Oxygen tension modulates neurite outgrowth in PC12 cells through a mechanism involving HIF and VEGF

Exploring allocryptopine as a neuroprotective agent against oxidative stress-induced neural apoptosis via Akt/GSK-3β/tau pathway modulation

Alzheimer's disease (AD) is characterized by neuronal loss due to hyperphosphorylated proteins induced by oxidative stress. AD remains a formidable challenge in the medical field, as current treatments focusing on single biomarkers have yielded limited success. Hence, there's a burgeoning interest in investigating novel compounds that can target mechanisms, offering alternative therapeutic approaches. The aim of this study is to investigate the effects of allocryptopine, an isoquinoline alkaloid, on mechanisms related to AD in order to develop alternative treatment strategies. In this study, the in vitro AD cell model was obtained by inducing nerve growth factor (NGF)-differentiated PC12 (dPC12) cells to oxidative stress with H2O2, and also the effect mechanism of different allocryptopine concentrations on the in vitro AD cell model was studied. The treatments' antioxidative effects at the ROS level and their regulation of the cell cycle were assessed through flow cytometry, while their anti-apoptotic effects were evaluated using both flow cytometry and qRT-PCR. Additionally, the phosphorylation levels of Akt, GSK-3β, and tau proteins were analyzed via western blot, and the interactions between Akt, GSK-3β, CDK5 proteins, and allocryptopine were demonstrated through molecular docking. Our study's conclusive results revealed that allocryptopine effectively suppressed intracellular ROS levels, while simultaneously enhancing the Akt/GSK-3β signaling pathway by increasing p-Akt and p-GSK-3β proteins. This mechanism played a critical role in inhibiting neural cell apoptosis and preventing tau hyperphosphorylation. Moreover, allocryptopine demonstrated its ability to regulate the G1/S cell cycle progression, leading to cell cycle arrest in the G1 phase, and facilitating cellular repair mechanisms, potentially contributing to the suppression of neural apoptosis. The in silico results of allocryptopine were shown to docking with the cyclin-dependent kinase 5 (CDK 5) playing a role in tau phosphorylation Akt and GSK-3β from target proteins. Therefore, the in silico study results supported the in vitro results. The results showed that allocryptopine can protect dPC12 cells from oxidative stress-induced apoptosis and hyperphosphorylation of the tau protein by regulating the Akt/GSK-3β signaling pathway. Based on these findings, it can be suggested that allocryptopine, with its ability to target biomarkers and its significant effects on AD-associated mechanisms, holds promise as a potential candidate for drug development in the treatment of AD. Further research and clinical trials are recommended in the future.

Hypoxia-responsive covalent organic framework by single NIR laser-triggered for multimodal synergistic therapy of triple-negative breast cancer

In recent years, laser-mediated photodynamic therapy and photothermal therapy have attracted widespread attention due to their minimally invasive, easy to operate characteristics and high specificity. However, the traditional photodynamic or photothermal therapy exist several shortcomings such as the hypoxic microenvironment, intracellular heat shock proteins or complex operation. In this study, covalent organic framework (COF) was used as the drug carrier to equip with the photosensitizer indocyanine green (ICG) and the hypoxia-activating prodrug AQ4N. The hyaluronic acid (HA) was modified on the surface of COF to obtain the HA-COF@ICG/AQ4N drug delivery system. HA-modified COF delivery systems can target tumor cells through recognize CD44 which is overexpressed in the surface of tumor cells membrane. Under the irradiation of single NIR laser, ICG that can excite the nanoplatform simultaneously produces a combined effect of photodynamic and photothermal. At the same time, photodynamic therapy through depleting intracellular oxygen exacerbates the hypoxic state of the tumor microenvironment, which in turn enhances AQ4N reduced to chemotherapeutic drug AQ4, producing a synergistic cascade antitumor effect. The results of our study by tumor cell and tumor spheroids indicated that the hypoxia-activated multi-functional nanoplatform could effectively inhibit the growth and metastasis of triple-negative breast cancer.

