Upregulation of miR-223 in the rat liver inhibits proliferation of hepatocytes under simulated microgravity

Molecular Mechanism of Microgravity-Induced Intestinal Flora Dysbiosis on the Abnormalities of Liver and Brain Metabolism

Space flight has many adverse effects on the physiological functions of astronauts. Certain similarities have been observed in some physiological processes of rodents and astronauts in space, although there are also differences. These similarities make rodents helpful models for initial investigations into space-induced physiological changes. This study uses a 3D-Clinostat to simulate microgravity and explores the role of microgravity in space flight-induced liver and brain abnormalities by comparing changes in the gut microbiota, serum metabolites, and the function and physiological biochemistry of liver and brain tissues between the simulated microgravity (SMG) group mice and the wild type (WT) group mice. The study, based on hematoxylin-eosin (HE) staining, 16S sequencing technology, and non-targeted metabolomics analysis, shows that the gut tissue morphology of the SMG group mice is abnormal, and the structure of the gut microbiota and the serum metabolite profile are imbalanced. Furthermore, using PICRUST 2 technology, we have predicted the functions of the gut microbiota and serum metabolites, and the results indicate that the liver metabolism and functions (including lipid metabolism, amino acid metabolism, and sugar metabolism, etc.) of the SMG group mice are disrupted, and the brain tissue metabolism and functions (including neurotransmitters and hormone secretion, etc.) are abnormal, suggesting a close relationship between microgravity and liver metabolic dysfunction and brain dysfunction. Additionally, the high similarity in the structure of the gut microbiota and serum metabolite profile between the fecal microbiota transplant (FMT) group mice and the SMG group mice, and the physiological and biochemical differences in liver and brain tissues compared to the WT group mice, suggest that microgravity induces imbalances in the gut microbiota, which in turn triggers abnormalities in liver and brain metabolism and function. Finally, through MetaMapp analysis and Pearson correlation analysis, we found that valeric acid, a metabolite of gut microbiota, is more likely to be the key metabolite that relates to microgravity-induced gut microbiota abnormalities, disorders of amino acid and lipid metabolism, and further induced metabolic or functional disorders in the liver and brain. This study has significant practical application value for deepening the understanding of the adaptability of living organisms in the space environment.

Apoptosis, Mitochondrial Autophagy, Fission, and Fusion Maintain Mitochondrial Homeostasis in Mouse Liver Under Tail Suspension Conditions

Microgravity can induce alterations in liver morphology, structure, and function, with mitochondria playing an important role in these changes. Tail suspension (TS) is a well-established model for simulating the effects of microgravity on muscles and bones, but its impact on liver function remains unclear. In the current study, we explored the regulatory mechanisms of apoptosis, autophagy, fission, and fusion in maintaining liver mitochondrial homeostasis in mice subjected to TS for 2 or 4 weeks (TS2 and TS4). The results showed the following: (1) No significant differences were observed in nuclear ultrastructure or DNA fragmentation between the control and TS-treated groups. (2) No significant differences were detected in the mitochondrial area ratio among the three groups. (3) Cysteine aspartic acid-specific protease 3 (Caspase3) activity and the Bcl-2-associated X protein (bax)/B-cell lymphoma-2 (bcl2) ratio were not higher in the TS2 and TS4 groups compared to the control group. (4) dynamin-related protein 1 (DRP1) protein expression was increased, while mitochondrial fission factor (MFF) protein levels were decreased in the TS2 and TS4 groups compared to the control, suggesting stable mitochondrial fission. (5) No significant differences were observed in the optic atrophy 1 (OPA1), mitofusin 1 and 2 (MFN1 and MFN2) protein expression levels across the three groups. (6) Mitochondrial autophagy vesicles were present in the TS2 and TS4 groups, with a significant increase in Parkin phosphorylation corresponding to the duration of the TS treatment. (7) ATP synthase and citrate synthase activities were significantly elevated in the TS2 group compared to the control group but were significantly reduced in the TS4 group compared to the TS2 group. In summary, the coordinated regulation of apoptosis, mitochondrial fission and fusion, and particularly mitochondrial autophagy preserved mitochondrial morphology and contributed to the restoration of the activities of these two key mitochondrial enzymes, thereby maintaining liver mitochondrial homeostasis in mice under TS conditions.

Influence of gut microbiome on metabolic diseases: a new perspective based on microgravity

Purpose

Microgravity, characterized by gravity levels of 10-3-10-6g, has been found to significantly impair various physiological systems in astronauts, including cardiovascular function, bone density, and metabolism. With the recent surge in human spaceflight, understanding the impact of microgravity on biological health has become paramount.

Methods

A comprehensive literature search was performed using the PubMed database to identify relevant publications pertaining to the interplay between gut microbiome, microgravity, space environment, and metabolic diseases.

Results

This comprehensive review primarily focuses on the progress made in investigating the gut microbiome and its association with metabolic diseases under microgravity conditions. Microgravity induces notable alterations in the composition, diversity, and functionality of the gut microbiome. These changes hold direct implications for metabolic disorders such as cardiovascular disease (CVD), bone metabolism disorders, energy metabolism dysregulation, liver dysfunction, and complications during pregnancy.

