Extracellular matrix deposition of bone marrow stroma enhanced by macromolecular crowding

Activin A is a Master Regulator of Phenotypic Switch in Adipose Stromal Cells Initiated by Activated Immune Cell-secreted IL-1β

Prolonged tissue ischemia and inflammation lead to organ deterioration and are often accompanied by microvasculature rarefaction, fibrosis, and elevated systemic Activin A (ActA), the level of which frequently correlates with disease severity. Mesenchymal stromal cells are prevalent in the perivascular niche and are likely involved in tissue homeostasis and pathology. This study investigated the effects of inflammatory cells on modulation of phenotype of adipose stromal cell (ASC) and the role of ActA in this process. Peripheral blood mononuclear cells were activated with LPS (aPBMC) and presented to ASC. Expression of smooth muscle/myofibroblast markers and ActA, TGFβ1-3 and CTGF was assessed in ASC. Silencing approaches were used to dissect the signaling cascade of aPBMC-induced acquisition of a myofibroblast phenotype by ASC. ASC co-cultured with aPBMC or exposed to the secretome of aPBMC upregulated smooth muscle cell markers αSMA, SM22α, and Calponin I, increased contractility, and initiated expression of ActA. IL-1β was sufficient to replicate this response, whereas blocking IL-1β eliminated aPBMC effects. ASC-derived ActA stimulated CTGF and αSMA expression in ASC; the latter independent of CTGF. Induction of αSMA in ASC by IL-1β or ActA-enriched media relied on extracellular enzymatic activity. ActA upregulated mRNA levels of several extracellular matrix proteins in ASC, albeit to a lesser degree than TGFβ1, and marginally increased cell contractility. In conclusion, the study suggests that aPBMC induce myofibroblast phenotype with weak fibrotic activity in perivascular progenitors, like ASC, through the IL-1β-ActA signaling axis, which also promotes CTGF secretion and these effects require ActA extracellular enzymatic processing.

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.

Advances in ex vivo expansion of hematopoietic stem and progenitor cells for clinical applications

As caretakers of the hematopoietic system, hematopoietic stem cells assure a lifelong supply of differentiated populations that are responsible for critical bodily functions, including oxygen transport, immunological protection and coagulation. Due to the far-reaching influence of the hematopoietic system, hematological disorders typically have a significant impact on the lives of individuals, even becoming fatal. Hematopoietic cell transplantation was the first effective therapeutic avenue to treat such hematological diseases. Since then, key use and manipulation of hematopoietic stem cells for treatments has been aspired to fully take advantage of such an important cell population. Limited knowledge on hematopoietic stem cell behavior has motivated in-depth research into their biology. Efforts were able to uncover their native environment and characteristics during development and adult stages. Several signaling pathways at a cellular level have been mapped, providing insight into their machinery. Important dynamics of hematopoietic stem cell maintenance were begun to be understood with improved comprehension of their metabolism and progressive aging. These advances have provided a solid platform for the development of innovative strategies for the manipulation of hematopoietic stem cells. Specifically, expansion of the hematopoietic stem cell pool has triggered immense interest, gaining momentum. A wide range of approaches have sprouted, leading to a variety of expansion systems, from simpler small molecule-based strategies to complex biomimetic scaffolds. The recent approval of Omisirge, the first expanded hematopoietic stem and progenitor cell product, whose expansion platform is one of the earliest, is predictive of further successes that might arise soon. In order to guarantee the quality of these ex vivo manipulated cells, robust assays that measure cell function or potency need to be developed. Whether targeting hematopoietic engraftment, immunological differentiation potential or malignancy clearance, hematopoietic stem cells and their derivatives need efficient scaling of their therapeutic potency. In this review, we comprehensively view hematopoietic stem cells as therapeutic assets, going from fundamental to translational.

Macromolecular crowding in human tenocyte and skin fibroblast cultures: A comparative analysis

Although human tenocytes and dermal fibroblasts have shown promise in tendon engineering, no tissue engineered medicine has been developed due to the prolonged ex vivo time required to develop an implantable device. Considering that macromolecular crowding has the potential to substantially accelerate the development of functional tissue facsimiles, herein we compared human tenocyte and dermal fibroblast behaviour under standard and macromolecular crowding conditions to inform future studies in tendon engineering. Basic cell function analysis made apparent the innocuousness of macromolecular crowding for both cell types. Gene expression analysis of the without macromolecular crowding groups revealed expression of tendon related molecules in human dermal fibroblasts and tenocytes. Protein electrophoresis and immunocytochemistry analyses showed significantly increased and similar deposition of collagen fibres by macromolecular crowding in the two cell types. Proteomics analysis demonstrated great similarities between human tenocyte and dermal fibroblast cultures, as well as the induction of haemostatic, anti-microbial and tissue-protective proteins by macromolecular crowding in both cell populations. Collectively, these data rationalise the use of either human dermal fibroblasts or tenocytes in combination with macromolecular crowding in tendon engineering.

Gums as Macromolecular Crowding Agents in Human Skin Fibroblast Cultures

Even though tissue-engineered medicines are under intense academic, clinical, and commercial investigation, only a handful of products have been commercialised, primarily due to the costs associated with their prolonged manufacturing. While macromolecular crowding has been shown to enhance and accelerate extracellular matrix deposition in eukaryotic cell culture, possibly offering a solution in this procrastinating tissue-engineered medicine development, there is still no widely accepted macromolecular crowding agent. With these in mind, we herein assessed the potential of gum Arabic, gum gellan, gum karaya, and gum xanthan as macromolecular crowding agents in WS1 skin fibroblast cultures (no macromolecular crowding and carrageenan were used as a control). Dynamic light scattering analysis revealed that all macromolecules had negative charge and were polydispersed. None of the macromolecules affected basic cellular function. At day 7 (the longest time point assessed), gel electrophoresis analysis revealed that all macromolecules significantly increased collagen type I deposition in comparison to the non-macromolecular crowding group. Also at day 7, immunofluorescence analysis revealed that carrageenan; the 50 µg/mL, 75 µg/mL, and 100 µg/mL gum gellan; and the 500 µg/mL and 1000 µg/mL gum xanthan significantly increased both collagen type I and collagen type III deposition and only carrageenan significantly increased collagen type V deposition, all in comparison to the non-macromolecular crowding group at the respective time point. This preliminary study demonstrates the potential of gums as macromolecular crowding agents, but more detailed biological studies are needed to fully exploit their potential in the development of tissue-engineered medicines.

Macromolecular crowding in equine bone marrow mesenchymal stromal cell cultures using single and double hyaluronic acid macromolecules

Macromolecular crowding (MMC) enhances and accelerates extracellular matrix (ECM) deposition in eukaryotic cell culture. Single hyaluronic acid (HA) molecules have not induced a notable increase in the amount and rate of deposited ECM. Thus, herein we assessed the physicochemical properties and biological consequences in equine bone marrow mesenchymal stromal cell cultures of single and mixed HA molecules and correlated them to the most widely used MMC agents, the FicollⓇ cocktail (FC) and carrageenan (CR). Dynamic light scattering analysis revealed that all HA cocktails had significantly higher hydrodynamic radius than the FC and CR; the FC and the 0.5 mg/ml 100 kDa and 500 kDa single HA molecules had the highest charge; and, in general, all molecules had high polydispersity index. Biological analyses revealed that none of the MMC agents affected cell morphology and basic cell functions; in general, CR outperformed all other macromolecules in collagen type I and V deposition; FC, the individual HA molecules and the HA cocktails outperformed CR in collagen type III deposition; FC outperformed CR and the individual HA molecules and the HA cocktails outperformed their constituent HA molecules in collagen type IV deposition; FC and certain HA cocktails outperformed CR and constituent HA molecules in collagen type VI deposition; and all individual HA molecules outperformed FC and CR and the HA cocktails outperformed their constituent HA molecules in laminin deposition. With respect to tri-lineage analysis, CR and HA enhanced chondrogenesis and osteogenesis, whilst FC enhanced adipogenesis. This work opens new avenues in mixed MMC in eukaryotic cell culture. STATEMENT OF SIGNIFICANCE: Mixed macromolecular crowding (MMC) in eukaryotic cell culture is still under-investigated. Herein, single and double hyaluronic acid (HA) macromolecules, along with the traditional MMC agents FicollⓇ cocktail (FC) and carrageenan (CR), were used as MMC agents in equine mesenchymal stromal cell cultures. Biological analysis showed that none of the MMC agents affected cell morphology and basic cell functions. Protein deposition analysis made apparent that CR outperformed all other macromolecules in collagen type I and collagen type V deposition, whilst FC, the individual HA macromolecules and the HA cocktails outperformed CR in collagen type III deposition. Tri-lineage analysis revealed that CR and HA enhanced chondrogenesis and osteogenesis, whilst FC enhanced adipogenesis. These data illustrate that MMC agents are not inert macromolecules.

