Grafting dopamine neurons in Parkinson's disease: do stem cells have a role in the future?

Previous studies have suggested that human umbilical cord blood (HUCB) may serve as a rich source of hematopoietic and nonhematopoietic stem cells and that conditions exist that can coax hematopoietic cells to express neural characteristics. In our laboratory, these cells were tested for several models of neurodegenerative diseases and spinal cord injuries. Through a series of transplantation studies we have begun to uncover the properties of HUCB-derived cells in neuropoietic regions of the neonatal (1) and aging rodent brain. The systematic application of phenotyping approaches to characterize survival, migratory potential and morphologic properties of the differentiated HUCB progeny within normal/unaffected brain will serve as a base for understanding the potential effect of these cells in the diseased brain.
Acknowledgements:  Supported in part by R01 6155039 (TZ). HUCB cells were obtained from Saneron CCEL Therapeutics, Inc. and BioWhittaker, Inc.     

Is Bax a mitochondrial mediator in apoptotic death of dopaminergic neurons in Parkinson's disease?

Bax is a proapoptotic member of the Bcl-2 family of proteins. It is believed to exert its action primarily by facilitating the release of cytochrome c from the mitochondrial intermembrane space into the cytosol, leading to caspase activation and cell death. Because alterations in mitochondrial respiratory function, caspase activation and cell death with morphologic features compatible with apoptosis have been observed post mortem in the brain of patients with Parkinson's disease, we tried to clarify the potential role of Bax in this process in an immunohistochemical study on normal and Parkinson's disease post-mortem brain and primary mesencephalic cell cultures treated with MPP(+). We found that Bax is expressed ubiquitously by dopaminergic (DA) neurons in post-mortem brain of normal and Parkinson's disease subjects as well as in vitro. Using an antibody to Bax inserted into the outer mitochondrial membrane as an index of Bax activation, no significant differences were observed between control and Parkinson's disease subjects, regardless of the mesencephalic subregion analysed. However, in Parkinson's disease subjects, the percentage of Bax-positive melanized SNpc neurons containing Lewy bodies, suggestive of DA neuronal suffering, was significantly higher than the overall percentage of Bax-positive neurons among melanized neurons. Furthermore, all melanized SNpc neurons in Parkinson's disease subjects with activated caspase-3 were also immunoreactive for Bax, suggesting that Bax anchored in the outer mitochondrial membrane of melanized SNpc neurons showing signs of neuronal suffering or apoptosis is increased compared with DA neurons that are apparently unaltered. Surprisingly, MPP(+) treatment of tyrosine hydroxylase (TH)-positive neurons in primary mesencephalic cultures did not cause redistribution of Bax, although cytochrome c was released from the mitochondria and nuclear condensation/fragmentation was induced. Taken together, these findings suggest that in the human pathology, Bax may be a cofactor in caspase activation, but our in vitro data fail to indicate a central role for Bax in apoptotic death of DA neurons in an experimental Parkinson's disease paradigm.     

Iron as catalyst for oxidative stress in the pathogenesis of Parkinson's disease?

The mechanisms leading to degeneration of melanized dopaminergic neurons in the brain stem, and particularly in the substantia nigra zona compacta (SNZC) in patients with Parkinson's disease (PD) are still unknown. Demonstration of increased iron Fe(III) in SNZC of PD brain has suggested that Fe-melanin interaction may contribute to oxidative neuronal damage. Energy dispersive X-ray electron microscopic analysis of the cellular distribution of trace elements revealed significant Fe-peaks, similar to those of a synthetic melanin-Fe(III) complex in intracytoplasmic electron-dense neuromelanin granules of SNZC neurons, with highest levels in a case of PD and Alzheimer's disease (AD). No Fe increase was found in Lewy bodies or in SN neurons of control specimens. The relevance of chemical reactions of dopamine (DA), 5-hydroxydopamine (5-OHDA), and 6-hydroxydopamine (6-OHDA) with Fe(III) and with dioxygen for the pathogenesis of PD was investigated. An initiating mechanism related to interaction between Fe and neuromelanin is suggested which results in accumulation of Fe(III) and a continuous production of cytotoxic species inducing a cascade of pathogenic reactions ultimately leading to neuronal death.     

