Simulated microgravity conditions enhance differentiation of cultured PC12 cells towards the neuroendocrine phenotype

Biomanufacturing of 3D Tissue Constructs in Microgravity and their Applications in Human Pathophysiological Studies

The growing interest in bioengineering in-vivo-like 3D functional tissues has led to novel approaches to the biomanufacturing process as well as expanded applications for these unique tissue constructs. Microgravity, as seen in spaceflight, is a unique environment that may be beneficial to the tissue-engineering process but cannot be completely replicated on Earth. Additionally, the expense and practical challenges of conducting human and animal research in space make bioengineered microphysiological systems an attractive research model. In this review, published research that exploits real and simulated microgravity to improve the biomanufacturing of a wide range of tissue types as well as those studies that use microphysiological systems, such as organ/tissue chips and multicellular organoids, for modeling human diseases in space are summarized. This review discusses real and simulated microgravity platforms and applications in tissue-engineered microphysiological systems across three topics: 1) application of microgravity to improve the biomanufacturing of tissue constructs, 2) use of tissue constructs fabricated in microgravity as models for human diseases on Earth, and 3) investigating the effects of microgravity on human tissues using biofabricated in vitro models. These current achievements represent important progress in understanding the physiological effects of microgravity and exploiting their advantages for tissue biomanufacturing.

Bioreactor Technologies for Enhanced Organoid Culture

An organoid is a 3D organization of cells that can recapitulate some of the structure and function of native tissue. Recent work has seen organoids gain prominence as a valuable model for studying tissue development, drug discovery, and potential clinical applications. The requirements for the successful culture of organoids in vitro differ significantly from those of traditional monolayer cell cultures. The generation and maturation of high-fidelity organoids entails developing and optimizing environmental conditions to provide the optimal cues for growth and 3D maturation, such as oxygenation, mechanical and fluidic activation, nutrition gradients, etc. To this end, we discuss the four main categories of bioreactors used for organoid culture: stirred bioreactors (SBR), microfluidic bioreactors (MFB), rotating wall vessels (RWV), and electrically stimulating (ES) bioreactors. We aim to lay out the state-of-the-art of both commercial and in-house developed bioreactor systems, their benefits to the culture of organoids derived from various cells and tissues, and the limitations of bioreactor technology, including sterilization, accessibility, and suitability and ease of use for long-term culture. Finally, we discuss future directions for improvements to existing bioreactor technology and how they may be used to enhance organoid culture for specific applications.

Differentiation of human induced pluripotent stem cells into functional lung alveolar epithelial cells in 3D dynamic culture

Introduction: Understanding lung epithelium cell development from human induced pluripotent stem cells (IPSCs) in vitro can lead to an individualized model for lung engineering, therapy, and drug testing. Method: We developed a protocol to produce lung mature type I pneumocytes using encapsulation of human IPSCs in 1.1% (w/v) alginate solution within a rotating wall bioreactor system in only 20 days without using feeder cells. The aim was to reduce exposure to animal products and laborious interventions in the future. Results: The three-dimensional (3D) bioprocess allowed cell derivation into endoderm, and subsequently into type II alveolar epithelial cells within a very short period. Cells successfully expressed surfactant proteins C and B associated with type II alveolar epithelial cells, and the key structure of lamellar bodies and microvilli was shown by transmission electron microscopy. The survival rate was the highest under dynamic conditions, which reveal the possibility of adapting this integration for large-scale cell production of alveolar epithelial cells from human IPSCs. Discussion: We were able to develop a strategy for the culture and differentiation of human IPSCs into alveolar type II cells using an in vitro system that mimics the in vivo environment. Hydrogel beads would offer a suitable matrix for 3D cultures and that the high-aspect-ratio vessel bioreactor can be used to increase the differentiation of human IPSCs relative to the results obtained with traditional monolayer cultures.

The Fight against Cancer by Microgravity: The Multicellular Spheroid as a Metastasis Model

Cancer is a disease exhibiting uncontrollable cell growth and spreading to other parts of the organism. It is a heavy, worldwide burden for mankind with high morbidity and mortality. Therefore, groundbreaking research and innovations are necessary. Research in space under microgravity (µg) conditions is a novel approach with the potential to fight cancer and develop future cancer therapies. Space travel is accompanied by adverse effects on our health, and there is a need to counteract these health problems. On the cellular level, studies have shown that real (r-) and simulated (s-) µg impact survival, apoptosis, proliferation, migration, and adhesion as well as the cytoskeleton, the extracellular matrix, focal adhesion, and growth factors in cancer cells. Moreover, the µg-environment induces in vitro 3D tumor models (multicellular spheroids and organoids) with a high potential for preclinical drug targeting, cancer drug development, and studying the processes of cancer progression and metastasis on a molecular level. This review focuses on the effects of r- and s-µg on different types of cells deriving from thyroid, breast, lung, skin, and prostate cancer, as well as tumors of the gastrointestinal tract. In addition, we summarize the current knowledge of the impact of µg on cancerous stem cells. The information demonstrates that µg has become an important new technology for increasing current knowledge of cancer biology.

Single-Use Bioreactors for Human Pluripotent and Adult Stem Cells: Towards Regenerative Medicine Applications

Research on human stem cells, such as pluripotent stem cells and mesenchymal stromal cells, has shown much promise in their use for regenerative medicine approaches. However, their use in patients requires large-scale expansion systems while maintaining the quality of the cells. Due to their characteristics, bioreactors have been regarded as ideal platforms to harbour stem cell biomanufacturing at a large scale. Specifically, single-use bioreactors have been recommended by regulatory agencies due to reducing the risk of product contamination, and many different systems have already been developed. This review describes single-use bioreactor platforms which have been used for human stem cell expansion and differentiation, along with their comparison with reusable systems in the development of a stem cell bioprocess for clinical applications.

The effects of microgravity on the digestive system and the new insights it brings to the life sciences

BACKGROUND

Weightlessness is a component of the complex space environment. It exerts adverse effects on the human body, and may pose unknown challenges to the implementation of space missions. The regular function of the digestive system is an important checkpoint for astronauts to conduct missions. Simulated microgravity can recreate the changes experienced by the human body in a weightless environment in space to a certain extent, providing technical support for the exploration of its mechanism and a practical method for other scientific research.

METHODS AND MATERIALS

In the present study, we reviewed and discussed the latest research on the effects of weightlessness or simulated microgravity on the digestive system, as well as the current challenges and future expectations for progress in medical science and further space exploration.

RESULTS

A series of studies have investigated the effects of weightlessness on the human digestive system. On one hand, weightlessness and the changing space environment may exert certain adverse effects on the human body. Studies based on cells or animals have demonstrated the complex effects on the human digestive system in response to weightlessness. On the other hand, a microgravity environment also facilitates the ideation of novel concepts for research in the domain of life science.

CONCLUSION

The effects of weightlessness on the digestive system are considerably complicated. The emergence of methods that help simulate a weightless environment provides a more convenient alternative for assessing the impact and the mechanism underlying the effect of weightlessness on the human body. In addition, the simulated microgravity environment facilitates the ideation of novel concepts for application in regenerative medicine and other fields of life science.

Enhanced Induction of Definitive Endoderm Differentiation of Mouse Embryonic Stem Cells in Simulated Microgravity

Directed in vitro differentiation of pluripotent stem cells toward definitive endoderm (DE) offers great research and therapeutic potential since these cells can further differentiate into cells of the respiratory and gastrointestinal tracts, as well as associated organs such as pancreas, liver, and thyroid. We hypothesized that culturing mouse embryonic stem cells (mESCs) under simulated microgravity (SMG) conditions in rotary bioreactors (BRs) will enhance the induction of directed DE differentiation. To test our hypothesis, we cultured the cells for 6 days in two-dimensional monolayer colony cultures or as embryoid bodies (EBs) in either static conditions or, dynamically, in the rotary BRs. We used flow cytometry and quantitative polymerase chain reaction to analyze the expression of marker proteins and genes, respectively, for pluripotency (Oct3/4) and mesendodermal (Brachyury T), endodermal (FoxA2, Sox17, CxCr4), and mesodermal (Vimentin, Meox1) lineages. Culture in the form of EBs in maintenance media in the presence of leukemia inhibitory factor, in static or SMG conditions, induced expression of some of the differentiation markers, suggesting heterogeneity of the cells. This is in line with previous studies showing that differentiation is initiated as cells are aggregated into EBs even without supplementing differentiation factors to the media. Culturing EBs in static conditions in differentiation media (DM) in the presence of activin A reduced Oct3/4 expression and significantly increased Brachyury T and CxCr4 expression, but downregulated FoxA2 and Sox17. However, culturing in SMG BRs in DM upregulated Brachyury T and all of the DE markers and reduced Oct3/4 expression, indicating the advantage of dynamic cultures in BRs to specifically enhance directed DE differentiation. Given the potential discrepancies between the SMG conditions on earth and actual microgravity conditions, as observed in other studies, future experiments in space flight are required to validate the effects of reduced gravity on mESC differentiation.

