Stem Cell Research: The Facts, the Myths and the Promises

Effectiveness of Topical Conditioned Medium of Stem Cells in Facial Skin Nonsurgical Resurfacing Modalities for Antiaging: Systematic Review and Meta-Analysis of Randomized Controlled Trials

Facial skin nonsurgical resurfacing modalities, including laser, chemical peeling, and microneedling, have become common due to increasing public concern about skin aging. The potential effect of stem cell conditioned medium (CM) for antiaging has been reported in recent years, and such medium may be able to improve the efficacy of resurfacing modalities. This study investigated the efficacy of topical CM combined with resurfacing in comparison with resurfacing alone. We searched the PubMed, Embase, and Cochrane Library databases for randomized controlled trials (RCTs). We used the Cochrane risk-of-bias tool (version 2) to assess the risk of bias of the included studies and Review Manager (version 5.4) for data analysis. Means and standard deviations of outcomes, namely wrinkle, pigmentation, pore, and overall improvement, were extracted. After screening, we included five RCTs in the analysis, four of which were quantitatively analyzed. The result revealed that stem cell CM significantly reduced wrinkles (P = 0.0006), pigmentation (P = 0.004), and pores (P = 0.01) and improved overall skin condition (P < 0.0001). In summary, we suggest that stem cell CM is a safe treatment that can enhance the efficacy of facial skin nonsurgical resurfacing modalities.Level of Evidence III This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Macrophage phagocytosis alters the MRI signal of ferumoxytol-labeled mesenchymal stromal cells in cartilage defects

Human mesenchymal stem cells (hMSCs) are a promising tool for cartilage regeneration in arthritic joints. hMSC labeling with iron oxide nanoparticles enables non-invasive in vivo monitoring of transplanted cells in cartilage defects with MR imaging. Since graft failure leads to macrophage phagocytosis of apoptotic cells, we evaluated in vitro and in vivo whether nanoparticle-labeled hMSCs show distinct MR signal characteristics before and after phagocytosis by macrophages. We found that apoptotic nanoparticle-labeled hMSCs were phagocytosed by macrophages while viable nanoparticle-labeled hMSCs were not. Serial MRI scans of hMSC transplants in arthritic joints of recipient rats showed that the iron signal of apoptotic, nanoparticle-labeled hMSCs engulfed by macrophages disappeared faster compared to viable hMSCs. This corresponded to poor cartilage repair outcomes of the apoptotic hMSC transplants. Therefore, rapid decline of iron MRI signal at the transplant site can indicate cell death and predict incomplete defect repair weeks later. Currently, hMSC graft failure can be only diagnosed by lack of cartilage defect repair several months after cell transplantation. The described imaging signs can diagnose hMSC transplant failure more readily, which could enable timely re-interventions and avoid unnecessary follow up studies of lost transplants.

Immunomodulation in stem cell differentiation into neurons and brain repair

Immunomodulators regulate stem cell activity at all stages of development as well as during adulthood. Embryonic stem cell (ESC) proliferation as well as neurogenic processes during embryonic development are controlled by factors of the immune system. We review here immunophenotypic expression patterns of  different stem cell types, including ESC, neural (NSC) and tissue-specific mesenchymal stem cells (MSC), and focus on immunodulatory properties of these cells. Immune and inflammatory responses, involving actions of cytokines as well as toll-like receptor (TLR) signaling are known to affect the differentiation capacity of NSC and MSC. Secretion of pro- and anti-inflammatory messengers by MSC have been observed as the consequence of TLR and cytokine activation and promotion of differentiation into specified phenotypes. As result of augmented differentiation capacity, stem cells secrete angiogenic factors including vascular endothelial growth factor, resulting in multifactorial actions in tissue repair. Immunoregulatory properties of tissue specific adult stem cells are put into the context of possible clinical applications.

Histological changes induced by Polyglycolic-Acid (PGA) scaffolds seeded with autologous adipose or muscle-derived stem cells when implanted on rabbit bladder

PURPOSE

To evaluate the morphological and histological changes induced by PGA scaffold seeded with autologous adipose or muscle derived stem cells implanted on rabbit bladder wall.

MATERIAL AND METHODS

Adipose derived stem cells (ADSCs) were obtained from the inguinal fat of eight rabbits and muscle derived stem cells (MDSCs) from the anterior tibial muscle of other eight rabbits. After culture and isolation, the cells were stained with Vybrant Red CM DiI and then implanted at third passage. Two PGA scaffolds were implanted on the bladder submucosa of each animal. On the right bladder side was implanted unseeded PGA scaffold while on the left side was implanted ADSCs or skeletal MDSCs seeded PGA scaffold. ADSCs were implanted in eight animals and MDSC in other eight animals. The animals were sacrificed at four and eight weeks. Histological evaluation was performed with Hematoxylin and Eosin, Masson's Trichrome and smooth muscle α-actin.