Systemic administration of neuregulin-1β1 protects dopaminergic neurons in a mouse model of Parkinson's disease

Neuregulin-1 (Nrg1) is genetically linked to schizophrenia, a disease caused by neurodevelopmental imbalance in dopaminergic function. The Nrg1 receptor ErbB4 is abundantly expressed on midbrain dopaminergic neurons. Nrg1 has been shown to penetrate blood-brain barrier, and peripherally administered Nrg1 activates ErbB4 and leads to a persistent hyperdopaminergic state in neonatal mice. These data prompted us to study the effect of peripheral administration of Nrg1 in the context of Parkinson's disease, a neurodegenerative disorder affecting the dopaminergic system in the adult brain. We observed that systemic injections of the extracellular domain of Nrg1β(1) (Nrg1β(1)-ECD) increased dopamine levels in the substantia nigra and striatum of adult mice. Nrg1β(1)-ECD injections also significantly protected the mouse nigrostriatal dopaminergic system morphologically and functionally against 6-hydroxydopamine-induced toxicity in vivo. Moreover, Nrg1β(1)-ECD also protected human dopaminergic neurons in vitro against 6-hydroxydopamine. In conclusion, we have identified Nrg1β(1)-ECD as a neurotrophic factor for adult mouse and human midbrain dopaminergic neurons with peripheral administratability, warranting further investigation as therapeutic option for Parkinson's disease patients.     

How to influence the mesenchymal stem cells fate? Emerging role of ectoenzymes metabolizing nucleotides

Extracellular purines, principally adenosine triphosphate and adenosine, are among the oldest evolutionary and widespread chemical messengers. The integrative view of purinergic signaling as a multistage coordinated cascade involves the participation of nucleotides/nucleosides, their receptors, enzymes metabolizing extracellular nucleosides and nucleotides as well as several membrane transporters taking part in the release and/or uptake of these molecules. In view of the emerging data, it is evident and widely accepted that an extensive network of diverse enzymatic activities exists in the extracellular space. The enzymes regulate the availability of nucleotide and adenosine receptor agonists, and consequently, the course of signaling events. The current data indicate that mesenchymal stem cells (MSCs) and cells induced to differentiate exhibit different sensitivity to purinergic ligands as well as a distinct activity and expression profiles of ectonucleotidases than mature cells. In the proposed review, we postulate for a critical role of these enzymatic players which, by orchestrating a fine-tune regulation of nucleotides concentrations, are integrally involved in modulation and diversification of purinergic signals. This specific hallmark of the MSC purinome should be linked with cell-specific biological potential and capacity for tissue regeneration. We anticipate this publication to be a starting point for scientific discussion and novel approach to the in vitro and in vivo regulation of the MSC properties.     

Can statin therapy really reduce the risk of Alzheimer's disease and slow its progression?

PURPOSE OF REVIEW: Statins are the most used cholesterol-lowering agents worldwide. Earlier studies suggested that they may have preventive effects in Alzheimer's disease. However, prospective studies have questioned this hypothesis. RECENT FINDINGS: Statins regulate beta-amyloid metabolism and microglial activation. Pathologically, patients with Alzheimer's disease have more severe atherosclerosis in cerebral arteries than do controls. Such lesions may cause cerebral hypoperfusion, a risk factor for dementia and cognitive decline. Although most population-based studies have failed to show a beneficial effect of statins in Alzheimer's disease, two randomized controlled trials suggested that statins slow cognitive decline in mild to moderate Alzheimer's disease. SUMMARY: There is still some hope that statins reduce the incidence of Alzheimer's disease and slow its progression. Large-scale randomized controlled trials of simvastatin and atorvastatin for mild to moderate Alzheimer's disease are underway, which might provide more conclusive results than earlier studies.     

II. Selective accumulation of MPP+ in the substantia nigra: A key to neurotoxicity?

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is rapidly metabolized to a 1-methyl-4-phenylpyridinium species (MPP+) in the squirrel monkey. After administration of toxic doses of MPTP, the concentration of MPP+ in the substantia nigra appears to increase during the first 72 hours, reaching the highest concentration of any central nervous system (CNS) tissue studied. In contrast, the concentration of this compound in other brain areas suggested time dependent elimination during the same period. Pretreatment of animals with the monoamine oxidase (MAO) inhibitor pargyline blocks both the neurotoxic action and the biotransformation of MPTP. In animals given pargyline and MPTP, initial MPTP levels are much higher in all brain regions than in those not receiving pargyline, but by 12 hours, MPTP levels had fallen rapidly in all regions except the substantia nigra and the eye. It may be that the selective toxicity of MPTP is related in some way to the accumulation of its oxidized metabolite in the substantia nigra.     