Magnetic levitational bioassembly of 3D tissue construct in space

Magnetic levitational bioassembly of three-dimensional (3D) tissue constructs represents a rapidly emerging scaffold- and label-free approach and alternative conceptual advance in tissue engineering. The magnetic bioassembler has been designed, developed, and certified for life space research. To the best of our knowledge, 3D tissue constructs have been biofabricated for the first time in space under microgravity from tissue spheroids consisting of human chondrocytes. Bioassembly and sequential tissue spheroid fusion presented a good agreement with developed predictive mathematical models and computer simulations. Tissue constructs demonstrated good viability and advanced stages of tissue spheroid fusion process. Thus, our data strongly suggest that scaffold-free formative biofabrication using magnetic fields is a feasible alternative to traditional scaffold-based approaches, hinting a new perspective avenue of research that could significantly advance tissue engineering. Magnetic levitational bioassembly in space can also advance space life science and space regenerative medicine.

Exploration of space to achieve scientific breakthroughs

Living organisms adapt to changing environments using their amazing flexibility to remodel themselves by a process called evolution. Environmental stress causes selective pressure and is associated with genetic and phenotypic shifts for better modifications, maintenance, and functioning of organismal systems. The natural evolution process can be used in complement to rational strain engineering for the development of desired traits or phenotypes as well as for the production of novel biomaterials through the imposition of one or more selective pressures. Space provides a unique environment of stressors (e.g., weightlessness and high radiation) that organisms have never experienced on Earth. Cells in the outer space reorganize and develop or activate a range of molecular responses that lead to changes in cellular properties. Exposure of cells to the outer space will lead to the development of novel variants more efficiently than on Earth. For instance, natural crop varieties can be generated with higher nutrition value, yield, and improved features, such as resistance against high and low temperatures, salt stress, and microbial and pest attacks. The review summarizes the literature on the parameters of outer space that affect the growth and behavior of cells and organisms as well as complex colloidal systems. We illustrate an understanding of gravity-related basic biological mechanisms and enlighten the possibility to explore the outer space environment for application-oriented aspects. This will stimulate biological research in the pursuit of innovative approaches for the future of agriculture and health on Earth.

The effects of microgravity on differentiation and cell growth in stem cells and cancer stem cells

A spaceflight has enormous influence on the health of space voyagers due to the combined effects of microgravity and cosmic radiation. Known effects of microgravity (μg) on cells are changes in differentiation and growth. Considering the commercialization of spaceflight, future space exploration, and long-term manned flights, research focusing on differentiation and growth of stem cells and cancer cells exposed to real (r-) and simulated (s-) μg is of high interest for regenerative medicine and cancer research. In this review, we focus on platforms to study r- and s-μg as well as the impact of μg on cancer stem cells in the field of gastrointestinal cancer, lung cancer, and osteosarcoma. Moreover, we review the current knowledge of different types of stem cells exposed to μg conditions with regard to differentiation and engineering of cartilage, bone, vasculature, heart, skin, and liver constructs.

An Air Bubble-Isolating Rotating Wall Vessel Bioreactor for Improved Spheroid/Organoid Formation

IMPACT STATEMENT

The rotating wall vessel (RWV) bioreactor is a powerful tool for the generation of sizeable, faster-growing organoids. However, the ideal, low-shear, modeled microgravity environment in the RWV is frequently disrupted by the formation of bubbles, a critical but understated failure mode. To address this, we have designed and fabricated a novel, modified RWV bioreactor capable of continuously removing bubbles while providing optimal fluid dynamics. We validated the capacity of this device with computational and empirical studies. We anticipate that our novel bioreactor will be more consistent and easier to use and may fill a unique and unmet niche in the burgeoning field of organoids.

Simulated microgravity increases polyploid giant cancer cells and nuclear localization of YAP

Physical cues are vital in determining cellular fate in cancer. In vitro 3D culture do not replicate forces present in vivo. These forces including tumor interstitial fluid pressure and matrix stiffness behave as switches in differentiation and metastasis, which are intricate features of cancer stem cells (CSCs). Gravity determines the effect of these physical factors on cell fate and functions as evident from microgravity experiments on space and ground simulations. Here, we described the role of simulation of microgravity (SMG) using rotary cell culture system (RCCS) in increasing stemness in human colorectal cancer cell HCT116. We observed distinct features of cancer stem cells including CD133/CD44 dual positive cells and migration in SMG which was not altered by autophagy induction or inhibition. 3D and SMG increased autophagy, but the flux was staggered under SMG. Increased unique giant cancer cells housing complete nuclear localization of YAP were observed in SMG. This study highlights the role of microgravity in regulating stemness in CSC and importance of physical factors in determining the same.

Modeling Host-Pathogen Interactions in the Context of the Microenvironment: Three-Dimensional Cell Culture Comes of Age

Tissues and organs provide the structural and biochemical landscapes upon which microbial pathogens and commensals function to regulate health and disease. While flat two-dimensional (2-D) monolayers composed of a single cell type have provided important insight into understanding host-pathogen interactions and infectious disease mechanisms, these reductionist models lack many essential features present in the native host microenvironment that are known to regulate infection, including three-dimensional (3-D) architecture, multicellular complexity, commensal microbiota, gas exchange and nutrient gradients, and physiologically relevant biomechanical forces (e.g., fluid shear, stretch, compression). A major challenge in tissue engineering for infectious disease research is recreating this dynamic 3-D microenvironment (biological, chemical, and physical/mechanical) to more accurately model the initiation and progression of host-pathogen interactions in the laboratory. Here we review selected 3-D models of human intestinal mucosa, which represent a major portal of entry for infectious pathogens and an important niche for commensal microbiota. We highlight seminal studies that have used these models to interrogate host-pathogen interactions and infectious disease mechanisms, and we present this literature in the appropriate historical context. Models discussed include 3-D organotypic cultures engineered in the rotating wall vessel (RWV) bioreactor, extracellular matrix (ECM)-embedded/organoid models, and organ-on-a-chip (OAC) models. Collectively, these technologies provide a more physiologically relevant and predictive framework for investigating infectious disease mechanisms and antimicrobial therapies at the intersection of the host, microbe, and their local microenvironments.

3D tissue-like assemblies: A novel approach to investigate virus-cell interactions

Virus-host cell interactions are most commonly analyzed in cells maintained in vitro as two-dimensional tissue cultures. However, these in vitro conditions vary quite drastically from the tissues that are commonly infected in vivo. Over the years, a number of systems have been developed that allow the establishment of three-dimensional (3D) tissue structures that have properties similar to their in vivo 3D counterparts. These 3D systems have numerous applications including drug testing, maintenance of large tissue explants, monitoring migration of human lymphocytes in tissues, analysis of human organ tissue development and investigation of virus-host interactions including viral latency. Here, we describe the establishment of tissue-like assemblies for human lung and neuronal tissue that we infected with a variety of viruses including the respiratory pathogens human parainfluenza virus type 3 (PIV3), respiratory syncytial virus (RSV) and SARS corona virus (SARS-CoV) as well as the human neurotropic herpesvirus, varicella-zoster virus (VZV).