Dimethyloxalylglycine (DMOG), a Hypoxia Mimetic Agent, Does Not Replicate a Rat Pheochromocytoma (PC12) Cell Biological Response to Reduced Oxygen Culture

Cells respond to reduced oxygen availability predominately by activation of the hypoxia-inducible factor (HIF) pathway. HIF activation upregulates hundreds of genes that help cells survive in the reduced oxygen environment. The aim of this study is to determine whether chemical-induced HIF accumulation mimics all aspects of the hypoxic response of cells. We compared the effects of dimethyloxalylglycine (DMOG) (a HIF stabiliser) on PC12 cells cultured in air oxygen (20.9% O_2, AO) with those cultured in either intermittent 20.9% O₂ to 2% O₂ (IH) or constant 2% O₂ (CN). Cell viability, cell cycle, HIF accumulation, reactive oxygen species (ROS) formation, mitochondrial function and differentiation were used to characterise the PC12 cells and evaluate the impact of DMOG. IH and CN culture reduced the increase in cell numbers after 72 and 96 h and MTT activity after 48 h compared to AO culture. Further, DMOG supplementation in AO induced a dose-dependent reduction in the increase in PC12 cell numbers and MTT activity. IH-cultured PC12 cells displayed increased and sustained HIF-1 expression over 96 h. This was accompanied by increased ROS and mitochondrial burden. PC12 cells in CN displayed little changes in HIF-1 expression or ROS levels. DMOG (0.1 mM) supplementation resulted in an IH-like HIF-1 profile. The mitochondrial burden and action potential of DMOG-supplemented PC12 cells did not mirror those seen in other conditions. DMOG significantly increased S phase cell populations after 72 and 96 h. No significant effect on PC12 cell differentiation was noted with IH and CN culture without induction by nerve growth factor (NGF), while DMOG significantly increased PC12 cell differentiation with and without NGF. In conclusion, DMOG and reduced oxygen levels stabilise HIF and affect mitochondrial activity and cell behaviour. However, DMOG does not provide an accurate replication of the reduced oxygen environments.

Dl-3-N-Butylphthalide Attenuates Hypoxic Injury of Neural Stem Cells by Increasing Hypoxia-Inducible Factor-1alpha

OBJECTIVE

To assess the potential effect of dl-3-N-butylphthalide (dl-NBP) for the proliferation and differentiation of neural stem cells (NSCs) against hypoxia and the underlying mechanism.

MATERIALS AND METHODS

Hippocampal NSCs were obtained from fetal rats. NSCs combined with dl-NBP and single NSCs were cultured. The impact of siRNA-mediated hypoxia-inducible factor-1alpha (HIF-1α) knockdown on NSCs was detected with western blotting (WB) and quantitative real-time reverse transcription polymerase chain reaction (RT-qPCR). Cell-counting kit-8 assay was used for evaluating the viability of NSCs. Levels of HIF-1α protein were measured using WB, and vascular endothelial growth factor (VEGF) expression was quantified using RT-qPCR and enzyme-linked immunosorbent assay.

RESULTS

Compared with 7 different concentrations of dl-NBP, 0.25 g/L was determined as the optimal concentration to significantly increase the viability of NSCs (p < 0.001). Dl-NBP can significantly increase the viability of hypoxic NSCs (p < 0.001) and improve the differentiation of hypoxic NSCs into astrocytes (p = 0.001) and oligodendrocytes (p < 0.001). Meanwhile, Dl-NBP can significantly elevate levels of HIF-1α protein (p < 0.001) and VEGF mRNA (p = 0.001) / protein (p < 0.001) in NSCs in the hypoxic environment. However, after transfection with HIF-1α siRNA in NSCs, the viability and differentiation of NSCs was not recovered using dl-NBP under the hypoxic condition, as well as levels of HIF-1α and VEGF.

