The biomechanical basis of biased epithelial tube elongation in lung and kidney development

Biomechanical Modelling of Porcine Kidney

In this study, the viscoelastic properties of porcine kidney in the upper, middle and lower poles were investigated using oscillatory shear tests. The viscoelastic properties were extracted in the form of the storage modulus and loss modulus in the frequency and time domain. Measurements were taken as a function of frequency from 0.1 Hz to 6.5 Hz at a shear strain amplitude of 0.01 and as function of strain amplitude from 0.001 to 0.1 at a frequency of 1 Hz. Measurements were also taken in the time domain in response to a step shear strain. Both the frequency and time domain data were fitted to a conventional Standard Linear Solid (SLS) model and a semi-fractional Kelvin-Voigt (SFKV) model with a comparable number of parameters. The SFKV model fitted the frequency and time domain data with a correlation coefficient of 0.99. Although the SLS model well fitted the time domain data and the storage modulus data in the frequency domain, it was not able to capture the variation in loss modulus with frequency with a correlation coefficient of 0.53. A five parameter Maxwell-Wiechert model was able to capture the frequency dependence in storage modulus and loss modulus better than the SLS model with a correlation of 0.85.

SimuCell3D: three-dimensional simulation of tissue mechanics with cell polarization

The three-dimensional (3D) organization of cells determines tissue function and integrity, and changes markedly in development and disease. Cell-based simulations have long been used to define the underlying mechanical principles. However, high computational costs have so far limited simulations to either simplified cell geometries or small tissue patches. Here, we present SimuCell3D, an efficient open-source program to simulate large tissues in three dimensions with subcellular resolution, growth, proliferation, extracellular matrix, fluid cavities, nuclei and non-uniform mechanical properties, as found in polarized epithelia. Spheroids, vesicles, sheets, tubes and other tissue geometries can readily be imported from microscopy images and simulated to infer biomechanical parameters. Doing so, we show that 3D cell shapes in layered and pseudostratified epithelia are largely governed by a competition between surface tension and intercellular adhesion. SimuCell3D enables the large-scale in silico study of 3D tissue organization in development and disease at a great level of detail.

Breaking the symmetry of cell contractility drives tubulogenesis via CXCL1 polarization

The intricate interplay between biomechanical and biochemical pathways in modulating morphogenesis is an interesting research topic. How biomechanical force regulates epithelial cell tubulogenesis remains poorly understood. Here, we established a model of tubulogenesis by culturing renal proximal tubular epithelial cells on a collagen gel while manipulating contractile force. Epithelial cells were dynamically self-organized into tubule-like structures by augmentation of cell protrusions and cell-cell association. Reduction and asymmetric distribution of phosphorylated myosin light chain 2, the actomyosin contractility, in cells grown on soft matrix preceded tube connection. Notably, reducing matrix stiffness via sonication of collagen fibrils and inhibiting actomyosin contractility with blebbistatin promoted tubulogenesis, whereas inhibition of cytoskeleton polymerization suppressed it. CXC chemokine ligand 1 (CXCL1) expression was transcriptionally upregulated in cells undergoing tubulogenesis. Additionally, inhibiting actomyosin contractility facilitated CXCL1 polarization and cell protrusions preceding tube formation. Conversely, inhibiting the CXCL1-CXC receptor 1 pathway hindered cell protrusions and tubulogenesis. Mechanical property asymmetry with cell-collagen fibril interaction patterns at cell protrusions and along the tube structure supported the association of anisotropic contraction with tube formation. Furthermore, suppressing the mechanosensing machinery of integrin subunit beta 1 reduced CXCL1 expression, collagen remodeling, and impaired tubulogenesis. In summary, symmetry breaking of cell contractility on a soft collagen gel promotes CXCL1 polarization at cell protrusions which in turn facilitates cell-cell association and thus tubule connection.

Mechanoresponse of Curved Epithelial Monolayers Lining Bowl-Shaped 3D Microwells

The optimal functioning of many organs relies on the curved architecture of their epithelial tissues. However, the mechanoresponse of epithelia to changes in curvature remains misunderstood. Here, bowl-shaped microwells in hydrogels are designed via photopolymerization to faithfully replicate the shape and dimensions of lobular structures. Leveraging these hydrogel-based microwells, curved epithelial monolayers are engineered, and how in-plane and Gaussian curvatures at the microwell entrance influence epithelial behavior is investigated. Cells and nuclei around the microwell edge display a more pronounced centripetal orientation as the in-plane curvature decreases, and enhanced cell straightness and speed. Moreover, cells reorganize their actin cytoskeleton by forming a supracellular actin cable at the microwell edge, with its size becoming more pronounced as the in-plane curvature decreases. The Gaussian curvature at the microwell entrance enhances the maturation of the supracellular actin cable architecture and leads to a vertical orientation of nuclei toward the bottom of the microwell. Increasing Gaussian curvature results in flattened and elongated nuclear morphologies characterized by highly compacted chromatin states. This approach provides better understanding of the mechanoresponse of curved epithelial monolayers curvatures lining lobular structures. In addition, bowl-shaped microwells offer a powerful platform to study curvature-dependent mechanotransduction pathways in anatomically relevant 3D structures.

