Mechanical Cues Regulating Proangiogenic Potential of Human Mesenchymal Stem Cells through YAP-Mediated Mechanosensing

Biomaterials-Based Strategies to Enhance Angiogenesis in Diabetic Wound Healing

Amidst the present healthcare issues, diabetes is unique as an emerging class of affliction with chronicity in a majority of the population. To check and control its effects, there have been huge turnover and constant development of management strategies, and though a bigger part of the health care area is involved in achieving its control and the related issues such as the effect of diabetes on wound healing and care and many of the works have reached certain successful outcomes, still there is a huge lack in managing it, with maximum effect yet to be attained. Studying pathophysiology and involvement of various treatment options, such as tissue engineering, application of hydrogels, drug delivery methods, and enhancing angiogenesis, are at constantly developing stages either direct or indirect. In this review, we have gathered a wide field of information and different new therapeutic methods and targets for the scientific community, paving the way toward more settled ideas and research advances to cure diabetic wounds and manage their outcomes.

Mechanoregulation of MSC spheroid immunomodulation

Mesenchymal stromal cells (MSCs) are widely used in cell-based therapies and tissue regeneration for their potent secretome, which promotes host cell recruitment and modulates inflammation. Compared to monodisperse cells, MSC spheroids exhibit improved viability and increased secretion of immunomodulatory cytokines. While mechanical stimulation of monodisperse cells can increase cytokine production, the influence of mechanical loading on MSC spheroids is unknown. Here, we evaluated the effect of controlled, uniaxial cyclic compression on the secretion of immunomodulatory cytokines by human MSC spheroids and tested the influence of load-induced gene expression on MSC mechanoresponsiveness. We exposed MSC spheroids, entrapped in alginate hydrogels, to three cyclic compressive regimes with varying stress (L) magnitudes (i.e., 5 and 10 kPa) and hold (H) durations (i.e., 30 and 250 s) L5H30, L10H30, and L10H250. We observed changes in cytokine and chemokine expression dependent on the loading regime, where higher stress regimes tended to result in more exaggerated changes. However, only MSC spheroids exposed to L10H30 induced human THP-1 macrophage polarization toward an M2 phenotype compared to static conditions. Static and L10H30 loading facilitated a strong, interlinked F-actin arrangement, while L5H30 and L10H250 disrupted the structure of actin filaments. This was further examined when the actin cytoskeleton was disrupted via Y-27632. We observed downregulation of YAP-related genes, and the levels of secreted inflammatory cytokines were globally decreased. These findings emphasize the essential role of mechanosignaling in mediating the immunomodulatory potential of MSC spheroids.

Injectable ultrasound-powered bone-adhesive nanocomposite hydrogel for electrically accelerated irregular bone defect healing

The treatment of critical-size bone defects with irregular shapes remains a major challenge in the field of orthopedics. Bone implants with adaptability to complex morphological bone defects, bone-adhesive properties, and potent osteogenic capacity are necessary. Here, a shape-adaptive, highly bone-adhesive, and ultrasound-powered injectable nanocomposite hydrogel is developed via dynamic covalent crosslinking of amine-modified piezoelectric nanoparticles and biopolymer hydrogel networks for electrically accelerated bone healing. Depending on the inorganic-organic interaction between the amino-modified piezoelectric nanoparticles and the bio-adhesive hydrogel network, the bone adhesive strength of the prepared hydrogel exhibited an approximately 3-fold increase. In response to ultrasound radiation, the nanocomposite hydrogel could generate a controllable electrical output (-41.16 to 61.82 mV) to enhance the osteogenic effect in vitro and in vivo significantly. Rat critical-size calvarial defect repair validates accelerated bone healing. In addition, bioinformatics analysis reveals that the ultrasound-responsive nanocomposite hydrogel enhanced the osteogenic differentiation of bone mesenchymal stem cells by increasing calcium ion influx and up-regulating the PI3K/AKT and MEK/ERK signaling pathways. Overall, the present work reveals a novel wireless ultrasound-powered bone-adhesive nanocomposite hydrogel that broadens the therapeutic horizons for irregular bone defects.

