Fluid shear triggers microvilli formation via mechanosensitive activation of TRPV6

M, Kim S, Lam PY, Conrads T, Conrads K, Han A, Menon R, Richardson LS. Modeling reproductive and pregnancy-associated tissues using organ-on-chip platforms: challenges, limitations, and the high throughput data frontier

Over the past decade, organ-on-chip technology (microphysiological systems or tissue chips) has reshaped in-vitro physiological and pathological modeling and pharmaceutical drug assessment. FDA Modernization Act 2.0 allows for alternatives to animal testing or the use of appropriate non-animal models/new approach methods (NAMs), such as Organ-on-chips (OC) platforms or in silico simulation models, to generate pre-clinical in-vitro drug trial data for regulatory purposes primes the microfluidic field to have exponential growth in the coming years. The changes in the approaches of regulatory agencies could significantly impact the development of therapeutics for use during pregnancy. However, limitations of the devices and molecular and biochemical assay shortfalls hinder the progress of the OOC field. This review describes available reproductive and pregnancy-related OOC platforms, and the current methodologies utilized to generate endpoint datasets (e.g., microscopic imaging, immunocytochemistry, real-time polymerase chain reaction, cytokine multiplex analysis). Microfluidic platform limitations, such as fewer number of cells or low supernatant volumes and restrictions regarding fabrication materials, are described. Novel approaches (e.g., spatial transcriptomics, imaging cytometry by time of flight, exosomes analysis using Exoview) to overcome these challenges are described. OOC platforms are primed to provide biologically relevant and clinically translational data that can revolutionize in-vitro physiological modeling, drug discovery, and toxicologic risk assessment. However, engineering adaptations to increase the throughput of devices (i.e., device arrays) and biological advancements to improve data throughput are both needed for these platforms to reach their full potential.

The role of calcium ions and the transient receptor potential vanilloid (TRPV) channel in bone remodelling and orthodontic tooth movement

During orthodontic treatment, the application of orthodontic forces to the periodontal tissues leads to the activation of osteoblasts and osteoclasts, which in turn induces bone remodelling and tooth movement. Calcium is a biologically essential element that exists in the internal environment and cells as calcium ions(Ca2+). The concentration of extracellular Ca2+ can affect the activity and function of osteoblasts and osteoclasts, as well as regulate bone remodelling. In the cell, calcium ions play a crucial role in cell signal transduction, acting as a second messenger. The orthodontic force increases intracellular Ca2+ concentration through a series of cascade reactions that affect the differentiation and apoptosis of osteoblasts and osteoclasts. Calcium channels on the cell membrane are crucial for intracellular and extracellular calcium transport. Transient Receptor Potential Vanilloid (TRPV) is a calcium ion permeable and mechanosensitive receptor comprising six calcium channel subtypes, TRPV1-6. This review will focus on the crucial role of Ca2+ in bone metabolism and provide a comprehensive description of the function and mechanism of each specific TRPV channel subtype in orthodontic tooth movement and bone remodelling.

The proteomic landscape of trophoblasts unravels calcium-dependent syncytialization processes and beta-chorionic gonadotropin (ß-hCG) production

BACKGROUND

The syncytiotrophoblast (STB) layer of the placenta is formed by cell fusion of cytotrophoblasts, acts as a feto-maternal barrier, is required for the production of pregnancy hormones such as chorionic gonadotropin, estradiol and progesterone and is also responsible for feto-maternal mineral exchange such as calcium. Adequate mineral supply and placental hormone production are essential for the maintenance of pregnancy, and disturbances in trophoblast integrity are associated with pregnancy complications. Since knowledge about the identity and expression levels of proteins in trophoblast and syncytiotrophoblast cells is limited so far, we analyzed the proteomes of trophoblast-like and syncytiotrophoblast-like BeWo cells under different calcium conditions. The investigation of protein expression profiles in combination with hormone assays can provide a better understanding of calcium-dependent cellular processes in trophoblasts and syncytiotrophoblasts.

METHODS

Here, we combine human trophoblast model cell cultures, hormone assays, antibody-based detection methods and high-resolution mass spectrometry analyzes to assess changes in cellular processes during syncytialization.

RESULTS

We monitored the changes in protein expression profiles during forskolin induced syncytialization of trophoblast-like cells in an unbiased manner and show that the expression of numerous proteins is strongly altered. Among them are enzymes of the glucocorticoid and sex hormones synthesis pathways such as cytochrome P450 (CYP) 19A1, CYP11A1, adrenodoxin (FDX1), hydroxysteroid dehydrogenase (HSD) 11β2 and HSD17β1, whose expression is strongly induced by syncytialization. The production of beta human chorionic gonadotropin (ß-hCG), progesterone and estradiol increase during syncytialization, while the secretion and synthesis of ß-hCG and the expression of several protein syncytiotrophoblast markers show a clear calcium dependence.

CONCLUSION

The broad applicability of semi-quantitative proteome profiling of cytotrophoblast- and syncytiotrophoblast-like cells provides new insights into signaling processes that occur in cytotrophoblasts /syncytiotrophoblasts during pregnancy.

Placental microphysiological systems: new advances on promising platforms that mimic the microenvironment of the human placenta

One of the most complex human physiological processes to study is pregnancy. Standard animal models, as well as two-dimensional models, lack the complexity and biological relevance required to accurately study such a physiological process. Recent studies have focused on the development of three-dimensional models based on microfluidic systems, designated as placental microphysiological systems (PMPSs). PMPS devices provide a model of the placental barrier through culturing relevant cell types in specific arrangements and media to mimic the in vivo environment of the maternal-fetal circulation. Here, recent developments of PMPS models for embryo uterine implantation, preeclampsia evaluation, and toxicological screening are presented. Studies that use bioprinting techniques are also discussed. Lastly, recent developments in endometrium microphysiological systems are reviewed. All these presented models showed their superiority compared to standard models in recapitulating the biological environment seen in vivo. However, several limitations regarding the types of cells and materials used for these systems were also widely reported. Despite the need for further improvements, PMPS models contribute to a better understanding of the biological mechanisms surrounding pregnancy and the respective pathologies.

Mechanoimmunology of T-Cell Activation

T-cell activation, a pivotal process in the adaptive immune response, is initiated when the T cell receptor (TCR) recognises and binds to antigenic peptide-major histocompatibility complex (pMHC) molecules on the cell membrane. Emerging evidence indicates that mechanical cues regulate T-cell activation by modulating TCR signalling and mechanotransduction pathways, although the precise underlying mechanisms remain elusive. This review highlights recent findings suggesting that the TCR functions as a mechanosensor, capable of sensing and transmitting mechanical forces through conformational changes. Key steps in T-cell mechanotransduction are discussed, including the roles of the cytoskeleton, mechanosensitive channels such as Piezo 1 and microvilli in facilitating activation. Additionally, we analyse the mechanical responses of chimeric antigen receptor T cells. Understanding the mechanobiological mechanisms underlying T-cell activation offers novel insights and potential strategies for advancing immunotherapies and treating immune-related disorders.

The Molecular Biology of Placental Transport of Calcium to the Human Foetus

From fertilisation to delivery, calcium must be transported into and within the foetoplacental unit for intracellular signalling. This requires very rapid, precisely located Ca2+ transfers. In addition, from around the eighth week of gestation, increasing amounts of calcium must be routed directly from maternal blood to the foetus for bone mineralisation through a flow-through system, which does not impact the intracellular Ca2+ concentration. These different processes are mediated by numerous membrane-sited Ca2+ channels, transporters, and exchangers. Understanding the mechanisms is essential to direct interventions to optimise foetal development and postnatal bone health and to protect the mother and foetus from pre-eclampsia. Ethical issues limit the availability of human foetal tissue for study. Our insight into the processes of placental Ca2+ handling is advancing rapidly, enabled by developing genetic, analytical, and computer technology. Because of their diverse sources, the reports of new findings are scattered. This review aims to pull the data together and to highlight areas of uncertainty. Areas needing clarification include trafficking, membrane expression, and recycling of channels and transporters in the placental microvilli; placental metabolism of vitamin D in gestational diabetes and pre-eclampsia; and the vascular effects of increased endothelial Orai expression by pregnancy-specific beta-1-glycoproteins PSG1 and PSG9.