CONCLUSION

Dl-NBP can reverse the weaker proliferation and differentiation power of NSCs in the hypoxic environment. The HIF-1α - VEGF pathway may be implicated in this protective effect of dl-NBP.

Hypoxic stress enhances extension and branching of dorsal root ganglion neuronal outgrowth

It has been shown that painful intervertebral discs (IVDs) were associated with a deeper innervation. However, the effect of the disc's degenerative microenvironment on neuronal outgrowth remains largely unknown. The focus of this study was to determine the influence of hypoxia on dorsal root ganglion (DRG) neurite outgrowth. Toward this aim, the DRG-derived cell line ND7/23 was either directly subjected to 2% or 20% oxygen conditions or exposed to conditioned medium (CM) collected from IVDs cultured under 2% or 20% oxygen. Viability and outgrowth analysis were performed following 3 days of exposure. Results obtained with the cell line were further validated on cultures of rabbit spinal DRG explants and dissociated DRG neurons. Results showed that hypoxia significantly increased neurite outgrowth length in ND7/23 cells, which was also validated in DRG explant and primary cell culture, although hypoxia conditioned IVD did not significantly increase ND7/23 neurite outgrowth. While hypoxia dramatically decreased the outgrowth frequency in explant cultures, it significantly increased collateral sprouting of dissociated neurons. Importantly, the hypoxia-induced decrease of outgrowth frequency at the explant level was not due to inhibition of outgrowth branching but rather to neuronal necrosis. In summary, hypoxia in DRG promoted neurite sprouting, while neuronal necrosis may reduce the density of neuronal outgrowth at the tissue level. These findings may help to explain the deeper neo-innervation found in the painful disc tissue.

HIGHLIGHTS

Hypoxia promoted elongation and branching of neurite outgrowth at single cell level, but reduced outgrowth density at tissue level, possibly due to hypoxia-induced neuronal necrosis; these findings may help to explain the deeper neo-innervation found in clinically painful tissues.

Bioprocessing strategies to enhance the challenging isolation of neuro-regenerative cells from olfactory mucosa

Olfactory ensheathing cells (OECs) are a promising potential cell therapy to aid regeneration. However, there are significant challenges in isolating and characterizing them. In the current study, we have explored methods to enhance the recovery of cells expressing OEC marker p75NTR from rat mucosa. With the addition of a 24-hour differential adhesion step, the expression of p75NTR was significantly increased to 73 ± 5% and 46 ± 18% on PDL and laminin matrices respectively. Additionally, the introduction of neurotrophic factor NT-3 and the decrease in serum concentration to 2% FBS resulted in enrichment of OECs, with p75NTR at nearly 100% (100 ± 0% and 98 ± 2% on PDL and laminin respectively), and candidate fibroblast marker Thy1.1 decreased to zero. Culturing OECs at physiologically relevant oxygen tension (2-8%) had a negative impact on p75NTR expression and overall cell survival. Regarding cell potency, co-culture of OECs with NG108-15 neurons resulted in more neuronal growth and potential migration at atmospheric oxygen. Moreover, OECs behaved similarly to a Schwann cell line positive control. In conclusion, this work identified key bioprocessing fundamentals that will underpin future development of OEC-based cell therapies for potential use in spinal cord injury repair. However, there is still much work to do to create optimized isolation methods.

Pathophysiology, screening and treatment of ROP: A multi-disciplinary perspective