RESULTS

We observed a mild inflammatory response in all the three groups. Seeded scaffolds induced higher lymphocytes and lower polimorphonuclear migration than controls. Fibrosis was more pronounced in the control groups. Smooth muscle α-actin was positive only in ADSC and MDSC seeded scaffolds. At four and eight weeks ADCSs and skeletal MDSCs labeled cells were found at the implant sites.

CONCLUSIONS

The implantation of PGA scaffolds seeded with ADSC and MDSC induced less fibrosis than control and smooth muscle regeneration.

Ultrastructural characteristics of three undifferentiated mouse embryonic stem cell lines and their differentiated three-dimensional derivatives: a comparative study

The fine structures of mouse embryonic stem cells (mESCs) grown as colonies and differentiated in three-dimensional (3D) culture as embryoid bodies (EBs) were analyzed by transmission electron microscopy. Undifferentiated mESCs expressed markers that proved their pluripotency. Differentiated EBs expressed different differentiation marker proteins from the three germ layers. The ultrastructure of mESCs revealed the presence of microvilli on the cell surfaces, large and deep infolded nuclei, low cytoplasm-to-nuclear ratios, frequent lipid droplets, nonprominent Golgi apparatus, and smooth endoplasmic reticulum. In addition, we found prominent juvenile mitochondria and free ribosomes-rich cytoplasm in mESCs. Ultrastructure of the differentiated mESCs as EBs showed different cell arrangements, which indicate the different stages of EB development and differentiation. The morphologies of BALB/c and 129 W9.5 EBs were very similar at day 4, whereas C57BL/6 EBs were distinct from the others at day 4. This finding suggested that differentiation of EBs from different cell lines occurs in the same pattern but not at the same rate. Conversely, the ultrastructure results of BALB/c and 129 W9.5 ESCs revealed differentiating features, such as the dilated profile of a rough endoplasmic reticulum. In addition, we found low expression levels of undifferentiated markers on the outer cells of BALB/c and 129 W9.5 mESC colonies, which suggests a faster differentiation potential.

Can we grow sperm? A translational perspective on the current animal and human spermatogenesis models

There have been tremendous advances in both the diagnosis and treatment of male factor infertility; however, the mechanisms responsible to recreate spermatogenesis outside of the testicular environment continue to elude andrologists. Having the ability to 'grow' human sperm would be a tremendous advance in reproductive biology with multiple possible clinical applications, such as a treatment option for men with testicular failure and azoospermia of multiple etiologies. To understand the complexities of human spermatogenesis in a research environment, model systems have been designed with the intent to replicate the testicular microenvironment. Currently, there are both in vivo and in vitro model systems. In vivo model systems involve the transplantation of either spermatogonial stem cells or testicular xenographs. In vitro model systems involve the use of pluripotent stem cells and complex coculturing and/or three-dimensional culturing techniques. This review discusses the basic methodologies, possible clinical applications, benefits and limitations of each model system. Although these model systems have greatly improved our understanding of human spermatogenesis, we unfortunately have not been successful in demonstrating complete human spermatogenesis outside of the testicle.

Arterially perfused neurosphere-derived cells distribute outside the ischemic core in a model of transient focal ischemia and reperfusion in vitro

Background

Treatment with neural stem cells represents a potential strategy to improve functional recovery of post-ischemic cerebral injury. The potential benefit of such treatment in acute phases of human ischemic stroke depends on the therapeutic viability of a systemic vascular delivery route. In spite of the large number of reports on the beneficial effects of intracerebral stem cells injection in experimental stroke, very few studies demonstrated the effectiveness of the systemic intravenous delivery approach.

Metodology/Principal Findings

We utilized a novel in vitro model of transient focal ischemia to analyze the brain distribution of neurosphere-derived cells (NCs) in the early 3 hours that follow transient occlusion of the medial cerebral artery (MCA). NCs obtained from newborn C57/BL6 mice are immature cells with self-renewal properties that could differentiate into neurons, astrocytes and oligodendrocytes. MCA occlusion for 30 minutes in the in vitro isolated guinea pig brain preparation was followed by arterial perfusion with 1×10⁶ NCs charged with a green fluorescent dye, either immediately or 60 minutes after reperfusion onset. Changes in extracellular pH and K⁺ concentration during and after MCAO were measured through ion-sensitive electrodes.

