Comparison of phenotypic markers and neural differentiation potential of multipotent adult progenitor cells and mesenchymal stem cells

A Review of the Evidence for Tryptophan and the Kynurenine Pathway as a Regulator of Stem Cell Niches in Health and Disease

Stem cells are ubiquitously found in various tissues and organs in the body, and underpin the body's ability to repair itself following injury or disease initiation, though repair can sometimes be compromised. Understanding how stem cells are produced, and functional signaling systems between different niches is critical to understanding the potential use of stem cells in regenerative medicine. In this context, this review considers kynurenine pathway (KP) metabolism in multipotent adult progenitor cells, embryonic, haematopoietic, neural, cancer, cardiac and induced pluripotent stem cells, endothelial progenitor cells, and mesenchymal stromal cells. The KP is the major enzymatic pathway for sequentially catabolising the essential amino acid tryptophan (TRP), resulting in key metabolites including kynurenine, kynurenic acid, and quinolinic acid (QUIN). QUIN metabolism transitions into the adjoining de novo pathway for nicotinamide adenine dinucleotide (NAD) production, a critical cofactor in many fundamental cellular biochemical pathways. How stem cells uptake and utilise TRP varies between different species and stem cell types, because of their expression of transporters and responses to inflammatory cytokines. Several KP metabolites are physiologically active, with either beneficial or detrimental outcomes, and evidence of this is presented relating to several stem cell types, which is important as they may exert a significant impact on surrounding differentiated cells, particularly if they metabolise or secrete metabolites differently. Interferon-gamma (IFN-γ) in mesenchymal stromal cells, for instance, highly upregulates rate-limiting enzyme indoleamine-2,3-dioxygenase (IDO-1), initiating TRP depletion and production of metabolites including kynurenine/kynurenic acid, known agonists of the Aryl hydrocarbon receptor (AhR) transcription factor. AhR transcriptionally regulates an immunosuppressive phenotype, making them attractive for regenerative therapy. We also draw attention to important gaps in knowledge for future studies, which will underpin future application for stem cell-based cellular therapies or optimising drugs which can modulate the KP in innate stem cell populations, for disease treatment.

Novel perspectives on the therapeutic role of cryptotanshinone in the management of stem cell behaviors for high-incidence diseases

Cryptotanshinone (CTS), a diterpenoid quinone, is found mostly in Salvia miltiorrhiza Bunge (S. miltiorrhiza) and plays a crucial role in many cellular processes, such as cell proliferation/self-renewal, differentiation and apoptosis. In particular, CTS’s profound physiological impact on various stem cell populations and their maintenance and fate determination could improve the efficiency and accuracy of stem cell therapy for high-incidence disease. However, as much promise CTS holds, these CTS-mediated processes are complex and multifactorial and many of the underlying mechanisms as well as their clinical significance for high-incidence diseases are not yet fully understood. This review aims to shed light on the impact and mechanisms of CTS on the actions of diverse stem cells and the involvement of CTS in the many processes of stem cell behavior and provide new insights for the application of CTS and stem cell therapy in treating high-incidence diseases.

Induced Neurodifferentiation of hBM-MSCs through Activation of the ERK/CREB Pathway via Pulsed Electromagnetic Fields and Physical Stimulation Promotes Neurogenesis in Cerebral Ischemic Models

Stroke is among the leading causes of death worldwide, and stroke patients are more likely to live with permanent disabilities even after treatment. Several treatments are being developed to improve the quality of life of patients; however, these treatments still have important limitations. Our study thus sought to evaluate the neural differentiation of human bone marrow mesenchymal stem cells (hBM-MSCs) at various pulsed electromagnetic field (PEMF) frequencies. Furthermore, the effects of selected frequencies in vivo were also evaluated using a mouse ischemia stroke model. Cell proliferation decreased by 20% in the PEMF group, as demonstrated by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay, and lactate dehydrogenase (LDH) secretion increased by approximately 10% in an LDH release assay. Fluorescence-activated cell sorting (FACS) analysis demonstrated that CD73 and CD105 were downregulated in the PEMF group at 60 Hz. Moreover, microtubule-associated protein 2 (MAP-2) and neurofilament light chain (NF-L) were upregulated in cell cultures at 60 and 75 Hz. To assess the effects of PEMF in vivo, cerebral ischemia mice were exposed to a PEMF at 60 Hz. Neural-related proteins were significantly upregulated in the PEMF groups compared with the control and cell group. Upon conducting rotarod tests, the cell/PEMF group exhibited significant differences in motor coordination at 13 days post-treatment when compared with the control and stem-cell-treated group. Furthermore, the cell and cell/PEMF group exhibited a significant reduction in the expression of matrix metalloproteinase-9 (MMP-9), tumor necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ) in the induced ischemic area compared with the control. Collectively, our findings demonstrated that PEMFs at 60 and 75 Hz could stimulate hBM-MSCs neural differentiation in vitro, in addition to promoting neurogenesis to enhance the functional recovery process by reducing the post-stroke inflammatory reaction.