[Roles of Trophoblast Differentiation, Cell Fusion, and Microvilli Formation in Placentation and Prospects for a Model for Their Assessment]

The placenta, which acts as an interface between fetal and maternal circulations, is an indispensable organ for fetal growth in mammalian pregnancy. It mediates the transportation of nutrients, the exchange of gases such as oxygen and carbon dioxide, and the excretion of waste products between the fetus and mother. The surface of placental villi is covered by two layers of mononuclear undifferentiated cytotrophoblasts (CT) and multinucleated syncytiotrophoblasts (ST). The formation of the multinucleated ST layer via fusion of CT is referred to as syncytialization, which is a well-characterized morphological sign of terminal differentiation. STs function not only as the placental barrier to separate maternal blood from fetal tissue but also as the main source of human chorionic gonadotropin (hCG) and progesterone (P4) during pregnancy. The significance of appropriate differentiation and fusion of CTs to form STs is demonstrated by the finding that disturbance of these processes is linked to the pathogenesis of pregnancy-associated complications such as hypertensive disorders of pregnancy (HDP) and fetal growth restriction (FGR). In this review, we focused on trophoblast differentiation, cell fusion and microvilli formation, and showed the role of short-chain fatty acid butyrate and progesterone receptor membrane component 1 (PGRMC1) in these processes. Furthermore, we described the evaluation of placental function and its prospects utilizing a quantitative trophoblast cell fusion system and microfluidic device.

Beyond 2D: Novel biomaterial approaches for modeling the placenta

This review considers fully three-dimensional biomaterial environments of varying complexity as these pertain to research on the placenta. The developments in placental cell sources are first considered, along with the corresponding maternal cells with which the trophoblast interact. We consider biomaterial sources, including hybrid and composite biomaterials. Properties and characterization of biomaterials are discussed in the context of material design for specific placental applications. The development of increasingly complicated three-dimensional structures includes examples of advanced fabrication methods such as microfluidic device fabrication and 3D bioprinting, as utilized in a placenta context. The review finishes with a discussion of the potential for in vitro, three-dimensional placenta research to address health disparities and sexual dimorphism, especially in light of the exciting recent changes in the regulatory environment for in vitro devices.

Engineering placental trophoblast fusion: A potential role for biomechanics in syncytialization

The process by which placental trophoblasts fuse to form the syncytiotrophoblast around the chorionic villi is not fully understood. Mechanical features of the in vivo and in vitro culture environments have recently emerged as having the potential to influence fusion efficiency, and considering these mechanical cues may ultimately allow predictive control of trophoblast syncytialization. Here, we review recent studies that suggest that biomechanical factors such as shear stress, tissue stiffness, and dimensionally-related stresses affect villous trophoblast fusion efficiency. We then discuss how these stimuli might arise in vivo and how they can be incorporated in cultures to study and enhance villous trophoblast fusion. We believe that this mechanical paradigm will provide novel insight into manipulating the syncytialization process to better engineer improved models, understand disease progression, and ultimately develop novel therapeutic strategies.

Origin and evolution of microvilli

BACKGROUND INFORMATION

Microvilli are finger-like, straight, and stable cellular protrusions that are filled with F-actin and present a stereotypical length. They are present in a broad range of cell types across the animal tree of life and mediate several fundamental functions, including nutrient absorption, photosensation, and mechanosensation. Therefore, understanding the origin and evolution of microvilli is key to reconstructing the evolution of animal cellular form and function. Here, we review the current state of knowledge on microvilli evolution and perform a bioinformatic survey of the conservation of genes encoding microvillar proteins in animals and their unicellular relatives.

RESULTS

We first present a detailed description of mammalian microvilli based on two well-studied examples, the brush border microvilli of enterocytes and the stereocilia of hair cells. We also survey the broader diversity of microvilli and discuss similarities and differences between microvilli and filopodia. Based on our bioinformatic survey coupled with carefully reconstructed molecular phylogenies, we reconstitute the order of evolutionary appearance of microvillar proteins. We document the stepwise evolutionary assembly of the "molecular microvillar toolkit" with notable bursts of innovation at two key nodes: the last common filozoan ancestor (correlated with the evolution of microvilli distinct from filopodia) and the last common choanozoan ancestor (correlated with the emergence of inter-microvillar adhesions).

CONCLUSION AND SIGNIFICANCE

We conclude with a scenario for the evolution of microvilli from filopodia-like ancestral structures in unicellular precursors of animals.

Transmembrane channel-like 4 and 5 proteins at microvillar tips are potential ion channels and lipid scramblases

Microvilli-membrane bound actin protrusions on the surface of epithelial cells-are sites of critical processes including absorption, secretion, and adhesion. Increasing evidence suggests microvilli are mechanosensitive, but underlying molecules and mechanisms remain unknown. Here, we localize transmembrane channel-like proteins 4 and 5 (TMC4 and 5) and calcium and integrin binding protein 3 (CIB3) to microvillar tips in intestinal epithelial cells, near glycocalyx insertion sites. We find that TMC5 colocalizes with CIB3 in cultured cells and that a TMC5 fragment forms a complex with CIB3 in vitro. Homology and AlphaFold2 models reveal a putative ion permeation pathway in TMC4 and 5, and molecular dynamics simulations predict both proteins can conduct ions and perform lipid scrambling. These findings raise the possibility that TMC4 and 5 interact with CIB3 at microvillar tips to form a mechanosensitive complex, akin to TMC1 and 2, and CIB2 and 3, within the mechanotransduction channel complex at the tips of inner ear stereocilia.

Organ-on-a-chip: future of female reproductive pathophysiological models

The female reproductive system comprises the internal and external genitalia, which communicate through intricate endocrine pathways. Besides secreting hormones that maintain the female secondary sexual characteristics, it also produces follicles and offspring. However, the in vitro systems have been very limited in recapitulating the specific anatomy and pathophysiology of women. Organ-on-a-chip technology, based on microfluidics, can better simulate the cellular microenvironment in vivo, opening a new field for the basic and clinical research of female reproductive system diseases. This technology can not only reconstruct the organ structure but also emulate the organ function as much as possible. The precisely controlled fluidic microenvironment provided by microfluidics vividly mimics the complex endocrine hormone crosstalk among various organs of the female reproductive system, making it a powerful preclinical tool and the future of pathophysiological models of the female reproductive system. Here, we review the research on the application of organ-on-a-chip platforms in the female reproductive systems, focusing on the latest progress in developing models that reproduce the physiological functions or disease features of female reproductive organs and tissues, and highlighting the challenges and future directions in this field.

