Muscle Atrophy Marker Expression Differs between Rotary Cell Culture System and Animal Studies

Identifying the potential therapeutic effects of miR‑6516 on muscle disuse atrophy

Muscle atrophy is a debilitating condition with various causes; while aging is one of these causes, reduced engagement in routine muscle‑strengthening activities also markedly contributes to muscle loss. Although extensive research has been conducted on microRNAs (miRNAs/miRs) and their associations with muscle atrophy, the roles played by miRNA precursors remain underexplored. The present study detected the upregulation of the miR‑206 precursor in cell‑free (cf)RNA from the plasma of patients at risk of sarcopenia, and in cfRNAs from the muscles of mice subjected to muscle atrophy. Additionally, a decline in the levels of the miR‑6516 precursor was observed in mice with muscle atrophy. The administration of mimic‑miR‑6516 to mice immobilized due to injury inhibited muscle atrophy by targeting and inhibiting cyclin‑dependent kinase inhibitor 1b (Cdkn1b). Based on these results, the miR‑206 precursor appears to be a potential biomarker of muscle atrophy, whereas miR‑6516 shows promise as a therapeutic target to alleviate muscle deterioration in patients with muscle disuse and atrophy.

Technology using simulated microgravity

The human body experiences constant stimulation from Earth's gravity, and the absence of gravity leads to various impacts at the cellular and tissue levels. Simulated microgravity (s-μg) has been employed on Earth to investigate these effects, circumventing the challenges of conducting experiments in space and providing an opportunity to understand the influence of microgravity on living organisms. Research focusing on stem cells and utilizing s-μg has enhanced our understanding of how microgravity affects stem cell morphology, migration, proliferation, and differentiation. Studies have used systems such as rotating wall vessels, random positioning machines, and clinostats. By uncovering the mechanisms underlying the observed changes in these studies, there is potential to identify therapeutic targets that regulate stem cell function and explore a range of applications, including stem cell-based regenerative medicine. This review will focus on the features of each device designed to simulate microgravity on Earth, as well as the stem cell experiments performed with those devices.

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.

Long-term human spaceflight and inflammaging: Does it promote aging?

Spaceflight and its associated stressors, such as microgravity, radiation exposure, confinement, circadian derailment and disruptive workloads represent an unprecedented type of exposome that is entirely novel from an evolutionary stand point. Within this perspective, we aimed to review the effects of prolonged spaceflight on immune-neuroendocrine systems, brain and brain-gut axis, cardiovascular system and musculoskeletal apparatus, highlighting in particular the similarities with an accelerated aging process. In particular, spaceflight-induced muscle atrophy/sarcopenia and bone loss, vascular and metabolic changes, hyper and hypo reaction of innate and adaptive immune system appear to be modifications shared with the aging process. Most of these modifications are mediated by molecular events that include oxidative and mitochondrial stress, autophagy, DNA damage repair and telomere length alteration, among others, which directly or indirectly converge on the activation of an inflammatory response. According to the inflammaging theory of aging, such an inflammatory response could be a driver of an acceleration of the normal, physiological rate of aging and it is likely that all the systemic modifications in turn lead to an increase of inflammaging in a sort of vicious cycle. The most updated countermeasures to fight these modifications will be also discussed in the light of their possible application not only for astronauts' benefit, but also for older adults on the ground.

Effects of Low Doses of L-Carnitine Tartrate and Lipid Multi-Particulate Formulated Creatine Monohydrate on Muscle Protein Synthesis in Myoblasts and Bioavailability in Humans and Rodents

