Neurotrophin-directed differentiation of human adult marrow stromal cells to dopaminergic-like neurons

Stem cells and cell replacement therapy for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder caused by a progressive degeneration of the midbrain dopamine (DA) neurons in the substantia nigra pars compacta (SNc) that predominantly affects the ventral population projecting to the dorsal striatum and leads to a gradual dysfunction of the motor system. There is currently no cure for PD. Pharmacological and surgical (e.g. deep brain stimulation) interventions can alleviate some of the symptoms, but lose their efficacy over time. The distinct loss of DA neurons in the SN offers the opportunity to assay neuronal cell replacement, and the clinical transplantation of fetal midbrain neuroblasts in PD patients has shown that this approach is feasible. However, there are multiple problems associated with the use of fetus-derived material, including limited availability. DA neurons derived from stem cells (SC) represent an alternative and unlimited cell source for cell replacement therapies. Currently, human pluripotent SC, such as embryonic (ES), and most recently, induced pluripotent stem cells (iPS), and multipotent (tissue-specific) adult SC are available, although the methodology for a reliable and efficient production of DA neurons necessary for biomedical applications is still underdeveloped. Here, we discuss some essentials for SC and SC-derived DA neurons to become therapeutic agents.

Cell-based therapeutic approaches for Parkinson's disease: progress and perspectives

Motor dysfunctions in Parkinson's disease are believed to be primarily due to the degeneration of dopaminergic neurons located in the substantia nigra pars compacta. Because a single-type cell population is depleted, Parkinson's disease is considered a primary target for cell replacement-based therapeutic strategies. Extensive studies have confirmed transplantation of donor neurons could be beneficial, yet identifying an alternative cell source is clearly essential. Human embryonic stem cells (hESCs) have been proposed as a renewable source of dopaminergic neurons for transplantation in Parkinson's disease; other potential sources could include neural stem cells (hNSCs) and adult mesenchymal stem cells (hMSCs). However, numerous difficulties avert practical application of stem cell-based therapeutic approaches for the treatment of Parkinson's disease. Among the latter, ethical, safety (including xeno- and tumor formation-associated risks) and technical issues stand out. This review aims to provide a balanced and updated outlook on various issues associated with stem cells in regard to their potential in the treatment of Parkinson's disease. Essential features of the individual stem cell subtypes, principles of available differentiation protocols, transplantation, and safety issues are discussed extensively.

Survival and immunogenicity of mesenchymal stem cells from the green fluorescent protein transgenic rat in the adult rat brain

BACKGROUND

A major technical limitation in preclinical cell replacement research is the ability to discriminate between donor and host tissue after transplantation. This problem has been lessened by the availability of transgenic animals that express "reporter" genes, such as green fluorescent protein (GFP).

OBJECTIVE

We determined the usefulness of one such transgenic reporter rat to assess the survival of bone marrow-derived rat mesenchymal stem cells (MSCs) following direct transplantation into the intact adult brain. We also sought to determine if the expression of GFP in the brain affected the survival of the MSCs or the host's neuroimmune response to the cells.

METHODS

Rats received intrastriatal injections of sterile transplantation medium, 100 000 normal MSCs, or 100 000 GFP-MSCs and were killed humanely 1, 4, 7, 28, and 42 days posttransplantation for astrocyte and microglial immunohistochemical staining.

RESULTS

GFP-MSCs were evident at each examination, although their survival declined over time. Graft volume estimates comparing normal and GFP-MSCs revealed that GFP expression did not adversely affect the survival of the stem cells in the brain. Furthermore, immunostaining for astrocytes and microglia revealed that expression of the reporter protein did not affect the immunogenicity of the stem cells.

CONCLUSIONS

These data indicate the usefulness of GFP for investigating the survival of MSCs following transplantation to the brain. However, the mechanisms responsible for the poor survival of the stem cells must be elucidated if these cells are to serve cell-based therapies for neurodegenerative disorders.

