Effects of microgravity on growing cultured skin constructs

Role of Apoptosis in Wound Healing and Apoptosis Alterations in Microgravity

Functioning as the outermost self-renewing protective layer of the human organism, skin protects against a multitude of harmful biological and physical stimuli. Consisting of ectodermal, mesenchymal, and neural crest-derived cell lineages, tissue homeostasis, and signal transduction are finely tuned through the interplay of various pathways. A health problem of astronauts in space is skin deterioration. Until today, wound healing has not been considered as a severe health concern for crew members. This can change with deep space exploration missions and commercial spaceflights together with space tourism. Albeit the molecular process of wound healing is not fully elucidated yet, there have been established significant conceptual gains and new scientific methods. Apoptosis, e.g., programmed cell death, enables orchestrated development and cell removal in wounded or infected tissue. Experimental designs utilizing microgravity allow new insights into the role of apoptosis in wound healing. Furthermore, impaired wound healing in unloading conditions would depict a significant challenge in human-crewed exploration space missions. In this review, we provide an overview of alterations in the behavior of cutaneous cell lineages under microgravity in regard to the impact of apoptosis in wound healing. We discuss the current knowledge about wound healing in space and simulated microgravity with respect to apoptosis and available therapeutic strategies.

Effect of microgravity on proliferation and differentiation of embryonic stem cells in an automated culturing system during the TZ-1 space mission

OBJECTIVE

Despite a great number of studies analysing the effects of microgravity on stem cell proliferation and differentiation, few of them have focused on real-time imaging estimates in space. Herein, we utilized the TZ-1 cargo spacecraft, automatic cell culture equipment and live cell imaging techniques to examine the effects of real microgravity on the proliferation and differentiation of mouse embryonic stem cells (mESCs).

MATERIALS AND METHODS

Oct4-GFP, Brachyury-GFP mESC and Oct4-GFP mESC-derived EBs were used as experimental samples in the TZ-1 spaceflight mission. These samples were seeded into chambers, cultured in an automatic cell culture device and were transported into space during the TZ-1 mission. Over 15 days of spaceflight, bright field and fluorescent images of cell growth were taken in micrography, and the medium was changed every day. Real-time image data were transferred to the ground for analysis.

RESULTS

Space microgravity maintains stemness and long-term survival of mESCs, promising 3D aggregate formation. Although microgravity did not significantly prevent the migration of EBs on the ECM substrate, it did prevent terminal differentiation of cells.

CONCLUSIONS

This study demonstrates that space microgravity might play a potential role in supporting 3D cell growth and maintenance of stemness in embryonic stem cells, while it may negatively affect terminal differentiation.

Modulation of Differentiation Processes in Murine Embryonic Stem Cells Exposed to Parabolic Flight-Induced Acute Hypergravity and Microgravity

Embryonic developmental studies under microgravity conditions in space are very limited. To study the effects of short-term altered gravity on embryonic development processes, we exposed mouse embryonic stem cells (mESCs) to phases of hypergravity and microgravity and studied the differentiation potential of the cells using wide-genome microarray analysis. During the 64th European Space Agency's parabolic flight campaign, mESCs were exposed to 31 parabolas. Each parabola comprised phases lasting 22 s of hypergravity, microgravity, and a repeat of hypergravity. On different parabolas, RNA was isolated for microarray analysis. After exposure to 31 parabolas, mESCs (P31 mESCs) were further differentiated under normal gravity (1 g) conditions for 12 days, producing P31 12-day embryoid bodies (EBs). After analysis of the microarrays, the differentially expressed genes were analyzed using different bioinformatic tools to identify developmental and nondevelopmental biological processes affected by conditions on the parabolic flight experiment. Our results demonstrated that several genes belonging to GOs associated with cell cycle and proliferation were downregulated in undifferentiated mESCs exposed to gravity changes. However, several genes belonging to developmental processes, such as vasculature development, kidney development, skin development, and to the TGF-β signaling pathway, were upregulated. Interestingly, similar enriched and suppressed GOs were obtained in P31 12-day EBs compared with ground control 12-day EBs. Our results show that undifferentiated mESCs exposed to alternate hypergravity and microgravity phases expressed several genes associated with developmental/differentiation and cell cycle processes, suggesting a transition from the undifferentiated pluripotent to a more differentiated stage of mESCs.