Bioactive MXene Promoting Angiogenesis and Skeletal Muscle Regeneration through Regulating M2 Polarization and Oxidation Stress

Complete repair of skeletal muscles caused by severe mechanical damage and muscle-related diseases remains a challenge. 2D Ti₃ C₂ T_x (MXene) possesses special photoelectromagnetic properties and has attracted considerable attention in materials science and engineering. However, the bioactive properties and potential mechanism of MXene in tissue engineering, especially in skeletal muscle regeneration, are unclear. Herein, the antioxidation and anti-inflammation activities of MXene and its effects on myogenic differentiation and regeneration of skeletal muscle in vivo are investigated. In vitro studies have shown that MXene has excellent antioxidation and anti-inflammatory properties, and promotes myogenic differentiation and angiogenesis. MXene can remove excess reactive oxygen species in macrophage cells to alleviate oxidative stress and induce the transformation of M1 macrophages into M2 macrophages to reduce excessive inflammation, which can significantly promote the proliferation and differentiation of myoblasts, as well as the proliferation, migration, and tube formation of endothelial cells. Animal experiments with rat tibial anterior muscle defects show that MXene can promote angiogenesis, muscle fiber formation, and skeletal muscle regeneration by regulating the cell microenvironment through anti-inflammatory and antioxidant pathways. The findings suggest that MXene can be used as a multifunctional bioactive material to enhance tissue regeneration through robust antioxidation, anti-inflammation, and angiogenesis activities.

Mesenchymal Stem Cells and Their Exocytotic Vesicles

Mesenchymal stem cells (MSCs), as a kind of pluripotent stem cells, have attracted much attention in orthopedic diseases, geriatric diseases, metabolic diseases, and sports functions due to their osteogenic potential, chondrogenic differentiation ability, and adipocyte differentiation. Anti-inflammation, anti-fibrosis, angiogenesis promotion, neurogenesis, immune regulation, and secreted growth factors, proteases, hormones, cytokines, and chemokines of MSCs have been widely studied in liver and kidney diseases, cardiovascular and cerebrovascular diseases. In recent years, many studies have shown that the extracellular vesicles of MSCs have similar functions to MSCs transplantation in all the above aspects. Here we review the research progress of MSCs and their exocrine vesicles in recent years.

Biomaterials directed activation of a cryostable therapeutic secretome in induced pluripotent stem cell derived mesenchymal stromal cells

Mesenchymal stem cell therapy has suffered from wide variability in clinical efficacy, largely due to heterogeneous starting cell populations and large-scale cell death during and after implantation. Optimizing the manufacturing process has led to reproducible cell populations that can be cryopreserved for clinical applications. Nevertheless, ensuring a reproducible cell state that persists after cryopreservation remains a significant challenge, and is necessary to ensure reproducible clinical outcomes. Here we demonstrate how matrix-conjugated hydrogel cell culture materials can normalize a population of induced pluripotent stem cell derived mesenchymal stem cells (iPSC-MSCs) to display a defined secretory profile that promotes enhanced neovascularization in vitro and in vivo. Using a protein-conjugated biomaterials screen we identified two conditions-1 kPa collagen and 10 kPa fibronectin coated polyacrylamide gels-that promote reproducible secretion of pro-angiogenic and immunomodulatory cytokines from iPSC-MSCs that enhance tubulogenesis of endothelial cells in Geltrex and neovascularization in chick chorioallantoic membranes. Using defined culture substrates alone, we demonstrate maintenance of secretory activity after cryopreservation for the first time. This advance provides a simple and scalable approach for cell engineering and subsequent manufacturing, toward normalizing and priming a desired cell activity for clinical regenerative medicine.

Adipose Tissue Development Relies on Coordinated Extracellular Matrix Remodeling, Angiogenesis, and Adipogenesis

Despite developing prenatally, the adipose tissue is unique in its ability to undergo drastic growth even after reaching its mature size. This development and subsequent maintenance rely on the proper coordination between the vascular niche and the adipose compartment. In this review, the process of adipose tissue development is broken down to explain (1) the ultrastructural matrix remodeling that is undertaken during simultaneous adipogenesis and angiogenesis, (2) the paracrine crosstalk involved during adipose development, (3) the mechanical regulators involved in adipose growth, and (4) the proteolytic and paracrine oversight for matrix remodeling during adipose development. It is crucial to gain a better understanding of the complex relationships that exist between adipose tissue and the vasculature during tissue development to provide insights into the pathological tissue expansion of obesity and to develop improved soft-tissue reconstruction techniques.