The intravenous administration of skin-derived mesenchymal stem cells ameliorates hearing loss and preserves cochlear hair cells in cisplatin-injected mice: SMSCs ameliorate hearing loss and preserve outer hair cells in mice

Mesenchymal stem cells (MSCs) can be isolated from different tissue origins, such as the bone marrow, the placenta, the umbilical cord, adipose tissues, and skin tissues. MSCs can secrete anti-inflammatory molecules and growth factors for tissue repair and remodeling. However, the ability of skin-derived MSCs (SMSCs) to repair cochlear damage and ameliorate hearing loss remains unclear. Cisplatin is a commonly used chemotherapeutic agent that has the side effect of ototoxicity due to inflammation and oxidative stress. This study investigated the effects of SMSCs on cisplatin-induced hearing loss in mice. Two independent experiments were designed for modeling cisplatin-induced hearing loss in mice, one for chronic toxicity (4 mg/kg intraperitoneal [IP] injection once per day for 5 consecutive days) and the other for acute toxicity (25 mg/kg IP injection once on day one). Three days after cisplatin injection, 1 × 10⁶ or 3 × 10⁶ SMSCs were injected through the tail vein. Data on auditory brain responses suggested that SMSCs could significantly reduce the hearing threshold of cisplatin-injected mice. Furthermore, immunohistochemical staining data suggested that SMSCs could significantly ameliorate the loss of cochlear hair cells, TUNEL-positive cells and cleaved caspase 3-positive cells in cisplatin-injected mice. Neuropathological gene analyses revealed that SMSCs treatment could downregulate the expression of cochlear genes involved in apoptosis, autophagy, chromatin modification, disease association, matrix remodeling, oxidative stress, tissue integrity, transcription, and splicing and unfolded protein responses. Additionally, SMSCs treatment could upregulate the expression of cochlear genes affecting the axon and dendrite structures, cytokines, trophic factors, the neuronal skeleton and those involved in carbohydrate metabolism, growth factor signaling, myelination, neural connectivity, neural transmitter release, neural transmitter response and reuptake, neural transmitter synthesis and storage, and vesicle trafficking. Results from TUNEL and caspase 3 staining further confirmed that cisplatin-induced apoptosis in cochlear tissues of cisplatin-injected mice could be reduced by SMSCs treatment. In conclusion, the evidence of the effects of SMSCs in favor of ameliorating ototoxicity-induced hearing loss suggests a potential clinical application.

Monitoring maturation of neural stem cell grafts within a host microenvironment

Neural stem cells (NSC) act as a versatile tool for neuronal cell replacement strategies to treat neurodegenerative disorders in which functional neurorestorative mechanisms are limited. While the beneficial effects of such cell-based therapy have already been documented in terms of neurodegeneration of various origins, a neurophysiological basis for improvement in the recovery of neurological function is still not completely understood. This overview briefly describes the cumulative evidence from electrophysiological studies of NSC-derived neurons, aimed at establishing the maturation of differentiated neurons within a host microenvironment, and their integration into the host circuits, with a particular focus on the neurogenesis of NSC grafts within the post-ischemic milieu. Overwhelming evidence demonstrates that the host microenvironment largely regulates the lineage of NSC grafts. This regulatory role, as yet underestimated, raises possibilities for the favoured maturation of a subset of neural phenotypes in order to gain timely remodelling of the impaired brain tissue and amplify the therapeutic effects of NSC-based therapy for recovery of neurological function.

A Comparison of Phenotypic and Functional Properties of Mesenchymal Stromal Cells and Multipotent Adult Progenitor Cells

Both Multipotent Adult Progenitor Cells and Mesenchymal Stromal Cells are bone-marrow derived, non-haematopoietic adherent cells, that are well-known for having immunomodulatory and pro-angiogenic properties, whilst being relatively non-immunogenic. However, they are phenotypically and functionally distinct cell types, which has implications for their efficacy in different settings. In this review we compare the phenotypic and functional properties of these two cell types, to help in determining which would be the superior cell type for different applications.