PTEN/FOXO3/AKT pathway regulates cell death and mediates morphogenetic differentiation of Colorectal Cancer Cells under Simulated Microgravity

Gravity is a major physical factor determining the stress and strain around cells. Both in space experiments and ground simulation, change in gravity impacts the viability and function of various types of cells as well as in vivo conditions. Cancer cells have been shown to die under microgravity. This can be exploited for better understanding of the biology and identification of novel avenues for therapeutic intervention. Here, we described the effect of microgravity simulated using Rotational Cell Culture System-High Aspect Ratio Vessel (RCCS-HARV) on the viability and morphological changes of colorectal cancer cells. We observed DLD1, HCT116 and SW620 cells die through apoptosis under simulated microgravity (SM). Gene expression analysis on DLD1 cells showed upregulation of tumor suppressors PTEN and FOXO3; leading to AKT downregulation and further induction of apoptosis, through upregulation of CDK inhibitors CDKN2B, CDKN2D. SM induced cell clumps had elevated hypoxia and mitochondrial membrane potential that led to adaptive responses like morphogenetic changes, migration and deregulated autophagy, when shifted to normal culture conditions. This can be exploited to understand the three-dimensional (3D) biology of cancer in the aspect of stress response. This study highlights the regulation of cell function and viability under microgravity through PTEN/FOXO3/AKT pathway.

In vitro three-dimensional development of mouse molar tooth germs in a rotary cell culture system

OBJECTIVE

In vitro tooth germ cultivation is an effective method to explore the mechanism of odontogenesis. The three-dimensional rotary cell culture system (RCCS) is typically used to culture simulated organs such as cartilage, skin, and bone. In this study, we established an in vitro tooth germ culture model using RCCS to investigate whether RCCS could provide an appropriate environment for tooth germ development in vitro.

METHODS

Mandibular first molar tooth germs from 1-day post-natal mice were cultured in RCCS for 3, 6, and 9 days. Tooth germ development was monitored via histology (hematoxylin & eosin staining), stereoscopic microscopy, and quantitative real-time PCR (RT-PCR).

RESULTS

Tooth germs cultured in RCCS maintained their typical spatial shape. Blood vessels were maintained on the dental follicle surface surrounding the crown. After cultivation, thick layers of dentin and enamel were secreted. Compared with tooth germs grown in jaw, the tooth germs grown in RCCS exhibited no significant difference in DMP1 or FGF10 expression at all time points.

CONCLUSIONS

Use of RCCS enhanced the development of tooth germs and allowed the tooth germs to maintain their spatial morphology. These results indicate that RCCS may be an effective culture system to investigate the mechanism of tooth development.

Microgravity assay of neuroblastoma: in vitro aggregation kinetics and organoid morphology correlate with MYCN expression

Neuroblastoma, the most common and deadly solid pediatric tumor, features genetic and biologic heterogeneity that defies simple risk assessments, drives diverse clinical behavior, and demands more extensive characterization. This research served to investigate the utility of a microgravity assay-rotary bioreactor culture-to evaluate and characterize the cell-specific, in vitro behavior of neuroblastoma cell lines: aggregation kinetics of single cells and the morphology of the formed structures, called organoids. Specifically, we examined the effect of amplification of the oncogene MYCN, a genetic factor that is strongly associated with poor clinical outcome. Three human neuroblastoma cell lines with varied MYCN expression (CHP-212 (unamplified), SK-N-AS (unamplified), IMR-32 (amplified)) were cultured in the microgravity rotary bioreactor. Simple aggregation kinetics were determined by periodically performing counts of non-aggregated single cells in the media. Organoids were harvested, stained with hematoxylin and eosin, and evaluated microscopically in terms of size and shape. The MYCN-amplified cell line (IMR32) aggregated much more rapidly than the unamplified cell lines, as indicated by a significantly lower area under its aggregation curve (single non-aggregated cells vs. time): IMR32=4.3, CHP-212 =12.4, SK-N-AS=9.8 (adhesion index ×10(5)). Further, the organoid morphology of the MYCN-amplified cell line was noticeably different compared to the unamplified lines. The CHP-212 and SK-N-AS cells formed spherical structures with average cross-sectional area 0.213 and 0.138 mm(2), respectively, and featured an outer viable zone of cells (average length of 0.175, 0.129 mm, respectively; the "diffusion distance"), surrounding an inner necrotic core. In contrast, the MYCN-amplified cell line formed a large single mass of cells but had a similar diffusion distance (0.175 mm). This microgravity assay provides a rapid, reproducible assessment of in vitro behavior of neuroblastoma, and the measured parameters, aggregation kinetics and organoid size and shape correlated with malignant potential in terms of MYCN amplification. This assay allows for the examination of cell-specific biologic and genetic factors that should provide valuable insight into the clinical behavior of neuroblastoma.

