Calcium channels activated by endothelin-1 in human trophoblast

Functional coupling between TRPV4 channel and TMEM16F modulates human trophoblast fusion

TMEM16F, a Ca2+-activated phospholipid scramblase (CaPLSase), is critical for placental trophoblast syncytialization, HIV infection, and SARS-CoV2-mediated syncytialization, however, how TMEM16F is activated during cell fusion is unclear. Here, using trophoblasts as a model for cell fusion, we demonstrate that Ca2+ influx through the Ca2+ permeable transient receptor potential vanilloid channel TRPV4 is critical for TMEM16F activation and plays a role in subsequent human trophoblast fusion. GSK1016790A, a TRPV4 specific agonist, robustly activates TMEM16F in trophoblasts. We also show that TRPV4 and TMEM16F are functionally coupled within Ca2+ microdomains in a human trophoblast cell line using patch-clamp electrophysiology. Pharmacological inhibition or gene silencing of TRPV4 hinders TMEM16F activation and subsequent trophoblast syncytialization. Our study uncovers the functional expression of TRPV4 and one of the physiological activation mechanisms of TMEM16F in human trophoblasts, thus providing us with novel strategies to regulate CaPLSase activity as a critical checkpoint of physiologically and disease-relevant cell fusion events.

Endothelin-1 induces lipolysis through activation of the GC/cGMP/Ca2+/ERK/CaMKIII pathway in 3T3-L1 adipocytes

Endothelin-1 (ET-1) is a potent vasoconstrictive peptide produced and secreted mainly by endothelial cells. Recent studies indicate that ET-1 can regulate lipid metabolism, which may increase the risk of insulin resistance. Our previous studies revealed that ET-1 induced lipolysis in adipocytes, but the underlying mechanisms were unclear. 3T3-L1 adipocytes were used to investigate the effect of ET-1 on lipolysis and the underlying mechanisms. Glycerol levels in the incubation medium and hormone-sensitive lipase (HSL) phosphorylation were used as indices for lipolysis. ET-1 significantly increased HSL phosphorylation and lipolysis, which were completely inhibited by ERK inhibitor (PD98059) and guanylyl cyclase (GC) inhibitor (LY83583). LY83583 reduced ET-1-induced ERK phosphorylation. A Ca2+-free medium and PLC inhibitor caused significant decreases in ET-1-induced lipolysis as well as ERK and HSL phosphorylation, and IP3 receptor activator (D-IP3) increased lipolysis. ET-1 increased cGMP production, which was not affected by depletion of extracellular Ca2+. On the other hand, LY83583 diminished the ET-1-induced Ca2+ influx. Transient receptor potential vanilloid-1 (TRPV-1) antagonist and shRNA partially inhibited ET-1-induced lipolysis. ET-1-induced lipolysis was completely suppressed by CaMKIII inhibitor (NH-125). These results indicate that ET-1 stimulates extracellular Ca2+ entry and activates the intracellular PLC/IP3/Ca2+ pathway through a cGMP-dependent pathway. The increased cytosolic Ca2+ that results from ET-1 treatment stimulates ERK and HSL phosphorylation, which subsequently induces lipolysis. ET-1 induces HSL phosphorylation and lipolysis via the GC/cGMP/Ca2+/ERK/CaMKIII signaling pathway in 3T3-L1 adipocytes.

Ryanodine receptor calcium release channels in trophoblasts and their role in cell migration