Conclusion/Significance

It is demonstrated that NCs injected through the vascular system do not accumulate in the ischemic core and preferentially distribute in non-ischemic areas, identified by combined electrophysiological and morphological techniques. Direct measurements of extracellular brain ions during and after MCA occlusion suggest that anoxia-induced tissue changes, such as extracellular acidosis, may prevent NCs from entering the ischemic area in our in vitro model of transitory focal ischemia and reperfusion suggesting a role played by the surrounding microenviroment in driving NCs outside the ischemic core. These findings strongly suggest that the potential beneficial effect of NCs in experimental focal brain ischemia is not strictly dependent on their homing into the ischemic region, but rather through a bystander mechanism possibly mediated by the release of neuroprotective factors in the peri-infarct region.

In vitro spermatogenesis as a method to bypass pre-meiotic or post-meiotic barriers blocking the spermatogenetic process: genetic and epigenetic implications in assisted reproductive technology

Pregnancies achieved by assisted reproduction technologies and particularly by ooplasmic injections of either in vivo or in vitro generated immature male germ cells are susceptible to genetic risks inherent to the male population treated with assisted reproduction and additional risks inherent to these innovative procedures. The documented, as well as the theoretical risks, are discussed in this review. These risks represent mainly the consequences of genetic abnormalities underlying male infertility and may become stimulators for the development of novel approaches and applications in the treatment of infertility. Recent data suggest that techniques employed for in vitro spermatogenesis, male somatic cell haploidization, stem cell differentiation in vitro and assisted reproductive technology may also affect the epigenetic characteristics of the male gamete, the female gamete, or may have an impact on early embryogenesis. They may be also associated with an increased risk for genomic imprinting abnormalities. Production of haploid male gametes in vitro may not allow the male gamete to undergo all the genetic and epigenetic alterations that the male gamete normally undergoes during in vivo spermatogenesis.

Stem cells in the lung parenchyma and prospects for lung injury therapy

Until recently, it was thought that only embryonic stem cells were pluripotent and that adult stem cells were restricted in their differentiative and regenerative potential to become the tissues in which they reside. However, the discovery that adult stem cells in one tissue can contribute to the formation of other tissues, especially after injury or cell damage, implies that stem cells have developmental plasticity. For example, haematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs) from bone marrow can be used to regenerate diverse tissues at distant sites, including the lung. This article reviews the character of stem cells in the lung parenchyma and focuses on the potential uses of adult stem cells in research of lung injury and lung disease therapies.

Human embryoid body-derived stem cells in co-culture with bladder smooth muscle and urothelium

OBJECTIVES

Human pluripotent stem cells have excellent regenerative abilities, making them attractive in bladder regeneration. Porcine small intestinal submucosa (SIS) is an established matrix well-suited to the urinary tract. We evaluated the ability of human embryonic germ (hEG) cell-derived stem cells to form a composite graft on SIS, grown alone or in combination with human bladder smooth muscle cells (SMCs) or urothelial (URO) cells.

METHODS

The hEG cell-derived cell line SDEC had the best-fit profile for smooth muscle, as determined by its gene and protein expression. SDEC cells were seeded on SIS, either on its serosal or mucosal surface, and cultured for 7 or 14 days. Co-cultures of stem cells with URO cells or SMCs were also assessed under similar conditions. The grafts were analyzed by histologic examination for cell growth, morphology, and matrix penetration.

RESULTS

SDEC cells grew in a monolayer on SIS, with a marked increase in three-dimensional growth when co-cultured with URO cells or SMCs. Penetration of the matrix was evident when seeded on the rough surface of the SIS, progressing with time. Stratification of the cell layers occurred on the smooth side of the SIS.

CONCLUSIONS

This is the first description of hEG cell-derived stem cells in co-culture with bladder cells. hEG cell-derived stem cells grow well on SIS even when seeded at low concentrations in the presence of bladder cells (URO cells or SMCs). These composite grafts will be ideal to evaluate the in vivo functional characteristics of stem cells using an animal model of bladder regeneration.

