Tissues throughout the human body exert finely-tuned specific functions even when there is considerable overlap in the cellular constituents. Even when the major cellular component of tissues is the same – for example in the case of smooth muscle-rich tissues – discrete phenotypes are evident. Yet, the molecular expression profiles underpinning such specialised functionality is often unclear. This presents a challenge for introducing new medicinal therapies for pathophysiologies: can one target what makes tissue functionality unique without producing unwanted effects on the features that are similar.
Such a scenario can be considered for the human uteroplacental unit. Ideally, one would like to target complications of pregnancy like pre-eclampsia (hypertension and proteinuria) or spontaneous preterm birth (early activation of parturition) by targeting particular types of smooth muscle tissues (e.g. arteries versus myometrium) without adversely affecting others. This situation is further complicated by the need to consider maternal and fetoplacental circumstances. Three smooth muscle-rich tissues of importance here are myometrium, maternal uterine (myometrial) arteries and placental arteries. Indeed, each display subtly distinct phenotypes suggesting that distinct molecular signatures may underlie these differences. As proteins determine cell/tissue structure and function, the aim of this work was to compare the proteome-wide expression profiles of these three tissues.
Paired uterine biopsies and placentas were obtained, following written informed consent (LREC 10/H0906/71), from healthy pregnant women undergoing elective Caesarean section at term (39-40 weeks gestation, n=9). Myometrial strips(M), myometrial arteries(MA) and placental chorionic plate arteries(PA) were each isolated, and cleaned of surrounding material, by careful microdissection, snap frozen in liquid N2 and stored at -80oC until further use. Frozen samples were homogenised (5% SDS in 50mM TEAB, pH 8.5), digested (1:20(w:w) trypsin:protein ratio, 47oC for 2hours) and peptides analysed in triplicate via liquid chromatography mass spectrometry(LC-MS) using SWATH[1].
5895 proteins were quantified (using ≥5 unique fragment ion intensities per peptide, log(2) transformed and median-corrected) and 2832 differentially expressed across the three tissue types (ANOVA with multiple corrections FDR<0.01). Hierarchical k-mean clustering indicated five main groupings of relative protein changes across the tissue types. Paired t-test (FDR<0.05) identified differentially expressed proteins between tissues as follows: M vs MA: 1277 proteins; M vs PA: 3376 proteins; MA vs PA: 2486 proteins. Multiple pathway enrichment analyses indicated that the three tissues possess distinct proteomic profiles with PA being the most distinguishable from the other two. Notable biological pathway differences across these tissues are proteins related to ribosomal structure, oxidative phosphorylation, cytoskeleton and extracellular matrix(ECM). One cluster was indicated by notably higher relative protein abundances from placental arteries than each of the other two tissue types. For example, identified in this cluster ECM laminin isoforms LAMB2 and LAMC1 had higher abundances in PA (log(2) fold-change: 4.94±0.57; 6.10±0.48 respectively), followed by MA (3.81±1.04; 5.33 ±0.36) and M (2.13±0.74; 4.81±0.44).
In summary, distinctive proteomic profiles are evident between human placental arteries, myometrial arteries and myometrium. This opens the possibility of uncovering the molecular signatures, and biological pathways, that serve to furnish different smooth muscle-rich tissues with specialised physiological (and pathophysiological) phenotypes.