Harnessing mesenchymal stem cell secretome: Effect of extracellular matrices on proangiogenic signaling

Modular, Vascularized Hypertrophic Cartilage Constructs for Bone Tissue Engineering Applications

Insufficient vascularization is the main barrier to creating engineered bone grafts for treating large and ischemic defects. Modular tissue engineering approaches have promise in this application because of the ability to combine tissue types and localize microenvironmental cues to drive desired cell function. In direct bone formation approaches, it is challenging to maintain sustained osteogenic activity, since vasculogenic cues can inhibit tissue mineralization. This study harnessed the physiological process of endochondral ossification to create multiphase tissues that allowed concomitant mineralization and vessel formation. Mesenchymal stromal cells in pellet culture were differentiated toward a cartilage phenotype, followed by induction to chondrocyte hypertrophy. Hypertrophic pellets (HPs) exhibited increased alkaline phosphatase activity, calcium deposition, and osteogenic gene expression relative to chondrogenic pellets. In addition, HPs secreted and sequestered angiogenic factors, and supported new blood vessel formation by cocultured endothelial cells and undifferentiated stromal cells. Multiphase constructs created by combining HPs and vascularizing microtissues and maintained in an unsupplemented basal culture medium were shown to support robust vascularization and sustained tissue mineralization. These results demonstrate a promising in vitro strategy to produce multiphase-engineered constructs that concomitantly support the generation of mineralized and vascularized tissue in the absence of exogenous osteogenic or vasculogenic medium supplements.

Tissue integrity and healing response in hypoestrogenic animal model treated by mesh implantation with addition of mesenchymal stem cell secretome

Background

Pelvic organ prolapse increases in prevalence and incidence in older women and hypoestrogenic conditions. Treatment with native tissue surgery has a fairly high recurrence rate. Mesh-augmented surgery is one of the most promising treatments for pelvic organ prolapse, with high effectiveness and low recurrence. Mesh-augmented surgery has a side effect of tissue erosion. The addition of secretome is expected to improve tissue integrity and reduce tissue erosion.

Aim

This study aimed to investigate the effect of adding the umbilical cord mesenchymal stem cell (UC-MSC) secretome on preventing tissue inflammatory responses, improving tissue integrity, and accelerating wound healing.

Methods

A total of 32 female New Zealand white rabbit hypoestrogenic models were divided into two groups: the control group with normal mesh and the secretome group with artificial mesh. Hypoestrogenic models were created using the bilateral ovariectomy method. Mesh implantation was performed using a surgical method on hypoestrogenic rabbits. The animals were euthanized on days 7, 14, 28, and 90 after mesh implantation. Histopathology parameters included angiogenesis formation, fibroblast number, and collagen deposition area.

Result

The results of this study showed that the number of angiogenesis, fibroblast, and collagen deposition data in the secretome group showed higher significantly (p < 0.05) than those in the control group on days 7, 14, 28, and 90 post mesh implantation. The formation of new blood vessels (angiogenesis) in the secretome group demonstrated a mean value of 9.81 ± 2.2 compared to 0.37 ± 0.03 in the control. The number of fibroblasts in the secretome group averaged 151.00 ± 8.14, in contrast to 34.00 ± 13.37 in the control group. Collagen formation in the secretome group was also higher, with a mean value of 80.02 ± 6.71 compared to 59.49 ± 4.61 in the control group over 90 days of observation.

Conclusion

The administration of secretomes from UC-MSC improved tissue integrity and accelerated wound healing.

Tissue integrity and healing response in hypoestrogenic animal model treated by mesh implantation with addition of mesenchymal stem cell secretome

Background

Pelvic organ prolapse increases in prevalence and incidence in older women and hypoestrogenic conditions. Treatment with native tissue surgery has a fairly high recurrence rate. Mesh-augmented surgery is one of the most promising treatments for pelvic organ prolapse, with high effectiveness and low recurrence. Mesh-augmented surgery has a side effect of tissue erosion. The addition of secretome is expected to improve tissue integrity and reduce tissue erosion.

Aim

This study aimed to investigate the effect of adding the umbilical cord mesenchymal stem cell (UC-MSC) secretome on preventing tissue inflammatory responses, improving tissue integrity, and accelerating wound healing.

