Therapeutic applications of mesenchymal/medicinal stem/signaling cells preconditioned with external factors: Are there more efficient approaches to utilize their regenerative potential?

Mesenchymal/medicinal stem/signaling cells (MSCs) have emerged as a promising treatment option for various disorders. However, the donor's age, advanced stage of disease, and prolonged in vitro expansion often diminish the innate regenerative potential of MSCs. Besides that, the absence of MSCs' comprehensive "pre-admission testing" can result in the injection of cells with reduced viability and function, which may negatively affect the overall outcome of MSC-based therapies. It is, therefore, essential to develop effective strategies to improve the impaired biological performance of MSCs. This review focuses on the comprehensive characterization of various methods of external MSCs stimulation (hypoxia, heat shock, caloric restriction, acidosis, 3D culture, and application of extracellular matrix) that augment their medicinal potential. To emphasize the significance of MSCs priming, we summarize the effects of individual and combined preconditioning approaches, highlighting their impact on MSCs' response to either physiological or pathological conditions. We further investigate the synergic action of exogenous factors to maximize MSCs' therapeutic potential. Not to omit the field of tissue engineering, the application of pretreated MSCs seeded on scaffolds is discussed as well.

The Neglected Uterine NK Cells/Hamperl Cells/Endometrial Stromal Granular Cell, or K Cells: A Narrative Review from History through Histology and to Medical Education.

Reproductive immunology is at the forefront of research interests, aiming to better understand the mechanisms of immune regulation during gestation. The relationship between the immune system and the implanting embryo is profound because the embryo is semi-allogenic but not targeted by the maternal immune system, as expected in graft-versus-host reactions. The most prominent cell population at the maternal-fetal interface is the population of uterine natural killer (uNK) cells. Uterine NK cells are two-faced immunologically active cells, bearing comparison with Janus, the ancient Roman god of beginnings and endings. Their first face can be seen as natural killer cells, namely lymphocytes, which are critical for host defense against viruses and tumors. Even though uNK cells contain cytolytic molecules, their cytotoxic effect is not applied to classical target cells in vivo, playing a permissive rather than a defensive role. Their second face is crucial in maintaining physiological gestation-uNK cells show critical immunomodulatory functions with the potential to control embryo implantation and trophoblast invasion, regulate placental vascular remodeling, and promote embryonic/fetal growth. Therefore, we believe that their current designation "natural killer cells" (the first "cytotoxic" Janus's face) is misleading and inappropriate, considering their principal function is supporting and maintaining pregnancy. In this narrative review, we will focus on three lesser-known areas of knowledge about uNK cells. First, from the point of view of histology, we will comprehensively map the history of the discovery of these cells, as well as the current histological possibilities of their identification within the endometrium. To be brief, the discovery of uNK cells is generally attributed to Herwig Hamperl, one of the most influential and prominent representatives of German pathology in the 20th century, and his co-worker, Gisela Hellweg. Secondly, we will discuss the interesting aspect of terminology, since uNK cells are probably one of the human cells with the highest number of synonymous names, leading to significant discrepancies in their descriptions in scientific literature. From the first description of this cell type, they were referred to as endometrial granulocytes, granular endometrial stromal cells, or large granular lymphocytes until the end of the 1980s and the beginning of the 1990s of the last century, when the first publications appeared where the name "uterine NK cells" was used. The third area of present review is medical teaching of histology and clinical embryology. We can confirm that uNK cells are, in most textbooks, overlooked and almost forgotten cells despite their enormous importance. In the present narrative review, we summarize the lesser-known historical and terminological facts about uNK cells. We can state that within the textbooks of histology and embryology, this important cell population is still "overlooked and neglected" and is not given the same importance as in fields of clinical research and clinical practice.

Stem Cells and Their Derivatives: An Implication for the Regeneration of Nonunion Fractures.