Mechanoimmunology: Are inflammatory epigenetic states of macrophages tuned by biophysical factors?

Many inflammatory diseases that are responsible for a majority of deaths are still uncurable, in part as the underpinning pathomechanisms and how to combat them is still poorly understood. Tissue-resident macrophages play pivotal roles in the maintenance of tissue homeostasis, but if they gradually convert to proinflammatory phenotypes, or if blood-born proinflammatory macrophages persist long-term after activation, they contribute to chronic inflammation and fibrosis. While biochemical factors and how they regulate the inflammatory transcriptional response of macrophages have been at the forefront of research to identify targets for therapeutic interventions, evidence is increasing that physical factors also tune the macrophage phenotype. Recently, several mechanisms have emerged as to how physical factors impact the mechanobiology of macrophages, from the nuclear translocation of transcription factors to epigenetic modifications, perhaps even DNA methylation. Insight into the mechanobiology of macrophages and associated epigenetic modifications will deliver novel therapeutic options going forward, particularly in the context of increased inflammation with advancing age and age-related diseases. We review here how biophysical factors can co-regulate pro-inflammatory gene expression and epigenetic modifications and identify knowledge gaps that require urgent attention if this therapeutic potential is to be realized.

Physics of Brain Cancer: Multiscale Alterations of Glioblastoma Cells under Extracellular Matrix Stiffening

The biology and physics underlying glioblastoma is not yet completely understood, resulting in the limited efficacy of current clinical therapy. Recent studies have indicated the importance of mechanical stress on the development and malignancy of cancer. Various types of mechanical stress activate adaptive tumor cell responses that include alterations in the extracellular matrix (ECM) which have an impact on tumor malignancy. In this review, we describe and discuss the current knowledge of the effects of ECM alterations and mechanical stress on GBM aggressiveness. Gradual changes in the brain ECM have been connected to the biological and physical alterations of GBM cells. For example, increased expression of several ECM components such as glycosaminoglycans (GAGs), hyaluronic acid (HA), proteoglycans and fibrous proteins result in stiffening of the brain ECM, which alters inter- and intracellular signaling activity. Several mechanosensing signaling pathways have been identified that orchestrate adaptive responses, such as Hippo/YAP, CD44, and actin skeleton signaling, which remodel the cytoskeleton and affect cellular properties such as cell–cell/ECM interactions, growth, and migration/invasion of GBM cells. In vitro, hydrogels are used as a model to mimic the stiffening of the brain ECM and reconstruct its mechanics, which we also discuss. Overall, we provide an overview of the tumor microenvironmental landscape of GBM with a focus on ECM stiffening and its associated adaptive cellular signaling pathways and their possible therapeutic exploitation.

Disrupted Surfaces of Porous Membranes Reduce Nuclear YAP Localization and Enhance Adipogenesis through Morphological Changes

The disrupted surface of porous membranes, commonly used in tissue-chip and cellular coculture systems, is known to weaken cell-substrate interactions. Here, we investigated whether disrupted surfaces of membranes with micron and submicron scale pores affect yes-associated protein (YAP) localization and differentiation of adipose-derived stem cells. We found that these substrates reduce YAP nuclear localization through decreased cell spreading, consistent with reduced cell-substrate interactions, and in turn enhance adipogenesis while decreasing osteogenesis.

Pro-angiogenic Potential of Mesenchymal Stromal Cells Regulated by Matrix Stiffness and Anisotropy Mimicking Right Ventricles

Capillary rarefaction is a hallmark of right ventricle (RV) failure. Mesenchymal stromal cell (MSC)-based therapy offers a potential treatment due to its pro-angiogenic function. However, the impact of RV tissue mechanics on MSC behavior is unclear, especially when referring to RV end-diastolic stiffness and mechanical anisotropy. In this study, we assessed MSC behavior on electrospun scaffolds with varied stiffness (normal vs failing RV) and anisotropy (isotropic vs anisotropic). In individual MSCs, we observed the highest vascular endothelial growth factor (VEGF) production and total tube length in the failing, isotropic group (2.00 ± 0.37, 1.53 ± 0.24), which was greater than the normal, isotropic group (0.70 ± 0.15, 0.55 ± 0.07; p < 0.05). The presence of anisotropy led to trends of increased VEGF production on normal groups (0.75 ± 0.09 vs 1.20 ± 0.17), but this effect was absent on failing groups. Our findings reveal synergistic effects of RV-like stiffness and anisotropy on MSC pro-angiogenic function and may guide MSC-based therapies for heart failure.

