Theoretical modeling of mechanical homeostasis of a mammalian cell under gravity-directed vector

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.

Microgravity and space radiation inhibit autophagy in human capillary endothelial cells, through either opposite or synergistic effects on specific molecular pathways

Microgravity and space radiation (SR) are two highly influential factors affecting humans in space flight (SF). Many health problems reported by astronauts derive from endothelial dysfunction and impaired homeostasis. Here, we describe the adaptive response of human, capillary endothelial cells to SF. Reference samples on the ground and at 1g onboard permitted discrimination between the contribution of microgravity and SR within the combined responses to SF. Cell softening and reduced motility occurred in SF cells, with a loss of actin stress fibers and a broader distribution of microtubules and intermediate filaments within the cytoplasm than in control cells. Furthermore, in space the number of primary cilia per cell increased and DNA repair mechanisms were found to be activated. Transcriptomics revealed the opposing effects of microgravity from SR for specific molecular pathways: SR, unlike microgravity, stimulated pathways for endothelial activation, such as hypoxia and inflammation, DNA repair and apoptosis, inhibiting autophagic flux and promoting an aged-like phenotype. Conversely, microgravity, unlike SR, activated pathways for metabolism and a pro-proliferative phenotype. Therefore, we suggest microgravity and SR should be considered separately to tailor effective countermeasures to protect astronauts' health.

Differential Contributions of Actin and Myosin to the Physical Phenotypes and Invasion of Pancreatic Cancer Cells

INTRODUCTION

Metastasis is a fundamentally physical process in which cells deform through narrow gaps and generate forces to invade surrounding tissues. While it is commonly thought that increased cell deformability is an advantage for invading cells, we previously found that more invasive pancreatic ductal adenocarcinoma (PDAC) cells are stiffer than less invasive PDAC cells. Here we investigate potential mechanisms of the simultaneous increase in PDAC cell stiffness and invasion, focusing on the contributions of myosin II, Arp2/3, and formins.

METHOD

We measure cell invasion using a 3D scratch wound invasion assay and cell stiffness using atomic force microscopy (AFM). To determine the effects of actin- and myosin-mediated force generation on cell stiffness and invasion, we treat cells with pharmacologic inhibitors of myosin II (blebbistatin), Arp2/3 (CK-666), and formins (SMIFH2).

RESULTS

We find that the activity of myosin II, Arp2/3, and formins all contribute to the stiffness of PDAC cells. Interestingly, we find that the invasion of PDAC cell lines is differentially affected when the activity of myosin II, Arp2/3, or formins is inhibited, suggesting that despite having similar tissue origins, different PDAC cell lines may rely on different mechanisms for invasion.

CONCLUSIONS

These findings deepen our knowledge of the factors that regulate cancer cell mechanotype and invasion, and incite further studies to develop therapeutics that target multiple mechanisms of invasion for improved clinical benefit.

Flow-enhanced priming of hESCs through H2B acetylation and chromatin decondensation

BACKGROUND

Distinct mechanical stimuli are known to manipulate the behaviors of embryonic stem cells (ESCs). Fundamental rationale of how ESCs respond to mechanical forces and the potential biological effects remain elusive. Here we conducted the mechanobiological study for hESCs upon mechanomics analysis to unravel typical mechanosensitive processes on hESC-specific fluid shear.

METHODS

hESC line H1 was subjected to systematically varied shear flow, and mechanosensitive proteins were obtained by mass spectrometry (MS) analysis. Then, function enrichment analysis was performed to identify the enriched gene sets. Under a steady shear flow of 1.1 Pa for 24 h, protein expressions were further detected using western blotting (WB), quantitative real-time PCR (qPCR), and immunofluorescence (IF) staining. Meanwhile, the cells were treated with 200 nM trichostatin (TSA) for 1 h as positive control to test chromatin decondensation. Actin, DNA, and RNA were then visualized with TRITC-labeled phalloidin, Hoechst 33342, and SYTO® RNASelect™ green fluorescent cell stain (Life Technologies), respectively. In addition, cell stiffness was determined with atomic force microscopy (AFM) and annexin V-PE was used to determine the apoptosis with a flow cytometer (FCM).