Mouse undifferentiated spermatogonial stem cells cultured as aggregates under simulated microgravity

Dynamic simulated microgravity (SMG) culture systems provide environments that stimulate stem cell proliferation and differentiation. However, the effect of SMG on spermatogonial stem cells (SSCs) remains unclear. Here, we used a rotating cell culture system (RCCS) to determine its effect on mouse SSC proliferation and differentiation. SSCs were enriched from mouse pub testis and cocultured with Sertoli cell feeders pre-treated with mitomycin C on fibrin scaffolds in a rotary bioreactor for 14 days. Our results show that mouse SSCs cultured in a rotary bioreactor exhibited enhanced proliferation surpassing those cultured in static conditions, although SSC cultures in SMG underwent a growth lag at initial 3 days. After 14 days, mouse SSCs and feeders grew into cell aggregates with average diameters of 242.63 ± 16.53 μm compared with those in conventional static culture (49.51 ± 15.64 μm). Related detection revealed that proliferating SSCs in SMG remained undifferentiated, maintained clone-forming capacity and were capable of differentiation into round spermatids with flagella. The growth characteristics of mouse SSCs in RCCS suggest that the resulting aggregates are similar to native in vivo cells. Rotary bioreactors that create SMG environments may be an alternative to conventional systems for the clinical application of SSCs.

Hypergravity stimulation enhances PC12 neuron-like cell differentiation

Altered gravity is a strong physical cue able to elicit different cellular responses, representing a largely uninvestigated opportunity for tissue engineering/regenerative medicine applications. Our recent studies have shown that both proliferation and differentiation of C2C12 skeletal muscle cells can be enhanced by hypergravity treatment; given these results, PC12 neuron-like cells were chosen to test the hypothesis that hypergravity stimulation might also affect the behavior of neuronal cells, in particular promoting an enhanced differentiated phenotype. PC12 cells were thus cultured under differentiating conditions for either 12 h or 72 h before being stimulated with different values of hypergravity (50 g and 150 g). Effects of hypergravity were evaluated at transcriptional level 1 h and 48 h after the stimulation, and at protein level 48 h from hypergravity exposure, to assess its influence on neurite development over increasing differentiation times. PC12 differentiation resulted strongly affected by the hypergravity treatments; in particular, neurite length was significantly enhanced after exposure to high acceleration values. The achieved results suggest that hypergravity might induce a faster and higher neuronal differentiation and encourage further investigations on the potential of hypergravity in the preparation of cellular constructs for regenerative medicine and tissue engineering purposes.

Analysis of embryoid bodies derived from human induced pluripotent stem cells as a means to assess pluripotency

Human induced pluripotent stem cells (hiPSCs) have core properties of unlimited self-renewal and differentiation potential and have emerged as exciting cell sources for applications in regenerative medicine, drug discovery, understanding of development, and disease etiology. Key among numerous criteria to assess pluripotency includes the in vivo teratoma assay that has been widely proposed as a standard functional assay to demonstrate the pluripotency of hiPSCs. Yet, the lack of reliability across methodologies, lack of definitive clinical significance, and associated expenses bring into question use of the teratoma assay as the “gold standard” for determining pluripotency. We propose use of the in vitro embryoid body (EB) assay as an important alternative to the teratoma assay. This paper summarizes the methodologies for creating EBs from hiPSCs and the subsequent analyses to assess pluripotency and proposes its use as a cost-effective, controlled, and reproducible approach that can easily be adopted to determine pluripotency of generated hiPSCs.

Simulated microgravity promoted differentiation of bipotential murine oval liver stem cells by modulating BMP4/Notch1 signaling

Faster growth and differentiation of liver stem cells to hepatocyte is one of the key factors during liver regeneration. In recent years, simulated microgravity, a physical force has shown to differentially regulate the differentiation and proliferation of stem cells. In the present work, we studied the effect of simulated microgravity on differentiation and proliferation of liver stem cells. The cells were subjected to microgravity, which was simulated using indigenously fabricated 3D clinostat. Proliferation, apoptosis, immunofluorescence assays and Western blot analysis were carried out to study the effects of simulated microgravity on liver stem cells. Microgravity treatment for 2 h enhanced proliferation of stem cells by twofold without inducing apoptosis and compromising cell viability. Analysis of hepatocyte nuclear factor 4-α (HNF4-α) expression after 2 h of microgravity treatment revealed that microgravity alone can induce the differentiation of stem cells within 2-3 days. Probing bone morphogenic protein 4 (BMP4) and Notch1 in microgravity treated stem cells elaborated downregulation of Notch1 and upregulation of BMP4 after 2 days of incubation. Further, blocking BMP4 using dorsomorphin and chordin conditioned media from chordin plasmid transfected cells attenuated microgravity mediated differentiation of liver stem cells. In conclusion, microgravity interplays with BMP4/Notch1 signaling in stem cells thus inducing differentiation of stem cells to hepatocytes. Present findings can be implicated in clinical studies where microgravity activated stem cells can regenerate the liver efficiently after liver injury.

Characterization of aggregation and protein expression of bovine corneal endothelial cells as microcarrier cultures in a rotating-wall vessel

Rotating-wall vessels are beneficial to tissue engineering in that the reconstituted tissue formed in these low-shear bioreactors undergoes extensive three-dimensional growth and differentiation. In the present study, bovine corneal endothelial (BCE) cells were grown in a high-aspect rotating-wall vessel (HARV) attached to collagen-coated Cytodex-3 beads as a representative monolayer culture to investigate factors during HARV cultivation which affect three-dimensional growth and protein expression. A collagen type I substratum in T-flask control cultures increased cell density of BCE cells at confluence by 40% and altered the expression of select proteins (43, 50 and 210 kDa). The low-shear environment in the HARV facilitated cell bridging between microcarrier beads to form aggregates containing upwards of 23 beads each, but it did not promote multilayer growth. A kinetic model of microcarrier aggregation was developed which indicates that the rate of aggregation between a single bead and an aggregate was nearly 10 times faster than between two aggregate and 60 times faster than between two single beads. These differences reflect changes in collision frequency and cell bridge formation. HARV cultivation altered the expression of cellular proteins (43 and 70 kDa) and matrix proteins (50, 73, 89 and 210 kDa) relative to controls perhaps due to hypoxia, fluid flow or distortion of cell shape. In addition to the insight that this work has provided into rotating-wall vessels, it could be useful in modeling aggregation in other cell systems, propagating human corneal endothelial cells for eye surgery and examining the response of endothelial cells to reduced shear.

How and why does the proteome respond to microgravity?

For medical and biotechnological reasons, it is important to study mammalian cells, animals, bacteria and plants exposed to simulated and real microgravity. It is necessary to detect the cellular changes that cause the medical problems often observed in astronauts, cosmonauts or animals returning from prolonged space missions. In order for in vitro tissue engineering under microgravity conditions to succeed, the features of the cell that change need to be known. In this article, we summarize current knowledge about the effects of microgravity on the proteome in different cell types. Many studies suggest that the effects of microgravity on major cell functions depend on the responding cell type. Here, we discuss and speculate how and why the proteome responds to microgravity, focusing on proteomic discoveries and their future potential.

Simulated microgravity promotes cellular senescence via oxidant stress in rat PC12 cells

Microgravity has a unique effect on biological organisms. Organs exposed to microgravity display cellular senescence, a change that resembles the aging process. To directly investigate the influence of simulated microgravity on neuronal original rat PC12 cells, we used a rotary cell culture system that simulates the microgravity environment on the earth. We found that simulated microgravity induced partial G1 phase arrest, upregulated senescence-associated beta-galactosidase (SA-beta-gal) activity, and activated both p53 and p16 protein pathways linked to cell senescence. The amount of reactive oxygen species (ROS) was also increased. The activity of intracellular antioxidant enzymes, such as superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT), was all significantly increased at 12h after the microgravity onset, yet decreased at 96h. Furthermore, concomitant block of ROS by the antioxidant N-acetylcysteine significantly inhibited the microgravity-induced upregulation of SA-beta-gal activity. These results suggest that exposure to simulated microgravity induces cellular senescence in PC12 cells via an increased oxidant stress.