The population of infants at risk for retinopathy of prematurity (ROP) varies by world region; in countries with well developed neonatal intensive care services, the highest risk infants are those born at less than 28 weeks gestational age (GA) and less than 1 kg at birth, while, in regions where many aspects of neonatal intensive and ophthalmological care are not routinely available, more mature infants up to 2000 g at birth and 37 weeks GA are also at risk for severe ROP. Treatment options for both groups of patients include standard retinal laser photocoagulation or, more recently, intravitreal anti-VEGF drugs. In addition to detection and treatment of ROP, this review highlights new opportunities created by telemedicine, where screening and diagnosis of ROP in remote locations can be undertaken by non-ophthalmologists using digital fundus cameras. The ophthalmological care of the ROP infant is undertaken in the wider context of neonatal care and general wellbeing of the infant. Because of this context, this review takes a multi-disciplinary perspective with contributions from retinal vascular biologists, pediatric ophthalmologists, an epidemiologist and a neonatologist. This review highlights the latest insights regarding cellular and molecular mechanisms in the formation of the retinal vasculature in the human infant, pathogenesis of ROP, detection and treatment of severe ROP, the risks and benefits of anti-VEGF therapy, the identification of new therapies over the horizon, and the optimal neonatal care regimen for best ROP outcomes, and the benefits and pitfalls of telemedicine in the remote screening and diagnosis of ROP, all of which have the potential to improve ROP outcomes.

VEGF expression correlates with neuronal differentiation and predicts a favorable prognosis in patients with neuroblastoma

Neuroblastoma (NB) is a childhood cancer with a low survival rate and great metastatic potential. Vascular endothelial growth factor (VEGF), an angiogenesis factor, has been found to be involved in CRT-related neuronal differentiation of NB cells. In this study, we further confirmed the role VEGF in NB through mouse xenograft model and clinical analysis from NB patients. In xenograft experiments, CRT overexpression effectively inhibited the tumor growth. In addition, the mRNA and protein levels of VEGF and differentiation marker GAP-43 were upregulated by induced CRT expression. However, no significant correlation between the expression level of VEGF and microvessel density was observed in human NB tumors, suggesting a novel mechanism of VEGF participating in NB tumorigenesis through an angiogenesis-independent pathway. In NB patients' samples, mRNA expression levels of CRT and VEGF were positively correlated. Furthermore, positive VEGF expression by immunostaining of NB tumors was found to correlate well with histological grade of differentiation and predicted a favorable prognosis. In conclusion, our findings suggest that VEGF is a favorable prognostic factor of NB and might affect NB tumor behavior through CRT-driven neuronal differentiation rather than angiogenesis that might shed light on a novel therapeutic strategy to improve the outcome of NB.

Hypoxia-inducible factor-1a contributes to dendritic overgrowth in tuberous sclerosis

Expression of hypoxia-inducible factor 1a (HIF1a) is increased under several pathological conditions such as hyperactive mechanistic target of rapamycin complex 1 (mTORC1) in tuberous sclerosis complex (TSC). Hyperactive mTORC1 and the resulting increased dendritic complexity of neurons are shared molecular and cellular alterations in several neurological disorders associated with cognitive disabilities. Despite some evidence that HIF1a contributes to dendritic overgrowth in vitro, it remains unknown whether increased HIF1a in TSC neurons could contribute to their increased dendritic complexity. To address this use in vivo, we generated TSC neurons by deleting Tsc1 in newborn olfactory bulb (OB) neurons of conditional Tsc1 transgenic mice using neonatal electroporation. In addition to their increased dendritic complexity, Tsc1(null) neurons have been reported to display increased Hif1a mRNA level and HIF1a transcriptional activity. We found that Tsc1(null)-dependent dendritic overgrowth was prevented by knocking down HIF1a or expressing a dominant negative HIF1a. In addition, overexpressing HIF1a in wild-type developing neurons resulted in increased dendritic complexity in vivo. These data highlight that an increase in HIF1a levels contributes to abnormal dendritic patterning in developing neurons under normal conditions and hyperactive mTORC1 conditions as in TSC.

