Microfluidic Screening Reveals Heparan Sulfate Enhances Human Mesenchymal Stem Cell Growth by Modulating Fibroblast Growth Factor-2 Transport

Sepsis-associated endothelial glycocalyx damage: a review of animal models, clinical evidence, and molecular mechanisms

In the mammalian cardiovascular system, endothelial glycocalyx is a gel-like layer that covers the luminal surface of endothelial cells (ECs) and plays crucial roles in vascular homeostasis, permeability and leukocyte adhesion. Degradation of this structure occurs early in sepsis and becomes accordingly dysfunctional. In severe cases, it is not self-regulated by the organism. However, the relationship between the glycocalyx and the occurrence and development of sepsis remains poorly understood. One possibility is that thinned glycocalyx promotes leukocyte recognition and adhesion, thereby facilitating the elimination of pathogens from infected areas. This may represent a protective mechanism developed by the organism during through evolutionary processes. However, if the damage persists and disrupts the dynamic balance of the microcirculation, interstitial edema or organ failure can occur. Thus, we asked the questions, what is the precise composition and structure of the glycocalyx? How is it degraded? What animal models are available to study the relationship between the glycocalyx and sepsis? What glycocalyx biomarkers are found in the blood of patients with sepsis? To determine whether sepsis can be treated by interfering with the glycocalyx, this study provides a systematic summary and discussion of the latest progress in addressing these questions.

In Vitro Characterization of Human Cell Sources in Collagen Type I Gel Scaffold for Meniscus Tissue Engineering

Strategies to repair the meniscus have achieved limited success; thus, a cell-based therapy combined with an appropriate biocompatible scaffold could be an interesting alternative to overcome this issue. The aim of this project is to analyze different cell populations and a collagen gel scaffold as a potential source for meniscus tissue engineering applications. Dermal fibroblasts (DFs) and mesenchymal stem cells (MSCs) isolated from adipose tissue (ASCs) or bone marrow (BMSCs) were analyzed. Two different fibro-chondrogenic media, M1 and M2, were tested, and qualitative and quantitative analyses were performed. Significant increases in glycosaminoglycans (GAGs) production and in fibro-cartilaginous marker expression were observed in MSCs in the presence of M1 medium. In addition, both ASCs and BMSCs cultured in M1 medium were used in association with the collagen hydrogel (MSCs-SCF) for the development of an in vitro meniscal-like tissue. Significant up-regulation in GAGs production and in the expression of aggrecan, collagen type I, and collagen type II was observed in BMSCs-SCF. This study improves knowledge of the potential of combining undifferentiated MSCs with a collagen gel as a new tissue engineering strategy for meniscus repair.

Enhancing BMP-2-mediated osteogenesis with a synthetic heparan sulfate mimetic

Bone morphogenetic protein 2 (BMP-2) is an osteoinductive protein and a potent inducers of bone formation, playing an essential role during bone fracture repair. Heparan sulfate (HS), a highly charged and linear polysaccharide, is known to interact with and enhance BMP-2 bioactivity. Despite showing potential as a potent adjuvant of the endogenous bone healing response, commercially available HS is derived from animal sources which are less desirable when considering translation into the clinic. In the present study, we screen twenty glycomimetics against BMP-2 to determine if fully synthetic analogues of HS can enhance the bioactivity of BMP-2 in vitro and bone healing in vivo. We found that a four-armed dendrimer harboring oversulfated maltose residues could bind BMP-2 with high affinity, enhance BMP-2 bioactivity in vitro and enhance bone regeneration in vivo. These data suggest fully synthetic glycomimetics are viable alternatives to naturally derived HS and offer an attractive alternative for clinical translation.

Managing the Heterogeneity of Mesenchymal Stem Cells for Cartilage Regenerative Therapy: A Review

Articular cartilage defects commonly result from trauma and are associated with significant morbidity. Since cartilage is an avascular, aneural, and alymphatic tissue with a poor intrinsic healing ability, the regeneration of functional hyaline cartilage remains a difficult clinical problem. Mesenchymal stem cells (MSCs) are multipotent cells with multilineage differentiation potential, including the ability to differentiate into chondrocytes. Due to their availability and ease of ex vivo expansion, clinicians are increasingly applying MSCs in the treatment of cartilage lesions. However, despite encouraging pre-clinical and clinical data, inconsistencies in MSC proliferative and chondrogenic potential depending on donor, tissue source, cell subset, culture conditions, and handling techniques remain a key barrier to widespread clinical application of MSC therapy in cartilage regeneration. In this review, we highlight the strategies to manage the heterogeneity of MSCs ex vivo for more effective cartilage repair, including reducing the MSC culture expansion period, and selecting MSCs with higher chondrogenic potential through specific genetic markers, surface markers, and biophysical attributes. The accomplishment of a less heterogeneous population of culture-expanded MSCs may improve the scalability, reproducibility, and standardisation of MSC therapy for clinical application in cartilage regeneration.

