Neurogenic differentiation of human adipose-derived stem cells: relevance of different signaling molecules, transcription factors, and key marker genes. Gene. 2012;511:427-436. [PMID: 23000064 DOI: 10.1016/j.gene.2012.09.038]

Adipose-derived stem cell therapy for spinal cord injuries: Advances, challenges, and future directions

Spinal cord injury (SCI) has limited treatment options for regaining function. Adipose-derived stem cells (ADSCs) show promise owing to their ability to differentiate into multiple cell types, promote nerve cell survival, and modulate inflammation. This review explores ADSC therapy for SCI, focusing on its potential for improving function, preclinical and early clinical trial progress, challenges, and future directions. Preclinical studies have demonstrated ADSC transplantation's effectiveness in promoting functional recovery, reducing cavity formation, and enhancing nerve regrowth and myelin repair. To improve ADSC efficacy, strategies including genetic modification and combination with rehabilitation are being explored. Early clinical trials have shown safety and feasibility, with some suggesting motor and sensory function improvements. Challenges remain for clinical translation, including optimizing cell survival and delivery, determining dosing, addressing tumor formation risks, and establishing standardized protocols. Future research should focus on overcoming these challenges and exploring the potential for combining ADSC therapy with other treatments, including rehabilitation and medication.

Promoting Immortalized Adipose-Derived Stem Cell Transdifferentiation and Proliferation into Neuronal-Like Cells through Consecutive 525 nm and 825 nm Photobiomodulation

Neuronal cells can be generated from adipose-derived stem cells (ADSCs) through biological or chemical inducers. Research has shown that this process may be optimized by the introduction of laser irradiation in the form of photobiomodulation (PBM) to cells. This in vitro study is aimed at generating neuronal-like cells with inducers, chemical or biological, and at furthermore treating these transdifferentiating cells with consecutive PBM of a 525 nm green (G) laser and 825 nm near-infrared (NIR) laser light with a fluence of 10 J/cm². Cells were exposed to induction type 1 (IT1): 3-isobutyl-1-methylxanthine (IBMX) (0.5 mM)+indomethacin (200 μM)+insulin (5 μg/ml) for 14 days, preinduced with β-mercaptoethanol (BME) (1 mM) for two days, and then incubated with IT2: β-hydroxyanisole (BHA) (100 μM)+retinoic acid (RA) (10-6 M)+epidermal growth factor (EGF) (10 ng/ml)+basic fibroblast growth factor (bFGF) (10 ng/ml) for 14 days and preinduced with β-mercaptoethanol (BME) (1 mM) for two days and then incubated with indomethacin (200 μM)+RA (1 μM)+forskolin (10 μM) for 14 days. The results were evaluated through morphological observations, viability, proliferation, and migration studies, 24 h, 48 h, and 7 days post-PBM. The protein detection of an early neuronal marker, neuron-specific enolase (NSE), and late, ciliary neurotrophic factor (CNTF), was determined with enzyme-linked immunosorbent assays (ELISAs). The genetic expression was also explored through real-time PCR. Results indicated differentiation in all experimental groups; however, cells that were preinduced showed higher proliferation and a higher differentiation rate than the group that was not preinduced. Within the preinduced groups, results indicated that cells treated with IT2 and consecutive PBM upregulated differentiation the most morphologically and physiologically.

Schisandrin A and B affect the proliferation and differentiation of neural stem cells

Schisandrin A and B (Sch A and B) are the important components of Asian dietary supplement and phytomedicine Schisandra chinensis (S. chinensis). They can enhance adult neurogenesis in vivo; however, these effects still need to be verified. Here NE-4 C neural stem cells (NSCs) were employed as the in vitro model and treated with Sch A and B at 0.1 μg/mL. EdU (5-Ethynyl-2'-deoxyuridine) labeling showed that both Sch A and B treatments enhanced NSC proliferation. Real-time PCR analysis showed the mRNA abundances of telomerase gene Tert and cell cycle gene Cyclin D1 were significantly up-regulated after the treatments. During the neurosphere induction, Sch B enhanced the neurosphere formation and neuronal differentiation, and increased the neurosphere semidiameters. Detection of the neuron differentiation marker Mapt indicates that both Sch A and B, especially Sch B, benefits the induced neuronal differentiation. Sch B treatment also enhanced mRNA expressions of the neurosphere-specific adhesion molecule Cdh2 and Wnt pathway-related genes including Mmp9, Cyclin D1 and β-catenin. Together, Sch A especially Sch B, promotes the proliferation, affects the survival, differentiation and neurogenesis of NSCs, which is consistent with their in vivo effects. This study provides further clue on the potential neuropharmacological effects of S. chinensis.

Adipose-Derived Stem Cell: "Treat or Trick"

Stem cells have been widely used for treating disease due to the various benefits they offer in the curing process. Several treatments using stem cells have undergone clinical trials, such as cell-based therapies for heart disease, sickle cell disease, thalassemia, etc. Adipose-derived stem cells are some of the many mesenchymal stem cells that exist in our body that can be harvested from the abdomen, thighs, etc. Adipose tissue is easy to harvest, and its stem cells can be obtained in higher volumes compared to stem cells harvested from bone marrow, for which a more invasive technique is required with a smaller volume obtained. Many scientists have expressed interest in investigating the role of adipose-derived stem cells in treating disease since their use was first described. This is due to these stem cells' ability to differentiate into multiple lineages and secrete a variety of growth factors and proteins. Previous studies have found that the hormones, cytokines, and growth factors contained in adipose tissue play major roles in the metabolic regulation of adipose tissue, as well as in energy balance and whole-body homeostasis through their endocrine, autocrine, and paracrine functions. These are thought to be important contributors to the process of tissue repair and regeneration. However, it remains unclear how effective and safe ADSCs are in treating diseases. The research that has been carried out to date is in order to investigate the impact of ADSCs in disease treatment, as described in this review, to highlight its "trick or treat" effect in medical treatment.