Trophoblasts are specialized epithelial cells of the placenta that are involved in invasion, communication and the exchange of materials between the mother and fetus. Cytoplasmic Ca²⁺ ([Ca²⁺]_c) plays critical roles in regulating such processes in other cell types, but relatively little is known about the mechanisms that control this second messenger in trophoblasts. In the current study, the presence of RyRs and their accessory proteins in placental tissues and in the BeWo choriocarcinoma, a model trophoblast cell-line, were examined using immunohistochemistry and Western immunoblotting. Contributions of RyRs to Ca²⁺ signalling and to random migration in BeWo cells were investigated using fura-2 fluorescent and brightfield videomicroscopy. The effect of RyR inhibition on reorganization of the F-actin cytoskeleton elicited by the hormone angiotensin II, was determined using phalloidin-labelling and confocal microscopy. RyR1 and RyR3 proteins were detected in trophoblasts of human first trimester and term placental villi, along with the accessory proteins triadin and calsequestrin. Similarly, RyR1, RyR3, triadin and calsequestrin were detected in BeWo cells. In this cell-line, activation of RyRs with micromolar ryanodine increased [Ca²⁺]_c, whereas pharmacological inhibition of these channels reduced Ca²⁺ transients elicited by the peptide hormones angiotensin II, arginine vasopressin and endothelin 1. Angiotensin II increased the velocity, total distance and Euclidean distance of random migration by BeWo cells and these effects were significantly reduced by tetracaine and by inhibitory concentrations of ryanodine. RyRs contribute to reorganization of the F-actin cytoskeleton elicited by angiotensin II, since inhibition of these channels restores the parallelness of these structures to control levels. These findings demonstrate that trophoblasts contain a suite of proteins similar to those in other cell types possessing highly developed Ca²⁺ signal transduction systems, such as skeletal muscle. They also indicate that these channels regulate the migration of trophoblast cells, a process that plays a key role in development of the placenta.

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.

Transposable elements, placental development, and oocyte activation: Cellular stress and AMPK links jumping genes with the creation of human life

Transposable elements (TEs), also known as "jumping genes", are DNA sequences first described by Nobel laureate Barbara McClintock that comprise nearly half of the human genome and are able to transpose or move from one genomic location to another. As McClintock also noted that a genome "shock" or stress may induce TE activation and transposition, accumulating evidence suggests that cellular stress (e.g. mediated by increases in intracellular reactive oxygen species [ROS] and calcium [Ca2+], etc.) induces TE mobilization in several model organisms and L1s (a member of the retrotransposon class of TEs) are active and capable of retrotransposition in human oocytes, human sperm, and in human neural progenitor cells. Cellular stress also plays a critical role in human placental development, with cytotrophoblast (CTB) differentiation leading to the formation of the syncytiotrophoblast (STB), a cellular layer that facilitates nutrient and gas exchange between the mother and the fetus. Syncytin-1, a protein that promotes fusion of CTB cells and is necessary for STB formation, and its receptor is found in human sperm and human oocytes, respectively, and increases in ROS and Ca2+ promote trophoblast differentiation and syncytin-1 expression. Cellular stress is also essential in promoting human oocyte maturation and activation which, similar to TE mobilization, can be induced by compounds that increase intracellular Ca2+ and ROS levels. AMPK is a master metabolic regulator activated by increases in ROS, Ca2+, and/or an AMP(ADP)/ATP ratio increase, etc. as well as compounds that induce L1 mobilization in human cells. AMPK knockdown inhibits trophoblast differentiation and AMPK-activating compounds that promote L1 mobility also enhance trophoblast differentiation. Cellular stressors that induce TE mobilization (e.g. heat shock) also promote oocyte maturation in an AMPK-dependent manner and the antibiotic ionomycin activates AMPK, promotes TE activation, and induces human oocyte activation, producing normal, healthy children. Metformin promotes AMPK-dependent telomerase activation (critical for telomere maintenance) and induces activation of the endonuclease RAG1 (promotes DNA cleavage and transposition) via AMPK. Both RAG1 and telomerase are derived from TEs. It is our hypothesis that cellular stress and AMPK links TE activation and transposition with placental development and oocyte activation, facilitating both human genome evolution and the creation of all human life. We also propose the novel observation that various cellular stress-inducing compounds (e.g. metformin, resveratrol, etc.) may facilitate beneficial TE activation and transposition and enhance fertilization and embryological development through a common mechanism of AMPK activation.

Endothelin-1: a key pathological factor in pre-eclampsia?