Luciferin-Bioinspired Click Ligation Enables Hydrogel Platforms with Fine-Tunable Properties for 3D Cell Culture

There is an increasing interest in coupling reactions for cross-linking of cell-encapsulating hydrogels under biocompatible, chemoselective, and tunable conditions. Inspired by the biosynthesis of luciferins in fireflies, here we exploit the cyanobenzothiazole-cysteine (CBT-Cys) click ligation to develop polyethylene glycol hydrogels as tunable scaffolds for cell encapsulation. Taking advantage of the chemoselectivity and versatility of CBT-Cys ligation, a highly flexible gel platform is reported here. We demonstrate luciferin-inspired hydrogels with important advantages for cell encapsulation applications: (i) gel precursors derived from inexpensive reagents and with good stability in aqueous solution (>4 weeks), (ii) adjustable gel mechanics within physiological ranges (E = 180-6240 Pa), (iii) easy tunability of the gelation rate (seconds to minutes) by external means, (iv) high microscale homogeneity, (v) good cytocompatibility, and (iv) regulable biological properties. These flexible and robust CBT-Cys hydrogels are proved as supportive matrices for 3D culture of different cell types, namely, fibroblasts and human mesenchymal stem cells. Our findings expand the toolkit of click chemistries for the fabrication of tunable biomaterials.

Proteoglycans and Glycosaminoglycans in Stem Cell Homeostasis and Bone Tissue Regeneration

Stem cells maintain a subtle balance between self-renewal and differentiation under the regulatory network supported by both intracellular and extracellular components. Proteoglycans are large glycoproteins present abundantly on the cell surface and in the extracellular matrix where they play pivotal roles in facilitating signaling transduction and maintaining stem cell homeostasis. In this review, we outline distinct proteoglycans profiles and their functions in the regulation of stem cell homeostasis, as well as recent progress and prospects of utilizing proteoglycans/glycosaminoglycans as a novel glycomics carrier or bio-active molecules in bone regeneration.

High-Throughput Routes to Biomaterials Discovery

Many existing clinical treatments are limited in their ability to completely restore decreased or lost tissue and organ function, an unenviable situation only further exacerbated by a globally aging population. As a result, the demand for new medical interventions has increased substantially over the past 20 years, with the burgeoning fields of gene therapy, tissue engineering, and regenerative medicine showing promise to offer solutions for full repair or replacement of damaged or aging tissues. Success in these fields, however, inherently relies on biomaterials that are engendered with the ability to provide the necessary biological cues mimicking native extracellular matrixes that support cell fate. Accelerating the development of such "directive" biomaterials requires a shift in current design practices toward those that enable rapid synthesis and characterization of polymeric materials and the coupling of these processes with techniques that enable similarly rapid quantification and optimization of the interactions between these new material systems and target cells and tissues. This manuscript reviews recent advances in combinatorial and high-throughput (HT) technologies applied to polymeric biomaterial synthesis, fabrication, and chemical, physical, and biological screening with targeted end-point applications in the fields of gene therapy, tissue engineering, and regenerative medicine. Limitations of, and future opportunities for, the further application of these research tools and methodologies are also discussed.

Highly parallelized human embryonic stem cell differentiation to cardiac mesoderm in nanoliter chambers on a microfluidic chip

Human stem cell-derived cells and tissues hold considerable potential for applications in regenerative medicine, disease modeling and drug discovery. The generation, culture and differentiation of stem cells in low-volume, automated and parallelized microfluidic chips hold great promise to accelerate the research in this domain. Here, we show that we can differentiate human embryonic stem cells (hESCs) to early cardiac mesodermal cells in microfluidic chambers that have a volume of only 30 nanoliters, using discontinuous medium perfusion. 64 of these chambers were parallelized on a chip which contained integrated valves to spatiotemporally isolate the chambers and automate cell culture medium exchanges. To confirm cell pluripotency, we tracked hESC proliferation and immunostained the cells for pluripotency markers SOX2 and OCT3/4. During differentiation, we investigated the effect of different medium perfusion frequencies on cell reorganization and the expression of the early cardiac mesoderm reporter MESP1mCherry by live-cell imaging. Our study demonstrates that microfluidic technology can be used to automatically culture, differentiate and study hESC in very low-volume culture chambers even without continuous medium perfusion. This result is an important step towards further automation and parallelization in stem cell technology.

