Canine placental changes in normal and abnormal parturition: a transcriptomic approach from prepartum to second stage labor

Abstract

The molecular mechanisms involved in canine parturition and the role of the placenta in this process remain unclear. This work aims to provide a thorough review of canine pregnancy, the placenta, and normal and abnormal parturition. Furthermore, in our study, we hypothesized that global gene expression profiling through RNA sequencing (RNAseq) would assist in the overall understanding of the role of the canine placenta throughout the parturition process. Twenty-two bitches were allocated into four groups: planned Cesarean section (C-section) at term pregnancy not in labor (PCS, n = 6, serum progesterone, P4 > 3.0 ng/ml); elective C-section in first stage labor (ECS, n = 6, P4 < 1.5 ng/ml); obstructive dystocia in second stage labor with spontaneous abdominal contractions (OD, n = 5); abnormal parturition progression diagnosed as primary uterine inertia (PUI, n = 5). One randomly collected placenta per dog during C-section was prepared and submitted for RNAseq. Transcripts for 13225 genes were detected and analyzed. The highest yield of differently expressed genes (DEG, n=1409) was identified in the OD vs PCS contrast (False Discovery rate [FDR]< 0.1 in edgeR and DESeq2). The OD group had 1121 upregulated genes, and the PCS had 288 upregulated genes relative to OD. The PUI vs PCS, OD vs PUI, and PUI vs ECS contrasts presented 8, 2, and 1 DEG, respectively. Functional characterization and enrichment analysis of the upregulated DEGs in the OD vs PCS contrast showed 109 pathways inferred to be activated in the OD group, which included but were not limited to the Rap1 and MAPK signaling pathways, cytokine-cytokine receptor interaction, leukocyte transendothelial migration, focal and cell adhesion molecules, complement and coagulation cascade, platelet activation, and oxytocin signaling. Collectively, functional analysis and KEGG pathways in the OD group appeared to be associated with immune-mediated processes, vascularization and VEGF signaling, hemostasis and platelet activation, tissue remodeling and oxytocin response. These findings corroborate the predominantly inflammatory nature of second-stage labor as strong uterine contractions develop and the placenta detaches for fetal expulsion. We were unable to definitively pinpoint the underlying placental cause for PUI.