Methods

A total of 32 female New Zealand white rabbit hypoestrogenic models were divided into two groups: the control group with normal mesh and the secretome group with artificial mesh. Hypoestrogenic models were created using the bilateral ovariectomy method. Mesh implantation was performed using a surgical method on hypoestrogenic rabbits. The animals were euthanized on days 7, 14, 28, and 90 after mesh implantation. Histopathology parameters included angiogenesis formation, fibroblast number, and collagen deposition area.

Result

The results of this study showed that the number of angiogenesis, fibroblast, and collagen deposition data in the secretome group showed higher significantly (p < 0.05) than those in the control group on days 7, 14, 28, and 90 post mesh implantation. The formation of new blood vessels (angiogenesis) in the secretome group demonstrated a mean value of 9.81 ± 2.2 compared to 0.37 ± 0.03 in the control. The number of fibroblasts in the secretome group averaged 151.00 ± 8.14, in contrast to 34.00 ± 13.37 in the control group. Collagen formation in the secretome group was also higher, with a mean value of 80.02 ± 6.71 compared to 59.49 ± 4.61 in the control group over 90 days of observation.

Conclusion

The administration of secretomes from UC-MSC improved tissue integrity and accelerated wound healing.

Various Hydrogel Types as a Potential In Vitro Angiogenesis Model

Angiogenesis, the formation of new blood vessels, is a fundamental process in both physiological repair mechanisms and pathological conditions, including cancer and chronic inflammation. Hydrogels are commonly used as in vitro models to mimic the extracellular matrix (ECM) and support endothelial cell behavior during angiogenesis. Mesenchymal stem cells further augment cell and tissue growth and are therefore widely used in regenerative medicine. Here we examined the combination of distinct hydrogel types-fibrin, collagen, and human platelet lysate (HPL)-on the formation of capillaries in a co-culture system containing human umbilical vein endothelial cells (HUVECs) and bone marrow-derived mesenchymal stem cells (BM-MSCs). The mechanical properties and structural changes of the hydrogels were characterized through scanning electron microscopy (SEM) and nanoindentation over 10 days. Fibrin and HPL gels sustained complex network formations, with HPL gels promoting even vascular tube formation of up to 10-fold capillary caliber. Collagen gels supported negligible angiogenesis. Our results suggest that HPL gels in combination with MSC-EC co-culture may be employed to obtain robust vascularization in tissue engineering. This study provides a comparative analysis of fibrin, collagen, and HPL hydrogels, focusing on their ability to support angiogenesis under identical conditions. Our findings demonstrate the superior performance of HPL gels in promoting robust vascular structures, highlighting their potential as a versatile tool for in vitro angiogenesis modeling.

Engineering cell-derived extracellular matrix for peripheral nerve regeneration

Extracellular matrices (ECMs) play a key role in nerve repair and are recognized as the natural source of biomaterials. In parallel to extensively studied tissue-derived ECMs (ts-ECMs), cell-derived ECMs (cd-ECMs) also have the capability to partially recapitulate the complicated regenerative microenvironment of native nerve tissues. Notably, cd-ECMs can avoid the shortcomings of ts-ECMs. Cd-ECMs can be prepared by culturing various cells or even autologous cells in vitro under pathogen-free conditions. And mild decellularization can achieve efficient removal of immunogenic components in cd-ECMs. Moreover, cd-ECMs are more readily customizable to achieve the desired functional properties. These advantages have garnered significant attention for the potential of cd-ECMs in neuroregenerative medicine. As promising biomaterials, cd-ECMs bring new hope for the effective treatment of peripheral nerve injuries. Herein, this review comprehensively examines current knowledge about the functional characteristics of cd-ECMs and their mechanisms of interaction with cells in nerve regeneration, with a particular focus on the preparation, engineering optimization, and scalability of cd-ECMs. The applications of cd-ECMs from distinct cell sources reported in peripheral nerve tissue engineering are highlighted and summarized. Furthermore, current limitations that should be addressed and outlooks related to clinical translation are put forward as well.