Despite advances in biomedical research, fracture nonunion rates have remained stable throughout the years. Long-bone fractures have a high likelihood of nonunion, but the specific biological pathways involved in this severe consequence are unknown. Fractures often heal in an organized sequence, including the production of a hematoma and an early stage of inflammation, the development of a soft callus and hard callus, and eventually the stage of bone remodeling. Deficient healing can result in a persistent bone defect with instability, discomfort, and loss of function. In the treatment of nonunions, mesenchymal stem cells (MSCs) prove to be a promising and safe alternative to the standard therapeutic strategies. Moreover, novel scaffolds are being created in order to use a synergistic biomimetic technique to rapidly generate bone tissue. MSCs respond to acellular biomimetic matrices by regenerating bone. Extracellular vesicles (EVs) derived from MSCs have recently gained interest in the field of musculoskeletal regeneration. Although many of these techniques and technologies are still in the preclinical stage and have not yet been approved for use in humans, novel approaches to accelerate bone healing via MSCs and/or MSC derivatives have the potential to reduce the physical, economic, and social burdens associated with nonhealing fractures and bone defects. In this review, we focus on providing an up-to-date summary of recent scientific studies dealing with the treatment of nonunion fractures in clinical and preclinical settings employing MSC-based therapeutic techniques.

Cell-Based and Selected Cell-Free Therapies for Myocardial Infarction: How Do They Compare to the Current Treatment Options?

Because of cardiomyocyte death or dysfunction frequently caused by myocardial infarction (MI), heart failure is a leading cause of morbidity and mortality in modern society. Paradoxically, only limited and non-curative therapies for heart failure or MI are currently available. As a result, over the past two decades research has focused on developing cell-based approaches promoting the regeneration of infarcted tissue. Cell-based therapies for myocardial regeneration include powerful candidates, such as multipotent stem cells (mesenchymal stem cells (MSCs), bone-marrow-derived stem cells, endothelial progenitor cells, and hematopoietic stem cells) and induced pluripotent stem cells (iPSCs). These possess unique properties, such as potency to differentiate into desired cell types, proliferation capacity, and patient specificity. Preclinical and clinical studies have demonstrated modest improvement in the myocardial regeneration and reduced infarcted areas upon transplantation of pluripotent or multipotent stem cells. Another cell population that need to be considered as a potential source for cardiac regeneration are telocytes found in different organs, including the heart. Their therapeutic effect has been studied in various heart pathologies, such as MI, arrhythmias, or atrial amyloidosis. The most recent cell-free therapeutic tool relies on the cardioprotective effect of complex cargo carried by small membrane-bound vesicles-exosomes-released from stem cells via exocytosis. The MSC/iPSC-derived exosomes could be considered a novel exosome-based therapy for cardiovascular diseases thanks to their unique content. There are also other cell-free approaches, e.g., gene therapy, or acellular cardiac patches. Therefore, our review provides the most recent insights into the novel strategies for myocardial repair based on the regenerative potential of different cell types and cell-free approaches.

Implication of Mesenchymal Stem Cells and Their Derivates for Osteochondral Regeneration.

Healing of articular cartilage defects presents a challenging issue, due to its regenerative shortcomings. Lacking vascularity and innervation of cartilage and low proliferative potential of chondrocytes are the main reasons for the limited healing potential of articular cartilage. Traditional reparative approaches are limited in their efficiency, hence there is a demand for novel reparative treatments. Mesenchymal stromal cells, preferred for clinical uses, can be readily derived from various sources and have been proven to have a therapeutic effect on cartilage and subchondral bone. Therefore, mesenchymal stromal cells, their derivates, and scaffolds have been utilized in research targeting osteochondral regeneration. The present review aims to comprehensively outline and discuss literature considering this topic published within last 5 years.

Telocytes in the Female Reproductive System: Up-to-Date Knowledge, Challenges and Possible Clinical Applications.