Intracerebral transplantation of autologous adipose-derived stem cells for chronic ischemic stroke: A phase I study

Current therapy does not provide significant benefits for patients with chronic stroke. Pre-clinical studies suggested that autologous adipose-derived stem cells have benefits for the treatment of chronic stroke. This Phase I open-label study was conducted to demonstrate the safety and efficacy of autologous adipose-derived stem cells (GXNPC1) in chronic stroke. Three patients with chronic stroke were treated with stereotactic implantation of autologous adipose-derived stem cells (1 × 10⁸ cells). The primary endpoints of safety evaluation included adverse events, over a 6 months post-implantation period. The secondary endpoints included improvements in neurological functions. Evolutional change of brain parenchyma was also followed with magnetic resonance imaging (MRI). All three participants improved significantly at 6 months follow-up. The extent of improvement from pre-treatment was: National Institutes of Health Stroke Scale improved 5-15 points, Barthel Index: 25-50 points, Berg balance scale 0-21 points and Fugl-Meyer modified sensation 3-28 points. All three patients had signal change along the implantation tract on MRI one month after surgery. There is no related safety issue through 6 months observation. Clinical measures of neurological symptoms of these patients with chronic stroke improved at 6 months without adverse effects after implantation of autologous adipose-derived stem cells (GXNPC1), which might be correlated with post-implantation changes on brain MRI. Clinical Trial Registration-URL: https://clinicaltrials.gov/ct2/show/NCT02813512?term=ADSC&cond=Stroke&cntry=TW&draw=2&rank=1 Unique identifier: NCT02813512.

The influence of reduced graphene oxide on stem cells: a perspective in peripheral nerve regeneration

Graphene and its derivatives are fascinating materials for their extraordinary electrochemical and mechanical properties. In recent decades, many researchers explored their applications in tissue engineering and regenerative medicine. Reduced graphene oxide (rGO) possesses remarkable structural and functional resemblance to graphene, although some residual oxygen-containing groups and defects exist in the structure. Such structure holds great potential since the remnant-oxygenated groups can further be functionalized or modified. Moreover, oxygen-containing groups can improve the dispersion of rGO in organic or aqueous media. Therefore, it is preferable to utilize rGO in the production of composite materials. The rGO composite scaffolds provide favorable extracellular microenvironment and affect the cellular behavior of cultured cells in the peripheral nerve regeneration. On the one hand, rGO impacts on Schwann cells and neurons which are major components of peripheral nerves. On the other hand, rGO-incorporated composite scaffolds promote the neurogenic differentiation of several stem cells, including embryonic stem cells, mesenchymal stem cells, adipose-derived stem cells and neural stem cells. This review will briefly introduce the production and major properties of rGO, and its potential in modulating the cellular behaviors of specific stem cells. Finally, we present its emerging roles in the production of composite scaffolds for nerve tissue engineering.

Neural priming of adipose-derived stem cells by cell-imprinted substrates

Cell-imprinting technology is a novel method for directing stem cell fate using substrates molded from target cells. Here, we fabricated and studied cell-imprinted substrates for neural priming in human adipose-derived stem cells in the absence of chemical cues. We molded polydimethylsiloxane silicone substrates on fixed differentiated neural progenitor cells (ReNcell^TMVM). The ReNcell^TMcell line consists of immortalized human neural progenitor cells that are capable to differentiate into neural cells. The fabricated cell-imprinted silicone substrates represent the geometrical micro- and nanotopology of the target cell morphology. During the molding procedure, no transfer of cellular proteins was detectable. In the first test with undifferentiated ReNcell^TMVM cells, the cell-imprinted substrates could accelerate neural differentiation. With adipose-derived stem cells cultivated on the imprinted substrates, we observed modifications of cell morphology, shifting from spread to elongated shape. Both immunofluorescence and quantitative gene expression analysis showed upregulation of neural stem cell and early neuronal markers. Our study, for the first time, demonstrated the effectiveness of cell-imprinted substrates for neural priming of adipose-derived stem cells for regenerative medicine applications.

Phenotypical Characterization and Neurogenic Differentiation of Rabbit Adipose Tissue-Derived Mesenchymal Stem Cells

Although the rabbit is a frequently used biological model, the phenotype of rabbit adipose-derived mesenchymal stem cells (rAT-MSCs) is not well characterized. One of the reasons is the absence of specific anti-rabbit antibodies. The study aimed to characterize rAT-MSCs using flow cytometry and PCR methods, especially digital droplet PCR, which confirmed the expression of selected markers at the mRNA level. A combination of these methods validated the expression of MSCs markers (CD29, CD44, CD73, CD90 and CD105). In addition, cells were also positive for CD49f, vimentin, desmin, α-SMA, ALDH and also for the pluripotent markers: NANOG, OCT4 and SOX2. Moreover, the present study proved the ability of rAT-MSCs to differentiate into a neurogenic lineage based on the confirmed expression of neuronal markers ENO2 and MAP2. Obtained results suggest that rAT-MSCs have, despite the slight differences in marker expression, the similar phenotype as human AT-MSCs and possess the neurodifferentiation ability. Accordingly, rAT-MSCs should be subjected to further studies with potential application in veterinary medicine but also, in case of their cryopreservation, as a source of genetic information of endangered species stored in the gene bank.

Adult Stem Cell Therapy for Premature Ovarian Failure: From Bench to Bedside

Premature ovarian failure (POF) is a devastating condition for women of childbearing age with serious health consequences, including distress, infertility, osteoporosis, autoimmune disorders, ischemic heart disease, and increased mortality. In addition to the mainstay estrogen therapy, stem cell therapy has been tested as the result of rapid progress in cell biology and reprogramming research. We hereby provide a review for the latest research and issues related with stem cell-based therapy for POF, and provide a commentary on various methods for enhancing its effect. Large amount of animal studies have demonstrated an extensive benefit of stem cells for failed ovarian recovering. As shown by such studies, stem cell therapy can result in recovery of hormonal levels, follicular activation, ovarian angiogenesis, and functional restoration. Meanwhile, a study of molecular pathways revealed that the function of stem cells mainly depends on their paracrine actions, which can produce multiple factors for the promotion of ovarian angiogenesis and regulation of cellular functions. Nevertheless, studies using disease models also revealed certain drawbacks. Clinical trials have shown that menstrual cycle and even pregnancy may occur in POF patients following transplantation of stem cells, although the limitations, including inadequate number of cases and space for the improvement of transplantation methodology. Only with its safety and effect get substantial improvement through laboratory experiments and clinical trials, can stem cell therapy really bring benefits to more patients. Additionally, effective pretreatment and appropriate transplantation methods for stem cells are also required. Taken together, stem cell therapy has shown a great potential for the reversal of POF and is stepping from bench to bedside. Impact statement Premature ovarian failure (POF) is a devastating condition with serious clinical consequences. The purpose of this review was to summarize the current status of stem cell therapy for POF. Considering the diversity of cell types and functions, a rigorous review is required for the guidance for further research into this field. Meanwhile, the challenges and prospect for clinical application of stem cell treatment, methodological improvements, and innovations are addressed.