Administrative and research policies required to bring cellular therapies from the research laboratory to the patient's bedside

The research process is a balance between the inherent risks of new discoveries and the risks of research participant safety. Conflicts of interest, inherent to the research process, as well as those introduced by emerging cellular therapies, have the potential to compromise safety. The relationship of trust between the researcher and the clinical trial participant facilitates objective decision making, in the best interest of both parties. In the setup of each clinical trial, investigators incorporate ethical, political, legal, financial, and regulatory considerations as protocols are established. Responsibility to abide by these decisions ensures a systematic process and safeguards participants in this process. The integrity of the research process is strengthened by identifying potential conflicting issues with the guiding principles established in the protocols, which may threaten the objectivity of involved parties and jeopardize safety of the participants. The rapid pace and changing paradigms of new discoveries in cellular therapies exaggerate existing conflicts and introduce new ones. Ethical issues raised by emerging cellular therapies include the division of opinions regarding the use of embryonic and fetal tissue to develop stem cell lines for research, the individual versus professional conscience of a researcher, overselling of outcomes as a result of the researcher's desire to be the first to discover a cellular therapy, and therapeutic misconception resulting from a participant's desire for a miracle cure. The basic ethical issue of whether stem cells should be utilized as a cellular therapy raises heated debates because some believe that it is not acceptable to use fetal material as a source of research material for future cures and others feel equally as strong that inaction is unethical because it results in needless suffering and death owing to the absence of this research. Political issues include the divergent position statements of presidential administrations on cellular therapy, variations in individual state laws, and states becoming involved in research funding, such as California's Proposition 71. Legal concerns include expanding private litigation with diversity of lawsuits, expanding lists of defendants, and the use of class-action lawsuits in research cases. Ownership issues also arise in terms of intellectual property, patents, and ownership of stem cells collected from minors, as in umbilical cord blood donations. Situations that challenge the regulatory processes established to ensure participant safety include differences in reporting requirements for private- and public-funded research and the lack of adequate funding and resources to implement and support the institutional review board (IRB) process. Financial considerations influence the development of clinical protocols, because funding is often limited. Financial incentives, personal investment in companies funding research activities, and fundraising pressures may present potential conflicts. In addition, the increasing role of emerging biotechnology start-up companies and pharmaceutical companies in clinical research introduces additional financial considerations. Administrative policies are needed to address these possible conflicts and ensure research participant safety as cellular therapies progress from the research laboratories to the patient's bedside. Administrative policies to ensure minimum standards of quality for emerging products before human clinical trials, policies to enforce consistent reporting requirements for private and public cellular research, policies to minimize financial conflicts of interest, policies to strengthen implementation of the existing IRB process and to structure into the process a consistent, systematic review of these identified conflicts, and policies to limit private litigation will help to preserve the objectivity of the review process and ultimately increase participant safety.

The disparate role of BMP in stem cell biology

Stem cells share several characteristics of cancer cells including loss of contact inhibition and immortality. Therefore, stem cells represent an excellent model system in which to define the molecular mechanisms underlying cancer development and progression. Several signal transduction pathways including leukemia inhibitory factor, Wnt and FGF have been demonstrated to function in stem cell self-renewal and differentiation. However, more recently bone morphogenetic proteins (BMPs) have emerged as key regulators of stem cell fate commitment. Intriguingly, BMPs have disparate roles in regulating the biology of embryonic stem (ES) cells compared with neural crest stem cells (NCSCs). Furthermore, although BMPs block neural differentiation of ES cells from both mouse and human, they contribute to self-renewal specifically in mouse ES cells. These observations strongly suggest that combinations of extracellular factors regulate stem cells, and that crosstalk between intracellular signaling pathways precisely defines stem cell fate commitment. In this review, we focus on the role of BMP signaling in mouse and human ES cells compared with NCSCs. We then discuss how the molecular effectors of BMP signaling may contribute to cancer, and thus represent potential targets for therapeutic intervention.

Adult stem cell lines in regenerative medicine and reconstructive surgery

In recent years, there has been a tremendous increase in the understanding of stem cell biology. The potential clinical applications lead to an extended interest in the use of stem cells in many medical disciplines. Multipotent adult stem cells seem to be almost comparable to embryonic stem cells with respect to their ability to differentiate into various tissues in vitro and in vivo, a function that has been termed "stem cell plasticity". In vivo experiments in rodents have shown that adult stem cells participate in tissue- and organ regeneration in almost all lesions. Although stem cell populations isolated from the bone marrow are usually a heterogeneous mix of different subpopulations, cloned adult stem cell lines from any source also show a broad spectrum of differentiation potential, e.g., osteogenesis, myogenesis, neurogenesis, or angiogenesis in wound healing. Angiogenesis in particular is a subject in tissue regeneration with tremendous implication in reconstructive surgery. This comprehensive plasticity makes it possible to use stem cell lines for biomedical research, tissue engineering, regenerative surgery, and organ repair. Adult stem cell lines are molecularly well defined with respect to transcription factors, active signal transduction pathways, and expression of receptors/ligand pairs. We performed experiments with adult stem cell lines, which are not subject to stem cell heterogeneity. Results obtained with stem cell lines can reliably be ascribed to the stem cell population under scrutiny. Adult stem cell lines can be obtained with the necessary quality and quantity also to study many effects of human stem cells in vitro and in vivo. In this paper, we summarize some of the tremendous therapeutic implications of adult stem cell lines in surgery and surgical research.

