The secretome of bone marrow mesenchymal stem cells-conditioned media varies with time and drives a distinct effect on mature neurons and glial cells (primary cultures)

The Central Nervous System Source Modulates Microglia Function and Morphology In Vitro

The regional heterogeneity of microglia was first described a century ago by Pio del Rio Hortega. Currently, new information on microglia heterogeneity throughout central nervous system (CNS) regions is being revealed by high-throughput techniques. It remains unclear whether these spatial specificities translate into different microglial behaviors in vitro. We cultured microglia isolated from the cortex and spinal cord and analyzed the effect of the CNS spatial source on behavior in vitro by applying the same experimental protocol and culture conditions. We analyzed the microglial cell numbers, function, and morphology and found a distinctive in vitro phenotype. We found that microglia were present in higher numbers in the spinal-cord-derived glial cultures, presenting different expressions of inflammatory genes and a lower phagocytosis rate under basal conditions or after activation with LPS and IFN-γ. Morphologically, the cortical microglial cells were more complex and presented longer ramifications, which were also observed in vivo in CX3CR1^+/GFP transgenic reporter mice. Collectively, our data demonstrated that microglial behavior in vitro is defined according to specific spatial characteristics acquired by the tissue. Thus, our study highlights the importance of microglia as a source of CNS for in vitro studies.

Characterisation of mesenchymal stem cells conditioned media obtained at different conditioning times: their effect on glial cells in in vitro scratch model

In this study, the bone marrow mesenchymal stem cells conditioned media (BMMSC-CM) obtained by conditioning for 24(CM24), 48(CM48) and 72(CM72) hours was characterised. In vitro, the impact of BMMSC-CM on the astrocyte migratory response and oligodendrocyte density was evaluated using the scratch model. The proteomic profiles of individual secretomes were analysed by mass spectrometry and the concentrations of four selected neurotrophins (BDNF, NGF, GDNF and VEGF) were determined by ELISA. Our results revealed an increased number of proteins at CM72, many of which are involved in neuroregenerative processes. ELISA documented a gradual increase in the concentration of two neurotrophins (NGF, VEGF), peaking at CM72. In vitro, the different effect of individual BMMSC-CM on astrocyte migration response and oligodendrocyte density was observed, most pronounced with CM72. The outcomes demonstrate that the prolonged conditioning results in increased release of detectable proteins, neurotrophic factors concentration and stronger effect on reparative processes in neural cell cultures.

Mesenchymal stromal cells for the treatment of Alzheimer’s disease: Strategies and limitations

Alzheimer’s disease (AD) is a major cause of age-related dementia and is characterized by progressive brain damage that gradually destroys memory and the ability to learn, which ultimately leads to the decline of a patient’s ability to perform daily activities. Although some of the pharmacological treatments of AD are available for symptomatic relief, they are not able to limit the progression of AD and have several side effects. Mesenchymal stem/stromal cells (MSCs) could be a potential therapeutic option for treating AD due to their immunomodulatory, anti-inflammatory, regenerative, antioxidant, anti-apoptotic, and neuroprotective effects. MSCs not only secret neuroprotective and anti-inflammatory factors to promote the survival of neurons, but they also transfer functional mitochondria and miRNAs to boost their bioenergetic profile as well as improve microglial clearance of accumulated protein aggregates. This review focuses on different clinical and preclinical studies using MSC as a therapy for treating AD, their outcomes, limitations and the strategies to potentiate their clinical translation.

Cell transplantation and secretome based approaches in spinal cord injury regenerative medicine

The axonal growth-restrictive character of traumatic spinal cord injury (SCI) makes finding a therapeutic strategy a very demanding task, due to the postinjury events impeditive to spontaneous axonal outgrowth and regeneration. Considering SCI pathophysiology complexity, it has been suggested that an effective therapy should tackle all the SCI-related aspects and provide sensory and motor improvement to SCI patients. Thus, the current aim of any therapeutic approach for SCI relies in providing neuroprotection and support neuroregeneration. Acknowledging the current SCI treatment paradigm, cell transplantation is one of the most explored approaches for SCI with mesenchymal stem cells (MSCs) being in the forefront of many of these. Studies showing the beneficial effects of MSC transplantation after SCI have been proposing a paracrine action of these cells on the injured tissues, through the secretion of protective and trophic factors, rather than attributing it to the action of cells itself. This manuscript provides detailed information on the most recent data regarding the neuroregenerative effect of the secretome of MSCs as a cell-free based therapy for SCI. The main challenge of any strategy proposed for SCI treatment relies in obtaining robust preclinical evidence from in vitro and in vivo models, before moving to the clinics, so we have specifically focused on the available vertebrate and mammal models of SCI currently used in research and how can SCI field benefit from them.

Minocycline exhibits synergism with conditioned medium of bone marrow mesenchymal stem cells against ischemic stroke

Several lines of evidence show that a conditioned medium of bone marrow mesenchymal stem cells (BM-MSCcm) improve functional recovery after ischemic stroke but do not reduce ischemic lesions. It is important to develop a treatment strategy that can exhibit a synergistic effect with BM-MSCcm against ischemic stroke. In this study, the effect of BM-MSCcm and/or minocycline was examined in culture and in a middle cerebral artery occlusion (MCAo) animal model. In neuron-glial cultures, BM-MSCcm and combined treatment, but not minocycline, effectively increased neuronal connection and oligodendroglial survival. In contrast, minocycline and combined treatment, but not BM-MSCcm, reduced toxin-induced free radical production in cultures. Either minocycline or BM-MSCcm, or in combination, conferred protective effects against oxygen glucose deprivation-induced cell damage. In an in vivo study, BM-MSCcm and minocycline were administered to rats 2 h after MCAo. Monotherapy with BM-MSCcm or minocycline after ischemic stroke resulted in 9.4% or 17.5% reduction in infarction volume, respectively, but there was no significant difference. Interestingly, there was a 33.9% significant reduction in infarction volume by combined treatment with BM-MSCcm and minocycline in an in vivo study. The combined therapy also significantly improved grasping power, which was not altered by monotherapy. Furthermore, combined therapy increased the expression of neuronal nuclei in the peri-infarct area and hippocampus, and concurrently decreased the expression of ED1 in rat brain and the peri-infarct zone. Our data suggest that minocycline exhibits a synergistic effect with BM-MSCcm against ischemic stroke not only to improve neurological functional outcome but also to reduce cerebral infarction.

