Biophysical cues to improve the immunomodulatory capacity of mesenchymal stem cells: The progress and mechanisms

Role of chemical groups in regulating membrane tension of mBMSCs under stretch stimulation

As a crucial mechanobiological regulator, the tension of the cell membrane plays a vital role in governing cellular adhesion, proliferation, and differentiation processes. Additionally, it displayed a dynamic response to mechanical microenvironmental changes. This research systematically examines the mechanoresponsive behaviors of mouse bone marrow mesenchymal stem cells (mBMSCs) that are cultured on poly(dimethylsiloxane) (PDMS) substrates which are functionalized with methyl (-CH3), amino (-NH2), and carboxyl (-COOH) groups. Under both static and stretching conditions, it is found that compared with the -CH3 surface, static culture on the -NH2 and -COOH functionalized surfaces significantly promotes the proliferation of mBMSCs and upregulates the expression of extracellular matrix adhesion-related genes, especially focal adhesion kinase (FAK) and integrin β1. Morphometric analysis reveals that there are concomitant increases in the cell spreading area and the number of pseudopods on these modified surfaces. Mechanical stretching stimulation not only amplifies these cellular responses but also leads to more uniform FAK distribution. The assessment by atomic force microscopy (AFM) shows that both chemical functionalization (-NH2/-COOH) and stretch stimulation reduce the deformability of the cell membrane, and the -NH2 modification exhibits a greater membrane-stiffening effect than -COOH.

Biomechanical force-primed periodontal ligament stem cells exhibit a tolerance effect against bacterial inflammation

OBJECTIVE

As mechanosensory cells, periodontal ligament stem cells (PDLSCs) react to mechanical force through proliferative, immunomodulatory, and regenerative actions that promote bone deposition. This study aimed to investigate how biomechanical compressive forces modulate PDLSCs' self-tolerance to proinflammatory responses.

METHODS

PDLSCs were cultured and characterized using flow cytometry. Intermittent compressive stress (ICF) was applied to the cells using a computerized-controlled apparatus, with a force of 1.5 g/cm² at 0.23 Hz for 24 hours. TLR4 activation was induced using lipopolysaccharides (LPS) from P. gingivalis, in the presence or absence of ICF. Pathway inhibitors targeting TGF-β receptor type 1, Rho kinase, and NF-kB were applied to investigate the signaling pathways. Pro-inflammatory cytokine levels were measured using qPCR and ELISA. Western blotting was performed to assess the protein expression of TLR4 and TGF-β1. Immunofluorescence staining was used to localize TLR4. Osteogenic differentiation and IDO enzymatic activity were assessed.

RESULTS

Our results showed that PDLSCs primed with ICF developed tolerance to self-inflammatory responses when exposed to LPS, as indicated by reduced levels of inflammatory factors such as interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ. This tolerance, specific to ICF-primed PDLSCs, was partially mediated by the NF-kB p65 signaling pathway. Additionally, ICF enhanced PDLSC immunosuppressive properties and restored osteogenic differentiation, which had been delayed by LPS/TLR4 activation. Notably, TLR4 responded directly to ICF stimulation.

CONCLUSIONS

This study demonstrated that priming inflamed PDLSCs with biomechanical compressive force induces a tolerance effect against infection-induced inflammation, promoting bone regeneration.

CLINICAL SIGNIFICANCE

This study underscores the critical role of tolerance mechanisms in maintaining PDLSCs homeostasis, highlights the intricate interplay between biomechanical forces and immune modulation, and provides new insights into manipulating stem cells and developing therapeutic strategies to enhance bone and tissue regeneration in immune-related disorders, particularly periodontal disease.

Cell origin and microenvironment: The players of differentiation capacity in human mesenchymal stem cells

Mesenchymal stem cells (MSCs) have several important properties that make them desirable for regenerative medicine. These properties include immunomodulatory ability, growth factor production, and differentiation into various cell types. Despite extensive research and promising results in clinical trials, our understanding of MSC biology, their mechanism of action, and their targeted and routine use in clinics is limited. Differentiation of human MSCs (hMSCs) is a complex process influenced by various elements such as growth factors, pharmaceutical compounds, microRNAs, 3D scaffolds, and mechanical and electrical stimulation. Research has shown that different culture conditions can affect the differentiation potential of hMSCs obtained from multiple fetal and adult sources. Additionally, it seems that what affects the differentiation capacities of these cells is their secretory characteristics, which are influenced by the origin of the cells and the local microenvironment where the cells are located. The review can provide insights into the microenvironment-based mechanisms involved in MSC differentiation, which can be valuable for future therapeutic applications.