MSCs-Derived Decellularised Matrix: Cellular Responses and Regenerative Dentistry

The decellularised extracellular matrix (dECM) of in vitro cell culture is a naturally derived biomaterial formed by the removal of cellular components. The compositions of molecules in the extracellular matrix (ECM) differ depending on various factors, including the culture conditions. Cell-derived ECM provides a 3-dimensional structure that has a complex influence on cell signalling, which in turn affects cell survival and differentiation. This review describes the effects of dECM derived from mesenchymal stem cells (MSCs) on cell responses, including cell migration, cell proliferation, and cell differentiation in vitro. Published articles were searched in the PubMed databases in 2005 to 2022, with assigned keywords (MSCs and decellularisation and cell culture). The 41 articles were reviewed, with the following criteria. (1) ECM was produced exclusively from MSCs; (2) decellularisation processes were performed; and (3) the dECM production was discussed in terms of culture systems and specific supplementations that are suitable for creating the dECM biomaterials. The dECM derived from MSCs supports cell adhesion, enhances cell proliferation, and promotes cell differentiation. Importantly, dECM derived from dental MSCs shows promise in regenerative dentistry applications. Therefore, the literature strongly supports cell-based dECMs as a promising option for innovative tissue engineering approaches for regenerative medicine.

Modular, Vascularized Hypertrophic Cartilage Constructs for Bone Tissue Engineering Applications

Insufficient vascularization is a main barrier to creating engineered bone grafts for treating large and ischemic defects. Modular tissue engineering approaches have promise in this application because of the ability to combine tissue types and to localize microenvironmental cues to drive desired cell function. In direct bone formation approaches, it is challenging to maintain sustained osteogenic activity, since vasculogenic cues can inhibit tissue mineralization. This study harnessed the physiological process of endochondral ossification to create multiphase tissues that allowed concomitant mineralization and vessel formation. Mesenchymal stromal cells in pellet culture were differentiated toward a cartilage phenotype, followed by induction to chondrocyte hypertrophy. Hypertrophic pellets exhibited increased alkaline phosphatase activity, calcium deposition, and osteogenic gene expression relative to chondrogenic pellets. In addition, hypertrophic pellets secreted and sequestered angiogenic factors, and supported new blood vessel formation by co-cultured endothelial cells and undifferentiated stromal cells. Multiphase constructs created by combining hypertrophic pellets and vascularizing microtissues and maintained in unsupplemented basal culture medium were shown to support robust vascularization and sustained tissue mineralization. These results demonstrate a new in vitro strategy to produce multiphase engineered constructs that concomitantly support the generation of mineralize and vascularized tissue in the absence of exogenous osteogenic or vasculogenic medium supplements.

Human mesenchymal stem cell secretomes: Factors affecting profiling and challenges in clinical application

The promising field of regenerative medicine is thrilling as it can repair and restore organs for various debilitating diseases. Mesenchymal stem cells are one of the main components in regenerative medicine that work through the release of secretomes. By adopting the use of the secretome in cell-free-based therapy, we may be able to address the challenges faced in cell-based therapy. As one of the components of cell-free-based therapy, secretome has the advantage of a better safety and efficacy profile than mesenchymal stem cells. However, secretome has its challenges that need to be addressed, such as its bioprocessing methods that may impact the secretome content and its mechanisms of action in clinical settings. Effective and standardization of bioprocessing protocols are important to ensure the supply and sustainability of secretomes for clinical applications. This may eventually impact its commercialization and marketability. In this review, the bioprocessing methods and their impacts on the secretome profile and treatment are discussed. This improves understanding of its fundamental aspects leading to potential clinical applications.

Effect of extracellular matrices on production and potency of mesenchymal stem cell-derived exosomes

Mesenchymal stem cell (MSC) derived exosomes have emerged as potential acellular therapeutics for various tissue regenerative applications. However, successful clinical translation of exosome-based therapy is limited by lack of a structured production platform. Thus, in this study, the effect of decellularized extracellular matrix (dECM) was assessed on the production and potency of exosomes secreted by bone marrow-derived human MSCs. The results indicate that there was a ∼2-fold increase in MSC-exosome production when MSCs were cultured on dECM compared to TCP. Further, our study revealed that dECM generation induced by ascorbic acid (AA) up to 100 µg mL-1 highly increased exosome yield thereby indicating a potential scale up method for MSC exosome production. The bioactivity of exosomes was investigated by their ability to improve the healing of wounded human skin explants. Wound closure was enhanced in the presence of exosomes isolated from MSCs cultured on ascorbic acid-induced dECM compared to TCP generated MSC-exosomes. In summary, this study suggests a promising solution to a major bottleneck in large-scale production of MSC exosomes for cell-free therapy.