Evidence that osteogenic and neurogenic differentiation capability of epidural adipose tissue-derived stem cells was more pronounced than in subcutaneous cells

Background/aim

The management of dura-related complications, such as the repairment of dural tears and reconstruction of large dural defects, remain the most challenging subjects of neurosurgery. Numerous surgical techniques and synthetic or autologous adjuvant materials have emerged as an adjunct to primary dural closure, which may result in further complications or side effects. Therefore, the subcutaneous autologous free adipose tissue graft has been recommended for the protection of the central nervous system and repairment of the meninges. In addition, human adipose tissue is also a source of multipotent stem cells. However, epidural adipose tissue seems more promising than subcutaneous because of the close location and intercellular communication with the spinal cord. Herein, it was aimed to define differentiation capability of both subcutaneous and epidural adipose tissue-derived stem cells (ASCs).

Materials and methods

Human subcutaneous and epidural adipose tissue specimens were harvested from the primary incisional site and the lumbar epidural space during lumbar spinal surgery, and ASCs were isolated.

Results

The results indicated that both types of ASCs expressed the cell surface markers, which are commonly expressed stem cells; however, epidural ASCs showed lower expression of CD90 than the subcutaneous ASCs. Moreover, it was demonstrated that the osteogenic and neurogenic differentiation capability of epidural adipose tissue-derived ASCs was more pronounced than that of the subcutaneous ASCs.

Conclusion

Consequently, the impact of characterization of epidural ASCs will allow for a new understanding for dural as well as central nervous system healing and recovery after an injury.

In Vitro Cultures of Adipose-Derived Stem Cells: An Overview of Methods, Molecular Analyses, and Clinical Applications

Adipose-derived stem cells (ASCs) exhibiting mesenchymal stem cell (MSC) characteristics, have been extensively studied in recent years. Because they have been shown to differentiate into lineages such as osteogenic, chondrogenic, neurogenic or myogenic, the focus of most of the current research concerns either their potential to replace bone marrow as a readily available and abundant source of MSCs, or to employ them in regenerative and reconstructive medicine. There is close to consensus regarding the methodology used for ASC isolation and culture, whereas a number of molecular analyses implicates them in potential therapies of a number of pathologies. When it comes to clinical application, there is a range of examples of animal trials and clinical studies employing ASCs, further emphasizing the advancement of studies leading to their more widespread use. Nevertheless, in vitro studies will most likely continue to play a significant role in ASC studies, both providing the molecular knowledge of their ex vivo properties and possibly serving as an important step in purification and application of those cells in a clinical setting. Therefore, it is important to consider current methods of ASC isolation, culture, and processing. Furthermore, molecular analyses and cell surface properties of ASCs are essential for animal studies, clinical studies, and therapeutic applications of the MSC properties.

The Cellular and Molecular Patterns Involved in the Neural Differentiation of Adipose-Derived Stem Cells

Injuries to the nervous system cause serious problems among affected patients by preventing them from the possibility of living a normal life. As this tissue possesses a reduced capacity of self-regeneration currently, lots of different strategies are being developed in order to make the regeneration in the nervous system possible. Among them, tissue engineering and stem cell-based therapies are to date very exploded fields and tremendous progress has been made in this direction. As the two main components of the nervous system, react differently to injuries and behave different during disease, it is clear that two separate regeneration approaches have been taken into consideration during development of treatment. Special attention is constantly given to the potential of adipose-derived stem cells for this kind of application. Due to the fact that they present remarkable properties, they can easily be obtained and have demonstrated that are capable of engaging in neural and glial lineages, adipose-derived stem cells are promising tools for the field of nervous system regeneration. Moreover, new insights into epigenetic control and modifications during the differentiation of adipose-derived stem cells towards the neural liege could provide new methods to maximize the regeneration process. In this review, we summarize the current applications of adipose-derived stem cells for neural regeneration and discuss in-depth molecular patterns involved in the differentiation of adipose-derived stem cells in neuron-like cells and Schwann-like cells.

Anti-aging effects exerted by Tetramethylpyrazine enhances self-renewal and neuronal differentiation of rat bMSCs by suppressing NF-kB signaling

In order to improve the therapeutic effects of mesenchymal stem cell (MSC)-based therapies for a number of intractable neurological disorders, a more favorable strategy to regulate the outcome of bone marrow MSCs (bMSCs) was examined in the present study. In view of the wide range of neurotrophic and neuroprotective effects, Tetramethylpyrazine (TMP), a biologically active alkaloid isolated from the herbal medicine Ligusticum wallichii, was used. It was revealed that treatment with 30–50 mg/l TMP for 4 days significantly increased cell viability, alleviated senescence by suppressing NF-κB signaling, and promoted bMSC proliferation by regulating the cell cycle. In addition, 40–50 mg/l TMP treatment may facilitate the neuronal differentiation of bMSCs, verified in the present study by presentation of neuronal morphology and expression of neuronal markers: microtubule-associated protein 2 (MAP-2) and neuron-specific enolase (NSE). The quantitative real-time polymerase chain reaction (qRT-PCR) revealed that TMP treatment may promote the expression of neurogenin 1 (Ngn1), neuronal differentiation 1 (NeuroD) and mammalian achaete–scute homolog 1 (Mash1). In conclusion, 4 days of 40–50 mg/l TMP treatment may significantly delay bMSC senescence by suppressing NF-κB signaling, and enhancing the self-renewal ability of bMSCs, and their potential for neuronal differentiation.

Adipose Tissue-Derived Stem Cells Have the Ability to Differentiate into Alveolar Epithelial Cells and Ameliorate Lung Injury Caused by Elastase-Induced Emphysema in Mice

Chronic obstructive pulmonary disease is a leading cause of mortality globally, with no effective therapy yet established. Adipose tissue-derived stem cells (ADSCs) are useful for ameliorating lung injury in animal models. However, whether ADSCs differentiate into functional cells remains uncertain, and no study has reported on the mechanism by which ADSCs improve lung functionality. Thus, in this study, we examined whether ADSCs differentiate into lung alveolar cells and are able to ameliorate lung injury caused by elastase-induced emphysema in model mice. Here, we induced ADSCs to differentiate into type 2 alveolar epithelial cells in vitro. We demonstrated that ADSCs can differentiate into type 2 alveolar epithelial cells in an elastase-induced emphysematous lung and that ADSCs improve pulmonary function of emphysema model mice, as determined with spirometry and ¹²⁹Xe MRI. These data revealed a novel function for ADSCs in promoting repair of the damaged lung by direct differentiation into alveolar epithelial cells.