The Neuroprotective Effect of Conditioned Medium from Human Adipose-Derived Mesenchymal Stem Cells is Impaired by N-acetyl Cysteine Supplementation

Oxidative stress is a common feature in neurodegenerative diseases associated with neuroinflammation, and therefore, has been proposed as a key target for novel therapies for these diseases. Recently, adipose-derived stem cell (ASC)-based cell therapy has emerged as a novel strategy for neuroprotection. In this study, we evaluate the therapeutic role of ASC-conditioned medium (ASC-CM) against H₂O₂-induced neurotoxicity in a new in vitro model of ec23/brain-derived neurotrophic factor (BDNF)-differentiated human SH-SY5Y neuron-like cells (SH-SY5Yd). In the presence of ASC-CM, stressed SH-SY5Yd cells recover normal axonal morphology (with an almost complete absence of H₂O₂-induced axonal beading), electrophysiological features, and cell viability. This beneficial effect of ASC-CM was associated with its antioxidant capacity and the presence of growth factors, namely, BDNF, glial cell line-derived neurotrophic factor, and transforming growth factor β1. Moreover, the neuroprotective effect of ASC-CM was very similar to that obtained from treatment with BDNF, an essential factor for SH-SY5Yd cell survival. Importantly, we also found that the addition of the antioxidant agent N-acetyl cysteine to ASC-CM abolished its restorative effect; this was associated with a strong reduction in reactive oxygen species (ROS), in contrast to the moderate decrease in ROS produced by ASC-CM alone. These results suggest that neuronal restorative effect of ASC-CM is associated with not only the release of essential neurotrophic factors, but also the maintenance of an appropriate redox state to preserve neuronal function.

Mesenchymal Stem Cells-derived Exosomes: A New Possible Therapeutic Strategy for Parkinson's Disease?

Parkinson’s disease (PD) is the second most prevalent neurodegenerative disorder worldwide. Clinically, it is characterized by severe motor complications caused by a progressive degeneration of dopaminergic neurons (DAn) and dopamine loss. Current treatment is focused on mitigating the symptoms through administration of levodopa, rather than on preventing DAn damage. Therefore, the use and development of neuroprotective/disease-modifying strategies is an absolute need, which can lead to promising gains on PD translational research. Mesenchymal stem cells (MSCs)–derived exosomes have been proposed as a promising therapeutic tool, since it has been demonstrated that they can act as biological nanoparticles with beneficial effects in different pathological conditions, including PD. Thus, considering their potential protective action in lesioned sites, MSCs-derived exosomes might also be active modulators of the neuroregeneration processes, opening a door for their future use as therapeutical strategies in human clinical trials. Therefore, in this review, we analyze the current understanding of MSCs-derived exosomes as a new possible therapeutic strategy for PD, by providing an overview about the potential role of miRNAs in the cellular and molecular basis of PD.

Influence of passage number on the impact of the secretome of adipose tissue stem cells on neural survival, neurodifferentiation and axonal growth

Mesenchymal stem cells (MSCs), and within them adipose tissue derived stem cells (ASCs), have been shown to have therapeutic effects on central nervous system (CNS) cell populations. Such effects have been mostly attributed to soluble factors, as well as vesicles, present in their secretome. Yet, little is known about the impact that MSC passaging might have in the secretion therapeutic profile. Our aim was to show how human ASCs (hASCs) passage number influences the effect of their secretome in neuronal survival, differentiation and axonal growth. For this purpose, post-natal rat hippocampal primary cultures, human neural progenitor cell (hNPCs) cultures and dorsal root ganglia (DRGs) explants were incubated with secretome, collected as conditioned media (CM), obtained from hASCs in P3, P6, P9 and P12. Results showed no differences when comparing percentages of MAP-2 positive cells (a mature neuronal marker) in neuronal cultures or hNPCs, after incubation with hASCs secretome from different passages. The same was observed regarding DRG neurite outgrowth. In order to characterize the secretomes obtained from different passages, a proteomic analysis was performed, revealing that its composition did not vary significantly with passage number P3 to P12. Results allowed us to identify several key proteins, such as pigment epithelium derived factor (PEDF), DJ-1, interleucin-6 (IL-6) and galectin, all of which have already proven to play neuroprotective and neurodifferentiating roles. Proteins that promote neurite outgrowth were also found present, such as semaphorin 7A and glypican-1. We conclude that cellular passaging does not influence significantly hASCs's secretome properties especially their ability to support post-natal neuronal survival, induce neurodifferentiation and promote axonal growth.

Exploiting the impact of the secretome of MSCs isolated from different tissue sources on neuronal differentiation and axonal growth

Cell transplantation using Mesenchymal stem cell (MSC) secretome have recently been presented as a possible free-based therapy for CNS related disorders. MSC secretome is rich in several bio-factors that act synergically towards the repair of damaged tissues, thus making it an ideal candidate for regenerative applications. Great effort is currently being made to map the molecules that compose the MSC secretome. Previous proteomic characterization of the secretome (in the form of conditioned media - CM) of MSCs derived from adipose tissue (ASC), bone-marrow (BMSC) and umbilical cord (HUCPVC) was performed by our group, where proteins relevant for neuroprotection, neurogenic, neurodifferentiation, axon guidance and growth functions were identified. Moreover, we have found significant differences among the expression of several molecules, which may indicate that their therapeutic outcome might be distinct. Having this in mind, in the present study, the neuroregulatory potential of ASC, BMSC and HUCPVC CM in promoting neurodifferentiation and axonal outgrowth was tested in vitro, using human telencephalon neuroprogenitor cells and dorsal root ganglion explants, respectively. The CM from the three MSC populations induced neuronal differentiation from human neural progenitor cells, as well as neurite outgrowth from dorsal root ganglion explants. Moreover, all the MSC populations promoted the same extent of neurodifferentiation, while ASC CM demonstrated higher potential in promoting axonal growth.

