Comparison of Microgravity Analogs to Spaceflight in Studies of Plant Growth and Development

Gravitational Influence on Human Living Systems and the Evolution of Species on Earth

Gravity constituted the only constant environmental parameter, during the evolutionary period of living matter on Earth. However, whether gravity has affected the evolution of species, and its impact is still ongoing. The topic has not been investigated in depth, as this would require frequent and long-term experimentations in space or an environment of altered gravity. In addition, each organism should be studied throughout numerous generations to determine the profound biological changes in evolution. Here, we review the significant abnormalities presented in the cardiovascular, immune, vestibular and musculoskeletal systems, due to altered gravity conditions. We also review the impact that gravity played in the anatomy of snakes and amphibians, during their evolution. Overall, it appears that gravity does not only curve the space–time continuum but the biological continuum, as well.

Module to Support Real-Time Microscopic Imaging of Living Organisms on Ground-Based Microgravity Analogs

Since opportunities for spaceflight experiments are scarce, ground-based microgravity simulation devices (MSDs) offer accessible and economical alternatives for gravitational biology studies. Among the MSDs, the random positioning machine (RPM) provides simulated microgravity conditions on the ground by randomizing rotating biological samples in two axes to distribute the Earth’s gravity vector in all directions over time. Real-time microscopy and image acquisition during microgravity simulation are of particular interest to enable the study of how basic cell functions, such as division, migration, and proliferation, progress under altered gravity conditions. However, these capabilities have been difficult to implement due to the constantly moving frames of the RPM as well as mechanical noise. Therefore, we developed an image acquisition module that can be mounted on an RPM to capture live images over time while the specimen is in the simulated microgravity (SMG) environment. This module integrates a digital microscope with a magnification range of 20× to 700×, a high-speed data transmission adaptor for the wireless streaming of time-lapse images, and a backlight illuminator to view the sample under brightfield and darkfield modes. With this module, we successfully demonstrated the real-time imaging of human cells cultured on an RPM in brightfield, lasting up to 80 h, and also visualized them in green fluorescent channel. This module was successful in monitoring cell morphology and in quantifying the rate of cell division, cell migration, and wound healing in SMG. It can be easily modified to study the response of other biological specimens to SMG.

The Emerging Role of Macrophages in Immune System Dysfunction under Real and Simulated Microgravity Conditions

In the process of exploring space, the astronaut's body undergoes a series of physiological changes. At the level of cellular behavior, microgravity causes significant alterations, including bone loss, muscle atrophy, and cardiovascular deconditioning. At the level of gene expression, microgravity changes the expression of cytokines in many physiological processes, such as cell immunity, proliferation, and differentiation. At the level of signaling pathways, the mitogen-activated protein kinase (MAPK) signaling pathway participates in microgravity-induced immune malfunction. However, the mechanisms of these changes have not been fully elucidated. Recent studies suggest that the malfunction of macrophages is an important breakthrough for immune disorders in microgravity. As the first line of immune defense, macrophages play an essential role in maintaining homeostasis. They activate specific immune responses and participate in large numbers of physiological activities by presenting antigen and secreting cytokines. The purpose of this review is to summarize recent advances on the dysfunction of macrophages arisen from microgravity and to discuss the mechanisms of these abnormal responses. Hopefully, our work will contribute not only to the future exploration on the immune system in space, but also to the development of preventive and therapeutic drugs against the physiological consequences of spaceflight.

Network Analysis of Gene Transcriptions of Arabidopsis thaliana in Spaceflight Microgravity

The transcriptomic datasets of the plant model organism Arabidopsis thaliana grown in the International Space Station provided by GeneLab have been mined to isolate the impact of spaceflight microgravity on gene expressions related to root growth. A set of computational tools is used to identify the hub genes that respond differently in spaceflight with controlled lighting compared to on the ground. These computational tools based on graph-theoretic approaches are used to infer gene regulatory networks from the transcriptomic datasets. The three main algorithms used for network analyses are Least Absolute Shrinkage and Selection Operator (LASSO), Pearson correlation, and the Hyperlink-Induced Topic Search (HITS) algorithm. Graph-based spectral analyses reveal distinct properties of the spaceflight microgravity networks for the Wassilewskija (WS), Columbia (Col)-0, and mutant phytochromeD (phyD) ecotypes. The set of hub genes that are significantly altered in spaceflight microgravity are mainly involved in cell wall synthesis, protein transport, response to auxin, stress responses, and catabolic processes. Network analysis highlights five important root growth-regulating hub genes that have the highest outdegree distribution in spaceflight microgravity networks. These concerned genes coding for proteins are identified from the Gene Regulatory Networks (GRNs) corresponding to spaceflight total light environment. Furthermore, network analysis uncovers genes that encode nucleotide-diphospho-sugar interconversion enzymes that have higher transcriptional regulation in spaceflight microgravity and are involved in cell wall biosynthesis.

