Enhancing stem cell survival in vivo for tissue repair

The ability to use progenitor cells for regenerative medicine remains an evolving but elusive clinical goal. A serious obstacle towards widespread use of stem cells for tissue regeneration is the challenges that face these cells when they are placed in vivo into a wound for therapy. These environments are hypoxic, acidic, and have an upregulation of inflammatory mediators creating a region that is hostile towards cellular survival. Within this environment, the majority of progenitor cells undergo apoptosis prior to participating in lineage differentiation and cellular integration. In order to maximize the clinical utility of stem cells, strategies must be employed to increase the cell's ability to survive in vivo through manipulation of both the stem cell and the surrounding environment. This review focuses on current advances and techniques being used to increase in vivo stem cell survival for the purpose of tissue regeneration.     

Stem cells, regenerative medicine, and animal models of disease

The field of stem cell biology and regenerative medicine is rapidly moving toward translation to clinical practice, and in doing so has become even more dependent on animal donors and hosts for generating cellular reagents and assaying their potential therapeutic efficacy in models of human disease. Advances in cell culture technologies have revealed a remarkable plasticity of stem cells from embryonic and adult tissues, and transplantation models are now needed to test the ability of these cells to protect at-risk cells and replace cells lost to injury or disease. With such a mandate, issues related to acceptable sources and controversial (e.g., chimeric) models have challenged the field to provide justification of their potential efficacy before the passage of new restrictions that may curb anticipated breakthroughs. Progress from the use of both in vitro and in vivo regenerative medicine models already offers hope both for the facilitation of stem cell phenotyping in recursive gene expression profile models and for the use of stem cells as powerful new therapeutic reagents for cancer, stroke, Parkinson's, and other challenging human diseases that result in movement disorders. This article describes research in support of the following three objectives: (1) To discover the best stem or progenitor cell in vitro protocols for isolating, expanding, and priming these cells to facilitate their massive propagation into just the right type of neuronal precursor cell for protection or replacement protocols for brain injury or disease, including those that affect movement such as Parkinson's disease and stroke; (2) To discover biogenic factors--compounds that affect stem/progenitor cells (e.g., from high-throughput screening and other bioassay approaches)--that will encourage reactive cell genesis, survival, selected differentiation, and restoration of connectivity in central nervous system movement and other disorders; and (3) To establish the best animal models of human disease and injury, using both small and large animals, for testing new regenerative medicine therapeutics.     

Characterization of cell signaling,morphology, and differentiation potential of human mesenchymal stem cells based on cell adhesion mechanism

It is essential to characterize the cellular properties of mesenchymal stem cell populations to maintain quality specifications and control in regenerative medicine. Biofunctional materials have been designed as artificial matrices for the stimulation of cell adhesion and specific cellular functions. We have developed recombinant maltose-binding protein (MBP)-fused proteins as artificial adhesion matrices to control human mesenchymal stem cell (hMSC) fate by using an integrin-independent heparin sulfate proteoglycans-mediated cell adhesion. In this study, we characterize cell adhesion-dependent cellular behaviors of human adipose-derived stem cells (hASCs) and human bone marrow stem cells (hBMSCs). We used an MBP-fused basic fibroblast growth factor (MF)-coated surface and fibronectin (FN)-coated surface to restrict and support, respectively, integrin-mediated adhesion. The cells adhered to MF exhibited restricted actin cytoskeleton organization and focal adhesion kinase phosphorylation. The hASCs and hBMSCs exhibited different cytoplasmic projection morphologies on MF. Both hASCs and hBMSCs differentiated more dominantly into osteogenic cells on FN than on MF. In contrast, hASCs differentiated more dominantly into adipogenic cells on MF than on FN, whereas hBMSCs differentiated predominantly into adipogenic cells on FN. The results indicate that hASCs exhibit a competitive differentiation potential (osteogenesis vs. adipogenesis) that depends on the cell adhesion matrix, whereas hBMSCs exhibit both adipogenesis and osteogenesis in integrin-mediated adhesion and thus hBMSCs have noncompetitive differentiation potential. We suggest that comparing differentiation behaviors of hMSCs with the diversity of cell adhesion is an important way to characterize hMSCs for regenerative medicine.     

