3D cell culture model: From ground experiment to microgravity study

Microgravity has been shown to induce many changes in cell growth and differentiation due to offloading the gravitational strain normally exerted on cells. Although many studies have used two-dimensional (2D) cell culture systems to investigate the effects of microgravity on cell growth, three-dimensional (3D) culture scaffolds can offer more direct indications of the modified cell response to microgravity-related dysregulations compared to 2D culture methods. Thus, knowledge of 3D cell culture is essential for better understanding the in vivo tissue function and physiological response under microgravity conditions. This review discusses the advances in 2D and 3D cell culture studies, particularly emphasizing the role of hydrogels, which can provide cells with a mimic in vivo environment to collect a more natural response. We also summarized recent studies about cell growth and differentiation under real microgravity or simulated microgravity conditions using ground-based equipment. Finally, we anticipate that hydrogel-based 3D culture models will play an essential role in constructing organoids, discovering the causes of microgravity-dependent molecular and cellular changes, improving space tissue regeneration, and developing innovative therapeutic strategies. Future research into the 3D culture in microgravity conditions could lead to valuable therapeutic applications in health and pharmaceuticals.

Enhanced vascularization andde novotissue formation in hydrogels made of engineered RGD-tagged spider silk proteins in the arteriovenous loop model

Due to its low immunogenic potential and the possibility to fine-tune their properties, materials made of recombinant engineered spider silks are promising candidates for tissue engineering applications. However, vascularization of silk-based scaffolds is one critical step for the generation of bioartificial tissues and consequently for clinical application. To circumvent insufficient vascularization, the surgically induced angiogenesis by means of arteriovenous loops (AVL) represents a highly effective methodology. Here, previously established hydrogels consisting of nano-fibrillary recombinant eADF4(C16) were transferred into Teflon isolation chambers and vascularized in the rat AVL model over 4 weeks. To improve vascularization, also RGD-tagged eADF4(C16) hydrogels were implanted in the AVL model over 2 and 4 weeks. Thereafter, the specimen were explanted and analyzed using histology and microcomputed tomography. We were able to confirm biocompatibility and tissue formation over time. Functionalizing eADF4(C16) with RGD-motifs improved hydrogel stability and enhanced vascularization even outperforming other hydrogels, such as fibrin. This study demonstrates that the scaffold ultrastructure as well as biofunctionalization with RGD-motifs are powerful tools to optimize silk-based biomaterials for tissue engineering applications.

Similarities and Differences in the GFP Movement in the Zygotic and Somatic Embryos of Arabidopsis

Intercellular signaling during embryo patterning is not well understood and the role of symplasmic communication has been poorly considered. The correlation between the symplasmic domains and the development of the embryo organs/tissues during zygotic embryogenesis has only been described for a few examples, including Arabidopsis. How this process occurs during the development of somatic embryos (SEs) is still unknown. The aim of these studies was to answer the question: do SEs have a restriction in symplasmic transport depending on the developmental stage that is similar to their zygotic counterparts? The studies included an analysis of the GFP distribution pattern as expressed under diverse promoters in zygotic embryos (ZEs) and SEs. The results of the GFP distribution in the ZEs and SEs showed that 1/the symplasmic domains between the embryo organs and tissues in the SEs was similar to those in the ZEs and 2/the restriction in symplasmic transport in the SEs was correlated with the developmental stage and was similar to the one in their zygotic counterparts, however, with the spatio-temporal differences and different PDs SEL value between these two types of embryos.

Specialized cytonemes induce self-organization of stem cells

Spatial cellular organization is fundamental for embryogenesis. Remarkably, coculturing embryonic stem cells (ESCs) and trophoblast stem cells (TSCs) recapitulates this process, forming embryo-like structures. However, mechanisms driving ESC-TSC interaction remain elusive. We describe specialized ESC-generated cytonemes that react to TSC-secreted Wnts. Cytoneme formation and length are controlled by actin, intracellular calcium stores, and components of the Wnt pathway. ESC cytonemes select self-renewal-promoting Wnts via crosstalk between Wnt receptors, activation of ionotropic glutamate receptors (iGluRs), and localized calcium transients. This crosstalk orchestrates Wnt signaling, ESC polarization, ESC-TSC pairing, and consequently synthetic embryogenesis. Our results uncover ESC-TSC contact-mediated signaling, reminiscent of the glutamatergic neuronal synapse, inducing spatial self-organization and embryonic cell specification.

Multiphoton microscopy analysis of extracellular collagen I network formation by mesenchymal stem cells

Collagen I is the major fibrous extracellular component of bone responsible for its ultimate tensile strength. In tissue engineering, one of the most important challenges for tissue formation is to get cells interconnected via a strong and functional extracellular matrix (ECM), mimicking as closely as possible the natural ECM geometry. Still missing in tissue engineering are: (a) a versatile, high-resolution and non-invasive approach to evaluate and quantify different aspects of ECM development within engineered biomimetic scaffolds online; and (b) deeper insights into the mechanism whereby cellular matrix production is enhanced in 3D cell-scaffold composites, putatively via enhanced focal adhesion linkage, over the 2D setting. In this study, we developed sensitive morphometric detection methods for collagen I-producing and bone-forming mesenchymal stem cells (MSCs), based on multiphoton second harmonic generation (SHG) microscopy, and used those techniques to compare collagen I production capabilities in 2D- and 3D-arranged cells. We found that stimulating cells with 1% serum in the presence of ascorbic acid is superior to other medium conditions tested, including classical osteogenic medium. In contrast to conventional 2D culture, having MSCs packed closely in a 3D environment presumably stimulates cells to produce strong and complex collagen I networks with defined network structures (visible in SHG images) and improves collagen production. Copyright © 2015 John Wiley & Sons, Ltd.

The GEX-2 and GEX-3 proteins are required for tissue morphogenesis and cell migrations in C. elegans

During body morphogenesis precisely coordinated cell movements and cell shape changes organize the newly differentiated cells of an embryo into functional tissues. Here we describe two genes, gex-2 and gex-3, whose activities are necessary for initial steps of body morphogenesis in Caenorhabditis elegans. In the absence of gex-2 and gex-3 activities, cells differentiate properly but fail to become organized. The external hypodermal cells fail to spread over and enclose the embryo and instead cluster on the dorsal side. Postembryonically gex-3 activity is required for egg laying and for proper morphogenesis of the gonad. GEX-2 and GEX-3 proteins colocalize to cell boundaries and appear to directly interact. GEX-2 and GEX-3 are highly conserved, with vertebrate homologs implicated in binding the small GTPase Rac and a GEX-3 Drosophila homolog, HEM2/NAP1/KETTE, that interacts genetically with Rac pathway mutants. Our findings suggest that GEX-2 and GEX-3 may function at cell boundaries to regulate cell migrations and cell shape changes required for proper morphogenesis and development.