Expression of the TRPM6 in mouse placental trophoblasts; potential role in maternal-fetal calcium transport

Placental ion channels: potential target of chemical exposure

The placenta is an important organ for the exchange of substances between the fetus and the mother, hormone secretion, and fetoplacental immunological defense. Placenta has an organ-specific distribution of ion channels and trophoblasts, and placental vessels express a large number of ion channels. Several placental housekeeping activities and pregnancy complications are at least partly controlled by ion channels, which are playing an important role in regulating hormone secretion, trophoblastic homeostasis, ion transport, and vasomotor activity. The function of several placental ion channels (Na, Ca, and Cl ion channels, cation channel, nicotinic acetylcholine receptors, and aquaporin-1) is known to be influenced by chemical exposure, i.e., their responses to different chemicals have been tested and confirmed in experimental models. Here, we review the possibility that placental ion channels are targets of toxicological concern in terms of placental function, fetal growth, and development.

Mapping the expression of transient receptor potential channels across murine placental development

Transient receptor potential (TRP) channels play prominent roles in ion homeostasis by their ability to control cation influx. Mouse placentation is governed by the processes of trophoblast proliferation, invasion, differentiation, and fusion, all of which require calcium signaling. Although certain TRP channels have been shown to contribute to maternal–fetal transport of magnesium and calcium, a role for TRP channels in specific trophoblast functions has been disregarded. Using qRT-PCR and in situ hybridisation, the spatio-temporal expression pattern of TRP channels in the mouse placenta across gestation (E10.5–E18.5) was assessed. Prominent expression was observed for Trpv2, Trpm6, and Trpm7. Calcium microfluorimetry in primary trophoblast cells isolated at E14.5 of gestation further revealed the functional activity of TRPV2 and TRPM7. Finally, comparing TRP channels expression in mouse trophoblast stem cells (mTSCs) and mouse embryonic stem cells (mESC) confirmed the specific expression of TRPV2 during placental development. Moreover, TRP channel expression was similar in mTSCs compared to primary trophoblasts and validate mTSC as a model to study TRP channels in placental development. Collectivity, our results identify a specific spatio-temporal TRP channel expression pattern in trophoblasts, suggesting a possible involvement in regulating the process of placentation.

TET1 and 5-Hydroxymethylation Preserve the Stem Cell State of Mouse Trophoblast

The ten-eleven translocation factor TET1 and its conferred epigenetic modification 5-hydroxymethylcytosine (5hmC) have important roles in maintaining the pluripotent state of embryonic stem cells (ESCs). We previously showed that TET1 is also essential to maintain the stem cell state of trophoblast stem cells (TSCs). Here, we establish an integrated panel of absolute 5hmC levels, genome-wide DNA methylation and hydroxymethylation patterns, transcriptomes, and TET1 chromatin occupancy in TSCs and differentiated trophoblast cells. We show that the combined presence of 5-methylcytosine (5mC) and 5hmC correlates with transcriptional activity of associated genes. Hypoxia can slow down the global loss of 5hmC that occurs upon differentiation of TSCs. Notably, unlike in ESCs and epiblast cells, most TET1-bound regions overlap with active chromatin marks and TFAP2C binding sites and demarcate putative trophoblast enhancer regions. These chromatin modification and occupancy patterns are highly informative to identify novel candidate regulators of the TSC state.

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5hmC to 5mC ratios correlate with gene activity in TS cells

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TS cell differentiation-associated loss of 5hmC is slowed down in hypoxia

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TET1 binding in TS cells forms long-range interactions with key trophoblast genes

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Intergenic TET1 binding sites in TS cells demarcate putative trophoblast enhancers

Maternal, placental and cordonal metallomic profiles in gestational diabetes mellitus

76 pregnant women, among them 38 affected by gestational diabetes mellitus (GDM) and 38 control subjects, were recruited at the University Hospital of Padua (Italy). Placenta samples, maternal whole blood and umbilical cord whole blood were collected after delivery and analysed via ICP-MS to determine the metallome, i.e. the whole elemental content. Results were statistically evaluated to evidence the correlation between the elemental concentrations in all samples and the presence of the disease. The results obtained in whole cord blood showed that many elements were correlated with GDM: Ca, Cu, Na, and Zn were present in higher concentration in GDM cord blood than in control samples, whereas Fe, K, Mn, P, Rb, S and Si showed an opposite trend. It was also highlighted that the cord blood from GDM patients exhibited an elemental composition more similar to that of the mother blood compared with the cord blood from control subjects. These results, in part interpreted in the light of the literature, open the possibility to use cord blood as a GDM marker, thus helping to delineate more accurate nutritional guidelines for pregnant women and to explain the biochemical processes occurring in the fetus and placenta during GDM.