Control of stem cell fate by engineering their micro and nanoenvironment

Stem cells are capable of long-term self-renewal and differentiation into specialised cell types, making them an ideal candidate for a cell source for regenerative medicine. The control of stem cell fate has become a major area of interest in the field of regenerative medicine and therapeutic intervention. Conventional methods of chemically inducing stem cells into specific lineages is being challenged by the advances in biomaterial technology, with evidence highlighting that material properties are capable of driving stem cell fate. Materials are being designed to mimic the clues stem cells receive in their in vivo stem cell niche including topographical and chemical instructions. Nanotopographical clues that mimic the extracellular matrix(ECM) in vivo have shown to regulate stem cell differentiation. The delivery of ECM components on biomaterials in the form of short peptides sequences has also proved successful in directing stem cell lineage. Growth factors responsible for controlling stem cell fate in vivo have also been delivered via biomaterials to provide clues to determine stem cell differentiation. An alternative approach to guide stem cells fate is to provide genetic clues including delivering DNA plasmids and small interfering RNAs via scaffolds. This review, aims to provide an overview of the topographical, chemical and molecular clues that biomaterials can provide to guide stem cell fate. The promising features and challenges of such approaches will be highlighted, to provide directions for future advancements in this exciting area of stem cell translation for regenerative medicine.     

Surface functionalization of nanobiomaterials for application in stem cell culture,tissue engineering,and regenerative medicine

Stem cell‐based approaches offer great application potential in tissue engineering and regenerative medicine owing to their ability of sensing the microenvironment and respond accordingly (dynamic behavior). Recently, the combination of nanobiomaterials with stem cells has paved a great way for further exploration. Nanobiomaterials with engineered surfaces could mimic the native microenvironment to which the seeded stem cells could adhere and migrate. Surface functionalized nanobiomaterial‐based scaffolds could then be used to regulate or control the cellular functions to culture stem cells and regenerate damaged tissues or organs. Therefore, controlling the interactions between nanobiomaterials and stem cells is a critical factor. However, surface functionalization or modification techniques has provided an alternative approach for tailoring the nanobiomaterials surface in accordance to the physiological surrounding of a living cells; thereby, enhancing the structural and functional properties of the engineered tissues and organs. Currently, there are a variety of methods and technologies available to modify the surface of biomaterials according to the specific cell or tissue properties to be regenerated. This review highlights the trends in surface modification techniques for nanobiomaterials and the biological relevance in stem cell‐based tissue engineering and regenerative medicine. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:554–567, 2016     

Mesenchymal stromal cells from umbilical cord blood

Mesenchymal Stromal Cells (MSC) are key candidates for cellular therapies. Although most therapeutic applications have focused on adult bone marrow derived MSC, increasing evidence suggests that MSC are present within a wide range of tissues. Umbilical cord blood (CB) has been proven to be a valuable source of hematopoietic stem cells, but its therapeutic potential extends beyond the hematopoietic component suggesting regenerative potential in solid organs as well. There is evidence that other stem or progenitor populations, such as MSC, exist in CB which might be responsible for these effects. Many different stem and progenitor cell populations have been postulated with potential ranging from embryonic like to lineage-committed progenitor cells. Based on the confusing data, this review focuses on a human CB derived, plastic adherent fibroblastoid population expressing similar characteristics to bone marrow derived MSC. It concentrates especially on concepts of isolation and expansion, comparing the phenotype with bone marrow derived MSC, describing the differentiation capacity and finally in the last the therapeutic potential with regard to regenerative medicine, stromal support, immune modulation and gene therapy.     