Are mesenchymal stem cells in rheumatoid arthritis the good or bad guys?

The advancements in our understanding of the inflammatory and immune mechanisms in rheumatoid arthritis (RA) have fuelled the development of targeted therapies that block cytokine networks and pathogenic immune cells, leading to a considerable improvement in the management of RA patients. Nonetheless, no therapy is curative and clinical remission does not necessarily correspond to non-progression of joint damage. Hence, the biomedical community has redirected scientific efforts and resources towards the investigation of other biological aspects of the disease, including the mechanisms driving tissue remodelling and repair. In this regard, stem cell research has attracted extraordinary attention, with the ultimate goal to develop interventions for the biological repair of damaged tissues in joint disorders, including RA. The recent evidence that mesenchymal stem cells (MSCs) with the ability to differentiate into cartilage are present in joint tissues raises an opportunity for therapeutic interventions via targeting intrinsic repair mechanisms. Under physiological conditions, MSCs in the joint are believed to contribute to the maintenance and repair of joint tissues. In RA, however, the repair function of MSCs appears to be repressed by the inflammatory milieu. In addition to being passive targets, MSCs could interact with the immune system and play an active role in the perpetuation of arthritis and progression of joint damage. Like MSCs, fibroblast-like synoviocytes (FLSs) are part of the stroma of the synovial membrane. During RA, FLSs undergo proliferation and contribute to the formation of the deleterious pannus, which mediates damage to articular cartilage and bone. Both FLSs and MSCs are contained within the mononuclear cell fraction in vitro, from which they can be culture expanded as plastic-adherent fibroblast-like cells. An important question to address relates to the relationship between MSCs and FLSs. MSCs and FLSs could be the same cell type with functional specialisation or represent different functional stages of the same stromal lineage. This review will discuss the roles of MSCs in RA and will address current knowledge of the relative identity between MSCs and FLSs. It will also examine the immunomodulatory properties of the MSCs and the potential to harness such properties for the treatment of RA.     

Gene expression of proteins of the vesicle cycle in dopaminergic neurons in modeling of Parkinson’s disease

It is assumed that one of the causes of the degeneration of dopaminergic neurons is the dysregulation of the vesicle cycle, which is ensured by a number of proteins including syntaxin I, synaptotagmin I, complexins I and II, and Rab5. It was shown that there is a compensatory increase in gene expression of proteins responsible for exocytosis at the preclinical stage of Parkinson’s disease (PD) in the in substantia nigra (SN) in mice. Conversely, in the model of the clinical stage of PD, the decreases of gene expression of proteins responsible for exocytosis, endocytosis, and neuronal survival, which may be among the triggers of motor dysfunctions.     

Are mesenchymal stem cells major sources of safe signals in immune system?

Numerous reports have shown that mesenchymal stem cells (MSCs) are implicated in immuno-regulation. Several factors expressed from MSCs, especially indoleamine 2,3-dioxygenase (IDO) and prostaglandin E2 (PGE2), are of importance in immuno-regulation on immune cells. In current minireview, we provided evidences to support a novel notion that MSCs may be a major source of "safe signals" in the immune system to balance "dangerous signals" based on a well accepted theory of "danger model". Furthermore, MSCs are of lifecycle characterized by age-and diseased-related changes, such as decreased growth rate, increased senescence, and altered morphology. Thus, defected and abnormal MSCs are implicated in auto-immune diseases, such as systemic lupus erythematosus (SLE). Clinically, it is important to determine clinical benefits and sides effects of cell therapies using autologous self-MSCs or healthy allogeneic MSCs in treatment of autoimmune diseases.     