RESULTS

Typical mechanosensitive proteins were unraveled upon mechanomics analysis under fluid shear related to hESCs in vivo. Functional analyses revealed significant alterations in histone acetylation, nuclear size, and cytoskeleton for hESC under shear flow. Shear flow was able to induce H2B acetylation and nuclear spreading by CFL2/F-actin cytoskeletal reorganization. The resulting chromatin decondensation and a larger nucleus readily accommodate signaling molecules and transcription factors.

CONCLUSIONS

Shear flow regulated chromatin dynamics in hESCs via cytoskeleton and nucleus alterations and consolidated their primed state.

Mechanical Point Loading Induces Cortex Stiffening and Actin Reorganization

Global cytoskeleton reorganization is well-recognized when cells are exposed to distinct mechanical stimuli, but the localized responses at a specified region of a cell are still unclear. In this work, we mapped the cell-surface mechanical property of single cells in situ before and after static point loading these cells using atomic force microscopy in PeakForce-Quantitative Nano Mechanics mode. Cell-surface stiffness was elevated at a maximum of 1.35-fold at the vicinity of loading site, indicating an enhanced structural protection of the cortex to the cell. Mechanical modeling also elucidated the structural protection from the stiffened cell cortex, in which 9-15% and 10-19% decrease of maximum stress and strain of the nucleus were obtained. Furthermore, the flat-ended atomic force microscopy probes were used to capture cytoskeleton reorganization after point loading quantitatively, revealing that the larger the applied force and the longer the loading time are, the more pronounced cytoskeleton reorganization is. Also, point loading using a microneedle combined with real-time confocal microscopy uncovered the fast dynamics of actin cytoskeleton reorganization for actin-stained live cells after point loading (<10 s). These results furthered the understandings in the transmission of localized mechanical forces into an adherent cell.

Cells´ Flow and Immune Cell Priming under alternating g-forces in Parabolic Flight

Gravitational stress in general and microgravity (µg) in particular are regarded as major stress factors responsible for immune system dysfunction in space. To assess the effects of alternating µg and hypergravity (hyper-g) on immune cells, the attachment of peripheral blood mononuclear cells (PBMCs) to adhesion molecules under flow conditions and the antigen-induced immune activation in whole blood were investigated in parabolic flight (PF). In contrast to hyper-g (1.8 g) and control conditions (1 g), flow and rolling speed of PBMCs were moderately accelerated during µg-periods which were accompanied by a clear reduction in rolling rate. Whole blood analyses revealed a "primed" state of monocytes after PF with potentiated antigen-induced pro-inflammatory cytokine responses. At the same time, concentrations of anti-inflammatory cytokines were increased and monocytes displayed a surface molecule pattern that indicated immunosuppression. The results suggest an immunologic counterbalance to avoid disproportionate immune responses. Understanding the interrelation of immune system impairing and enhancing effects under different gravitational conditions may support the design of countermeasures to mitigate immune deficiencies in space.

An integration design of gas exchange, bubble separation, and flow control in a space cell culture system on board the SJ-10 satellite

Pathophysiological changes of astronauts under space microgravity involve complex factors and require an integrative perspective to fully understand the mechanisms. The readouts from space cell biology experiments strongly depend on the hardware and especially the cell bioreactor that is used in distinct spacecraft. Herein, a specialized cell culture bioreactor is designed for culturing mammalian cells on board the SJ-10 satellite. This hardware focuses mainly on satisfying the requirements of gas exchange, bubble separation, and flow control, as well as their functional and structural integration on cell culture within the technical and environmental constraints of the spacecraft platform under microgravity. A passive bubble separator is constructed and is connected in series to an individual cell culture chamber to remove the bubbles that were produced in orbit during cell growth. A moderate flow rate is preset to provide sufficient mass transfer and low shear stress in a well-designed flow circuit. Together with other modules of temperature control, in situ microscopic imaging, and online imaging acquisition, this novel space cell culture system is successfully used to culture human endothelial cells and rat bone marrow-derived mesenchymal stem cells in the SJ-10 mission. The advantages and shortcomings of the integration design are discussed for this type of the hardware.