The neuroprotective effect of rat adipose tissue-derived mesenchymal stem cell-conditioned medium on cortical neurons using an in vitro model of SCI inflammation

Objectives In this study, a new approach was used with an in vitro model in which neural cells were exposed to conditioned media from the injured spinal cord (SCI-CM) mimicking a local inflammatory microenvironment . Subsequently, the neuroprotective effect of rat adipose tissue-derived msesenchymal stem cell-conditioned media (ATMSC-CM) was investigated through a cell-free based therapy, which was used to treat cortical neurons and astrocytes under inflammation. Methods Primary cell cultures isolated from postnatal day (P6) Wistar rat brain cortex were exposed to SCI-CM derived from the central lesion, rostral and caudal segments of injured spinal cord. After 48 h incubation, the SCI-CM was replaced and primary cultures were cultivated either in DMEM media alone or in ATMSC-CM for 72 h. The impact of ATMSC-CM on the viability of neurons and astrocytes was assessed using a CyQUANT® Direct Cell Proliferation Assay Kit as well as immunocytochemistry analysis. Results Immunocytochemical analysis revealed significant decrease in the number of MAP2 positive neurons exposed to SCI-CM compared to Control. Protection by ATMSC-CM was associated with increased survival of neurons compared to primary culture cultivated in DMEM media alone. The ATMSC-CM effect on astrocytes was more variable and without any significant impact. Conclusion The results demonstrate that SCI-CM mimicking inflammation can reduce cortical neuron survival, and subsequent exposure to ATMSC-CM can stabilize the neuronal population most likely via released neuroprotective and trophic factors. In addition, astrogliosis was not affected by ATMSC-CM.

Tips on How to Collect and Administer the Mesenchymal Stem Cell Secretome for Central Nervous System Applications

Human mesenchymal stem cells (hMSCs) have been proposed as possible therapeutic agents for central nervous system (CNS) disorders. Recently, it has been suggested that their effects are mostly mediated through their secretome, which contains a number of neuroregulatory molecules capable of increasing cell proliferation, differentiation, and survival in different physiological conditions. Here, we present an overview of the hMSC secretome as a possible candidate in the creation of new cell-free therapies, demonstrating the process of its collection and route of administration, focusing our attention on their effects in CNS regenerative medicine.

Mesenchymal stem/stromal cells-a key mediator for regeneration after perinatal morbidity?

Perinatal complications in both term- and preterm-born infants are a leading cause of neonatal morbidities and mortality. Infants face different challenges in the neonatal intensive care unit with long-term morbidities such as perinatal brain injury and bronchopulmonary dysplasia being particularly devastating. While advances in perinatal medicine have improved our understanding of the pathogenesis, effective therapies to prevent and/or reduce the severity of these disorders are still lacking. The potential of mesenchymal stem/stromal cell (MSC) therapy has emerged during the last two decades, and an increasing effort is conducted to address brain- and lung-related morbidities in neonates at risk. Various studies support the notion that MSCs have protective effects. MSCs are an easy source and may be readily available after birth in a clinical setting. MSCs' mechanisms of action are diverse, including migration and homing, release of growth factors and immunomodulation, and the potential to replace injured cells. Here, we review the pathophysiology of perinatally acquired brain and lung injuries and focus on MSCs as potential candidates for therapeutic strategies summarizing preclinical and clinical evidence.

Neurotrophin Signaling and Stem Cells-Implications for Neurodegenerative Diseases and Stem Cell Therapy

Neurotrophins (NTs) are members of a neuronal growth factor protein family whose action is mediated by the tropomyosin receptor kinase (TRK) receptor family receptors and the p75 NT receptor (p75NTR), a member of the tumor necrosis factor (TNF) receptor family. Although NTs were first discovered in neurons, recent studies have suggested that NTs and their receptors are expressed in various types of stem cells mediating pivotal signaling events in stem cell biology. The concept of stem cell therapy has already attracted much attention as a potential strategy for the treatment of neurodegenerative diseases (NDs). Strikingly, NTs, proNTs, and their receptors are gaining interest as key regulators of stem cells differentiation, survival, self-renewal, plasticity, and migration. In this review, we elaborate the recent progress in understanding of NTs and their action on various stem cells. First, we provide current knowledge of NTs, proNTs, and their receptor isoforms and signaling pathways. Subsequently, we describe recent advances in the understanding of NT activities in various stem cells and their role in NDs, particularly Alzheimer's disease (AD) and Parkinson's disease (PD). Finally, we compile the implications of NTs and stem cells from a clinical perspective and discuss the challenges with regard to transplantation therapy for treatment of AD and PD.

Conditioned Medium from Placental Mesenchymal Stem Cells Reduces Oxidative Stress during the Cryopreservation of Ex Vivo Expanded Umbilical Cord Blood Cells

Background

The limited cell dose in umbilical cord blood (UCB) necessitates ex vivo expansion of UCB. Further, the effective cryopreservation of these expanded cells is important in widening their use in the clinics. During cryopreservation, cells experience oxidative stress due to the generation of reactive oxygen species (ROS). Conditioned medium from mesenchymal stem cells (MSCs-CM) has been shown to alleviate the oxidative stress during wound healing, Alzheimer’s disease and ischemic disease. This premise prompted us to investigate the influence of MSCs-CM during cryopreservation of expanded UCB cells.