Closing the phenotypic gap between transformed neuronal cell lines in culture and untransformed neurons

Studies of neuronal dysfunction in the central nervous system (CNS) are frequently limited by the failure of primary neurons to propagate in vitro. Neuronal cell lines can be substituted for primary cells but they often misrepresent normal conditions. We hypothesized that a three-dimensional (3D) cell culture system would drive the phenotype of transformed neurons closer to that of untransformed cells, as has been demonstrated in non-neuronal cell lines. In our studies comparing 3D versus two-dimensional (2D) culture, neuronal SH-SY5Y (SY) cells underwent distinct morphological changes combined with a significant drop in their rate of cell division. Expression of the proto-oncogene N-myc and the RNA-binding protein HuD was decreased in 3D culture as compared to standard 2D conditions. We observed a decline in the anti-apoptotic protein Bcl-2 in 3D culture, coupled with increased expression of the pro-apoptotic proteins Bax and Bak. Moreover, thapsigargin (TG)-induced apoptosis was enhanced in the 3D cells. Microarray analysis demonstrated significantly differing mRNA levels for over 700 genes in the cells of the two culture types, and indicated that alterations in the G1/S cell-cycle progression contributed to the diminished doubling rate in the 3D-cultured SY cells. These results demonstrate that a 3D culture approach narrows the phenotypic gap between neuronal cell lines and primary neurons. The resulting cells may readily be used for in vitro research of neuronal pathogenesis.

Real-time assessment of three-dimensional cell aggregation in rotating wall vessel bioreactors in vitro

Until now, tissue engineering and regenerative medicine have lacked non-invasive techniques for monitoring and manipulating three-dimensional (3D) tissue assembly from specific cell sources. We have set out to create an intelligent system that automatically diagnoses and monitors cell-cell aggregation as well as controls 3D growth of tissue-like constructs (organoids) in real time. The capability to assess, in real time, the kinetics of aggregation and organoid assembly in rotating wall vessel (RWV) bioreactors could yield information regarding the biological mechanics of tissue formation. Through prototype iterations, we have developed a versatile high-resolution 'horizontal microscope' that assesses cell-cell aggregation and tissue-growth parameters in a bioreactor and have begun steps to intelligently control the development of these organoids in vitro. The first generation system was composed of an argon-ion laser that excited fluorescent beads at 457 nm and fluorescent cells at 488 nm while each was suspended in a high-aspect rotating vessel (HARV) type RWV bioreactor. An optimized system, which we introduce here, is based on a diode pumped solid state (DPSS) green laser that emits a wavelength at 532 nm. By exciting both calibration beads and stained cells with laser energy and viewing them in real time with a charge-coupled device (CCD) video camera, we have captured the motion of individual cells, observed their trajectories, and analyzed their aggregate formation. Future development will focus on intelligent feedback mechanisms in silico to control organoid formation and differentiation in bioreactors. As to the duration of this entire multistep protocol, the laser system will take about 1 h to set up, followed by 1 h of staining either beads or cells. Inoculating the bioreactors with beads or cells and starting the system will take approximately 1 h, and the video-capture segments, depending on the aims of the experiment, can take from 30 s to 5 min each. The total duration of a specific experimental protocol will also depend on the specific cell type used and on its population-doubling times so that the required numbers of cells are obtained.

Proteomics and genomics of microgravity

Many serious adverse physiological changes occur during spaceflight. In the search for underlying mechanisms and possible new countermeasures, many experimental tools and methods have been developed to study microgravity caused physiological changes, ranging from in vitro bioreactor studies to spaceflight investigations. Recently, genomic and proteomic approaches have gained a lot of attention; after major scientific breakthroughs in the fields of genomics and proteomics, they are now widely accepted and used to understand biological processes. Understanding gene and/or protein expression is the key to unfolding the mechanisms behind microgravity-induced problems and, ultimately, finding effective countermeasures to spaceflight-induced alterations. Significant progress has been made in identifying the genes/proteins responsible for these changes. Although many of these genes and/or proteins were observed to be either upregulated or downregulated, however, no large-scale genomics and proteomics studies have been published so far. This review aims at summarizing the current status of microgravity-related genomics and proteomics studies and stimulating large-scale proteomics and genomics research activities.

Three-dimensional organotypic models of human colonic epithelium to study the early stages of enteric salmonellosis

In vitro cell culture models used to study how Salmonella initiates disease at the intestinal epithelium would benefit from the recognition that organs and tissues function in a three-dimensional (3-D) environment and that this spatial context is necessary for development of cultures that more realistically resemble in vivo tissues/organs. Our aim was to establish and characterize biologically meaningful 3-D models of human colonic epithelium and apply them to study the early stages of enteric salmonellosis. The human colonic cell line HT-29 was cultured in 3-D and characterized by immunohistochemistry, histology, and scanning electron microscopy. Wild-type Salmonella typhimurium and an isogenic SPI-1 type three secretion system (TTSS) mutant derivative (invA) were used to compare the interactions with 3-D cells and monolayers in adherence/invasion, tissue pathology, and cytokine expression studies. The results showed that 3-D culture enhanced many characteristics normally associated with fully differentiated, functional intestinal epithelia in vivo, including better organization of junctional, extracellular matrix, and brush-border proteins, and highly localized mucin production. Wild-type Salmonella demonstrated increased adherence, but significantly lower invasion for 3-D cells. Interestingly, the SPI-I TTSS mutant showed wild-type ability to invade into the 3-D cells but did not cause significant structural changes to these cells. Moreover, 3-D cells produced less interleukin-8 before and after Salmonella infection. These results suggest that 3-D cultures of human colonic epithelium provide valuable alternative models to study human enteric salmonellosis with potential for novel insight into Salmonella pathogenesis.

Enhanced Neurotrophin Synthesis and Molecular Differentiation in Non-Transformed Human Retinal Progenitor Cells Cultured in a Rotating Bioreactor

One approach to the treatment of retinal diseases, such as retinitis pigmentosa, is to replace diseased or degenerating cells with healthy cells. Even if all of the problems associated with tissue transplant were to be resolved, the availability of tissue would remain an ongoing problem. We have previously shown that transformed human retinal cells can be grown in a NASA-developed horizontally rotating culture vessel (bioreactor) to form three-dimensional-like structures with the expression of several retinal specific proteins. In this study, we have investigated growth of non-transformed human retinal progenitors (retinal stem cells) in a rotating bioreactor. This rotating culture vessel promotes cell-cell interaction between similar and dissimilar cells. We cultured retinal progenitors (Ret 1-4) alone or as a co-culture with human retinal pigment epithelial cells (RPE, D407) in this system to determine if 3D structures can be generated from non-transformed progenitors. Our second goal was to determine if the formation of 3D structures correlates with the upregulation of neurotrophins, basic fibroblast growth factor (bFGF), transforming growth factor alpha (TGFalpha), ciliary neurotrophic factor (CNTF), and brain-delivered neurotrophic factor (BDNF). These factors have been implicated in progenitor cell proliferation, commitment, differentiation, and survival. We also investigated the expression of the following retinal specific proteins in this system: neuron specific enolase (NSE); tyrosine hydroxylase (TH); D(2)D(3), D(4) receptors; protein kinase-C alpha (PKCalpha), and calbindin. The 3D structures generated were characterized by phase and scanning transmission electron microscopy. Retinal progenitors, cultured alone or as a co-culture in the rotating bioreactor, formed 3D structures with some degree of differentiation, accompanied by the upregulation of bFGF, CNTF, and TGFalpha. Brain-derived neurotrophic factor, which is expressed in vivo in RPE (D407), was not expressed in monolayer cultures of RPE but expressed in the rotating bioreactor-cultured RPE and retinal progenitors (Ret 1-4). Upregulation of neurotrophins was noted in all rotating bioreactor-cultured cells. Also, upregulation of D(4) receptor, calbindin, and PKCalpha was noted in the rotating bioreactor-cultured cells. We conclude that non-transformed retinal progenitors can be grown in the rotating bioreactor to form 3D structures with some degree of differentiation. We relied on molecular and biochemical analysis to characterize differentiation in cells grown in the rotating bioreactor.

