Cyclic stretch-induced mechanical stress to the cell nucleus inhibits ultraviolet radiation-induced DNA damage

Unlocking the Potential of Curcumae Rhizoma Aqueous Extract in Stress Resistance and Extending Lifespan in Caenorhabditis elegans

The enhancement of stress resistance is crucial for delaying aging and extending a healthy lifespan. Traditional Chinese medicine (TCM), a cherished treasure of Chinese heritage, has shown potential in mitigating stress and promoting longevity. This study integrates network pharmacology and in vivo analysis to investigate the mechanisms and effects of Curcumae Rhizoma (C. Rhizoma), known as "E Zhu" in Chinese. Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS) identified 10 active compounds in its aqueous extract, interacting with 128 stress-related targets. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed pathways such as stress response, FoxO signaling, and insulin resistance. In Caenorhabditis elegans, 10 mg/mL of C. Rhizoma aqueous extract improved resistance to UV, thermal, oxidative, and pathogen-induced stress, extending lifespan in a dose-dependent manner. Mechanistically, it reduced reactive oxygen species (ROS), increased superoxide dismutase (SOD) activity, and enhanced UV resistance via the insulin/IGF-1 pathway and DAF-16 translocation. Molecular docking highlighted hexahydrocurcumin (HHC) and related compounds as key bioactives. Furthermore, we also observed that C. Rhizoma aqueous extract significantly extended both the lifespan and healthspan of nematodes. These findings highlight the potential of C. Rhizoma in stress mitigation and longevity promotion, offering valuable insights into the therapeutic applications of TCM.

Overstretching alveolar epithelial type II cells decreases surfactant secretion via actin polymerization and intracellular trafficking alteration

Pulmonary surfactant is essential for maintaining proper lung function. Alveolar epithelial type II (AE2) cells secrete surfactants via lamellar bodies (LBs). In tidal loading during each breath, the physiological cyclic stretching of AE2 cells promotes surfactant secretion. Excessive stretching inhibits surfactant secretion, which is considered to contribute to the development of lung damage. However, its precise mechanism remains unknown. This study tested whether actin polymerization and intracellular transport are required for pulmonary surfactant secretion and the association of actin polymerization and transport in identical human AE2-derived A549 cells using live-cell imaging, not in the bulk cells population. We found that overstretching approximately doubled actin polymerization into filaments (F-actin) and suppressed LB secretion by half in the fluorescent area ratio, compared with physiological stretching (F-actin: 1.495 vs 0.643 (P < 0.01); LB: 0.739 vs 0.332 (P < 0.01)). An inhibitor of actin polymerization increased LB secretion. Intracellular tracking using fluorescent particles revealed that cyclic stretching shifted the particle motion perpendicularly to the direction of stretching according to the orientation of the F-actin (proportion of perpendicular axis motion prior particle: 0h 40.12 % vs 2h 63.13 % (P < 0.01)), and particle motion was restricted over time in the cells subjected to overstretching, indicating that overstretching regulates intracellular transport dynamics (proportion of stop motion particle: 0h 1.01 % vs 2h 11.04 % (P < 0.01)). These findings suggest that overstretching changes secretion through the cytoskeleton: overstretching AE2 cells inhibits pulmonary surfactant secretion, at least through accelerating actin polymerization and decreasing intracellular trafficking, and the change in actin orientation would modulate intracellular trafficking.

Effect of mechanical forces on cellular response to radiation

While the cellular interactions and biochemical signaling has been investigated for long and showed to play a major role in the cell's fate, it is now also evident that mechanical forces continuously applied to the cells in their microenvironment are as important for tissue homeostasis. Mechanical cues are emerging as key regulators of cellular drug response and we aimed to demonstrate in this review that such effects should also be considered vital for the cellular response to radiation. In order to explore the mechanobiology of the radiation response, we reviewed the main mechanoreceptors and transducers, including integrin-mediated adhesion, YAP/TAZ pathways, Wnt/β-catenin signaling, ion channels and G protein-coupled receptors and showed their implication in the modulation of cellular radiosensitivity. We then discussed the current studies that investigated a direct effect of mechanical stress, including extracellular matrix stiffness, shear stress and mechanical strain, on radiation response of cancer and normal cells and showed through preliminary results that such stress effectively can alter cell response after irradiation. However, we also highlighted the limitations of these studies and emphasized some of the contradictory data, demonstrating that the effect of mechanical cues could involve complex interactions and potential crosstalk with numerous cellular processes also affected by irradiation. Overall, mechanical forces alter radiation response and although additional studies are required to deeply understand the underlying mechanisms, these effects should not be neglected in radiation research as they could reveal new fundamental knowledge for predicting radiosensitivity or understanding resistance to radiotherapy.

