IGF1R), insulin receptor substrate 1 (IRS1), IRS2, and glucose transporters (SLC2A2 and SLC2A4). β-Actin was used as a control gene.Results:Serum glucose and IGF-I levels in SGA neonates were significantly lower. The cord serum insulin levels were similar between AGA and SGA neonates. The IRS2 mRNA expression was significantly higher in SGA than in AGA neonates (P < 0.05). The IRS2 mRNA expression was significantly higher in hypoglycemic SGA neonates than in normoglycemic SGA neonates.Conclusions:We determined that intrauterine growth restriction induces increased IRS2 mRNA expression in cord blood, without hyperinsulinemia. The increased expression of IRS2 mRNA might be associated with abnormal glucose metabolism in SGA neonates. Our findings might lead to the elucidation of abnormal glucose metabolism in SGA neonates.

Cord Blood from SGA Preterm Infants Exhibits Increased GLUT4 mRNA Expression

“…24 In contrast, preterm SGA infants showed decreased levels of serum insulin and increased levels of SLC2A4 mRNA, which was translated to GLUT4 glucose-transporter protein, compared to preterm AGA infants, unlike in term infants. 24 No statistical difference was observed in IRS2 mRNA expression, which was increased in the full-term SGA infants, as observed in a previous study. 24 This is in contrast with the observations for term infants.…”

“…We immediately measured the levels of plasma glucose, serum insulin, C-peptide, and IGF-1 using 5-8 mL of cord blood collected from the umbilical vein at birth as described previously. 24 Hypoglycemia was defined as plasma glucose levels < 50 mg/dL (< 2.8 mmol/ L). When hypoglycemia was detected, treatment was instituted by feeding milk or by intravenous glucose infusion.…”

“…Quantitative RT-PCR was performed as described previously. 24 Briefly, cord blood samples were collected immediately after birth into PAX gene® Blood RNA Tubes (Becton, Dickinson and Company, UK), and total RNA from umbilical cord blood was purified using the reagents provided in the PAX gene® Blood RNA Kit (QIAGEN, Germany) within 5 days, followed by reverse transcription. First-strand cDNA synthesis was performed as described previously.…”

“…First-strand cDNA synthesis was performed as described previously. 24 Quantitative realtime PCR analysis was applied to evaluate expression of IGF1R, INSR, IRS1, IRS2, and glucose transporter 4 (SLC2A4, known as GLUT4) mRNA by using ViiA 7® Real-Time PCR System (Thermo Fisher Scientific Inc., MA) with Universal Probe Library (Roche Molecular Systems, Inc., CA) and TaqMan Gene Expression Assay (Thermo Fisher Scientific Inc., MA). In this study, SLC2A2 mRNA, one of the targets of our previous study, could not be analyzed due to technical issues.…”

“…23 Accordingly, we have previously studied to evaluate how SGA impact insulin/ IGF signaling pathway, and have shown that term SGA infants have abnormal insulin/IGF signaling as higher IRS2 mRNA levels were detected in SGA subjects. 24 In this study, we investigated insulin/IGF signaling in cord blood from preterm infants to determine how preterm and SGA impact insulin/IGF signaling pathway.…”