Methodology/Principle findings

CM-was collected from cord/placental MSCs(C-MSCs-CM, P-MSC-CM). UCB CD34⁺cells were expanded as suspension cultures in serum free medium containing cytokines for 10 days. Cells were frozen with/without C-MSCs-CM and or P-MSCs-CM in the conventional freezing medium containing 20%FCS +10%DMSO using a programmable freezer and stored in liquid nitrogen. Upon revival, cells frozen with MSCs-CM were found to be superior to cells frozen in conventional medium in terms of viability, CD34⁺content and clonogenecity. Priming of revived cells for 48 hrs with MSCs-CM further improved their transplantation ability, as compared to those cultured without MSCs-CM. P-MSCs-CM radically reduced the oxidative stress in cryopreserved cells, resulting in better post thaw functionality of CD34⁺ cells than with C-MSCs-CM. The observed cryoprotective effect of MSCs-CM was primarily due to anti-oxidative and anti-apoptotic properties of the MSCs-CM and not because of the exosomes secreted by them.

Conclusions/Significance

Our data suggest that MSCs-CM can serve as a valuable additive to the freezing or the priming medium for expanded UCB cells, which would increase their clinical applicability.

Metabolic determinants of the immune modulatory function of neural stem cells

Background

Neural stem cells (NSCs) display tissue trophic and immune modulatory therapeutic activities after transplantation in central nervous system disorders. The intercellular interplay between stem cells and target immune cells is increased in NSCs exposed to inflammatory cues. Here, we hypothesize that inflammatory cytokine signalling leads to metabolic reprogramming of NSCs regulating some of their immune modulatory effects.

Methods

NSC lines were prepared from the subventricular zone (SVZ) of 7–12-week-old mice. Whole secretome-based screening and analysis of intracellular small metabolites was performed in NSCs exposed to cocktails of either Th1-like (IFN-γ, 500 U/ml; TNF-α, 200 U/ml; IL-1β, 100 U/ml) or Th2-like (IL-4, IL-5 and IL-13; 10 ng/ml) inflammatory cytokines for 16 h in vitro. Isotopologues distribution of arginine and downstream metabolites was assessed by liquid chromatography/mass spectrometry in NSCs incubated with U-¹³C₆ L-arginine in the presence or absence of Th1 or Th2 cocktails (Th1 NSCs or Th2 NSCs). The expression of arginase I and II was investigated in vitro in Th1 NSCs and Th2 NSCs and in vivo in the SVZ of mice with experimental autoimmune encephalomyelitis, as prototypical model of Th1 cell-driven brain inflammatory disease. The effects of the inflammatory cytokine signalling were studied in NSC-lymph node cells (LNC) co-cultures by flow cytometry-based analysis of cell proliferation following pan-arginase inhibition with N^ω-hydroxy-nor-arginine (nor-NOHA).

Results

Cytokine-primed NSCs showed significantly higher anti-proliferative effect in co-cultures vs. control NSCs. Metabolomic analysis of intracellular metabolites revealed alteration of arginine metabolism and increased extracellular arginase I activity in cytokine-primed NSCs. Arginase inhibition by nor-NOHA partly rescued the anti-proliferative effects of cytokine-primed NSCs.

Conclusions

Our work underlines the use of metabolic profiling as hypothesis-generating tools that helps unravelling how stem cell-mediated mechanisms of tissue restoration become affected by local inflammatory responses. Among different therapeutic candidates, we identify arginase signalling as novel metabolic determinant of the NSC-to-immune system communication.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0667-7) contains supplementary material, which is available to authorized users.

Bone marrow mesenchymal stem cell therapy in ischemic stroke: mechanisms of action and treatment optimization strategies

Animal and clinical studies have confirmed the therapeutic effect of bone marrow mesenchymal stem cells on cerebral ischemia, but their mechanisms of action remain poorly understood. Here, we summarize the transplantation approaches, directional migration, differentiation, replacement, neural circuit reconstruction, angiogenesis, neurotrophic factor secretion, apoptosis, immunomodulation, multiple mechanisms of action, and optimization strategies for bone marrow mesenchymal stem cells in the treatment of ischemic stroke. We also explore the safety of bone marrow mesenchymal stem cell transplantation and conclude that bone marrow mesenchymal stem cell transplantation is an important direction for future treatment of cerebral ischemia. Determining the optimal timing and dose for the transplantation are important directions for future research.

An Optimized Approach to Recover Secreted Proteins from Fibroblast Conditioned-Media for Secretomic Analysis

The proteins secreted by a particular type of cell, the secretome, play important roles in the regulation of many physiological processes via paracrine/autocrine mechanisms, and they are of increasing interest to help understanding rare diseases and to identify potential biomarkers and therapeutic targets. To facilitate ongoing research involving secreted proteins, we revisited cell culture protocols and whole secreted protein enrichment protocols. A reliable method for culturing and precipitating secreted protein from patient-derived fibroblast conditioned-medium was established. The method is based on the optimization of cell confluency and incubation time conditions. The well-established carrier-based TCA-DOC protein precipitation method was consistently found to give higher protein recovery yield. According to our results, we therefore propose that protein enrichment should be performed by TCA-DOC precipitation method after 48 h at 95% of confluence in a serum-deprived culture medium. Given the importance of secreted proteins as a source to elucidate the pathogenesis of rare diseases, especially neurological disorders, this approach may help to discover novel candidate biomarkers with potential clinical significance.