Applications of azo-based probes for imaging retinal hypoxia

We report the design and synthesis of an activatable molecular imaging probe to detect hypoxia in mouse models of retinal vascular diseases. Hypoxia of the retina has been associated with the initiation and progression of blinding retinal vascular diseases including age-related macular degeneration, diabetic retinopathy, and retinopathy of prematurity. In vivo retinal imaging of hypoxia may be useful for early detection and timely treatment of retinal diseases. To achieve this goal, we synthesized HYPOX-3, a near-infrared (NIR) imaging agent coupled to a dark quencher, Black Hole Quencher 3 (BHQ3), which has been previously reported to contain a hypoxia-sensitive cleavable azo-bond. HYPOX-3 was cleaved in hypoxic retinal cell culture and animal models, enabling detection of hypoxia with high signal-to-noise ratios without acute toxicity. HYPOX-3 fluorescences in hypoxic cells and tissues and was undetectable under normoxia. These imaging agents are promising candidates for imaging retinal hypoxia in preclinical disease models and patients.

Calreticulin Regulates VEGF-A in Neuroblastoma Cells

Calreticulin (CRT) has been previously correlated with the differentiation of neuroblastoma (NB), implying a favorable prognostic factor. Vascular endothelial growth factor (VEGF) has been reported to participate in the behavior of NB. This study investigated the association of CRT and VEGF-A in NB cells. The expressions of VEGF-A and HIF-1α, with overexpression or knockdown of CRT, were measured in three NB cells (SH-SY5Y, SK-N-DZ, and stNB-V1). An inducible CRT NB cell line and knockdown CRT stable cell lines were also established. The impacts of CRT overexpression on NB cell apoptosis, proliferation, and differentiation were also evaluated. We further examined the role of VEGF-A in the NB cell differentiation via VEGF receptor blockade. Constitutive overexpression of CRT led to NB cell differentiation without proliferation. Thus, an inducible CRT stNB-V1 cell line was generated by a tetracycline-regulated gene system. CRT overexpression increased VEGF-A and HIF-1α messenger RNA (mRNA) expressions in SH-SY5Y, SK-N-DZ, and stNB-V1 cells. CRT overexpression also enhanced VEGF-A protein expression and secretion level in conditioned media in different NB cell lines. Knockdown of CRT decreased VEGF-A and HIF-1α mRNA expressions and lowered VEGF-A protein expression and secretion level in conditioned media in different NB cell lines. We further demonstrated that NB cell apoptosis was not affected by CRT overexpression in stNB-V1 cells. Nevertheless, overexpression of CRT suppressed cell proliferation and enhanced cell differentiation in stNB-V1 cells, whereas blockage of VEGFR-1 markedly suppressed the expression of neuron-specific markers including GAP43, NSE2, and NFH, as well as TrkA, a molecular marker indicative of NB cell differentiation. Our findings suggest that VEGF-A is involved in CRT-related neuronal differentiation in NB. Our work may provide important information for developing a new therapeutic strategy to improve the outcome of NB patients.

Effect of hypoxia on generation of neurospheres from adipose tissue-derived canine mesenchymal stromal cells

Adipose tissue-derived mesenchymal stromal cells (AT-MSCs) are good candidates for cell therapy due to the accessibility of fat tissue and the abundance of AT-MSCs therein. Neurospheres are free-floating spherical condensations of cells with neural stem/progenitor cell (NSPC) characteristics that can be derived from AT-MSCs. The aims of this study were to examine the influence of oxygen (O2) tension on generation of neurospheres from canine AT-MSCs (AT-cMSCs) and to develop a hypoxic cell culture system to enhance the survival and therapeutic benefit of generated neurospheres. AT-cMSCs were cultured under varying oxygen tensions (1%, 5% and 21%) in a neurosphere culture system. Neurosphere number and area were evaluated and NSPC markers were quantified using real-time quantitative PCR (qPCR). Effects of oxygen on neurosphere expression of hypoxia inducible factor 1, α subunit (HIF1A) and its target genes, erythropoietin receptor (EPOR), chemokine (C-X-C motif) receptor 4 (CXCR4) and vascular endothelial growth factor (VEGF), were quantified by qPCR. Neural differentiation potential was evaluated in 21% O2 by cell morphology and qPCR. Neurospheres were successfully generated from AT-cMSCs at all O2 tensions. Expression of nestin mRNA (NES) was significantly increased after neurosphere culture and was significantly higher in 1% O2 compared to 5% and 21% O2. Neurospheres cultured in 1% O2 had significantly increased levels of VEGF and EPOR. There was a significant increase in CXCR4 expression in neurospheres generated at all O2 tensions. Neurosphere culture under hypoxia had no negative effect on subsequent neural differentiation. This study suggests that generation of neurospheres under hypoxia could be beneficial when considering these cells for neurological cell therapies.