Carrageenan-Based Crowding and Confinement Combination Approach to Increase Collagen Deposition for In Vitro Tissue Development

Connective tissue models grown from cell monolayers can be instrumental in a variety of biomedical fields such as drug screening, wound healing, and regenerative engineering. However, while connective tissues contain abundant fibrillar collagen, achieving a sufficient assembly and retention of fibrillar collagen in vitro is challenging. Unlike the dilute cell culture environment, the body's environment is characterized by a high density of soluble macromolecules (crowding) and macromolecular networks (confinement), which contribute to extracellular matrix (ECM) assembly in vivo. Consequently, macromolecular crowding (MMC) has been successfully used to enhance the processing of type I procollagen, leading to significant increases in fibrillar collagen assembly and accumulation during in vitro culture of a variety of cell types. In this study, we developed a combination approach using a carrageenan hydrogel, which released soluble macromolecules and served as a confinement barrier. We first evaluated the local carrageenan release and then confirmed the effectiveness of this combination approach on collagen accumulation by the human MG-63 bone cell line. Additionally, computational modeling of oxygen and glucose transport within the culture system showed no negative effects of the hydrogel and its releasates on cell viability.

Discriminant Principal Component Analysis of ToF-SIMS Spectra for Deciphering Compositional Differences of MSC-Secreted Extracellular Matrices

Identifying characteristic extracellular matrix (ECM) variants is a key challenge in mechanistic biology, bioengineering, and medical diagnostics. The reported study demonstrates the potential of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to detect subtle differences between human mesenchymal stromal cell (MSC)-secreted ECM types as induced by exogenous stimulation or emerging pathology. ToF-SIMS spectra of decellularized ECM samples are evaluated by discriminant principal component analysis (DPCA), an advanced multivariate analysis technique, to decipher characteristic compositional features. To establish the approach, signatures of major ECM proteins are determined from samples of pre-defined mixtures. Based on that, sets of ECM variants produced by MSCs in vitro are analyzed. Differences in the content of collagen, fibronectin, and laminin in the ECM resulting from the combined supplementation of MSC cultures with polymers that induce macromolecular crowding and with ascorbic acid are detected from the DPCA of ToF-SIMS spectra. The results are verified by immunostaining. Finally, the comparative ToF-SIMS analysis of ECM produced by MSCs of healthy donors and patients suffering from myelodysplastic syndrome display the potential of the novel methodology to reveal disease-associated alterations of the ECM composition.

Rapid formation of 3D: Decellularized extracellular matrix spheroids for enhancing bone formation

Bone marrow mesenchymal stem cell sheet-derived spheroids (BMSCs spheroids) have been widely studied as native bioactive scaffolds. However, the abundant cells in BMSCs spheroids cause immunogenicity and make them difficult to store. This paper aimed to construct a new bioactive scaffold called 3D-decellularized extracellular matrix spheroids (ECM spheroids) via decellularization of BMSCs spheroids to enhance bone formation. Hematoxylin and eosin staining (HE), nuclear and cytoskeletal fluorescence, immunofluorescence (IF), and scanning electron microscopy (SEM) were utilized to detect the characteristics and components of ECM spheroids. Furthermore, the biological properties of migration, adhesion, and recellularization of cells in ECM spheroids were assessed in vitro, and bone formation was evaluated in rat calvarial defects. The results showed that both the nuclei and cytoskeleton in ECM spheroids were greatly altered and one of the major components of FN was intact. The migration, adhesion, and recellularization potential were improved in vitro. Meanwhile, ECM spheroids promoted osteogenesis in rat skull defects after 3 months (p < .01). In conclusion, ECM spheroids were successfully prepared and proven to promote cell migration, adhesion, and proliferation. Bone formation in vivo was also accelerated. We believe that ECM spheroids can be used as bioactive and biocompatible 3D scaffolds in the future.

Macromolecular crowding and decellularization method increase the growth factor binding potential of cell-secreted extracellular matrices

Recombinant growth factors are used in tissue engineering to stimulate cell proliferation, migration, and differentiation. Conventional methods of growth factor delivery for therapeutic applications employ large amounts of these bioactive cues. Effective, localized growth factor release is essential to reduce the required dose and potential deleterious effects. The endogenous extracellular matrix (ECM) sequesters native growth factors through its negatively charged sulfated glycosaminoglycans. Mesenchymal stromal cells secrete an instructive extracellular matrix that can be tuned by varying culture and decellularization methods. In this study, mesenchymal stromal cell-secreted extracellular matrix was modified using λ-carrageenan as a macromolecular crowding (MMC) agent and decellularized with DNase as an alternative to previous decellularized extracellular matrices (dECM) to improve growth factor retention. Macromolecular crowding decellularized extracellular matrix contained 7.7-fold more sulfated glycosaminoglycans and 11.7-fold more total protein than decellularized extracellular matrix, with no significant difference in residual DNA. Endogenous BMP-2 was retained in macromolecular crowding decellularized extracellular matrix, whereas BMP-2 was not detected in other extracellular matrices. When implanted in a murine muscle pouch, we observed increased mineralized tissue formation with BMP-2-adsorbed macromolecular crowding decellularized extracellular matrix in vivo compared to conventional decellularized extracellular matrix. This study demonstrates the importance of decellularization method to retain endogenous sulfated glycosaminoglycans in decellularized extracellular matrix and highlights the utility of macromolecular crowding to upregulate sulfated glycosaminoglycan content. This platform has the potential to aid in the delivery of lower doses of BMP-2 or other heparin-binding growth factors in a tunable manner.

Macromolecular crowding in animal component-free, xeno-free and foetal bovine serum media for human bone marrow mesenchymal stromal cell expansion and differentiation

Background: Cell culture media containing undefined animal-derived components and prolonged in vitro culture periods in the absence of native extracellular matrix result in phenotypic drift of human bone marrow stromal cells (hBMSCs). Methods: Herein, we assessed whether animal component-free (ACF) or xeno-free (XF) media formulations maintain hBMSC phenotypic characteristics more effectively than foetal bovine serum (FBS)-based media. In addition, we assessed whether tissue-specific extracellular matrix, induced via macromolecular crowding (MMC) during expansion and/or differentiation, can more tightly control hBMSC fate. Results: Cells expanded in animal component-free media showed overall the highest phenotype maintenance, as judged by cluster of differentiation expression analysis. Contrary to FBS media, ACF and XF media increased cellularity over time in culture, as measured by total DNA concentration. While MMC with Ficoll™ increased collagen deposition of cells in FBS media, FBS media induced significantly lower collagen synthesis and/or deposition than the ACF and XF media. Cells expanded in FBS media showed higher adipogenic differentiation than ACF and XF media, which was augmented by MMC with Ficoll™ during expansion. Similarly, Ficoll™ crowding also increased chondrogenic differentiation. Of note, donor-to-donor variability was observed for collagen type I deposition and trilineage differentiation capacity of hBMSCs. Conclusion: Collectively, our data indicate that appropriate screening of donors, media and supplements, in this case MMC agent, should be conducted for the development of clinically relevant hBMSC medicines.

