Stem Cell Released Molecules and Exosomes in Tissue Engineering

Characterization and bioassays of extracellular vesicles extracted by tangential flow filtration

Aim: To evaluate the efficiency of tangential flow filtration (TFF) in improving the yield of human umbilical cord mesenchymal stem cell (MSC)-derived extracellular vesicles (hucMSC-EVs) while promoting cell regeneration under oxidative stress. Methods: HucMSC-EVs were extracted from supernatants by ultracentrifugation (UC-EVs) and TFF (TFF-EVs), followed by feature characterization and bioactivity assays. Results: The yield of TFF-EVs increased 18-times compared with that of UC-EVs. TFF-EVs displayed proliferation-promoting ability similar to that of UC-EVs in the damaged HaCaT cell model with ultraviolet radiation B (UVB) and H₂O₂. Furthermore, the antiapoptotic effects of TFF-EVs were improved, whereby the apoptosis rate exhibited a 3.7-fold decrease. Conclusion: HucMSC-EVs extracted by TFF show a higher yield and rejuvenate the damaged HaCaT cells induced by oxidative stress.

Challenges and strategy in treatment with exosomes for cell-free-based tissue engineering in dentistry

In dentistry, problems of craniofacial, osteochondral, periodontal tissue, nerve, pulp or endodontics injuries, and osteoarthritis need regenerative therapy. The use of stem cells in dental tissue engineering pays a lot of increased attention, but there are challenges for its clinical applications. Therefore, cell-free-based tissue engineering using exosomes isolated from stem cells is regarded an alternative approach in regenerative dentistry. However, practical use of exosome is restricted by limited secretion capability of cells. For future regenerative treatment with exosomes, efficient strategies for large-scale clinical applications are being studied, including the use of ceramics-based scaffold to enhance exosome production and secretion which can resolve limited exosome secretory from the cells when compared with the existing methods available. Indeed, more research needs to be done on these strategies going forward.

Oxygen releasing materials: Towards addressing the hypoxia-related issues in tissue engineering

Manufacturing macroscale cell-laden architectures is one of the biggest challenges faced nowadays in the domain of tissue engineering. Such living constructs, in fact, pose strict requirements for nutrients and oxygen supply that can hardly be addressed through simple diffusion in vitro or without a functional vasculature in vivo. In this context, in the last two decades, a substantial amount of work has been carried out to develop smart materials that could actively provide oxygen-release to contrast local hypoxia in large-size constructs. This review provides an overview of the currently available oxygen-releasing materials and their synthesis and mechanism of action, highlighting their capacities under in vitro tissue cultures and in vivo contexts. Additionally, we also showcase an emerging concept, herein termed as "living materials as releasing systems", which relies on the combination of biomaterials with photosynthetic microorganisms, namely algae, in an "unconventional" attempt to supply the damaged or re-growing tissue with the necessary supply of oxygen. We envision that future advances focusing on tissue microenvironment regulated oxygen-supplying materials would unlock an untapped potential for generating a repertoire of anatomic scale, living constructs with improved cell survival, guided differentiation, and tissue-specific biofunctionality.

Molecular consequences of fetal alcohol exposure on amniotic exosomal miRNAs with functional implications for stem cell potency and differentiation

Alcohol (ethanol, EtOH) consumption during pregnancy can result in fetal alcohol spectrum disorders (FASDs), which are characterized by prenatal and postnatal growth restriction and craniofacial dysmorphology. Recently, cell-derived extracellular vesicles, including exosomes and microvesicles containing several species of RNAs (exRNAs), have emerged as a mechanism of cell-to-cell communication. However, EtOH's effects on the biogenesis and function of non-coding exRNAs during fetal development have not been explored. Therefore, we studied the effects of maternal EtOH exposure on the composition of exosomal RNAs in the amniotic fluid (AF) using rat fetal alcohol exposure (FAE) model. Through RNA-Seq analysis we identified and verified AF exosomal miRNAs with differential expression levels specifically associated with maternal EtOH exposure. Uptake of purified FAE AF exosomes by rBMSCs resulted in significant alteration of molecular markers associated with osteogenic differentiation of rBMSCs. We also determined putative functional roles for AF exosomal miRNAs (miR-199a-3p, miR-214-3p and let-7g) that are dysregulated by FAE in osteogenic differentiation of rBMSCs. Our results demonstrate that FAE alters AF exosomal miRNAs and that exosomal transfer of dysregulated miRNAs has significant molecular effects on stem cell regulation and differentiation. Our results further suggest the usefulness of assessing molecular alterations in AF exRNAs to study the mechanisms of FAE teratogenesis that should be further investigated by using an in vivo model.

Rescue of degenerating neurons and cells by stem cell released molecules: using a physiological renormalization strategy

Evidence suggests that adult stem cell types and progenitor cells act collectively in a given tissue to maintain and heal organs, such as muscle, through a release of a multitude of molecules packaged into exosomes from the different cell types. Using this principle for the development of bioinspired therapeutics that induces homeostatic renormalization, here we show that the collection of molecules released from four cell types, including mesenchymal stem cells, fibroblast, neural stem cells, and astrocytes, rescues degenerating neurons and cells. Specifically, oxidative stress induced in a human recombinant TDP-43- or FUS-tGFP U2OS cell line by exposure to sodium arsenite was shown to be significantly reduced by our collection of molecules using in vitro imaging of FUS and TDP-43 stress granules. Furthermore, we also show that the collective secretome rescues cortical neurons from glutamate toxicity as evidenced by increased neurite outgrowth, reduced LDH release, and reduced caspase 3/7 activity. These data are the first in a series supporting the development of stem cell-based exosome systems therapeutics that uses a physiological renormalization strategy to treat neurodegenerative diseases.