Advanced 3D scaffolds for corneal stroma regeneration: a preclinical progress

Corneal stromal defects represent a significant global cause of blindness, necessitating innovative therapeutic strategies to address the limitations of conventional treatments, such as corneal transplantation. Tissue engineering, a cornerstone of regenerative medicine, offers a transformative approach by leveraging biomaterial-based solutions to restore damaged tissues. Among these, three-dimensional (3D) scaffolds fabricated using advanced techniques like 3D printing have emerged as a promising platform for corneal regeneration. These scaffolds replicate the native extracellular matrix (ECM) architecture, providing a biomimetic microenvironment that supports cell proliferation, differentiation, and tissue integration. This review highlights recent advances in the design and fabrication of 3D scaffolds for corneal stroma engineering (CSE), emphasizing the critical interplay between scaffold architecture, mechanical properties, and bioactive signaling in directing cellular behavior and tissue regeneration. Likewise, we emphasize the diverse range of biomaterials utilized in scaffold fabrication, highlighting their influence on cellular interactions and tissue reconstruction. By elucidating the complex relationship between scaffold design and biologics, this review aims to illuminate the evolution of next-generation strategies for engineering functional corneal tissue. Eventually, this review will provide a comprehensive synthesis of the current state-of-the-art in 3D scaffold-based corneal tissue engineering (CTE), offering insights that could advance progress toward effective vision restoration therapies.

Mechanical stretch promotes the migration of mesenchymal stem cells via Piezo1/F-actin/YAP axis

Mesenchymal stem cells (MSCs) have self-renewal ability and the potential for multi-directional differentiation, and their clinical application has promising prospects, but improving the migration ability of MSCs in vivo is one of the challenges. We previously determined mechanical stretch at 1 Hz with 10 % strain for 8 h can significantly promote MSC migration, however, the molecular mechanism remains poorly understood. Here, we reported that the expression and activity of yes-associated protein (YAP) are upregulated after mechanical stretch. As a classical inhibitor of the YAP-TEAD activity and YAP protein, the treatment of verteporfin (VP) suppressed mechanical stretch-promoted MSC migration. We also observed F-actin polymerization after mechanical stretch. Next, we used Latrunculin A (Lat A), the most widely used reagent to depolymerize actin filaments, to treat MSCs and we found that Lat A treatment inhibits MSC migration by suppressing YAP expression and activity. In addition, the protein expression of Piezo1 was also upregulated after mechanical stretch. Knockdown of Piezo1 suppressed mechanical stretch-promoted MSC migration by restraining F-actin polymerization. Together, these findings demonstrate the role of Piezo1/F-actin/YAP signaling pathway in MSC migration under mechanical stretch, providing new experimental evidence for an in-depth understanding the mechanobiological mechanism of MSC migration.

Effects of Hydrogels on Mesenchymal Stem/Stromal Cells Paracrine Activity and Extracellular Vesicles Production

Mesenchymal stem/stromal cells (MSCs) are a valuable source of paracrine factors, as they have a remarkable secretory capacity, and there is a sizeable knowledge base to develop industrial and clinical production protocols. Promising cell-free approaches for tissue regeneration and immunomodulation are driving research towards secretome applications, among which extracellular vesicles (EVs) are steadily gaining attention. However, the manufacturing and application of EVs is limited by insufficient yields, knowledge gaps, and low standardization. Facing these limitations, hydrogels represent a versatile three-dimensional (3D) culture platform that can incorporate extracellular matrix (ECM) components to mimic the natural stem cell environment in vitro; via these niche-mimicking properties, hydrogels can regulate MSCs' morphology, adhesion, proliferation, differentiation and secretion capacities. However, the impact of the hydrogel's architectural, biochemical and biomechanical properties on the production of EVs remains poorly understood, as the field is still in its infancy and the interdependency of culture parameters compromises the comparability of the studies. Therefore, this review summarizes and discusses the reported effects of hydrogel encapsulation and culture on the secretion of MSC-EVs. Considering the effects of cell-material interactions on the overall paracrine activity of MSCs, we identify persistent challenges from low standardization and process control, and outline future paths of research, such as the synergic use of hydrogels and bioreactors to enhance MSC-EV generation.