A dynamic flow fetal membrane organ-on-a-chip system for modeling the effects of amniotic fluid motion

Fetal membrane (amniochorion), the innermost lining of the intrauterine cavity, surround the fetus and enclose amniotic fluid. Unlike unidirectional blood flow, amniotic fluid subtly rocks back and forth, and thus, the innermost amnion epithelial cells are continuously exposed to low levels of shear stress from fluid undulation. Here, we tested the impact of fluid motion on amnion epithelial cells (AECs) as a bearer of force impact and their potential vulnerability to cytopathologic changes that can destabilize fetal membrane functions. A previously developed amnion membrane (AM) organ-on-chip (OOC) was utilized but with dynamic flow to culture human fetal amnion membrane cells. The applied flow was modulated to perfuse culture media back and forth for 48 h to mimic fluid motion. A static culture condition was used as a negative control, and oxidative stress (OS) condition was used as a positive control representing pathophysiological changes. The impacts of fluidic motion were evaluated by measuring cell viability, cellular transition, and inflammation. Additionally, scanning electron microscopy (SEM) imaging was performed to observe microvilli formation. The results show that regardless of the applied flow rate, AECs and AMCs maintained their viability, morphology, innate meta-state, and low production of pro-inflammatory cytokines. E-cadherin expression and microvilli formation in the AECs were upregulated in a flow rate-dependent fashion; however, this did not impact cellular morphology or cellular transition or inflammation. OS treatment induced a mesenchymal morphology, significantly higher vimentin to cytokeratin 18 (CK-18) ratio, and pro-inflammatory cytokine production in AECs, whereas AMCs did not respond in any significant manner. Fluid motion and shear stress, if any, did not impact AEC cell function and did not cause inflammation. Thus, when using an amnion membrane OOC model, the inclusion of a dynamic flow environment is not necessary to mimic in utero physiologic cellular conditions of an amnion membrane.

A multi-organ, feto-maternal interface organ-on-chip, models pregnancy pathology and is a useful preclinical extracellular vesicle drug trial platform

Pregnant women and their fetuses are often excluded from clinical trials due to missing drug-related pre-clinical trial information at the human feto-maternal interface (FMi). The two interfaces-placenta/decidua and fetal membranes/decidua are gatekeepers of drug transport; however, testing their functions is impractical during pregnancy. Limitations of current in-vivo/in-vitro models have hampered drug development and testing during pregnancy. Hence, major complications like preterm births and maternal and neonatal mortalities remain high. Advancements in organ-on-chip (OOC) platforms to test drug kinetics and efficacy and novel extracellular vesicle-based fetal drug delivery are expected to accelerate preclinical trials related to pregnancy complications. Here we report the development and testing of a humanized multi-organ fetal membrane/placenta (fetal)-decidua (maternal) interface OOC (FMi-PLA-OOC) that contains seven cell types interconnected through microchannels to maintain intercellular interactions as seen in-utero. Cytotoxicity, propagation, mechanism of action, and efficacy of engineered extracellular vesicles containing anti-inflammatory interleukin (IL)-10 (eIL-10) were evaluated to reduce FMi inflammation associated with preterm birth. A healthy and disease model (lipopolysaccharide-infectious inflammation) of the FMi-PLA-OOC was created and co-treated with eIL-10. eIL-10 propagated from the maternal to fetal side within 72-hours, localized in all cell types, showed no cytotoxicity, activated IL-10 signaling pathways, and reduced lipopolysaccharide-induced inflammation (minimized NF-kB activation and proinflammatory cytokine production). These data recapitulated eIL-10s' ability to reduce inflammation and delay infection-associated preterm birth in mouse models, suggesting FMi-PLA-OOC as an alternative approach to using animal models. Additionally, we report the utility of eIL-10 that can traverse through FMis to reduce inflammation-associated pregnancy complications.

A Dynamic Flow Fetal Membrane Organ-on-a-Chip System for Modeling the Effects of Amniotic Fluid Motion

Fetal membrane(amniochorion), the innermost lining of the intrauterine cavity, surround the fetus and enclose amniotic fluid. Unlike unidirectional blood flow, amniotic fluid subtly rocks back and forth, and thus, the innermost amnion epithelial cells are continuously exposed to low levels of shear stress from fluid undulation. Here, we tested the impact of fluid motion on amnion epithelial cells (AECs) as a bearer of force impact and their potential vulnerability to cytopathologic changes that can destabilize fetal membrane functions. An amnion membrane (AM) organ-on-chip (OOC) was utilized to culture human fetal amnion membrane cells. The applied flow was modulated to perfuse culture media back and forth for 48 hours flow culture to mimic fluid motion. Static culture condition was used as a negative control, and oxidative stress (OS) condition was used as a positive control for pathophysiological changes. The impacts of fluidic motion were evaluated by measuring cell viability, cellular transition, and inflammation. Additionally, scanning electron microscopy (SEM) imaging was performed to observe microvilli formation. The results show that regardless of the applied flow rate, AECs and AMCs maintained their viability, morphology, innate meta-state, and low production of pro-inflammatory cytokines. E-cadherin expression and microvilli formation in the AECs were upregulated in a flow rate-dependent fashion; however, this did not impact cellular morphology or cellular transition or inflammation. OS treatment induced a mesenchymal morphology, significantly higher vimentin to CK-18 ratio, and pro-inflammatory cytokine production in AECs, whereas AMCs did not respond in any significant manner. Fluid motion and shear stress, if any, did not impact AEC cell function and did not cause inflammation. Thus, when using an amnion membrane OOC model, the inclusion of a flow culture environment is not necessary to mimic any in utero physiologic cellular conditions of fetal membrane-derived cells.

A Microphysiological Model to Mimic the Placental Remodeling during Early Stage of Pregnancy under Hypoxia-Induced Trophoblast Invasion

Placental trophoblast invasion is critical for establishing the maternal-fetal interface, yet the mechanisms driving trophoblast-induced maternal arterial remodeling remain elusive. To address this gap, we developed a three-dimensional microfluidic placenta-on-chip model that mimics early pregnancy placentation in a hypoxic environment. By studying human umbilical vein endothelial cells (HUVECs) under oxygen-deprived conditions upon trophoblast invasion, we observed significant HUVEC artery remodeling, suggesting the critical role of hypoxia in placentation. In particular, we found that trophoblasts secrete matrix metalloproteinase (MMP) proteins under hypoxic conditions, which contribute to arterial remodeling by the degradation of extracellular matrix components. This MMP-mediated remodeling is critical for facilitating trophoblast invasion and proper establishment of the maternal-fetal interface. In addition, our platform allows real-time monitoring of HUVEC vessel contraction during trophoblast interaction, providing valuable insights into the dynamic interplay between trophoblasts and maternal vasculature. Collectively, our findings highlight the importance of MMP-mediated arterial remodeling in placental development and underscore the potential of our platform to study pregnancy-related complications and evaluate therapeutic interventions.

The chicken chorioallantoic membrane assay revisited - A face-lifted approach for new perspectives in placenta research

The study of very early human placentation is largely limited due to ethical restrictions on the use of embryonic tissue and the fact that the placental anatomy of common laboratory animal models varies considerably from that of humans. In recent years several promising models, including trophoblast stem cell-derived organoids, have been developed that have also proven useful for the study of important trophoblast differentiation processes. However, the consideration of maternal blood flow in trophoblast invasion models currently appears to be limited to animal models. An almost forgotten model to study the invasive behavior of trophoblasts is to culture them in vitro on the chicken chorioallantoic membrane (CAM), showing an extraembryonic vascular network in its mesenchymal stroma that is continuously perfused by the chicken embryonic blood circulation. Here, we present an extension of the previously described ex ovo CAM assay and describe the use of cavity-bearing trophoblast spheroids obtained from the first trimester cell line ACH-3P. We demonstrate how spheroids penetrated the CAM and that erosion of CAM vessels by trophoblasts led to filling of the spheroid cavities with chicken blood, mimicking initial steps of intervillous space blood perfusion. Moreover, we prove that this model is useful for state-of-the-art techniques including immunofluorescence and in situ padlock probe hybridization, making it a versatile tool to study aspects of trophoblast invasion in presence of blood flow.