From their initial description in 2005 to this day, telocytes (TCs) have been described in the ovary, uterine tubes, uterus, vagina, mammary gland, and placenta. Their morphological features, immunophenotype, physiological functions, and roles in disease have been thoroughly documented in both animal models and human subjects. TCs, with their extremely long cytoplasmic processes called telopodes, play a pivotal role in the morphological and functional interconnection of all the components of the interstitial compartment, but also with constituents of the parenchyma. Although there is no specific immunohistochemical marker for their identification, the most cited are CD 117, CD 34, platelet-derived growth factor receptor (PDGFR), vimentin, and specific markers typical for the female reproductive system (FRS)-estrogen and progesterone receptors (ER and PR). This immunophenotype provides important clues to their physiological roles. Their main functions include the regulation of hormone-dependent processes, intercellular signaling, immune surveillance, microenvironmental maintenance, and the nursing of stem cells. In a situation where TCs are functionally or morphologically decimated, many disease entities may develop, including premature ovarian failure, endometriosis, ectopic pregnancy, infertility, preeclampsia, or even breast cancer. The common denominator of many of these conditions is that their etiopathogenesis is either partially known or completely obscure. Even though the exact role of TCs in these conditions is yet to be revealed, multiple lines of research indicate that their future clinical application may enrich diagnostic-therapeutic strategies of countless conditions. TCs are also heavily debated in terms of their possible use in regenerative medicine and tissue engineering. Some of the concepts related to TC research are strongly substantiated by experimental data, while others are highly speculative. Only future research endeavors will clearly distinguish dead-end lines of research from genuine contributions to the field.

Rheumatoid arthritis: From synovium biology to cell-based therapy.

Rheumatoid arthritis (RA) is a chronic inflammatory disease that affects the synovial joints and, if not treated properly, can lead to multiple progressive articular and extra-articular damage. Its pathogenesis is primarily associated with an inadequate immune response and dysregulated cytokine production. However, RA is also linked to disruption in oxygen metabolism, impaired redox signaling, acidosis and aberrant intercellular communication. Even though treatment modalities have made RA a manageable disease, a significant number of patients still do not respond satisfactorily or suffer considerably from the adverse events of conventional therapy. In recent years, cell-based strategies, especially the administration of the mesenchymal/medicinal stem/signaling cells (MSCs), have been proposed as a novel and very promising therapeutic approach. RA patients may benefit from the potent anti-inflammatory and immunomodulatory properties and tissue-repair potential of MSCs. Furthermore, the satisfactory safety profile of MSC therapy has been already demonstrated in several clinical studies. This review summarizes current understanding of the pathomechanism behind RA at the molecular and cellular level and focuses on MSC-based clinical research and applications of MSCs for RA treatment.

Stem Cells and Their Derivatives-Implications for Alveolar Bone Regeneration: A Comprehensive Review.

Oral and craniofacial bone defects caused by congenital disease or trauma are widespread. In the case of severe alveolar bone defect, autologous bone grafting has been considered a "gold standard"; however, the procedure has several disadvantages, including limited supply, resorption, donor site morbidity, deformity, infection, and bone graft rejection. In the last few decades, bone tissue engineering combined with stem cell-based therapy may represent a possible alternative to current bone augmentation techniques. The number of studies investigating different cell-based bone tissue engineering methods to reconstruct alveolar bone damage is rapidly rising. As an interdisciplinary field, bone tissue engineering combines the use of osteogenic cells (stem cells/progenitor cells), bioactive molecules, and biocompatible scaffolds, whereas stem cells play a pivotal role. Therefore, our work highlights the osteogenic potential of various dental tissue-derived stem cells and induced pluripotent stem cells (iPSCs), the progress in differentiation techniques of iPSCs into osteoprogenitor cells, and the efforts that have been made to fabricate the most suitable and biocompatible scaffold material with osteoinductive properties for successful bone graft generation. Moreover, we discuss the application of stem cell-derived exosomes as a compelling new form of "stem-cell free" therapy.

Cardiac Telocytes 16 Years on-What Have We Learned So Far, and How Close Are We to Routine Application of the Knowledge in Cardiovascular Regenerative Medicine?