In vitro neural differentiation of bone marrow stromal cells induced by cocultured olfactory ensheathing cells

Bone marrow stromal cells (BMSCs) could be induced to differentiate into neural cells under certain conditions, nevertheless, optimal protocols that could be reproducible and reliable in generating transplantable BMSCs in vitro are still not available. We studied for the first time the neural differentiation of BMSCs induced by coculturing with olfactory ensheathing cells (OECs). BMSCs and OECs were isolated from bone marrow and nasal olfactory lamina propria of adult SD rats respectively, then brought to coculture with transwell culture dishes. At various time points (0h, 6h, 12h, 24h, 72h, 1 week and 2 weeks post-coculture), BMSCs were morphologically observed and processed for immunofluorescence and reverse transcription-polymerase chain reaction (RT-PCR). The number of cells assuming neural morphology dramatically increased at 1- and 2-week-post-coculture, so as the number of immunoreactive cells labeled by neural markers NSE, beta-III-tubulin, MAP2, GFAP and p75(NTR). Our findings demonstrate that BMSCs can efficiently differentiate into neural cells when coculturing with OECs, and the present protocol provides an alternative neurogenesis pathway for generating sufficient numbers of neural cells from BMSCs.

Can cellular models revolutionize drug discovery in Parkinson's disease?

The study of mechanisms that underlie Parkinson's disease (PD), as well as translational drug development, has been hindered by the lack of appropriate models. Both cell culture systems and animal models have limitations, and to date none faithfully recapitulate all of the clinical and pathological phenotypes of the disease. In this review we examine the various cell culture model systems of PD, with a focus on different stem cell models that can be used for investigating disease mechanisms as well as drug discovery for PD. We conclude with a discussion of recent discoveries in the field of stem cell biology that have led to the ability to reprogram somatic cells to a pluripotent state via the use of a combination of genetic factors; these reprogrammed cells are termed "induced pluripotent stem cells" (iPSCs). This groundbreaking technique allows for the derivation of patient-specific cell lines from individuals with sporadic forms of PD and also those with known disease-causing mutations. Such cell lines have the potential to serve as a human cellular model of neurodegeneration and PD when differentiated into dopaminergic neurons. The hope is that these iPSC-derived dopaminergic neurons can be used to replicate the key molecular aspects of neural degeneration associated with PD. If so, this approach could lead to transformative new tools for the study of disease mechanisms. In addition, such cell lines can be potentially used for high-throughput drug screening. While not the focus of this review, ultimately it is envisioned that techniques for reprogramming of somatic cells may be optimized to a point sufficient to provide potential new avenues for stem cell-based restorative therapies.

Lentiviral delivery of LMX1a enhances dopaminergic phenotype in differentiated human bone marrow mesenchymal stem cells

Human mesenchymal stem cells (MSCs) reside in the bone marrow and are known for their ability to differentiate along the mesenchymal lineage (fat, bone, and cartilage). Recent works have suggested the possibility that these cells are also capable of differentiating toward the neuroectodermal lineage. Using lentiviral gene delivery, we sought to reprogram the bone marrow-derived MSCs toward dopaminergic differentiation through delivery of LMX1a, which was reported to be a key player in dopaminergic differentiation in both developmental animal models and embryonic stem cells. Transduction of cells with fluorescent reporter genes confirmed efficiency of gene delivery. On incubation of the LMX1a transduced cells in differentiation medium, the LMX1a protein was concentrated in the cells' nuclei and specific dopaminergic developmental genes were upregulated. Moreover, the transduced cells expressed higher levels of tyrosine hydroxylase, the rate limiting enzyme in dopamine synthesis, and secreted significantly higher level of dopamine in comparison to nontransduced cells. We hereby present a novel strategy to facilitate the dopaminergic differentiation of bone marrow-derived MSCs as a possible cell source for autologous transplantation for Parkinsonian patients in the future.

Repair of tissues by adult stem/progenitor cells (MSCs): controversies, myths, and changing paradigms

Research on stem cells has progressed at a rapid pace and, as might be anticipated, the results have generated several controversies, a few myths and a change in a major paradigm. Some of these issues will be reviewed in this study with special emphasis on how they can be applied to the adult stem/progenitor cells from bone marrow, referred to as MSCs.

