Regenerative Medicine: Past and Present

Tissue engineering has tremendous potential for the treatment of a wide range of medical conditions. In combination with this, the developments in the fields of embryonic stem cells (ES) and adult stem cells are leading to a whole new generation of therapies. However, for any treatment to be successful, a number of key issues must be addressed; in particular the choice of cell and scaffold types used and the methods required to overcome immune rejection of any transplant. The 1-day EuroSciCon meeting, at the MI Centre in London, UK, on November 17, 2006, covered the recent advances in the fields of tissue engineering and regenerative medicine. Entitled ‘Tissue Engineering Today, Not Tomorrow’, the meeting drew presenters from throughout Europe and as far afield as Japan. It focused on the key areas of development in stem cell differentiation, scaffold development and immune modulation, each with a clinical setting or scenario in mind. The conference was opened by Dame Julia Polak (Imperial college, London, UK), who gave an interesting overview of the processes involved in developing tissue engineering from the laboratory into the clinic. Specific examples were given for the importance of biochemical and physical microenvironments on ES cell differentiation and how gene overexpression of osterix can induce bone formation. The use of bioglass for bone regeneration and collagen–polyglycolic acid composite scaffolds for bladder tissue engineering were also given. In conclusion, Dame Polak discussed how the fields of stem cells, tissue engineering, gene therapy, nanotechnology and regenerative medicine are all converging for clinical application to save lives. This gave a good introduction to the themes of the remaining talks.

From Tissue Engineering to Organ Engineering

Cell cultures and stem cell studies have revolutionized the field of biotechnology and regenerative medicine by opening various medicine sectors that were once closed due to lack of information and technology. The potent ability of stem cells has proven to be really significant in the field of medical research for treating degenerative diseases and disorders, thus developing novel therapeutics. Induced pluripotent stem cells are created by reprogramming adult cells to behave like an embryonic-like pluripotent state cell. The reprogramming of cells is done by introducing specific combinations or sets of genes into the cells using viral vectors. This in turn resets the genetic program and reprograms the cells in a way that the cells can differentiate into any type of cell in the human body. Induced pluripotent stem cells have the ability to self-renew and differentiate into all cell types, also including gametes. This type of stem cell can be cultured in lab, and have been proven to renew themselves indefinitely. These cells can be reprogrammed from cells obtained from any healthy person or patient. Stem cells are considered as a valuable resource in the field of medicine but pluripotent stem cells in nature are embryonic stem cells, so their study and isolation posed multiple ethical barriers to be overcome, and inducing pluripotent nature in adult cells has proven to be a solution to overcome those barriers. Induced pluripotent stem cells are considered to be the key for regenerative medicine as their potent ability can be manipulated to replace any diseased or damaged tissues. The authors have discussed the current status of induced pluripotent stem cells and their potential future prospects in this paper. There are also a lot of ethical and legal challenges and opportunities that must be overcome to fully exploit the potential of stem cells. Overall, the aim of this paper is to shed light on the significance of the study and development of stem cells and its research in the field of medicine, and its potential to formulate newer therapies and therapeutics. The authors tend to provide an overview of stem cell research and hope to inspire further research and development in this area to generate significant results in novel and effective stem-cell based therapies.

Patients suffering from diseased and injured organs may be treated with transplanted organs. However, there is a severe shortage of donor organs which is worsening yearly due to the aging population. Scientists in the field of tissue engineering apply the principles of cell transplantation, materials science, and bioengineering to construct biological substitutes that will restore and maintain normal function in diseased and injured tissues. Both therapeutic cloning (nucleus from a donor cell is transferred into an enucleated oocyte), and parthenogenesis (oocyte is activated and stimulated to divide), permit extraction of pluripotent embryonic stem cells, and offer a potentially limitless source of cells for tissue engineering applications. The stem cell field is also advancing rapidly, opening new options for therapy. The present article reviews recent progress in tissue engineering and describes applications of these new technologies that may offer novel therapies for patients with end-stage organ failure.

Stem cells are classified by their tissue source. Embryonic stem cells that derived from inner cell mass of blastocyst stage embryos are highly proliferative in their undifferentiated state. A multipotent type of mesenchymal stem cells isolated from different type of tissues such as bone marrow, fat tissue etc. The dynamics of embryonic and adult stem cell cycles are profoundly dissimilar than the culture of stem cells. After improving the culture conditions and differentiation potentials, differentiated stem cells are the first cells to be preferred in modern regenerative medicine and tissue engineering. This review article focuses on the cell-based therapy on orthopedic problems. We explore the challenges associated with bone repair and regeneration using embryonic or mesenchymal stem cells that use undifferentiated or/and differentiated condition. This paper also discusses optimizing the best cell type, differentiation condition and using them on bone tissue engineering in future investigation.