Comparative study of the neural differentiation capacity of mesenchymal stromal cells from different tissue sources: An approach for their use in neural regeneration therapies

Mesenchymal stem cells (MSCs) can trans/differentiate to neural precursors and/or mature neurons and promote neuroprotection and neurogenesis. The above could greatly benefit neurodegenerative disorders as well as in the treatment of post-traumatic and hereditary diseases of the central nervous system (CNS). In order to attain an ideal source of adult MSCs for the treatment of CNS diseases, adipose tissue, bone marrow, skin and umbilical cord derived MSCs were isolated and studied to explore differences with regard to neural differentiation capacity. In this study, we demonstrated that MSCs from several tissues can differentiate into neuron-like cells and differentially express progenitors and mature neural markers. Adipose tissue MSCs exhibited significantly higher expression of neural markers and had a faster proliferation rate. Our results suggest that adipose tissue MSCs are the best candidates for the use in neurological diseases.

Mapping theme trends and knowledge structure on adipose-derived stem cells: a bibliometric analysis from 2003 to 2017

AIM

To investigate the theme trends and knowledge structure of adipose-derived stem cells (ADSCs) related literatures by using bibliometric analysis.

MATERIALS & METHODS

Co-word analysis, strategic diagram and social network analysis were employed.

RESULTS

In line with strategic diagrams, ADSC differentiation and transplantation as main undeveloped themes in 2003-2007 were partially replaced by regeneration medicine and ADSCs for myocardial infarction in 2008 to 2012, and then partially replaced by miRNAs in ADSC genetics and nerve regeneration in 2013 to 2017. Based on social network analysis, regenerative medicine/methods, myocardial infarction/therapy, as well as miRNAs/genetics, and nerve regeneration/physiology were considered the emerging hot spots in 2008 to 2012 and 2013 to 2017.

CONCLUSION

The undeveloped themes and emerging hot spots could be considered as new research topics.

Conditioned Media From Glial Cells Promote a Neural-Like Connexin Expression in Human Adipose-Derived Mesenchymal Stem Cells

The expression of neuronal and glial connexins (Cxs) has been evaluated in adipose-derived mesenchymal stem cells (ASCs) whose neural differentiation was promoted by a conditioned medium (CM) obtained from cultures of olfactory ensheathing cells (OECs) or Schwann cells (SCs). By immunocytochemistry and flow cytometer analysis it was found that Cx43 was already considerably expressed in naïve ASCs and further increased after 24 h and 7 days from CM exposition. Cx32 and Cx36 were significantly improved in conditioned cultures compared to control ASCs, whereas a decreased expression was noticed in the absence of CM treatments. Cx47 was virtually absent in any conditions. Altogether, high basal levels and induced increases of Cx43 expression suggest a potential attitude of ASCs toward an astrocyte differentiation, whereas the lack of Cx47 would indicate a poor propensity of ASCs to become oligodendrocytes. CM-evoked Cx32 and Cx36 increases showed that a neuronal- or a SC-like differentiation can be promoted by using this strategy. Results further confirm that environmental cues can favor an ASC neural differentiation, either as neuronal or glial elements. Of note, the use of glial products present in CM rather than the addition of chemical agents to achieve such differentiation would resemble "more physiological" conditions of differentiation. As a conclusion, the overexpression of typical neural Cxs would indicate the potential capability of neural-like ASCs to interact with neighboring neural cells and microenvironment.

SOX-11 regulates LINE-1 retrotransposon activity during neuronal differentiation

Activity of the human long interspersed nuclear elements-1 (LINE-1) retrotransposon occurs mainly in early embryonic development and during hippocampal neurogenesis. SOX-11, a transcription factor relevant to neuronal development, has unknown functions in the control of LINE-1 retrotransposon activity during neuronal differentiation. To study the dependence of LINE-1 activity on SOX-11 during neuronal differentiation, we induced differentiation of human SH-SY5Y neuroblastoma cells and adult adipose mesenchymal stem cells (hASCs) to a neuronal fate and found increased LINE-1 activity. We also show that SOX-11 protein binding to the LINE-1 promoter is higher in differentiating neuroblastoma cells, while knock-down of SOX-11 inhibits the induction of LINE-1 transcription in differentiating conditions. These results suggest that activation of LINE-1 retrotransposition during neuronal differentiation is mediated by SOX-11.

Molecular Mechanisms of Transdifferentiation of Adipose-Derived Stem Cells into Neural Cells: Current Status and Perspectives

Neurological diseases can severely compromise both physical and psychological health. Recently, adult mesenchymal stem cell- (MSC-) based cell transplantation has become a potential therapeutic strategy. However, most studies related to the transdifferentiation of MSCs into neural cells have had disappointing outcomes. Better understanding of the mechanisms underlying MSC transdifferentiation is necessary to make adult stem cells more applicable to treating neurological diseases. Several studies have focused on adipose-derived stromal/stem cell (ADSC) transdifferentiation. The purpose of this review is to outline the molecular characterization of ADSCs, to describe the methods for inducing ADSC transdifferentiation, and to examine factors influencing transdifferentiation, including transcription factors, epigenetics, and signaling pathways. Exploring and understanding the mechanisms are a precondition for developing and applying novel cell therapies.

Autologous transplantation of adipose-derived stem cells improves functional recovery of skeletal muscle without direct participation in new myofiber formation

BACKGROUND

Skeletal muscle has a remarkable regenerative capacity. However, extensive damage that exceeds the self-regenerative ability of the muscle can lead to irreversible fibrosis, scarring, and significant loss of function. Adipose-derived stem cells (ADSC) are a highly abundant source of progenitor cells that have been previously reported to support the regeneration of various muscle tissues, including striated muscles. The aim of this study was to evaluate the effect of ADSC transplantation on functional skeletal muscle regeneration in an acute injury model.