Cyclically stretched ACL fibroblasts emigrating from spheroids adapt their cytoskeleton and ligament-related expression profile

Mechanical stress of ligaments varies; hence, ligament fibroblasts must adapt their expression profile to novel mechanomilieus to ensure tissue resilience. Activation of the mechanoreceptors leads to a specific signal transduction, the so-called mechanotransduction. However, with regard to their natural three-dimensional (3D) microenvironment cell reaction to mechanical stimuli during emigrating from a 3D spheroid culture is still unclear. This study aims to provide a deeper understanding of the reaction profile of anterior cruciate ligament (ACL)-derived fibroblasts exposed to cyclic uniaxial strain in two-dimensional (2D) monolayer culture and during emigration from 3D spheroids with respect to cell survival, cell and cytoskeletal orientation, distribution, and expression profile. Monolayers and spheroids were cultured in crosslinked polydimethyl siloxane (PDMS) elastomeric chambers and uniaxially stretched (14% at 0.3 Hz) for 48 h. Cell vitality, their distribution, nuclear shape, stress fiber orientation, focal adhesions, proliferation, expression of ECM components such as sulfated glycosaminoglycans, collagen type I, decorin, tenascin C and cell-cell communication-related gap junctional connexin (CXN) 43, tendon-related markers Mohawk and tenomodulin (myodulin) were analyzed. In contrast to unstretched cells, stretched fibroblasts showed elongation of stress fibers, cell and cytoskeletal alignment perpendicular to strain direction, less rounded cell nuclei, increased numbers of focal adhesions, proliferation, amplified CXN43, and main ECM component expression in both cultures. The applied cyclic stretch protocol evoked an anabolic response and enhanced tendon-related marker expression in ACL-derived fibroblasts emigrating from 3D spheroids and seems also promising to support in future tissue formation in ACL scaffolds seeded in vitro with spheroids.

Design of a 3D printed, motorized, uniaxial cell stretcher for microscopic and biochemical analysis of mechanotransduction

Cells respond to mechanical cues from their environment through a process of mechanosensing and mechanotransduction. Cell stretching devices are important tools to study the molecular pathways responsible for cellular responses to mechanobiological processes. We describe the development and testing of a uniaxial cell stretcher that has applications for microscopic as well as biochemical analyses. By combining simple fabrication techniques with adjustable control parameters, the stretcher is designed to fit a variety of experimental needs. The stretcher can be used for static and cyclic stretching. As a proof of principle, we visualize stretch induced deformation of cell nuclei via incremental static stretch, and changes in IEX1 expression via cyclic stretching. This stretcher is easily modified to meet experimental needs, inexpensive to build, and should be readily accessible for most laboratories with access to 3D printing.

Chromatin rigidity provides mechanical and genome protection

The nucleus is the organelle in the cell that contains the genome and its associate proteins which is collectively called chromatin. New work has shown that chromatin and its compaction level, dictated largely through histone modification state, provides rigidity to protect and stabilize the nucleus. Alterations in chromatin, its mechanics, and downstream loss of nuclear shape and stability are hallmarks of human disease. Weakened nuclear mechanics and abnormal morphology have been shown to cause rupturing of the nucleus which results in nuclear dysfunction including DNA damage. Thus, the rigidity provided by chromatin to maintain nuclear mechanical stability also provides its own protection from DNA damage via compartmentalization maintenance.

TENSCell: Imaging of Stretch-Activated Cells Reveals Divergent Nuclear Behavior and Tension

Mechanisms of cellular and nuclear mechanosensation are unclear, partially because of a lack of methods that can reveal dynamic processes. Here, we present a new concept for a low-cost, three-dimensionally printed device that enables high-magnification imaging of cells during stretch. We observed that nuclei of mouse embryonic skin fibroblasts underwent rapid (within minutes) and divergent responses, characterized by nuclear area expansion during 5% strain but nuclear area shrinkage during 20% strain. Only responses to low strain were dependent on calcium signaling, whereas actin inhibition abrogated all nuclear responses and increased nuclear strain transfer and DNA damage. Imaging of actin dynamics during stretch revealed similar divergent trends, with F-actin shifting away from (5% strain) or toward (20% strain) the nuclear periphery. Our findings emphasize the importance of simultaneous stimulation and data acquisition to capture mechanosensitive responses and suggest that mechanical confinement of nuclei through actin may be a protective mechanism during high mechanical stretch or loading.