Towards the Standardization of Mesenchymal Stem Cell Secretome-Derived Product Manufacturing for Tissue Regeneration

Mesenchymal stem cell secretome or conditioned medium (MSC-CM) is a combination of biomolecules and growth factors in cell culture growth medium, secreted by mesenchymal stem cells (MSCs), and the starting point of several derived products. MSC-CM and its derivatives could be applied after injuries and could mediate most of the beneficial regenerative effects of MSCs without the possible side effects of using MSCs themselves. However, before the clinical application of these promising biopharmaceuticals, several issues such as manufacturing protocols and quality control must be addressed. This review aims to underline the influence of the procedure for conditioned medium production on the quality of the secretome and its derivatives and highlights the questions considering cell sources and donors, cell expansion, cell passage number and confluency, conditioning period, cell culture medium, microenvironment cues, and secretome-derived product purification. A high degree of variability in MSC secretomes is revealed based on these parameters, confirming the need to standardize and optimize protocols. Understanding how bioprocessing and manufacturing conditions interact to determine the quantity, quality, and profile of MSC-CM is essential to the development of good manufacturing practice (GMP)-compliant procedures suitable for replacing mesenchymal stem cells in regenerative medicine.

Multimodular vascularized bone construct comprised of vasculogenic and osteogenic microtissues

Bioengineered bone designed to heal large defects requires concomitant development of osseous and vascular tissue to ensure engraftment and survival. Adult human mesenchymal stromal cells (MSC) are promising in this application because they have demonstrated both osteogenic and vasculogenic potential. This study employed a modular approach in which cells were encapsulated in biomaterial carriers (microtissues) designed to support tissue-specific function. Osteogenic microtissues consisting of MSC embedded in a collagen-chitosan matrix; vasculogenic (VAS) microtissues consisted of endothelial cells and MSC in a fibrin matrix. Microtissues were precultured under differentiation conditions to induce appropriate MSC lineage commitment, and were then combined in a surrounding fibrin hydrogel to create a multimodular construct. Results demonstrated the ability of microtissues to support lineage commitment, and that preculture primes the microtissues for the desired function. Combination of osteogenic and vasculogenic microtissues into multimodular constructs demonstrated that osteogenic priming resulted in sustained osteogenic activity even when cultured in vasculogenic medium, and that vasculogenic priming induced a pericyte-like phenotype that resulted in development of a primitive vessel network in the constructs. The modular approach allows microtissues to be separately precultured to harness the dual differentiation potential of MSC to support both bone and blood vessel formation in a unified construct.

Single-cell transcriptome atlas of human mesenchymal stem cells exploring cellular heterogeneity

BACKGROUND

The heterogeneity of mesenchymal stem cells (MSCs) is poorly understood, thus limiting clinical application and basic research reproducibility. Advanced single-cell RNA sequencing (scRNA-seq) is a robust tool used to analyse for dissecting cellular heterogeneity. However, the comprehensive single-cell atlas for human MSCs has not been achieved.

METHODS

This study used massive parallel multiplexing scRNA-seq to construct an atlas of > 130 000 single-MSC transcriptomes across multiple tissues and donors to assess their heterogeneity. The most widely clinically utilised tissue resources for MSCs were collected, including normal bone marrow (n = 3), adipose (n = 3), umbilical cord (n = 2), and dermis (n = 3).

RESULTS

Seven tissue-specific and five conserved MSC subpopulations with distinct gene-expression signatures were identified from multiple tissue origins based on the high-quality data, which has not been achieved previously. This study showed that extracellular matrix (ECM) highly contributes to MSC heterogeneity. Notably, tissue-specific MSC subpopulations were substantially heterogeneous on ECM-associated immune regulation, antigen processing/presentation, and senescence, thus promoting inter-donor and intra-tissue heterogeneity. The variable dynamics of ECM-associated genes had discrete trajectory patterns across multiple tissues. Additionally, the conserved and tissue-specific transcriptomic-regulons and protein-protein interactions were identified, potentially representing common or tissue-specific MSC functional roles. Furthermore, the umbilical-cord-specific subpopulation possessed advantages in immunosuppressive properties.