Immunity in Space: Prokaryote Adaptations and Immune Response in Microgravity

Immune dysfunction has long been reported by medical professionals regarding astronauts suffering from opportunistic infections both during their time in space and a short period afterwards once back on Earth. Various species of prokaryotes onboard these space missions or cultured in a microgravity analogue exhibit increased virulence, enhanced formation of biofilms, and in some cases develop specific resistance for specific antibiotics. This poses a substantial health hazard to the astronauts confined in constant proximity to any present bacterial pathogens on long space missions with a finite number of resources including antibiotics. Furthermore, some bacteria cultured in microgravity develop phenotypes not seen in Earth gravity conditions, providing novel insights into bacterial evolution and avenues for research. Immune dysfunction caused by exposure to microgravity may increase the chance of bacterial infection. Immune cell stimulation, toll-like receptors and pathogen-associated molecular patterns can all be altered in microgravity and affect immunological crosstalk and response. Production of interleukins and other cytokines can also be altered leading to immune dysfunction when responding to bacterial infection. Stem cell differentiation and immune cell activation and proliferation can also be impaired and altered by the microgravity environment once more adding to immune dysfunction in microgravity. This review elaborates on and contextualises these findings relating to how bacteria can adapt to microgravity and how the immune system subsequently responds to infection.

Root Tropisms: New Insights Leading the Growth Direction of the Hidden Half

Tropisms are essential responses of plants, orienting growth according to a wide range of stimuli. Recently, considerable attention has been paid to root tropisms, not only to improve cultivation systems, such as those developed for plant-based life support systems for future space programs, but also to increase the efficiency of root apparatus in water and nutrient uptake in crops on Earth. To date, the Cholodny–Went theory of differential auxin distribution remains the principal tropistic mechanism, but recent findings suggest that it is not generally applicable to all root tropisms, and new molecular pathways are under discussion. Therefore, an in-depth understanding of the mechanisms and functions underlying root tropisms is needed. Contributions to this special issue aimed to embrace reviews and research articles that deepen molecular, physiological, and anatomical processes orchestrating root tropisms from perception of the stimulus to bending. The new insights will help in elucidating plant–environment interactions, providing potential applications to improve plant growth on Earth and in space where microgravity diminishes or nullifies the gravitropism dominance.

Advantages and Limitations of Current Microgravity Platforms for Space Biology Research

Human Space exploration has created new challenges and new opportunities for science. Reaching beyond the Earth’s surface has raised the issue of the importance of gravity for the development and the physiology of biological systems, while giving scientists the tools to study the mechanisms of response and adaptation to the microgravity environment. As life has evolved under the constant influence of gravity, gravity affects biological systems at a very fundamental level. Owing to limited access to spaceflight platforms, scientists rely heavily on on-ground facilities that reproduce, to a different extent, microgravity or its effects. However, the technical constraints of counterbalancing the gravitational force on Earth add complexity to data interpretation. In-flight experiments are also not without their challenges, including additional stressors, such as cosmic radiation and lack of convection. It is thus extremely important in Space biology to design experiments in a way that maximizes the scientific return and takes into consideration all the variables of the chosen setup, both on-ground or on orbit. This review provides a critical analysis of current ground-based and spaceflight facilities. In particular, the focus was given to experimental design to offer the reader the tools to select the appropriate setup and to appropriately interpret the results.

Fundamental Biological Features of Spaceflight: Advancing the Field to Enable Deep-Space Exploration

Research on astronaut health and model organisms have revealed six features of spaceflight biology that guide our current understanding of fundamental molecular changes that occur during space travel. The features include oxidative stress, DNA damage, mitochondrial dysregulation, epigenetic changes (including gene regulation), telomere length alterations, and microbiome shifts. Here we review the known hazards of human spaceflight, how spaceflight affects living systems through these six fundamental features, and the associated health risks of space exploration. We also discuss the essential issues related to the health and safety of astronauts involved in future missions, especially planned long-duration and Martian missions.

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.