DNA nanostructures for exploring cell-cell communication

The process of coordinating between the same or multiple types of cells to jointly execute various instructions in a controlled and carefully regulated environment is a very appealing field. In order to provide clearer insight into the role of cell-cell interactions and the cellular communication of this process in their local communities, several interdisciplinary approaches have been employed to enhance the core understanding of this phenomenon. DNA nanostructures have emerged in recent years as one of the most promising tools in exploring cell-cell communication and interactions due to their programmability and addressability. Herein, this review is dedicated to offering a new perspective on using DNA nanostructures to explore the progress of cell-cell communication. After briefly outlining the anchoring strategy of DNA nanostructures on cell membranes and the subsequent dynamic regulation of DNA nanostructures, this paper highlights the significant contribution of DNA nanostructures in monitoring cell-cell communication and regulating its interactions. Finally, we provide a quick overview of the current challenges and potential directions for the application of DNA nanostructures in cellular communication and interactions.

Trophoblast organoids with physiological polarity model placental structure and function

Human trophoblast organoids (TOs) are a three-dimensional ex vivo culture model that can be used to study various aspects of placental development, physiology and pathology. However, standard culturing of TOs does not recapitulate the cellular orientation of chorionic villi in vivo given that the multi-nucleated syncytiotrophoblast (STB) develops largely within the inner facing surfaces of these organoids (STBin). Here, we developed a method to culture TOs under conditions that recapitulate the cellular orientation of chorionic villi in vivo. We show that culturing STBin TOs in suspension with gentle agitation leads to the development of TOs containing the STB on the outer surface (STBout). Using membrane capacitance measurements, we determined that the outermost surface of STBout organoids contain large syncytia comprising >50 nuclei, whereas STBin organoids contain small syncytia (<10 nuclei) and mononuclear cells. The growth of TOs under conditions that mimic the cellular orientation of chorionic villi in vivo thus allows for the study of a variety of aspects of placental biology under physiological conditions.

Collagen VI Deficiency Impairs Tendon Fibroblasts Mechanoresponse in Ullrich Congenital Muscular Dystrophy

The pericellular matrix (PCM) is a specialized extracellular matrix that surrounds cells. Interactions with the PCM enable the cells to sense and respond to mechanical signals, triggering a proper adaptive response. Collagen VI is a component of muscle and tendon PCM. Mutations in collagen VI genes cause a distinctive group of inherited skeletal muscle diseases, and Ullrich congenital muscular dystrophy (UCMD) is the most severe form. In addition to muscle weakness, UCMD patients show structural and functional changes of the tendon PCM. In this study, we investigated whether PCM alterations due to collagen VI mutations affect the response of tendon fibroblasts to mechanical stimulation. By taking advantage of human tendon cultures obtained from unaffected donors and from UCMD patients, we analyzed the morphological and functional properties of cellular mechanosensors. We found that the length of the primary cilia of UCMD cells was longer than that of controls. Unlike controls, in UCMD cells, both cilia prevalence and length were not recovered after mechanical stimulation. Accordingly, under the same experimental conditions, the activation of the Hedgehog signaling pathway, which is related to cilia activity, was impaired in UCMD cells. Finally, UCMD tendon cells exposed to mechanical stimuli showed altered focal adhesions, as well as impaired activation of Akt, ERK1/2, p38MAPK, and mechanoresponsive genes downstream of YAP. By exploring the response to mechanical stimulation, for the first time, our findings uncover novel unreported mechanistic aspects of the physiopathology of UCMD-derived tendon fibroblasts and point at a role for collagen VI in the modulation of mechanotransduction in tendons.

Shear stress in the intervillous space promotes syncytial formation of iPS cells-derived trophoblasts†

The intervillous space of human placenta is filled with maternal blood, and villous trophoblasts are constantly exposed to the shear stress generated by maternal blood pressure and flow throughout the entire gestation period. However, the effects of shear stress on villous trophoblasts and their biological significance remain unknown. Here, using our recently established naïve human pluripotent stem cells-derived cytotrophoblast stem cells (nCTs) and a device that can apply arbitrary shear stress to cells, we investigated the impact of shear stress on early-stage trophoblasts. After 72 h of exposure to 10 dyn/cm2 shear stress, nCTs became fused and multinuclear, and mRNA expression of the syncytiotrophoblast (ST) markers, such as glial cell missing 1, endogenous retrovirus group W member 1 envelope, chorionic gonadotropin subunit beta 3, syndecan 1, pregnancy specific beta-1-glycoprotein 3, placental growth factor, and solute carrier family 2 member 1 were significantly upregulated compared to static conditions. Immunohistochemistry showed that shear stress increased fusion index, human chorionic gonadotropin secretion, and human placental lactogen secretion. Increased microvilli formation on the surface of nCTs under flow conditions was detected using scanning electron microscopy. Intracellular cyclic adenosine monophosphate significantly increased under flow conditions. Moreover, transcriptome analysis of nCTs subjected to shear stress revealed that shear stress upregulated ST-specific genes and downregulated CT-specific genes. Collectively, these findings indicate that shear stress promotes the differentiation of nCTs into ST.

Trophoblast stem cell-based organoid models of the human placental barrier

Human placental villi have essential roles in producing hormones, mediating nutrient and waste exchange, and protecting the fetus from exposure to xenobiotics. Human trophoblast organoids that recapitulate the structure of villi could provide an important in vitro tool to understand placental development and the transplacental passage of xenobiotics. However, such organoids do not currently exist. Here we describe the generation of trophoblast organoids using human trophoblast stem (TS) cells. Following treatment with three kinds of culture medium, TS cells form spherical organoids with a single outer layer of syncytiotrophoblast (ST) cells that display a barrier function. Furthermore, we develop a column-type ST barrier model based on the culture condition of the trophoblast organoids. The bottom membrane of the column is almost entirely covered with syndecan 1-positive ST cells. The barrier integrity and maturation levels of the model are confirmed by measuring transepithelial/transendothelial electrical resistance (TEER) and the amount of human chorionic gonadotropin. Further analysis reveals that the model can be used to derive the apparent permeability coefficients of model compounds. In addition to providing a suite of tools for the study of placental development, our trophoblast models allow the evaluation of compound transfer and toxicity, which will facilitate drug development.

Small-artery-mimicking multi-layered 3D co-culture in a self-folding porous graphene-based film

In vitro vessel-mimicking models have been spotlighted as a powerful tool for investigating cellular behaviours in vascular development and diseases. However, it is still challenging to create micro-scale tubular tissues while mimicking the structural features of small arteries. Here, we propose a 3D culture model of small vascular tissue using a self-folding graphene-based porous film. Vascular endothelial cells were encapsulated within the self-folding film to create a cellular construct with a controlled curvature radius ranging from 10 to 100 μm, which is comparable to the size of a human arteriole. Additionally, vascular endothelial cells and smooth muscle cells were separately co-cultured on the inner and outer surfaces of the folded film, respectively. The porous wall worked as a permeable barrier between them, affecting the cell-cell communications like the extracellular layer in the artery wall. Thus, the culture model recapitulates the structural features of a small artery and will help us better understand intercellular communications at the artery wall in physiological and pathological conditions.

A comprehensive review of human trophoblast fusion models: recent developments and challenges

As an essential component of the maternal-fetal interface, the placental syncytiotrophoblast layer contributes to a successful pregnancy by secreting hormones necessary for pregnancy, transporting nutrients, mediating gas exchange, balancing immune tolerance, and resisting pathogen infection. Notably, the deficiency in mononuclear trophoblast cells fusing into multinucleated syncytiotrophoblast has been linked to adverse pregnancy outcomes, such as preeclampsia, fetal growth restriction, preterm birth, and stillbirth. Despite the availability of many models for the study of trophoblast fusion, there exists a notable disparity from the ideal model, limiting the deeper exploration into the placental development. Here, we reviewed the existing models employed for the investigation of human trophoblast fusion from several aspects, including the development history, latest progress, advantages, disadvantages, scope of application, and challenges. The literature searched covers the monolayer cell lines, primary human trophoblast, placental explants, human trophoblast stem cells, human pluripotent stem cells, three-dimensional cell spheres, organoids, and placenta-on-a-chip from 1938 to 2023. These diverse models have significantly enhanced our comprehension of placental development regulation and the underlying mechanisms of placental-related disorders. Through this review, our objective is to provide readers with a thorough understanding of the existing trophoblast fusion models, making it easier to select most suitable models to address specific experimental requirements or scientific inquiries. Establishment and application of the existing human placental trophoblast fusion models.