Conclusion

This novel perspective is crucial for preparing for deep space exploration and interstellar migration, where understanding the complex interplay between the gut microbiome and metabolic health becomes indispensable.

Simulated microgravity altered the gene expression profiles and inhibited the proliferation of Kupffer cells in the early phase by downregulating LMO2 and EZH2

Microgravity is a primary challenge that need to overcome, when human travel to space. Our study provided evidence that Kupffer cells (KCs) are sensitive to simulated microgravity (SMG), and no similar research report has been found in the literature. Using transcriptome sequencing technology, it was showed that 631 genes were upregulated and 801 genes were downregulated in KCs after treatment under SMG for 3 days. The GO analysis indicated that the proliferation of KCs was affected when exposed to SMG for 3 days. CCK-8 assay confirmed that the proliferation of KCs was inhibited in the third day under the environment of SMG. Furthermore, we identified 8 key genes that affect the proliferation of KCs and predicted 2 transcription factors (TFs) that regulate the 8 key genes. Significantly, we found that microgravity could affect the expression of LMO2 and EZH2 to reduce the transcription of Racgap1, Ccna2, Nek2, Aurka, Plk1, Haus4, Cdc20, Bub1b, which resulting in the reduction in KCs proliferation. These finding suggested that the inhibition of KCs proliferation under microgravity may influence the homeostasis of liver, and LMO2 and EZH2 can be the targets in management of KCs' disturbance in the future practice of space medicine.

Potential Roles of YAP/TAZ Mechanotransduction in Spaceflight-Induced Liver Dysfunction

Microgravity exposure during spaceflight causes the disordered regulation of liver function, presenting a specialized mechano-biological coupling process. While YAP/TAZ serves as a typical mechanosensitive pathway involved in hepatocyte metabolism, it remains unclear whether and how it is correlated with microgravity-induced liver dysfunction. Here, we discussed liver function alterations induced by spaceflight or simulated effects of microgravity on Earth. The roles of YAP/TAZ serving as a potential bridge in connecting liver metabolism with microgravity were specifically summarized. Existing evidence indicated that YAP/TAZ target gene expressions were affected by mechanotransductive pathways and phase separation, reasonably speculating that microgravity might regulate YAP/TAZ activation by disrupting these pathways via cytoskeletal remodeling or nuclear deformation, or disturbing condensates formation via diffusion limit, and then breaking liver homeostasis.

Hepatology in space: Effects of spaceflight and simulated microgravity on the liver

Microgravity as experienced during spaceflight affects a number of physiological processes in various organs. However, effects on the liver have yet been poorly documented. Nevertheless, the liver is a metabolically highly active organ involved in carbohydrate metabolism, lipid metabolism and xenobiotic biotransformation. The present paper provides an overview of the effects of microgravity on the liver observed in experimental animals during actual spaceflight and upon simulation of microgravity on Earth. These include (i) induction of liver injury and inflammation associated with apoptosis and oxidative stress, (ii) changes in liver carbohydrate metabolism resulting in the onset of a diabetogenic phenotype, (iii) modifications in hepatic lipid metabolism leading to early non-alcoholic fatty liver disease and (iv) alterations of the hepatic xenobiotic biotransformation machinery. Although most of these observations remain to be fully validated in humans, appropriate measures to counteract liver pathogenesis should be considered, especially in view of long-term space missions.

Evaluation of the Effects of Microgravity on Activated Primary Human Hepatic Stellate Cells

In recent years, research has been conducted to develop new medical treatments by simulating environments existing in space, such as zero-gravity. In this study, we evaluated the cell proliferation and gene expression of activated primary human hepatic stellate cells (HHSteCs) under simulated microgravity (SMG). Under SMG, cell proliferation was slower than in 1 G, and the evaluation of gene expression changes on day 1 of SMG by serial analysis of gene expression revealed the presence of Sirtuin, EIF2 signaling, hippo signaling, and epithelial adherence junction signaling. Moreover, reactive oxygen species were upregulated under SMG, and when N-acetyl-cystein was added, no difference in proliferation between SMG and 1 G was observed, suggesting that the oxidative stress generated by mitochondrial dysfunction caused a decrease in proliferation. Upstream regulators such as smad3, NFkB, and FN were activated, and cell-permeable inhibitors such as Ly294002 and U0126 were inhibited. Immunohistochemistry performed to evaluate cytoskeletal changes showed that more β-actin was localized in the cortical layer under SMG.

MiR-223 as a Regulator and Therapeutic Target in Liver Diseases

MicroRNAs (miRNAs) are endogenous non-coding single-stranded small molecule RNAs consisting of 20–24 nucleotides that are highly conserved in species evolution. Expression of miRNAs is strictly tissue-specific, and it is chronological in fungi and plants, as well as in animals. MiR-223 has been shown to play a key role in innate immunity, and dysregulation of its expression contributes to the pathogenesis of multiple inflammatory diseases, and cancers. In this article the biosynthesis and functions of miR-223 in innate immunity are reviewed, and the role of miR-223 in liver physiopathology and therapeutic prospects are highlighted.