Simultaneous PKC and cAMP activation induces differentiation of human dental pulp stem cells into functionally active neurons

The plasticity of dental pulp stem cells (DPSCs) has been demonstrated by several studies showing that they appear to self-maintain through several passages, giving rise to a variety of cells. The aim of the present study was to differentiate DPSCs to mature neuronal cells showing functional evidence of voltage gated ion channel activities in vitro. First, DPSC cultures were seeded on poly-l-lysine coated surfaces and pretreated for 48h with a medium containing basic fibroblast growth factor and the demethylating agent 5-azacytidine. Then neural induction was performed by the simultaneous activation of protein kinase C and the cyclic adenosine monophosphate pathway. Finally, maturation of the induced cells was achieved by continuous treatment with neurotrophin-3, dibutyryl cyclic AMP, and other supplementary components. Non-induced DPSCs already expressed vimentin, nestin, N-tubulin, neurogenin-2 and neurofilament-M. The inductive treatment resulted in decreased vimentin, nestin, N-tubulin and increased neurogenin-2, neuron-specific enolase, neurofilament-M and glial fibrillary acidic protein expression. By the end of the maturation period, all investigated genes were expressed at higher levels than in undifferentiated controls except vimentin and nestin. Patch clamp analysis revealed the functional activity of both voltage-dependent sodium and potassium channels in the differentiated cells. Our results demonstrate that although most surviving cells show neuronal morphology and express neuronal markers, there is a functional heterogeneity among the differentiated cells obtained by the in vitro differentiation protocol described herein. Nevertheless, this study clearly indicates that the dental pulp contains a cell population that is capable of neural commitment by our three step neuroinductive protocol.

Mesenchymal and neural stem cells labeled with HEDP-coated SPIO nanoparticles: in vitro characterization and migration potential in rat brain

Mesenchymal stem cells (MSC) may transdifferentiate into neural cells in vitro under the influence of matrix molecules and growth factors present in neurogenic niches. However, further experiments on the behavior of such stem cells remain to be done in vivo. In this study, rat MSC (rMSC) have been grafted in a neurogenic environment of the rat brain, the subventricular zone (SVZ), in order to detect and follow their migration using superparamagnetic iron oxide (SPIO) nanoparticles. We sought to characterize the potential effect of iron loading on the behavior of rMSC as well as to address the potential of rMSC to migrate when exposed to the adequate brain microenvironment. 1-hydroxyethylidene-1.1-bisphosphonic acid (HEDP)-coated SPIO nanoparticles efficiently labeled rMSC without significant adverse effects on cell viability and on the in vitro differentiation potential. In opposition to iron-labeled rat neural stem cells (rNSC), used as a positive control, iron-labeled rMSC did not respond to the SVZ microenvironment in vivo and did not migrate, unless a mechanical lesion of the olfactory bulb was performed. This confirmed the known potential of iron-labeled rMSC to migrate toward lesions and, as far as we know, this is the first study describing such a long distance migration from the SVZ toward the olfactory bulb through the rostral migratory stream (RMS).

Enhanced tyrosine hydroxylase expression in PC12 cells co-cultured with feline mesenchymal stem cells

Mesenchymal stem cells (MSCs) secrete a variety of neuroregulatory molecules, such as nerve growth factor, brain-derived neurotrophic factor, and glial cell-derived neurotrophic factor, which upregulate tyrosine hydroxylase (TH) gene expression in PC12 cells. Enhancing TH gene expression is a critical step for treatment of Parkinson's disease (PD). The objective of this study was to assess the effects of co-culturing PC12 cells with MSCs from feline bone marrow on TH protein expression. We divided the study into three groups: an MSC group, a PC12 cell group, and the combined MSC + PC12 cell group (the co-culture group). All cells were cultured in DMEM-HG medium supplemented with 10% fetal bovine serum for three days. Thereafter, the cells were examined using western blot analysis and immunocytochemistry. In western blots, the co-culture group demonstrated a stronger signal at 60 kDa than the PC12 cell group (p<0.001). TH was not expressed in the MSC group, either in western blot or immunocytochemistry. Thus, the MSCs of feline bone marrow can up-regulate TH expression in PC12 cells. This implies a new role for MSCs in the neurodegenerative disease process.