Human adult pluripotency: Facts and questions

Cellular reprogramming and induced pluripotent stem cell(IPSC) technology demonstrated the plasticity of adult cell fate, opening a new era of cellular modelling and introducing a versatile therapeutic tool for regenerative medicine.While IPSCs are already involved in clinical trials for various regenerative purposes, critical questions concerning their medium-and long-term genetic and epigenetic stability still need to be answered. Pluripotent stem cells have been described in the last decades in various mammalian and human tissues(such as bone marrow, blood and adipose tissue). We briefly describe the characteristics of human-derived adult stem cells displaying in vitro and/or in vivo pluripotency while highlighting that the common denominators of their isolation or occurrence within tissue are represented by extreme cellular stress. Spontaneous cellular reprogramming as a survival mechanism favoured by senescence and cellular scarcity could represent an adaptative mechanism. Reprogrammed cells could initiate tissue regeneration or tumour formation dependent on the microenvironment characteristics. Systems biology approaches and lineage tracing within living tissues can be used to clarify the origin of adult pluripotent stem cells and their significance for regeneration and disease.     

Stem cell engineering in bioreactors for large‐scale bioprocessing

Stem cells are promising cell sources for many biomedical applications including cell therapy, regenerative medicine, and drug discovery. However, the commonly used static tissue culture vessels can only generate a low number of cells. To provide an adequate number of stem cells for clinical applications, a scalable process based on bioreactors is needed. Stem cells can be either cultured as free cells/aggregates in suspension or as adherent cells on the solid substrates. Based on the cell property, different bioreactor configurations are developed to better expand stem cells while maintaining their differentiation capacity. In this review, several major types of bioreactor systems and their applications in stem cell engineering are discussed. Continued advancements in bioprocess and bioreactor research and development are important to engineer stem cells for their use in biomedical applications.     

Mesenchymal stem cells from development to postnatal joint homeostasis, aging, and disease

Joint morphogenesis involves signaling pathways and growth factors that recur in the adult life with less redundancy to safeguard joint homeostasis. Loss of such homeostasis due to abnormal signaling networks as in aging could lead to diseases such as osteoarthritis. Stem cells are the cellular counterpart and targets of the morphogenetic signals, and they function to maintain the tissues by ensuring replacement of cells lost to physiological turnover, injury, aging, and disease. Mesenchymal stem cells (MSCs) are key players in regenerative medicine for their ability to differentiate toward multiple lineages such as cartilage and bone, but they age along the host body and senesce when serially passaged in culture. Understanding correlations between aging and its effects on MSCs is of the utmost importance to explain how aging happens and unravel the underlying mechanisms. The investigation of the MSC senescence in culture will help in developing more efficient and standardized cell culture methods for cellular therapies in skeletal regenerative medicine. An important area to explore in biomedical sciences is the role of endogenous stem cell niches in joint homeostasis, remodeling, and disease. It is anticipated that an understanding of the stem cell niches and related remodeling signals will allow the development of pharmacological interventions to support effective joint tissue regeneration, to restore joint homeostasis, and to prevent osteoarthritis.     

A molecular view of stem cell and cancer cell self-renewal

With the recent advances in cell biology and molecular genetics, scientists were able to isolate and culture tissue-specific stem cells from various sources and define their properties. The challenge has now shifted to understanding the genetic programs controlling the stem cell state, i.e. self-renewal and multipotential. Cracking the molecular codes that govern the stem cell state turns out to be a difficult task. This is in part because a single gene may exhibit distinct activities when expressed in different cell types. Comprehending the cell-context dependent readout of any given gene requires an integrated knowledge of the complex cellular machinery, a platform which can be provided by the research on stem cells. This review is an attempt to formulate a model for the self-renewal machinery operating in stem cells and cancer cells. Insight into this issue at the molecular and cellular levels will no doubt facilitate the realization of the stem cell potential in both regenerative medicine and anticancer therapy.     