Tail suspension delays ectopic ossification in proteoglycan-induced ankylosing spondylitis in mice via miR-103/DKK1

Ankylosing spondylitis (AS), characterized by inflammatory lesions and osteophyte formation, is a common immune rheumatic disease affecting the sacroiliac and axial joints. A high-intensity mechanical load is known to accelerate the heterotopic ossification associated with enthesitis in AS. Thus, the present study explored whether decreased mechanical load could delay the heterotopic ossification in AS. First, 24-week-old female BALB/c mice were induced with proteoglycan (PG) to establish an AS model. The AS-induced pathological and bone morphological changes of the sacroiliac joint were confirmed by hematoxylin and eosin staining and microCT analysis, respectively. Subsequently, the mice were treated with interventions of different mechanical loads. Using reverse transcription-quantitative PCR, it was revealed that expression levels of the osteogenesis-related genes bone morphogenetic protein-2, runt-related transcription factor 2 and osteocalcin were significantly reduced in sacroiliac bone tissue after intervention with a reduced mechanical load. The level of mechanosensory microRNA (miR)-103 increased in response to reduced mechanical loads. Consistently, in groups with reduced mechanical load, proteins with mechanical functions, including ρ-associated coiled-coil-containing protein kinase 1 (ROCK1), phosphorylated (p)-Erk1/2 and β-catenin, were reduced compared with the PG control. A dual-luciferase assay verified that miR-103 binds to the 3'-untranslated region end of Rock1 mRNA, thus negatively regulating the activity of Rock1 and affecting pathological ossification during AS. However, immunohistochemical staining indicated that the expression of dickkopf Wnt signaling pathway inhibitor 1, an inhibitor of the Wnt/β-catenin pathway, was increased in sacroiliac tissues. The results indicated that tail suspension decreased the mechanical load, thus reducing the bone formation in AS mice. Furthermore, tail suspension could inhibit the activation of mechanical kinase ROCK1 and p-Erk1/2 in the MAPK signaling pathway by upregulating miR-103, thereby inhibiting the classical osteogenesis-related Wnt/β-catenin pathway in AS. In summary, the present study uncovered the ameliorative effect of suspension on AS and its therapeutic potential for AS.

Next-generation sequencing analysis of circulating micro-RNA expression in response to parabolic flight as a spaceflight analogue

Understanding physiologic reactions to weightlessness is an indispensable requirement for safe human space missions. This study aims to analyse changes in the expression of circulating miRNAs following exposure to gravitational changes. Eight healthy volunteers (age: 24.5 years, male: 4, female: 4) were included. Each subject underwent 31 short-term phases of weightlessness and hypergravity induced by parabolic flight as a spaceflight analogue. At baseline, 1 and 24 h after parabolic flight, venous blood was withdrawn. Analysis of circulating miRNAs in serum was conducted by means of next generation sequencing. In total, 213 miRNAs were robustly detected (TPM > 5) by small RNA sequencing in all 24 samples. Four miRNAs evidenced a significant change in expression after adjusting for multiple testing. Only miR-223-3p showed a consistent significant decrease 24 h after parabolic flight compared to baseline values and values at 1 h after parabolic flight. miR-941 and miR-24-3p showed a significant decrease 24 h after parabolic flight compared to 1 h after parabolic flight but not to baseline values. miR-486-5p showed a significant increase 24 h after parabolic flight compared to 1 h after parabolic flight but not to baseline values. A target network analysis identified genes of the p53 signaling pathway and the cell cycle highly enriched among the targets of the four microRNAs. Our findings suggest cellular adaption to gravitational changes at the post-transcriptional level. Based on our results, we suggest a change in cell cycle regulation as potential explanation for adaptational changes observed in space missions.

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.

Progress in research of digestive system trauma and stress injury under microgravity environment

The last two decades have witnessed the rapid develop-ment of China's manned spaceflight industry. Studies have showed that the weightlessness environment has a series of adverse effects on the human body. Due to the complexity of the structure and function of the digestive system, the impact of weightlessness on the digestive system has certain particularity. How to ensure the steady state of the digestive system during astronaut's space mission and in the training under simulated weightlessness needs to be studied urgently. This review focuses on the progress in the research of digestive system trauma, stress injury, and repair under microgravity environment.

A microRNA signature and TGF-β1 response were identified as the key master regulators for spaceflight response

Translating fundamental biological discoveries from NASA Space Biology program into health risk from space flights has been an ongoing challenge. We propose to use NASA GeneLab database to gain new knowledge on potential systemic responses to space. Unbiased systems biology analysis of transcriptomic data from seven different rodent datasets reveals for the first time the existence of potential “master regulators” coordinating a systemic response to microgravity and/or space radiation with TGF-β1 being the most common regulator. We hypothesized the space environment leads to the release of biomolecules circulating inside the blood stream. Through datamining we identified 13 candidate microRNAs (miRNA) which are common in all studies and directly interact with TGF-β1 that can be potential circulating factors impacting space biology. This study exemplifies the utility of the GeneLab data repository to aid in the process of performing novel hypothesis–based research.