Redox control of the senescence regulator interleukin-1α and the secretory phenotype

Senescent cells accumulate in aged tissue and are causally linked to age-associated tissue degeneration. These non-dividing, metabolically active cells are highly secretory and alter tissue homeostasis, creating an environment conducive to metastatic disease progression. IL-1α is a key senescence-associated (SA) proinflammatory cytokine that acts as a critical upstream regulator of the SA secretory phenotype (SASP). We established that SA shifts in steady-state H2O2 and intracellular Ca(2+) levels caused an increase in IL-1α expression and processing. The increase in intracellular Ca(2+) promoted calpain activation and increased the proteolytic cleavage of IL-1α. Antioxidants and low oxygen tension prevented SA IL-1α expression and restricted expression of SASP components IL-6 and IL-8. Ca(2+) chelation or calpain inhibition prevented SA processing of IL-1α and its ability to induce downstream cytokine expression. Conditioned medium from senescent cells treated with antioxidants or Ca(2+) chelators or cultured in low oxygen markedly reduced the invasive capacity of proximal metastatic cancer cells. In this paracrine fashion, senescent cells promoted invasion by inducing an epithelial-mesenchymal transition, actin reorganization, and cellular polarization of neighboring cancer cells. Collectively, these findings demonstrate how SA alterations in the redox state and Ca(2+) homeostasis modulate the inflammatory phenotype through the regulation of the SASP initiator IL-1α, creating a microenvironment permissive to tumor invasion.

Physiological oxygen level is critical for modeling neuronal metabolism in vitro

In vitro models are important tools for studying the mechanisms that govern neuronal responses to injury. Most neuronal culture methods employ nonphysiological conditions with regard to metabolic parameters. Standard neuronal cell culture is performed at ambient (21%) oxygen levels, whereas actual tissue oxygen levels in the mammalian brain range from 1% to 5%. In this study, we examined the consequences of oxygen level on the viability and metabolism of primary cultures of cortical neurons. Our results indicate that physiological oxygen level (5% O(2)) has a beneficial effect on cortical neuronal survival and mitochondrial function in vitro. Moreover, oxygen level affects metabolic fluxes: glucose uptake and glycolysis was enhanced at physiological oxygen level, whereas glucose oxidation and fatty acid oxidation were reduced. Adenosine monophosphate-activated protein kinase (AMPK) was more activated in 5% O(2) and appears to play a role in these metabolic effects. Inhibiting AMPK activity with compound C decreased glucose uptake, intracellular ATP level, and viability in neurons cultured in 5% O(2). These data indicate that oxygen level is an important parameter to consider when modeling neuronal responses to stress in vitro.

Visfatin induces neurite outgrowth in PC12 cells via ERK1/2 signaling pathway

The angiogenic and inflammatory functions of visfatin and its effect on vascular cells, are fairly well known. However, its role within the nervous system remains largely unclear. To gain insight into this area, we studied the neuritogenic effect of visfatin on PC12 rat pheochromocytoma cells. We investigated whether visfatin gene expression, which is upregulated by hypoxia in cancer cells, is associated with neuritogenesis in PC12 cells. Using RT-PCR, Western blot analysis, ELISA, morphological observations, and immunostaining, we initially showed that CoCl(2), a hypoxic mimetic agent, upregulated visfatin gene expression along with neurite outgrowth in PC12 cells. We also showed that visfatin stimulated neurite outgrowth in PC12 cells. Moreover, in PC12 cells, visfatin evoked the activation of the extracellular signal-regulated kinase 1/2 (ERK1/2), which is closely linked to neuritogenesis. Visfatin-induced outgrowth of neurites was prevented by inhibition of the ERK1/2 pathway. Taken together, our results demonstrate for the first time that visfatin induces neurite outgrowth in PC12 cells via the activation of an ERK-dependent pathway, and suggest that visfatin may exert various biological, physiological, and pathological functions in not only the vascular system but also the nervous system.