PGC-1α attenuates the oxidative stress-induced impaired osteogenesis and angiogenesis regulation effects of mesenchymal stem cells in the presence of diabetic serum

Oxidative stress is believed to induce dysfunction of the bone remodeling process and be associated with progressive loss of bone mass. The peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α) is a master controller during mitochondrial biogenesis and the antioxidant response. We postulated that PGC-1α could function as a cyto-protective e?ector in mesenchymal stem cells (MSCs) under oxidative stress conditions. In this study, diabetic serum was firstly used to treat MSCs to induce oxidative damage. The anti-oxidative protective effects of PGC-1α overexpression on MSCs, as well as MSCs’ osteogenesis and angiogenic regulation effects were investigated in vitro. Results showed that diabetic conditions induced significantly increase of intracellular oxidative damage and mitochondrial permeability transition pore (mPTP) opening activity, decrease of cellular viability, and osteogenic differentiation and pro-angiogenic regulation effects of MSCs. However, the diabetic conditions induced oxidative impair on MSCs were significantly alleviated via PGC-1α overexpression under diabetic conditions. Taken together, this study indicates the anti-oxidative treatment potential of PGC-1α regulation as a promising strategy to promote coupling pro-osteogenesis and pro-angiogenesis effects of MSCs.     

Neuropeptides to replace serum in cryopreservation of mesenchymal stromal cells?

Background aimsThe therapeutic potential of human mesenchymal stromal cells (MSCs) has generated considerable interest in a wide variety of areas. MSC banking is feasible, but the optimal technique of cryopreservation remains to be determined.MethodsTo reduce dimethyl sulfoxide (DMSO) concentration in cryopreservation medium, DMSO was replaced with sucrose or trehalose. To increase cell survival and proliferation rates after thawing and to eliminate the need for fetal bovine serum (FBS), neuropeptides of the vasoactive intestinal peptide/glucose-dependent insulinotropic peptide/pituitary adenylate cyclase activating polypeptide family were added to the cryopreservation medium. Cell survival was analyzed by a trypan blue dye exclusion assay. Cell proliferation of cryopreserved MSCs was determined after 7 days of culture.ResultsNo significant differences in cell survival rates were detected between cryopreservation solutions with 5% and 10% DMSO, independently of the addition of trehalose or sucrose. Cell proliferation rates tended to be highest when MSCs were frozen in 5% DMSO + trehalose. FBS could be replaced by human albumin (HA) without loss in cell survival and proliferation potential. With FBS, the addition of neuropeptides could increase cell survival and proliferation rates. Without FBS or HA, cell survival and proliferation rates in the presence of neuropeptides were comparable to rates achieved with FBS or HA.ConclusionsClassic cryopreservation with 10% DMSO could be replaced by 5% DMSO + 30 mmol/L trehalose. FBS could be replaced by HA or neuropeptides without loss in cell survival and proliferation potential. The addition of neuropeptides in the cryopreservation medium containing FBS could increase the cell proliferation rate and consequently cellular output.     

Can human embryonic stem cells contribute to the discovery of safer and more effective drugs?

Few scientific achievements have received such irresistible attention from scientists, clinicians, and the general public as the ability of human embryonic stem (hES) cells to differentiate into functional cell types for regenerative medicine. The most immediate benefit of neurons, cardiomyocytes, and insulin-secreting cells derived from hES cells, however, may reside in their application in drug discovery and toxicology. The availability of renewable human cells with functional similarities to their in vivo counterparts is the first landmark for a new generation of cell-based assays. The development of cell-based assays using human cells that are physiological targets of drug activity will increase the robustness of target validation and efficacy, high-throughput screening (HTS), structure-activity relationship (SAR), and should introduce safer drugs into clinical trials and the marketplace. The pluripotency of embryonic stem cells, that is, the capacity to generate multiple cell types, is a novel path for the discovery of 'regenerative drugs', the pursuit of small molecules that promote tissue repair (neurogenesis, cardiogenesis) or proliferation of resident stem cells in different organs, thus creating drugs that work by a novel mechanism.     

