Cell shape, cytoskeletal mechanics, and cell cycle control in angiogenesis

New Perspectives on the Organization of Living Tissue and the Ongoing Connective Tissue/Fascia Nomenclature Debate, as Revealed by Intra-Tissue Endoscopy That Provides Real-Time Images During Surgical Procedures

Intra-tissue endoscopy, providing real-time images at all scales, from macroscopic to microscopic, from inside living tissue during surgical procedures, has revealed the existence of a body-wide fibrillar architecture that extends from the surface of the skin to the cell. Different types of cells are housed within this fibrillar architecture and gather together to carry out specific functions. This challenges the commonly accepted notion of the organization of living matter that associates separate organs with connective tissue packaging. We are thus confronted with the global nature of the living human body and its vital processes. This paper sets out to describe the architecture of this fibrillar network which could be assimilated with the fascial tissue and which attributes a more constitutive role to connective tissue. It also demonstrates how movements within this fibrillar network can occur with minimal local distortion while maintaining tissue continuity. The authors propose that the gliding of tissues can be explained by the existence of a highly adaptable fibrillar network that enables the gliding of distinct anatomical structures such as tendons and muscles, without any dynamic influence on the surrounding tissues. The authors propose a new model of tissue movement based on the observation of a ubiquitous dynamic polyhedric fibrillar network with an apparently dispersed and complex pattern of organization, that forms fluid-filled microvolumes, and is found everywhere in the human body. Furthermore, this fibrillar network appears to act as a force absorption system, in addition to providing a framework or scaffolding for cells throughout the body. Observation during intra-tissue endoscopy suggests that this fundamental architectural organization extends into the extracellular matrix that is the natural environment of all cells in the living body, regardless of their size, location or specific function.

The TissueTractor: A Device for Applying Large Strains to Tissues and Cells for Simultaneous High-Resolution Live Cell Microscopy

Mechanical strain substantially influences tissue shape and function in various contexts from embryonic development to disease progression. Disruptions in these processes can result in congenital abnormalities and short-circuit mechanotransduction pathways. Manipulating strain in live tissues is crucial for understanding its impact on cellular and subcellular activities, unraveling the interplay between mechanics and cells. Existing tools, such as optogenetic modulation of strain, are limited to small strains over limited distances and durations. Here, a high-strain stretcher system, the TissueTractor, is introduced to enable simultaneous high-resolution spatiotemporal imaging of live cells and tissues under strain applications varying from 0% to over 100%. We use the system with organotypic explants from Xenopus laevis embryos, where applied tension reveals cellular strain heterogeneity and remodeling of intracellular keratin filaments. To highlight the device's adaptability, the TissueTractor is also used to study two other mechanically sensitive cell types with distinct physiological roles: human umbilical vein endothelial cells and mouse neonatal cardiomyocytes, revealing cell morphological changes under significant strain. The results underscore the potential of the TissueTractor for investigating mechanical cues that regulate tissue dynamics and morphogenesis.

Efficacy of one-hour negative pressure wound therapy and magnetic field energy in wound healing

OBJECTIVE

Wound healing is an important aspect of health but needs further research to identify the effects and interactions of different treatment approaches on healing. The aims of this study were to investigate the effectiveness of one-hour negative pressure wound therapy (NPWT) and compare histological differences between one-hour NPWT and magnetic field energy (MFE) in rats on early-stage wound healing, wound size and angiogenesis.

METHOD

Standardised wounds were created on Wistar rats that were allocated and divided into NPWT, MFE and control groups. Both treatments were applied for 1 hour/day for 10 days. Wound size, histological changes and wound area blood flow were assessed.

RESULTS

The wound size of all groups was similar on days 0, 2 and 10. The MFE group's wound size was smaller than the NPWT group on days 4, 6 and 8 (p<0.05). Development of the granulation tissue in both the one-hour NPWT and MFE groups was greater than in the control group. Additionally, the inflammatory phase was shorter, and wounds entered the proliferative stage faster in the MFE group than both of the other groups.

CONCLUSION

Treatment with MFE may be more effective in terms of early stage wound closure and angiogenesis. On the other hand, the NPWT group's wound area blood flow was significantly greater than the other two groups. MFE is superior to one-hour NPWT in terms of wound area and angiogenesis. Furthermore, it is worthwhile to note that one-hour NPWT increases bloodflow in the wound area, which stimulates healing.

Modulation of Cell Response through the Covalent Binding of Fibronectin to Titanium Substrates

Titanium (Ti-6Al-4V) substrates were functionalized through the covalent binding of fibronectin, and the effect of the existence of this extracellular matrix protein on the surface of the material was assessed by employing mesenchymal stem cell (MSC) cultures. The functionalization process comprised the usage of the activation vapor silanization (AVS) technique to deposit a thin film with a high surface density of amine groups on the material, followed by the covalent binding of fibronectin to the amine groups using the N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) crosslinking chemistry. The biological effect of the fibronectin on murine MSCs was assessed in vitro. It was found that functionalized samples not only showed enhanced initial cell adhesion compared with bare titanium, but also a three-fold increase in the cell area, reaching values comparable to those found on the polystyrene controls. These results provide compelling evidence of the potential to modulate the response of the organism to an implant through the covalent binding of extracellular matrix proteins on the prosthesis.

Emerging role of caldesmon in cancer: A potential biomarker for colorectal cancer and other cancers

Colorectal cancer (CRC) is a devastating disease, mainly because of metastasis. As a result, there is a need to better understand the molecular basis of invasion and metastasis and to identify new biomarkers and therapeutic targets to aid in managing these tumors. The actin cytoskeleton and actin-binding proteins are known to play an important role in the process of cancer metastasis because they control and execute essential steps in cell motility and contractility as well as cell division. Caldesmon (CaD) is an actin-binding protein encoded by the CALD1 gene as multiple transcripts that mainly encode two protein isoforms: High-molecular-weight CaD, expressed in smooth muscle, and low-molecular weight CaD (l-CaD), expressed in nonsmooth muscle cells. According to our comprehensive review of the literature, CaD, particularly l-CaD, plays a key role in the development, metastasis, and resistance to chemoradiotherapy in colorectal, breast, and urinary bladder cancers and gliomas, among other malignancies. CaD is involved in many aspects of the carcinogenic hallmarks, including epithelial mesenchymal transition via transforming growth factor-beta signaling, angiogenesis, resistance to hormonal therapy, and immune evasion. Recent data show that CaD is expressed in tumor cells as well as in stromal cells, such as cancer-associated fibroblasts, where it modulates the tumor microenvironment to favor the tumor. Interestingly, CaD undergoes selective tumor-specific splicing, and the resulting isoforms are generally not expressed in normal tissues, making these transcripts ideal targets for drug design. In this review, we will analyze these features of CaD with a focus on CRC and show how the currently available data qualify CaD as a potential candidate for targeted therapy in addition to its role in the diagnosis and prognosis of cancer.