Stem cells as delivery vehicles for regenerative medicinechallenges and perspectives

The use of stem cells as carriers for therapeutic agents is an appealing modality for targeting tissues or organs of interest. Combined delivery of cells together with various information molecules as therapeutic agents has the potential to enhance, modulate or even initiate local or systemic repair processes, increasing stem cell efficiency for regenerative medicine applications. Stem-cell-mediated delivery of genes, proteins or small molecules takes advantage of the innate capability of stem cells to migrate and home to injury sites. As the native migratory properties are affected by in vitro expansion, the existent methods for enhancing stem cell targeting capabilities(modified culture methods, genetic modification, cell surface engineering) are described. The role of various nanoparticles in eq-uipping stem cells with therapeutic small molecules is revised together with their class-specific advantages and shortcomings. Modalities to circumvent common challenges when designing a stem-cell-mediated targeted delivery system are described as well as future prospects in using this approach for regenerative medicine applications.     

Imaging stem cell implant for cellular-based therapies

Stem cell-based cellular therapy represents a promising outlook for regenerative medicine. Imaging techniques provide a means for noninvasive, repeated, and quantitative tracking of stem cell implant or transplant. From initial deposition to the survival, migration and differentiation of the transplant/implanted stem cells, imaging allows monitoring of the infused cells in the same live object over time. The current review briefly summarizes and compares existing imaging methods for cell labeling and imaging in animal models. Several studies performed by our group using different imaging techniques are described, with further discussion on the issues with these current imaging approaches and potential directions for future development in stem cell imaging.     

Biophysical factors in the regulation of asymmetric division of stem cells

Stem cells are a promising cell source for regenerative medicine due to their characteristics of self‐renewal and differentiation. The intricate balance between these two cell fates is maintained by precisely controlled symmetric and asymmetric cell divisions. Asymmetric division has a fundamental importance in maintaining tissue homeostasis and in the development of multi‐cellular organisms. For example, during development, asymmetric cell divisions are responsible for the formation of the body axis. Mechanistically, mitotic spindle dynamics determine the assembly and separation of chromosomes and regulate the orientation of cell division. Interestingly, symmetric and asymmetric cell division is not mutually exclusive and a range of factors are involved in such cell‐fate decisions, the measurement of which can provide efficient and reliable information on the regenerative potential of a cell. The balance between self‐renewal and differentiation in stem cells is controlled by various biophysical and biochemical cues. Although the role of biochemical factors in asymmetric stem cell division has been widely studied, the effect of biophysical cues in stem‐cell self‐renewal is not comprehensively understood. Herein, we review the biological relevance of stem‐cell asymmetric division to regenerative medicine and discuss the influences of various intrinsic and extrinsic biophysical cues in stem‐cell self‐renewal. This review particularly aims to inform the clinical translation of efforts to control the self‐renewal ability of stem cells through the tuning of various biophysical cues.     

Mesenchymal stem cells in the umbilical cord: phenotypic characterization, secretome and applications in central nervous system regenerative medicine

Mesenchymal Stem Cells (MSCs), have been defined and characterized by: 1) their ability to adhere to plastic culture flasks; 2) the positive expression of CD105, CD73, CD90 membrane antigens, and the lack of expression of others (e.g CD45 and CD34) and 3) the ability of differentiation under adequate conditions along the osteogenic, chondrogenic and adipogenic lineages. In recent years cells with these characteristics have been isolated from the Wharton Jelly (WJ) of the Umbilical Cord (UC). Similarly to bone marrow MSCs they have shown multilineage differentiation potential and to be able to provide trophic support to neighboring cells. According to the literature, there are two main populations of cells with a mesenchymal character within the human UC: Wharton's Jelly Mesenchymal Stem Cells (WJ-MSCs) and Human Umbilical Cord Perivascular Cells (HUCPVCs). In the present work our aim is to make a comprehensive review on MSCs populations of the WJ and how these cell populations may be used for future applications in CNS regenerative medicine. Following a brief insight on the general characteristics of MSC like cells, we will discuss the possible sources of stem cells within the WJ and the cord itself (apart UC blood), as well as their phenotypic character. As it has already been shown that these cells hold a strong trophic support to neighbouring cell populations, we will then focus on their secretome, namely which molecules have already been identified within it and their role in phenomena such as immunomodulation. The possible applications of these cells populations to CNS regenerative medicine will be addressed by critically reviewing the work that has been performed so far in this field. Finally, a brief insight will be made on what in the authors' opinion are the major challenges in the field for the future application of these cell populations in CNS regenerative medicine.     