Overexpression of microRNA-202-3p protects against myocardial ischemia-reperfusion injury through activation of TGF-β1/Smads signaling pathway by targeting TRPM6

MicroRNAs (miRNAs) have been found to act as key regulators in the pathogenesis of myocardial ischemic-reperfusion (I/R) injury. In this study, we explore the role and mechanism of microRNA-202-3p (miR-202-3p) in regulating cardiomyocyte apoptosis, in respective of the TGF-β1/Smads signaling pathway by targeting the transient receptor potential cation channel, subfamily M, member 6 (TRPM6). The targeting relationship between miR-202-3p and TRPM6 was verified by a dual-luciferase reporter gene assay. Sprague-Dawley rat models of myocardial I/R injury were initially established and treated with different mimics, inhibitors and siRNAs to test the effects of miR-202-3p and TRPM6 on myocardial I/R injury. The levels of inflammatory factors; IL-1β, IL-6, TNF-α as well as the degree of myocardial fibrosis and cardiomyocyte apoptosis were determined in rats transfected with different plasmids. TRPM6 was found to be the target of miR-202-3p. Up-regulated miR-202-3p or knockdown of TRPM-6 alleviated oxidative stress and inflammatory response, reduced ventricular mass, altered cardiac hemodynamics, suppressed myocardial infarction, attenuated cell apoptosis, and inhibited myocardial fibrosis. MiR-202-3p overexpression activates the TGF-β1/Smads signaling pathway by negatively regulating TRPM6 expression. Taken together, these findings suggest that miR-202-3p offers protection against ventricular remodeling after myocardial I/R injury via activation of the TGF-β1/Smads signaling pathway.

Establishing life is a calcium-dependent TRiP: Transient receptor potential channels in reproduction

Calcium plays a key role in many different steps of the reproduction process, from germ cell maturation to placental development. However, the exact function and regulation of calcium throughout subsequent reproductive events remains rather enigmatic. Successful pregnancy requires the establishment of a complex dialogue between the implanting embryo and the endometrium. On the one hand, endometrial cell will undergo massive changes to support an implanting embryo, including stromal cell decidualization. On the other hand, trophoblast cells from the trophectoderm surrounding the inner cell mass will differentiate and acquire new functions such as hormone secretion, invasion and migration. The need for calcium in the different gestational processes implicates the presence of specialized ion channels to regulate calcium homeostasis. The superfamily of transient receptor potential (TRP) channels is a class of calcium permeable ion channels that is involved in the transformation of extracellular stimuli into the influx of calcium, inducing and coordinating underlying signaling pathways. Although the necessity of calcium throughout reproduction cannot be negated, the expression and functionality of TRP channels throughout gestation remains elusive. This review provides an overview of the current evidence regarding the expression and function of TRP channels in reproduction.

TRPM6 and TRPM7 differentially contribute to the relief of heteromeric TRPM6/7 channels from inhibition by cytosolic Mg2+ and Mg·ATP

TRPM6 and its homologue TRPM7 are α-kinase-coupled divalent cation-selective channels activated upon reduction of cytosolic levels of Mg²⁺ and Mg·ATP. TRPM6 is vital for organismal Mg²⁺ balance. However, mechanistically the cellular role and functional nonredundancy of TRPM6 remain incompletely understood. Comparative analysis of native currents in primary cells from TRPM6- versus TRPM7-deficient mice supported the concept that native TRPM6 primarily functions as a constituent of heteromeric TRPM6/7 channels. However, heterologous expression of the human TRPM6 protein engendered controversial results with respect to channel characteristics including its regulation by Mg²⁺ and Mg·ATP. To resolve this issue, we cloned the mouse TRPM6 (mTRPM6) cDNA and compared its functional characteristics to mouse TRPM7 (mTRPM7) after heterologous expression. Notably, we observed that mTRPM6 and mTRPM7 differentially regulate properties of heteromeric mTRPM6/7 channels: In the presence of mTRPM7, the extreme sensitivity of functionally expressed homomeric mTRPM6 to Mg²⁺ is tuned to higher concentrations, whereas mTRPM6 relieves mTRPM7 from the tight inhibition by Mg·ATP. Consequently, the association of mTRPM6 with mTRPM7 allows for high constitutive activity of mTRPM6/7 in the presence of physiological levels of Mg²⁺ and Mg·ATP, thus laying the mechanistic foundation for constant vectorial Mg²⁺ transport specifically into epithelial cells.

Physiological roles of zinc transporters: molecular and genetic importance in zinc homeostasis

Zinc (Zn) is an essential trace mineral that regulates the expression and activation of biological molecules such as transcription factors, enzymes, adapters, channels, and growth factors, along with their receptors. Zn deficiency or excessive Zn absorption disrupts Zn homeostasis and affects growth, morphogenesis, and immune response, as well as neurosensory and endocrine functions. Zn levels must be adjusted properly to maintain the cellular processes and biological responses necessary for life. Zn transporters regulate Zn levels by controlling Zn influx and efflux between extracellular and intracellular compartments, thus, modulating the Zn concentration and distribution. Although the physiological functions of the Zn transporters remain to be clarified, there is growing evidence that Zn transporters are related to human diseases, and that Zn transporter-mediated Zn ion acts as a signaling factor, called "Zinc signal". Here we describe critical roles of Zn transporters in the body and their contribution at the molecular, biochemical, and genetic levels, and review recently reported disease-related mutations in the Zn transporter genes.