Development of cloned embryos from porcine neural stem cells and amniotic fluid-derived stem cells

Stem cell-derived extracellular vesicles (EVs) have shown great promise in the field of regenerative medicine and tissue engineering. Recently, human bone marrow-derived mesenchymal stem cell (BMSC)-derived EVs have been considered for bone tissue engineering applications. In this study, we evaluated the osteogenic capability of placental stem cell (PSC)-derived EVs and compared them to the well-characterized BMSC-derived EVs. EVs were extracted from three designated time points (0, 7, and 21 days) after osteogenic differentiation. The results showed that the PSC-derived EVs had much higher protein and lipid concentrations than EVs derived from BMSCs. The extracted EVs were characterized by observing their morphology and size distribution before utilizing next-generation sequencing to determine their microRNA (miRNA) profiles. A total of 306 miRNAs within the EVs were identified, of which 64 were significantly expressed in PSC-derived EVs that related to osteogenic differentiation. In vitro osteogenic differentiation study indicated the late-stage (21-day extracted)-derived EVs higher osteogenic enhancing capability when compared with the early stage-derived EVs. We demonstrated that EVs derived from PSCs could be a new source of EVs for bone tissue engineering applications.

Embryonic stem cells are pluripotent and capable of unlimited self-renewal. Elucidation of the underlying molecular mechanism may contribute to the advancement of cell-based regenerative medicine. In the present work, we performed a large scale analysis of the phosphoproteome in mouse embryonic stem (mES) cells. Using multiplex strategies, we detected 4581 proteins and 3970 high confidence distinct phosphosites in 1642 phosphoproteins. Notably, 22 prominent phosphorylated stem cell marker proteins with 39 novel phosphosites were identified for the first time by mass spectrometry, including phosphorylation sites in NANOG (Ser-65) and RE1 silencing transcription factor (Ser-950 and Thr-953). Quantitative profiles of NANOG peptides obtained during the differentiation of mES cells revealed that the abundance of phosphopeptides and non-phosphopeptides decreased with different trends. To our knowledge, this study presents the largest global characterization of phosphorylation in mES cells. Compared with a study of ultimately differentiated tissue cells, a bioinformatics analysis of the phosphorylation data set revealed a consistent phosphorylation motif in human and mouse ES cells. Moreover, investigations into phosphorylation conservation suggested that phosphoproteins were more conserved in the undifferentiated ES cell state than in the ultimately differentiated tissue cell state. However, the opposite conclusion was drawn from this conservation comparison with phosphosites. Overall, this work provides an overview of phosphorylation in mES cells and is a valuable resource for the future understanding of basic biology in mES cells.

In the field of regenerative medicine, stem cell therapeutic development has emerged as a key technological area. Since the establishment and characterization of human embryonic stem cell lines by James Thomson in 1998, stem cell research has expanded rapidly, accelerating industrialization through the strategic protection of intellectual property (IP) rights. As technological specialization and clinical trial expansion have progressed-particularly since 2015-the feasibility of commercialization has increased. However, IP analyses in the stem cell field have largely been limited to fragmented patent trend studies. This study analyzed the characteristics and limitations of stem cell-based IP and examined the correlations among scientific publications, patent activity, and clinical trials by stem cell type from 2000 to 2020. The findings revealed significant differences among stem cell categories. In particular, adult stem cells (ASCs) demonstrated strong positive correlations between patent filings and SCI-indexed publications (R2=0.947), as well as between patent activity and clinical trials (R2=0.945), suggesting a high level of technological maturity and translational potential. In contrast, embryonic and induced pluripotent stem cells showed relatively weaker correlations. The results indicate that ASC-based IP is closely associated with clinical development and commercialization potential. This study provides strategic insights into the potential for proactive commercialization based on the importance of patents in the stem cell therapeutic industry.