Matrix anisotropy promotes angiogenesis in a density-dependent manner

Angiogenesis is necessary for wound healing, tumorigenesis, implant inosculation, and homeostasis. In each situation, matrix structure and mechanics play a role in determining whether new vasculatures can establish transport to new or hypoxic tissues. Neovessel growth and directional guidance are sensitive to three-dimensional (3-D) matrix anisotropy and density, although the individual and integrated roles of these matrix features have not been fully recapitulated in vitro. We developed a tension-based method to align 3-D collagen constructs seeded with microvessel fragments in matrices of three levels of collagen fibril anisotropy and two levels of collagen density. The extent and direction of neovessel growth from the parent microvessel fragments increased with matrix anisotropy and decreased with density. The proangiogenic effects of anisotropy were attenuated at higher matrix densities. We also examined the impact of matrix anisotropy in an experimental model of neovessel invasion across a tissue interface. Matrix density was found to dictate the success of interface crossing, whereas interface curvature and fibril alignment were found to control directional guidance. Our findings indicate that complex configurations of matrix density and alignment can facilitate or complicate the establishment or maintenance of vascular networks in pathological and homeostatic angiogenesis. Furthermore, we extend preexisting methods for tuning collagen anisotropy in thick constructs. This approach addresses gaps in tissue engineering and cell culture by supporting the inclusion of large multicellular structures in prealigned constructs.NEW & NOTEWORTHY Matrix anisotropy and density have a considerable effect on angiogenic vessel growth and directional guidance. However, the current literature relies on 2-D and simplified models of angiogenesis (e.g., tubulogenesis and vasculogenesis). We present a method to align 3-D collagen scaffolds embedded with microvessel fragments to different levels of anisotropy. Neovessel growth increases with anisotropy and decreases with density, which may guide angiogenic neovessels across tissue interfaces such as during implant inosculation and tumorigenesis.

2,3-Difunctionalized Benzo[b]thiophene Scaffolds Possessing Potent Antiangiogenic Properties

A new class of 2-anilino-3-cyanobenzo[b]thiophenes (2,3-ACBTs) was studied for its antiangiogenic activity for the first time. One of the 2,3-ACBTs inhibited tubulogenesis in a dose-dependent manner without any toxicity. The 2,3-ACBTs significantly reduced neovascularization in both ex vivo and in vivo angiogenic assays without affecting the proliferation of endothelial cells. Neovascularization was limited through reduced phosphorylation of Akt/Src and depolymerization of f-actin and β-tubulin filaments, resulting in reduced migration of cells. In addition, the 2,3-ACBT compound disrupted the preformed angiogenic tubules, and docking/competitive binding studies showed that it binds to VEGFR2. Compound 2,3-ACBT had good stability and intramuscular profile, translating in suppressing the tumor angiogenesis induced in a xenograft model. Overall, the present study suggests that 2,3-ACBT arrests angiogenesis by regulating the Akt/Src signaling pathway and deranging cytoskeletal filaments of endothelial cells.

Multiple regression analysis of a comprehensive transcriptomic data assembly elucidates mechanically- and biochemically-driven responses to focused ultrasound blood-brain barrier disruption

Background: Focused ultrasound (FUS) blood brain barrier disruption (BBBD) permits the noninvasive, targeted, and repeatable delivery of drugs to the brain. FUS BBBD also elicits secondary responses capable of augmenting immunotherapies, clearing amyloid-β and hyperphosphorylated tau, and driving neurogenesis. Leveraging these secondary effects will benefit from an understanding of how they correlate to the magnitude of FUS BBBD and are differentially affected by the mechanical and biochemical stimuli imparted during FUS BBBD.

Methods: We aggregated 75 murine transcriptomes in a multiple regression framework to identify genes expressed in proportion to biochemical (i.e. contrast MR image enhancement (CE)) or mechanical (i.e. harmonic acoustic emissions from MB-activation (MBA)) stimuli associated with FUS BBBD. Models were constructed to control for potential confounders, such as sex, anesthesia, and sequencing batch.

Results: MBA and CE differentially predicted expression of 1,124 genes 6 h or 24 h later. While there existed overlap in the transcripts correlated with MBA vs CE, MBA was principally predictive of expression of genes associated with endothelial reactivity while CE chiefly predicted sterile inflammation gene sets. Over-representation analysis identified transcripts not previously linked to BBBD, including actin filament organization, which is likely important for BBB recovery. Transcripts and pathways associated with neurogenesis, microglial activation, and amyloid-β clearance were significantly correlated to BBBD metrics.

Conclusions: The secondary effects of BBBD may have the potential to be tuned by modulating FUS parameters during BBBD, and MBA and CE may serve as independent predictors of transcriptional reactions in the brain.

The Amot/integrin protein complex transmits mechanical forces required for vascular expansion

Vascular development is a complex multistep process involving the coordination of cellular functions such as migration, proliferation, and differentiation. How mechanical forces generated by cells and transmission of these physical forces control vascular development is poorly understood. Using an endothelial-specific genetic model in mice, we show that deletion of the scaffold protein Angiomotin (Amot) inhibits migration and expansion of the physiological and pathological vascular network. We further show that Amot is required for tip cell migration and the extension of cellular filopodia. Exploiting in vivo and in vitro molecular approaches, we show that Amot binds Talin and is essential for relaying forces between fibronectin and the cytoskeleton. Finally, we provide evidence that Amot is an important component of the endothelial integrin adhesome and propose that Amot integrates spatial cues from the extracellular matrix to form a functional vascular network.

Potential role of active decompression with distraction sugosteogenesis for the management of odontogenic cystic lesions: a retrospective review of 10 cases

PURPOSE

The aim of this paper is to describe active decompression and distraction sugosteogenesis as an alternative for the management of odontogenic cystic lesions. The technique, demographics, success rate, and complications will be presented.

PATIENTS AND METHODS

A retrospective case series study design was implemented. This included patients found in our database from 2015 to 2018 with a diagnosis of any odontogenic cyst, in whom active decompression with distraction sugosteogenesis was implemented. The patient's medical history, demographics, radiographic characteristics of the cyst, technique/device employed, complications, and rate of success were recorded.

RESULTS

The sample consisted of 10 patients, with a mean age of 19.6 years (range 14-34). Sixty percent of all cases occurred in male patients and 40% in females. Forty percent of cases were consistent with odontogenic keratocysts with all cysts presenting in the mandible. No maxillary cases were documented. Seventy percent of such lesions were unilocular and 30% multilocular. Cortical fenestration/perforation was documented in 30% of cases and 1 pathologic fracture was seen. Active decompression was performed for an average of 37 days (range 30-50 days). With this system, radiographic resolution occurred in 1-3 months in 50% of cases, 6-12 months in 30% of cases, and 12 months in 20% of cases. Mean follow-up was 24.3 months. No recurrence was documented. Complications included fistula development (2 cases), flap dehiscence (1 case), and the size of the intraoral unit.

CONCLUSIONS

This investigation reviewed the authors' 5-year experience employing active decompression with distraction sugosteogenesis for the management of odontogenic cystic lesions and showed that this is a reliable alternative for the management of odontogenic cysts.

Modeling and live imaging of mechanical instabilities in the zebrafish aorta during hematopoiesis

All blood cells originate from hematopoietic stem/progenitor cells (HSPCs). HSPCs are formed from endothelial cells (ECs) of the dorsal aorta (DA), via endothelial-to-hematopoietic transition (EHT). The zebrafish is a primary model organism to study the process in vivo. While the role of mechanical stress in controlling gene expression promoting cell differentiation is actively investigated, mechanisms driving shape changes of the DA and individual ECs remain poorly understood. We address this problem by developing a new DA micromechanical model and applying it to experimental data on zebrafish morphogenesis. The model considers the DA as an isotropic tubular membrane subjected to hydrostatic blood pressure and axial stress. The DA evolution is described as a movement in the dimensionless controlling parameters space: normalized hydrostatic pressure and axial stress. We argue that HSPC production is accompanied by two mechanical instabilities arising in the system due to the plane stress in the DA walls and show how a complex interplay between mechanical forces in the system drives the emerging morphological changes.