Heparan Sulfate Proteoglycans: Key Mediators of Stem Cell Function

Heparan sulfate proteoglycans (HSPGs) are an evolutionarily ancient subclass of glycoproteins with exquisite structural complexity. They are ubiquitously expressed across tissues and have been found to exert a multitude of effects on cell behavior and the surrounding microenvironment. Evidence has shown that heterogeneity in HSPG composition is crucial to its functions as an essential scaffolding component in the extracellular matrix as well as a vital cell surface signaling co-receptor. Here, we provide an overview of the significance of HSPGs as essential regulators of stem cell function. We discuss the various roles of HSPGs in distinct stem cell types during key physiological events, from development through to tissue homeostasis and regeneration. The contribution of aberrant HSPG production to altered stem cell properties and dysregulated cellular homeostasis characteristic of cancer is also reviewed. Finally, we consider approaches to better understand and exploit the multifaceted functions of HSPGs in influencing stem cell characteristics for cell therapy and associated culture expansion strategies.

A biomimetic collagen-bone granule-heparan sulfate combination scaffold for BMP2 delivery

Bone morphogenetic protein 2 (BMP2)-induced bone regeneration is most efficacious when a carrier can deliver the growth factor into the defect site while minimizing off-target effects. The control of BMP2 release by such carriers is proving one of the most critical aspects of BMP2 therapy. Thus, increasing numbers of biomaterials are being developed to satisfy the simultaneous need for sustained release, reduced rates of degradation and enhanced activity of the growth factor. Here we report on a biomimetic scaffold consisting of bovine collagen type I, bone granules (Intergraft™), and heparan sulfate with increased affinity for BMP2 (HS3). The HS3 and collagen were complexed and then crosslinked via a simple dehydrothermal method. When loaded with a clinically relevant amount of BMP2 (1.25 mg/cc), the HS3-functionalised scaffolds were able to retain up to 58% of the initial amount of BMP2 over 27 days, approximately 3-fold higher than scaffolds without HS3. The bioactivity of the retained BMP2 was confirmed by gene expression in myoblast cells (C2C12) cultured on the scaffolds under osteogenic stimulation. Together these data demonstrate the efficacy of HS3 as a material to improve the performance collagen/bone granule-based scaffolds.

Vascular Endothelial Growth Factor 165-Binding Heparan Sulfate Promotes Functional Recovery From Cerebral Ischemia

BACKGROUND AND PURPOSE

Although VEGF₁₆₅ (vascular endothelial growth factor-165) is able to enhance both angiogenesis and neurogenesis, it also increases vascular permeability through the blood-brain barrier. Heparan sulfate (HS) sugars play important roles in regulating VEGF bioactivity in the pericellular compartment. Here we asked whether an affinity-purified VEGF₁₆₅-binding HS (HS7) could augment endogenous VEGF activity during stroke recovery without affecting blood-brain barrier function.

METHODS

Both rat brain endothelial cell line 4 and primary rat neural progenitor cells were used to evaluate the potential angiogenic and neurogenic effects of HS7 in vitro. For in vivo experiments, male Sprague-Dawley rats were subjected to 100 minutes of transient focal cerebral ischemia, then treated after 4 days with either PBS or HS7. One week later, infarct volume, behavioral sequelae, immunohistochemical markers of angiogenesis and neural stem cell proliferation were assessed.

RESULTS

HS7 significantly enhanced VEGF₁₆₅-mediated angiogenesis in rat brain endothelial cell line 4 brain endothelial cells, and increased the proliferation and differentiation of primary neural progenitor cells, both via the VEGFR2 (vascular endothelial growth factor receptor 2) pathway. Intracerebroventricular injection of HS7 improved neurological outcome in ischemic rats without changing infarct volumes. Immunostaining of the compromised cerebrum demonstrated increases in collagen IV/Ki67 and nestin/Ki67 after HS7 exposure, consistent with its ability to promote angiogenesis and neurogenesis, without compromising blood-brain barrier integrity.

CONCLUSIONS

A VEGF-activating glycosaminoglycan sugar, by itself, is able to enhance endogenous VEGF₁₆₅ activity during the post-ischemic recovery phase of stroke.