MicroRNA-135a-5p promotes neuronal differentiation of pluripotent embryonal carcinoma cells by repressing Sox6/CD44 pathway

MicroRNA-135a-5p has been reported to play a potential role in the generation of new neurons. However, the underlying targets of miR-135a-5p in regulating neuronal differentiation have been poorly understood. Our study recently has uncovered that Sox6 and CD44 genes were significantly downregulated during neuronal differentiation of P19 cells, a multipotent cell type. We then found that Sox6 directly bound to the promoter of CD44. Importantly, we identified Sox6 as a direct target of miR-135a-5p. Additionally, we demonstrated that miR-135a-5p is crucial for the neuronal differentiation of P19 cells. More significantly, we found that Sox6 overexpression could overturn miR-135a-5p-mediated neuronal differentiation and dendrite development. In conclusion, these findings indicated that miR-135a-5p/Sox6/CD44 axis provides an important molecular target mechanism for neurodifferentiation.

Therapeutic efficacy of multipotent adult progenitor cells versus mesenchymal stem cells in experimental autoimmune encephalomyelitis

AIM

In this study, we have evaluated the therapeutic efficacy of mouse multipotent adult progenitor cells (mMAPCs) in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, and compared it with mouse mesenchymal stem cells (mMSCs).

MATERIALS & METHODS

We administered PKH26-labeled mMAPC and mMSC into EAE mice and evaluated their therapeutic efficacy.

RESULTS

The mMAPC-treated mice in comparison with the mMSC group exhibited a higher suppression of EAE (p < 0.05), and a higher fold expression of neuronal genes GAP43, NG2, PDGFR, Nestin, SMI 32, BDNF and NT 3 in spinal cord (p < 0.05), suggesting a better neuroprotective and regenerative potential of mMAPC than mMSC.

CONCLUSION

MAPC may be a potential cell type, which is superior to mesenchymal stem cell for the treatment of EAE/multiple sclerosis.

In patients with chronic aplastic anemia, bone marrow-derived MSCs regulate the Treg/Th17 balance by influencing the Notch/RBP-J/FOXP3/RORγt pathway

The standard treatment for aplastic anemia (AA) in young patients is a matched sibling hematopoietic stem cell transplant. Transfusion of a chronic AA patient with allogeneic bone marrow–derived mesenchymal stromal cells (BMMSCs) is currently being developed as a cell-based therapy, and the safety and efficacy of such transfusions are being continuously improved. Nevertheless, the mechanisms by which BMMSCs exert their therapeutic effects remain to be elucidated. In this study, mesenchymal stromal cells (MSCs) obtained from bone marrow donors were concentrated and intravenously injected into 15 chronic AA patients who had been refractory to prior immunosuppressive therapy. We showed that BMMSCs modulate the levels of Th1, Th2, Th17 and Treg cells, as well as their related cytokines in chronic AA patients. Furthermore, the percentages of Th1 and Th17 cells among the H-MSCs decreased significantly, while the percentage Treg cells increased. The Notch/RBP-J/FOXP3/RORγt pathway was involved in modulating the Treg/Th17 balance after MSCs were transfused in vitro. Additionally, the role played by transfused MSCs in regulating the Treg/Th17 balance via the Notch/RBP-J/FOXP3/RORγt pathway was further confirmed in an AA mouse model. In summary, in humans with chronic AA, BMMSCs regulate the Treg/Th17 balance by affecting the Notch/RBP-J/FOXP3/RORγt pathway.

All the Tested Human Somatic Cells Express Both Oct4A and Its Pseudogenes but Express Oct4A at Much Lower Levels Compared with Its Pseudogenes and Human Embryonic Stem Cells