Substrate stiffness modulates osteogenic and adipogenic differentiation of osteosarcoma through PIEZO1 mediated signaling pathway

Most osteosarcoma (OS) cases exhibit poor differentiation at the histopathological level. Disruption of the normal osteogenic differentiation process results in the unregulated proliferation of precursor cells, which is a critical factor in the development of OS. Differentiation therapy aims to slow disease progression by restoring the osteogenic differentiation process of OS cells and is considered a new approach to treating OS. However, there are currently few studies on the mechanism of differentiation of OS, which puts the development of differentiation therapeutic drugs into a bottleneck. Substrate stiffness can regulate differentiation in mesenchymal stem cells. Evidence supports that mesenchymal stem cells and osteoblast precursors are the origin of OS. In this study, we simulated different stiffnesses in vitro to investigate the mechanism of substrate stiffness affecting differentiation of OS. We demonstrate that Piezo type mechanosensitive ion channel component 1 (PIEZO1) plays a critical regulatory role in sensing substrate stiffness in osteogenic and adipogenic differentiation of OS. When OS cells are cultured on the stiff substrate, integrin subunit beta 1 (ITGB1) increases and cooperates with PIEZO1 to promote Yes-Associated Protein (YAP) entering the nucleus, and may inhibit EZH2, thereby inhibiting H3K27me3 and increasing RUNX2 expression, and cells differentiate toward osteogenesis. Our results provide new insights for research on differentiation treatment of OS and are expected to help identify new targets for future drug design.

Improving the therapeutic profile of MSCs: Cytokine priming reduces donor-dependent heterogeneity and enhances their immunomodulatory capacity

Introduction

MSCs exhibit regenerative, anti-inflammatory and immunomodulatory properties due to the large amount of cytokines, chemokines and growth factors they secrete. MSCs have been extensively evaluated in clinical trials, however, in some cases their therapeutic effects are variable. Therefore, strategies to improve their therapeutic potential, such as preconditioning with proinflammatory factors, have been proposed. Several priming approaches have provided non-conclusive results, and the duration of priming effects on MSC properties or their response to a second inflammatory stimulus have not been fully addressed.

Methods

We have investigated the impact of triple cytokine priming in MSCs on their characterization and viability, their transcriptomic profile, the functionality of innate and acquired immune cells, as well as the maintenance of the response to priming over time, their subsequent responsiveness to a second inflammatory stimulus.

Results

Priming MSCs with proinflammatory cytokines (CK-MSCs) do not modify the differentiation capacity of MSCs, nor their immunophenotype and viability. Moreover, cytokine priming enhances the anti-inflammatory and immunomodulatory properties of MSCs against NK and dendritic cells, while maintaining the same T cell immunomodulatory capacity as unstimulated MSCs. Thus, they decrease T-lymphocytes and NK cell proliferation, inhibit the differentiation and allostimulatory capacity of dendritic cells and promote the differentiation of monocytes with an immunosuppressive profile. In addition, we have shown for the first time that proinflammatory priming reduces the variability between different donors and MSC origins. Finally, the effect on CK-MSC is maintained over time and even after a secondary inflammatory stimulus.

Conclusions

Cytokine-priming improves the therapeutic potential of MSCs and reduces inter-donor variability.

The proliferation/migration ability mediated by CD151/PI3K/AKT pathway determines the therapeutic effect of hUC-MSCs transplantation on rheumatoid arthritis

OBJECTIVE

To elucidate the underlying mechanism by which the proliferation and migration abilities of human umbilical cord mesenchymal stem cells (hUC-MSCs) determine their therapeutic efficacy in rheumatoid arthritis treatment.

METHODS

The DBA/1J mice were utilized to establish a collagen-induced RA (CIA) mouse model and to validate the therapeutic efficacy of hUC-MSCs transfected with CD151 siRNA. RNA-seq, QT-PCR and western blotting were utilized to evaluate the mRNA and protein levels of the PI3K/AKT pathway, respectively.

RESULTS

IFN-γ significantly enhanced the proliferation and migration abilities of hUC-MSCs, up-regulating the expression of CD151, a gene related to cell proliferation and migration. Effective inhibition of this effect was achieved through CD151 siRNA treatment. However, IFN-γ did not affect hUC-MSCs differentiation or changes in cell surface markers. Additionally, transplantation of CD151-interfered hUC-MSCs (siRNA-CD151-hUC-MSCs) resulted in decreased colonization in the toes of CIA mice and worse therapeutic effects compared to empty vector treatment (siRNA-NC-hUC-MSCs).