Endothelin (ET)-1 has been implicated in a diverse range of signalling events in a wide variety of target tissues. Given its potent vasoactive function and the prevalence of hypertension in pre-eclampsia, there has been extensive research on the role of ET-1 in this disorder. Indeed, ET-1 has been suggested to contribute to hypertension in pre-eclampsia. Recently, ET-1 has also been implicated in the induction of both oxidative stress and endoplasmic reticulum stress in pre-eclampsia; each of which has been proposed to contribute to many of the clinical manifestations of this disorder. ET-1 has been shown to activate key signalling molecules that lead to induction of these stress pathways. The use of ET-receptor antagonists could block oxidative and endoplasmic reticulum stress. Hence, further research into the role of ET-1 in pre-eclampsia may lead to the development of possible strategies to circumvent these stress pathways and the associated pathology that occurs in pre-eclampsia. Endothelin (ET)-1 has been implicated in a diverse range of signalling events in a wide variety of target tissues. Given its potent vasoactive function and the prevalence of hypertension in pre-eclampsia, there has been extensive research on the role of ET-1 in this disorder. Indeed, ET-1 has been suggested to contribute to hypertension in pre-eclampsia. Recently, ET-1 has also been implicated in the induction of both oxidative stress and endoplasmic reticulum stress in pre-eclampsia, each of which has been proposed to contribute to many of the clinical manifestations of this disorder. ET-1 has been shown to activate key signalling molecules that lead to induction of these stress pathways. The use of ET-receptor antagonists could block oxidative and endoplasmic reticulum stress. Hence, further research into the role of ET-1 in pre-eclampsia may lead to the development of possible strategies to circumvent these stress pathways and the associated pathology that occurs in pre-eclampsia.

Endothelin-1 stimulates proliferation of first-trimester trophoblasts via the A- and B-type receptor and invasion via the B-type receptor

CONTEXT

Endothelin-1 (ET-1) stimulates proliferation and invasion of first-trimester human trophoblast cells.

OBJECTIVE

To test the hypothesis that ET-1 effects are mediated by different receptor subtypes [ET receptor (ETR)-A and ETR-B].

DESIGN

The location of ETR in trophoblast cell columns (wk 6-12) was investigated by immunohistochemistry and autoradiography. Trophoblasts were isolated from first-trimester human placentas and proliferative and invasive subpopulations separated using an integrin α6 antibody. Cells were incubated for 24 h with 10 μm ET-1 and different ETR antagonists: PD142893 (unselective), BQ-610 (ETR-A), and RES-701-1 (ETR-B). After ETR down-regulation by antisense oligonucleotides, proliferation (thymidine incorporation, protein synthesis) and invasion (Matrigel invasion) were measured. ETR expression in isolated cells was analyzed by Western blotting and semiquantitative RT-PCR.

RESULTS

Both ETR are expressed in both subpopulations in the cell column with predominance of ETR-A in the proximal part and proliferative subpopulation, whereas ETR-B is present at similar levels in both subpopulations. These results were confirmed at the mRNA level. ET-1 increased proliferation (maximum 267% of control) and invasion (maximum 288% of control) of first-trimester trophoblasts. The mitogenic ET-1 effect was inhibited (P < 0.05) by 40-80% with each receptor antagonist and by 44 and 40%, respectively, by ETR-A and ETR-B antisense oligonucleotides. The invasion-promoting effect was almost completely blocked in the presence of the ETR-B antagonists.

CONCLUSION

The effect of ET-1 on cell proliferation in first-trimester trophoblasts is mediated by both ETR, whereas its effect on invasion is mediated predominantly by ETR-B. These effects are in line with the receptor subtype location.