METHODS

Mouse ADSC were isolated from subcutaneous fat tissue and transplanted with a collagen hydrogel into the crushed tibialis anterior muscle of mice. Recovering muscles were analyzed for gene and protein expression by real-time quantitative polymerase chain reaction and immunohistochemistry. The muscle contractility was assessed by myography in an organ bath system.

RESULTS

Intramuscular transplantation of ADSC into crushed tibialis anterior muscle leads to an improved muscle regeneration with ADSC residing in the damaged area. We did not observe ADSC differentiation into new muscle fibers or endothelial cells. However, the ADSC-injected muscles had improved contractility in comparison with the collagen-injected controls 28 days post-transplantation. Additionally, an increase in fiber cross-sectional size and in the number of mature fibers with centralized nuclei was observed.

CONCLUSIONS

ADSC transplantation into acute damaged skeletal muscle significantly improves functional muscle tissue regeneration without direct participation in muscle fiber formation. Cellular therapy with ADSC represents a novel approach to promote skeletal muscle regeneration.

Neurogenic differentiation of adipose derived stem cells on graphene-based mat

Adipose derived stem cells (ADSCs) have been proved as an abundant and accessible cell source with the ability to differentiate into neuron-like cells. However, the low differentiation efficiency puts forward an important challenge to practical applications in clinic. Considering of the good biocompatibility of graphene-based materials and the potential interaction between graphene and cells mentioned in previous studies, herein, we investigated the effect of graphene oxide (GO) and reduced graphene oxide (rGO) mats on neurogenic differentiation of the ADSCs. We demonstrated the excellent capabilities of graphene-based mats, especially GO to support the neural differentiation of ADSCs. By comparing the observation under an optical microscope and fluorescence microscope, the conversion rate of neuron-like cells reached about 90%. We consider that GO mat is better for promoting the differentiation of ADSCs into neuron-like cells, which compared to rGO based platforms. Meanwhile, we made an analysis of the mechanism by which graphene induced the differentiation of ADSCs to neuron-like cells. The data obtained here highlight the effect of GO mat on neurogenic differentiation of ADSCs and implicate the potential of graphene-based materials in application of neural tissue engineering for the limited self-repair capability of nerve cells.

The role of miR-122-5p in negatively regulating T-box brain 1 expression on the differentiation of mouse bone mesenchymal stem cells

To achieve neuronal differentiation of mouse bone mesenchymal stem cells (bMSCs) into neuron-like cells and explore the role of miR-122-5p that may regulate T-box brain 1 (Tbr1) expression during the induction. BMSCs were cultured and induced with butylated hydroxyanisole, retinoic acid (RA), basic fibroblast growth factor, and nerve growth factor in vitro. The cells were stained for neuron-specific enolase (NSE) and β-III-tubulin by immunocytochemistry/immunofluorescence. MiR-122-5p that may regulate Tbr1 expression was predicted by bioinformatics and identified using a Dual-Luciferase assay. The expressions of miR-122-5p and Tbr1 were determined by real-time PCR and western blot before and after the induction. After infection of miR-122-5p, the expressions of Tbr1, NSE, and tauons were measured. BMSCs showed a short spindle shape with a uniform distribution. After 14 days, the induced cells showed neuronal traits with a pyramidal appearance. TargetScan and miRanda showed that miR-122-5p was well complementary with the target site of the Tbr1 3'-untranslated region. Identified by the Dual-Luciferase assay, we found that miR-122-5p could inhibit Tbr1 expression by binding to its 3'-untranslated region. Furthermore, the expressions of Tbr1 mRNA and protein were decreased by real-time PCR and western blot. Overexpression of miR-122-5p downregulated the expressions of Tbr1, NSE, and tauons. MiR-122-5p may negatively regulate Tbr1 expression to affect the differentiation of bMSCs into neuron-like cells.

Andrographolide Promotes Neural Differentiation of Rat Adipose Tissue-Derived Stromal Cells through Wnt/β-Catenin Signaling Pathway

Adipose tissue-derived stromal cells (ADSCs) are a high-yield source of pluripotent stem cells for use in cell-based therapies. We explored the effect of andrographolide (ANDRO, one of the ingredients of the medicinal herb extract) on the neural differentiation of rat ADSCs and associated molecular mechanisms. We observed that rat ADSCs were small and spindle-shaped and expressed multiple stem cell markers including nestin. They were multipotent as evidenced by adipogenic, osteogenic, chondrogenic, and neural differentiation under appropriate conditions. The proportion of cells exhibiting neural-like morphology was higher, and neurites developed faster in the ANDRO group than in the control group in the same neural differentiation medium. Expression levels of the neural lineage markers MAP2, tau, GFAP, and β-tubulin III were higher in the ANDRO group. ANDRO induced a concentration-dependent increase in Wnt/β-catenin signaling as evidenced by the enhanced expression of nuclear β-catenin and the inhibited form of GSK-3β (pSer9). Thus, this study shows for the first time how by enhancing the neural differentiation of ADSCs we expect that ANDRO pretreatment may increase the efficacy of adult stem cell transplantation in nervous system diseases, but more exploration is needed.

Directly Induced Neural Differentiation of Human Adipose-Derived Stem Cells Using Three-Dimensional Culture System of Conductive Microwell with Electrical Stimulation

Adipose-derived stem cells (ADSCs) have the capacity to differentiate into neural precursor cells which can be used for nerve regeneration. However, their inherently low neurogenic differentiation efficiency limits further clinical applications. This study was designed to promote neurogenic differentiation efficacy of ADSCs by integrating conductive hydrogel-based microwells with electrical stimulation (ES). We hypothesize that ADSCs will differentiate more efficiently into neural precursor cells when electrically stimulated in conductive hydrogel microwells. To make the conductive hydrogel-based microwell, polyethylene glycol (PEG) diacrylate aqueous solution mixed with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) was patterned with the polydimethylsiloxane mold and exposed to UV light to induce photo-cross-linking of the conductive hydrogel. After seeding the ADSCs in the microwells, the cells formed distinct cell spheres in PEG microwells and wide disks in the PEG/PEDOT:PSS microwells. Although the microwells yielded varying three-dimensional (3D) cell aggregate structure, cell viability was not affected. After neurogenic differentiation with ES, the ADSC aggregates in PEG/PEDOT:PSS microwells with ES expressed greater positive neuronal differentiation markers compared to nonstimulated PEG/PEDOT:PSS microwells. Although all neuronal gene expression levels were greater in PEG microwells with ES, the increased rates of gene expression levels between treated and untreated PEG/PEDOT:PSS microwells were much higher compared to PEG microwells. This would mean that electrically stimulating ADSC aggregates in conductive microwells is an effective method in increasing neurogenic differentiation. Therefore, we propose a most effective strategy taking advantage of a 3D conductive culture system which can be useful in a wide variety of electrical application.