Loss of polarity regulators initiates gasdermin-E-mediated pyroptosis in syncytiotrophoblasts

The syncytiotrophoblast is a human epithelial cell that is bathed in maternal blood on the maternal-facing surface of the human placenta. It therefore acts as a barrier and exchange interface between the mother and fetus. Syncytiotrophoblast dysfunction is a feature of pregnancy pathologies, like preeclampsia. Dysfunctional syncytiotrophoblasts display a loss of microvilli, which is a marker of aberrant apical-basal polarization, but little data exist about the regulation of syncytiotrophoblast polarity. Atypical PKC isoforms are conserved polarity regulators. Thus, we hypothesized that aPKC isoforms regulate syncytiotrophoblast polarity. Using human placental explant culture and primary trophoblasts, we found that loss of aPKC activity or expression induces syncytiotrophoblast gasdermin-E-dependent pyroptosis, a form of programmed necrosis. We also establish that TNF-α induces an isoform-specific decrease in aPKC expression and gasdermin-E-dependent pyroptosis. Therefore, aPKCs are homeostatic regulators of the syncytiotrophoblast function and a pathogenically relevant pro-inflammatory cytokine leads to the induction of programmed necrosis at the maternal-fetal interface. Hence, our results have important implications for the pathobiology of placental disorders like preeclampsia.

Novel In Vitro Models for Cell Differentiation and Drug Transport Studies of the Human Intestine

The most common in vitro model for absorption, distribution, metabolism, and excretion (ADME) purposes is currently the Caco-2 cell line. However, clear differences in gene and protein expression towards the small intestine and an, at best, fair prediction accuracy of intestinal drug absorption restrict the usefulness of a model for intestinal epithelial cells. To overcome these limitations, we evaluated a panel of low-passaged patient-derived colorectal cancer cell lines of the HROC collection concerning similarities to small intestinal epithelial cells and their potential to predict intestinal drug absorption. After initial screening of a larger panel, ten cell lines with confluent outgrowth and long-lasting barrier-forming potential were further characterized in close detail. Tight junctional complexes and microvilli structures were detected in all lines, anda higher degree of differentiation was observed in 5/10 cell lines. All lines expressed multiple transporter molecules, with the expression levels in three lines being close to those of small intestinal epithelial cells. Compared with the Caco-2 model, three HROC lines demonstrated both higher similarity to jejunal epithelial tissue cells and higher regulatory potential of relevant drug transporters. In summary, these lines would be better-suited human small intestinal epithelium models for basic and translational research, especially for ADME studies.

Fluid shear stress induces a shift from glycolytic to amino acid pathway in human trophoblasts

BACKGROUND

The human placenta, a tissue with a lifespan limited to the period of pregnancy, is exposed to varying shear rates by maternal blood perfusion depending on the stage of development. In this study, we aimed to investigate the effects of fluidic shear stress on the human trophoblast transcriptome and metabolism.

RESULTS

Based on a trophoblast cell line cultured in a fluidic flow system, changes caused by shear stress were analyzed and compared to static conditions. RNA sequencing and bioinformatics analysis revealed an altered transcriptome and enriched gene ontology terms associated with amino acid and mitochondrial metabolism. A decreased GLUT1 expression and reduced glucose uptake, together with downregulated expression of key glycolytic rate-limiting enzymes, hexokinase 2 and phosphofructokinase 1 was observed. Altered mitochondrial ATP levels and mass spectrometry data, suggested a shift in energy production from glycolysis towards mitochondrial oxidative phosphorylation. This shift in energy production could be supported by increased expression of glutamic-oxaloacetic transaminase variants in response to shear stress as well as under low glucose availability or after silencing of GLUT1. The shift towards amino acid metabolic pathways could be supported by significantly altered amino acid levels, like glutamic acid, cysteine and serine. Downregulation of GLUT1 and glycolytic rate-limiting enzymes, with concomitant upregulation of glutamic-oxaloacetic transaminase 2 was confirmed in first trimester placental explants cultured under fluidic flow. In contrast, high fluid shear stress decreased glutamic-oxaloacetic transaminase 2 expression in term placental explants when compared to low flow rates. Placental tissue from pregnancies with intrauterine growth restriction are exposed to high shear rates and showed also decreased glutamic-oxaloacetic transaminase 2, while GLUT1 was unchanged and glycolytic rate-limiting enzymes showed a trend to be upregulated. The results were generated by using qPCR, immunoblots, quantification of immunofluorescent pictures, padlock probe hybridization, mass spectrometry and FRET-based measurement.

CONCLUSION

Our study suggests that onset of uteroplacental blood flow is accompanied by a shift from a predominant glycolytic- to an alternative amino acid converting metabolism in the villous trophoblast. Rheological changes with excessive fluidic shear stress at the placental surface, may disrupt this alternative amino acid pathway in the syncytiotrophoblast and could contribute to intrauterine growth restriction.

Creating mini-pregnancy models in vitro with clinical perspectives

During the last decade, organs-on-chips or organoids microphysiological analysis platforms (MAP) have garnered attention in the practical applications of disease models, drug discovery, and developmental biology. Research on pregnant women has firm limitations due to ethical issues; thus, remodelling human pregnancy in vitro is highly beneficial for treatment modality development via disease remodelling or drug monitoring. This review highlights current efforts in bioengineering devices to reproduce human pregnancy and emphasises the significant convergence of biology, engineering, and maternal-foetal medicine. First, we review recent achievements in culturing cells from tissues involved in pregnancy; specifically, trophoblasts from the placenta. Second, we highlight developments in the reconstitution of pregnancy-related female reproductive organs across several structural and functional interpretations. Last, we examine research on the fundamental comprehension of pregnancy-associated diseases to find bioengineering solutions. Recreating human pregnancy through an engineered model is naturally complex; nevertheless, challenges are inevitable to progress precision medicine.

Development of a human iPSC-derived placental barrier-on-chip model

Although recently developed placenta-on-chip systems opened promising perspectives for placental barrier modeling, they still lack physiologically relevant trophoblasts and are poorly amenable to high-throughput studies. We aimed to implement human-induced pluripotent stem cells (hiPSC)-derived trophoblasts into a multi-well microfluidic device to develop a physiologically relevant and scalable placental barrier model. When cultured in a perfused micro-channel against a collagen-based matrix, hiPSC-derived trophoblasts self-arranged into a 3D structure showing invasive behavior, fusogenic and endocrine activities, structural integrity, and expressing placental transporters. RNA-seq analysis revealed that the microfluidic 3D environment boosted expression of genes related to early placental structural development, mainly involved in mechanosensing and cell surface receptor signaling. These results demonstrated the feasibility of generating a differentiated primitive syncytium from hiPSC in a microfluidic platform. Besides expanding hiPSC-derived trophoblast scope of applications, this study constitutes an important resource to improve placental barrier models and boost research and therapeutics evaluation in pregnancy.

Recent advances in in vitro skin-on-a-chip models for drug testing

INTRODUCTION

The skin is an organ that has the largest surface area and provides a barrier against external environment. While providing protection, it also interacts with other organs in the body and has implications in various diseases. Development of physiologically realistic in vitro models of the skin in the context of the whole body is important for studying these diseases, and will be a valuable tool for pharmaceutical, cosmetics, and food industry.