Osteoprotegerin is sensitive to actomyosin tension in human periodontal ligament fibroblasts

Periodontal ligament fibroblasts (PdLFs) are an elongated cell type in the periodontium with matrix and bone regulatory functions which become abnormal in periodontal disease (PD). Here we found that the normally elongated and oriented PdLF nucleus becomes rounded and loses orientation in a mouse model of PD. Using in vitro micropatterning of cultured primary PdLF cell shape, we show that PdLF elongation correlates with nuclear elongation and the presence of thicker, contractile F-actin fibers. The rounded nuclei in mouse PD models in vivo are, therefore, indicative of reduced actomyosin tension. Inhibiting actomyosin contractility by inhibiting myosin light chain kinase, Rho kinase or myosin ATPase activity, in cultured PdLFs each consistently reduced messenger RNA levels of bone regulatory protein osteoprotegerin (OPG). Infection of cultured PdLFs with two different types of periodontal bacteria (Porphyromonas gingivalis and Fusobacterium nucleatum) failed to recapitulate the observed nuclear rounding in vivo, upregulated nonmuscle myosin II phosphorylation and downregulated OPG. Collectively, our results add support to the hypothesis that PdLF contractility becomes decreased and contributes to disease progression in PD.

Near Simultaneous Laser Scanning Confocal and Atomic Force Microscopy (Conpokal) on Live Cells

Techniques available for micro- and nano-scale mechanical characterization have exploded in the last few decades. From further development of the scanning and transmission electron microscope, to the invention of atomic force microscopy, and advances in fluorescent imaging, there have been substantial gains in technologies that enable the study of small materials. Conpokal is a portmanteau that combines confocal microscopy with atomic force microscopy (AFM), where a probe "pokes" the surface. Although each technique is extremely effective for the qualitative and/or quantitative image collection on their own, Conpokal provides the capability to test with blended fluorescence imaging and mechanical characterization. Designed for near simultaneous confocal imaging and atomic force probing, Conpokal facilitates experimentation on live microbiological samples. The added insight from paired instrumentation provides co-localization of measured mechanical properties (e.g., elastic modulus, adhesion, surface roughness) by AFM with subcellular components or activity observable through confocal microscopy. This work provides a step by step protocol for the operation of laser scanning confocal and atomic force microscopy, simultaneously, to achieve same cell, same region, confocal imaging, and mechanical characterization.

Short-term angiotensin II treatment regulates cardiac nanomechanics via microtubule modifications

Mechanical properties of single myocytes contribute to the whole heart performance, but the measurement of mechanics in living cells at high resolution with minimal force interaction remains challenging. Angiotensin II (AngII) is a peptide hormone that regulates a number of physiological functions, including heart performance. It has also been shown to contribute to cell mechanics by inducing cell stiffening. Using non-contact high-resolution Scanning Ion Conductance Microscopy (SICM), we determine simultaneously cell topography and membrane transverse Young's modulus (YM) by a constant pressure application through a nanopipette. While applying pressure, the vertical position is recorded and a deformation map is generated from which YM can be calculated and corrected for the uneven geometry. High resolution of this method also allows studying specific membrane subdomains, such as Z-grooves and crests. We found that short-term AngII treatment reduces the transversal YM in isolated adult rat cardiomyocytes acting via an AT1 receptor. Blocking either a TGF-β1 receptor or Rho kinase abolishes this effect. Analysis of the cytoskeleton showed that AngII depletes microtubules by decreasing long-lived detyrosinated and acetylated microtubule populations. Interestingly, in the failing cardiomyocytes, which are stiffer than controls, the short-term AngII treatment also reduces the YM, thus normalizing the mechanical state of cells. This suggests that the short-term softening effect of AngII on cardiac cells is opposite to the well-characterized long-term hypertrophic effect. In conclusion, we generate a precise nanoscale indication map of location-specific transverse cortical YM within the cell and this can substantially advance our understanding of cellular mechanics in a physiological environment, for example in isolated cardiac myocytes.

Nuclear actin regulates cell proliferation and migration via inhibition of SRF and TEAD

Actin dynamics regulate cell behaviour in response to physiological signals. Here we demonstrate a novel role for nuclear actin in inhibiting cell proliferation and migration. We demonstrate that physiological signals that elevate cAMP, which is anti-mitogenic in vascular smooth muscle cells, increases nuclear actin monomer levels. Expression of a nuclear-targeted polymerisation-defective actin mutant (NLS-ActinR62D) inhibited proliferation and migration. Preventing nuclear actin monomer accumulation by enhancing its nuclear export or polymerisation reversed the anti-mitogenic and anti-migratory effects of cAMP. Transcriptomic analysis identified repression of proliferation and migration associated genes regulated by serum response factor (SRF) and TEA Domain (TEAD) transcription factors. Accordingly, NLS-ActinR62D inhibited SRF and TEAD activity and target gene expression, and these effects were reversed by constitutively-active mutants of the TEAD and SRF co-factors YAP, TAZ and MKL1. In summary, intranuclear actin inhibits proliferation and migration by inhibiting YAP-TEAD and MKL-SRF activity. This mechanism explains the anti-mitogenic and anti-migratory properties of physiological signals that elevate cAMP. SUMMARY: McNeill et al show that increased levels of intranuclear actin monomer inhibit cell proliferation and migration by inhibiting MKL1-SRF and YAP/TAZ-TEAD-dependent gene expression. This mechanism mediates the anti-mitogenic and anti-migratory effects of physiological signals that elevate cyclic-AMP.

Cultivated Orostachys japonicus extract inhibits VEGF-induced angiogenesis via regulation of VEGFR2 signaling pathway in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Orostachys japonicus A. Berger (O. japonicus), so-called Wa-song in Korea, a traditional food and medicine that grows on mountain rocks and roof tiles. Wa-song containing various phenolic compounds have been reported as a medicinal plant for prevention of fibrosis, cancer, inflammation, and oxidative damage.

AIM OF THE STUDY

The present study was designed to examine the anti-angiogenic effects of cultivated Orostachys japonicus 70% ethanol extract (CE) in vascular endothelial growth factor (VEGF)-stimulated human umbilical vein endothelial cells (HUVECs).

MATERIALS AND METHODS

CE was prepared with 70% ethanol. HUVECs, rat aortic rings, and matrigel plug in mice were treated with CE (10-20 μg/mL) and VEGF (20-50 ng/mL), and the anti-angiogenic activities of CE were analyzed by SRB, wound healing, trans-well invasion, capillary-like tubule formation, rat aortas, Western blot, and matrigel plug assay. Phenolic compounds in CE were analyzed using a high-performance liquid chromatography (HPLC)-PDA system.

RESULTS

Treatment of CE (10-20 μg/mL) markedly suppressed proliferation of HUVECs in the presence (from 136.5% to 112.2%) or absence of VEGF (from 100.0% to 92.1%). The proliferation inhibitory effect of CE was caused by G0/G1 cell cycle arrest, and the decrease of CDK-2, CDK-4, Cyclin D1 and Cyclin E1. Furthermore, CE treatment showed significant angiogenesis inhibitory effects on motility, invasion and micro-vessel formation of HUVECs, rat aortic rings and subcutaneous matrigels under VEGF-stimulation condition. In HUVECs, CE-induced anti-angiogenic effect was regulated by inhibition of the PI3K/AKT/mTOR, MAPK/p38, MAPK/ERK, FAK-Src, and VEGF-VEGFR2 signaling pathways.

