Maternal Heat Stress Alters Expression of Genes Associated with Nutrient Transport Activity and Metabolism in Female Placentae from Mid-Gestating Pigs

Abstract

Placental insufficiency is a known consequence of maternal heat stress during gestation in farm animals. The molecular regulation of placentae during the stress response is little known in pigs. This study aims to identify differential gene expression in pig placentae caused by maternal heat exposure during early to mid-gestation. RNA sequencing (RNA-seq) was performed on female placental samples from pregnant pigs exposed to thermoneutral control (CON; constant 20 °C; n = 5) or cyclic heat stress (HS; cyclic 28 to 33 °C; n = 5) conditions between d40 and d60 of gestation. On d60 of gestation, placental efficiency (fetal/placental weight) was decreased (p = 0.023) by maternal HS. A total of 169 genes were differentially expressed (FDR ≤ 0.1) between CON and HS placentae of female fetuses, of which 35 genes were upregulated and 134 genes were downregulated by maternal HS. The current data revealed transport activity (FDR = 0.027), glycoprotein biosynthetic process (FDR = 0.044), and carbohydrate metabolic process (FDR = 0.049) among the terms enriched by the downregulated genes (HS vs. CON). In addition, solute carrier (SLC)-mediated transmembrane transport (FDR = 0.008) and glycosaminoglycan biosynthesis (FDR = 0.027), which modulates placental stroma synthesis, were identified among the pathways enriched by the downregulated genes. These findings provide evidence that heat-stress induced placental inefficiency may be underpinned by altered expression of genes associated with placental nutrient transport capacity and metabolism. A further understanding of the molecular mechanism contributes to the identification of placental gene signatures of summer infertility in pigs.

Keywords: RNA-seq; gestation; heat stress; pigs; placenta; placental insufficiency; transport activity.

Figure 1

Volcano plot of the differentially expressed genes (DEGs) in female placentae. Blue, red, and grey dots denote downregulated ((FDR (false discovery rate) ≤ 0.1), upregulated (FDR ≤ 0.1), and non-differentially expressed (FDR > 0.1) genes in heat stress placentae (n = 5) compared to control placentae (n = 5). Gene symbols associated with placental transport activity are labelled.

Figure 2

Functional classification of differentially expressed genes in placentae between heat stress (n = 5) and control (n = 5) groups in the gene ontology (GO) domains of (A) Molecular function, (B) Biological process and (C) Protein class.

Figure 3

Gene ontology (GO) terms significantly enriched (FDR ≤ 0.05) by the downregulated genes in heat stress placentae (n = 5) compared to control placentae (n = 5) in the GO domains of (A) Molecular function, (B) Biological process and (C) Cellular component. Fold enrichment: No. genes observed in the gene list/No. genes expected.

Figure 4

Relative protein expression of glucose transporter 2 (GLUT2; (A)) and peptide transporter 1 (PEPT1; (B)) in placentae between control (CON, n = 5) and heat stress (HS, n = 5) groups. Target protein expression was normalised to total protein loaded and expressed as normalised signals (arbitrary units). * p < 0.05. Error bars: standard error of the means.