AREA COVERED

This article covers the basic background in skin structure, physiology, as well as drug metabolism in the skin, and dermatological diseases. We summarize various in vitro skin models currently available, and novel in vitro models based on organ-on-a-chip technology. We also explain the concept of multi-organ-on-a-chip and describe recent developments in this field aimed at recapitulating the interaction of the skin with other organs in the body.

EXPERT OPINION

Recent development in the organ-on-a-chip field has enabled the development of in vitro model systems that resemble human skin more closely than conventional models. In near future, we will be seeing various model systems that allow researchers to study complex diseases in a more mechanistic manner, which will help the development of new pharmaceuticals for such diseases.

Visualization of Cell Membrane Tension Regulated by the Microfilaments as a "Shock Absorber" in Micropatterned Cells

The extracellular stress signal transmits along the cell membrane-cytoskeleton-focal adhesions (FAs) complex, regulating the cell function through membrane tension. However, the mechanism of the complex regulating membrane tension is still unclear. This study designed polydimethylsiloxane stamps with specific shapes to change the actin filaments' arrangement and FAs' distribution artificially in live cells, visualized the membrane tension in real time, and introduced the concept of information entropy to describe the order degree of the actin filaments and plasma membrane tension. The results showed that the actin filaments' arrangement and FAs' distribution in the patterned cells were changed significantly. The hypertonic solution resulted in the plasma membrane tension of the pattern cell changing more evenly and slowly in the zone rich in cytoskeletal filaments than in the zone lacking filaments. In addition, the membrane tension changed less in the adhesive area than in the non-adhesive area when destroying the cytoskeletal microfilaments. This suggested that patterned cells accumulated more actin filaments in the zone where FAs were difficult to generate to maintain the stability of the overall membrane tension. The actin filaments act as shock absorbers to cushion the alternation in membrane tension without changing the final value of membrane tension.

Healthy and diseased placental barrier on-a-chip models suitable for standardized studies

Pathologies associated with uteroplacental hypoxia, such as preeclampsia are among the leading causes of maternal and perinatal morbidity in the world. Its fundamental mechanisms are yet poorly understood due to a lack of good experimental models. Here we report an in vitro model of the placental barrier, based on co-culture of trophoblasts and endothelial cells against a collagen extracellular matrix in a microfluidic platform. The model yields a functional syncytium with barrier properties, polarization, secretion of relevant extracellular membrane components, thinning of the materno-fetal space, hormone secretion, and transporter function. The model is exposed to low oxygen conditions and perfusion flow is modulated to induce a pathological environment. This results in reduced barrier function, hormone secretion, and microvilli as well as an increased nuclei count, characteristics of preeclamptic placentas. The model is implemented in a titer plate-based microfluidic platform fully amenable to high-throughput screening. We thus believe this model could aid mechanistic understanding of preeclampsia and other placental pathologies associated with hypoxia/ischemia, as well as support future development of effective therapies through target and compound screening campaigns. STATEMENT OF SIGNIFICANCE: : The human placenta is a unique organ sustaining fetus growth but is also the source of severe pathologies, such as Preeclampsia. Though leading cause of perinatal mortality in the world, preeclampsia remains untreatable due to a lack of relevant in vitro placenta models. To better understand the pathology, we have developed 3D placental barrier models in a microfluidic device. The platform allows parallel culture of 40 perfused physiological miniaturized placental barriers, comprising a differentiated syncytium and endothelium that have been validated for transporter functions. Exposure to a hypoxic and ischemic environment enabled the mimicking of preeclamptic characteristics in high-throughput, which we believe could lead to a better understanding of the pathology as well as support future effective therapies development.

Melatonin Supplementation during the Late Gestational Stage Enhances Reproductive Performance of Sows by Regulating Fluid Shear Stress and Improving Placental Antioxidant Capacity

In this study, the effects of daily melatonin supplementation (2 mg/kg) at the late gestational stage on the reproductive performance of the sows have been investigated. This treatment potentially increased the litter size and birth survival rate and significantly increased the birth weight as well as the weaning weight and survival rate of piglets compared to the controls. The mechanistic studies have found that these beneficial effects of melatonin are not mediated by the alterations of reproductive hormones of estrogen and progesterone, nor did the glucose and lipid metabolisms, but they were the results of the reduced oxidative stress in placenta associated with melatonin supplementation. Indeed, the melatonergic system, including mRNAs and proteins of AANAT, MTNR1A and MTNR1B, has been identified in the placenta of the sows. The RNA sequencing of placental tissue and KEGG analysis showed that melatonin activated the placental tissue fluid shear stress pathway to stimulate the Nrf2 signaling pathway, which upregulated its several downstream antioxidant genes, including MGST1, GSTM3 and GSTA4, therefore, suppressing the placental oxidative stress. All these actions may be mediated by the melatonin receptor of MTNR1B.

Ezrin and Its Phosphorylated Thr567 Form Are Key Regulators of Human Extravillous Trophoblast Motility and Invasion

The protein ezrin has been shown to enhance cancer cell motility and invasion leading to malignant behaviours in solid tumours, but a similar regulatory function in the early physiological reproduction state is, however, much less clear. We speculated that ezrin may play a key role in promoting first-trimester extravillous trophoblast (EVT) migration/invasion. Ezrin, as well as its Thr567 phosphorylation, were found in all trophoblasts studied, whether primary cells or lines. Interestingly, the proteins were seen in a distinct cellular localisation in long, extended protrusions in specific regions of cells. Loss-of-function experiments were carried out in EVT HTR8/SVneo and Swan71, as well as primary cells, using either ezrin siRNAs or the phosphorylation Thr567 inhibitor NSC668394, resulting in significant reductions in both cell motility and cellular invasion, albeit with differences between the cells used. Our analysis further demonstrated that an increase in focal adhesion was, in part, able to explain some of the molecular mechanisms involved. Data collected using human placental sections and protein lysates further showed that ezrin expression was significantly higher during the early stage of placentation and, importantly, clearly seen in the EVT anchoring columns, further supporting the potential role of ezrin in regulating migration and invasion in vivo.

Experimental human placental models for studying uptake, transport and toxicity of micro- and nanoplastics

Micro- and nanoplastics (MNPs) are ubiquitous in the environment and have recently been found in human lungs, blood and placenta. However, data on the possible effects of MNPs on human health is extremely scarce. The potential toxicity of MNPs during pregnancy, a period of increased susceptibility to environmental insults, is of particular concern. The placenta provides a unique interface between maternal and fetal circulation which is essential for in utero survival and healthy pregnancy. Placental toxicokinetics and toxicity of MNPs are still largely unexplored and the limited studies performed up to now focus mainly on polystyrene particles. Practical and ethical considerations limit research options in humans, and extrapolation from animal studies is challenging due to marked differences between species. Nevertheless, diverse in vitro and ex vivo human placental models exist e.g., plasma membrane vesicles, mono-culture and co-culture of placental cells, placenta-on-a-chip, villous tissue explants, and placental perfusion that can be used to advance this research area. The objective of this concise review is to recapitulate different human placental models, summarize the current understanding of placental uptake, transport and toxicity of MNPs and define knowledge gaps. Moreover, we provide perspectives for future research urgently needed to assess the potential hazards and risks of MNP exposure to maternal and fetal health.

Multi-scale Modelling of Shear Stress on the Syncytiotrophoblast: Could Maternal Blood Flow Impact Placental Function Across Gestation?