CONCLUSION

This study demonstrated that CE might be used as a potential natural substance, multi-targeted angiogenesis inhibitor, functional food material.

A histological analysis of chronic wounds treated with negative pressure wound therapy to aid healing: a case series

OBJECTIVE

Our aim was to examine histopathological changes in three chronic wounds, and to assess whether the application of negative pressure wound therapy (NPWT) changes the wound bed environment.

METHOD

- Results: We recruited three patients were recruited who had a non-healing wounds in excess of eight weeks. Histopathological changes in the wound bed supported the evidence that NPWT changes the wound bed environment by reducing inflammatory damage and facilitating wound bed perfusion with angiogenesis.

CONCLUSION

We suggest that NPWT is a valuable adjunct to aid chronic wound healing. In this case series, we observed histopathological changes and improvement in the wounds, following one week's treatment with NPWT. Further analysis should be done to demonstrate any interaction between the cells involved in the wound healing process is enhanced, growth factor performance is optimised and cell migration is achieved following NPWT, in order to facilitate the healing process.

Imaging the Dynamic Interaction Between Sprouting Microvessels and the Extracellular Matrix

Thorough understanding of growth and evolution of tissue vasculature is fundamental to many fields of medicine including cancer therapy, wound healing, and tissue engineering. Angiogenesis, the growth of new vessels from existing ones, is dynamically influenced by a variety of environmental factors, including mechanical and biophysical factors, chemotactic factors, proteolysis, and interaction with stromal cells. Yet, dynamic interactions between neovessels and their environment are difficult to study with traditional fixed time imaging techniques. Advancements in imaging technologies permit time-series and volumetric imaging, affording the ability to visualize microvessel growth over 3D space and time. Time-lapse imaging has led to more informative investigations of angiogenesis. The environmental factors implicated in angiogenesis span a wide range of signals. Neovessels advance through stromal matrices by forming attachments and pulling and pushing on their microenvironment, reorganizing matrix fibers, and inducing large deformations of the surrounding stroma. Concurrently, neovessels secrete proteolytic enzymes to degrade their basement membrane, create space for new vessels to grow, and release matrix-bound cytokines. Growing neovessels also respond to a host of soluble and matrix-bound growth factors, and display preferential growth along a cytokine gradient. Lastly, stromal cells such as macrophages and mesenchymal stem cells (MSCs) interact directly with neovessels and their surrounding matrix to facilitate sprouting, vessel fusion, and tissue remodeling. This review highlights how time-lapse imaging techniques advanced our understanding of the interaction of blood vessels with their environment during sprouting angiogenesis. The technology provides means to characterize the evolution of microvessel behavior, providing new insights and holding great promise for further research on the process of angiogenesis.

EWMA Document: Negative Pressure Wound Therapy

1. Introduction Since its introduction in clinical practice in the early 1990's negative pressure wounds therapy (NPWT) has become widely used in the management of complex wounds in both inpatient and outpatient care.¹ NPWT has been described as a effective treatment for wounds of many different aetiologies^2,3 and suggested as a gold standard for treatment of wounds such as open abdominal wounds,^4-6 dehisced sternal wounds following cardiac surgery^7,8 and as a valuable agent in complex non-healing wounds.^9,10 Increasingly, NPWT is being applied in the primary and home-care setting, where it is described as having the potential to improve the efficacy of wound management and help reduce the reliance on hospital-based care.¹¹ While the potential of NPWT is promising and the clinical use of the treatment is widespread, highlevel evidence of its effectiveness and economic benefits remain sparse.^12-14 The ongoing controversy regarding high-level evidence in wound care in general is well known. There is a consensus that clinical practice should be evidence-based, which can be difficult to achieve due to confusion about the value of the various approaches to wound management; however, we have to rely on the best available evidence. The need to review wound strategies and treatments in order to reduce the burden of care in an efficient way is urgent. If patients at risk of delayed wound healing are identified earlier and aggressive interventions are taken before the wound deteriorates and complications occur, both patient morbidity and health-care costs can be significantly reduced. There is further a fundamental confusion over the best way to evaluate the effectiveness of interventions in this complex patient population. This is illustrated by reviews of the value of various treatment strategies for non-healing wounds, which have highlighted methodological inconsistencies in primary research. This situation is confounded by differences in the advice given by regulatory and reimbursement bodies in various countries regarding both study design and the ways in which results are interpreted. In response to this confusion, the European Wound Management Association (EWMA) has been publishing a number of interdisciplinary documents^15-19 with the intention of highlighting: The nature and extent of the problem for wound management: from the clinical perspective as well as that of care givers and the patients Evidence-based practice as an integration of clinical expertise with the best available clinical evidence from systematic research The nature and extent of the problem for wound management: from the policy maker and healthcare system perspectives The controversy regarding the value of various approaches to wound management and care is illustrated by the case of NPWT, synonymous with topical negative pressure or vacuum therapy and cited as branded VAC (vacuum-assisted closure) therapy. This is a mode of therapy used to encourage wound healing. It is used as a primary treatment of chronic wounds, in complex acute wounds and as an adjunct for temporary closure and wound bed preparation preceding surgical procedures such as skin grafts and flap surgery. Aim An increasing number of papers on the effect of NPWT are being published. However, due to the low evidence level the treatment remains controversial from the policy maker and health-care system's points of view-particularly with regard to evidence-based medicine. In response EWMA has established an interdisciplinary working group to describe the present knowledge with regard to NPWT and provide overview of its implications for organisation of care, documentation, communication, patient safety, and health economic aspects. These goals will be achieved by the following: Present the rational and scientific support for each delivered statement Uncover controversies and issues related to the use of NPWT in wound management Implications of implementing NPWT as a treatment strategy in the health-care system Provide information and offer perspectives of NPWT from the viewpoints of health-care staff, policy makers, politicians, industry, patients and hospital administrators who are indirectly or directly involved in wound management.

Periodontal cell mechanotransduction

The periodontium is a structurally and functionally complex tissue that facilitates the anchorage of teeth in jaws. The periodontium consists of various cell types including stem cells, fibroblasts and epithelial cells. Cells of the periodontium are constantly exposed to mechanical stresses generated by biological processes such as the chewing motions of teeth, by flows generated by tongue motions and by forces generated by implants. Mechanical stresses modulate the function of cells in the periodontium, and may play a significant role in the development of periodontal disease. Here, we review the literature on the effect of mechanical forces on periodontal cells in health and disease with an emphasis on molecular and cellular mechanisms.

Type 1 diabetes alters ischemia-induced gene expression

Peripheral Artery Disease (PAD) is a chronic, activity-limiting disease that is caused by atherosclerotic occlusion of blood vessels outside the heart. Type 1 Diabetes (T1D) not only increases an individual's likelihood of developing PAD, but also contributes to poor clinical outcomes after PAD manifestation. Although there is some evidence suggesting that hyperglycemia might alter expression of genes involved in regulating PAD severity or outcomes, our knowledge about the specific genes and pathways involved remains incomplete. We induced experimental PAD or hind limb ischemia in T1D and non-diabetic mice and subjected the ischemic gastrocnemius muscle tissues to genome-wide mRNA transcriptome and pathway analysis. We identified 513 probe sets that represented 443 different genes with highly significant expression differences (p < 0.005) between the ischemic diabetic and ischemic non-diabetic muscle tissues. Moreover, pathway analysis of the differentially expressed genes identified pathways involved in essential biological processes such as "cell cycle," "DNA replication," "metabolic pathways," "focal adhesion," "regulation of actin cytoskeleton," and "nucleotide excision repair". Taken together, our data offer the opportunity to test hypotheses on the roles played by the altered genes/molecular pathways in poor PAD outcomes in diabetes. Such studies may lead to the development of specific therapies to improve PAD outcomes in patients with comorbid diabetes.