Calcium signaling in placenta

The placenta sustains the developing fetus throughout gestation and its major functions include nutrition, gas and waste exchange via a variety of passive or active mechanisms. Up to 30 g of calcium (Ca(2+)) actively crosses the trophoblast layer during human pregnancy. The Ca(2+) ion not only plays an important role for skeletal development but is also an essential second messenger. This review is intended to highlight the implications of Ca(2+) signaling during reproduction and specifically placentation. Initially, a Ca(2+) wave induces fertilization of the oocyte. The intracellular Ca(2+) concentration is key for the blastocyst implantation, proper placental development and function. Current knowledge of many proteins involved in placental Ca(2+) regulation and their function in pathologic conditions is largely limited. Recent studies, however, point to alterations in Ca(2+) homeostasis in placental pathologies such as pre-eclampsia (PE) and intrauterine growth restriction (IUGR). A broader understanding of the role of Ca(2+) signaling during human reproduction may offer insight into impaired pregnancy outcomes.

Sources of calcium in agonist-induced contraction of rat distal colon smooth muscle in vitro

AIM: To study the origin of calcium necessary for agonist-induced contraction of the distal colon in rats.

METHODS: The change in intracellular calcium concentration ([Ca²⁺]_i) evoked by elevating external Ca²⁺ was detected by fura 2/AM fluorescence. Contractile activity was measured with a force displacement transducer. Tension was continuously monitored and recorded using a Powerlab 4/25T data acquisition system with an ML110 bridge bioelectric physiographic amplifier.

RESULTS: Store depletion induced Ca²⁺ influx had an effect on [Ca²⁺]_i. In nominally Ca²⁺-free medium, the sarco-endoplasmic reticulum Ca²⁺-ATPase inhibitor thapsigargin (1 &mgr;mol/L) increased [Ca²⁺]_i from 68 to 241 nmol/L, and to 458 (P < 0.01) and 1006 nmol/L (P < 0.01), respectively, when 1.5 mmol/L and 3.0 mmol/L extracellular Ca²⁺ was reintroduced. Furthermore, the change in [Ca²⁺]_i was observed with verapamil (5 &mgr;mol/L), La³⁺ (1 mmol/L) or KCl (40 mmol/L) in the bathing solution. These channels were sensitive to La³⁺ (P < 0.01), insensitive to verapamil, and voltage independent. In isolated distal colons we found that in normal Krebs solution, contraction induced by acetylcholine (ACh) was partially inhibited by verapamil, and the inhibitory rate was 41% (P < 0.05). On the other hand, in Ca²⁺-free Krebs solution, ACh induced transient contraction due to Ca²⁺ release from the intracellular stores. The transient contraction lasted until the Ca²⁺ store was depleted. Restoration of extracellular Ca²⁺ in the presence of atropine produced contraction, mainly due to Ca²⁺ influx. Such contraction was not inhibited by verapamil, but was decreased by La³⁺ (50 &mgr;mol/L) from 0.96 to 0.72 g (P < 0.01).

CONCLUSION: The predominant source of activator Ca²⁺ for the contractile response to agonist is extracellular Ca²⁺, and intracellular Ca²⁺ has little role to play in mediating excitation-contraction coupling by agonists in rat distal colon smooth muscle in vitro. The influx of extracellular Ca²⁺ is mainly mediated through voltage-, receptor- and store-operated Ca²⁺ channels, which can be used as an alternative to develop new drugs targeted on the dysfunction of digestive tract motility.

Endothelin1-induced Ca(2+) mobilization is altered in calvarial osteoblastic cells of Cx43(+/- ) mice

During bone remodeling, osteoblastic (OB) cells have a central role leading to the production of extracellular matrix and its subsequent mineralization. As revealed by human physiopathologies, the OB differentiation process is essential for the control of calcium metabolism and normal bone formation. Moreover, accumulating data in the field of bone development suggest that connexin 43 (Cx43)-mediated gap junctional communication plays an important role in OB differentiation and function. Since Ca(2+) has a central role in OB physiology, the aim of the present study was to investigate the hypothetical involvement of Cx43 in OB calcium homeostasis. We performed measurements of intracellular calcium activity ([Ca(2+)]( i )) by a cytofluorimetric method using Fluo-4 as a calcium indicator and endothelin-1 (ET-1) as a physiological calcium-mobilizing factor on cultured OB cells isolated from calvaria of Cx43(+/-) and Cx43(+/+) mice. Partial deletion of the Cx43 gene induced a significant decrease in the [Ca(2+)]( i ) rise elicited by ET-1. This reduction was not correlated to a decrease or a modification of ET receptor subtype expression as assessed by real-time reverse-transcription polymerase chain reaction. Pharmacological investigations led us to demonstrate that the significant difference in [Ca(2+)]( i ) peak amplitude during the ET-1 action was associated with decreased calcium influx involving L-type voltage-sensitive calcium channels, whereas calcium release from intracellular stores and implication of phospholipase C were not affected by the reduced expression of Cx43. In conclusion, our data demonstrate for the first time that the Cx43 level of expression and/or function is able to modulate the [Ca(2+)]( i ) mobilization in OB cells.