Enhancing the Efficacy of Stem Cell Therapy with Glycosaminoglycans

Human mesenchymal stem cell (hMSC) therapy offers significant potential for osteochondral regeneration. Such applications require their ex vivo expansion in media frequently supplemented with fibroblast growth factor 2 (FGF2). Particular heparan sulfate (HS) fractions stabilize FGF2-FGF receptor complexes. We show that an FGF2-binding HS variant (HS8) accelerates the expansion of freshly isolated bone marrow hMSCs without compromising their naivety. Importantly, the repair of osteochondral defects in both rats and pigs is improved after treatment with HS8-supplemented hMSCs (MSC^HS8), when assessed histologically, biomechanically, or by MRI. Thus, supplementing hMSC culture media with an HS variant that targets endogenously produced FGF2 allows the elimination of exogenous growth factors that may adversely affect their therapeutic potency.

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An FGF2-binding heparan sulfate (HS8) accelerates the ex vivo expansion of hMSCs

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hMSCs expanded with HS8 maintain stem cell characteristics and potency

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HS8-expanded hMSCs improve osteochondral regeneration in animal models

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HS8 is an effective bio-additive for the scale up of highly potent hMSCs

Multivariate patterning of human pluripotent cells under perfusion reveals critical roles of induced paracrine factors in kidney organoid development

Creating complex multicellular kidney organoids from pluripotent stem cells shows great promise. Further improvements in differentiation outcomes, patterning, and maturation of specific cell types are, however, intrinsically limited by standard tissue culture approaches. We describe a novel full factorial microbioreactor array-based methodology to achieve rapid interrogation and optimization of this complex multicellular differentiation process in a facile manner. We successfully recapitulate early kidney tissue patterning events, exploring more than 1000 unique conditions in an unbiased and quantitative manner, and define new media combinations that achieve near-pure renal cell type specification. Single-cell resolution identification of distinct renal cell types within multilayered kidney organoids, coupled with multivariate analysis, defined the definitive roles of Wnt, fibroblast growth factor, and bone morphogenetic protein signaling in their specification, exposed retinoic acid as a minimal effector of nephron patterning, and highlighted critical contributions of induced paracrine factors on cell specification and patterning.

Modular operation of microfluidic chips for highly parallelized cell culture and liquid dosing via a fluidic circuit board

Microfluidic systems enable automated and highly parallelized cell culture with low volumes and defined liquid dosing. To achieve this, systems typically integrate all functions into a single, monolithic device as a "one size fits all" solution. However, this approach limits the end users' (re)design flexibility and complicates the addition of new functions to the system. To address this challenge, we propose and demonstrate a modular and standardized plug-and-play fluidic circuit board (FCB) for operating microfluidic building blocks (MFBBs), whereby both the FCB and the MFBBs contain integrated valves. A single FCB can parallelize up to three MFBBs of the same design or operate MFBBs with entirely different architectures. The operation of the MFBBs through the FCB is fully automated and does not incur the cost of an extra external footprint. We use this modular platform to control three microfluidic large-scale integration (mLSI) MFBBs, each of which features 64 microchambers suitable for cell culturing with high spatiotemporal control. We show as a proof of principle that we can culture human umbilical vein endothelial cells (HUVECs) for multiple days in the chambers of this MFBB. Moreover, we also use the same FCB to control an MFBB for liquid dosing with a high dynamic range. Our results demonstrate that MFBBs with different designs can be controlled and combined on a single FCB. Our novel modular approach to operating an automated microfluidic system for parallelized cell culture will enable greater experimental flexibility and facilitate the cooperation of different chips from different labs.

Evaluation of fibroblast growth factor-2 on the proliferation of osteogenic potential and protein expression of stem cell spheroids composed of stem cells derived from bone marrow

Fibroblast growth factor-2 (FGF-2) is reported to have various functions and is considered a key human mesenchymal stem cell mitogen, often supplemented to increase human mesenchymal stem cell growth rates. The purpose of this study was to evaluate the effects of FGF-2 on cellular viability and osteogenic differentiation using three-dimensional cell spheroids of stem cells. Three-dimensional cell spheroids were fabricated using concave silicon elastomer-based microwells in the presence of FGF-2 at concentrations of 0, 30, 60 and 90 ng/ml. Qualitative cellular viability was determined with a confocal microscope, and quantitative cellular viability was evaluated using a Cell Counting Kit-8 assay. Alkaline phosphatase activity and Alizarin Red S staining were used to assess osteogenic differentiation. Spheroids were well formed in silicon elastomer-based concave microwells on Day 1. The average spheroid diameters at Day 1 for FGF-2 at 0, 30, 60 and 90 ng/ml were 202.2±3.0, 206.6±22.6, 208.8±6.8 and 196.6±26.7 µm, respectively (P>0.05). The majority of the cells in the cell spheroids emitted green fluorescence. The relative Cell Counting Kit-8 assay values for FGF-2 at 0, 30, 60 and 90 ng/ml at Day 1 were 100.0±5.5, 101.8±8.8, 99.2±4.8 and 103.4±9.6% (P>0.05). The addition of FGF-2 at 60 ng/ml concentration produced the highest value for alkaline phosphatase activity. Mineralized extracellular deposits were evenly observed in each group, and the highest value was identified for FGF-2 groups at 60 ng/ml concentration for Alizarin Red S staining. Based on these findings, it was concluded that FGF-2 may increase alkaline phosphatase activity or Alizarin Red S staining, and further studies are needed to fully elucidate the mechanisms of FGF-2.