Cardiac Fibrotic Remodeling on a Chip with Dynamic Mechanical Stimulation

Cardiac tissue is characterized by being dynamic and contractile, imparting the important role of biomechanical cues in the regulation of normal physiological activity or pathological remodeling. However, the dynamic mechanical tension ability also varies due to extracellular matrix remodeling in fibrosis, accompanied with the phenotypic transition from cardiac fibroblasts (CFs) to myofibroblasts. It is hypothesized that the dynamic mechanical tension ability regulates cardiac phenotypic transition within fibrosis in a strain-mediated manner. In this study, a microdevice that is able to simultaneously and accurately mimic the biomechanical properties of the cardiac physiological and pathological microenvironment is developed. The microdevice can apply cyclic compressions with gradient magnitudes (5-20%) and tunable frequency onto gelatin methacryloyl (GelMA) hydrogels laden with CFs, and also enables the integration of cytokines. The strain-response correlations between mechanical compression and CFs spreading, and proliferation and fibrotic phenotype remolding, are investigated. Results reveal that mechanical compression plays a crucial role in the CFs phenotypic transition, depending on the strain of mechanical load and myofibroblast maturity of CFs encapsulated in GelMA hydrogels. The results provide evidence regarding the strain-response correlation of mechanical stimulation in CFs phenotypic remodeling, which can be used to develop new preventive or therapeutic strategies for cardiac fibrosis.

Distraction Sugosteogenesis: Its Biologic Bases and Therapeutic Principles

PURPOSE

Recently, the terms sugosteogenesis and distraction sugosteogenesis have been introduced to the scientific literature. While the former describes a biologic phenomenon, the latter refers to the clinical technique which relies on the accelerated normal bone healing process that takes place at the osseous walls surrounding a cystic cavity when active negative pressure is applied. The purpose of this study is to provide the biologic bases and the therapeutic principles of this emerging technique. Employing well-stablished biologic principles, clinical evidence from analogous techniques, emerging experimental data, and circumstantial evidence, this study presents the possible mechanism of action of the evacuator for odontogenic cysts (Evocyst), a closed, vacuum-like drain system intended to treat cystic conditions using negative pressure.

METHODS

A review of the literature was done. Keywords for the Medline search were: marsupialization, decompression, odontogenic cysts, effects of negative pressure on bone, and negative pressure wound therapy. In addition, relevant publications from the reference list of the retrieved studies were considered. The matches were evaluated for relevance and analyzed accordingly. Clinical reports used to illustrate the concept of distraction sugosteogenesis were performed following the Declaration of Helsinki on medical protocol and ethics.

RESULTS

Currently, the standard of care to manage odontogenic cystic lesions includes marsupialization, enucleation and curettage, decompression, and surgical resection. However, there is a need for an alternative option in which the entity could be treated while promoting bone formation. With large odontogenic cystic conditions treated in a short period of time, distraction sugosteogenesis appears to be a choice.

CONCLUSION

The application of negative pressure to osseous cells produces a stretching that creates mechanical cues that trigger signaling pathways, promotes fluid flow, and enhances angiogenesis. All of them, combined, may explain sugosteogenesis. The clinical application of such parameters may explain the good clinical results obtained with the Evocyst.

Filopodia and focal adhesions: An integrated system driving branching morphogenesis in neuronal pathfinding and angiogenesis

Single cell branching during development in vertebrates is typified by neuronal branching to form neurites and vascular branches formed by sprouting angiogenesis. Neurons and endothelial tip cells possess subcellular protrusions that share many common features from the morphological to the molecular level. Both systems utilize filopodia as their cellular protrusion organelles and depend on specific integrin-mediated adhesions to the local extracellular matrix for guidance in their pathfinding. We discuss the similar molecular machineries involved in these two types of cell branch formation and use their analogy to propose a new mechanism for angiogenic filopodia function, namely as adhesion assembly sites. In support of this model we provide primary data of angiogenesis in zebrafish in vivo showing that the actin assembly factor VASP participates in both filopodia formation and adhesion assembly at the base of the filopodia, enabling forward progress of the tip cell. The use of filopodia and their associated adhesions provide a common mechanism for neuronal and endothelial pathfinding during development in response to extracellular matrix cues.

Plocabulin, a novel tubulin-binding agent, inhibits angiogenesis by modulation of microtubule dynamics in endothelial cells

BACKGROUND

Vascular supply of tumors is one of the main targets for cancer therapy. Here, we investigated if plocabulin (PM060184), a novel marine-derived microtubule-binding agent, presents antiangiogenic and vascular-disrupting activities.

METHODS

The effects of plocabulin on microtubule network and dynamics were studied on HUVEC endothelial cells. We have also studied its effects on capillary tube structures formation or destabilization in three-dimensional collagen matrices. In vivo experiments were performed on different tumor cell lines.

RESULTS

In vitro studies show that, at picomolar concentrations, plocabulin inhibits microtubule dynamics in endothelial cells. This subsequently disturbs the microtubule network inducing changes in endothelial cell morphology and causing the collapse of angiogenic vessels, or the suppression of the angiogenic process by inhibiting the migration and invasion abilities of endothelial cells. This rapid collapse of the endothelial tubular network in vitro occurs in a concentration-dependent manner and is observed at concentrations lower than that affecting cell survival. The in vitro findings were confirmed in tumor xenografts where plocabulin treatment induced a large reduction in vascular volume and induction of extensive necrosis in tumors, consistent with antivascular effects.

CONCLUSIONS

Altogether, these data suggest that an antivascular mechanism is contributing to the antitumor activities of plocabulin.

Cellular Microbiaxial Stretching to Measure a Single-Cell Strain Energy Density Function

The stress in a cell due to extracellular mechanical stimulus is determined by its mechanical properties, and the structural organization of many adherent cells suggests that their properties are anisotropic. This anisotropy may significantly influence the cells' mechanotransductive response to complex loads, and has important implications for development of accurate models of tissue biomechanics. Standard methods for measuring cellular mechanics report linear moduli that cannot capture large-deformation anisotropic properties, which in a continuum mechanics framework are best described by a strain energy density function (SED). In tissues, the SED is most robustly measured using biaxial testing. Here, we describe a cellular microbiaxial stretching (CμBS) method that modifies this tissue-scale approach to measure the anisotropic elastic behavior of individual vascular smooth muscle cells (VSMCs) with nativelike cytoarchitecture. Using CμBS, we reveal that VSMCs are highly anisotropic under large deformations. We then characterize a Holzapfel-Gasser-Ogden type SED for individual VSMCs and find that architecture-dependent properties of the cells can be robustly described using a formulation solely based on the organization of their actin cytoskeleton. These results suggest that cellular anisotropy should be considered when developing biomechanical models, and could play an important role in cellular mechano-adaptation.