Oct4 pseudogenes and isoforms seriously confuse the detection of the pluripotency-associated Oct4A expression in somatic cells, which in many cases was not accurately determined. This confusion has recently been discussed, but the wrong conclusions have continuously been made. Most studies failed to detect the expression of Oct4 pseudogenes and isoforms in somatic cells but detected only Oct4A, for which the detection signals incorrectly came from its pseudogenes and isoforms. Some studies detected the expression of only Oct4 pseudogenes in somatic cells but failed to detect Oct4A. The other studies failed to detect the expression of any Oct4 genes. Oct4A is more homologous to its pseudogenes than its isoforms, and it is much more difficult to distinguish Oct4A from its pseudogenes, so this study focused on them. In this study, the strict experimental procedures were followed. Three pairs of Oct4A-specific polymerase chain reaction (PCR) primers were carefully designed and tested by sequencing reverse transcription-polymerase chain reaction (RT-PCR) clones, which showed that only one of them was truly specific to Oct4A. RT-PCR was also performed with the primers amplifying both Oct4A and its pseudogenes, and several hundreds of PCR clones from each cell type were sequenced to reliably distinguish the low-abundant Oct4A from its high-abundant pseudogenes. Western blot, immunocytochemistry, and flow cytometric analyses were performed with three Oct4 antibodies to confirm the results of Oct4 mRNA expression. This study undoubtedly made the correct conclusions about Oct4 expression in human somatic cells and showed that all the tested human somatic cells expressed both Oct4A and its pseudogenes but expressed Oct4A at much lower levels compared with its pseudogenes.

Beneficial effects of bone marrow-derived mesenchymal stem cell transplantation in a non-immune model of demyelination

Multiple sclerosis (MS) is an autoimmune disease characterized by demyelination and axonal loss throughout the central nervous system. Most of the previous studies that have been conducted to evaluate the efficacy of mesenchymal stem cells (MSCs) have utilized immune models such as experimental autoimmune encephalomyelitis (EAE). However, with this experimental setting, it is not clear whether the MSCs exert the functional improvement via an indirect consequence of MSC-mediated immunomodulation or via a direct replacement of the lost cells, paracrine actions, and/or an enhancement of endogenous repair. This study is the first to demonstrate the capability of intravenously injected bone marrow-derived MSCs (BM-MSCs) to migrate, engraft, and improve the demyelination in the non-immune cuprizone model of MS. The ultrastructural analysis conducted in this study revealed that the observed histological improvement was due to both reduced demyelination and enhanced remyelination. However, the detected remyelination was not graft-derived as no differentiation of the transplanted cells towards the oligodendroglial phenotype was detected. In addition, the transplanted cells modulated the glial response and reduced apoptosis. These results suggest that the therapeutic potential of BM-MSCs for MS is not only dependent on their immunosuppressive and immunomodulatory nature but also on their ability to enhance endogenous repair and induce oligo/neuroprotection. Proving the efficacy of BM-MSCs in a non-immune model of MS and evaluating the underlying mechanisms should enrich our knowledge of how these cells exert their beneficial effects and may eventually help us to enhance and maintain an efficacious and sustainable cell therapy for MS.

Concise review: Stem cell therapies for amyotrophic lateral sclerosis: recent advances and prospects for the future

Amyotrophic lateral sclerosis (ALS) is a lethal disease involving the loss of motor neurons. Although the mechanisms responsible for motor neuron degeneration in ALS remain elusive, the development of stem cell-based therapies for the treatment of ALS has gained widespread support. Here, we review the types of stem cells being considered for therapeutic applications in ALS, and emphasize recent preclinical advances that provide supportive rationale for clinical translation. We also discuss early trials from around the world translating cellular therapies to ALS patients, and offer important considerations for future clinical trial design. Although clinical translation is still in its infancy, and additional insight into the mechanisms underlying therapeutic efficacy and the establishment of long-term safety are required, these studies represent an important first step toward the development of effective cellular therapies for the treatment of ALS.

Epigallocatechin-3-gallate suppresses the lipid deposition through the apoptosis during differentiation in bovine bone marrow mesenchymal stem cells

Epigallocatechin gallate (EGCG), a major component of tea, has known effects on obesity, fatty liver, and obesity-related cancer. We explored the effects of EGCG on the differentiation of bovine mesenchymal stem cells (BMSCs, which are multipotent) in a dose- and time-dependent manner. Differentiating BMSCs were exposed to various concentrations of EGCG (0, 10, 50, 100, and 200 µM) for 2, 4, and 6 days. BMSCs were cultured in Dulbecco's modified Eagle's medium (DMEM)/high-glucose medium with adipogenic inducers for 6 days, and the expression levels of various genes involved in adipogenesis were measured using real-time polymerase chain reaction (PCR) and Western blotting. We assessed apoptosis by flow cytometry and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining of control and EGCG-exposed cells. We found that EGCG significantly suppressed fat deposition and cell viability (P < 0.05). The mRNA and protein levels of various adipogenic factors were measured. Expression of the genes encoding peroxisome proliferator-activated receptor gamma (PPARG), CCAAT/enhancer-binding protein alpha (CEBPA), fatty acid-binding protein 4 (FABP4), and stearoyl-CoA desaturase (SCD) were diminished by EGCG during adipogenic differentiation (P < 0.05). We also found that EGCG lowered the expression levels of the adipogenic proteins encoded by these genes (P < 0.05). EGCG induced apoptosis during adipogenic differentiation (P < 0.05). Thus, exposure to EGCG potentially inhibits adipogenesis by triggering apoptosis; the data suggest that EGCG inhibits adipogenic differentiation in BMSCs.