Do we really need to differentiate mesenchymal stem cells into insulin-producing cells for attenuation of the autoimmune responses in type 1 diabetes: immunoprophylactic effects of precursors to insulin-producing cells

BACKGROUND

Type 1 diabetes (T1D) is a multifactorial autoimmune disorder where pancreatic beta cells are lost before the clinical manifestations of the disease. Administration of mesenchymal stem cells (MSCs) or MSCs differentiated into insulin-producing cells (IPCs) have yielded limited success when used therapeutically. We have evaluated the immunoprophylactic potentials of precursors to insulin-producing cells (pIPCs) and IPCs in nonobese diabetic (NOD) mice to ask a basic question: do we need to differentiate MSCs into IPCs or will pIPCs suffice to attenuate autoimmune responses in T1D?

METHODS

Bone marrow-derived MSCs from Balb/c mice were characterized following the International Society for Cellular Therapy (ISCT) guidelines. MSCs cultured in high-glucose media for 11 to 13 passages were characterized for the expression of pancreatic lineage genes using real-time polymerase chain reaction. Expression of the PDX1 gene in pIPCs was assessed using Western blot and fluorescence-activated cell sorting (FACS). Triple-positive MSCs were differentiated into IPCs using a three-step protocol after sorting them for cell surface markers, i.e. CD29, CD44, and SCA-1. Nonobese diabetic mice were administered pIPCs, IPCs, or phosphate-buffered saline (PBS) into the tail vein at weeks 9 or 10 and followed-up for 29-30 weeks for fasting blood glucose levels. Two consecutive blood sugar levels of more than 250 mg/dl were considered diabetic.

RESULTS

MSCs grown in high-glucose media for 11 to 13 passages expressed genes of the pancreatic lineage such as PDX1, beta2, neurogenin, PAX4, Insulin, and glucagon. Furthermore, Western blot and FACS analysis for PDX-1, a transcription factor necessary for beta cell maturation, confirmed that these cells were precursors of insulin-producing cells (pIPCs). NOD mice administered with pIPCs were better protected from developing diabetes with a protective efficacy of 78.4% (p < 0.009); however, administration of IPCs gave protective efficacy of 55% at the end of 28-30 weeks.

CONCLUSIONS

Precursors to insulin-producing cells seem to have better potential to arrest autoimmune response in type 1 diabetes when administered before the onset of the disease in NOD mice. When translated to humans, autologous mesenchymal stem cells grown in high-glucose media for 10 to 13 passages may have beneficial effects in individuals at high risk of developing type 1 diabetes.

Distinctive crypt shape in a sessile serrated adenoma/polyp: Distribution of Ki67-, p16INK4a-, WNT5A-positive cells and intraepithelial lymphocytes

Serrated lesions in the colorectum are currently predominantly classified as hyperplastic polyps (HPs), sessile serrated adenomas/polyps (SSA/Ps), and traditional serrated adenomas (TSAs) according to their morphology. However, the histological morphology and the molecular changes in the serrated lesions are still unclear. We performed immunohistochemistry for Ki67, p16^INK4a, and WNT5A in human HPs (n=22), SSA/Ps (n=41), and TSAs (n=19). The distribution of Ki67 and p16^INK4a positive cells in TSAs was different from that in HPs and SSA/Ps. Co-expression of Ki67 and P16^INK4a was infrequent in HPs and SSA/Ps; p16^INK4a-positive cells were found in the crypt cleft and stromal WNT5A-positive stromal cells were localized near the cleft in SSA/Ps, while intraepithelial lymphocytes (IELs) in SSA/Ps were more abundant than HPs. In conclusion, our study provides evidence that HPs branch because of the increase in and patchy distribution of senescent and proliferative cells, with increased and misdistributed stromal and inflammatory cells, which might contribute to creation of L- and/or T-shaped crypts, which are of distinctive shapes in SSA/Ps. Our findings may facilitate better understanding and therapy in the serrated lesions.

The regenerative role of adipose-derived stem cells (ADSC) in plastic and reconstructive surgery

The potential use of stem cell-based therapies for the repair and regeneration of various tissues and organs offers a paradigm shift in plastic and reconstructive surgery. The use of either embryonic stem cells (ESC) or induced pluripotent stem cells (iPSC) in clinical situations is limited because of regulations and ethical considerations even though these cells are theoretically highly beneficial. Adult mesenchymal stem cells appear to be an ideal stem cell population for practical regenerative medicine. Among these cells, adipose-derived stem cells (ADSC) have the potential to differentiate the mesenchymal, ectodermal and endodermal lineages and are easy to harvest. Additionally, adipose tissue yields a high number of ADSC per volume of tissue. Based on this background knowledge, the purpose of this review is to summarise and describe the proliferation and differentiation capacities of ADSC together with current preclinical data regarding the use of ADSC as regenerative tools in plastic and reconstructive surgery.

An Overview of Neural Differentiation Potential of Human Adipose Derived Stem Cells

There is wide interest in application of adult stem cells due to easy to obtain with a minimal patient discomfort, capable of producing cell numbers in large quantities and their immunocompatible properties without restriction by ethical concerns. Among these stem cells, multipotent mesenchymal stem cells (MSCs) from human adipose tissue are considered as an ideal source for various regenerative medicine. In spite of mesodermal origin of human adipose-derived stem cells (hADSCs), these cells have differentiation potential toward mesodermal and non-mesodermal lineages. Up to now, several studies have shown that hADSCs can undergo transdifferentiation and produce cells outside of their lineage, especially into neural cells when they are transferred to a specific cell environment. The purpose of this literature review is to provide an overview of the existing state of knowledge of the differentiation potential of hADSCs, specifically their ability to give rise to neuronal cells. The following review discusses different protocols considered for differentiation of hADSCs to neural cells, the neural markers that are used in each procedure and possible mechanisms that are involved in this differentiation.