Dynamic Model for Characterizing Contractile Behaviors and Mechanical Properties of a Cardiomyocyte

Studies on the contractile dynamics of heart cells have attracted broad attention for the development of both heart disease therapies and cardiomyocyte-actuated micro-robotics. In this study, a linear dynamic model of a single cardiomyocyte cell was proposed at the subcellular scale to characterize the contractile behaviors of heart cells, with system parameters representing the mechanical properties of the subcellular components of living cardiomyocytes. The system parameters of the dynamic model were identified with the cellular beating pattern measured by a scanning ion conductance microscope. The experiments were implemented with cardiomyocytes in one control group and two experimental groups with the drugs cytochalasin-D or nocodazole, to identify the system parameters of the model based on scanning ion conductance microscope measurements, measurement of the cellular Young's modulus with atomic force microscopy indentation, measurement of cellular contraction forces using the micro-pillar technique, and immunofluorescence staining and imaging of the cytoskeleton. The proposed mathematical model was both indirectly and qualitatively verified by the variation in cytoskeleton, beating amplitude, and contractility of cardiomyocytes among the control and the experimental groups, as well as directly and quantitatively validated by the simulation and the significant consistency of 90.5% in the comparison between the ratios of the Young's modulus and the equivalent comprehensive cellular elasticities of cells in the experimental groups to those in the control group. Apart from mechanical properties (mass, elasticity, and viscosity) of subcellular structures, other properties of cardiomyocytes have also been studied, such as the properties of the relative action potential pattern and cellular beating frequency. This work has potential implications for research on cytobiology, drug screening, mechanisms of the heart, and cardiomyocyte-based bio-syncretic robotics.

Cell micropatterning reveals the modulatory effect of cell shape on proliferation through intracellular calcium transients

The mechanism by which cell shape regulates the function of the cell is one of the most important biological issues, but it remains unclear. Here, we investigated the effect of the regulation of cell shape on proliferation by using a micropatterning approach to confine MC3T3-E1 cells into specific shapes. Our results show that the proliferation rate for rectangle-, triangle-, square- and circle-shaped osteoblasts increased sequentially and was related to the nuclear shape index (NSI) but not the cell shape index (CSI). Interestingly, intracellular calcium transients also displayed different patterns, with the number of Ca²⁺ peaks increasing with the NSI in shaped cells. Further causal investigation revealed that the gene expression levels of the inositol 1,4,5-triphosphate receptor 1 (IP3R1) and sarco/endoplasmic reticulum Ca²⁺-ATPase 2 (SERCA2), two major calcium cycling proteins in the endoplasmic reticulum (ER), were increased with an increase in NSI as a result of nuclear volume changes. Moreover, the down-regulation of IP3R1 and/or SERCA2 using shRNAs in circle-shaped or control osteoblasts resulted in changes in intracellular calcium transient patterns and cell proliferation rates towards that of smaller-NSI-shaped cells. Our results indicate that changes in cell shape changed nuclear morphology and then the gene expression of IP3R1 and SERCA2, which produced different intracellular calcium transient patterns. The patterns of intracellular calcium transients then determined the proliferation rate of the shaped osteoblasts.

Multifrequency Optomechanical Stiffness Measurement of Single Adherent Cells on a Solid Substrate with High Throughput

Mechanical properties of a cell reflect its biological and pathological conditions and there have been active research efforts to develop high-throughput platforms to mechanically characterize single cells. Yet, many of these research efforts are focused on suspended cells and use a flow-through configuration. In this paper, the stiffness of single adherent cells are optomechanically characterized using the vibration-induced phase shift (VIPS) without detaching them from the substrate. With the VIPS measurements, the frequency and amplitude dependency of the cell stiffness is investigated and statistically significant difference in the cell stiffness is confirmed after exposure to various drugs affecting cytoskeleton network. Furthermore, a 3-dimensional finite element model of a cell on a vibrating substrate is developed to extract the mechanical property from the measured VIPS. The developed technique can characterize the mechanical properties of single adherent cells at multiple frequencies with high throughput and will provide valuable clues in understanding cell mechanics.

Transcriptomic alterations in Sitophilus zeamais in response to allyl isothiocyanate fumigation

To study the fumigation mechanisms of Allyl isothiocyanate (AITC) a promising biorational alternative to present fumigants (phosphine and methyl bromide), and provide theoretical basis for its further development in the control of stored grain pests, this research presents a transcriptome analysis of Sitophilus zeamais fumigated with AITC at the concentration of LC₅₀ (5.69μg/mL) and control over 8h. 21,869,022 and 23,873,110 clean reads in insects fumigated with AITC and control were gained, respectively. The results of RNA-seq were confirmed by qRT-PCR determination of the expression levels of NADH dehydrogenase subunit 6 and Vacuolar ATP synthase subunit B in the insects fumigated with AITC at different concentrations. After enrichment analysis of differentially expressed genes, 117 over-expressed and 271 down-regulated transcripts were gained. Following GO enrichment, these transcripts were classified into 38 GO subgroups (at level 2), and the majority enriched GO terms were "Binding" "Cell process" and "metabolic". KEGG enrichment analysis showed that the majority enriched pathway were "Folding, sorting and degradation", "Transport and catabolism", "Energy metabolism", and "Carbohydrate metabolism". Connected with previous researches on mechanisms of isothiocyanates, cytoskeleton collapse and mitochondria dysfunction are proposed to be significant lethal mechanisms of AITC.

Precoating of biphasic calcium phosphate bone substitute with atelocollagen enhances bone regeneration through stimulation of osteoclast activation and angiogenesis

Type I collagen (Col) is a naturally polymerizing protein and important extracellular matrix bone component. The aim of this study was to improve bone regeneration capacity by precoating the surface of biphasic calcium phosphate (BCP) granules with AT-Col, and evaluating its biological effects. BCP granules were precoated with AT-Col using adsorption and lyophilization method. Morphology of AT-Col precoated surfaces was observed using scanning electron microscopy (SEM). Biocompatibility and osteogenic activity of AT-Col were determined in vitro with human mesenchymal stem cell (hMSCs). In vivo bone healing efficiency and related biological effects were determined using a rabbit calvarial defect model. SEM results revealed numerous irregularly distributed AT-Col polymer clusters on BCP granule surface. Biocompatibility experiments demonstrated that AT-Col was non-cytotoxic, and that cell proliferation, adhesion, and osteogenic activity were improved by AT-Col precoating. After in vivo surgical implantation into bone defects, new bone formation was improved by AT-Col granule precoating. Specifically, 8 weeks post-surgery, percentage bone volume was significantly higher in AT-Col/BCP animals (35.02 ± 1.89%) compared with BCP-treated animals (8.94 ± 1.47%) (p < 0.05). Furthermore, tartrate-resistant acid phosphatase staining and CD31 immunohistochemical staining revealed that osteoclast activation and new blood vessel formation in vivo were also induced by AT-Col precoating. Collectively, these data indicate that AT-Col/BCP may be potentially used as a bone substitute to enable effective bone regeneration through enhanced new blood vessel formation and osteoclast activation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1446-1456, 2017.

Dynamic, mechanical integration between nucleus and cell- where physics meets biology

Nuclear motions like rotation, translation and deformation suggest that the nucleus is acted upon by mechanical forces. Molecular linkages with the cytoskeleton are thought to transfer forces to the nuclear surface. We developed an approach to apply reproducible, known mechanical forces to the nucleus in spread adherent cells and quantified the elastic response of the mechanically integrated nucleus-cell. The method is sensitive to molecular perturbations and revealed new insight into the function of the LINC complex. While these experiments revealed elastic behaviors, turnover of the cytoskeleton by assembly/disassembly and binding/unbinding of linkages are expected to dissipate any stored mechanical energy in the nucleus or the cytoskeleton. Experiments investigating nuclear forces over longer time scales demonstrated the mechanical principle that expansive/compressive stresses on the nuclear surface arise from the movement of the cell boundaries to shape and position the nucleus. Such forces can shape the nucleus to conform to cell shapes during cell movements with or without myosin activity.