Simulated microgravity promotes nitric oxide-supported angiogenesis via the iNOS-cGMP-PKG pathway in macrovascular endothelial cells

Angiogenesis is a physiological process involving the growth of blood vessel in response to specific stimuli. The present study shows that limited microgravity treatments induce angiogenesis by activating macrovascular endothelial cells. Inhibition of nitric oxide production using pharmacological inhibitors and inducible nitric oxide synthase (iNOS) small interfering ribo nucleic acid (siRNA) abrogated microgravity induced nitric oxide production in macrovascular cells. The study further delineates that iNOS acts as a molecular switch for the heterogeneous effects of microgravity on macrovascular, endocardial and microvascular endothelial cells. Further dissection of nitric oxide downstream signaling confirms that simulated microgravity induces angiogenesis via the cyclic guanosine monophosphate (cGMP)-PKG dependent pathway.

Generation of a tumor spheroid in a microgravity environment as a 3D model of melanoma

An in vitro 3D model was developed utilizing a synthetic microgravity environment to facilitate studying the cell interactions. 2D monolayer cell culture models have been successfully used to understand various cellular reactions that occur in vivo. There are some limitations to the 2D model that are apparent when compared to cells grown in a 3D matrix. For example, some proteins that are not expressed in a 2D model are found up-regulated in the 3D matrix. In this paper, we discuss techniques used to develop the first known large, free-floating 3D tissue model used to establish tumor spheroids. The bioreactor system known as the High Aspect Ratio Vessel (HARVs) was used to provide a microgravity environment. The HARVs promoted aggregation of keratinocytes (HaCaT) that formed a construct that served as scaffolding for the growth of mouse melanoma. Although there is an emphasis on building a 3D model with the proper extracellular matrix and stroma, we were able to develop a model that excluded the use of matrigel. Immunohistochemistry and apoptosis assays provided evidence that this 3D model supports B16.F10 cell growth, proliferation, and synthesis of extracellular matrix. Immunofluorescence showed that melanoma cells interact with one another displaying observable cellular morphological changes. The goal of engineering a 3D tissue model is to collect new information about cancer development and develop new potential treatment regimens that can be translated to in vivo models while reducing the use of laboratory animals.

Production of a novel fibroblast-populated platelet matrix cocultured with keratinocytes

We have developed a new method for the production of a dermal matrix equivalent. Human platelets were used to dilute human fibroblasts. The platelet mix was placed in a cell culture well. Addition of 200 microL of a thrombin solution caused gel formation. Gels were overlaid with standard Iscove's growth medium supplemented with 10% fetal bovine serum, insulin, and N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid buffer. Medium was exchanged regularly. Keratinocytes were plated on top of selected gels and elevated to the air-liquid interface. The gels were harvested weekly, fixed, cut, and stained with hematoxylin and eosin stains and immunostains for collagens I, III, and IV and cytokeratins. Digital image analysis was used to quantitate collagen production. Growth factors, including transforming growth factor-beta (TGF-beta), platelet-derived growth factor, and vitamin C were added. Staining identified fibroblasts within the gels with a surrounding fibrous matrix. Immunostaining for cytokeratin identified keratinocytes on the gel surface. Immunostaining revealed the fibrous matrix to be composed of collagen I and III and some collagen IV. Digital image analysis demonstrated that greater TGF-beta concentration resulted in greater collagen production. These differences were statistically significant. With development of this construct, a viable dermal/epidermal replacement may be possible. TGF-beta enhances collagen production by fibroblasts in this matrix.

Cellular adaptations to hypoxia and acidosis during somatic evolution of breast cancer

Conceptual models of carcinogenesis typically consist of an evolutionary sequence of heritable changes in genes controlling proliferation, apoptosis, and senescence. We propose that these steps are necessary but not sufficient to produce invasive breast cancer because intraductal tumour growth is also constrained by hypoxia and acidosis that develop as cells proliferate into the lumen and away from the underlying vessels. This requires evolution of glycolytic and acid-resistant phenotypes that, we hypothesise, is critical for emergence of invasive cancer. Mathematical models demonstrate severe hypoxia and acidosis in regions of intraductal tumours more than 100 μm from the basement membrane. Subsequent evolution of glycolytic and acid-resistant phenotypes leads to invasive proliferation. Multicellular spheroids recapitulating ductal carcinoma in situ (DCIS) microenvironmental conditions demonstrate upregulated glucose transporter 1 (GLUT1) as adaptation to hypoxia followed by growth into normoxic regions in qualitative agreement with model predictions. Clinical specimens of DCIS exhibit periluminal distribution of GLUT-1 and Na⁺/H⁺ exchanger (NHE) indicating transcriptional activation by hypoxia and clusters of the same phenotype in the peripheral, presumably normoxic regions similar to the pattern predicted by the models and observed in spheroids. Upregulated GLUT-1 and NHE-1 were observed in microinvasive foci and adjacent intraductal cells. Adaptation to hypoxia and acidosis may represent key events in transition from in situ to invasive cancer.