Bone marrow mesenchymal stromal cell-derived extracellular matrix displays altered glycosaminoglycan structure and impaired functionality in Myelodysplastic Syndromes

Myelodysplastic syndromes (MDS) comprise a heterogeneous group of hematologic malignancies characterized by clonal hematopoiesis, one or more cytopenias such as anemia, neutropenia, or thrombocytopenia, abnormal cellular maturation, and a high risk of progression to acute myeloid leukemia. The bone marrow microenvironment (BMME) in general and mesenchymal stromal cells (MSCs) in particular contribute to both the initiation and progression of MDS. However, little is known about the role of MSC-derived extracellular matrix (ECM) in this context. Therefore, we performed a comparative analysis of in vitro deposited MSC-derived ECM of different MDS subtypes and healthy controls. Atomic force microscopy analyses demonstrated that MDS ECM was significantly thicker and more compliant than those from healthy MSCs. Scanning electron microscopy showed a dense meshwork of fibrillar bundles connected by numerous smaller structures that span the distance between fibers in MDS ECM. Glycosaminoglycan (GAG) structures were detectable at high abundance in MDS ECM as white, sponge-like arrays on top of the fibrillar network. Quantification by Blyscan assay confirmed these observations, with higher concentrations of sulfated GAGs in MDS ECM. Fluorescent lectin staining with wheat germ agglutinin and peanut agglutinin demonstrated increased deposition of N-acetyl-glucosamine GAGs (hyaluronan (HA) and heparan sulfate) in low risk (LR) MDS ECM. Differential expression of N-acetyl-galactosamine GAGs (chondroitin sulfate, dermatan sulfate) was observed between LR- and high risk (HR)-MDS. Moreover, increased amounts of HA in the matrix of MSCs from LR-MDS patients were found to correlate with enhanced HA synthase 1 mRNA expression in these cells. Stimulation of mononuclear cells from healthy donors with low molecular weight HA resulted in an increased expression of various pro-inflammatory cytokines suggesting a contribution of the ECM to the inflammatory BMME typical of LR-MDS. CD34⁺ hematopoietic stem and progenitor cells (HSPCs) displayed an impaired differentiation potential after cultivation on MDS ECM and modified morphology accompanied by decreased integrin expression which mediate cell-matrix interaction. In summary, we provide evidence for structural alterations of the MSC-derived ECM in both LR- and HR-MDS. GAGs may play an important role in this remodeling processes during the malignant transformation which leads to the observed disturbance in the support of normal hematopoiesis.

Macromolecular crowding transforms regenerative medicine by enabling the accelerated development of functional and truly three-dimensional cell assembled micro tissues

Scaffold-free in vitro organogenesis exploits the innate ability of cells to synthesise and deposit their own extracellular matrix to fabricate tissue-like assemblies. Unfortunately, cell-assembled tissue engineered concepts require prolonged ex vivo culture periods of very high cell numbers for the development of a borderline three-dimensional implantable device, which are associated with phenotypic drift and high manufacturing costs, thus, hindering their clinical translation and commercialisation. Herein, we report the accelerated (10 days) development of a truly three-dimensional (338.1 ± 42.9 μm) scaffold-free tissue equivalent that promotes fast wound healing and induces formation of neotissue composed of mature collagen fibres, using human adipose derived stem cells seeded at only 50,000 cells/cm2 on an poly (N-isopropylacrylamide-co-N-tert-butylacrylamide (PNIPAM86-NTBA14) temperature-responsive electrospun scaffold and grown under macromolecular crowding conditions (50 μg/ml carrageenan). Our data pave the path for a new era in scaffold-free regenerative medicine.

Macromolecular crowding in the development of a three-dimensional organotypic human breast cancer model

Although cell-derived matrices are at the forefront of scientific research and technological innovation for the development of in vitro tumour models, their two-dimensional structure and low extracellular matrix composition restrict their capacity to accurately predict toxicity of candidate molecules. Herein, we assessed the potential of macromolecular crowding (a biophysical phenomenon that significantly enhances and accelerates extracellular matrix deposition, resulting in three-dimensional tissue surrogates) in improving cell-derived matrices in vitro tumour models. Among the various decellularisation protocols assessed (NH4OH, DOC, SDS/EDTA, NP40), the NP40 appeared to be the most effective in removing cellular matter and the least destructive to the deposited matrix. Among the various cell types (mammary, skin, lung fibroblasts) used to produce the cell-derived matrices, the mammary fibroblast derived matrices produced under macromolecular crowding conditions and decellularised with NP40 resulted in significant increase in focal adhesion molecules, matrix metalloproteinases and proinflammatory cytokines, when seeded with MDA-MB-231 cells. Further, macromolecular crowding derived matrices significantly increased doxorubicin resistance and reduced the impact of intracellular reactive oxygen species mediated cell death. Collectively our data clearly illustrate the potential of macromolecular crowding in the development of cell-derived matrices-based in vitro tumour models that more accurately resemble the tumour microenvironment.

It is time to crowd your cell culture media - Physicochemical considerations with biological consequences

In vivo, the interior and exterior of cells is populated by various macromolecules that create an extremely crowded milieu. Yet again, in vitro eukaryotic cell culture is conducted in dilute culture media that hardly imitate the native tissue density. Herein, the concept of macromolecular crowding is discussed in both intracellular and extracellular context. Particular emphasis is given on how the physicochemical properties of the crowding molecules govern and determine kinetics, equilibria and mechanism of action of biochemical and biological reactions, processes and functions. It is evidenced that we are still at the beginning of appreciating, let alone effectively implementing, the potential of macromolecular crowding in permanently differentiated and stem cell culture systems.

Transforming eukaryotic cell culture with macromolecular crowding

In multicellular organisms, the intracellular and extracellular spaces are considerably packed with a diverse range of macromolecular species. Yet, standard eukaryotic cell culture is performed in dilute, and deprived of macromolecules culture media, that barely imitate the density and complex macromolecular composition of tissues. Essentially, we drown cells in a sea of media and then expect them to perform physiologically. Herein, we argue the use of macromolecular crowding (MMC) in eukaryotic cell culture for regenerative medicine and drug discovery purposes.

Hyaluronic Acid as Macromolecular Crowder in Equine Adipose-Derived Stem Cell Cultures

The use of macromolecular crowding in the development of extracellular matrix-rich cell-assembled tissue equivalents is continuously gaining pace in regenerative engineering. Despite the significant advancements in the field, the optimal macromolecular crowder still remains elusive. Herein, the physicochemical properties of different concentrations of different molecular weights hyaluronic acid (HA) and their influence on equine adipose-derived stem cell cultures were assessed. Within the different concentrations and molecular weight HAs, the 10 mg/mL 100 kDa and 500 kDa HAs exhibited the highest negative charge and hydrodynamic radius, and the 10 mg/mL 100 kDa HA exhibited the lowest polydispersity index and the highest % fraction volume occupancy. Although HA had the potential to act as a macromolecular crowding agent, it did not outperform carrageenan and Ficoll®, the most widely used macromolecular crowding molecules, in enhanced and accelerated collagen I, collagen III and collagen IV deposition.

Scaffold-free cell-based tissue engineering therapies: advances, shortfalls and forecast

Cell-based scaffold-free therapies seek to develop in vitro organotypic three-dimensional (3D) tissue-like surrogates, capitalising upon the inherent capacity of cells to create tissues with efficiency and sophistication that is still unparalleled by human-made devices. Although automation systems have been realised and (some) success stories have been witnessed over the years in clinical and commercial arenas, in vitro organogenesis is far from becoming a standard way of care. This limited technology transfer is largely attributed to scalability-associated costs, considering that the development of a borderline 3D implantable device requires very high number of functional cells and prolonged ex vivo culture periods. Herein, we critically discuss advancements and shortfalls of scaffold-free cell-based tissue engineering strategies, along with pioneering concepts that have the potential to transform regenerative and reparative medicine.