Design of Tissue-engineered Nanoscaffold Through Self-assembly of Peptide Amphiphile

In order to mimic in vivo topography of the native tissue created by extracellular matrix (ECM) components, which make up all soft tissues, the surface features of each biomaterial should be considered as a nanodimensional structure. In this study, an artificial ECM was designed to mimic the nanostructured topography created by ECM components in native tissue. The proliferation and differentiation of mesenchymal stem cells (MSCs) was investigated in a three dimensional (3-D) network of nanofibers formed by the self-assembly of peptide amphiphile (PA) molecules. PA was synthesized by standard solid phase chemistry that ends with the alkylation of the NH2 terminus of the peptide. The sequence of arginine-glycine-aspartic acid (RGD) was included in peptide design as well. A 3-D network of nanofibers was formed by mixing MSC suspensions in a media with dilute aqueous solution of PA. The attachment, proliferation and osteogenic differentiation of MSCs were influenced by the self-assembled PA nanofibers as the cell scaffold and the values were significantly high compared with those in the static culture (2-D tissue culture plate).

Universally Conserved Relationships between Nuclear Shape and Cytoplasmic Mechanical Properties in Human Stem Cells

The ability of cells to proliferate, differentiate, transduce extracellular signals and assemble tissues involves structural connections between nucleus and cytoskeleton. Yet, how the mechanics of these connections vary inside stem cells is not fully understood. To address those questions, we combined two-dimensional particle-tracking microrheology and morphological measures using variable reduction techniques to measure whether cytoplasmic mechanics allow for discrimination between different human adherent stem cell types and across different culture conditions. Here we show that nuclear shape is a quantifiable discriminant of mechanical properties in the perinuclear cytoskeleton (pnCSK) of various stem cell types. Also, we find the pnCSK is a region with different mechanical properties than elsewhere in the cytoskeleton, with heterogeneously distributed locations exhibiting subdiffusive features, and which obeys physical relations conserved among various stem cell types. Finally, we offer a prospective basis to discriminate between stem cell types by coupling perinuclear mechanical properties to nuclear shape.

Differentiation of mesenchymal stem cells for cartilage tissue engineering: Individual and synergetic effects of three-dimensional environment and mechanical loading

Chondrogenesis of dedifferentiated chondrocytes and mesenchymal stem cells is influenced not only by soluble molecules like growth factors, but also by the cell environment itself. The latter is achieved through both mechanical cues - which act as stimulation factor and influences nutrient transport - and adhesion to extracellular matrix cues - which determine cell shape. Although the effects of soluble molecules and cell environment have been intensively addressed, few observations and conclusions about the interaction between the two have been achieved. In this work, we review the state of the art on the single effects between mechanical and biochemical cues, as well as on the combination of the two. Furthermore, we provide a discussion on the techniques currently used to determine the mechanical properties of materials and tissues generated in vitro, their limitations and the future research needs to properly address the identified problems.

STATEMENT OF SIGNIFICANCE

The importance of biomechanical cues in chondrogenesis is well known. This paper reviews the existing literature on the effect of mechanical stimulation on chondrogenic differentiation of mesenchymal stem cells in order to regenerate hyaline cartilage. Contradictory results found with respect to the effect of different modes of external loading can be explained by the different properties of the scaffolding system that holds the cells, which determine cell adhesion and morphology and spatial distribution of cells, as well as the stress transmission to the cells. Thus, this review seeks to provide an insight into the interplay between external loading program and scaffold properties during chondrogenic differentiation. The review of the literature reveals an important gap in the knowledge in this field and encourages new experimental studies. The main issue is that in each of the few cases in which the interplay is investigated, just two groups of scaffolds are compared, leaving intermediate adhesion conditions out of study. The authors propose broader studies implementing new high-throughput techniques for mechanical characterization of tissue engineering constructs and the inclusion of fatigue analysis as support methodology to more exhaustive mechanical characterization.

Cell elasticity with altered cytoskeletal architectures across multiple cell types

The cytoskeleton is primarily responsible for providing structural support, localization and transport of organelles, and intracellular trafficking. The structural support is supplied by actin filaments, microtubules, and intermediate filaments, which contribute to overall cell elasticity to varying degrees. We evaluate cell elasticity in five different cell types with drug-induced cytoskeletal derangements to probe how actin filaments and microtubules contribute to cell elasticity and whether it is conserved across cell type. Specifically, we measure elastic stiffness in primary chondrocytes, fibroblasts, endothelial cells (HUVEC), hepatocellular carcinoma cells (HUH-7), and fibrosarcoma cells (HT 1080) subjected to two cytoskeletal destabilizers: cytochalasin D and nocodazole, which disrupt actin and microtubule polymerization, respectively. Elastic stiffness is measured by atomic force microscopy (AFM) and the disruption of the cytoskeleton is confirmed using fluorescence microscopy. The two cancer cell lines showed significantly reduced elastic moduli values (~0.5kPa) when compared to the three healthy cell lines (~2kPa). Non-cancer cells whose actin filaments were disrupted using cytochalasin D showed a decrease of 60-80% in moduli values compared to untreated cells of the same origin, whereas the nocodazole-treated cells showed no change in elasticity. Overall, we demonstrate actin filaments contribute more to elastic stiffness than microtubules but this result is cell type dependent. Cancer cells behaved differently, exhibiting increased stiffness as well as stiffness variability when subjected to nocodazole. We show that disruption of microtubule dynamics affects cancer cell elasticity, suggesting therapeutic drugs targeting microtubules be monitored for significant elastic changes.

Cellular Biomechanics in Drug Screening and Evaluation: Mechanopharmacology

The study of mechanobiology is now widespread. The impact of cell and tissue mechanics on cellular responses is well appreciated. However, knowledge of the impact of cell and tissue mechanics on pharmacological responsiveness, and its application to drug screening and mechanistic investigations, have been very limited in scope. We emphasize the need for a heightened awareness of the important bidirectional influence of drugs and biomechanics in all living systems. We propose that the term 'mechanopharmacology' be applied to approaches that employ in vitro systems, biomechanically appropriate to the relevant (patho)physiology, to identify new drugs and drug targets. This article describes the models and techniques that are being developed to transform drug screening and evaluation, ranging from a 2D environment to the dynamic 3D environment of the target expressed in the disease of interest.

Hypoxia alters the recruitment of tropomyosins into the actin stress fibres of neuroblastoma cells

Background

Neuroblastoma is the most common extracranial solid tumor of childhood. The heterogeneous microenvironment of solid tumors contains hypoxic regions associated with poor prognosis and chemoresistance. Hypoxia implicates the actin cytoskeleton through its essential roles in motility, invasion and proliferation. However, hypoxia-induced changes in the actin cytoskeleton have only recently been observed in human cells. Tropomyosins are key regulators of the actin cytoskeleton and we hypothesized that tropomyosins may mediate hypoxic phenotypes.

Methods

Neuroblastoma (SH-EP) cells were incubated ± hypoxia (1 % O₂, 5 % CO₂) for up to 144 h, before examining the cytoskeleton by confocal microscopy and Western blotting.

Results

Hypoxic cells were characterized by a more organized actin cytoskeleton and a reduced ability to degrade gelatin substrates. Hypoxia significantly increased mean actin filament bundle width (72 h) and actin filament length (72–96 h). This correlated with increased hypoxic expression and filamentous organization of stabilizing tropomyosins Tm1 and Tm2. However, isoform specific changes in tropomyosin expression were more evident at 96 h.