The placenta is a critical fetal exchange organ, with a complex branching tree-like structure. Its surface is covered by a single multinucleated cell, the syncytiotrophoblast, which bathes in maternal blood for most of pregnancy. Mechanosensing protein expression by the syncytiotrophoblast at term suggests that shear stress exerted by maternal blood flow may modulate placental development and function. However, it is not known how the mechanosensitive capacity of the syncytiotrophoblast, or the shear stress it experiences, change across gestation. Here, we show that the syncytiotrophoblast expresses both mechanosensitive ion channels (Piezo 1, Polycystin 2, TRPV6) and motor proteins associated with primary cilia (Dynein 1, IFT88, Kinesin 2), with higher staining for all these proteins seen in late first trimester placentae than at term. MicroCT imaging of placental tissue was then used to inform computational models of blood flow at the placentone scale (using a porous media model), and at the villous scale (using explicit flow simulations). These two models are then linked to produce a combined model that allows the variation of shear stress across both these scales simultaneously. This combined model predicts that the range of shear stress on the syncytiotrophoblast is higher in the first-trimester than at term (0.8 dyne/cm² median stress compared to 0.04 dyne/cm²) when considering both these scales. Together, this suggests that the nature of blood flow through the intervillous space, and the resulting shear stress on the syncytiotrophoblast have important influences on placental morphogenesis and function from early in pregnancy.

Building the brush border, one microvillus at a time

Microvilli are actin bundle-supported surface protrusions assembled by diverse cell types to mediate biochemical and physical interactions with the external environment. Found on the surface of some of the earliest animal cells, primordial microvilli likely contributed to bacterial entrapment and feeding. Although millions of years of evolution have repurposed these protrusions to fulfill diverse roles such as detection of mechanical or visual stimuli in inner ear hair cells or retinal pigmented epithelial cells, respectively, solute uptake remains a key essential function linked to these structures. In this mini review, we offer a brief overview of the composition and structure of epithelial microvilli, highlight recent discoveries on the growth of these protrusions early in differentiation, and point to fundamental questions surrounding microvilli biogenesis that remain open for future studies.

Chloroquine is a safe autophagy inhibitor for sustaining the expression of antioxidant enzymes in trophoblasts

Inhibition of autophagy contributes to the pathophysiology of preeclampsia. Although chloroquine (CHQ) is an autophagy inhibitor, it can reduce the occurrence of preeclampsia in women with systemic lupus erythematosus. To clarify this important clinical question, this study aimed to address the safety of CHQ in trophoblast cells from the viewpoint of homeostasis, in which the anti-oxidative stress (OS) response and autophagy are involved. We used Western blotting to evaluate the protein levels in the trophoblast cells. The expression levels of heme oxygenase-1 (HO-1), an anti-OS enzyme, mediate resistance to OS induced by hydrogen peroxide (H₂O₂) in trophoblast cell lines. Among the autophagy modulators, bafilomycin A1 (BAF), an autophagy inhibitor, but not autophagy activators, suppressed HO-1 expression in BeWo cells; CHQ did not suppress HO-1 expression in BeWo cells. To clarify the role of autophagy in HO-1 induction, we observed no difference in HO-1 induction by H₂O₂ between autophagy-normal and autophagy-deficient cells. As for the mechanism of HO-1 induction by OS, BAF suppressed HO-1 induction by downregulating the expression of neighbor of BRCA1 gene 1 (NBR1) in the selective p62-NBR1-nuclear factor erythroid 2-related factor 2 (Nrf2) autophagy pathway. CHQ did not inhibit HO-1 expression by sustaining NBR1 expression in human villous tissues compared to BAF treatment. In conclusion, CHQ is a safer medicine than BAF for sustaining NBR1, which resist against OS in trophoblasts by connecting selective autophagy and the anti-OS response.

Critical design parameters to develop biomimetic organ-on-a-chip models for the evaluation of the safety and efficacy of nanoparticles

INTRODUCTION

Organ-on-a-chip (OOC) models are based on microfluidics and can recapitulate the healthy and diseased microstructure of organs¹ and tissues and the dynamic microenvironment inside the human body. However, the use of OOC models to evaluate the safety and efficacy of nanoparticles (NPs) is still in the early stages.

AREAS COVERED

The different design parameters of the microfluidic chip and the mechanical forces generated by fluid flow play a pivotal role in simulating the human environment. This review discusses the role of different key parameters on the performance of OOC models. These include the flow pattern, flow rate, shear stress (magnitude, rate, and distribution), viscosity of the media, and the microchannel dimensions and shape. We also discuss how the shear stress and other mechanical forces affect the transport of NPs across biological barriers, cell uptake, and their biocompatibility.

EXPERT OPINION

We describe several good practices and design parameters to consider for future OOC research. We submit that following these recommendations will help realize the full potential of the OOC models in the preclinical evaluation of novel therapies, including NPs.

3D microfluidics-assisted modeling of glucose transport in placental malaria

The human placenta is a critical organ, mediating the exchange of nutrients, oxygen, and waste products between fetus and mother. Placental malaria (PM) resulted from Plasmodium falciparum infections causes up to 200 thousand newborn deaths annually, mainly due to low birth weight, as well as 10 thousand mother deaths. In this work, a placenta-on-a-chip model is developed to mimic the nutrient exchange between the fetus and mother under the influence of PM. In this model, trophoblasts cells (facing infected or uninfected blood simulating maternal blood and termed “trophoblast side”) and human umbilical vein endothelial cells (facing uninfected blood simulating fetal blood and termed “endothelial” side) are cultured on the opposite sides of an extracellular matrix gel in a compartmental microfluidic system, forming a physiological barrier between the co-flow tubular structure to mimic a simplified maternal–fetal interface in placental villi. The influences of infected erythrocytes (IEs) sequestration through cytoadhesion to chondroitin sulfate A (CSA) expressed on the surface of trophoblast cells, a critical feature of PM, on glucose transfer efficiency across the placental barrier was studied. To create glucose gradients across the barrier, uninfected erythrocyte or IE suspension with a higher glucose concentration was introduced into the “trophoblast side” and a culture medium with lower glucose concentration was introduced into the “endothelial side”. The glucose levels in the endothelial channel in response to CSA-adherent erythrocytes infected with CS2 line of parasites in trophoblast channel under flow conditions was monitored. Uninfected erythrocytes served as a negative control. The results demonstrated that CSA-binding IEs added resistance to the simulated placental barrier for glucose perfusion and decreased the glucose transfer across this barrier. The results of this study can be used for better understanding of PM pathology and development of models useful in studying potential treatment of PM.

Placental Nanoparticle Uptake-On-a-Chip: The Impact of Trophoblast Syncytialization and Shear Stress

The placenta is a dynamic and complex organ that plays an essential role in the health and development of the fetus. Placental disorders can affect the health of both the mother and the fetus. There is currently an unmet clinical need to develop nanoparticle-based therapies to target and treat placental disorders. However, little is known about the interaction of nanoparticles (NPs) with the human placenta under biomimetic conditions. Specifically, the impact of shear stress exerted on the trophoblasts (placental epithelial cells) by the maternal blood flow, the gradual fusion of the trophoblasts along the gestation period (syncytialization), and the impact of microvilli formation on the cell uptake of NPs is not known. To this end, we designed dynamic placenta-on-a-chip models using BeWo cells to recapitulate the micro-physiological environment, and we induced different degrees of syncytialization via chemical induction with forskolin. We characterized the degree of syncytialization quantitatively by measuring beta human chorionic gonadotropin (β-hCG) secretion, as well as qualitatively by immunostaining the tight junction protein, ZO-1, and counter nuclear staining. We also characterized microvilli formation under static and dynamic conditions via F-actin staining. We used these models to measure the cell uptake of chondroitin sulfate a binding protein (CSA) conjugated and control liposomes using confocal microscopy, followed by image analysis. Interestingly, exposure of the cells to a dynamic flow of media intrinsically induced syncytialization and microvilli formation compared to static controls. Under dynamic conditions, BeWo cells produced more β-hCG in conditions that increased the cell exposure time to forskolin (p < 0.005). Our cell uptake results clearly show a combined effect of the exerted shear stress and forskolin treatment on the cell uptake of liposomes as uptake increased in forskolin exposed conditions (p < 0.05). Overall, the difference in the extent of cell uptake of liposomes among the different conditions clearly displays a need for the development of dynamic models of the placenta that consider the changes in the placental cell phenotype along the gestation period, including syncytialization, microvilli formation, and the expression of different transport and uptake receptors. Knowledge generated from this work will inform future research aiming at developing drug delivery systems targeting the placenta.