The primary objective of this study was to investigate the potential synergy between low doses of L-carnitine tartrate and creatine monohydrate to induce muscle protein synthesis and anabolic pathway activation in primary human myoblasts. In addition, the effects of Lipid multi-particulates (LMP) formulation on creatine stability and bioavailability were assessed in rodents and healthy human subjects. When used individually, L-carnitine tartrate at 50 µM and creatine monohydrate at 0.5 µM did not affect myoblast protein synthesis and signaling. However, when combined, they led to a significant increase in protein synthesis. Increased AKT and RPS6 phosphorylation were observed with 50 µM L-carnitine tartrate 5 µM creatine in combination in primary human myoblasts. When Wistar rats were administered creatine with LMP formulation at either 21 or 51 mg/kg, bioavailability was increased by 27% based on the increase in the area under the curve (AUC) at a 51 mg/kg dose compared to without LMP formulation. Tmax and Cmax were unchanged. Finally, in human subjects, a combination of LMP formulated L-carnitine at 500 mg (from L-carnitine tartrate) with LMP formulated creatine at 100, 200, or 500 mg revealed a significant and dose-dependent increase in plasma creatine concentrations. Serum total L-carnitine levels rose in a similar manner in the three combinations. These results suggest that a combination of low doses of L-carnitine tartrate and creatine monohydrate may lead to a significant and synergistic enhancement of muscle protein synthesis and activation of anabolic signaling. In addition, the LMP formulation of creatine improved its bioavailability. L-carnitine at 500 mg and LMP-formulated creatine at 200 or 500 mg may be useful for future clinical trials to evaluate the effects on muscle protein synthesis.

Update on the effects of microgravity on the musculoskeletal system

With the reignited push for manned spaceflight and the development of companies focused on commercializing spaceflight, increased human ventures into space are inevitable. However, this venture would not be without risk. The lower gravitational force, known as microgravity, that would be experienced during spaceflight significantly disrupts many physiological systems. One of the most notably affected systems is the musculoskeletal system, where exposure to microgravity causes both bone and skeletal muscle loss, both of which have significant clinical implications. In this review, we focus on recent advancements in our understanding of how exposure to microgravity affects the musculoskeletal system. We will focus on the catabolic effects microgravity exposure has on both bone and skeletal muscle cells, as well as their respective progenitor stem cells. Additionally, we report on the mechanisms that underlie bone and muscle tissue loss resulting from exposure to microgravity and then discuss current countermeasures being evaluated. We reveal the gaps in the current knowledge and expound upon how current research is filling these gaps while also identifying new avenues of study as we continue to pursue manned spaceflight.

Artificial tissue creation under microgravity conditions: Considerations and future applications

Traditional tissue engineering methods often fail to promote robust cell growth and differentiation, limiting the development of functioning tissues. However, the microgravity conditions created by rotating wall vessel bioreactors minimize shear stress and unload the gravitational force usually placed on cells. In a microgravity environment, cell proliferation, cell differentiation, and the 3D organization of cells are altered, potentially encouraging the formation of more biosimilar artificial tissues for certain cell types. Additionally, cells in these engineered tissues display lowered immunogenicity, pointing to the transplantation potential of tissues engineered in microgravity conditions. However, these benefits are not consistent across all cell types, and the long-term impact of microgravity on tissue development and stability remains an unanswered question. Even so, there is potential that with further research, microgravity tissue engineering will have productive clinical applications for medical and pharmaceutical purposes.

Dragon's Blood Regulates Rac1-WAVE2-Arp2/3 Signaling Pathway to Protect Rat Intestinal Epithelial Barrier Dysfunction Induced by Simulated Microgravity