Secretome of mesenchymal progenitors from the umbilical cord acts as modulator of neural/glial proliferation and differentiation

It was recently shown that the conditioned media (CM) of Human Umbilical Cord Perivascular Cells (HUCPVCs), a mesenchymal progenitor population residing within the Wharton Jelly of the umbilical cord, was able to modulate in vitro the survival and viability of different neuronal and glial cells populations. In the present work, we aimed to assess if the secretome of HUCPVCs is able to 1) induce the differentiation of human telencephalon neural precursor cells (htNPCs) in vitro, and 2) modulate neural/glial proliferation, differentiation and survival in the dentate gyrus (DG) of adult rat hippocampus. For this purpose, two separate experimental setups were performed: 1) htNPCs were incubated with HUCPVCs-CM for 5 days after which neuronal differentiation was assessed and, 2) HUCPVCs, or their respective CM, were injected into the DG of young adult rats and their effects assessed 7 days later. Results revealed that the secretome of HUCPVCs was able to increase neuronal cell differentiation in vitro; indeed, higher densities of immature (DCX(+) cells) and mature neurons (MAP-2(+) cells) were observed when htNPCs were incubated with the HUCPVCs-CM. Additionally, when HUCPVCs and their CM were injected in the DG, results revealed that both cells or CM were able to increase the endogenous proliferation (BrdU(+) cells) 7 days after injection. It was also possible to observe an increased number of newborn neurons (DCX(+) cells), upon injection of HUCPVCs or their respective CM. Finally western blot analysis revealed that after CM or HUCPVCs transplantation, there was an increase of fibroblast growth factor-2 (FGF-2) and, to a lesser extent, of nerve growth factor (NGF) in the DG tissue. Concluding, our results have shown that the transplantation of HUCPVCs or the administration of their secretome were able to potentiate neuronal survival and differentiation in vitro and in vivo.

Do hypoxia/normoxia culturing conditions change the neuroregulatory profile of Wharton Jelly mesenchymal stem cell secretome?

Introduction

The use of human umbilical cord Wharton Jelly-derived mesenchymal stem cells (hWJ-MSCs) has been considered a new potential source for future safe applications in regenerative medicine. Indeed, the application of hWJ-MSCs into different animal models of disease, including those from the central nervous system, has shown remarkable therapeutic benefits mostly associated with their secretome. Conventionally, hWJ-MSCs are cultured and characterized under normoxic conditions (21 % oxygen tension), although the oxygen levels within tissues are typically much lower (hypoxic) than these standard culture conditions. Therefore, oxygen tension represents an important environmental factor that may affect the performance of mesenchymal stem cells in vivo. However, the impact of hypoxic conditions on distinct mesenchymal stem cell characteristics, such as the secretome, still remains unclear.

Methods

In the present study, we have examined the effects of normoxic (21 % O₂) and hypoxic (5 % O₂) conditions on the hWJ-MSC secretome. Subsequently, we address the impact of the distinct secretome in the neuronal cell survival and differentiation of human neural progenitor cells.

Results

The present data indicate that the hWJ-MSC secretome collected from normoxic and hypoxic conditions displayed similar effects in supporting neuronal differentiation of human neural progenitor cells in vitro. However, proteomic analysis revealed that the use of hypoxic preconditioning led to the upregulation of several proteins within the hWJ-MSC secretome.

Conclusions

Our results suggest that the optimization of parameters such as hypoxia may lead to the development of strategies that enhance the therapeutic effects of the secretome for future regenerative medicine studies and applications.

Stem cells as drug delivery methods: application of stem cell secretome for regeneration

Mesenchymal stem cells (MSCs) are a unique cell population defined by their ability to indefinitely self-renew, differentiate into multiple cell lineages, and form clonal cell populations. It was originally thought that this ability for broad plasticity defined the therapeutic potential of MSCs. However, an expanding body of recent literature has brought growing awareness to the remarkable array of bioactive molecules produced by stem cells. This protein milieu or "secretome" comprises a diverse host of cytokines, chemokines, angiogenic factors, and growth factors. The autocrine/paracrine role of these molecules is being increasingly recognized as key to the regulation of many physiological processes including directing endogenous and progenitor cells to sites of injury as well as mediating apoptosis, scarring, and tissue revascularization. In fact, the immunomodulatory and paracrine role of these molecules may predominantly account for the therapeutic effects of MSCs given that many in vitro and in vivo studies have demonstrated limited stem cell engraftment at the site of injury. While the study of such a vast protein array remains challenging, technological advances in the field of proteomics have greatly facilitated our ability to analyze and characterize the stem cell secretome. Thus, stem cells can be considered as tunable pharmacological storehouses useful for combinatorial drug manufacture and delivery. As a cell-free option for regenerative medicine therapies, stem cell secretome has shown great potential in a variety of clinical applications including the restoration of function in cardiovascular, neurodegenerative, oncologic, and genitourinary pathologies.

Nanotechnology versus stem cell engineering: in vitro comparison of neurite inductive potentials

Purpose

Innovative nerve conduits for peripheral nerve reconstruction are needed in order to specifically support peripheral nerve regeneration (PNR) whenever nerve autotransplantation is not an option. Specific support of PNR could be achieved by neurotrophic factor delivery within the nerve conduits via nanotechnology or stem cell engineering and transplantation.

Methods

Here, we comparatively investigated the bioactivity of selected neurotrophic factors conjugated to iron oxide nanoparticles (np-NTFs) and of bone marrow-derived stem cells genetically engineered to overexpress those neurotrophic factors (NTF-BMSCs). The neurite outgrowth inductive activity was monitored in culture systems of adult and neonatal rat sensory dorsal root ganglion neurons as well as in the cell line from rat pheochromocytoma (PC-12) cell sympathetic culture model system.

Results

We demonstrate that np-NTFs reliably support numeric neurite outgrowth in all utilized culture models. In some aspects, especially with regard to their long-term bioactivity, np-NTFs are even superior to free NTFs. Engineered NTF-BMSCs proved to be less effective in induction of sensory neurite outgrowth but demonstrated an increased bioactivity in the PC-12 cell culture system. In contrast, primary nontransfected BMSCs were as effective as np-NTFs in sensory neurite induction and demonstrated an impairment of neuronal differentiation in the PC-12 cell system.