Hippo signaling pathway and respiratory diseases

The hippo signaling pathway is a highly conserved evolutionary signaling pathway that plays an important role in regulating cell proliferation, organ size, tissue development, and regeneration. Increasing evidences consider that the hippo signaling pathway is involved in the process of respiratory diseases. Hippo signaling pathway is mainly composed of mammalian STE20-like kinase 1/2 (MST1/2), large tumor suppressor 1/2 (LATS1/2), WW domain of the Sav family containing protein 1 (SAV1), MOB kinase activator 1 (MOB1), Yes-associated protein (YAP) or transcriptional coactivator with PDZ-binding motif (TAZ), and members of the TEA domain (TEAD) family. YAP is the cascade effector of the hippo signaling pathway. The activation of YAP promotes pulmonary arterial vascular smooth muscle cells (PAVSMCs) proliferation, which leads to pulmonary vascular remodeling; thereby the pulmonary arterial hypertension (PAH) is aggravated. While the loss of YAP leads to high expression of inflammatory genes and the accumulation of inflammatory cells, the pneumonia is consequently exacerbated. In addition, overexpressed YAP promotes the proliferation of lung fibroblasts and collagen deposition; thereby the idiopathic pulmonary fibrosis (IPF) is promoted. Moreover, YAP knockout reduces collagen deposition and the senescence of adult alveolar epithelial cells (AECs); hence the IPF is slowed. In addition, hippo signaling pathway may be involved in the repair of acute lung injury (ALI) by promoting the proliferation and differentiation of lung epithelial progenitor cells and intervening in the repair of pulmonary capillary endothelium. Moreover, the hippo signaling pathway is involved in asthma. In conclusion, the hippo signaling pathway is involved in respiratory diseases. More researches are needed to focus on the molecular mechanisms by which the hippo signaling pathway participates in respiratory diseases.

Perfused Platforms to Mimic Bone Microenvironment at the Macro/Milli/Microscale: Pros and Cons

As life expectancy increases, the population experiences progressive ageing. Ageing, in turn, is connected to an increase in bone-related diseases (i.e., osteoporosis and increased risk of fractures). Hence, the search for new approaches to study the occurrence of bone-related diseases and to develop new drugs for their prevention and treatment becomes more pressing. However, to date, a reliable in vitro model that can fully recapitulate the characteristics of bone tissue, either in physiological or altered conditions, is not available. Indeed, current methods for modelling normal and pathological bone are poor predictors of treatment outcomes in humans, as they fail to mimic the in vivo cellular microenvironment and tissue complexity. Bone, in fact, is a dynamic network including differently specialized cells and the extracellular matrix, constantly subjected to external and internal stimuli. To this regard, perfused vascularized models are a novel field of investigation that can offer a new technological approach to overcome the limitations of traditional cell culture methods. It allows the combination of perfusion, mechanical and biochemical stimuli, biological cues, biomaterials (mimicking the extracellular matrix of bone), and multiple cell types. This review will discuss macro, milli, and microscale perfused devices designed to model bone structure and microenvironment, focusing on the role of perfusion and encompassing different degrees of complexity. These devices are a very first, though promising, step for the development of 3D in vitro platforms for preclinical screening of novel anabolic or anti-catabolic therapeutic approaches to improve bone health.

Mechanical Stimulation on Mesenchymal Stem Cells and Surrounding Microenvironments in Bone Regeneration: Regulations and Applications

Treatment of bone defects remains a challenge in the clinic. Artificial bone grafts are the most promising alternative to autologous bone grafting. However, one of the limiting factors of artificial bone grafts is the limited means of regulating stem cell differentiation during bone regeneration. As a weight-bearing organ, bone is in a continuous mechanical environment. External mechanical force, a type of biophysical stimulation, plays an essential role in bone regeneration. It is generally accepted that osteocytes are mechanosensitive cells in bone. However, recent studies have shown that mesenchymal stem cells (MSCs) can also respond to mechanical signals. This article reviews the mechanotransduction mechanisms of MSCs, the regulation of mechanical stimulation on microenvironments surrounding MSCs by modulating the immune response, angiogenesis and osteogenesis, and the application of mechanical stimulation of MSCs in bone regeneration. The review provides a deep and extensive understanding of mechanical stimulation mechanisms, and prospects feasible designs of biomaterials for bone regeneration and the potential clinical applications of mechanical stimulation.