Systems biology approach to developing S2RM-based “systems therapeutics” and naturally induced pluripotent stem cells

The degree to, and the mechanisms through, which stem cells are able to build, maintain, and heal the body have only recently begun to be understood. Much of the stem cell’s power resides in the release of a multitude of molecules, called stem cell released molecules (SRM). A fundamentally new type of therapeutic, namely “systems therapeutic”, can be realized by reverse engineering the mechanisms of the SRM processes. Recent data demonstrates that the composition of the SRM is different for each type of stem cell, as well as for different states of each cell type. Although systems biology has been successfully used to analyze multiple pathways, the approach is often used to develop a small molecule interacting at only one pathway in the system. A new model is emerging in biology where systems biology is used to develop a new technology acting at multiple pathways called “systems therapeutics”. A natural set of healing pathways in the human that uses SRM is instructive and of practical use in developing systems therapeutics. Endogenous SRM processes in the human body use a combination of SRM from two or more stem cell types, designated as S²RM, doing so under various state dependent conditions for each cell type. Here we describe our approach in using state-dependent SRM from two or more stem cell types, S²RM technology, to develop a new class of therapeutics called “systems therapeutics.” Given the ubiquitous and powerful nature of innate S²RM-based healing in the human body, this “systems therapeutic” approach using S²RM technology will be important for the development of anti-cancer therapeutics, antimicrobials, wound care products and procedures, and a number of other therapeutics for many indications.

Immunomodulatory Potential of Human Adipose Mesenchymal Stem Cells Derived Exosomes on in vitro Stimulated T Cells

In the recent years, it has been demonstrated that the biological activity of mesenchymal stem cells (MSCs) is mediated through the release of paracrine factors. Many of these factors are released into exosomes, which are small membranous vesicles that participate in cell–cell communication. Exosomes from MSCs are thought to have similar functions to MSCs such as repairing and regeneration of damaged tissue, but little is known about the immunomodulatory effect of these vesicles. Based on an extensive bibliography where the immunomodulatory capacity of MSCs has been demonstrated, here we hypothesized that released exosomes from MSCs may have an immunomodulatory role on the differentiation, activation and function of different lymphocyte subsets. According to this hypothesis, in vitro experiments were performed to characterize the immunomodulatory effect of human adipose MSCs derived exosomes (exo-hASCs) on in vitro stimulated T cells. The phenotypic characterization of cytotoxic and helper T cells (activation and differentiation markers) together with functional assays (proliferation and IFN-γ production) demonstrated that exo-hASCs exerted an inhibitory effect in the differentiation and activation of T cells as well as a reduced T cell proliferation and IFN-γ release on in vitro stimulated cells. In summary, here we demonstrate that MSCs-derived exosomes are a cell-derived product that could be considered as a therapeutic agent for the treatment of inflammation-related diseases.

Using a systems-based approach to overcome reductionist strategies in the development of diagnostics

Systems biology is a recent addition to the necessary but insufficient reductionist approach used in biological research. Systems biology is focused on understanding living things as a function of their various interactions at multiple levels: not simply as a sum of all their individual parts at any one level. This integrative approach yields predictive models of the normal state, the disease state and therapeutic actions. Although molecular biology has collected an enormous amount of information, including the sequencing of the entire human genome in the year 2000, few real-world applications have resulted from this molecular approach. The pharmaceutical industry's R&D expenditure has increased substantially since 2000, but the number of approved therapeutics has dropped simultaneously, due in part to over-reliance on reductionist genomic, and not systems, approaches. Instead of using reductionist genomics approaches alone, genomics should be incorporated into a multi-level systems biology approach to develop diagnostics and therapeutics.

Stem cell therapy without the cells

As an example of the burgeoning importance of stem cell therapy, this past month the California Institute for Regenerative Medicine (CIRM) has approved $70 million to create a new network of stem cell clinical trial centers. Much work in the last decade has been devoted to developing the use of autologous and allogeneic adult stem cell transplants to treat a number of conditions, including heart attack, dementia, wounds, and immune system-related diseases. The standard model teaches us that adult stem cells exists throughout most of the body and provide a means to regenerate and repair most tissues through replication and differentiation. Although we have often witnessed the medical cart placed in front of the scientific horse in the development of stem cell therapies outside of academic circles, great strides have been made, such as the use of purified stem cells¹ instead of whole bone marrow transplants in cancer patients, where physicians avoid re-injecting the patients with their own cancer cells.² We most often think of stem cell therapy acting to regenerate tissue through replication and then differentiation, but recent studies point to the dramatic effects adult stem cells exert in the repair of various tissues through the release of paracrine and autocrine substances, and not simply through differentiation. Indeed, up to 80% of the therapeutic effect of adult stem cells has been shown to be through paracrine mediated actions.³ That is, the collected types of molecules released by the stem cells, called the secretome, or stem cell released molecules (SRM), number in the 100s, including proteins, microRNA, growth factors, antioxidants, proteasomes, and exosomes, and target a multitude of biological pathways through paracrine actions. The composition of the different molecule types in SRM is state dependent, and varies with cell type and conditions such as age and environment.