Geometric effects position renal vesicles during kidney development

During kidney development, reciprocal signaling between the epithelium and the mesenchyme coordinates nephrogenesis with branching morphogenesis of the collecting ducts. The mechanism that positions the renal vesicles, and thus the nephrons, relative to the branching ureteric buds has remained elusive. By combining computational modeling and experiments, we show that geometric effects concentrate the key regulator, WNT9b, at the junctions between parent and daughter branches where renal vesicles emerge, even when uniformly expressed in the ureteric epithelium. This curvature effect might be a general paradigm to create non-uniform signaling in development.

A novel perfusion bioreactor promotes the expansion of pluripotent stem cells in a 3D-bioprinted tissue chamber

While the field of tissue engineering has progressed rapidly with the advent of 3D bioprinting and human induced pluripotent stem cells (hiPSCs), impact is limited by a lack of functional, thick tissues. One way around this limitation is to 3D bioprint tissues laden with hiPSCs. In this way, the iPSCs can proliferate to populate the thick tissue mass prior to parenchymal cell specification. Here we design a perfusion bioreactor for an hiPSC-laden, 3D-bioprinted chamber with the goal of proliferating the hiPSCs throughout the structure prior to differentiation to generate a thick tissue model. The bioreactor, fabricated with digital light projection, was optimized to perfuse the interior of the hydrogel chamber without leaks and to provide fluid flow around the exterior as well, maximizing nutrient delivery throughout the chamber wall. After 7 days of culture, we found that intermittent perfusion (15 s every 15 min) at 3 ml min-1provides a 1.9-fold increase in the density of stem cell colonies in the engineered tissue relative to analogous chambers cultured under static conditions. We also observed a more uniform distribution of colonies within the tissue wall of perfused structures relative to static controls, reflecting a homogeneous distribution of nutrients from the culture media. hiPSCs remained pluripotent and proliferative with application of fluid flow, which generated wall shear stresses averaging ∼1.0 dyn cm-2. Overall, these promising outcomes following perfusion of a stem cell-laden hydrogel support the production of multiple tissue types with improved thickness, and therefore increased function and utility.

The upper airway parameters: the potential diagnostic clues for congenital intrathoracic lesions

BACKGROUND

The diagnosis of congenital intrathoracic lesions still has limitations. The airway development was influenced by intrathoracic factors. Whether the diagnostic value of the upper airway parameters in congenital intrathoracic lesions has not been confirmed.

OBJECTIVES

We aimed to compare fetal upper airway parameters between normal fetuses and fetuses with intrathoracic lesions, and we tried to verify its diagnostic value in intrathoracic lesions.

METHODS

This was an observational case-control study. In the control group, 77 women were screened at 20-24 weeks' gestational age, 23 were screened at 24-28 weeks' gestational age, and 27 were screened at 28-34 weeks' gestational age. In the case group, 41 cases were enrolled (6 cases of intrathoracic bronchopulmonary sequestration, 22 of congenital pulmonary airway malformations, and 13 of congenital diaphragmatic hernia). Fetal upper airway parameters (tracheal width, the narrowest lumen width, and width of the subglottic cavity and laryngeal vestibule) were measured using ultrasound equipment. The correlations between fetal upper airway parameters and gestational age, and the differences in fetal upper airway parameters between cases and controls, were analyzed. The standardized airway paraments were acquired, and their potential diagnostic value for congenital intrathoracic lesions were analyzed.

RESULTS

The fetal upper airway parameters of both groups were positively correlated with the gestational age: The control group, tracheal width (R² = 0.569, p < 0.001), narrowest lumen width (R² = 0.429, p < 0.001), subglottic cavity width (R² = 0.551, p < 0.001), laryngeal vestibule width (R² = 0.349, p < 0.001). The case group (tracheal width R² = 0.474, p < 0.001) narrowest lumen width (R² = 0.425, p < 0.001), subglottic cavity width (R² = 0.623, p < 0.001), laryngeal vestibule width (R² = 0.347, p < 0.001). Fetal upper airway parameters of the cases group were smaller than those of the controls group. The tracheal width in fetuses with congenital diaphragmatic hernia was the smallest among the other case groups studied. The standardized tracheal width has the best diagnostic value for congenital intrathoracic lesions in the standardized airway paraments (the area under the ROC curve was 0.894), and has a high diagnostic value for congenital pulmonary airway malformations and congenital diaphragmatic hernia (the area under the ROC curve was 0.911 and 0.992, respectively).

CONCLUSION

Fetal upper airway parameters differ between normal fetuses and fetuses with intrathoracic lesions, and might offer potential diagnostic clues for congenital intrathoracic lesions.