The regeneration of a diseased heart is one of the principal challenges of modern cardiovascular medicine. There has been ongoing research on stem-cell-based therapeutic approaches. A cell population called telocytes (TCs) described only 16 years ago largely contributed to the research area of cardiovascular regeneration. TCs are cells with small bodies and extremely long cytoplasmic projections called telopodes, described in all layers of the heart wall. Their functions include cell-to-cell signaling, stem-cell nursing, mechanical support, and immunoregulation, to name but a few. The functional derangement or quantitative loss of TCs has been implicated in the pathogenesis of myocardial infarction, heart failure, arrhythmias, and many other conditions. The exact pathomechanisms are still unknown, but the loss of regulative, integrative, and nursing functions of TCs may provide important clues. Therefore, a viable avenue in the future modern management of these conditions is TC-based cell therapy. TCs have been previously transplanted into a mouse model of myocardial infarction with promising results. Tandem transplantation with stem cells may provide additional benefit; however, many underresearched areas need to be addressed in future research before routine application of TC-based cell therapy in human subjects. These include the standardization of protocols for isolation, cultivation, and transplantation, quantitative optimization of TC transplants, cost-effectivity analysis, and many others.

Generation of Pancreatic ß-cells From iPSCs and their Potential for Type 1 Diabetes Mellitus Replacement Therapy and Modelling.

Diabetes type 1 (T1D) is a common autoimmune disease characterized by permanent destruction of the insulin-secreting ß-cells in pancreatic islets, resulting in a deficiency of the glucose-lowering hormone insulin and persisting high blood glucose levels. Insulin has to be replaced by regular subcutaneous injections, and blood glucose level must be monitored due to the risk of hyperglycemia. Recently, transplantation of new pancreatic ß-cells into T1D patients has come to be considered one of the most potentially effective treatments for this disease. Therefore, much effort has focused on understanding the regulation of ß-cells. Induced pluripotent stem cells (iPSCs) represent a valuable source for T1D modelling and cell replacement therapy because of their ability to differentiate into all cell types in vitro. Recent advances in stem cell-based therapy and gene-editing tools have enabled the generation of functionally adult pancreatic ß-cells derived from iPSCs. Although animal and human pancreatic development and ß-cell physiology have significant differences, animal models represent an important tool in evaluating the therapeutic potential of iPSC-derived ß-cells on type 1 diabetes treatment. This review outlines the recent progress in iPSC-derived ß-cell differentiation methods, disease modelling, and future perspectives.

Recent Progress in the Regeneration of Spinal Cord Injuries by Induced Pluripotent Stem Cells.

Regeneration of injuries occurring in the central nervous system, particularly spinal cord injuries (SCIs), is extremely difficult. The complex pathological events following a SCI often restrict regeneration of nervous tissue at the injury site and frequently lead to irreversible loss of motor and sensory function. Neural stem/progenitor cells (NSCs/NPCs) possess neuroregenerative and neuroprotective features, and transplantation of such cells into the site of damaged tissue is a promising stem cell-based therapy for SCI. However, NSC/NPCs have mostly been induced from embryonic stem cells or fetal tissue, leading to ethical concerns. The pioneering work of Yamanaka and colleagues gave rise to the technology to induce pluripotent stem cells (iPSCs) from somatic cells, overcoming these ethical issues. The advent of iPSCs technology has meant significant progress in the therapy of neurodegenerative disease and nerve tissue damage. A number of published studies have described the successful differentiation of NSCs/NPCs from iPSCs and their subsequent engraftment into SCI animal models, followed by functional recovery of injury. The aim of this present review is to summarize various iPSC- NPCs differentiation methods, SCI modelling, and the current status of possible iPSC- NPCs- based therapy of SCI.

Regenerative Medicine in Orthopaedics and Trauma: Challenges, Regulation and Ethical Issues.

The ability of stem cells to self-renew and differentiate into cell types of different lineages forms the basis of regenerative medicine, which focuses on repairing or regenerating damaged or diseased tissues. This has a huge potential to revolutionize medicine. It is anticipated that in future, stem cell therapy will be able to restore function in all major organs. Intensive research has been on-going to bring stem cell therapy from bench to bedside as it holds promise of widespread applications in different areas of medicine. This is also applicable to orthopaedics, where stem cell transplantation could benefit complications like spinal cord injury, critical bone defects, cartilage repair or degenerative disc disorders. Stem cell therapy has a potential to change the field of orthopaedics from surgical replacements and reconstructions to a field of regeneration and prevention. This article summarizes advances in stem cell applications in orthopaedics as well as discussing regulation and ethical issues related to the use of stem cells.

iPS cell technologies and their prospect for bone regeneration and disease modeling: A mini review.