TRANSIENT MAINTENANCE IN BIOREACTOR IMPROVES HEALTH OF NEURONAL CELLS

To examine whether a neuronal cell suspension can be held in vitro for a relatively short period without compromising survival rates and functionality, we have set up an experimental protocol planning 24 h of suspension culture in a rotary wall vessel (RWV) bioreactor before plating in a conventional adherent system. Apoptosis measurement and activated caspase-8, -9, and -3 detection have demonstrated that survey of the cells was not affected. The activity of major antioxidant enzymes (AOE), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT), was significantly decreased in RWV-maintained cells. A significant decrease of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) is coupled with a level of activated nuclear factor-kappaB (NF-kappaB) protein significantly lower in RVW cells than in the control. On the contrary, the level of IL-6 expression did not change between the test and the control. A significant up-regulation of growth-associated protein-43 (GAP-43), peroxisome proliferator-activated receptor-beta/delta (PPARbeta/delta), and acyl-CoA synthetase 2 (ACS2) in RWV cells has been detected. We provide the evidence that primary neuronal cells, at an early stage of development, can be maintained in a suspension condition before adherent plating. This experimental environment does not induce detrimental effects but may have an activator role, leading cells to development and maturation in a tridimensional state.

Effect of simulated microgravity on oxidation-sensitive gene expression in PC12 cells

Oxygen utilization by and oxygen dependence of cellular processes may be different in biological systems that are exposed to microgravity (micro-g). A baseline in which cellular changes in oxygen sensitive molecular processes occur during micro-g conditions would be important to pursue this question. The objective of this research is to analyze oxidation-sensitive gene expression in a model cell line [rat pheochromocytoma (PC12)] under simulated micro-g conditions. The PC12 cell line is well characterized in its response to oxygen, and is widely recognized as a sensitive model for studying the responses of oxygen-sensitive molecular and cellular processes. This study uses the rotating wall vessel bioreactor (RWV) designed at NASA to simulate micro-g. Gene expression in PC12 cells in response to micro-g was analyzed by DNA microarray technology. The microarray analysis of PC12 cells cultured for 4 days under simulated micro-g under standardized oxygen environment conditions revealed more than 100 genes whose expression levels were changed at least twofold (up-regulation of 65 genes and down-regulation of 39 genes) compared with those from cells in the unit gravity (unit-g) control. This study observed that genes involved in the oxidoreductase activity category were most significantly differentially expressed under micro-g conditions. Also, known oxidation-sensitive transcription factors such as hypoxia-inducible factor-2alpha, c-myc, and the peroxisome proliferator-activated receptor-gamma were changed significantly. Our initial results from the gene expression microarray studies may provide a context in which to evaluate the effect of varying oxygen environments on the background of differential gene regulation of biological processes under variable gravity conditions.

The role of connexins in the differentiation of NT2 cells in Sertoli-NT2 cell tissue constructs grown in the rotating wall bioreactor

Neural transplantation is developing as a successful treatment for neurodegenerative diseases such as Parkinson's disease. The human Ntera-2/D1 (NT2) cell line is an attractive alternative to the use of human fetal neurons as a cell source for transplantation. We have explored combining NT2 cells, as a neuronal source, and Sertoli cells, which may act as a graft facilitator to enhance neuronal survival and differentiation, and ameliorate the host immune response, into a tissue construct for use in cell replacement therapy for neurodegenerative disease. This Sertoli-NT2-aggregated cell (SNAC) tissue construct is formed in the high aspect ratio vessel (HARV) bioreactor. NT2 cells differentiate to dopaminergic NT2N neurons within the SNAC tissue construct without retinoic acid. We report here that the gap junction protein connexin 43 is decreased among differentiated NT2N neurons. Inhibition of connexin 43 with 18beta glycyrrhetinic acid and carbenoxolone, a glycyrrhetinic acid derivative, during formation of the SNAC tissue constructs disrupts the differentiation of NT2 cells. Therefore, connexin 43 is important in the differentiation of NT2 cells in the SNAC tissue construct.

Formation and structure of transplantable tissue constructs generated in simulated microgravity from Sertoli cells and neuron precursors

Cell transplantation therapy for Parkinson's disease (PD) has received much attention as a potential treatment protocol for this neurodegenerative condition. Although there have been promising successes with this approach, it remains problematic, especially regarding the inability to provide immediate trophic support to the newly grafted cells and the inability to prevent acute and/or long-term graft rejection by the host. To address these issues of cell graftability, we have created a novel tissue construct from isolated rat Sertoli cells (SC) and the NTerra-2 immortalized human neuron precursor cell line (NT2) utilizing NASA-developed simulated microgravity technology. The two cell types were cocultured at a 1:4 (SC/NT2) ratio in the High Aspect Rotating Vessel (HARV) biochamber for 3 days, after which a disc-shaped aggregate (1-4 mm diameter) was formed. Sertoli neuron aggregated cells (SNAC) were collected by gravity sedimentation and processed either for light and electron microscopy or for fluorescent immunocytochemistry. Intra-SNAC clusters of SC and NT2 cells were identified by anti-human mitochondrial protein (huMT--specific for NT2 cells) and cholera toxin subunit B (CTb--specific for SC). There was little evidence of cell death throughout the aggregate and the absence of central necrosis, as might be expected in such a large aggregate in vitro. Ultrastructurally, SC did not express junctional modifications with NT2 cells nor with adjacent SC as is typical of SC in vivo and, in some protocols, in vitro. NT2 cells, however, showed distinct intercellular junction-like densities with adjacent NT2 cells, often defining canaliculi-like channels between the microvillus borders of the cells. The results show that the use of simulated microgravity coculture provides a culture environment suitable for the formation of a unique and viable Sertoli-NT2 (i.e., SNAC) tissue construct displaying intra-aggregate cellular organization. The structural integration of SC with NT2 cells provides a novel transplantable tissue source, which can be tested to determine if SC will suppress rejection of the grafted NT2 cells and provide for their short- and long-term trophic support in situ in the treatment of experimental PD.

Bioreactor cultivation enhances the efficiency of human embryoid body (hEB) formation and differentiation

The promise of human embryonic stem cells (hESCs) to provide an unlimited supply of cells for cell therapy and tissue engineering depends on the availability of a controllable bioprocess for their expansion and differentiation. We describe for the first time the formation of differentiating human embryoid bodies (hEBs) in rotating bioreactors to try and control their agglomeration. The efficacy of the dynamic process compared to static cultivation in Petri dishes was analyzed with respect to the yield of hEB formation and differentiation. Quantitative analyses of hEBs, DNA and protein contents, and viable cell concentration, as measures for culture cellularity and scale-up, revealed 3-fold enhancement in generation of hEBs compared to the static culture. Other metabolic indices such as glucose consumption, lactic acid production, and pH pointed to efficient cell expansion and differentiation in the dynamic cultures. The type of rotating vessel had a significant impact on the process of hEB formation and agglomeration. In the slow turning lateral vessel (STLV), hEBs were smaller in size and no large necrotic centers were seen, even after 1-month cultivation. In the high aspect rotating vessel (HARV), hEB agglomeration was massive. The appearance of representative tissues derived from the three germ layers as well as primitive neuronal tube organization, blood vessel formation, and specific-endocrine secretion indicated that the initial developmental events are not altered in the dynamically formed hEBs. Collectively, our study defines the culture conditions in which control over the aggregation of differentiating hESCs is obtained, thus enabling scaleable cell production for clinical and industrial applications.

Rapid differentiation of NT2 cells in Sertoli–NT2 cell tissue constructs grown in the rotating wall bioreactor

Cell replacement therapy is of great interest as a long-term treatment of neurodegenerative diseases such as Parkinson's disease (PD). We have previously shown that Sertoli cells (SC) provide neurotrophic support to transplants of dopaminergic fetal neurons and NT2N neurons, derived from the human clonal precursors cell line NTera2/D1 (NT2), which differentiate into dopaminergic NT2N neurons when exposed to retinoic acid. We have created SC-NT2 cell tissue constructs cultured in the high aspect ratio vessel (HARV) rotating wall bioreactor. Sertoli cells, NT2, and SC plus NT2 cells combined in starting ratios of 1:1, 1:2, 1:4 and 1:8 were cultured in the HARV in DMEM with 10% fetal bovine serum and 1% growth factor reduced Matrigel for 3 days, without retinoic acid. Conventional, non-HARV, cultures grown in the same culture medium were used as controls. The presence of tyrosine hydroxylase (TH) was assessed in all culture conditions. Sertoli-neuron-aggregated-cell (SNAC) tissue constructs grown at starting ratios of 1:1 to 1:4 contained a significant amount of TH after 3 days of culture in the HARV. No TH was detected in SC HARV cultures, or SC, NT2 or SC-NT2 conventional co-cultures. Quantitative stereology of immunolabled 1:4 SNAC revealed that approximately 9% of NT2 cells differentiate into TH-positive (TH+) NT2N neurons after 3 days of culture in the HARV, without retinoic acid. SNAC tissue constructs also released dopamine (DA) when stimulated with KCl, suggesting that TH-positive NT2N neurons in the SNAC adopted a functional dopaminergic phenotype. SNAC tissue constructs may be an important source of dopaminergic neurons for neuronal transplantation.