Bone marrow mesenchymal stem cells overexpressing human basic fibroblast growth factor increase vasculogenesis in ischemic rats

Administration or expression of growth factors, as well as implantation of autologous bone marrow cells, promote in vivo angiogenesis. This study investigated the angiogenic potential of combining both approaches through the allogenic transplantation of bone marrow-derived mesenchymal stem cells (MSCs) expressing human basic fibroblast growth factor (hbFGF). After establishing a hind limb ischemia model in Sprague Dawley rats, the animals were randomly divided into four treatment groups: MSCs expressing green fluorescent protein (GFP-MSC), MSCs expressing hbFGF (hbFGF-MSC), MSC controls, and phosphate-buffered saline (PBS) controls. After 2 weeks, MSC survival and differentiation, hbFGF and vascular endothelial growth factor (VEGF) expression, and microvessel density of ischemic muscles were determined. Stable hbFGF expression was observed in the hbFGF-MSC group after 2 weeks. More hbFGF-MSCs than GFP-MSCs survived and differentiated into vascular endothelial cells (P<0.001); however, their differentiation rates were similar. Moreover, allogenic transplantation of hbFGF-MSCs increased VEGF expression (P=0.008) and microvessel density (P<0.001). Transplantation of hbFGF-expressing MSCs promoted angiogenesis in an in vivo hind limb ischemia model by increasing the survival of transplanted cells that subsequently differentiated into vascular endothelial cells. This study showed the therapeutic potential of combining cell-based therapy with gene therapy to treat ischemic disease.

Acute graft-versus-host disease: a bench-to-bedside update

Over the past 5 years, many novel approaches to early diagnosis, prevention, and treatment of acute graft-versus-host disease (aGVHD) have been translated from the bench to the bedside. In this review, we highlight recent discoveries in the context of current aGVHD care. The most significant innovations that have already reached the clinic are prophylaxis strategies based upon a refinement of our understanding of key sensors, effectors, suppressors of the immune alloreactive response, and the resultant tissue damage from the aGVHD inflammatory cascade. In the near future, aGVHD prevention and treatment will likely involve multiple modalities, including small molecules regulating immunologic checkpoints, enhancement of suppressor cytokines and cellular subsets, modulation of the microbiota, graft manipulation, and other donor-based prophylaxis strategies. Despite long-term efforts, major challenges in treatment of established aGVHD still remain. Resolution of inflammation and facilitation of rapid immune reconstitution in those with only a limited response to corticosteroids is a research arena that remains rife with opportunity and urgent clinical need.

Enhanced adipogenicity of bone marrow mesenchymal stem cells in aplastic anemia

Fatty bone marrow (BM) and defective hematopoiesis are a pathologic hallmark of aplastic anemia (AA). We have investigated adipogenic and osteogenic potential of BM mesenchymal stem cells (BM-MSC) in 10 AA patients (08 males and 02 females) with median age of 37 years (range: 06 to 79 years) and in the same number of age and sex matched controls. It was observed that BM-MSC of AA patients had a morphology, phenotype, and osteogenic differentiation potential similar to control subjects but adipocytes differentiated from AA BM-MSC had a higher density and larger size of lipid droplets and they expressed significantly higher levels of adiponectin and FABP4 genes and proteins as compared to control BM-MSC (P < 0.01 for both). Thus our data shows that AA BM-MSC have enhanced adipogenicity, which may have an important implication in the pathogenesis of the disease.

Role of mesenchymal stem cells in cell life and their signaling

Mesenchymal stem cells (MSCs) have various roles in the body and cellular environment, and the cellular phenotypes of MSCs changes in different conditions. MSCs support the maintenance of other cells, and the capacity of MSCs to differentiate into several cell types makes the cells unique and full of possibilities. The involvement of MSCs in the epithelial-mesenchymal transition is an important property of these cells. In this review, the role of MSCs in cell life, including their application in therapy, is first described, and the signaling mechanism of MSCs is investigated for a further understanding of these cells.