Optimization of extracellular matrix production from human induced pluripotent stem cell-derived fibroblasts for scaffold fabrication for application in wound healing

Extracellular matrix is a key component of all tissues, including skin and it plays a crucial role in the complex events of wound healing. These events are impaired in chronic wounds, with chronic inflammation and infection often present in these non-healing wounds. Many tissue engineering approaches for wound healing provide a scaffold to mimic the native matrix. Fibroblasts derived from iPS cells (iPSF) represent a novel source of matrix rich in pro-regenerative components, which can be used for scaffold fabrication to improve wound healing. However, in vitro production of matrix by cells for scaffold fabrication requires long cell culturing times which increases cost. The aim of this work is to optimize the iPSF matrix production by boosting matrix deposition, without affecting its composition. A good candidate technique to achieve this goal is macromolecular crowding, which is known to promote conversion of procollagen into mature collagen and its accumulation. We tested two molecular crowders, Ficoll and Carrageenan-in combination with ascorbic acid-over a prolonged period of time. Ficoll in combination with ascorbic acid notably increased collagen deposition and matrix dry weight compared to ascorbic acid alone, and did not affect matrix composition as measured by RT-PCR. Interestingly, Carrageenan did not affect collagen quantity, but it significantly increased glycosaminoglycan deposition. Finally, we successfully fabricated scaffolds from harvested matrix and confirmed their ability for cell growth and viability. This work lays the foundation for development of a time and cost effective protocol for novel iPSF ECM production for tissue engineering scaffolds.

Bioinspired in vitro microenvironments to control cell fate: focus on macromolecular crowding

The development of therapeutic regenerative medicine and accurate drug discovery cell-based products requires effective, with respect to obtaining sufficient numbers of viable, proliferative, and functional cell populations, cell expansion ex vivo. Unfortunately, traditional cell culture systems fail to recapitulate the multifaceted tissue milieu in vitro, resulting in cell phenotypic drift, loss of functionality, senescence, and apoptosis. Substrate-, environment-, and media-induced approaches are under intense investigation as a means to maintain cell phenotype and function while in culture. In this context, herein, the potential of macromolecular crowding, a biophysical phenomenon with considerable biological consequences, is discussed.

Growth factor and macromolecular crowding supplementation in human tenocyte culture

Cell-assembled tissue engineering strategies hold great potential in regenerative medicine, as three-dimensional tissue-like modules can be produced, even from a patient's own cells. However, the development of such implantable devices requires prolonged in vitro culture time, which is associated with cell phenotypic drift. Considering that the cells in vivo are subjected to numerous stimuli, multifactorial approaches are continuously gaining pace towards controlling cell fate during in vitro expansion. Herein, we assessed the synergistic effect of simultaneous and serial growth factor supplementation (insulin growth factor-1, platelet-derived growth factor ββ, growth differentiation factor 5 and transforming growth factor β3) to macromolecular crowding (carrageenan) in human tenocyte function; collagen synthesis and deposition; and gene expression. TGFβ3 supplementation (without/with carrageenan) induced the highest (among all groups) DNA content. In all cases, tenocyte proliferation was significantly increased as a function of time in culture, whilst metabolic activity was not affected. Carrageenan supplementation induced significantly higher collagen deposition than groups without carrageenan (without/with any growth factor). Of all the growth factors used, TGFβ3 induced the highest collagen deposition when used together with carrageenan in both simultaneous and serial fashion. At day 13, gene expression analysis revealed that TGFβ3 in serial supplementation to carrageenan upregulated the most and downregulated the least collagen- and tendon- related genes and upregulated the least and downregulated the most osteo-, chondro-, fibrosis- and adipose- related trans-differentiation genes. Collectively, these data clearly advocate the beneficial effects of multifactorial approaches (in this case, growth factor and macromolecular crowding supplementation) in the development of functional cell-assembled tissue surrogates.

Macromolecular Crowding as a Tool to Screen Anti-fibrotic Drugs: The Scar-in-a-Jar System Revisited

An unsolved therapeutic problem in fibrosis is the overproduction of collagen. In order to screen the effect of anti-fibrotic drugs on collagen deposition, the Scar-in-a-Jar approach has been introduced about a decade ago. With macromolecular crowding a rapid deposition of collagen is seen, resulting in a substantial decrease in culture time, but the system has never been tested in an adequate way. We therefore have compared six different macromolecular crowders [Ficoll PM 70 (Fc70), Ficoll PM 400 (Fc400), a mixture of Ficoll 70 and 400 (Fc70/400), polyvinylpyrrolidone 40 (PVP40), polyvinylpyrrolidone 360 (PVP360), neutral dextran 670 (ND670), dextran sulfate 500 (DxS500), and carrageenan (CR)] under profibrotic conditions (addition of TGFβ1) with primary human adult dermal fibroblasts in the presence of 0.5 and 10% FBS. We found that (1) collagen deposition and myofibroblast formation was superior with 0.5% FBS, (2) DxS500 and CR results in an aberrant collagen deposition pattern, (3) ND670 does not increase collagen deposition, and (4) CR, DxS500, and Fc40/700 affected important phenotypical properties of the cells when cultured under pro-fibrotic conditions, whereas PVP40 and PVP360 did less or not. Because of viscosity problems with PVP360, we conclude that PVP40 is the most optimal crowder for the screening of anti-fibrotic drugs. Finally, the effect of various concentrations of Imatinib, Galunisertib, Omipalisib or Nintedanib on collagen deposition and myofibroblast formation was tested with PVP40 as the crowder.

A biomimetic model of 3D fluid extracellular macromolecular crowding microenvironment fine-tunes ovarian cancer cells dissemination phenotype

An early fundamental step in ovarian cancer progression is the dissemination of cancer cells through liquid environments, one of them being cancer ascites accumulated in the peritoneal cavity. These biological fluids are highly crowded with a high total macromolecule concentration. This biophysical property of fluids is widely used in tissue engineering for a few decades now, yet is largely underrated in cancer biomimetic models. To unravel the role of fluids extracellular macromolecular crowding (MMC), we exposed ovarian cancer cells (OCC) to high molecular weight inert polymer solutions. High macromolecular composition of extracellular liquid presented a differential effect: i) it impeded non-adherent OCC aggregation in suspension and, decreased their adhesion; ii) it promoted adherent OCC migration by decreasing extracellular matrix deposition. Besides, there seemed to be a direct link between the extracellular MMC and intracellular processes, especially the actin cytoskeleton organization and the nucleus morphology. In conclusion, extracellular fluid MMC orients OCC dissemination phenotype. Integrating MMC seems crucial to produce more relevant mimetic 3D in vitro fluid models to study ovarian dissemination but also to screen drugs.

Cell derived extracellular matrix-rich biomimetic substrate supports podocyte proliferation, differentiation and maintenance of native phenotype

Current technologies and available scaffold materials do not support long-term cell viability, differentiation and maintenance of podocytes, the ultra-specialized kidney resident cells that are responsible for the filtration of the blood. We developed a new platform which imitates the native kidney microenvironment by decellularizing fibroblasts grown on surfaces with macromolecular crowding. Human immortalized podocytes cultured on this platform displayed superior viability and metabolic activity up to 28 days compared to podocytes cultured on tissue culture plastic surfaces. The new platform displayed a softer surface and an abundance of growth factors and associated molecules. More importantly it enabled podocytes to display molecules responsible for their structure and function and a superior development of intercellular connections/interdigitations, consistent with maturation. The new platform can be used to study podocyte biology, test drug toxicity and determine whether sera from patients with podocytopathies are involved in the expression of glomerular pathology.

Spider Silk Fusion Proteins for Controlled Collagen Binding and Biomineralization

The development of biomaterials for the interface between tendon and bone is important for realizing functional tendon replacements. Toward the development of new materials for such applications, engineered recombinant spider silk proteins were modified with peptide tag sequences derived from noncollagenous proteins in bone, so-called SIBLING proteins, such as osteopontin and sialoprotein, which are known to interact with collagen and to initiate mineralization. Materials made of these spider silk-SIBLING hybrids were analyzed concerning mineralization and interaction with cells. They showed enhanced calcium phosphate formation upon incubation in mineralization agents. In gradient films, MC3T3-E1 mouse preosteoblasts adhered preferentially along the gradient toward the variant with a collagen binding motif.