The effects of microgravity on stem cells and the new insights it brings to tissue engineering and regenerative medicine

Pluripotent cells have the potential to differentiate into all of the cell types of an animal. This unique cell state is governed by an interconnected network of transcription factors. Among these, Oct4 plays an essential role both in the development of pluripotent cells in the embryo and in the self-renewal of its in vitro counterpart, embryonic stem (ES) cells. Furthermore, Oct4 is one of the four Yamanaka factors and its overexpression alone can generate induced pluripotent stem (iPS) cells. Recent reports underscore Oct4 as an essential regulator of opposing cell state transitions, such as pluripotency establishment and differentiation into embryonic germ lineages. Here we discuss these recent studies and the potential mechanisms underlying these contrasting functions of Oct4.

The idea of being able to replace, restore, or regenerate damaged or diseased tissues and organs in order to establish normal function in the human body has never been so prominent and possible than with the development of the field of regenerative medicine. Using material from the body or activating the body’s own repair mechanisms to prepare and grow or heal irreparable tissues or organs is now a real possibility, as demonstrated by research and clinical studies published over the last 10 years. Born from the collaboration of several biomedical disciplines and clinical approaches, regenerative medicine promises the real possibility of not only replacing pharmaceutical solutions to disease but also paves the road to a more autologous and holistic approach in clinical treatment of disease and disease control. Historically, the foundation of regenerative medicine was cemented with the successful transplantation of corneas, soft tissue, and bone in the early twentieth century. The first kidney transplantation in 1954 was followed by pancreas, liver, and heart transplants in the 1960s and success continued in the 1980s with heart– lung and living donor liver and lung transplants. Progressively, an increase in demand for tissues and organs and subsequent decrease in organ availability has left a need for new technology to meet the demand for suitable organs and organ donors as well as leading to an increase in the disgraceful enterprise of black market organs. Currently, tissueengineered skin used for burn survivors and diabetic ulcers, products derived from tissue engineering to induce bone growth and regeneration, as well as the autologous reintroduction of ex-vivo engineered bladder are a reality, once again establishing a firm foothold for the development of further and more advanced applications for regenerative medicine. The discovery of stem cells by the Russian histologist Alexander Maksimov in 1908, as part of his theory of hematopoiesis followed by Joseph Altman and Gopal Das in the 1960s presenting evidence of constant stem cell activity in the brain and the demonstration of self-renewing cells found in the bone marrow of mice by James E. Till and Ernest A. McCulloch in 1963, established stem cell research and the development of stem cell therapy as a new and very promising and exciting discipline for regenerative medicine. Embryonic and adult stem cells are available from a variety of sources and hold variable differentiation potential, not to mention the myriad potential therapeutic applications, albeit associated with some ethical and political concerns. Mammalian stem cells can be sourced from either the embryo or the adult organism. Embryonic stem cells originate from the inner cell mass of blastocysts, whereas adult stem and progenitor cells can be found in various tissues repairing or replenishing adult tissue. Of specific interest and application in regenerative medicine are autologous adult stem cells accessible from bone marrow, adipose tissue, or blood. Contemporary stem cell therapy includes bone marrow transplants for the treatment of leukemia, whereas extensive current research is undertaken for the implementation of stem cell therapy for the treatment of cancer, spinal cord injuries, and Parkinson’s disease, as well as multiple sclerosis and muscle conditions including heart disease. The use of vascular grafts for heart bypass surgery and cardiovascular disease treatment have been researched extensively and are at the pre-clinical trial stage. Advances in therapeutic applications do not come without much debate and controversy surrounding risks associated with it. The risk that transplanted stem cells could form tumors and metastasize uncontrollably is but one of the concerns of stem cell therapy. Inducing forced expression of specific genes in order to derive pluripotent stem cells from non-pluripotent cells generate the so-called induced pluripotent stem cell (iPSC). However, significant risk is associated with reprogramming of adult cells to obtain iPSCs. Potentially, this risk could limit their use in patients. The use of viruses to genomically alter the cells may lead to the expression of cancer-causing oncogenes. Low-level laser therapy (LLLT) has been scientifically proven as a beneficial therapeutic modality for numerous diseases and diseased conditions. Using very specific laser and light-emitting diode irradiation parameters, specific cellular activities can be induced, namely, cellular proliferation and viability while stimulating mitochondrial activity, thereby increasing adenosine triphosphate (ATP) production, synthesis of DNA and RNA, and activating cellsignaling cascades including the production of reactive oxygen species (ROS), nitric oxide (NO) release, activating cytochrome c oxidase, and modifying intracellular organelle membrane activity, calcium flux, and expression of stress proteins. The molecular mechanism underlying these cellular activities is less well understood, and several research groups are conducting intensive research studies in an effort to elucidate the relation between these biological