CONCLUSION

In summary, this work provides timely and great insights into MSC heterogeneity at multiple levels. This MSC atlas taxonomy also provides a comprehensive understanding of cellular heterogeneity, thus revealing the potential improvements in MSC-based therapeutic efficacy.

Modulation of Inherent Niches in 3D Multicellular MSC Spheroids Reconfigures Metabolism and Enhances Therapeutic Potential

Multicellular spheroids show three-dimensional (3D) organization with extensive cell–cell and cell–extracellular matrix interactions. Owing to their native tissue-mimicking characteristics, mesenchymal stem cell (MSC) spheroids are considered promising as implantable therapeutics for stem cell therapy. Herein, we aim to further enhance their therapeutic potential by tuning the cultivation parameters and thus the inherent niche of 3D MSC spheroids. Significantly increased expression of multiple pro-regenerative paracrine signaling molecules and immunomodulatory factors by MSCs was observed after optimizing the conditions for spheroid culture. Moreover, these alterations in cellular behaviors may be associated with not only the hypoxic niche developed in the spheroid core but also with the metabolic reconfiguration of MSCs. The present study provides efficient methods for manipulating the therapeutic capacity of 3D MSC spheroids, thus laying solid foundations for future development and clinical application of spheroid-based MSC therapy for regenerative medicine.

Pharmacological Preconditioning Improves the Viability and Proangiogenic Paracrine Function of Hydrogel-Encapsulated Mesenchymal Stromal Cells

The efficacy of cell therapy is limited by low retention and survival of transplanted cells in the target tissues. In this work, we hypothesize that pharmacological preconditioning with celastrol, a natural potent antioxidant, could improve the viability and functions of mesenchymal stromal cells (MSC) encapsulated within an injectable scaffold. Bone marrow MSCs from rat (rMSC) and human (hMSC) origin were preconditioned for 1 hour with celastrol 1 μM or vehicle (DMSO 0.1% v/v), then encapsulated within a chitosan-based thermosensitive hydrogel. Cell viability was compared by alamarBlue and live/dead assay. Paracrine function was studied first by quantifying the proangiogenic growth factors released, followed by assessing scratched HUVEC culture wound closure velocity and proliferation of HUVEC when cocultured with encapsulated hMSC. In vivo, the proangiogenic activity was studied by evaluating the neovessel density around the subcutaneously injected hydrogel after one week in rats. Preconditioning strongly enhanced the viability of rMSC and hMSC compared to vehicle-treated cells, with 90% and 75% survival versus 36% and 58% survival, respectively, after 7 days in complete media and 80% versus 64% survival for hMSC after 4 days in low serum media (p < 0.05). Celastrol-treated cells increased quantities of proangiogenic cytokines compared to vehicle-pretreated cells, with a significant 3.0-fold and 1.8-fold increase of VEGFa and SDF-1α, respectively (p < 0.05). The enhanced paracrine function of preconditioned MSC was demonstrated by accelerated growth and wound closure velocity of injured HUVEC monolayer (p < 0.05) in vitro. Moreover, celastrol-treated cells, but not vehicle-treated cells, led to a significant increase of neovessel density in the peri-implant region after one week in vivo compared to the control (blank hydrogel). These results suggest that combining cell pretreatment with celastrol and encapsulation in hydrogel could potentiate MSC therapy for many diseases, benefiting particularly ischemic diseases.

Impact of mesenchymal stem cell-secretome-loaded hydrogel on proliferative and migratory activities of hyperglycemic fibroblasts

Disruption of the reparative process, often found in diabetic patients, results in chronic, non-healing wounds that significantly impact a patient's quality of life. This highlights the need of new therapeutic options to improve the healing of diabetic wounds. In this study, we focused on developing a cell-free hydrogel dressing loaded with mesenchymal stem cell (MSC)-conditioned media (CM) to potentially improve the healing of hard-to-heal wounds. We simulated a hyperglycemic environment by incubating human dermal fibroblasts in a high glucose environment (30 mM) and validated that MSC-CM rescued the impaired functions (proliferation and migration) of hyperglycemic fibroblasts. Further, we investigated the effect of loading MSC-CM in gelatin methacrylate (GelMA)-poly (ethylene glycol) diacrylate (PEGDA) hybrid hydrogels in improving the proliferative activity of glucose-treated fibroblasts. The controlled release of bioactive factors from MSC-CM loaded GelMA-PEGDA hydrogels promoted the metabolic activity of hyperglycemic fibroblasts. In addition, the growth rate of hyperglycemic fibroblasts was found to be similar to that of normal fibroblasts. Our observations, thus, suggest the potential application of cell-free, MSC-secretome-loaded hydrogel in the healing of diabetic or chronic wounds.