An Overview of Different Strategies to Recreate the Physiological Environment in Experimental Erythropoiesis

Human erythropoiesis is a complex process leading to the production of mature, enucleated erythrocytes (RBCs). It occurs mainly at bone marrow (BM), where hematopoietic stem cells (HSCs) are engaged in the early erythroid differentiation to commit into erythroid progenitor cells (burst-forming unit erythroid (BFU-E) and colony-forming unit erythroid (CFU-E)). Then, during the terminal differentiation, several erythropoietin-induced signaling pathways trigger the differentiation of CFU-E on successive stages from pro-erythroblast to reticulocytes. The latter are released into the circulation, finalizing their maturation into functional RBCs. This process is finely regulated by the physiological environment including the erythroblast-macrophage interaction in the erythroblastic island (EBI). Several human diseases have been associated with ineffective erythropoiesis, either by a defective or an excessive production of RBCs, as well as an increase or a hemoglobinization defect. Fully understanding the production of mature red blood cells is crucial for the comprehension of erythroid pathologies as well as to the field of transfusion. Many experimental approaches have been carried out to achieve a complete differentiation in vitro to produce functional biconcave mature RBCs. However, the various protocols usually fail to achieve enough quantities of completely mature RBCs. In this review, we focus on the evolution of erythropoiesis studies over the years, taking special interest in efforts that were made to include the microenvironment and erythroblastic islands paradigm. These more physiological approaches will contribute to a deeper comprehension of erythropoiesis, improve the treatment of dyserythropoietic disorders, and break through the barriers in massive RBCs production for transfusion.

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.

Native extracellular matrix, synthesized ex vivo by bone marrow or adipose stromal cells, faithfully directs mesenchymal stem cell differentiation

Mesenchymal stem cells (MSCs) are highly responsive to cues in the microenvironment (niche) that must be recapitulated ex vivo to study their authentic behavior. In this study, we hypothesized that native bone marrow (BM)- and adipose (AD)-derived extracellular matrices (ECM) were unique in their ability to control MSC behavior. To test this, we compared proliferation and differentiation of bone marrow (BM)-derived MSCs when maintained on native decellularized ECM produced by BM versus AD stromal cells (i.e. BM- versus AD-ECM). We found that both ECMs contained similar types of collagens but differed in the relative abundance of each. Type VI collagen was the most abundant (≈60% of the total collagen present), while type I was the next most abundant at ≈30%. These two types of collagen were found in nearly equal proportions in both ECMs. In contrast, type XII collagen was almost exclusively found in AD-ECM, while types IV and V were only found in BM-ECM. Physically and mechanically, BM-ECM was rougher and stiffer, but less adhesive, than AD-ECM. During 14 days in culture, both ECMs supported BM-MSC proliferation better than tissue culture plastic (TCP), although MSC-related surface marker expression remained relatively high on all three culture surfaces. BM-MSCs cultured in osteogenic (OS) differentiation media on BM-ECM displayed a significant increase in calcium deposition in the matrix, indicative of osteogenesis, while BM-MSCs cultured on AD-ECM in the presence of adipogenic (AP) differentiation media showed a significant increase in Oil Red O staining, indicative of adipogenesis. Further, culture on BM-ECM significantly increased BM-MSC-responsiveness to rhBMP-2 (an osteogenic inducer), while culture on AD-ECM enhanced responsiveness to rosiglitazone (an adipogenic inducer). These findings support our hypothesis and indicate that BM- and AD-ECMs retain unique elements, characteristic of their tissue-specific microenvironment (niche), which promote retention of MSC differentiation state (i.e. "stemness") during expansion and direct cell response to lineage-specific inducers. This study provides a new paradigm for precisely controlling MSC fate to a desired cell lineage for tissue-specific cell-based therapies.

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

The low engraftment and retention rate of mesenchymal stem cells (MSCs) at the target site indicates that the potential benefits of MSC-based therapies can be attributed to their paracrine signaling. In this study, the extracellular matrices (ECMs) deposited by bone marrow-derived human MSCs in the presence and absence of ascorbic acid was characterized. MSCs were seeded on top of decellularized ECM (dECM) and the concentrations of proangiogenic and antiangiogenic molecules released in culture (conditioned) media was compared. Effects of ECM derived from MSCs with different passage numbers on MSC secretome was also investigated. Our study revealed that the expression of proangiogenesis-related factors were upregulated when MSCs were harvested on dECMs, irrespective of media supplementation, as compared with those cultured on tissue culture plates. In addition, dECM generated in the presence of ascorbic acid promoted the expression of proangiogenic molecules as compared with dECM-derived in absence of media supplementation. Further, it was observed that the effectiveness of dECM to stimulate proangiogenic signaling of MSCs was reduced as cell passage number was increased from P3 to P5. The proliferation as well as capillary morphogenesis of human umbilical vein endothelial cells (HUVECs) in the presence of conditioned media were enhanced compared with the normal HUVECs culture media. These data indicate that the secretory signatures of MSCs and consequently, the therapeutic efficacy of MSCs can be regulated by presentation of dECM composition and variation of its composition.

Sodium Hyaluronate Supplemented Culture Media as a New hMSC Chondrogenic Differentiation Media-Model for in vitro/ex vivo Screening of Potential Cartilage Repair Therapies

Surgical strategies to treat articular cartilage injury such as microfracture, expose human bone marrow stem cells (hMSCs) to synovial fluid and its components. High molecular weight hyaluronan (hMwt HA) is one of the most abundant bioactive macromolecules of healthy synovial fluid (hSF) and it plays an important role in the protection of opposing articular cartilage surfaces within the synovial joint. Although hMwt HA has been extensively used to attempt the engineering of the cartilage tissue, its effect as media supplement has not been established. Indeed, current media are often simple in their composition and doesn't recapitulate the rheological and biological features of hSF. In addition, critical in vivo molecules that can potentially change the chondrogenic behavior of hBMSCs to make the in vitro results more predictive of the real in vivo outcome, are lacking. In order to be one step closer to the in vivo physiology of hSF, a new culture media supplemented with physiological level of hMwt HA was developed and the effect of the hMwt HA on the chondrogenesis of hMSCs that would be present in a traumatic defect after marrow stimulation techniques, was investigated. hBMSC-seeded fibrin-polyurethane constructs were cultured in a serum free chondropermissive control medium (HA- TGFβ-). This medium was further supplemented with 10 ng/mL TGFβ1 (HA- TGFβ+) or 2 mg/ml hMwt HA 1.8 MDa (HA+ TGFβ-) or both (HA+ TGFβ+). Alternatively, 1 MDa HA was mixed with the fibrin at 0.2 mg/ml (HASc TGFβ+). The effect of hMwt HA on hMSC differentiation was investigated at the gene expression level by RT-qPCR and total DNA, sulfated glycosaminoglycans and Safranin O staining were evaluated. Addition of hMwt HA to the culture media, significantly increased the synthesis of sulfated glycosaminoglycans, especially in the early days of chondrogenesis, and reduced the upregulation of the hypertrophic cartilage marker collagen X. hMwt HA added inside the fibrin gel(HASc TGF+) led to the best matrix deposition. hMwt HA can be one key medium component in a more reliable in vitro/ex vivo system to reduce in vitro artifacts, enable more accurate pre-screening of potential cartilage repair therapies and reduce the need for animal studies.

An insight into cell-laden 3D-printed constructs for bone tissue engineering

In this review, we have spotlighted various combinations of bioinks to optimize the biofabrication of 3D bone constructs.