Umbilical cord blood: a unique source of pluripotent stem cells for regenerative medicine

It is estimated that almost 1 in 3 individuals in the United States might benefit from regenerative medicine therapy. Unfortunately, embryonic stem (ES) cell therapies are currently limited by ethical, political, biological and regulatory hurdles. Thus, for the foreseeable future, the march of regenerative medicine to the clinic will depend upon the development of non-ES cell therapies. Current sources of non-ES cells easily available in large numbers can be found in the bone marrow, adipose tissue and umbilical cord blood. Each of these types of stem cells has already begun to be utilized to treat a variety of diseases. This review will show that cord blood (CB) contains multiple populations of ES-like and other pluripotential stem cells, capable of giving rise to hematopoietic, epithelial, endothelial, and neural tissues both in vitro and in vivo. Cumulatively, the identification and isolation of these populations of pluripotent stem cells within cord blood represents a scientific breakthrough that could potentially impact every field of medicine, via their use in regenerative medicine. Thus, CB stem cells are amenable to treatment of a wide variety of diseases including cardiovascular, hepatic, ophthalmic, orthopaedic, neurological and endocrine diseases.     

Prospects for stem cell therapeutics: myths and medicines

With common scientific themes and experimental strategies, stem cell biology is evolving into a recognizable discipline. Its clinical arm, regenerative medicine, is also gaining momentum-invigorated by the potential of stem cells to provide treatments for a host of medical conditions that are poorly served by drug therapy. But are the expectations for stem cell therapies realistic or overstated? In the past year, neurons, insulin-producing cells, and hematopoietic stem cells have been generated from embryonic stem cells or cultivated from somatic tissues of the adult. These cells have yielded modest and preliminary hints of functional reconstitution in animal models. Although encouraging, significant hurdles remain before the promise of stem cells will be realized in the clinic.     

In vitro recapitulation of neural development using embryonic stem cells: from neurogenesis to histogenesis

Embryonic stem (ES) cells have been successfully used over the past decade to generate specific types of neuronal cells. In addition to its value for regenerative medicine, ES cell culture also provides versatile experimental systems for analyzing early neural development. These systems are complimentary to conventional animal models, particularly because they allow unique constructive (synthetic) approaches, for example, step-wise addition of components. Here we review the ability of ES cells to generate not only specific neuronal populations but also functional neural tissues by recapitulating microenvironments in early mammalian development. In particular, we focus on cerebellar neurogenesis from mouse ES cells, and explain the basic ideas for positional information and self-formation of polarized neuroepithelium. Basic research on developmental signals has fundamentally contributed to substantial progress in stem cell technology. We also discuss how in vitro model systems using ES cells can shed new light on the mechanistic understanding of organogenesis, taking an example of recent progress in self-organizing histogenesis.     

Increased stem cell proliferation in the spinal cord of adult amyotrophic lateral sclerosis transgenic mice

Harnessing the regenerative potential of the central nervous system to repopulate depleted cellular populations from endogenous stem cells would be a novel approach for the treatment of neurological diseases resulting from cell death. Consequently, understanding if and how the central nervous system is capable of such regeneration would determine if such an approach is feasible. In this report, we provide evidence of widespread regenerative response in the spinal cord of amyotrophic lateral sclerosis transgenic mice. However, this regenerative response appears to be largely unproductive. We demonstrate that there is significantly increased gliogenesis, but an absence of convincing neurogenesis. The fact that the neurodegenerative process stimulates a regenerative response suggests that the adult spinal cord has at least limited ability for regeneration. Further studies will determine if this endogenous regenerative process can be enhanced and directed so as to slow or even reverse the natural progression of this devastating disease.