Conclusions

This study demonstrates hypoxia-induced changes in the recruitment of high molecular weight tropomyosins into the actin stress fibres of a human cancer. While hypoxia induced clear changes in actin organization compared with parallel normoxic cultures of neuroblastoma, the precise role of tropomyosins in this hypoxic actin reorganization remains to be determined.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1741-8) contains supplementary material, which is available to authorized users.

Optomechanical measurement of the stiffness of single adherent cells

Recent advances in mechanobiology have accumulated strong evidence showing close correlations between the physiological conditions and mechanical properties of cells. In this paper, a novel optomechanical technique to characterize the stiffness of single adherent cells attached on a substrate is reported. The oscillation in a cell's height on a vertically vibrating reflective substrate is measured with a laser Doppler vibrometer as apparent changes in the phase of the measured velocity. This apparent phase shift and the height oscillation are shown to be affected by the mechanical properties of human colorectal adenocarcinoma cells (HT-29). The reported optomechanical technique can provide high-throughput stiffness measurement of single adherent cells over time with minimal perturbation.

Lighting Up the Force: Investigating Mechanisms of Mechanotransduction Using Fluorescent Tension Probes

The ability of cells to sense the physical nature of their surroundings is critical to the survival of multicellular organisms. Cellular response to physical cues from adjacent cells and the extracellular matrix leads to a dynamic cycle in which cells respond by remodeling their local microenvironment, fine-tuning cell stiffness, polarity, and shape. Mechanical regulation is important in cellular development, normal morphogenesis, and wound healing. The mechanisms by which these finely balanced mechanotransduction events occur, however, are not well understood. In large part, this is due to the limited availability of tools to study molecular mechanotransduction events in live cells. Several classes of molecular tension probes have been recently developed which are rapidly transforming the study of mechanotransduction. Molecular tension probes are primarily based on fluorescence resonance energy transfer (FRET) and report on piconewton scale tension events in live cells. In this minireview, we describe the two main classes of tension probes, genetically encoded tension sensors and immobilized tension sensors, and discuss the advantages and limitations of each type. We discuss future opportunities to address major biological questions and outline the challenges facing the next generation of molecular tension probes.

Role of cytoskeleton network in anisosmotic volume changes of intact and permeabilized A549 cells

Recently we found that cytoplasm of permeabilized mammalian cells behaves as a hydrogel displaying intrinsic osmosensitivity. This study examined the role of microfilaments and microtubules in the regulation of hydrogel osmosensitivity, volume-sensitive ion transporters, and their contribution to volume modulation of intact cells. We found that intact and digitonin-permeabilized A549 cells displayed similar rate of shrinkage triggered by hyperosmotic medium. It was significantly slowed-down in both cell preparations after disruption of actin microfilaments by cytochalasin B, suggesting that rapid water release by intact cytoplasmic hydrogel contributes to hyperosmotic shrinkage. In hyposmotic swelling experiments, disruption of microtubules by vinblastine attenuated the maximal amplitude of swelling in intact cells and completely abolished it in permeabilized cells. The swelling of intact cells also triggered ~10-fold elevation of furosemide-resistant (86)Rb+ (K+) permeability and the regulatory volume decrease (RVD), both of which were abolished by Ba2+. Interestingly, RVD and K+ permeability remained unaffected in cytocholasin/vinblastine treated cells demonstrating that cytoskeleton disruption has no direct impact on Ba2+-sensitive K+-channels involved in RVD. Our results show, for the first time, that the cytoskeleton network contributes directly to passive cell volume adjustments in anisosmotic media via the modulation of the water retained by the cytoplasmic hydrogel.

Activation of mechanosensitive ion channel TRPV4 normalizes tumor vasculature and improves cancer therapy

Tumor vessels are characterized by abnormal morphology and hyper-permeability that together cause inefficient delivery of chemotherapeutic agents. Although VEGF has been established as a critical regulator of tumor angiogenesis, the role of mechanical signaling in the regulation of tumor vasculature or tumor endothelial cell (TEC) function is not known. Here, we show that the mechanosensitive ion channel TRPV4 regulates tumor angiogenesis and tumor vessel maturation via modulation of TEC mechanosensitivity. We found that TEC exhibit reduced TRPV4 expression and function, which is correlated with aberrant mechanosensitivity towards ECM stiffness, increased migration and abnormal angiogenesis by TEC. Further, syngeneic tumor experiments revealed that the absence of TRPV4 induced increased vascular density, vessel diameter and reduced pericyte coverage resulting in enhanced tumor growth in TRPV4 KO mice. Importantly, overexpression or pharmacological activation of TRPV4 restored aberrant TEC mechanosensitivity, migration and normalized abnormal angiogenesis in vitro by modulating Rho activity. Finally, a small molecule activator of TRPV4, GSK1016790A, in combination with anti-cancer drug Cisplatin, significantly reduced tumor growth in WT mice by inducing vessel maturation. Our findings demonstrate TRPV4 channels to be critical regulators of tumor angiogenesis and represent a novel target for anti-angiogenic and vascular normalization therapies.

Bending of the looping heart: differential growth revisited

In the early embryo, the primitive heart tube (HT) undergoes the morphogenetic process of c-looping as it bends and twists into a c-shaped tube. Despite intensive study for nearly a century, the physical forces that drive looping remain poorly understood. This is especially true for the bending component, which is the focus of this paper. For decades, experimental measurements of mitotic rates had seemingly eliminated differential growth as the cause of HT bending, as it has commonly been thought that the heart grows almost exclusively via hyperplasia before birth and hypertrophy after birth. Recently published data, however, suggests that hypertrophic growth may play a role in looping. To test this idea, we developed finite-element models that include regionally measured changes in myocardial volume over the HT. First, models based on idealized cylindrical geometry were used to simulate the bending process in isolated hearts, which bend without the complicating effects of external loads. With the number of free parameters in the model reduced to the extent possible, stress and strain distributions were compared to those measured in embryonic chick hearts that were isolated and cultured for 24 h. The results show that differential growth alone yields results that agree reasonably well with the trends in our data, but adding active changes in myocardial cell shape provides closer quantitative agreement with stress measurements. Next, the estimated parameters were extrapolated to a model based on realistic 3D geometry reconstructed from images of an actual chick heart. This model yields similar results and captures quite well the basic morphology of the looped heart. Overall, our study suggests that differential hypertrophic growth in the myocardium (MY) is the primary cause of the bending component of c-looping, with other mechanisms possibly playing lesser roles.

Cytotoxicity evaluation of biodegradable Zn-3Mg alloy toward normal human osteoblast cells

The recent proposal of using Zn-based alloys for biodegradable implants was not supported with sufficient toxicity data. This work, for the first time, presents a thorough cytotoxicity evaluation of Zn-3Mg alloy for biodegradable bone implants. Normal human osteoblast cells were exposed to the alloy's extract and three main cell-material interaction parameters: cell health, functionality and inflammatory response, were evaluated. Results showed that at the concentration of 0.75mg/ml alloy extract, cell viability was reduced by ~50% through an induction of apoptosis at day 1; however, cells were able to recover at days 3 and 7. Cytoskeletal changes were observed but without any significant DNA damage. The downregulation of alkaline phosphatase protein levels did not significantly affect the mineralization process of the cells. Significant differences of cyclooxygenase-2 and prostaglandin E2 inflammatory biomarkers were noticed, but not interleukin 1-beta, indicating that the cells underwent a healing process after exposure to the alloy. Detailed analysis on the cell-material interaction is further discussed in this paper.