Resveratrol Exerts Dosage-Dependent Effects on the Self-Renewal and Neural Differentiation of hUC-MSCs

Resveratrol (RES) plays a critical role in the fate of cells and longevity of animals via activation of the sirtuins1 (SIRT1) gene. In the present study, we intend to investigate whether RES could promote the self-renewal and neural-lineage differentiation in human umbilical cord derived MSCs (hUC-MSCs) in vitro at concentrations ranging from 0.1 to 10 μM, and whether it exerts the effects by modulating the SIRT1 signaling. Herein, we demonstrated that RES at the concentrations of 0.1, 1 and 2.5 μM could promote cell viability and proliferation, mitigate senescence and induce expression of SIRT1 and Proliferating Cell Nuclear Antigen (PCNA) while inhibit the expression of p53 and p16. However, the effects were reversed by 5 and 10 μM of RES. Furthermore, RES could promote neural differentiation in a dose-dependent manner as evidenced by morphological changes and expression of neural markers (Nestin, βIII-tubulin and NSE), as well as pro-neural transcription factors Neurogenin (Ngn)1, Ngn2 and Mash1. Taken together, RES exerts a dosage-dependent effect on the self-renewal and neural differentiation of hUC-MSCs via SIRT1 signaling. The current study provides a new strategy to regulate the fate of hUC-MSCs and suggests a more favorable in vitro cell culture conditions for hUC-MSCs-based therapies for some intractable neurological disorders.

Inducing Stem Cell Myogenesis Using NanoScript

Transcription factors (TFs) are multidomain proteins that play a critical role in orchestrating stem cell differentiation, but several limitations hinder the full potential of TF-based gene regulation. Here we report a unique strategy to emulate TFs and differentiate stem cells in a nonviral approach using an artificial, nanoparticle-based transcription factor called NanoScript. The NanoScript platform consists of a gold nanoparticle functionalized with small molecules that mimic the various domains of TFs. As a result, NanoScript mimics the function and structure of TF proteins. Specifically, NanoScript was designed to regulate muscle cell differentiation by targeting myogenic regulatory factors (MRFs), which play an important role in inducing myogenesis. This NanoScript-MRF is stable in physiological environments, localizes within the nucleus, induces differentiation of adipose-derived mesenchymal stem cells into mature muscle cells in 7 days, and is naturally excreted from induced muscle cells. As such, NanoScript represents a safe and powerful tool for applications requiring gene manipulation.

Current progress in use of adipose derived stem cells in peripheral nerve regeneration

Unlike central nervous system neurons; those in the peripheral nervous system have the potential for full regeneration after injury. Following injury, recovery is controlled by schwann cells which replicate and modulate the subsequent immune response. The level of nerve recovery is strongly linked to the severity of the initial injury despite the significant advancements in imaging and surgical techniques. Multiple experimental models have been used with varying successes to augment the natural regenerative processes which occur following nerve injury. Stem cell therapy in peripheral nerve injury may be an important future intervention to improve the best attainable clinical results. In particular adipose derived stem cells (ADSCs) are multipotent mesenchymal stem cells similar to bone marrow derived stem cells, which are thought to have neurotrophic properties and the ability to differentiate into multiple lineages. They are ubiquitous within adipose tissue; they can form many structures resembling the mature adult peripheral nervous system. Following early in vitro work; multiple small and large animal in vivo models have been used in conjunction with conduits, autografts and allografts to successfully bridge the peripheral nerve gap. Some of the ADSC related neuroprotective and regenerative properties have been elucidated however much work remains before a model can be used successfully in human peripheral nerve injury (PNI). This review aims to provide a detailed overview of progress made in the use of ADSC in PNI, with discussion on the role of a tissue engineered approach for PNI repair.

Differentiation of equine mesenchymal stromal cells into cells of neural lineage: potential for clinical applications

Mesenchymal stromal cells (MSCs) are able to differentiate into extramesodermal lineages, including neurons. Positive outcomes were obtained after transplantation of neurally induced MSCs in laboratory animals after nerve injury, but this is unknown in horses. Our objectives were to test the ability of equine MSCs to differentiate into cells of neural lineage in vitro, to assess differences in morphology and lineage-specific protein expression, and to investigate if horse age and cell passage number affected the ability to achieve differentiation. Bone marrow-derived MSCs were obtained from young and adult horses. Following demonstration of stemness, MSCs were neurally induced and microscopically assessed at different time points. Results showed that commercially available nitrogen-coated tissue culture plates supported proliferation and differentiation. Morphological changes were immediate and all the cells displayed a neural crest-like cell phenotype. Expression of neural progenitor proteins, was assessed via western blot or immunofluorescence. In our study, MSCs generated from young and middle-aged horses did not show differences in their ability to undergo differentiation. The effect of cell passage number, however, is inconsistent and further experiments are needed. Ongoing work is aimed at transdifferentiating these cells into Schwann cells for transplantation into a peripheral nerve injury model in horses.

Combined effect of nerve growth factor and brain‑derived neurotrophic factor on neuronal differentiation of neural stem cells and the potential molecular mechanisms

Neural stem cells (NSCs) are important pluripotent stem cells, which have potential applications in cell replacement therapy. Brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) have been demonstrated to exert a marked impact on the proliferation and differentiation of NSCs. The effects of NGF, BDNF, and BDNF combined with NGF on NSC neuronal differentiation and the possible mechanisms for these effects were investigated in this study. An adherent monolayer culture was employed to obtain highly homogeneous NSCs. The cells were divided into four groups: Control, NGF, BDNF and combination (BDNF + NGF) groups. Neuron differentiation was examined using immunocytochemistry and phospho-extracellular signal-regulated kinase (p-ERK) levels were analyzed using western blotting. Reverse transcription polymerase chain reaction was used to measure the mRNA expression levels of the HES1, HES5, MASH1, NGN1 and NeuroD transcription factors at different time intervals following neurotrophin-induced differentiation. NGF and BDNF were observed to induce NSC neuronal differentiation, and β-tubulin III-positive cells and p-ERK expression levels were highest in the NGF + BDNF combination group at all time points. The proportion of β-tubulin III-positive neurons in each group was associated with the expression levels of MASH1, NGN1 and NeuroD in the group. In conclusion, BDNF combined with NGF significantly improved NSC neuronal differentiation, which may provide support for the practical application of NSCs in neurodegenerative diseases.