Use of an adult rat retinal explant model for screening of potential retinal ganglion cell neuroprotective therapies

PURPOSE. To validate an established adult organotypic retinal explant culture system for use as an efficient medium-throughput screening tool to investigate novel retinal ganglion cell (RGC) neuroprotective therapies. METHODS. Optimal culture conditions for detecting RGC neuroprotection in rat retinal explants were identified. Retinal explants were treated with various recognized, or purported, neuroprotective agents and cultured for either 4 or 7 days ex vivo. The number of cells surviving in the RGC layer (RGCL) was quantified using histologic and immunohistochemical techniques, and statistical analyses were applied to detect neuroprotective effects. RESULTS. The ability to replicate previously reported in vivo RGC neuroprotection in retinal explants was verified by demonstrating that caspase inhibition, brain-derived neurotrophic factor treatment, and stem cell transplantation all reduced RGCL cell loss in this model. Further screening of potential neuroprotective pharmacologic agents demonstrated that betaxolol, losartan, tafluprost, and simvastatin all alleviated RGCL cell loss in retinal explants, supporting previous reports. However, treatment with brimonidine did not protect RGCL neurons from death in retinal explant cultures. Explants cultured for 4 days ex vivo proved most sensitive for detecting neuroprotection. CONCLUSIONS. The current adult rat retinal explant culture model offers advantages over other models for screening potential neuroprotective drugs, including maintenance of neurons in situ, control of environmental conditions, and dissociation from other factors such as intraocular pressure. Verification that neuroprotection by previously identified RGC-protective therapies could be replicated in adult retinal explant cultures suggests that this model could be used for efficient medium-throughput screening of novel neuroprotective therapies for retinal neurodegenerative disease.

Bone marrow stromal cells as replacement cells for Parkinson's disease: generation of an anatomical but not functional neuronal phenotype

The focus of cell replacement therapies (CRTs) for Parkinson's disease has been on delivering dopamine-producing cells to the striatum. Fetal grafts have proven the feasibility of this approach, but an appropriate source of replacement cells has restricted the clinical translation. Bone marrow stromal cells (BMSCs) have been heralded as an ideal source of dopaminergic (DAergic) replacement cells, as they are viewed as ethically acceptable, easily procured, and readily expanded. It is known that they confer functional benefits, particularly in stroke models, through the release of neurotrophic factors, but their transdifferentiation into neurons is still under contention. We sought to evaluate the neuronal phenotype and functional capacity of adult rat BMSCs after exposure to a novel multistep in vitro differentiation protocol compared with cells exposed to other reported neuronal differentiation conditions. We employed a systematic, comprehensive method of assessment to determine the neuronal differentiation capacity of BMSCs. Our fluorescence-activated cell sorting, immunofluorescent and semiquantitative polymerase chain reaction results confirmed that undifferentiated BMSCs isolated based on their adherence to plastic are of mesenchymal origin and express a range of lineage markers. After exposure to preinduction and neuronal induction steps, BMSCs down-regulate markers of other lineages but fail, as assessed by patch clamp, to differentiate into functional neurons. Thus, for BMSCs to be considered a source of DAergic neuronal replacement cells, their ability to transdifferentiate terminally along a neuronal lineage first must be clarified before attempting to direct more complex specification process required for them to be used in Parkinson's-disease-focused CRTs.