Bone disorders are a group of varied acute and chronic traumatic, degenerative, malignant or congenital conditions affecting the musculoskeletal system. They are prevalent in society and, with an ageing population, the incidence and impact on the population's health is growing. Severe persisting pain and limited mobility are the major symptoms of the disorder that impair the quality of life in affected patients. Current therapies only partially treat the disorders, offering management of symptoms, or temporary replacement with inert materials. However, during the last few years, the options for the treatment of bone disorders have greatly expanded, thanks to the advent of regenerative medicine. Skeletal cell-based regeneration medicine offers promising reparative therapies for patients. Mesenchymal stem (stromal) cells from different tissues have been gradually translated into clinical practice; however, there are a number of limitations. The introduction of reprogramming methods and the subsequent production of induced pluripotent stem cells provides a possibility to create human-specific models of bone disorders. Furthermore, human-induced pluripotent stem cell-based autologous transplantation is considered to be future breakthrough in the field of regenerative medicine. The main goal of the present paper is to review recent applications of induced pluripotent stem cells in bone disease modeling and to discuss possible future therapy options. The present article contributes to the dissemination of scientific and pre-clinical results between physicians, mainly orthopedist and thus supports the translation to clinical practice.

Stem cell regenerative potential for plastic and reconstructive surgery.

Stem cells represent heterogeneous population of undifferentiated cells with unique characteristics of long term self renewal and plasticity. Moreover, they are capable of active migration to diseased tissues, secretion of different bioactive molecules, and they have immunosuppressive potential as well. They occur in all tissues through life and are involved in process of embryogenesis and regeneration. During last decades stem cells attracted significant attention in each field of medicine, including plastic and reconstructive surgery. The main goal of the present review article is to present and discuss the potential of stem cells and to provide information about their safe utilization in chronic wounds and fistulae healing, scar management, breast reconstruction, as well as in bone, tendon and peripheral nerve regeneration.

Comparative analysis of mesenchymal stromal cells from different tissue sources in respect to articular cartilage tissue engineering.

The main goal of this study was a comparison of biological properties of mesenchymal stromal cells (MSCs) obtained from bone marrow, adipose tissue and umbilical cord with respect to articular cartilage regeneration. MSCs were isolated and expanded in vitro up to the third passage. The kinetics of proliferation was analyzed by cell analyzer CEDEX XS and expression of selected markers was assessed by flow cytometry. The morphology was analyzed by inverted microscope and TEM. Pellet culture system and chondrogenic medium containing TGF-ß1 was used to induce chondrogenic differentiation. Chondrogenesis was analyzed by real-time PCR; the expression of collagen type I and type II was compared. MSCs from all sources showed similar kinetics of proliferation and shared expression of CD73, CD90 and CD105; and were negative for CD14, CD20, CD34 and CD45. Observation under inverted microscope and TEM showed similar morphology of all analyzed MSCs. Cells from all sources underwent chondrogenic differentiation - they expressed collagen type II and acid mucopolysaccharides typical for hyaline cartilage. On the basis of obtained results it should be emphasized that MSCs from bone marrow, adipose tissue and umbilical cord share biological properties. They possess the chondrogenic potential and may be utilized in cartilage tissue engineering.

Recent approaches and challenges in iPSCs: modeling and cell-based therapy of Alzheimer's disease.