Conclusion

Our results evidence that nanotechnology as used in our setup is superior over stem cell engineering when it comes to in vitro models for PNR. Furthermore, np-NTFs can easily be suspended in regenerative hydrogel matrix and could be delivered that way to nerve conduits for future in vivo studies and medical application.

Wnts enhance neurotrophin-induced neuronal differentiation in adult bone-marrow-derived mesenchymal stem cells via canonical and noncanonical signaling pathways

Wnts were previously shown to regulate the neurogenesis of neural stem or progenitor cells. Here, we explored the underlying molecular mechanisms through which Wnt signaling regulates neurotrophins (NTs) in the NT-induced neuronal differentiation of human mesenchymal stem cells (hMSCs). NTs can increase the expression of Wnt1 and Wnt7a in hMSCs. However, only Wnt7a enables the expression of synapsin-1, a synaptic marker in mature neurons, to be induced and triggers the formation of cholinergic and dopaminergic neurons. Human recombinant (hr)Wnt7a and general neuron makers were positively correlated in a dose- and time-dependent manner. In addition, the expression of synaptic markers and neurites was induced by Wnt7a and lithium, a glycogen synthase kinase-3β inhibitor, in the NT-induced hMSCs via the canonical/β-catenin pathway, but was inhibited by Wnt inhibitors and frizzled-5 (Frz5) blocking antibodies. In addition, hrWnt7a triggered the formation of cholinergic and dopaminergic neurons via the non-canonical/c-jun N-terminal kinase (JNK) pathway, and the formation of these neurons was inhibited by a JNK inhibitor and Frz9 blocking antibodies. In conclusion, hrWnt7a enhances the synthesis of synapse and facilitates neuronal differentiation in hMSCS through various Frz receptors. These mechanisms may be employed widely in the transdifferentiation of other adult stem cells.

The Secretome of Bone Marrow and Wharton Jelly Derived Mesenchymal Stem Cells Induces Differentiation and Neurite Outgrowth in SH-SY5Y Cells

The goal of this study was to determine and compare the effects of the secretome of mesenchymal stem cells (MSCs) isolated from human bone-marrow (BMSCs) and the Wharton jelly surrounding the vein and arteries of the umbilical cord (human umbilical cord perivascular cells (HUCPVCs)) on the survival and differentiation of a human neuroblastoma cell line (SH-SY5Y). For this purpose, SH-SY5Y cells were differentiated with conditioned media (CM) from the MSCs populations referred above. Retinoic acid cultured cells were used as control for neuronal differentiated SH-SY5Y cells. SH-SY5Y cells viability assessment revealed that the secretome of BMSCs and HUCPVCs, in the form of CM, was able to induce their survival. Moreover, immunocytochemical experiments showed that CM from both MSCs was capable of inducing neuronal differentiation of SH-SY5Y cells. Finally, neurite lengths assessment and quantitative real-time reverse-transcription polymerase chain reaction (RT-PCR) analysis demonstrated that CM from BMSCs and HUCPVCs differently induced neurite outgrowth and mRNA levels of neuronal markers exhibited by SH-SY5Y cells. Overall, our results show that the secretome of both BMSCs and HUCPVCs was capable of supporting SH-SY5Y cells survival and promoting their differentiation towards a neuronal phenotype.

In vitro evaluation of cell-seeded chitosan films for peripheral nerve tissue engineering

Natural biomaterials have attracted an increasing interest in the field of tissue-engineered nerve grafts, representing a possible alternative to autologous nerve transplantation. With the prospect of developing a novel entubulation strategy for transected nerves with cell-seeded chitosan films, we examined the biocompatibility of such films in vitro. Different types of rat Schwann cells (SCs)--immortalized, neonatal, and adult-of the chitosan substrate. Both cell types were viable on the biomaterial and showed different metabolic activities and proliferation behavior, indicating cell-type-specific cell-biomaterial interaction. Moreover, the cell types also displayed their typical morphology. In cocultures adult SCs used the BMSCs as a feeder layer and no negative interactions between both cell types were detected. Further, the chitosan films allow neurite outgrowth from dissociated sensory neurons, which is additionally supported on film preseeded with SC-BMSC cocultures. The presented chitosan films therefore demonstrate high potential for their use in tissue-engineered nerve grafts.

Soluble factors secreted by differentiating embryonic stem cells stimulate exogenous cell proliferation and migration

INTRODUCTION

Stem cells are being investigated as catalysts of tissue regeneration to either directly replace or promote cellularity lost as a result of traumatic injury or degenerative disease. In many reports, despite low numbers of stably integrated cells, the transient presence of cells delivered or recruited to sites of tissue remodeling globally benefits functional recovery. Such findings have motivated the need to determine how paracrine factors secreted from transplanted cells may be capable of positively impacting endogenous repair processes and somatic cell responses.

METHODS

Embryonic stem cells were differentiated as embryoid bodies (EBs) in vitro and media conditioned by EBs were collected at different intervals of time. Gene and protein expression analysis of several different growth factors secreted by EBs were examined by polymerase chain reaction and enzyme-linked immunosorbent assay analysis, respectively, as a function of time. The proliferation and migration of fibroblasts and endothelial cells treated with EB conditioned media was examined compared with unconditioned and growth media controls.

RESULTS

The expression of several growth factors, including bone morphogenic protein-4, insulin-like growth factors and vascular endothelial growth factor-A, increased during the course of embryonic stem cell (ESC) differentiation as EBs. Conditioned media collected from EBs at different stages of differentiation stimulated proliferation and migration of both fibroblasts and endothelial cells, based on 5-bromo-2'-deoxyuridine incorporation and transwell assays, respectively.