Polycystin-2 cation channel function in the human syncytiotrophoblast is regulated by microtubular structures

Polycystin-2 (PC2), encoded by PKD2, which is one of the genes whose mutations cause polycystic kidney disease, is abundantly produced in the apical domain of the syncytiotrophoblast (hST) of term human placenta. PC2, a TRP-type (TRPP2) non-selective cation channel, is present in primary cilia of renal epithelial cells, a microtubule-based ancillary structure with sensory function. The hST has abundant cytoskeletal structures, and actin filament dynamics regulate PC2 channel function in this epithelium. However, it is expected that the apical hST excludes microtubular structures. Here, we demonstrated by Western blot and immunocytochemical analyses that hST apical vesicles indeed contain microtubule structural components, including tubulin isoforms, acetylated alpha-tubulin, and the kinesin motor proteins KIF3A and KIF3B. PC2 and tubulin were substantially colocalized in hST vesicles. Treatment of hST vesicles with either the microtubular disrupter colchicine (15 microM) or the microtubular stabilizer paclitaxel (taxol, 15 microM) resulted in distinct patterns of microtubular re-organization and PC2 redistribution. We also observed that changes in microtubular dynamics regulate PC2 channel function. Addition of colchicine rapidly inhibited PC2 channel activity in lipid-bilayer reconstituted hST membranes. Addition of either tubulin and GTP, or taxol, however, stimulated PC2 channel activity in control hST membranes. Interestingly, we found that the kinesin motor protein KIF3A was capable of increasing PC2 channel activity in hST. We believe that the data are the first to provide a direct demonstration of a microtubular interaction with PC2 in the hST. This interaction thus plays an important regulatory role in the control of ion transport in the human placenta.

Endothelin-1 inhibits human osteoblastic cell differentiation: Influence of connexin-43 expression level

Gap junctional intercellular communication (GJIC) permits coordinated cellular activities during developmental and differentiation processes. In bone, the involvement of the gap junctional protein, connexin-43 (Cx43), and of GJIC in osteoblastic differentiation and mineralization of the extracellular matrix has been previously demonstrated. Former studies have shown that endothelin-1 (ET-1) was also implicated in the control of osteoblastic proliferation and differentiation. However, depending on the cellular models, ET-1 has been shown to decrease or increase osteoblastic differentiation markers. As no data were available on the ET-1 effect on GJIC and Cx43 expression in osteoblastic cells, we analyzed here the possible crosstalk between Cx43 and ET-1 in a human cell line (hFOB 1.19) which displays different Cx43 expression levels and phenotypes when cultured at 33.5 or 39 degrees C. The presence of ET-1 (10(-8) M) for 2-12 days of culture did not significantly alter the proliferation rate of hFOB cells whatever their phenotype. In contrast, ET-1 induced a differential inhibitory effect on the biochemical differentiation markers (alkaline phosphatase activity and osteocalcin expression) with a significant reduction in the differentiated phenotype at 39 degrees C, whereas no effects were measured at 33.5 degrees C. The inhibitory effect was linked to a decrease of GJIC and of Cx43 both at transcriptional and protein levels. Altogether, our results suggest that Cx43 expression level could influence the action of ET-1 on human osteoblastic cell differentiation. Our data also indicate that the gap junctional protein could play a pivotal role in the response of osteoblasts to mitogenic factors implicated in bone pathologies.