Effects of simulated microgravity on the development and maturation of dissociated cortical neurons

Although a wealth of evidence supports the hypothesis that some functions of the nervous system may be altered during exposure to microgravity, the possible changes in basic neuronal physiology are not easy to assess. Indeed, few studies have examined whether microgravity affects the development of neurons in culture. In the present study, a suspension of dissociated cortical cells from rat embryos were exposed to 24 h of simulated microgravity before plating in a normal adherent culture system. Both preexposed and control cells were used after a period of 7-10 d in vitro. The vitality and the level of reactive oxygen species of cultures previously exposed did not differ from those of normal cultures. Cellular characterization by immunostaining with a specific antibody displayed normal neuronal phenotype in control cells, whereas pretreatment in simulated microgravity revealed an increase of glial fibrillary acidic protein fluorescence in the elongated stellate glial cells. Electrophysiological recording indicated that the electrical properties of neurons preexposed were comparable with those of controls. Overall, our results indicate that a short time of simulated microgravity preexposure does not affect dramatically the ability of dissociated neural cells to develop and differentiate in an adherent culture system.

Generation of 3D retina-like structures from a human retinal cell line in a NASA bioreactor

Replacement of damaged cells is a promising approach for treatment of age-related macular degeneration (AMD) and retinitis pigmentosa (RP); however, availability of donor tissue for transplantation remains a major obstacle. Key factors for successful engineering of a tissue include the identification of a neural cell line that is: homogeneous but can be expanded to give rise to multiple cells types; is nontumorigenic, yet capable of secreting neurotrophic factors; and is able to form three-dimensional (3D), differentiated structures. The goal of this study was to test the feasibility of tissue engineering from a multipotential human retinal cell line using a NASA-developed bioreactor. A multipotential human retinal precursor cell line was used to generate 3D structures. In addition, retinal pigment epithelium (RPE) cells were cocultured with neural cells to determine if 3D retinal structures could be generated in the bioreactor with cells grown on laminin-coated cytodex 3 beads. Cell growth, morphology, and differentiation were monitored by light and scanning electron microscopy, Western blot analysis, and analysis of glucose use and lactate production. The neuronal retinal precursor cell line cultured in a bioreactor gave rise to most retinal cell types seen in monolayer culture. They formed composite structures with cell-covered beads associated with one another in a tissue-like array. The beginning of layering and/or separation of cell types was observed. The neuronal cell types previously seen in monolayer cultures were also seen in the bioreactor. Some of the retinal cells differentiate into photoreceptors in the bioreactor with well-developed outer segment-like structures, a process that is critical for retinal function. Moreover, the neuronal cells that were generated resembled their in vivo phenotype more closely than those grown under other conditions. Outer segments were almost never seen in the monolayer cultures, even in the presence of photoreceptor-inducing growth factors such as basic fibroblast growth factor (bFGF) and transforming growth factor (TGF-alpha). Muller cells were occasionally seen when retinal, RPE cells were cocultured with retinal cells in the bioreactor. These have never been seen in this retinal cell line before. Cells grown in the bioreactor expressed several proteins specific for the retinal cell types: opsin, protein kinase C-alpha, dopamine receptor D4, tyrosine hydroxylase, and calbindin.

On-line monitoring of human prostate cancer cells in a perfusion rotating wall vessel by near-infrared spectroscopy

PC-3 human prostate cancer cells have been cultivated in a rotating wall vessel in which glucose, lactate, and glutamine profiles were monitored noninvasively and in real time by near-infrared (NIR) spectroscopy. The calibration models were based on off-line spectra from tissue culture experiments described previously (Rhiel et al., Biotechnol Bioeng 77:73-82). Monitoring performance was improved by Fourier filtering of the spectra and initial off-set adjustment. The resulting standard errors of predictions were 0.95, 0.74, and 0.39 mM for glucose, lactate, and glutamine, respectively. The concentration of ammonia could not be accurately measured from the same spectra. In addition, metabolite uptake and production rates were determined for PC-3 prostate cancer cells during exponential growth in batch-mode cultivation. Cells grew with a doubling time of 21 h and consumed glucose and glutamine at rates of 6.8 and 1.8 x 10(-17) mol/cell.s, respectively. This resulted in lactate and ammonia production rates of 11.9 and 1.3 x 10(-17) mol/cell.s, respectively. Compared with other monitoring technologies, this technology has many advantages for spaceflights and stand-alone units; for instance, calibration can be performed at one time and then applied in a reagentless, low-maintenance way at a later time. The resulting concentration information can be incorporated into closed-loop control schemes, thereby leading to better in vitro models of in vivo behavior.

Nr0b1 and its network partners are expressed early in murine embryos prior to steroidogenic axis organogenesis

Ahch is an orphan nuclear receptor encoded by Nr0b1 on the murine X chromosome and is the ortholog of human DAX1. Nr0b1/NR0B1 expression at appropriate dosages is required for normal steroidogenic axis development: mutation of the human ortholog, NR0B1, results in adrenal hypoplasia congenita and hypogonadotropic hypogonadism; and duplication or transgenic overexpression in humans or mice, respectively, results in XY phenotypic females, a phenotype known as dosage sensitive sex-reversal. Complete loss of Nr0b1 by targeted deletion has been hypothesized to be lethal in embryonic stem (ES) cells and preliminary evidence suggested that ES cells might express Nr0b1. These investigations examined Nr0b1 expression and its network partners in both cultured ES cells and preimplantation embryos. We cultured ES cells in the absence or presence of differentiation agents and analyzed expression of Nr0b1 and associated network partners by northern blot hybridization and reverse transcriptase-polymerase chain reaction. Nrob1 was highly expressed by totipotent ES cells with reduced expression following induction toward individual germ layer fates. Nr5a1/Sf1, Wt1 and other genes that encode proteins known to interact with Nr0b1 were also expressed. Immunohistochemical analysis of preimplantation embryos for Ahch and key partners confirmed in vivo expression of network components. These findings are consistent with the existence of a potentially functional network of transcription factors, including Ahch, very early in embryonic development. These results validate ES cells as a developmentally dynamic model for mechanistic investigations into this regulatory network early in embryogenesis preceding organogenesis.

Collagen expression in tissue engineered cartilage of aged human articular chondrocytes in a rotating bioreactor

This study describes the culture and three-dimensional assembly of aged human articular chondrocytes under controlled oxygenation and low shear stress in a rotating-wall vessel. Chondrocytes cultured in monolayer were released and placed without any scaffold as a single cell suspension in a rotating bioreactor for 12 weeks. Samples were analyzed with immunohistochemistry, molecular biology and electron microscopy. During serial monolayer cultures chondrocytes dedifferentiated to a "fibroblast-like" structure and produced predominantly collagen type I. When these dedifferentiated cells were transferred to the rotating bioreactor, the cells showed a spontaneous aggregation and formation of solid tissue during the culture time. Expression of collagen type II and other components critical for the extracellular cartilage matrix could be detected. Transmission electron microscopy revealed a fine network of randomly distributed collagen fibrils. This rotating bioreactor proves to be a useful tool for providing an environment that enables dedifferentiated chondrocytes to redifferentiate and produce a cartilage-specific extracellular matrix.