CONCLUSIONS

Overall, these results demonstrate that differentiating ESCs express increasing amounts of various growth factors over time that altogether are capable of stimulating mitogenic and motogenic activity of exogenous cell populations.

From basics to clinical: a comprehensive review on spinal cord injury

Spinal cord injury (SCI) is a devastating neurological disorder that affects thousands of individuals each year. Over the past decades an enormous progress has been made in our understanding of the molecular and cellular events generated by SCI, providing insights into crucial mechanisms that contribute to tissue damage and regenerative failure of injured neurons. Current treatment options for SCI include the use of high dose methylprednisolone, surgical interventions to stabilize and decompress the spinal cord, and rehabilitative care. Nonetheless, SCI is still a harmful condition for which there is yet no cure. Cellular, molecular, rehabilitative training and combinatorial therapies have shown promising results in animal models. Nevertheless, work remains to be done to ascertain whether any of these therapies can safely improve patient's condition after human SCI. This review provides an extensive overview of SCI research, as well as its clinical component. It starts covering areas from physiology and anatomy of the spinal cord, neuropathology of the SCI, current clinical options, neuronal plasticity after SCI, animal models and techniques to assess recovery, focusing the subsequent discussion on a variety of promising neuroprotective, cell-based and combinatorial therapeutic approaches that have recently moved, or are close, to clinical testing.

Proteome of brain glia: the molecular basis of diverse glial phenotypes

Several different types of nonneuronal glial cells with diverse phenotypes are present in the CNS, and all have distinct indispensible functions. Although glial cells primarily provide neurons with metabolic and structural support in the healthy brain, they may switch phenotype from a "resting" to a "reactive" state in response to pathological insults. Furthermore, this reactive gliosis is an invariant feature of the pathogeneses of CNS maladies. The glial proteome serves as a signature of glial phenotype, and not only executes physiological functions, but also acts as a molecular mediator of the reactive glial phenotype. The glial proteome is also involved in intra- and intercellular communications as exemplified by glia-glia and neuron-glia interactions. The utilization of authoritative proteomic tools and the bioinformatic analyses have helped to profile the brain glial proteome and explore the molecular mechanisms of diverse glial phenotypes. Furthermore, technologic innovations have equipped the field of "glioproteomics" with refined tools for studies of the expression, interaction, and function of glial proteins in the healthy and in the diseased CNS. Glioproteomics is expected to contribute to the elucidation of the molecular mechanisms of CNS pathophysiology and to the discovery of biomarkers and theragnostic targets in CNS disorders.

Effects of bone marrow mesenchymal stromal cells on gross motor function measure scores of children with cerebral palsy: a preliminary clinical study

BACKGROUND AIMS

Pre-clinical evidence indicates that autologous bone marrow-derived mesenchymal stromal cell (BM-MSC) transplantation improves motor function in patients with central nervous system disorders.

METHODS

After providing informed consent, 52 patients with cerebral palsy (CP) who met the study criteria received BM-MSC transplantation. Gross motor function was assessed using the Gross Motor Function Measure (GMFM)-88 and GMFM-66 scales at baseline (before transplantation) and at 1 month, 6 months and 18 months post-transplantation. The participants completed the trial without visible side effects. The GMFM-66 percentile (motor growth curves) was used as the control index of motor function to exclude the interference of improvement with age.

RESULTS

The score domains A, B, C and D and the total GMFM-88 and GMFM-66 scores in participants increased at 1 month, 6 months and 18 months post-transplantation compared with the baseline value (P < 0.01). The scores of domain E also increased at 6 months and 18 months post-transplantation, although they were not significantly increased at 1 month post-transplantation. There were significant increases in the GMFM-66 score and the GMFM-66 percentile corresponding to patient age and Gross Motor Function Classification System level after cell transplantation.

CONCLUSIONS

Autologous BM-MSC transplantation appears to be a feasible, safe and effective therapy for patients with CP. The treatment improved the development of children with CP with regard to motor function.

Mesenchymal stem cells secretome: a new paradigm for central nervous system regeneration?

The low regeneration potential of the central nervous system (CNS) represents a challenge for the development of new therapeutic strategies. Mesenchymal stem cells (MSCs) have been proposed as a possible therapeutic tool for CNS disorders. In addition to their differentiation potential, it is well accepted nowadays that their beneficial actions can also be mediated by their secretome. Indeed, it was already demonstrated, both in vitro and in vivo, that MSCs are able to secrete a broad range of neuroregulatory factors that promote an increase in neurogenesis, inhibition of apoptosis and glial scar formation, immunomodulation, angiogenesis, neuronal and glial cell survival, as well as relevant neuroprotective actions on different pathophysiological contexts. Considering their protective action in lesioned sites, MSCs' secretome might also improve the integration of local progenitor cells in neuroregeneration processes, opening a door for their future use as therapeutical strategies in human clinical trials. Thus, in this review we analyze the current understanding of MSCs secretome as a new paradigm for the treatment of CNS neurodegenerative diseases.

Evidence for high translational potential of mesenchymal stromal cell therapy to improve recovery from ischemic stroke

Although ischemic stroke is a major cause of morbidity and mortality, current therapies benefit only a small proportion of patients. Transplantation of mesenchymal stromal cells (MSC, also known as mesenchymal stem cells or multipotent stromal cells) has attracted attention as a regenerative therapy for numerous diseases, including stroke. Mesenchymal stromal cells may aid in reducing the long-term impact of stroke via multiple mechanisms that include induction of angiogenesis, promotion of neurogenesis, prevention of apoptosis, and immunomodulation. In this review, we discuss the clinical rationale of MSC for stroke therapy in the context of their emerging utility in other diseases, and their recent clinical approval for treatment of graft-versus-host disease. An analysis of preclinical studies examining the effects of MSC therapy after ischemic stroke indicates near-universal agreement that MSC have significant favorable effect on stroke recovery, across a range of doses and treatment time windows. These results are interpreted in the context of completed and ongoing human clinical trials, which provide support for MSC as a safe and potentially efficacious therapy for stroke recovery in humans. Finally, we consider principles of brain repair and manufacturing considerations that will be useful for effective translation of MSC from the bench to the bedside for stroke recovery.