Combination of acellular nerve graft and schwann cells-like cells for rat sciatic nerve regeneration

Objective. To investigate the effect of tissue engineering nerve on repair of rat sciatic nerve defect. Methods. Forty-five rats with defective sciatic nerve were randomly divided into three groups. Rats in group A were repaired by acellular nerve grafts only. Rats in group B were repaired by tissue engineering nerve. In group C, rats were repaired by autogenous nerve grafts. After six and twelve weeks, sciatic nerve functional index (SFI), neural electrophysiology (NEP), histological and transmission electron microscope observation, recovery ratio of wet weight of gastrocnemius muscle, regenerated myelinated nerve fibers number, nerve fiber diameter, and thickness of the myelin sheath were measured to assess the effect. Results. After six and twelve weeks, the recovery ratio of SFI and wet weight of gastrocnemius muscle, NEP, and the result of regenerated myelinated nerve fibers in groups B and C were superior to that of group A (P < 0.05), and the difference between groups B and C was not statistically significant (P > 0.05). Conclusion. The tissue engineering nerve composed of acellular allogenic nerve scaffold and Schwann cells-like cells can effectively repair the nerve defect in rats and its effect was similar to that of the autogenous nerve grafts.

Effect of ginsenoside Rg1 on proliferation and neural phenotype differentiation of human adipose-derived stem cells in vitro

AIMS

To investigate whether ginsenoside Rg1 can promote neural phenotype differentiation of human adipose-derived stem cells (hASCs) in vitro.

METHODS

hASCs were isolated from lipo-aspirates, and characterized by specific cell markers and multilineage differentiation capacity after culturing to the 3rd passage. Cultured hASCs were treated with neural inductive media alone (group A, control) or inductive media plus 10, 50, or 100 μg/mL ginsenoside Rg1 (groups B, C, and D, respectively). Cell proliferation was assessed by CCK-8 assay. Neuron specific enolase (NSE) and microtubule-associated protein-2 (MAP-2) levels were measured by Western blot. mRNA levels of growth associated protein-43 (GAP-43), neural cell adhesion molecule (NCAM), and synapsin-1 (SYN-1) were determined by real-time PCR.

RESULTS

Ginsenoside Rg1 promoted the proliferation of hASCs (groups B, C, and D) and resulted in higher expression of NSE and MAP-2 compared with the control group. Gene expression levels of GAP-43, NCAM, and SYN-1 in the test groups were higher than that in thw control. The results displayed a dose-dependent effect of ginsenoside Rg1 on cell proliferation and neural phenotype differentiation.

CONCLUSION

This study indicated that ginsenoside Rg1 promotes cell proliferation and neural phenotype differentiation of hASCs in vitro, suggesting a potential use for hASCs in neural regeneration medicine.

Neurogenesis of neural crest-derived periodontal ligament stem cells by EGF and bFGF

Neuroregenerative medicine is an ever-growing field in which regeneration of lost cells/tissues due to a neurodegenerative disease is the ultimate goal. With the scarcity of available replacement alternatives, stem cells provide an attractive source for regenerating neural tissue. While many stem cell sources exist, including: mesenchymal stem cells, embryonic stem cells, and induced pluripotent stem cells, the limited cellular potency, technical difficulties, and ethical considerations associated with these make finding alternate sources a desirable goal. Periodontal ligament stem cells (PDLSCs) derived from the neural crest were induced into neural-like cells using a combination of epidermal growth factor, and basic fibroblast growth factor. Morphological changes were evident in our treated group, seen under both light microscopy and scanning electron microscopy. A statistically significant increase in the expression of neuron-specific β-tubulin III and the neural stem/progenitor cell marker nestin, along with positive immunohistochemical staining for glial fibrillary acidic protein, demonstrated the success of our treatment in inducing both neuronal and glial phenotypes. Positive staining for synaptophysin demonstrated neural connections and electrophysiological recordings indicated that when subjected to whole-cell patch clamping, our treated cells displayed inward currents conducted through voltage-gated sodium (Na(+) ) channels. Taken together, our results indicate the success of our treatment in inducing PDLSCs to neural-like cells. The ease of sourcing and expansion, their embryologic neural crest origin, and the lack of ethical implications in their use make PDLSCs an attractive source for use in neuroregenerative medicine.

Expression of neural markers by undifferentiated mesenchymal-like stem cells from different sources

The spontaneous expression of neural markers, already demonstrated in bone marrow (BM) mesenchymal stem cells (MSCs), has been considered as evidence of the MSCs' predisposition to differentiate toward neural lineages, supporting their use in stem cell-based therapy for neural repair. In this study we have evaluated, by immunocytochemistry, immunoblotting, and flow cytometry experiments, the expression of neural markers in undifferentiated MSCs from different sources: human adipose stem cells (hASCs), human skin-derived mesenchymal stem cells (hS-MSCs), human periodontal ligament stem cells (hPDLSCs,) and human dental pulp stem cells (hDPSCs). Our results demonstrate that the neuronal markers βIII-tubulin and NeuN, unlike other evaluated markers, are spontaneously expressed by a very high percentage of undifferentiated hASCs, hS-MSCs, hPDLSCs, and hDPSCs. Conversely, the neural progenitor marker nestin is expressed only by a high percentage of undifferentiated hPDLSCs and hDPSCs. Our results suggest that the expression of βIII-tubulin and NeuN could be a common feature of stem cells and not exclusive to neuronal cells. This could result in a reassessment of the use of βIII-tubulin and NeuN as the only evidence proving neuronal differentiation. Further studies will be necessary to elucidate the relevance of the spontaneous expression of these markers in stem cells.

Current applications of adipose-derived stem cells and their future perspectives

Adult stem cells have a great potential to treat various diseases. For these cell-based therapies, adipose-derived stem cells (ADSCs) are one of the most promising stem cell types, including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). ESCs and iPSCs have taken center stage due to their pluripotency. However, ESCs and iPSCs have limitations in ethical issues and in identification of characteristics, respectively. Unlike ESCs and iPSCs, ADSCs do not have such limitations and are not only easily obtained but also uniquely expandable. ADSCs can differentiate into adipocytes, osteoblasts, chondrocytes, myocytes and neurons under specific differentiation conditions, and these kinds of differentiation potential of ADSCs could be applied in regenerative medicine e.g., skin reconstruction, bone and cartilage formation, etc. In this review, the current status of ADSC isolation, differentiation and their therapeutic applications are discussed.