Hyaluronic acid as a macromolecular crowding agent for production of cell-derived matrices

Cell-derived matrices (CDMs) provide an exogenous source of human extracellular matrix (ECM), with applications as cell delivery vehicles, substrate coatings for cell attachment and differentiation, and as biomaterial scaffolds. However, commercial application of CDMs has been hindered due to the prolonged culture time required for sufficient ECM accumulation. One approach to increasing matrix deposition in vitro is macromolecular crowding (MMC), which is a biophysical phenomenon that limits the diffusion of ECM precursor proteins, resulting in increased ECM accumulation at the cell layer. Hyaluronic acid (HA), a natural MMC highly expressed in vivo during fetal development, has been shown to play a role in ECM production, but has not been investigated as a macromolecule for increasing cell-mediated ECM deposition in vitro. In the current study, we hypothesized that HA can act as a MMC, and increase cell-mediated ECM production. Human dermal fibroblasts were cultured for 3, 7, or 14 days with 0%, 0.05%, or 0.5% high molecular weight HA. Ficoll 70/400 was used as a positive control. SDS-PAGE, Sircol, and hydroxyproline assays indicated that 0.05% HA-treated cultures had significantly higher mean collagen deposition at 14 days, whereas Ficoll 70/400-treated cultures had significantly lower collagen production compared to the HA and untreated controls. However, fluorescent immunostaining of ECM proteins and quantification of mean gray values did not indicate statistically significant differences in ECM production in HA or Ficoll 70/400-treated cultures compared to untreated controls. Raman imaging (a marker-free spectral imaging method) indicated that HA increased ECM deposition in human dermal fibroblasts. These results are consistent with decreases in CDM stiffness observed in Ficoll 70/400-treated cultures by atomic force microscopy. Overall, these results indicate that there are macromolecule- and cell type- dependent effects on matrix assembly, turnover, and stiffness in cell-derived matrices. STATEMENT OF SIGNIFICANCE: Cell-derived matrices (CDMs) are versatile biomaterials with many regenerative medicine applications, including as cell and drug delivery vehicles and scaffolds for wound healing and tissue regeneration. While CDMs have several advantages, their commercialization has been limited due to the prolonged culture time required to achieve CDM synthesis in vitro. In this study, we explored the use of hyaluronic acid (HA) as a macromolecular crowder in human fibroblast cell cultures to support production of CDM biomaterials. Successful application of macromolecular crowding will allow development of human cell-derived, xeno-free biomaterials that re-capitulate the native human tissue microenvironment.

Fibrillar fibronectin plays a key role as nucleator of collagen I polymerization during macromolecular crowding-enhanced matrix assembly

Macromolecular crowding is used by tissue engineers to accelerate extracellular matrix assembly in vitro, however, most mechanistic studies focus on the impact of crowding on collagen fiber assembly and largely ignore the highly abundant provisional matrix protein fibronectin. We show that the accelerated collagen I assembly as induced by the neutral crowding molecule Ficoll is regulated by cell access to fibronectin. Ficoll treatment leads to significant increases in the amount of surface adherent fibronectin, which can readily be harvested by cells to speed up fibrillogenesis. FRET studies reveal that Ficoll crowding also upregulates the total amount of fibronectin fibers in a low-tension state through upregulating fibronectin assembly. Since un-stretched fibronectin fibers have more collagen binding sites to nucleate the onset of collagen fibrillogenesis, our data suggest that the Ficoll-induced upregulation of low-tension fibronectin fibers contributes to enhanced collagen assembly in crowded conditions. In contrast, chemical cross-linking of fibronectin to the glass substrate prior to cell seeding prevents early force mediated fibronectin harvesting from the substrate and suppresses upregulation of collagen I assembly in the presence of Ficoll, even though the crowded environment is known to drive enzymatic cleavage of procollagen and collagen fiber formation. To show that our findings can be exploited for tissue engineering applications, we demonstrate that the addition of supplemental fibronectin in the form of an adsorbed coating markedly improves the speed of tissue formation under crowding conditions.

The role of anthrax toxin protein receptor 1 as a new mechanosensor molecule and its mechanotransduction in BMSCs under hydrostatic pressure

Anthrax toxin protein receptor (ANTXR) 1 has many similarities to integrin and is regarded in some respects as a single-stranded integrin protein. However, it is not clear whether ANTXR1 responds to mechanical signals secondary to the activation of integrins or whether it is a completely new, independent and previously undiscovered mechanosensor that responds to an undefined subset of mechanical signaling molecules. Our study demonstrates that ANTXR1 is a novel mechanosensor on the cell membrane, acting independently from the classical mechanoreceptor molecule integrinβ1. We show that bone marrow stromal cells (BMSCs) respond to the hydrostatic pressure towards chondrogenic differentiation partly through the glycogen synthase kinase (GSK) 3β/β-Catenin signaling pathway, which can be partly regulated by ANTXR1 and might be related to the direct binding between ANTXR1 and low-density lipoprotein receptor-related protein (LRP) 5/6. In addition, ANTXR1 specifically activates Smad2 and upregulates Smad4 expression to facilitate the transport of activated Smad2 to the nucleus to regulate chondrogenesis, which might be related to the direct binding between ANTXR1 and Actin/Fascin1. We also demonstrate that ANTXR1 binds to some extent with integrinβ1, but this interaction does not affect the expression and function of either protein under pressure. Thus, we conclude that ANTXR1 plays a crucial role in BMSC mechanotransduction and controls specific signaling pathways that are distinct from those of integrin to influence the chondrogenic responses of BMSCs under hydrostatic pressure.

A high content, phenotypic 'scar-in-a-jar' assay for rapid quantification of collagen fibrillogenesis using disease-derived pulmonary fibroblasts

BACKGROUND

Excessive extracellular matrix (ECM) deposition is a hallmark feature in fibrosis and tissue remodelling diseases. Typically, mesenchymal cells will produce collagens under standard 2D cell culture conditions, however these do not assemble into fibrils. Existing assays for measuring ECM production are often low throughput and not disease relevant. Here we describe a robust, high content, pseudo-3D phenotypic assay to quantify mature fibrillar collagen deposition which is both physiologically relevant and amenable to high throughput compound screening. Using pulmonary fibroblasts derived from patients with idiopathic pulmonary fibrosis (IPF), we developed the 'scar-in-a-jar' assay into a medium-throughput phenotypic assay to robustly quantify collagen type I deposition and other extracellular matrix (ECM) proteins over 72 h.

RESULTS

This assay utilises macromolecular crowding to induce an excluded volume effect and enhance enzyme activity, which in combination with TGF-β1 stimulation significantly accelerates ECM production. Collagen type I is upregulated approximately 5-fold with a negligible effect on cell number. We demonstrate the robustness of the assay achieving a Z prime of approximately 0.5, and % coefficient of variance (CV) of < 5 for the assay controls SB-525334 (ALK5 inhibitor) and CZ415 (mTOR inhibitor). This assay has been used to confirm the potency of a number of potential anti-fibrotic agents. Active compounds from the 'scar-in-a-jar' assay can be further validated for other markers of ECM deposition and fibroblast activation such as collagen type IV and α-smooth muscle actin exhibiting a 4-fold and 3-fold assay window respectively.

CONCLUSION

In conclusion, we have developed 'scar -in-a-jar is' into a robust disease-relevant medium-throughput in vitro assay to accurately quantify ECM deposition. This assay may enable iterative compound profiling for IPF and other fibroproliferative and tissue remodelling diseases.