Mesenchymal stem cells from human umbilical cord express preferentially secreted factors related to neuroprotection, neurogenesis, and angiogenesis

Mesenchymal stem cells (MSCs) are promising tools for the treatment of diseases such as infarcted myocardia and strokes because of their ability to promote endogenous angiogenesis and neurogenesis via a variety of secreted factors. MSCs found in the Wharton’s jelly of the human umbilical cord are easily obtained and are capable of transplantation without rejection. We isolated MSCs from Wharton’s jelly and bone marrow (WJ-MSCs and BM-MSCs, respectively) and compared their secretomes. It was found that WJ-MSCs expressed more genes, especially secreted factors, involved in angiogenesis and neurogenesis. Functional validation showed that WJ-MSCs induced better neural differentiation and neural cell migration via a paracrine mechanism. Moreover, WJ-MSCs afforded better neuroprotection efficacy because they preferentially enhanced neuronal growth and reduced cell apoptotic death of primary cortical cells in an oxygen-glucose deprivation (OGD) culture model that mimics the acute ischemic stroke situation in humans. In terms of angiogenesis, WJ-MSCs induced better microvasculature formation and cell migration on co-cultured endothelial cells. Our results suggest that WJ-MSC, because of a unique secretome, is a better MSC source to promote in vivo neurorestoration and endothelium repair. This study provides a basis for the development of cell-based therapy and carrying out of follow-up mechanistic studies related to MSC biology.

The secretome of alginate-encapsulated limbal epithelial stem cells modulates corneal epithelial cell proliferation

Limbal epithelial stem cells may ameliorate limbal stem cell deficiency through secretion of therapeutic proteins, delivered to the cornea in a controlled manner using hydrogels. In the present study the secretome of alginate-encapsulated limbal epithelial stem cells is investigated. Conditioned medium was generated from limbal epithelial stem cells encapsulated in 1.2% (w/v) calcium alginate gels. Conditioned medium proteins separated by 1-D gel electrophoresis were visualized by silver staining. Proteins of interest including secreted protein acidic and rich in cysteine, profilin-1, and galectin-1 were identified by immunoblotting. The effect of conditioned medium (from alginate-encapsulated limbal epithelial stem cells) on corneal epithelial cell proliferation was quantified and shown to significantly inhibit (P≤0.05) their growth. As secreted protein acidic and rich in cysteine was previously reported to attenuate proliferation of epithelial cells, this protein may be responsible, at least in part, for inhibition of corneal epithelial cell proliferation. We conclude that limbal epithelial stem cells encapsulated in alginate gels may regulate corneal epithelialisation through secretion of inhibitory proteins.

The stem cell secretome and its role in brain repair

Compelling evidence exists that non-haematopoietic stem cells, including mesenchymal (MSCs) and neural/progenitor stem cells (NPCs), exert a substantial beneficial and therapeutic effect after transplantation in experimental central nervous system (CNS) disease models through the secretion of immune modulatory or neurotrophic paracrine factors. This paracrine hypothesis has inspired an alternative outlook on the use of stem cells in regenerative neurology. In this paradigm, significant repair of the injured brain may be achieved by injecting the biologics secreted by stem cells (secretome), rather than implanting stem cells themselves for direct cell replacement. The stem cell secretome (SCS) includes cytokines, chemokines and growth factors, and has gained increasing attention in recent years because of its multiple implications for the repair, restoration or regeneration of injured tissues. Thanks to recent improvements in SCS profiling and manipulation, investigators are now inspired to harness the SCS as a novel alternative therapeutic option that might ensure more efficient outcomes than current stem cell-based therapies for CNS repair. This review discusses the most recent identification of MSC- and NPC-secreted factors, including those that are trafficked within extracellular membrane vesicles (EVs), and reflects on their potential effects on brain repair. It also examines some of the most convincing advances in molecular profiling that have enabled mapping of the SCS.

Combining adult stem cells and olfactory ensheathing cells: the secretome effect

Adipose-derived adult stem cells (ASCs), bone marrow mesenchymal stem cells (bmMSCs), and human umbilical cord perivascular cells (HUCPVCs) tissue have been widely tested for regenerative applications, such as bone regeneration. Moreover, olfactory ensheathing cells (OECs) show promise in promoting spinal cord injury (SCI) regeneration. Our group recently proposed the use of a hybrid scaffold targeting both vertebral bone repair and SCI regeneration. According to this concept, both MSCs and OECs should be in close contact to be influenced by the factors that are involved in secretion. For this reason, here we studied the effects of the OEC secretome on the metabolic activity and proliferation of ASCs, bmMSCs, and HUCPVCs. The stem cells' secretome effects on metabolic activity and proliferation of the OECs were also considered. In co-cultures of OECs with ASCs, bmMSCs, or HUCPVCs, the metabolic activity/viability, proliferation, and total cell numbers were measured after 2 and 7 days of culture. The results demonstrated that the secretome of OECs has a positive effect on the metabolic activity and proliferation of MSCs from different origins, especially on ASCs. Furthermore, in general, the stem cells' secretome also had a positive effect on the OECs behavior, particularly when ASCs were in co-culture with OECs. These results suggest that the most suitable combination of cells to be used in our hybrid scaffold is the OECs with the ASCs. Finally, this work adds new knowledge to the cell therapy field, bringing new information about paracrine interactions between OECs and distinct mesenchymal stems.