Microgravity-induced hepatogenic differentiation of rBMSCs on board the SJ-10 satellite

Bone marrow-derived mesenchymal stem cells (BMSCs) are able to differentiate into functional hepatocytelike cells, which are expected to serve as a potential cell source in regenerative medicine, tissue engineering, and clinical treatment of liver injury. Little is known about whether and how space microgravity is able to direct the hepatogenic differentiation of BMSCs in the actual space microenvironment. In this study, we examined the effects of space microgravity on BMSC hepatogenic differentiation on board the SJ-10 Recoverable Scientific Satellite. Rat BMSCs were cultured and induced in hepatogenic induction medium for 3 and 10 d in custom-made space cell culture hardware. Cell growth was monitored periodically in orbit, and the fixed cells and collected supernatants were retrieved back to the Earth for further analyses. Data indicated that space microgravity improves the differentiating capability of the cells by up-regulating hepatocyte-specific albumin and cytokeratin 18. The resulting cells tended to be maturated, with an in-orbit period of up to 10 d. In space, mechanosensitive molecules of β1-integrin, β-actin, α-tubulin, and Ras homolog gene family member A presented enhanced expression, whereas those of cell-surface glycoprotein CD44, intercellular adhesion molecule 1, vascular cell adhesion molecule 1, vinculin, cell division control protein 42 homolog, and Rho-associated coiled-coil kinase yielded reduced expression. Also observed in space were the depolymerization of actin filaments and the accumulation of microtubules and vimentin through the altered expression and location of focal adhesion complexes, Rho guanosine 5'-triphosphatases, as well as the enhanced exosome-mediated mRNA transfer. This work furthers the understanding of the underlying mechanisms of space microgravity in directing hepatogenic differentiation of BMSCs.-Lü, D., Sun, S., Zhang, F., Luo, C., Zheng, L., Wu, Y., Li, N., Zhang, C., Wang, C., Chen, Q., Long, M. Microgravity-induced hepatogenic differentiation of rBMSCs on board the SJ-10 satellite.

Microgravity-Induced Alterations of Inflammation-Related Mechanotransduction in Endothelial Cells on Board SJ-10 Satellite

Endothelial cells (ECs) are mechanosensitive cells undergoing morphological and functional changes in space. Ground-based study has provided a body of evidences about how ECs can respond to the effect of simulated microgravity, however, these results need to be confirmed by spaceflight experiments in real microgravity. In this work, we cultured EA.hy926 ECs on board the SJ-10 Recoverable Scientific Satellite for 3 and 10 days, and analyzed the effects of space microgravity on the ECs. Space microgravity suppressed the glucose metabolism, modulated the expression of cellular adhesive molecules such as ICAM-1, VCAM-1, and CD44, and depressed the pro-angiogenesis and pro-inflammation cytokine secretion. Meanwhile, it also induced the depolymerization of actin filaments and microtubules, promoted the vimentin accumulation, restrained the collagen I and fibronectin deposition, regulated the mechanotransduction through focal adhesion kinase and Rho GTPases, and enhanced the exosome-mediated mRNA transfer. Unlike the effect of simulated microgravity, neither three-dimensional growth nor enhanced nitric oxide production was observed in our experimental settings. This work furthers the understandings in the effects and mechanisms of space microgravity on ECs, and provides useful information for future spaceflight experimental design.