CONCLUSION

IFN-γ facilitates the proliferation and migration of hUC-MSCs through the CD151/PI3K/AKT pathway. The therapeutic efficacy of siRNA-CD151-hUC-MSCs was found to be inferior to that of siRNA-NC-hUC-MSCs.

Stimuli-Responsive Substrates to Control the Immunomodulatory Potential of Stromal Cells

Mesenchymal stromal cells (MSCs) have broad immunomodulatory properties that range from regulation, proliferation, differentiation, and immune cell activation to secreting bioactive molecules that inhibit inflammation and regulate immune response. These properties provide MSCs with high therapeutic potency that has been shown to be relevant to tissue engineering and regenerative medicine. Hence, researchers have explored diverse strategies to control the immunomodulatory potential of stromal cells using polymeric substrates or scaffolds. These substrates alter the immunomodulatory response of MSCs, especially through biophysical cues such as matrix mechanical properties. To leverage these cell-matrix interactions as a strategy for priming MSCs, emerging studies have explored the use of stimuli-responsive substrates to enhance the therapeutic value of stromal cells. This review highlights how stimuli-responsive materials, including chemo-responsive, microenvironment-responsive, magneto-responsive, mechano-responsive, and photo-responsive substrates, have specifically been used to promote the immunomodulatory potential of stromal cells by controlling their secretory activity.

The Myofibroblast Fate of Therapeutic Mesenchymal Stromal Cells: Regeneration, Repair, or Despair?

Mesenchymal stromal cells (MSCs) can be isolated from various tissues of healthy or patient donors to be retransplanted in cell therapies. Because the number of MSCs obtained from biopsies is typically too low for direct clinical application, MSC expansion in cell culture is required. However, ex vivo amplification often reduces the desired MSC regenerative potential and enhances undesired traits, such as activation into fibrogenic myofibroblasts. Transiently activated myofibroblasts restore tissue integrity after organ injury by producing and contracting extracellular matrix into scar tissue. In contrast, persistent myofibroblasts cause excessive scarring-called fibrosis-that destroys organ function. In this review, we focus on the relevance and molecular mechanisms of myofibroblast activation upon contact with stiff cell culture plastic or recipient scar tissue, such as hypertrophic scars of large skin burns. We discuss cell mechanoperception mechanisms such as integrins and stretch-activated channels, mechanotransduction through the contractile actin cytoskeleton, and conversion of mechanical signals into transcriptional programs via mechanosensitive co-transcription factors, such as YAP, TAZ, and MRTF. We further elaborate how prolonged mechanical stress can create persistent myofibroblast memory by direct mechanotransduction to the nucleus that can evoke lasting epigenetic modifications at the DNA level, such as histone methylation and acetylation. We conclude by projecting how cell culture mechanics can be modulated to generate MSCs, which epigenetically protected against myofibroblast activation and transport desired regeneration potential to the recipient tissue environment in clinical therapies.

Matrix stiffness-dependent regulation of immunomodulatory genes in human MSCs is associated with the lncRNA CYTOR

Cell-matrix interactions in 3D environments significantly differ from those in 2D cultures. As such, mechanisms of mechanotransduction in 2D cultures are not necessarily applicable to cell-encapsulating hydrogels that resemble features of tissue architecture. Accordingly, the characterization of molecular pathways in 3D matrices is expected to uncover insights into how cells respond to their mechanical environment in physiological contexts, and potentially also inform hydrogel-based strategies in cell therapies. In this study, a bone marrow-mimetic hydrogel was employed to systematically investigate the stiffness-responsive transcriptome of mesenchymal stromal cells. High matrix rigidity impeded integrin-collagen adhesion, resulting in changes in cell morphology characterized by a contractile network of actin proximal to the cell membrane. This resulted in a suppression of extracellular matrix-regulatory genes involved in the remodeling of collagen fibrils, as well as the upregulation of secreted immunomodulatory factors. Moreover, an investigation of long noncoding RNAs revealed that the cytoskeleton regulator RNA (CYTOR) contributes to these 3D stiffness-driven changes in gene expression. Knockdown of CYTOR using antisense oligonucleotides enhanced the expression of numerous mechanoresponsive cytokines and chemokines to levels exceeding those achievable by modulating matrix stiffness alone. Taken together, our findings further our understanding of mechanisms of mechanotransduction that are distinct from canonical mechanotransductive pathways observed in 2D cultures.