Simulated microgravity suppresses osteoblast phenotype, Runx2 levels and AP-1 transactivation

Conditions of disuse such as bed rest, space flight, and immobilization result in decreased mechanical loading of bone, which is associated with reduced bone mineral density and increased fracture risk. Mechanisms involved in this process are not well understood but involve the suppression of osteoblast function. To elucidate the influence of mechanical unloading on osteoblasts, a rotating wall vessel (RWV) was employed as a ground based model of simulated microgravity. Mouse MC3T3-E1 osteoblasts were grown on microcarrier beads for 14 days and then placed in the RWV for 24 h. Consistent with decreased bone formation during actual spaceflight conditions, alkaline phosphatase and osteocalcin expression were decreased by 80 and 50%, respectively. In addition, runx2 expression and AP-1 transactivation, key regulators of osteoblast differentiation and bone formation, were reduced by more than 60%. This finding suggests that simulated microgravity could promote dedifferentiation and/or transdifferentiation to alternative cell types; however, markers of adipocyte, chondrocyte, and myocyte lineages were not induced by RWV exposure. Taken together, our results indicate that simulated microgravity may suppress osteoblast differentiation through decreased runx2 and AP-1 activities.

Low-Shear modeled microgravity alters the Salmonella enterica serovar typhimurium stress response in an RpoS-independent manner

We have previously demonstrated that low-shear modeled microgravity (low-shear MMG) serves to enhance the virulence of a bacterial pathogen, Salmonella enterica serovar Typhimurium. The Salmonella response to low-shear MMG involves a signaling pathway that we have termed the low-shear MMG stimulon, though the identities of the low-shear MMG stimulon genes and regulatory factors are not known. RpoS is the primary sigma factor required for the expression of genes that are induced upon exposure to different environmental-stress signals and is essential for virulence in mice. Since low-shear MMG induces a Salmonella acid stress response and enhances Salmonella virulence, we reasoned that RpoS would be a likely regulator of the Salmonella low-shear MMG response. Our results demonstrate that low-shear MMG provides cross-resistance to several environmental stresses in both wild-type and isogenic rpoS mutant strains. Growth under low-shear MMG decreased the generation time of both strains in minimal medium and increased the ability of both strains to survive in J774 macrophages. Using DNA microarray analysis, we found no evidence of induction of the RpoS regulon by low-shear MMG but did find that other genes were altered in expression under these conditions in both the wild-type and rpoS mutant strains. Our results indicate that, under the conditions of these studies, RpoS is not required for transmission of the signal that induces the low-shear MMG stimulon. Moreover, our studies also indicate that low-shear MMG can be added to a short list of growth conditions that can serve to preadapt an rpoS mutant for resistance to multiple environmental stresses.

MAP and src kinases control the induction of AP-1 members in response to changes in mechanical environment in osteoblastic cells

The activating protein-1 (AP-1) complex plays a critical role in bone physiology, including its response to strain. We studied gene expression and nuclear translocation kinetics of the seven AP-1 members, after substrate deformation (Flexcell) or simulated microgravity (Clinostat), in osteoblastic ROS17/2.8 cells. Gene expression and nuclear translocation of all the AP-1 members were induced, under both conditions, with differences in their kinetics, except fosB mRNA in the Clinostat. Downregulation of protein kinase C (PKC) and COX1/2 or inhibition of ERK1/2, p38(MAPK) or src kinases had no major effect on AP-1 mRNA expression in the Flexcell. In contrast, ERK1/2, p38(MAPK) and src kinases treatment blocked nuclear translocation of almost all the AP-1 members in both models, except Fra-1, JunD after deformation and Fra-1, JunB after clinorotation. Thus, changes in the osteoblastic mechanical environment induced a dramatic induction of most of the AP-1 members with specific kinetics and involved MAPK and src kinase pathways, which differed whether the cells were stretched or clinorotated.

Rhythmicity of engraftment and altered cell cycle kinetics of cytokine-cultured murine marrow in simulated microgravity compared with static cultures

Space flight with associated microgravity is complicated by "astronaut's anemia" and other hematologic abnormalities. Altered erythroid differentiation, red cell survival, plasma volume, and progenitor numbers have been reported. We studied the impact of microgravity on engraftable stem cells, culturing marrow cells in rotary wall vessel (RWV) culture chambers mimicking microgravity and in normal gravity nonadherent Teflon bottles. A quantitative competitive engraftment technique was assessed under both conditions in lethally irradiated hosts. We assessed 8-wk engraftable stem cells over a period spanning at least one cell cycle for cytokine (FLT-3 ligand, thrombopoietin [TPO], steel factor)-activated marrow stem cells. Engraftable stem cells were supported out to 56 h under microgravity conditions, and this support was superior to that seen in normal-gravity Teflon bottle cultures out to 40 h, with Teflon bottle culture support superior to RWV from 40 to 56 h. A nadir of stem cell number was seen at 40 h in Teflon and 48 h in RWV, suggesting altered marrow stem cell cycle kinetics under microgravity. This is the first study of engraftable stem cells under microgravity conditions, and the differences between microgravity and normal gravity cultures may present opportunities for unique future stem cell expansion strategies.

Effect of culture in a rotating wall bioreactor on the physiology of differentiated neuron-like PC12 and SH-SY5Y cells

A variety of evidence suggests that nervous system function is altered during microgravity, however, assessing changes in neuronal physiology during space flight is a non-trivial task. We have used a rotating wall bioreactor with a high aspect ratio vessel (HARV), which simulates the microgravity environment, to investigate the how the viability, neurite extension, and signaling of differentiated neuron-like cells changes in different culture environments. We show that culture of differentiated PC12 and SH-SY5Y cells in the simulated microgravity HARV bioreactor resulted in high cell viability, moderate neurite extension, and cell aggregation accompanied by NO production. Neurite extension was less than that seen in static cultures, suggesting that less than optimal differentiation occurs in simulated microgravity relative to normal gravity. Cells grown in a mixed vessel under normal gravity (a spinner flask) had low viability, low neurite extension, and high glutamate release. This work demonstrates the feasibility of using a rotating wall bioreactor to explore the effects of simulated microgravity on differentiation and physiology of neuron-like cells.

Permanent phenotypic and genotypic changes of prostate cancer cells cultured in a three-dimensional rotating-wall vessel

A three-dimensional (3D) integrated rotating-wall vessel cell-culture system was used to evaluate the interaction between a human prostate cancer cell line, LNCaP, and microcarrier beads alone, or microcarrier beads previously seeded with either prostate or bone stromal cells. Upon coculture of LNCaP cells with microcarrier beads either in the presence or in the absence of prostate or bone stromal cells, 3D prostate organoids were formed with the expected hormonal responsiveness to androgen, increased cell growth, and prostate-specific antigen production. In this communication, we define permanent phenotypic and genotypic changes of LNCaP cells upon coculture with microcarrier beads alone, or with microcarrier beads previously seeded with either prostate or bone stromal cells. Most notably, we observed selective genetic changes, i.e., chromosomal losses or gains, as evaluated by both conventional cytogenetic and comparative genomic hybridization, in LNCaP sublines derived from the prostate organoids. Moreover, the derivative LNCaP cells appear to have altered growth profiles, and exhibit permanent and stable changes in response to androgen, estrogen, and growth factors. The derivative LNCaP sublines showed increased anchorage-independent growth rate, and enhanced tumorigenicity and metastatic potential when inoculated orthotopically in castrated athymic mice. Our results support the hypothesis that further nonrandom genetic and phenotypic changes in prostate cancer epithelial cells can occur through an event that resembles "adaptive mutation" such as has been described in bacteria subjected to nutritional starvation. The occurrence of such permanent changes may be highly contact dependent, and appears to be driven by specific microenvironmental factors surrounding the tumor cell epithelium grown as 3D prostate organoids.