Strategies for improving adipose-derived stem cells for tissue regeneration

Adipose-derived stem cells (ADSCs) have promising applications in tissue regeneration. Currently, there are only a few ADSC products that have been approved for clinical use. The clinical application of ADSCs still faces many challenges. Here, we review emerging strategies to improve the therapeutic efficacy of ADSCs in tissue regeneration. First, a great quantity of cells is often needed for the stem cell therapies, which requires the advanced cell expansion technologies. In addition cell-derived products are also required for the development of ‘cell-free’ therapies to overcome the drawbacks of cell-based therapies. Second, it is necessary to strengthen the regenerative functions of ADSCs, including viability, differentiation and paracrine ability, for the tissue repair and regeneration required for different physiological and pathophysiological conditions. Third, poor delivery efficiency also restricts the therapeutic effect of ADSCs. Effective methods to improve cell delivery include alleviating harsh microenvironments, enhancing targeting ability and prolonging cell retention. Moreover, we also point out some critical issues about the sources, effectiveness and safety of ADSCs. With these advanced strategies to improve the therapeutic efficacy of ADSCs, ADSC-based treatment holds great promise for clinical applications in tissue regeneration.

Extracellular matrix stiffness controls VEGF165 secretion and neuroblastoma angiogenesis via the YAP/RUNX2/SRSF1 axis

Aberrant variations in angiogenesis have been observed in tumor tissues with abnormal stiffness of extracellular matrix (ECM). However, it remains largely unclear how ECM stiffness influences tumor angiogenesis. Numerous studies have reported that vascular endothelial growth factor-A (VEGF-A) released from tumor cells plays crucial roles in angiogenesis. Hence, we demonstrated the role of ECM stiffness in VEGF-A release from neuroblastoma (NB) cells and the underlying mechanisms. Based on 17 NB clinical samples, a negative correlation was observed between the length of blood vessels and stiffness of NB tissues. In vitro, an ECM stiffness of 30 kPa repressed the secretion of VEGF₁₆₅ from NB cells which subsequently inhibited the tube formation of human umbilical vein endothelial cells (HUVECs). Knocked down VEGF₁₆₅ in NB cells or blocked VEGF₁₆₅ with neutralizing antibodies both repressed the tube formation of HUVECs. Specifically, 30 kPa ECM stiffness repressed the expression and nuclear accumulation of Yes-associated protein (YAP) to regulate the expression of Serine/Arginine Splicing Factor 1 (SRSF1) via Runt-related transcription factor 2 (RUNX2), which may then subsequently induce the expression and secretion of VEGF₁₆₅ in NB tumor cells. Through implantation of 3D col-Tgels with different stiffness into nude mice, the inhibitory effect of 30 kPa on NB angiogenesis was confirmed in vivo. Furthermore, we found that the inhibitory effect of 30 kPa stiffness on NB angiogenesis was reversed by YAP overexpression, suggesting the important role of YAP in NB angiogenesis regulated by ECM stiffness. Overall, our work not only showed a regulatory effect of ECM stiffness on NB angiogenesis, but also revealed a new signaling axis, YAP-RUNX2-SRSF1, that mediates angiogenesis by regulating the expression and secretion of VEGF₁₆₅ from NB cells. ECM stiffness and the potential molecules revealed in the present study may be new therapeutic targets for NB angiogenesis.