Peptoid-Cross-Linked Hydrogel Stiffness Modulates Human Mesenchymal Stromal Cell Immunoregulatory Potential in the Presence of Interferon-Gamma

Human mesenchymal stromal cell (hMSC) manufacturing requires the production of large numbers of therapeutically potent cells. Licensing with soluble cytokines improves hMSC therapeutic potency by enhancing secretion of immunoactive factors but typically decreases proliferative ability. Soft hydrogels, however, have shown promise for boosting immunomodulatory potential, which may compensate for decreased proliferation. Here, hydrogels are cross-linked with peptoids of different secondary structures to generate substrates of various bulk stiffnesses but fixed network connectivity. Secretions of interleukin 6, monocyte chemoattractive protein-1, macrophage colony-stimulating factor, and vascular endothelial growth factor are shown to depend on hydrogel stiffness in the presence of interferon gamma (IFN-γ) supplementation, with soft substrates further improving secretion. The immunological function of these secreted cytokines is then investigated via coculture of hMSCs seeded on hydrogels with primary peripheral blood mononuclear cells (PBMCs) in the presence and absence of IFN-γ. Cocultures with hMSCs seeded on softer hydrogels show decreased PBMC proliferation with IFN-γ. To probe possible signaling pathways, immunofluorescent studies probe the nuclear factor kappa B pathway and demonstrate that IFN-γ supplementation and softer hydrogel mechanics lead to higher activation of this pathway. Overall, these studies may allow for production of more efficacious therapeutic hMSCs in the presence of IFN-γ.

Mechanosignaling YAP/TAZ-TEAD Axis Regulates the Immunomodulatory Properties of Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) have gained significant attention in cell therapies due to their multipotency and immunomodulatory capacities. The transcriptional co-activators YAP/TAZ, central to the mechanotransduction system in MSCs, dominantly direct MSCs lineage commitment. However, their role in immunomodulation remains elusive. Accordingly, this present study aimed to investigate the role of mechanotransducer YAP/TAZ and their binding target transcriptional factor, TEAD, in the immunomodulatory capacities of human bone marrow-derived MSCs. Reducing YAP/TAZ activity by altering the matrix stiffness, disrupting the F-actin integrity with chemical inhibitors, or using siRNAs increased the expression of immunomodulatory genes, such as TSG-6 and IDO, upon TNF-α stimulation. Similarly, transfection of TEAD siRNA also increased the immunomodulatory capacities in MSCs. RNA-seq analysis and inhibition assays demonstrated that the immunomodulatory capacities caused by YAP/TAZ-TEAD axis disruption were due to the NF-κB signaling pathway activation. Then, we also evaluated the in vivo anti-inflammatory efficacy of MSCs in a dextran sulfate sodium (DSS)-induced mice colitis model. The administration of human MSCs transfected with TEAD siRNA, which exhibited enhanced immunomodulatory properties in vitro, significantly ameliorated inflammatory bowel disease symptoms, such as body weight loss and acute colon inflammation, in the DSS-induced mice colitis model. Our findings underscore the mechanosignaling YAP/TAZ-TEAD axis as a regulator of MSCs immunomodulation. Targeting these signaling pathways could herald promising MSCs-based therapies for immune disorders.

Factors Defining Human Adipose Stem/Stromal Cell Immunomodulation in Vitro

Human adipose tissue-derived stem/stromal cells (hASCs) are adult multipotent mesenchymal stem/stromal cells with immunomodulatory capacities. Here, we present up-to-date knowledge on the impact of different experimental and donor-related factors on hASC immunoregulatory functions in vitro. The experimental determinants include the immunological status of hASCs relative to target immune cells, contact vs. contactless interaction, and oxygen tension. Factors such as the ratio of hASCs to immune cells, the cellular context, the immune cell activation status, and coculture duration are also discussed. Conditioning of hASCs with different approaches before interaction with immune cells, hASC culture in xenogenic or xenofree culture medium, hASC culture in two-dimension vs. three-dimension with biomaterials, and the hASC passage number are among the experimental parameters that greatly may impact the hASC immunosuppressive potential in vitro, thus, they are also considered. Moreover, the influence of donor-related characteristics such as age, sex, and health status on hASC immunomodulation in vitro is reviewed. By analysis of the literature studies, most of the indicated determinants have been investigated in broad non-standardized ranges, so the results are not univocal. Clear conclusions cannot be drawn for the fine-tuned scenarios of many important factors to set a standard hASC immunopotency assay. Such variability needs to be carefully considered in further standardized research. Importantly, field experts' opinions may help to make it clearer.