Polydispersity and negative charge are key modulators of extracellular matrix deposition under macromolecular crowding conditions

Macromolecular crowding is a biophysical phenomenon that stems from the volume excluded by macromolecules, as they undergo steric repulsion and electrostatic interactions. The excluded volume depends on the shape, size, charge and polydispersity of the molecules. Although theoretical/computational models have been used to assess the influence of macromolecular crowding in biological media, real-time experiments are scarce. Herein, we evaluated the influence of hydrodynamic radius, charge and polydispersity of (a) various concentrations of different crowders (carrageenan, Ficoll™ and dextran sulphate); (b) various molecular weights of different crowders (70, 400 and 100 kDa of Ficoll™ and 10, 100 and 500 kDa of dextran sulphate) and (c) various cocktails of the same crowders (cocktails of various concentrations of different molecular weights Ficoll™ and dextran sulphate) on extracellular matrix deposition in human dermal fibroblast culture. The use of crowding cocktails with different molecular weight/concentrations of Ficoll™ or dextran sulphate molecules led to increased polydispersity and enhanced collagen type I deposition in comparison to their mono-domain counterparts. Carrageenan, however, induced the highest deposition of collagen type I due to its negative charge and inherent polydispersity. Our data contribute to a better understanding of the influence of the biophysical properties of the crowders on extracellular matrix deposition in vitro. STATEMENT OF SIGNIFICANCE: Macromolecular crowding is a biophysical phenomenon that accelerates and enhances extracellular matrix deposition in cell culture systems. Herein, we demonstrate that negatively charged and polydispersed macromolecules or cocktails of macromolecules, as opposed to neutral and monodomain macromolecules, induce highest extracellular matrix deposition in human dermal fibroblast cultures.

Generation and characterization of a functional human adipose-derived multipotent mesenchymal stromal cell line

Multipotent mesenchymal stromal cells (MSC) and MSC-derived products have emerged as promising therapeutic tools. To fully exploit their potential, further mechanistic studies are still necessary and bioprocessing needs to be optimized, which requires an abundant supply of functional MSC for basic research. To address this need, here we used a novel technology to establish a human adipose-derived MSC line with functional characteristics representative of primary MSC. Primary MSC were isolated and subjected to lentiviral transduction with a library of expansion genes. Clonal cell lines were generated and evaluated on the basis of their morphology, immunophenotype, and proliferation potential. One clone (K5 iMSC) was then selected for further characterization. This clone had integrated a specific transgene combination including genes involved in stemness and maintenance of adult stem cells. Favorably, the K5 iMSC showed cell characteristics resembling juvenile MSC, as they displayed a shorter cell length and enhanced migration and proliferation compared with the non-immortalized original primary MSC (p < 0.05). Still, their immunophenotype and differentiation potential corresponded to the original primary MSC and the MSC definition criteria, and cytogenetic analyses revealed no clonal aberrations. We conclude that the technology used is applicable to generate functional MSC lines for basic research and possible future bioprocessing applications.

Multifactorial bottom-up bioengineering approaches for the development of living tissue substitutes

Bottom-up bioengineering utilizes the inherent capacity of cells to build highly sophisticated structures with high levels of biomimicry. Despite the significant advancements in the field, monodomain approaches require prolonged culture time to develop an implantable device, usually associated with cell phenotypic drift in culture. Herein, we assessed the simultaneous effect of macromolecular crowding (MMC) and mechanical loading in enhancing extracellular matrix (ECM) deposition while maintaining tenocyte (TC) phenotype and differentiating bone marrow stem cells (BMSCs) or transdifferentiating neonatal and adult dermal fibroblasts toward tenogenic lineage. At d 7, all cell types presented cytoskeleton alignment perpendicular to the applied load independently of the use of MMC. MMC enhanced ECM deposition in all cell types. Gene expression analysis indicated that MMC and mechanical loading maintained TC phenotype, whereas tenogenic differentiation of BMSCs or transdifferentiation of dermal fibroblasts was not achieved. Our data suggest that multifactorial bottom-up bioengineering approaches significantly accelerate the development of biomimetic tissue equivalents.-Gaspar, D., Ryan, C. N. M., Zeugolis, D. I. Multifactorial bottom-up bioengineering approaches for the development of living tissue substitutes.

The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development

Collagen is the oldest and most abundant extracellular matrix protein that has found many applications in food, cosmetic, pharmaceutical, and biomedical industries. First, an overview of the family of collagens and their respective structures, conformation, and biosynthesis is provided. The advances and shortfalls of various collagen preparations (e.g., mammalian/marine extracted collagen, cell-produced collagens, recombinant collagens, and collagen-like peptides) and crosslinking technologies (e.g., chemical, physical, and biological) are then critically discussed. Subsequently, an array of structural, thermal, mechanical, biochemical, and biological assays is examined, which are developed to analyze and characterize collagenous structures. Lastly, a comprehensive review is provided on how advances in engineering, chemistry, and biology have enabled the development of bioactive, 3D structures (e.g., tissue grafts, biomaterials, cell-assembled tissue equivalents) that closely imitate native supramolecular assemblies and have the capacity to deliver in a localized and sustained manner viable cell populations and/or bioactive/therapeutic molecules. Clearly, collagens have a long history in both evolution and biotechnology and continue to offer both challenges and exciting opportunities in regenerative medicine as nature's biomaterial of choice.

Chasing Chimeras - The elusive stable chondrogenic phenotype

The choice of the best-suited cell population for the regeneration of damaged or diseased cartilage depends on the effectiveness of culture conditions (e.g. media supplements, three-dimensional scaffolds, mechanical stimulation, oxygen tension, co-culture systems) to induce stable chondrogenic phenotype. Herein, advances and shortfalls in in vitro, preclinical and clinical setting of various in vitro microenvironment modulators on maintaining chondrocyte phenotype or directing stem cells towards chondrogenic lineage are critically discussed. Chondrocytes possess low isolation efficiency, limited proliferative potential and rapid phenotypic drift in culture. Mesenchymal stem cells are relatively readily available, possess high proliferation potential, exhibit great chondrogenic differentiation capacity, but they tend to acquire a hypertrophic phenotype when exposed to chondrogenic stimuli. Embryonic and induced pluripotent stem cells, despite their promising in vitro and preclinical data, are still under-investigated. Although a stable chondrogenic phenotype remains elusive, recent advances in in vitro microenvironment modulators are likely to develop clinically- and commercially-relevant therapies in the years to come.

Macromolecular crowding for materials-directed controlled self-assembly

Macromolecular crowding refers to intracellular environments where various macromolecules, including proteins and nucleic acids, are present at high total concentrations. Its influence on biological processes has been investigated using a highly concentrated in vitro solution of water-soluble polymers as a model. Studies have revealed significant effects of macromolecular crowding on the thermodynamic equilibria and dynamics of biomolecular self-assembly in vivo. Recently, macromolecular crowding has attracted materials scientists, especially those in bio-related areas, as a tool to control molecular/colloidal self-assembly. Macromolecular crowding has been exploited to control the structure of supramolecular materials, assemble nanomaterials, and improve the performance of polymeric materials. Furthermore, nanostructured materials have been shown to be an interesting alternative to water-soluble polymers for creating crowded environments for controlled self-assembly. In this review article, we summarize recent progress in research on macromolecular crowding for controlled self-assembly in bio-related materials chemistry.

Delivery of cellular factors to regulate bone healing

Bone tissue has a strong intrinsic regenerative capacity, thanks to a delicate and complex interplay of cellular and molecular processes, which tightly involve the immune system. Pathological settings of anatomical, biomechanical or inflammatory nature may lead to impaired bone healing. Innovative strategies to enhance bone repair, including the delivery of osteoprogenitor cells or of potent cytokines/morphogens, indicate the potential of 'orthobiologics', but are not fully satisfactory. Here, we review different approaches based on the delivery of regenerative cues produced by cells but in cell-free, possibly off-the-shelf configurations. Such strategies exploit the paracrine effect of the secretome of mesenchymal stem/stromal cells, presented in soluble form, shuttled through extracellular vesicles, or embedded within the network of extracellular matrix molecules. In addition to osteoinductive molecules, attention is given to factors targeting the resident immune cells, to reshape inflammatory and immunity processes from scarring to regenerative patterns.