Kidney Development: Recent Insights from Technological Advances

The kidney is a complex organ, and how it forms is a fascinating process. New technologies, such as single-cell transcriptomics, and enhanced imaging modalities are offering new approaches to understand the complex and intertwined processes during embryonic kidney development.

[Take-home messages from the COPD 2021 biennial of the French Society of Respiratory Diseases. Understanding to so as to better innovate]

INTRODUCTION

The first COPD biennial organized by the French Society of Respiratory Diseases (SPLF) took place on 17 December 2021.

STATE OF THE ART

The objective of the biennial was to discuss current knowledge regarding COPD pathophysiology, current treatments, research development, and future therapeutic approaches.

PERSPECTIVES

The different lecturers laid emphasis on the complexity of pathophysiologic mechanisms including bronchial, bronchiolar and parenchymal alterations, and also dwelt on the role of microbiota composition in COPD pathenogenesis. They pointed out that addition to inhaled treatments, ventilatory support and endoscopic approaches have been increasingly optimized. The development of new therapeutic pathways such as biotherapy and cell therapy (stem cells…) call for further exploration.

CONCLUSIONS

The dynamism of COPD research was repeatedly underlined, and needs to be further reinforced, the objective being to "understand so as to better innovate" so as to develop effective new strategies for treatment and management of COPD.

Engineering multiscale structural orders for high-fidelity embryoids and organoids

Embryoids and organoids hold great promise for human biology and medicine. Herein, we discuss conceptual and technological frameworks useful for developing high-fidelity embryoids and organoids that display tissue- and organ-level phenotypes and functions, which are critically needed for decoding developmental programs and improving translational applications. Through dissecting the layers of inputs controlling mammalian embryogenesis, we review recent progress in reconstructing multiscale structural orders in embryoids and organoids. Bioengineering tools useful for multiscale, multimodal structural engineering of tissue- and organ-level cellular organization and microenvironment are also discussed to present integrative, bioengineering-directed approaches to achieve next-generation, high-fidelity embryoids and organoids.

Organoid models: assessing lung cell fate decisions and disease responses

Organoids can be derived from various cell types in the lung, and they provide a reproducible and tractable model for understanding the complex signals driving cell fate decisions in a regenerative context. In this review, we provide a retrospective account of organoid methodologies and outline new opportunities for optimizing these methods to further explore emerging concepts in lung biology. Moreover, we examine the benefits of integrating organoid assays with in vivo modeling to explore how the various niches and compartments in the respiratory system respond to both acute and chronic lung disease. The strategic implementation and improvement of organoid techniques will provide exciting new opportunities to understand and identify new therapeutic approaches to ameliorate lung disease states.

3D cell neighbour dynamics in growing pseudostratified epithelia

During morphogenesis, epithelial sheets remodel into complex geometries. How cells dynamically organise their contact with neighbouring cells in these tightly packed tissues is poorly understood. We have used light-sheet microscopy of growing mouse embryonic lung explants, three-dimensional cell segmentation, and physical theory to unravel the principles behind 3D cell organisation in growing pseudostratified epithelia. We find that cells have highly irregular 3D shapes and exhibit numerous neighbour intercalations along the apical-basal axis as well as over time. Despite the fluidic nature, the cell packing configurations follow fundamental relationships previously described for apical epithelial layers, that is, Euler's polyhedron formula, Lewis' law, and Aboav-Weaire's law, at all times and across the entire tissue thickness. This arrangement minimises the lateral cell-cell surface energy for a given cross-sectional area variability, generated primarily by the distribution and movement of nuclei. We conclude that the complex 3D cell organisation in growing epithelia emerges from simple physical principles.

Organ-Specific Branching Morphogenesis

A common developmental process, called branching morphogenesis, generates the epithelial trees in a variety of organs, including the lungs, kidneys, and glands. How branching morphogenesis can create epithelial architectures of very different shapes and functions remains elusive. In this review, we compare branching morphogenesis and its regulation in lungs and kidneys and discuss the role of signaling pathways, the mesenchyme, the extracellular matrix, and the cytoskeleton as potential organ-specific determinants of branch position, orientation, and shape. Identifying the determinants of branch and organ shape and their adaptation in different organs may reveal how a highly conserved developmental process can be adapted to different structural and functional frameworks and should provide important insights into epithelial morphogenesis and developmental disorders.

The people behind the papers – Lisa Conrad, Steve Runser, Roman Vetter and Dagmar Iber

Epithelial tubes perform crucial functions in various organs, providing routes for the transport of fluids and gases. A new paper in Development addresses the question of how epithelial tubes elongate during development, using a combination of mouse organ culture and mathematical modelling. To find out more about the work, we met four of its authors: PhD students Lisa Conrad and Steven Runser, senior scientist Roman Vetter, and their supervisor Dagmar Iber, Professor in the Department of Biosystems Science and Engineering at ETH Zurich.