Erythroid cell growth and differentiation in vitro in the simulated microgravity environment of the NASA rotating wall vessel bioreactor

Prolonged exposure of humans and experimental animals to the altered gravitational conditions of space flight has adverse effects on the lymphoid and erythroid hematopoietic systems. Although some information is available regarding the cellular and molecular changes in lymphocytes exposed to microgravity, little is known about the erythroid cellular changes that may underlie the reduction in erythropoiesis and resultant anemia. We now report a reduction in erythroid growth and a profound inhibition of erythropoietin (Epo)-induced differentiation in a ground-based simulated microgravity model system. Rauscher murine erythroleukemia cells were grown either in tissue culture vessels at 1 x g or in the simulated microgravity environment of the NASA-designed rotating wall vessel (RWV) bioreactor. Logarithmic growth was observed under both conditions; however, the doubling time in simulated microgravity was only one-half of that seen at 1 x g. No difference in apoptosis was detected. Induction with Epo at the initiation of the culture resulted in differentiation of approximately 25% of the cells at 1 x g, consistent with our previous observations. In contrast, induction with Epo at the initiation of simulated microgravity resulted in only one-half of this degree of differentiation. Significantly, the growth of cells in simulated microgravity for 24 h prior to Epo induction inhibited the differentiation almost completely. The results suggest that the NASA RWV bioreactor may serve as a suitable ground-based microgravity simulator to model the cellular and molecular changes in erythroid cells observed in true microgravity.

Optimized suspension culture: the rotating-wall vessel

Suspension culture remains a popular modality, which manipulates mechanical culture conditions to maintain the specialized features of cultured cells. The rotating-wall vessel is a suspension culture vessel optimized to produce laminar flow and minimize the mechanical stresses on cell aggregates in culture. This review summarizes the engineering principles, which allow optimal suspension culture conditions to be established, and the boundary conditions, which limit this process. We suggest that to minimize mechanical damage and optimize differentiation of cultured cells, suspension culture should be performed in a solid-body rotation Couette-flow, zero-headspace culture vessel such as the rotating-wall vessel. This provides fluid dynamic operating principles characterized by 1) solid body rotation about a horizontal axis, characterized by colocalization of cells and aggregates of different sedimentation rates, optimally reduced fluid shear and turbulence, and three-dimensional spatial freedom; and 2) oxygenation by diffusion. Optimization of suspension culture is achieved by applying three tradeoffs. First, terminal velocity should be minimized by choosing microcarrier beads and culture media as close in density as possible. Next, rotation in the rotating-wall vessel induces both Coriolis and centrifugal forces, directly dependent on terminal velocity and minimized as terminal velocity is minimized. Last, mass transport of nutrients to a cell in suspension culture depends on both terminal velocity and diffusion of nutrients. In the transduction of mechanical culture conditions into cellular effects, several lines of evidence support a role for multiple molecular mechanisms. These include effects of shear stress, changes in cell cycle and cell death pathways, and upstream regulation of secondary messengers such as protein kinase C. The discipline of suspension culture needs a systematic analysis of the relationship between mechanical culture conditions and biological effects, emphasizing cellular processes important for the industrial production of biological pharmaceuticals and devices.

The simulated microgravity environment maintains key metabolic functions and promotes aggregation of primary porcine hepatocytes

The high aspect ratio vessel allows the culture of primary porcine hepatocytes in an environment of low shear stress and simulated microgravity. Primary porcine hepatocytes have been difficult to maintain in culture long term while preserving their metabolic functions. This study was carried out in order to characterise key metabolic functions of cell aggregates formed by primary porcine hepatocytes cultured in a high aspect ratio vessel for a predetermined period of 21 days. 10(8) porcine hepatocytes were loaded into the high aspect ratio vessel and continuously rotated during the experiments. 0.7 ml of the culture medium was sampled on days 1, 2, 4, 7, 10, 14 and 21. 1H nuclear magnetic resonance spectroscopy of the culture medium, using the presaturation technique, assessed the following: glucose metabolism, glutamine synthesis and ketogenesis. There was glucose breakdown anaerobically during the first 10 days as manifested by lactate production and pyruvate and threonine consumption. After day 10 there was significantly smaller lactate production (day 1 vs day 10 P < 0.01), and significantly smaller pyruvate (day 1 vs day 14 P < 0.03) and threonine consumption (day 1 vs day 10 P < 0.002), indicative of an aerobic metabolic pattern. Significantly more glutamate was produced after day 10 (day 1 vs day 10 P < 0.031), and more glutamine was consumed after day 14. There was a steadily diminishing production of acetate which reached a minimum on day 14 (day 2 vs day 14 P < 0.00014). After an initial 10 day period of acclimatisation cell aggregates formed in the high aspect ratio vessel switched from the anaerobic pattern of metabolism to the more efficient aerobic pattern, which was exhibited until the experiments were terminated. The high aspect ratio vessel is suitable for long-term culture of porcine hepatocytes and it is worthwhile carrying out scale-up feasibility studies.

Adult stem cell plasticity and methods of detection

The ability to selectively produce one or more differentiated cell types at will from totipotent stem cells would be of profound clinical importance, as it would enable the specific replacement of damaged/dysfunctional cell types within the body, potentially curing numerous diseases. Until recently, it was thought that the only cells that possessed sufficient immaturity to be capable of giving rise to more than one tissue type in vitro and in vivo were the embryonic stem cells. However, recent studies have now provided compelling evidence that the adult bone marrow, brain and skeletal muscle contain stem cells that possess the remarkable ability to trans-differentiate and give rise to progeny of alternate embryologic derivations. These recent findings have shattered the existing dogma that the stages of embryologic development are irreversible. In this review, we present a brief summary of the most significant findings in the field of stem cell plasticity, emphasizing studies involving the hematopoietic system, discussing the models used thus far, and finishing with our findings on human stem cell plasticity using the fetal sheep model.

Erythroid cell growth and differentiation in vitro in the simulated microgravity environment of the NASA rotating wall vessel bioreactor

Prolonged exposure of humans and experimental animals to the altered gravitational conditions of space flight has adverse effects on the lymphoid and erythroid hematopoietic systems. Although some information is available regarding the cellular and molecular changes in lymphocytes exposed to microgravity, little is known about the erythroid cellular changes that may underlie the reduction in erythropoiesis and resultant anemia. We now report a reduction in erythroid growth and a profound inhibition of erythropoietin (Epo)-induced differentiation in a ground-based simulated microgravity model system. Rauscher murine erythroleukemia cells were grown either in tissue culture vessels at 1 x g or in the simulated microgravity environment of the NASA-designed rotating wall vessel (RWV) bioreactor. Logarithmic growth was observed under both conditions; however, the doubling time in simulated microgravity was only one-half of that seen at 1 x g. No difference in apoptosis was detected. Induction with Epo at the initiation of the culture resulted in differentiation of approximately 25% of the cells at 1 x g, consistent with our previous observations. In contrast, induction with Epo at the initiation of simulated microgravity resulted in only one-half of this degree of differentiation. Significantly, the growth of cells in simulated microgravity for 24 h prior to Epo induction inhibited the differentiation almost completely. The results suggest that the NASA RWV bioreactor may serve as a suitable ground-based microgravity simulator to model the cellular and molecular changes in erythroid cells observed in true microgravity.

NEURAL PRECURSOR CELLS FORM RUDIMENTARY TISSUE-LIKE STRUCTURES IN A ROTATING-WALL VESSEL BIOREACTOR

We have analyzed the biology of embryonic, epidermal growth factor-responsive murine neural precursor cells cultured in the high-aspect ratio vessel (HARV). Within 2-3 d of rotary-cell culture, such cells formed multiple, macroscopic, three-dimensional structures that were orders of magnitude larger than the cellular clusters ("neurospheres") formed by these cells in conventional stationary-flask cultures. Each HARV structure was composed of a multilayered cellular shell surrounding one or more central cavities that were bordered by pyknotic cell nuclei. Although the cells in the HARV structures were more pleomorphic than those in neurospheres, the structures did not appear to represent primitive neural tumors: the formation of HARV structures by precursor cells was not an irreversible phenotypic change, and the structures did not originate from the clonal expansion of single-progenitor cells; the growth rate and invasiveness of the cells in HARVs were less than those in flasks; and HARV-cultured cells did not form tumors after subcutaneous inoculation into the flanks of NOD-scid/scid mice. Immunohistochemical analysis suggested that HARV structures might be novel "prototissues" characterized by a crude, but organized, architecture, with a surface layer of immature proliferating cells (nestin- and proliferating cell nuclear antigen-positive) that enclosed strata of more differentiated cells (beta-tubulin III- and glial fibrillary acidic protein-positive) within. Rotary-cell culture may have significant implications for the eventual utility of neural precursors for clinical neurotransplantation.