The lack of effective therapies for different neurodegenerative disorders has placed huge burdens on society. To overcome the restricted capacity of the central nervous system for regeneration, the promising alternative would be to use stem cells for more effective treatment of chronic degenerative and inflammatory neurological conditions and also of acute neuronal damage and from injuries or cerebrovascular diseases. The generation of induced pluripotent stem cells from somatic cells by the ectopic expression of specific transcription factors has provided the regenerative medicine field with a new tool for investigating and treating neurodegenerative diseases, including Alzheimer's disease (AD). This technology provides an alternative to traditional approaches, such as nuclear transfer and somatic cell fusion using embryonic stem cells. However, due to a problem in standardization of certain reprogramming techniques and systems research, the induced pluripotent stem cell-based technology is still in its infancy. The present paper is aimed at a brief review of the current status in modeling and cell-based therapies for AD.

Recent advances in iPSC technologies involving cardiovascular and neurodegenerative disease modeling.

Cardiovascular and neurodegenerative diseases are the most common health threats in developed countries. Limited cell derivation and cell number in cardiac tissue makes it difficult to study the cardiovascular disease using the existing cardiac cell model. Regarding the neurodegenerative disorders, the most potential sources of cell therapeutics such as fetal-derived primary neurons and human embryonic stem cells (ESCs) are associated with ethical or technical limitations. The successful derivation of human-induced pluripotent stem cells (iPSCs) by de-differentiation of somatic cells offers significant potential to overcome hurdles in the field of the replacement therapy. Human iPSCs are functionally similar to human embryonic stem cells, and can be derived autologously without the ethical challenges associated with human ESCs. The iPSCs can, in turn, be differentiated into all cell types including neurons, cardiac cells, blood and liver cells, etc. Recently, target tissues derived from human iPSCs such as cardiomyocytes (CMs) or neurons have been used for new disease modeling and regenerative medicine therapies. Diseases models could be advantageous in the development of personalized medicine of various pathological conditions. This paper reviews efforts aimed at both the practical development of iPSCs, differentiation to neural/cardiac lineages, and the further use of these iPSCs-derived cells for disease modeling, as well as drug toxicity testing.

Perspectives of induced pluripotent stem cells for cardiovascular system regeneration.

Induced pluripotent stem cells (iPSCs) hold great promise for basic research and regenerative medicine. They offer the same advantages as embryonic stem cells (ESCs) and moreover new perspectives for personalized medicine. iPSCs can be generated from adult somatic tissues by over-expression of a few defined transcription factors, including Oct4, Sox2, Klf4, and c-myc. For regenerative medicine in particular, the technology provides great hope for patients with incurable diseases or potentially fatal disorders such as heart failure. The endogenous regenerative potentials of adult hearts are extremely limited and insufficient to compensate for myocardial loss occurring after myocardial infarction. Recent discoveries have demonstrated that iPSCs have the potential to significantly advance future cardiovascular regenerative therapies. Moreover, iPSCs can be generated from somatic cells of patients with genetic basis for their disease. This human iPSC derivates offer tremendous potential for new disease models. This paper reviews current applications of iPSCs in cardiovascular regenerative medicine and discusses progress in modeling cardiovascular diseases using iPSCs-derived cardiac cells.

Induced pluripotent stem cells and their implication for regenerative medicine.

In 2006 Yamanaka's group showed that stem cells with properties similar to embryonic stem cells could be generated from mouse fibroblasts by introducing four genes. These cells were termed induced pluripotent stem cells (iPSCs). Because iPSCs avoid many of ethical concerns associated with the use of embryonic material, they have great potential in cell-based regenerative medicine. They are suitable also for other various purposes, including disease modelling, personalized cell therapy, drug or toxicity screening and basic research. Moreover, in the future, there might become possible to generate organs for human transplantation. Despite these progresses, several studies have raised the concern for genetic and epigenetic abnormalities of iPSCs that could contribute to immunogenicity of some cells differentiated from iPSCs. Recent methodological improvements are increasing the ease and efficacy of reprogramming, and reducing the genomic modification. However, to minimize or eliminate genetic alternations in the derived iPSC line creation, factor-free human iPSCs are necessary. In this review we discuss recent possibilities of using iPSCs for clinical applications and new advances in field of their reprogramming methods. The main goal of present article was to review the current knowledge about iPSCs and to discuss their potential for regenerative medicine.