In Full Force. Mechanotransduction and Morphogenesis during Homeostasis and Tissue Regeneration

Blood flow-induced angiocrine signals promote organ growth and regeneration

Recently, we identified myeloid-derived growth factor (MYDGF) as a blood flow-induced angiocrine signal that promotes human and mouse hepatocyte proliferation and survival. Here, we review literature reporting changes in blood flow after partial organ resection in the liver, lung, and kidney, and we describe the angiocrine signals released by endothelial cells (ECs) upon blood flow alterations in these organs. While hepatocyte growth factor (HGF) and MYDGF are important angiocrine signals for liver regeneration, by now, angiocrine signals have also been reported to stimulate hyperplasia and/or hypertrophy during the regeneration of lungs and kidneys. In addition, angiocrine signals play a critical role in tumor growth. Understanding the mechano-elastic properties and flow-mediated alterations in the organ-specific microvasculature is crucial for therapeutic approaches to maintain organ health and initiate organ renewal.

Nuclear envelope dynamics in connection to chromatin remodeling

The nucleus is a central organelle of eukaryotic cells undergoing dynamic structural changes during cellular fundamental processes such as proliferation and differentiation. These changes rely on the integration of developmental and stress signals at the nuclear envelope (NE), orchestrating responses at the nucleo-cytoplasmic interface for efficient genomic functions such as DNA transcription, replication and repair. While in animals, correlation has already been established between NE dynamics and chromatin remodeling using last-generation tools and cutting-edge technologies, this topic is just emerging in plants, especially in response to mechanical cues. This review summarizes recent data obtained in this field with more emphasis on the mechanical stress response. It also highlights similarities/differences between animal and plant cells at multiples scales, from the structural organization of the nucleo-cytoplasmic continuum to the functional impacts of NE dynamics.

The force-dependent filamin A-G3BP1 interaction regulates phase-separated stress granule formation

Filamin A (FLNA) is an actin crosslinking protein that mediates mechanotransduction. External and internal mechanical forces, through the actin cytoskeleton, can induce conformational changes of the FLNA molecule to expose cryptic binding sites for its binding partners. Here, we identified Ras GTPase-activating protein SH3 domain-binding protein 1 (G3BP1) as a new FLNA mechanobinding partner. Unlike other FLNA binding partners to the mechanosensing domain repeat 21 (R21), G3BP1 requires an additional neighboring repeat R22 to interact. We demonstrated that their interaction occurs in the cytosol of living cells in an actin polymerization-dependent manner. We also mapped the FLNA-binding site on G3BP1 and found that a F360A point mutation in the RNA recognition motif disrupts the interaction. RNA interfered with the FLNA-G3BP1 interaction, and FLNA did not localize in RNA-rich stress granules (SGs). Disruption of the interaction was sufficient to promote phase-separated SG formation, and arsenite treatment further stimulated the formation of SGs. Taken together, these data identify G3BP1 as a new mechanobinding protein that interacts with the FLNA mechanosensing domain R21 and suggest that SG formation is partially regulated by mechanical force.

Interaction of LARP4 to filamin A mechanosensing domain regulates cell migrations

Filamin A (FLNA) is an actin cross-linking protein that mediates mechanotransduction. Force-dependent conformational changes of FLNA molecule expose cryptic binding site of FLNA, allowing interaction with partners such as integrin, smoothelin, and fimbacin. Here, we identified La-related protein 4 (LARP4) as a new FLNA mechanobinding partner. LARP4 specifically interacts with the cleft formed by C and D strands of immunoglobulin-like repeat 21 (R21) which is blocked by A strand of R20 without force. We validated the interaction between LARP4 and FLNA R21 both in vivo and in vitro. We also determined the critical amino acid that is responsible for the interaction and generated the non-FLNA-binding mutant LARP4 (F277A in human: F273A in mouse Larp4) that disrupts the interaction. Fluorescence recovery after photobleaching (FRAP) of GFP-labeled LARP4 in living cells demonstrated that mutant LARP4 diffuses faster than WT LARP4. Proximity ligation assay (PLA) also confirmed their interaction and disruption of actin polymerization diminishes the interaction. Data mining of RNAseq analysis of LARP4 knockdown (KD) HEK293T cells suggested that LARP4 is involved in morphogenesis and cell motility. Consistent with this prediction, we found that KD of LARP4 increases cell migration speed and expression of the F277A mutant LARP4 in LARP4-KD cells also leads to a higher cell migration speed compared to WT LARP4. These results demonstrated that the LARP4 interaction with FLNA regulates cell migration.

Molecular mechanisms of exercise contributing to tissue regeneration

Physical activity has been known as an essential element to promote human health for centuries. Thus, exercise intervention is encouraged to battle against sedentary lifestyle. Recent rapid advances in molecular biotechnology have demonstrated that both endurance and resistance exercise training, two traditional types of exercise, trigger a series of physiological responses, unraveling the mechanisms of exercise regulating on the human body. Therefore, exercise has been expected as a candidate approach of alleviating a wide range of diseases, such as metabolic diseases, neurodegenerative disorders, tumors, and cardiovascular diseases. In particular, the capacity of exercise to promote tissue regeneration has attracted the attention of many researchers in recent decades. Since most adult human organs have a weak regenerative capacity, it is currently a key challenge in regenerative medicine to improve the efficiency of tissue regeneration. As research progresses, exercise-induced tissue regeneration seems to provide a novel approach for fighting against injury or senescence, establishing strong theoretical basis for more and more "exercise mimetics." These drugs are acting as the pharmaceutical alternatives of those individuals who cannot experience the benefits of exercise. Here, we comprehensively provide a description of the benefits of exercise on tissue regeneration in diverse organs, mainly focusing on musculoskeletal system, cardiovascular system, and nervous system. We also discuss the underlying molecular mechanisms associated with the regenerative effects of exercise and emerging therapeutic exercise mimetics for regeneration, as well as the associated opportunities and challenges. We aim to describe an integrated perspective on the current advances of distinct physiological mechanisms associated with exercise-induced tissue regeneration on various organs and facilitate the development of drugs that mimics the benefits of exercise.