A Heparan Sulfate Device for the Regeneration of Osteochondral Defects

IMPACT STATEMENT

Repairing damaged joint cartilage remains a significant challenge. Treatment involving microfracture, tissue grafting, or cell therapy provides some benefit, but seldom regenerates lost articular cartilage. Providing a point-of-care solution that is cell and tissue free has the potential to transform orthopedic treatment for such cases. Glycosaminoglycans such as heparan sulfate (HS) are well suited for this purpose because they provide a matrix that enhances the prochondrogenic activities of growth factors normally found at sites of articular damage. In this study, we show the potential of a novel HS device, which is free of exogenous cells or growth factors, in regenerating osteochondral defects.

Microenvironmental support for cell delivery to the inner ear

Transplantation of mesenchymal stromal cells (MSC) presents a promising approach not only for the replacement of lost or degenerated cells in diseased organs but also for local drug delivery. It can potentially be used to enhance the safety and efficacy of inner ear surgeries such as cochlear implantation. Options for enhancing the effects of MSC therapy include modulating cell behaviour with customized bio-matrixes or modulating their behaviour by ex vivo transfection of the cells with a variety of genes. In this study, we demonstrate that MSC delivered to the inner ear of guinea pigs or to decellularized cochleae preferentially bind to areas of high heparin concentration. This presents an opportunity for modulating cell behaviour ex vivo. We evaluated the effect of carboxymethylglucose sulfate (Cacicol^®), a heparan sulfate analogue on spiral ganglion cells and MSC and demonstrated support of neuronal survival and support of stem cell proliferation.

Microtechnology applied to stem cells research and development

Microfabrication and microfluidics contribute to the research of cellular functions of cells and their interaction with their environment. Previously, it has been shown that microfluidics can contribute to the isolation, selection, characterization and migration of cells. This review aims to provide stem cell researchers with a toolkit of microtechnology (mT) instruments for elucidating complex stem cells functions which are challenging to decipher with traditional assays and animal models. These microdevices are able to investigate about the differentiation and niche interaction, stem cells transcriptomics, therapeutic functions and the capture of their secreted microvesicles. In conclusion, microtechnology will allow a more realistic assessment of stem cells properties, driving and accelerating the translation of regenerative medicine approaches to the clinic.

Amelioration of cadmium-induced testes' damage in rats by the bone marrow mesenchymal stem cells

Cadmium (Cd) and its compounds are highly toxic to virtually all organ systems of the mammals. Cd-induced testicular injuries have been reported in various animal species, using different protocols. The self-renewal capacity and the ability to generate different specialized cell types make the mesenchymal stem cells (MSCs) one of the ideal choices for restoring tissue damages of various etiologies. The use of bone marrow-derived MSCs (BM-MSCs) is among the most recent strategies to repair the Cd-induced testicular damage, but empirical studies in this regard are largely missing. Keeping in view the CD-induced testicular damage and the suggested restorative functions of BM-MSCs, the objectives of the current study were twofold: to induce testicular injury in Sprague-Dawley (SD) rats by a single intraperitoneal (i.p.) 2mg/kg Cd injection; and to study the reparative potential of BM-MSCs in Cd-induced testicular damage in adult male rats. The SD rats were randomly divided into three groups (n = 10 each): control (untreated), Cd-group (i.p. 2mg/kg Cd), and Cd+SC group (i.p. 2mg/kg Cd plus two intravenous doses of 1 × 106 BM-MSCs via penile vein). After four weeks, Cd-group showed a significantly lower (p < 0.05) weight-gain, sperm count, and sperm viability, as well as led to testicular atrophy, necrosis, fibrosis, calcification, and marked perivascular lymphocytic infiltration, as compared to the untreated controls. As hypothesized, the rats exposed to Cd, but treated with BM-MSCs (Cd+SC group), showed a lesser degree of Cd-induced damage. In conclusion, the findings of current investigation indicate a reversal of Cd-induced testicular injury by BM-MSCs. The study supports the previously suggested notion that BM-MSCs can repair the Cd-induced testes' damage in rats.