Can the outcomes of mesenchymal stem cell‐based therapy for myocardial infarction be improved? Providing weapons and armour to cells

Use of mesenchymal stem cell (MSC) transplantation after myocardial infarction (MI) has been found to have infarct‐limiting effects in numerous experimental and clinical studies. However, recent meta‐analyses of randomized clinical trials on MSC‐based MI therapy have highlighted the need for improving its efficacy. There are two principal approaches for increasing therapeutic effect of MSCs: (i) preventing massive MSC death in ischaemic tissue and (ii) increasing production of cardioreparative growth factors and cytokines with transplanted MSCs. In this review, we aim to integrate our current understanding of genetic approaches that are used for modification of MSCs to enable their improved survival, engraftment, integration, proliferation and differentiation in the ischaemic heart. Genetic modification of MSCs resulting in increased secretion of paracrine factors has also been discussed. In addition, data on MSC preconditioning with physical, chemical and pharmacological factors prior to transplantation are summarized. MSC seeding on three‐dimensional polymeric scaffolds facilitates formation of both intercellular connections and contacts between cells and the extracellular matrix, thereby enhancing cell viability and function. Use of genetic and non‐genetic approaches to modify MSC function holds great promise for regenerative therapy of myocardial ischaemic injury.     

Overexpression of HIF-1α in mesenchymal stem cells contributes to repairing hypoxic-ischemic brain damage in rats

Preclinical researches on mesenchymal stem cells (MSCs) transplantation, which is used to treat hypoxic-ischemic (HI) brain damage, have received inspiring achievements. However, the insufficient migration of active cells to damaged tissues has limited their potential therapeutic effects. There are some evidences that hypoxia inducible factor-1 alpha (HIF-1α) promotes the viability and migration of the cells. Here, we aim to investigate whether overexpression of HIF-1α in MSCs could improve the viability and migration capacity of cells, and its therapeutic efficiency on HI brain damage. In the study, MSCs with HIF-1α overexpression was achieved by recombinant lentiviral vector and transplanted to the rats subsequent to HI. Our data indicated that overexpression of HIF-1α promoted the viability and migration of MSCs, HIF-1α overexpressed MSCs also had a stronger therapeutic efficiency on HI brain damaged treatment by mitigating the injury on behavioral and histological changes evoked by HI insults, accompanied with more MSCs migrating to cerebral damaged area. This study demonstrated that HIF-1α overexpression could increase the MSCs’ therapeutic efficiency in HI and the promotion of the cells’ directional migration to cerebral HI area by overexpression may be responsible for it, which showed that transplantation of MSCs with HIF-1α overexpression is an attractive therapeutic option to treat HI-induced brain injury in the future.     

Can mesenchymal cells undergo collective cell migration? The case of the neural crest

Cell migration is critical for proper development of the embryo and is also used by many cell types to perform their physiological function. For instance, cell migration is essential for immune cells to monitor the body and for epithelial cells to heal a wound whereas, in cancer cells, acquisition of migratory capabilities is a critical step towards malignancy. Migratory cells are often categorized into two groups: mesenchymal cells, produced by an epithelium-to-mesenchyme transition, that undergo solitary migration and epithelial-like cells which migrate collectively. However, on some occasions, mesenchymal cells may travel in large, dense groups and exhibit key features of collectively migrating cells such as coordination and cooperation. Here, using data published on Neural Crest cells, a highly invasive mesenchymal cell population that extensively migrate throughout the embryo, we explore the idea that other mesenchymal cells, including cancer cells, might be able to undergo collective cell migration under certain conditions and discuss how they could do so.     

Glial cell line-derived neurotrophic factor receptor-α1 expressed in striatum in trans regulates development and injury response of dopamine neurons of the substantia nigra

Many of the cellular effects of glial cell line-derived neurotrophic factor are initiated by binding to GNDF family receptor alpha-1 (GFRα1), and mediated by diverse intracellular signaling pathways, most notably through the Ret tyrosine kinase. Ret may be activated by the cell autonomous expression of GFRα1 ('in cis'), or by its non-cell autonomous presence ('in trans'), in either a soluble or immobilized state. GFRα1 is expressed in the striatum, a target of the dopaminergic projection of the substantia nigra. To determine whether post-synaptic expression of GFRα1 in striatum in trans has effects on the development or adult responses to injury of dopamine neurons, we have created transgenic mice in which GFRα1 expression is selectively increased in striatum and other forebrain targets of the dopaminergic projection. Post-synaptic GFRα1 has profound effects on the development of dopamine neurons, resulting in a 40% increase in their adult number. This morphologic effect was associated with an augmented motor response to amphetamine. In adult mice, post-synaptic GFRα1 expression did not affect neuron survival following neurotoxic lesion, but it did increase the preservation of striatal dopaminergic innervation. We conclude that post-synaptic striatal GFRα1 expression has important effects on the biology of dopamine neurons in vivo.