Effect of Therapeutic Ultrasound on the Mechanical and Biological Properties of Fibroblasts

Purpose

This paper explores the effect of therapeutic ultrasound on the mechanical and biological properties of ligament fibroblasts.

Methods and Results

We assessed pulsed ultrasound doses of 1.0 and 2.0 W/cm2 at 1 MHz frequency for five days on ligament fibroblasts using a multidisciplinary approach. Atomic force microscopy showed a decrease in cell elastic modulus for both doses, but the treated cells were still viable based on flow cytometry. Finite element method analysis exhibited visible cytoskeleton displacements and decreased harmonics in treated cells. Colorimetric assay revealed increased cell proliferation, while scratch assay showed increased migration at a low dose. Enzyme-linked immunoassay detected increased collagen and fibronectin at a high dose, and immunofluorescence imaging technique visualized β-actin expression for both treatments.

Conclusion

Both doses of ultrasound altered the fibroblast mechanical properties due to cytoskeletal reorganization and enhanced the regenerative and remodeling stages of cell repair.

Lay Summary

Knee ligament injuries are a lesion of the musculoskeletal system frequently diagnosed in active and sedentary lifestyles in young and older populations. Therapeutic ultrasound is a rehabilitation strategy that may lead to the regenerative and remodeling of ligament wound healing. This research demonstrated that pulsed therapeutic ultrasound applied for 5 days reorganized the ligament fibroblasts structure to increase the cell proliferation and migration at a low dose and to increase the releasing proteins that give the stiffness of the healed ligament at a high dose.

Future Works

Future research should further develop and confirm that therapeutic ultrasound may improve the regenerative and remodeling stages of the ligament healing process applied in clinical trials in active and sedentary lifestyles in young and older populations.

Graphical abstract

Crosstalk between basal extracellular matrix adhesion and building of apical architecture during morphogenesis

Tissues build complex structures like lumens and microvilli to carry out their functions. Most of the mechanisms used to build these structures rely on cells remodelling their apical plasma membranes, which ultimately constitute the specialised compartments. In addition to apical remodelling, these shape changes also depend on the proper attachment of the basal plasma membrane to the extracellular matrix (ECM). The ECM provides cues to establish apicobasal polarity, and it also transduces forces that allow apical remodelling. However, physical crosstalk mechanisms between basal ECM attachment and the apical plasma membrane remain understudied, and the ones described so far are very diverse, which highlights the importance of identifying the general principles. Here, we review apicobasal crosstalk of two well-established models of membrane remodelling taking place during Drosophila melanogaster embryogenesis: amnioserosa cell shape oscillations during dorsal closure and subcellular tube formation in tracheal cells. We discuss how anchoring to the basal ECM affects apical architecture and the mechanisms that mediate these interactions. We analyse this knowledge under the scope of other morphogenetic processes and discuss what aspects of apicobasal crosstalk may represent widespread phenomena and which ones are used to build subsets of specialised compartments.

Compressive Buckling Fabrication of 3D Cell-Laden Microstructures

Tissue architecture is a prerequisite for its biological functions. Recapitulating the three-dimensional (3D) tissue structure represents one of the biggest challenges in tissue engineering. Two-dimensional (2D) tissue fabrication methods are currently in the main stage for tissue engineering and disease modeling. However, due to their planar nature, the created models only represent very limited out-of-plane tissue structure. Here compressive buckling principle is harnessed to create 3D biomimetic cell-laden microstructures from microfabricated planar patterns. This method allows out-of-plane delivery of cells and extracellular matrix patterns with high spatial precision. As a proof of principle, a variety of polymeric 3D miniature structures including a box, an octopus, a pyramid, and continuous waves are fabricated. A mineralized bone tissue model with spatially distributed cell-laden lacunae structures is fabricated to demonstrate the fabrication power of the method. It is expected that this novel approach will help to significantly expand the utility of the established 2D fabrication techniques for 3D tissue fabrication. Given the widespread of 2D fabrication methods in biomedical research and the high demand for biomimetic 3D structures, this method is expected to bridge the gap between 2D and 3D tissue fabrication and open up new possibilities in tissue engineering and regenerative medicine.

Mechanosensitive Pathways in Heart Development: Findings from Chick Embryo Studies

The heart is the first organ that starts to function in a developing embryo. It continues to undergo dramatic morphological changes while pumping blood to the rest of the body. Genetic regulation of heart development is partly governed by hemodynamics. Chick embryo is a major animal model that has been used extensively in cardiogenesis research. To reveal mechanosensitive pathways, a variety of surgical interferences and chemical treatments can be applied to the chick embryo to manipulate the blood flow. Such manipulations alter expressions of mechanosensitive genes which may anticipate induction of morphological changes in the developing heart. This paper aims to present different approaches for generating clinically relevant disturbed hemodynamics conditions using this embryonic chick model and to summarize identified mechanosensitive genes using the model, providing insights into embryonic origins of congenital heart defects.