Engineering the MSC Secretome: A Hydrogel Focused Approach

The therapeutic benefits of exogenously delivered mesenchymal stromal/stem cells (MSCs) have been largely attributed to their secretory properties. However, clinical translation of MSC-based therapies is hindered due to loss of MSC regenerative properties during large-scale expansion and low survival/retention post-delivery. These limitations might be overcome by designing hydrogel culture platforms to modulate the MSC microenvironment. Hydrogel systems could be engineered to i) promote MSC proliferation and maintain regenerative properties (i.e., stemness and secretion) during ex vivo expansion, ii) improve MSC survival, retention, and engraftment in vivo, and/or iii) direct the MSC secretory profile using tailored biochemical and biophysical cues. Herein, it is reviewed how hydrogel material properties (i.e., matrix modulus, viscoelasticity, dimensionality, cell adhesion, and porosity) influence MSC secretion, mediated through cell-matrix and cell-cell interactions. In addition, it is highlighted how biochemical cues (i.e., small molecules, peptides, and proteins) can improve and direct the MSC secretory profile. Last, the authors' perspective is provided on future work toward the understanding of how microenvironmental cues influence the MSC secretome, and designing the next generation of biomaterials, with optimized biophysical and biochemical cues, to direct the MSC secretory profile for improved clinical translation outcomes.

Whole Heart Engineering: Advances and Challenges

Bioengineering a solid organ for organ replacement is a growing endeavor in regenerative medicine. Our approach - recellularization of a decellularized cadaveric organ scaffold with human cells - is currently the most promising approach to building a complex solid vascularized organ to be utilized in vivo, which remains the major unmet need and a key challenge. The 2008 publication of perfusion-based decellularization and partial recellularization of a rat heart revolutionized the tissue engineering field by showing that it was feasible to rebuild an organ using a decellularized extracellular matrix scaffold. Toward the goal of clinical translation of bioengineered tissues and organs, there is increasing recognition of the underlying need to better integrate basic science domains and industry. From the perspective of a research group focusing on whole heart engineering, we discuss the current approaches and advances in whole organ engineering research as they relate to this multidisciplinary field's 3 major pillars: organ scaffolds, large numbers of cells, and biomimetic bioreactor systems. The success of whole organ engineering will require optimization of protocols to produce biologically-active scaffolds for multiple organ systems, and further technological innovation both to produce the massive quantities of high-quality cells needed for recellularization and to engineer a bioreactor with physiologic stimuli to recapitulate organ function. Also discussed are the challenges to building an implantable vascularized solid organ.

Seaweed polysaccharides as macromolecular crowding agents

Development of mesenchymal stem cell-based tissue engineered implantable devices requires prolonged in vitro culture for the development of a three-dimensional implantable device, which leads to phenotypic drift, thus hindering the clinical translation and commercialisation of such approaches. Macromolecular crowding, a biophysical phenomenon based on the principles of excluded-volume effect, dramatically accelerates and increases extracellular matrix deposition during in vitro culture. However, the optimal macromolecular crowder is still elusive. Herein, we evaluated the biophysical properties of various concentrations of different seaweed in origin sulphated polysaccharides and their effect on human adipose derived stem cell cultures. Carrageenan, possibly due to its high sulphation degree, exhibited the highest negative charge values. No correlation was observed between the different concentrations of the crowders and charge, polydispersity index, hydrodynamic radius and fraction volume occupancy across all crowders. None of the crowders, but arabinogalactan, negatively affected cell viability. Carrageenan, fucoidan, galactofucan and ulvan increased extracellular matrix (especially collagen type I and collagen type V) deposition. Carrageenan induced the highest osteogenic effect and galactofucan and fucoidan demonstrated the highest chondrogenic effect. All crowders were relatively ineffective with respect to adipogenesis. Our data highlight the potential of sulphated seaweed polysaccharides for tissue engineering purposes.