Neural differentiation and potential use of stem cells from the human umbilical cord for central nervous system transplantation therapy

The human umbilical cord is a rich source of autologous stem and progenitor cells. Interestingly, subpopulations of these, particularly mesenchymal-like cells from both cord blood and the cord stroma, exhibited a potential to be differentiated into neuron-like cells in culture. Umbilical cord blood stem cells have demonstrated efficacy in reducing lesion sizes and enhancing behavioral recovery in animal models of ischemic and traumatic central nervous system (CNS) injury. Recent findings also suggest that neurons derived from cord stroma mesenchymal cells could alleviate movement disorders in hemiparkinsonian animal models. We review here the neurogenic potential of umbilical cord stem cells and discuss possibilities of their exploitation as an alternative to human embryonic stem cells or neural stem cells for transplantation therapy of traumatic CNS injury and neurodegenerative diseases.

Induction of human mesenchymal stem cells into dopamine-producing cells with different differentiation protocols

Several reports have shown that human mesenchymal stem cells (MSCs) are capable of differentiating outside the mesenchymal lineage. We sought to induce MSCs to differentiate into dopamine-producing cells for potential use in autologous transplantation in patients with Parkinson's disease (PD). Following cell culture with various combinations of differentiation agents under serum-free defined conditions, different levels of up-regulation were observed in the protein expression of tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis. Further analysis of selected differentiation protocols revealed that the induced cells displayed a neuron-like morphology and expressed markers suggesting neuronal differentiation. In addition, there was an increase in Nurr 1, the dopaminergic transcription factor gene, concomitant with a decrease gamma-aminobutyric acid (GABA)ergic marker expression, suggesting a specific dopaminergic direction. Moreover, the induced cells secreted dopamine in response to depolarization. These results demonstrate the great therapeutic potential of human MSCs in PD.

Specification of a dopaminergic phenotype from adult human mesenchymal stem cells

Dopamine (DA) neurons derived from stem cells are a valuable source for cell replacement therapy in Parkinson disease, to study the molecular mechanisms of DA neuron development, and for screening pharmaceutical compounds that target DA disorders. Compared with other stem cells, MSCs derived from the adult human bone marrow (BM) have significant advantages and greater potential for immediate clinical application. We report the identification of in vitro conditions for inducing adult human MSCs into DA cells. Using a cocktail that includes sonic hedgehog and fibroblast growth factors, human BM-derived MSCs were induced in vitro to become DA cells in 12 days. Based on tyrosine hydroxylase (TH) expression, the efficiency of induction was determined to be approximately 67%. The cells develop a neuronal morphology expressing the neuronal markers NeuN and beta III tubulin, but not glial markers, glial fibrillary acidic protein and Olig2. As the cells acquire a postmitotic neuronal fate, they downregulate cell cycle activator proteins cyclin B, cyclin-dependent kinase 2, and proliferating cell nuclear antigen. Molecular characterization revealed the expression of DA-specific genes such as TH, Pitx3, Nurr1, DA transporter, and vesicular monoamine transporter 2. The induced MSCs also synthesize and secrete DA in a depolarization-independent manner. The latter observation is consistent with the low expression of voltage gated Na(+) and Ca(2+) channels in the induced MSCs and suggests that the cells are at an immature stage of development likely representing DA neuronal progenitors. Taken together, the results demonstrate the ability of adult human BM-derived MSCs to form DA cells in vitro.

Spontaneous expression of neural phenotype and NGF, TrkA, TrkB genes in marrow stromal cells

Marrow stromal cells (MSCs) have the ability to provide growth factors and differentiate into neural-like cells on treating with EGF, bFGF and other factors. We wanted to explore whether growth factors secreted by MSCs itself could induce self-differentiation into neural-like cells. Here, we show that even in the absence of inducing factors, rMSCs spontaneously differentiate into neural-like cells expressing neural markers, such as nestin, beta-tubulin III, Doublecortin (DCX), microtubule-associated protein 2 (MAP2) and neuron-specific enolase (NSE). Furthermore, some cells become neurosphere-like growing in suspension. Compared with control and neural-like rMSCs induced by epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF), we found using real-time PCR that self-differentiating rMSCs (SDrMSCs) expressed significantly higher levels of neurotrophic high-affinity receptors (TrkA and TrkB). Coincident with neural marker expression, nerve growth factor (NGF) mRNA was significantly higher than controls despite lower protein levels in the supernatant. Our study suggests that rMSCs have the potential to differentiate into neural cells spontaneously in culture and may contribute towards the natural function of MSCs for neural system in vivo.