Efforts to create an artificial testis: culture systems of male germ cells under biochemical conditions resembling the seminiferous tubular biochemical environment

Induction of meiotic and post-meiotic alterations of male germ cells in vitro has been the target of several research efforts since 1960. However, to date, the establishment of an ideal culture system in which spermatogonial stem cells can be maintained and directed to proliferate and undergo meiosis and complete spermiogenesis does not exist. This is attributed to the difficulties concerning the isolation and purification of defined subpopulations of germ cells and the establishment of male germ cell lines. In addition, there is no adequate knowledge regarding the optimal biochemical conditions that promote the survival and differentiation of germ cells in long-term cultures. This review focuses on the methodologies that have been proved sufficient to achieve differentiation of cultured male germ cells. Furthermore, the factors regulating spermatogenesis and the technical prerequisites to achieve differentiation of cultured male germ cells are described. Finally, the role of in vitro cultures of immature diploid germ cells in the therapeutic management of men negative for haploid cells in their testes and the subsequent potential genetic and epigenetic risks are discussed.

Therapeutic potential of stem cells in perinatal medicine

Increasing evidence suggests that stem cells have tremendous potential to facilitate repair of damaged tissue and to exert protective influences that limit the extent of damage. Their inherent capacity to respond to signals generated by damaged tissue, migrate to these regions and either replace dead tissue or deliver protection by secretion of specific growth hormones and protective factors, suggests that they might have unrivalled therapeutic potential in perinatal medicine. A further potential of stem cells is their use in gene repair strategies for genetic disorders; an application which is exceedingly interesting from a perinatal perspective. Because of the relatively small size of infants and their capacity for future growth, stem cell therapy could be more successful in newborns than in older children or adults. In practical terms, the placenta, with its large reservoir of fetal blood, offers the ideal source of autologous stem cells. This affords the opportunity for stem cells to be collected and used, either directly ex vivo or after in vitro modulation, both for disorders in the neonatal period and for those arising later in life. The organs most affected from tissue damage in the neonatal period are the brain and the lung. So far, the most promising application of stem cells might be in the treatment of neurological injury. In this review we discuss recent research findings with adult stem cell therapy and their potential use in perinatal medicine. Furthermore, specific animal models suitable to explore the patho-physiological mechanisms of stem cell transplantation after neurological injury will be discussed. This review gives an overview of basic science findings and their possible role for clinical application with regards to the therapeutic potential of stem cells in perinatal medicine. Medline was searched for journal selection in peer-reviewed journals with high impact scores, which were relevant to this topic. All articles were in English and the search was not limited by publication year. However, the oldest publication was dated 1988 (reference 1).

Ultrastructure of human embryonic stem cells and spontaneous and retinoic acid-induced differentiating cells

Ultrastructural and immunohistochemical studies of 4 groups of cells-(human embryonic stem cells (hES), embryoid bodies (EB), and spontaneously and retinoic acid (RA)-induced differentiating cells)-were carried out to investigate their detailed phenotype. Immunohistochemically, the EB cells showed strong immunoreactivity for CD34, CD117, and nestin. Differentiating cells expressed pancytokertin, vimentin, CD31, CD56, GFAP, nestin, and NeuN as well as CD34, and c-Kit. However, synaptophysin and neurofilaments were not present in these same differentiating cells. Transmission electron microscopy showed that hES and EB cells were very similar to germ cells or cells of the inner cell mass. Spontaneously and RA-induced differentiating cells exhibited epithelial, mesenchymal, endodermal, and neuronal phenotypes. The perikarya of the neuronal cells had rich RERs (Nissl substance) and long cytoplasmic processes filled with numerous neural tubules. However, neither synaptic junctions nor synaptic vesicles were developed. In our study, RA treatment with brain-derived growth factor and TGFalpha in neuron differentiation medium induced not only neuronal differentiation but also pluripotential differentiation. Full neuronal differentiation did not occur after 2 weeks in culture, as no synaptic junctions and synaptic vesicles developed.