In Situ Visualization of Dynamic Cellular Effects of Phospholipid Nanoparticles via High-Speed Scanning Ion Conductance Microscopy

Phospholipid nanoparticles have been actively employed for numerous biomedical applications. A key factor in ensuring effective and safe applications of these nanomaterials is the regulation of their interactions with target cells, which is significantly dependent on an in-depth understanding of the nanoparticle-cell interactions. To date, most studies investigating these nano-bio interactions have been performed under static conditions and may lack crucial real-time information. It is, however, noteworthy that the nanoparticle-cell interactions are highly dynamic. Consequently, to gain a deeper insight into the cellular effects of phospholipid nanoparticles, real-time observation of cellular dynamics after nanoparticle introduction is necessary. Herein, a proof-of-concept in situ visualization of the dynamic cellular effects of sub-100 nm phospholipid nanoparticles using high-speed scanning ion conductance microscopy (HS-SICM) is reported. It is revealed that upon introduction into the cellular environment, within a short timescale of hundreds of seconds, phospholipid nanoparticles can selectively modulate the edge motility and surface roughness of healthy fibroblast and cancerous epithelial cells. Furthermore, the dynamic deformation profiles of these cells can be selectively altered in the presence of phospholipid nanoparticles. This work is anticipated to further shed light on the real-time nanoparticle-cell interactions for improved formulation of phospholipid nanoparticles for numerous bioapplications.

Physical organogenesis of the gut

The gut has been a central subject of organogenesis since Caspar Friedrich Wolff’s seminal 1769 work ‘De Formatione Intestinorum’. Today, we are moving from a purely genetic understanding of cell specification to a model in which genetics codes for layers of physical–mechanical and electrical properties that drive organogenesis such that organ function and morphogenesis are deeply intertwined. This Review provides an up-to-date survey of the extrinsic and intrinsic mechanical forces acting on the embryonic vertebrate gut during development and of their role in all aspects of intestinal morphogenesis: enteric nervous system formation, epithelium structuring, muscle orientation and differentiation, anisotropic growth and the development of myogenic and neurogenic motility. I outline numerous implications of this biomechanical perspective in the etiology and treatment of pathologies, such as short bowel syndrome, dysmotility, interstitial cells of Cajal-related disorders and Hirschsprung disease.

Organ-on-a-chip for perinatal biology experiments

Cell culture and organ explant systems have traditionally been used by scientists in the reproductive biology and perinatal medicine area to address various research questions. Although most are unrelated to human pregnancy, animal models were also extensively used to study various mechanisms associated with pregnancy and parturition. However, limitations of traditional approaches have shifted the attention to the use of organ on a chip (OOC) technology. OOC platform simulates an organ using cells, and OOCs are biomimetic microfluidic systems comprising multiple cell types from an organ that mimic the environment of a physiological organ. OOC maintains intercellular interactions and helps to recreate organ physiology as expected for utero in perinatal medicine research. This short review introduces some basic concepts of OOC, and its utility based on some published reports.

Fluidic Flow Enhances the Differentiation of Placental Trophoblast-Like 3D Tissue from hiPSCs in a Perfused Macrofluidic Device

The human placenta serves as a multifunctional organ to maintain the proper development of a fetus. However, our knowledge of the human placenta is limited due to the lack of appropriate experimental models. In this work, we created an in vitro placental trophoblast-like model via self-organization of human induced pluripotent stem cells (hiPSCs) in a perfused 3D culture macrofluidic device. This device allowed cell seeding, in situ trophoblast lineage differentiation, and formation of trophoblast-like tissues from hiPSCs in a biomimetic microenvironment. It incorporated extracellular matrix (ECM) and fluid flow in a single device. After trophoblast lineage differentiation, we were able to generate the 3D clusters with major cell types of the human placenta, including trophoblast progenitor cytotrophoblasts (CTBs), differentiated subtypes, syncytiotrophoblasts (STBs), and extravillous trophoblasts (EVTs) under long-term 3D culture (∼23 days). Moreover, the formed tissues exhibited enhanced expressions of CTB-, STB-, and EVT-related markers at the level of genes and proteins under a dynamic culture compared with static conditions. RNA-seq analysis revealed the higher expression of trophoblast-specific genes in 3D tissues, indicating the essential role of fluid flow to promote the trophoblast differentiation of hiPSCs. The established placental 3D model combined a bioengineering strategy with developmental principles, providing a promising platform for the study of placental biology in a biomimetic microenvironment in health and disease.

Modelling human placental villous development: designing cultures that reflect anatomy

The use of in vitro tools to study trophoblast differentiation and function is essential to improve understanding of normal and abnormal placental development. The relative accessibility of human placentae enables the use of primary trophoblasts and placental explants in a range of in vitro systems. Recent advances in stem cell models, three-dimensional organoid cultures, and organ-on-a-chip systems have further shed light on the complex microenvironment and cell-cell crosstalk involved in placental development. However, understanding each model's strengths and limitations, and which in vivo aspects of human placentation in vitro data acquired does, or does not, accurately reflect, is key to interpret findings appropriately. To help researchers use and design anatomically accurate culture models, this review both outlines our current understanding of placental development, and critically considers the range of established and emerging culture models used to study this, with a focus on those derived from primary tissue.

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.

Calcium selective channel TRPV6: Structure, function, and implications in health and disease

Calcium-selective channel TRPV6 (Transient Receptor Potential channel family, Vanilloid subfamily member 6) belongs to the TRP family of cation channels and plays critical roles in transcellular calcium (Ca2+) transport, reuptake of Ca2+ into cells, and maintaining a local low Ca2+ environment for certain biological processes. Recent crystal and cryo-electron microscopy-based structures of TRPV6 have revealed mechanistic insights on how the protein achieves Ca2+ selectivity, permeation, and inactivation by calmodulin. The TRPV6 protein is expressed in a range of epithelial tissues such as the intestine, kidney, placenta, epididymis, and exocrine glands such as the pancreas, prostate and salivary, sweat, and mammary glands. The TRPV6 gene is a direct transcriptional target of the active form of vitamin D and is efficiently regulated to meet the body's need for Ca2+ demand. In addition, TRPV6 is also regulated by the level of dietary Ca2+ and under physiological conditions such as pregnancy and lactation. Genetic models of loss of function in TRPV6 display hypercalciuria, decreased bone marrow density, deficient weight gain, reduced fertility, and in some cases alopecia. The models also reveal that the channel plays an indispensable role in maintaining maternal-fetal Ca2+ transport and low Ca2+ environment in the epididymal lumen that is critical for male fertility. Most recently, loss of function mutations in TRPV6 gene is linked to transient neonatal hyperparathyroidism and early onset chronic pancreatitis. TRPV6 is overexpressed in a wide range of human malignancies and its upregulation is strongly correlated to tumor aggressiveness, metastasis, and poor survival in selected cancers. This review summarizes the current state of knowledge on the expression, structure, biophysical properties, function, polymorphisms, and regulation of TRPV6. The aberrant expression, polymorphisms, and dysfunction of this protein linked to human diseases are also discussed.