Transplantation of engineered bone tissue using a rotary three-dimensional culture system

Bone is a complex, highly structured, mechanically active, three-dimensional (3-D) tissue composed of cellular and matrix elements. We previously published a report on in situ collagen gelation using a rotary 3-D culture system (CG-RC system) for the construction of large tissue specimens. The objective of the current study was to evaluate the feasibility of bone tissue engineering using our CG-RC system. Osteoblasts from the calvaria of newborn Wistar rats were cultured in the CG-RC system for up to 3 wk. The engineered 3-D tissues were implanted into the backs of nude mice and calvarial round bone defects in Wistar rats. Cell metabolic activity, mineralization, and bone-related proteins were measured in vitro in the engineered 3-D tissues. Also, the in vivo histological features of the transplanted, engineered 3-D tissues were evaluated in the animal models. We found that metabolic activity increased in the engineered 3-D tissues during cultivation, and that sufficient mineralization occurred during the 3 wk in the CG-RC system in vitro. One mo posttransplantation, the transplants to nude mice remained mineralized and were well invaded by host vasculature. Of particular interest, 2 mo posttransplantation, the transplants into the calvarial bone defects of rats were replaced by new mature bone. Thus, this study shows that large 3-D osseous tissue could be produced in vitro and that the engineered 3-D tissue had in vivo osteoinductive potential when transplanted into ectopic locations and into bone defects. Therefore, this system should be a useful model for bone tissue engineering.

Hindlimb unloading depresses corneal epithelial wound healing in mice

C57BL/6 mice were subjected to hindlimb unloading (HU) for a period of 3 wk to determine the possible effects on epithelial wound healing. A standardized corneal epithelial wound was performed, and parameters of the inflammatory response and reepithelialization were analyzed over an observation period of 96 h. Wound closure was significantly retarded in mice during HU with reepithelialization being delayed by ∼12 h. Both epithelial migration and cell division were significantly depressed and delayed. The inflammatory response to epithelial wounding was also significantly altered during HU. Neutrophils, as detected by the Gr-1 marker, were initially elevated above normal levels before wounding and during the first few hours afterward, but there was a significant reduction in neutrophil response to wounding at times where neutrophil influx and migration in controls were vigorous. A similar pattern was seen with CD11b+CD11c+ cells (monocyte lineage). Langerhans cells are normally resident within the peripheral corneal epithelium. They respond to injury by initially leaving the epithelial site within 6 h and returning to normal levels by 96 h, 2 days after reepithelialization is complete. During HU, this pattern is distinctly different, with Langerhans cell numbers slowly diminishing, reaching a nadir at 96 h, which is significantly below normal. Evidence for systemic effects of HU is provided by findings that collagen deposition within subcutaneous sponges was significantly reduced during HU. In conclusion, HU, a ground-based model simulating some physiological aspects of spaceflight, impairs wound repair of corneas. Multiple factors, both local and systemic, likely contribute to this delayed wound healing.

Clinorotation-induced weightlessness influences the cytoskeleton of glial cells in culture

During and after spaceflight astronauts experience neurophysiological alterations. To investigate if the impairment observed might be traced back to cytomorphology, we undertook a ground based research using a random positioning machine (clinostat) as a simulation method for microgravity. The outcome of the study was represented by cytoskeletal changes occurring in cultured glial cells (C(6) line) after 15 min, 30 min, 1 h, 20 h and 32 h under simulated microgravity. Glia is fundamental for brain function and it is essential for the normal health of the entire nervous system. Our data showed that after 30 min under simulated microgravity the cytoskeleton was damaged: microfilaments (F-actin) and intermediate filaments (Vimentin, Glial Fibrillary Acidic Proteins GFAP) were highly disorganised, microtubules (alpha-tubulin) lost their radial array, the overall cellular shape was deteriorated, and the nuclei showed altered chromatin condensations and DNA fragmentation. This feature got less dramatic after 20 h of simulated microgravity when glial cells appeared to reorganise their cytoskeleton and mitotic figures were present. The research was carried out by immunohistochemistry using antibodies to alpha-tubulin, vimentin and GFAP, and cytochemical labelling of F-actin (Phalloidin-TRIC). The nuclei were stained with propidium iodide or 4,6-diamidino-2-phenylindole dihydrochloride (DAPI). The cells were observed at the conventional and/or the confocal laser scanning microscope. Samples were also observed at the scanning electron microscope (SEM). Our data showed that in weightlessness alterations occur already visible at the scale of the single cell; if this may lead to the neurophysiological problems observed in flight is yet to be established.