Making microenvironments: A look into incorporating macromolecular crowding into in vitro experiments, to generate biomimetic microenvironments which are capable of directing cell function for tissue engineering applications

Biomimetic microenvironments are key components to successful cell culture and tissue engineering in vitro. One of the most accurate biomimetic microenvironments is that made by the cells themselves. Cell-made microenvironments are most similar to the in vivo state as they are cell-specific and produced by the actual cells which reside in that specific microenvironment. However, cell-made microenvironments have been challenging to re-create in vitro due to the lack of extracellular matrix composition, volume and complexity which are required. By applying macromolecular crowding to current cell culture protocols, cell-made microenvironments, or cell-derived matrices, can be generated at significant rates in vitro. In this review, we will examine the causes and effects of macromolecular crowding and how it has been applied in several in vitro systems including tissue engineering.

Growth Factor-Reinforced ECM Fabricated from Chemically Hypoxic MSC Sheet with Improved In Vivo Wound Repair Activity

MSC treatment can promote cutaneous wound repair through multiple mechanisms, and paracrine mediators secreted by MSC are responsible for most of its therapeutic benefits. Recently, MSC sheet composed of live MSCs and their secreted ECMs was reported to promote wound healing; however, whether its ECM alone could accelerate wound closure remained unknown. In this study, Nc-ECM and Cc-ECM were prepared from nonconditioned and CoCl₂-conditioned MSC sheets, respectively, and their wound healing properties were evaluated in a mouse model of full-thickness skin defect. Our results showed that Nc-ECM can significantly promote wound repair through early adipocyte recruitment, rapid reepithelialization, enhanced granulation tissue growth, and augmented angiogenesis. Moreover, conditioning of MSC sheet with CoCl₂ dramatically enriched its ECM with collagen I, collagen III, TGF-β1, VEGF, and bFGF via activation of HIF-1α and hence remarkably improved its ECM's in vivo wound healing potency. All the Cc-ECM-treated wounds completely healed on day 7, while Nc-ECM-treated wounds healed about 85.0% ± 8.6%, and no-treatment wounds only healed 69.8% ± 9.6% (p < 0.05). Therefore, we believe that such growth factor-reinforced ECM fabricated from chemically hypoxic MSC sheet has the potential for clinical translation and will lead to a MSC-derived, cost-effective, bankable biomaterial for wound management.

Label-free relative quantification of secreted proteins as a non-invasive method for the quality control of chondrogenesis in bioengineered substitutes for cartilage repair

Cartilage tissue engineering is making progress, but the competing available strategies still leave room for improvement and consensual overviews regarding the best combinations of scaffolds and cell sources are limited by the capacity to compare them directly. In addition, because most strategies involve autologous cell transfer, once these are optimized, the resulting implants require individual quality control prior to grafting in order to emphasize patient-to-patient differential responsiveness to engineering processes. Here, cartilage substitutes prepared from human mesenchymal stem cells undergoing chondrogenic differentiation within distinct scaffolds were used as pilot samples to investigate the pertinence of a novel method with the aim of characterizing the implants. The limits and advantages of analysing, by label-free liquid chromatography-coupled matrix-assisted laser desorption and ionization (LC-MALDI) mass spectrometry, the secreted proteome released into culture medium by engineered cartilage tissues were investigated and compared with more classically used methods for biomaterial characterization. This method did not require sacrificing the biomaterials and robustly evidenced their chondrogenic statuses. In more detail, the method highlighted differences between batches prepared from distinct donors. It was adapted to distinct scaffolds and allowed a comparison of the influence of individual engineering steps, such as growth factor combinations and oxygen tension. Finally, it evidenced subtle changes between replicate substitutes within a series, thereby distinguishing the least and most accomplished ones. We conclude that relative quantification of secreted proteins through label-free LC-MALDI will be useful, not only to orientate engineering methodologies, but also to ultimately provide non-invasive quality control of engineered tissue substitutes for the repair of cartilage and possibly other connective tissues.

Macromolecular crowding for tailoring tissue-derived fibrillated matrices

Tissue-derived fibrillated matrices can be instrumental for the in vitro reconstitution of multiphasic extracellular microenvironments. However, despite of several advantages, the obtained scaffolds so far offer a rather narrow range of materials characteristics only. In this work, we demonstrate how macromolecular crowding (MMC) - the supplementation of matrix reconstitution media with synthetic or natural macromolecules in ways to create excluded volume effects (EVE) - can be employed for tailoring important structural and biophysical characteristics of kidney-derived fibrillated matrices. Porcine kidneys were decellularized, ground and the obtained extracellular matrix (ECM) preparations were reconstituted under varied MMC conditions. We show that MMC strongly influences the fibrillogenesis kinetics and impacts the architecture and the elastic modulus of the reconstituted matrices, with diameters and relative alignment of fibrils increasing at elevated concentrations of the crowding agent Ficoll400, a nonionic synthetic polymer of sucrose. Furthermore, we demonstrate how MMC modulates the distribution of key ECM molecules within the reconstituted matrix scaffolds. As a proof of concept, we compared different variants of kidney-derived fibrillated matrices in cell culture experiments referring to specific requirements of kidney tissue engineering approaches. The results revealed that MMC-tailored matrices support the morphogenesis of human umbilical vein endothelial cells (HUVECs) into capillary networks and of murine kidney stem cells (KSCs) into highly branched aggregates. The established methodology is concluded to provide generally applicable new options for tailoring tissue-specific multiphasic matrices in vitro.

STATEMENT OF SIGNIFICANCE

Tissue-derived fibrillated matrices can be instrumental for the in vitro reconstitution of multiphasic extracellular microenvironments. However, despite of several advantages, the obtained scaffolds so far offer a rather narrow range of materials characteristics only. Using the kidney matrix as a model, we herein report a new approach for tailoring tissue-derived fibrillated matrices by means of macromolecular crowding (MMC), the supplementation of reconstitution media with synthetic or natural macromolecules. MMC-modulation of matrix reconstitution is demonstrated to allow for the adjustment of fibrillation kinetics and nano-architecture, fiber diameter, alignment, and matrix elasticity. Primary human umbilical vein endothelial cells (HUVEC) and murine kidney stem cells (KSC) were cultured within different variants of fibrillated kidney matrix scaffolds. The results showed that MMC-tailored matrices were superior in supporting desired morphogenesis phenomena of both cell types.

Bone marrow niche-mimetics modulate HSPC function via integrin signaling

The bone marrow (BM) microenvironment provides critical physical cues for hematopoietic stem and progenitor cell (HSPC) maintenance and fate decision mediated by cell-matrix interactions. However, the mechanisms underlying matrix communication and signal transduction are less well understood. Contrary, stem cell culture is mainly facilitated in suspension cultures. Here, we used bone marrow-mimetic decellularized extracellular matrix (ECM) scaffolds derived from mesenchymal stromal cells (MSCs) to study HSPC-ECM interaction. Seeding freshly isolated HSPCs adherent (AT) and non-adherent (SN) cells were found. We detected enhanced expansion and active migration of AT-cells mediated by ECM incorporated stromal derived factor one. Probing cell mechanics, AT-cells displayed naïve cell deformation compared to SN-cells indicating physical recognition of ECM material properties by focal adhesion. Integrin αIIb (CD41), αV (CD51) and β3 (CD61) were found to be induced. Signaling focal contacts via ITGβ3 were identified to facilitate cell adhesion, migration and mediate ECM-physical cues to modulate HSPC function.

Low oxygen tension and macromolecular crowding accelerate extracellular matrix deposition in human corneal fibroblast culture

Development of implantable devices based on the principles of in vitro organogenesis has been hindered due to the prolonged time required to develop an implantable device. Herein we assessed the influence of serum concentration (0.5% and 10%), oxygen tension (0.5%, 2% and 20%) and macromolecular crowding (75 μg/ml carrageenan) in extracellular matrix deposition in human corneal fibroblast culture (3, 7 and 14 days). The highest extracellular matrix deposition was observed after 14 days in culture at 0.5% serum, 2% oxygen tension and 75 μg/ml carrageenan. These data indicate that low oxygen tension coupled with macromolecular crowding significantly accelerate the development of scaffold-free tissue-like modules. Copyright © 2016 John Wiley & Sons, Ltd.