Current status of myocardial restoration via the paracrine function of mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) have been studied for nearly two decades as a therapy for myocardial restoration. An emerging direction to repair myocardium is through their paracrine function, which includes the utilization of MSC-derived conditioned medium or extracellular vesicles. In this review, we go over the unique characteristics of MSCs that make it suitable for "off the shelf," cell-free regenerative therapy, current MSC-derived cell-free approaches including their advantages and disadvantages, and the known mechanisms of action of the paracrine effect of MSCs. With a summary of the clinical trials and preclinical studies of MSC-derived cell-free therapy, we classify the aforementioned mechanisms into angiogenesis, immunomodulation, extracellular matrix remodeling, antiapoptosis, and antioxidation. Particularly, we discuss on ways researchers have worked toward enhancing these desired properties to improve the therapeutic outcomes and the investigation of mechanobiology involved in MSC paracrine function. Lastly, we bring up the remaining challenges in this arising field and suggestions for future directions to improve our understanding and control over the potential of MSC paracrine function for myocardial restoration.

Bioengineered Multicellular Liver Microtissues for Modeling Advanced Hepatic Fibrosis Driven Through Non-Alcoholic Fatty Liver Disease

Despite considerable efforts in modeling liver disease in vitro, it remains difficult to recapitulate the pathogenesis of the advanced phases of non-alcoholic fatty liver disease (NAFLD) with inflammation and fibrosis. Here, a liver-on-a-chip platform with bioengineered multicellular liver microtissues is developed, composed of four major types of liver cells (hepatocytes, endothelial cells, Kupffer cells, and stellate cells) to implement a human hepatic fibrosis model driven by NAFLD: i) lipid accumulation in hepatocytes (steatosis), ii) neovascularization by endothelial cells, iii) inflammation by activated Kupffer cells (steatohepatitis), and iv) extracellular matrix deposition by activated stellate cells (fibrosis). In this model, the presence of stellate cells in the liver-on-a-chip model with fat supplementation showed elevated inflammatory responses and fibrosis marker up-regulation. Compared to transforming growth factor-beta-induced hepatic fibrosis models, this model includes the native pathological and chronological steps of NAFLD which shows i) higher fibrotic phenotypes, ii) increased expression of fibrosis markers, and iii) efficient drug transport and metabolism. Taken together, the proposed platform will enable a better understanding of the mechanisms underlying fibrosis progression in NAFLD as well as the identification of new drugs for the different stages of NAFLD.

Stimulating Extracellular Vesicles Production from Engineered Tissues by Mechanical Forces

Extracellular vesicles (EVs) have emerged as a promising strategy to promote tissue regeneration. However, overcoming the low EV production yield remains a big challenge in translating EV-based therapies to the clinical practice. Current EV production relies heavily on 2D cell culture, which is not only less physiologically relevant to cells but also requires substantial medium and space. In this study, we engineered tissues seeded with stem cells from dental pulp or adipose tissues, or skeletal muscle cells, and significantly enhanced the EV production yield by applying mechanical stimuli, including flow and stretching, in bioreactors. Further mechanistic investigation revealed that this process was mediated by yes-associated protein (YAP) mechanosensitivity. EVs from mechanically stimulated dental pulp stem cells on 3D scaffolds displayed superior capability in inducing axonal sprouting than the 2D counterparts. Our results demonstrate the promise of this strategy to boost EV production and optimize their functional performance toward clinical translation.

Resistance Mechanisms of Anti-angiogenic Therapy and Exosomes-Mediated Revascularization in Cancer

Anti-angiogenic therapies (AATs) have been widely used for cancer treatment. But the beneficial effects of AATs are short, because AAT-induced tumor revascularization facilitates the tumor relapse. In this mini-review, we described different forms of tumor neovascularization and revascularization including sprouting angiogenesis, vessel co-option, intussusceptive angiogenesis, and vasculogenic mimicry, all of which are closely mediated by vascular endothelial growth factor (VEGF), angiopoietins, matrix metalloproteinases, and exosomes. We also summarized the current findings for the resistance mechanisms of AATs including enhancement in pro-angiogenic cytokines, heterogeneity in tumor-associated endothelial cells (ECs), crosstalk between tumor cells and ECs, masking of extracellular vesicles, matrix stiffness and contributions from fibroblasts, macrophages and adipocytes in the tumor microenvironment. We highlighted the revascularization following AATs, particularly the role of exosome stimulating factors such as hypoxia and miRNA, and that of exosomal cargos such as cytokines, miRNAs, lncRNAs, and circRNAs from the tumor ECs in angiogenesis and revascularization. Finally, we proposed that renormalization of tumor ECs would be a more efficient cancer therapy than the current AATs.