Dragon’s Blood is a red resin from Dracaena cochinchinensis (Lour.) S.C. Chen (Yunnan, China). As a traditional Chinese medicinal herb, it has shown protective effects on intestinal disorders. Microgravity could alter intestinal homeostasis. However, the potential herbal drugs for preventing intestine epithelial barrier (IEB) dysfunction under microgravity are not available. This study aimed to investigate the effects of Dragon’s Blood (DB) on microgravity-induced IEB injury and explore its underlying mechanism. A rat tail-suspension model was used to simulate microgravity (SMG). Histomorphology, ultrastructure, permeability, and expression of junction proteins in jejunum, ileum, and colon of SMG rats were determined. Proteomic analysis was used to identify differentially expressed proteins (DEPs) in rat ileum mucosa altered by DB. The potential mechanism of DB to protect IEB dysfunction was validated by western blotting. The effects of several components in DB were evaluated in SMG-treated Caco-2 cells. DB protected against IEB disruption by repairing microvilli and crypts, inhibiting inflammatory factors, lowering the permeability and upregulating the expression of tight and adherens junction proteins in the ileum of SMG rats. Proteomic analysis showed that DB regulated 1080 DEPs in rat ileum mucosa. DEPs were significantly annotated in cell–cell adhesion, focal adhesion, and cytoskeleton regulation. DB increased the expression of Rac1-WAVE2-Arp2/3 pathway proteins and F-actin to G-actin ratio, which promoted the formation of focal adhesions. Loureirin C in DB showed a protective effect on epithelial barrier injury in SMG-treated Caco-2 cells. DB could protect against IEB dysfunction induced by SMG, and its mechanism is associated with the formation of focal adhesions mediated by the Rac1-WAVE2-Arp2/3 pathway, which benefits intestinal epithelial cell migration and barrier repair.

Studies on host-foodborne bacteria in intestinal three-dimensional cell culture model indicate possible mechanisms of interaction

Spheroids of intestinal cells (Caco-2) were used to evaluate the adhesion/invasion ability of Listeria monocytogenes (pathogen) and Lactobacillus sakei 1 (potential probiotic). Besides, transcriptomic analyses of Caco-2 cells in three dimensional cultures were done, with the aim of revealing possible host-foodborne bacteria interactions. Result of adhesion assay for L. monocytogenes in Caco-2 spheroids was 22.86 ± 0.33%, but it was stimulated in acidic pH (4.5) and by the presence of 2% sucrose (respectively, 32.56 ± 1.35% and 33.25 ± 1.26%). Conversely, the invasion rate of L. monocytogenes was lower at pH 4.5, in comparison with non-stressed controls (18.89 ± 1.05% and 58.65 ± 0.30%, respectively). L. sakei 1 adhered to Caco-2 tridimensional cell culture (27.30 ± 2.64%), with no invasiveness. There were 19 and 21 genes down and upregulated, respectively, in tridimensional Caco-2 cells, upon infection with L. monocytogenes, which involved immunity, apoptosis; cytoprotective responses, cell signalling-regulatory pathways. It was evidenced despite activation or deactivation of several pathways in intestinal cells to counteract infection, the pathogen was able to hijack many host defense mechanisms. On the other hand, the probiotic candidate L. sakei 1 was correlated with decreased transcription of two genes in Caco-2 cells, though it stimulated the expression of 14 others, with diverse roles in immunity, apoptosis, cytoprotective response and cell signalling-regulatory pathways. Our data suggest the use of tridimensional cell culture to mimic the intestinal epithelium is a good model for gathering broad information on the putative mechanisms of interaction between host and bacteria of importance for food safety, which can serve as a basis for further in-depth investigation.

Silkworm Silk Fiber Bundles as Improved In Vitro Scaffolds for Skeletal Muscle

To mimic skeletal muscle tissues in vitro, native and transgenic spider silk/silkworm silks were seeded with C2C12 myoblasts to observe if these three-dimensional substrates are preferable to a traditional two-dimensional polystyrene cell culture surface. Silks were wound around an acrylic chassis to produce a novel, three-dimensional cell culture device with suspended muscle fibers that genetically and morphologically resemble native skeletal muscle tissue. The transgenic spider silk/silkworm silk has never before been studied for this application. Genetic expression verified skeletal muscle lineage and differentiation, while fluorescent imaging verified contractile protein synthesis. Genetic analysis also revealed an increase in expression of the Myh2 contractile protein gene on silkworm silks, particularly on the transgenic silk. Mechanical properties and protein secondary structure content of the silks indicated correlation between substrate properties and Myh2 gene expression. This increase in contractile protein gene expression suggests that biologically derived silk substrates that are suspended may be a preferable substrate for in vitro muscle modeling because of the proteinaceous character and mechanical flexibility of the silk.