Cell transplantation has come to the forefront of regenerative medicine alongside the discovery and application of stem cells in both research and clinical settings. There are several types of stem cells currently being used for pre-clinical regenerative therapies, each with unique characteristics, benefits and limitations. This brief review will focus on recent basic science advancements made with embryonic stem cells and induced pluripotent stem cells. Both embryonic stem cells and induced pluripotent stem cells provide platforms for new neurons to replace dead and/or dying cells following injury. Due to their capacity for reprogramming and differentiation into any neuronal type, research in preclinical rodent models has shown that embryonic stem cells and induced pluripotent stem cells can integrate, survive and form connections in the nervous system similar to de novo cells. Going forward however, there are some limitations to consider with the use of either stem cell type. Ethically, embryonic stem cells are not an ideal source of cells, genetically, induced pluripotent stem cells are not ideal in terms of personalized treatment for those with certain genetic diseases the latter of which may guide regenerative medicine away from personalized stem cell based therapies and into optimized stem cell banks. Nonetheless, the potential of these stem cells in central nervous system regenerative therapy is only beginning to be appreciated. For example, through genetic modification, stem cells serve as ideal platforms to reintroduce missing or downregulated molecules into the nervous system to further induce regenerative growth. In this review, we highlight the limitations of stem cell based therapies whilst discussing some of the means of overcoming these limitations.

It is a great pleasure to ring in the year 2012 with the launch of the American Journal of Stem Cells (www.ajsc.us). This new peer reviewed open access online journal aims to provide to the biomedical community cutting edge insight into the latest developments in the fast paced stem cell field. The format of the journal will facilitate rapid dissemination of research findings to the broadest audience. The topics are open to all adult and embryonic stem cells and everything in between. Due to the multidisciplinary nature of the stem cell field, it is expected that some manuscripts will bring for example computational or biophysical expertise into the fold. Stem cell research has blossomed in the past several decades and shows no signs of slowing down. The research has moved from early observations of stem cells being defined as functional entities to now including prospective isolation and purification of stem cells based on their immunophenotypic, molecular, metabolic, and biochemical make up. Additional new insights into stem cell heterogeneity and advances in study of single stem cells, as opposed to populations, promise to further advance purification and directed differentiation based on finding the right “recipe” of transcription factors and target genes. Such major advances will be critical for improving our understanding of the biological and pathological development of tissues and organs, as well as the mechanisms underlying self-renewal and tissue-specific regeneration, which will ultimately facilitate downstream therapeutic applications. The great potential for adult stem cells has already been realized in the clinic using stem cell enriched populations and new applications and optimizations are in progress. The initial excitement regarding embryonic stem cells and induced pluripotent stem cells is tempered only by the realization that many obstacles need to be carefully passed in order to develop a safe and effective product for clinical testing. The pace of discovery in this area has been remarkable and equally so the pace for overcoming technical limitations and improving safety suggests that these cells will eventually be ready for prime time. There is clearly no better time to publish in the stem cell field. All of the Editors-in-Chief and Editorial Board are enthusiastic about the ability of this journal to provide ongoing contributions to the field. The Editors are committed to advancing the discipline of stem cells and regenerative medicine and welcome your manuscripts covering all aspects of stem cell biology. The American Journal of Stem Cells is your resource and we are looking forward to receiving your best reviews and original articles.

Stem cell niche refers to the microenvironment where stem cells reside in living organisms. Several elements define the niche and regulate stem cell characteristics, such as stromal support cells, gap junctions, soluble factors, extracellular matrix proteins, blood vessels and neural inputs. In the last years, different studies demonstrated the presence of cKit+ cells in human and murine amniotic fluid, which have been defined as amniotic fluid stem (AFS) cells. Firstly, we characterized the murine cKit+ cells present both in the amniotic fluid and in the amnion. Secondly, to analyze the AFS cell microenvironment, we injected murine YFP+ embryonic stem cells (ESC) into the amniotic fluid of E13.5 wild type embryos. Four days after transplantation we found that YFP+ sorted cells maintained the expression of pluripotency markers and that ESC adherent to the amnion were more similar to original ESC in respect to those isolated from the amniotic fluid. Moreover, cytokines evaluation and oxygen concentration analysis revealed in this microenvironment the presence of factors that are considered key regulators in stem cell niches. This is the first indication that AFS cells reside in a microenvironment that possess specific characteristics able to maintain stemness of resident and exogenous stem cells.