Assessment of myometrial transcriptome changes associated with spontaneous human labour by high‐throughput RNA‐seq

Abstract

New Findings r What is the central question of this study?In this study, we sought to survey the total transcript repertoire of human myometrium, comparing samples taken from patients at term who were not in labour with samples taken at term in spontaneous labour. These sequenced transcriptomes show the repertoire of possible proteins and their variants in myometrial smooth muscle, as well as transcriptional changes associated with term spontaneous labour. r What is the main finding and its importance?We describe, for the first time, the transcriptome of the human myometrial samples taken from patients prior to and after the onset of spontaneous labour. We document a significant number of novel transcripts of both protein-coding mRNA and microRNA. This information will be useful for the development of novel therapeutics and the formulation of new hypotheses to be tested by physiological experimentation.The transition of the human uterus from a quiescent to a contractile state takes place over a number of weeks. On such biological time scales, cellular phenotype is modified by changes in the transcriptome, which in turn is under the control of the underlying endocrine, paracrine, and biophysical processes resulting from the ongoing pregnancy. In this study, we characterize the transition of the human myometrial transcriptome at term from not in labour (NIL) to in labour (LAB) using high throughput RNA sequencing (RNA-seq). RNA was isolated from the myometrium of uterine biopsies from patients at term who were not in labour (n = 5) and at term in spontaneous labour (n = 5) without augmentation. A total of 143.6 million separate reads were sequenced, achieving, on average, ß13 times coverage of the expressed human transcriptome per sample. Principal component analysis indicated that the NIL and LAB transcriptomes could be distinguished as two distinct clusters. A comparison of the NIL and LAB groups, using three different statistical approaches (baySeq, edgeR, and DESeq), demonstrated an overlap of 764 differentially expressed genes. A comparison with currently available microarray data revealed only a partial overlap in differentially expressed genes. We conclude that the described RNA-seq data sets represent the first fully annotated catalogue of expressed mRNAs in human myometrium. When considered together, the full expression repertoire and the differentially

Alterations in gap junction connexin43/connexin45 ratio mediate a transition from quiescence to excitation in a mathematical model of the myometrium

“…These authors showed that Cx43 expression remains unchanged between the two sample groups, whereas Cx45 expression is significantly downregulated in the 'in labour' group in comparison with the 'not-in-labour' group (electronic supplementary material, figure S12). These results are in accordance with our data, which furthermore suggest that the significant changes found by Chan et al [35] were owing to changes in expression taking place in the inner myometrium as opposed to the outer myometrium. Our model simulations show that an elevated proportion of Cx43 proteins is a key factor in modulating conductance.…”

“…Our experimental data indicate downregulation of Cx45 expression in the rat as labour approaches, in contrast to Cx43 expression where no change at the end of pregnancy appears to be evident. Chan et al [35] found similar results in human myometrium, analysing the RNA of myometrial samples from pregnant women (five from women in labour, and five from women at full term, but not in labour). These authors showed that Cx43 expression remains unchanged between the two sample groups, whereas Cx45 expression is significantly downregulated in the 'in labour' group in comparison with the 'not-in-labour' group (electronic supplementary material, figure S12).…”

BK Ca channel regulates calcium oscillations induced by alpha-2-macroglobulin in human myometrial smooth muscle cells

“…First, myosin light chain kinase and myosin light chain phosphatase are inhibited by phosphorylation and dephosphorylation, respectively (8 ] i to basal levels (9). The predominant K + channel in the myometrium is the largeconductance, voltage-gated, Ca 2+ -activated K + channel (BK Ca ), also known as MaxiK/hSlo/KCa1.1 (10)(11)(12). Opening of the BK Ca channel provides a strong repolarizing current to maintain MSMCs at a polarized membrane potential, thus preventing voltage-gated Ca 2+ influx and contraction.…”

Functional insights into modulation of BKCa channel activity to alter myometrial contractility

“…This transition is controlled, in part, by a complex regulation of ion channel activity. Multiple types of ion channels are responsible for changes in the membrane potential in MSMCs (Sanborn, 2000; Shmygol et al, 2007a; Chan et al, 2014); potassium channels, in particular, play an important role in controlling membrane potential and attenuating excitation to maintain quiescence in pre-labor MSMCs.…”