Retraction
Following the publication of this article [1], concerns were raised regarding the results presented in Figs 9, 10, 14C, and 14J. Specifically,
- Several repetitive elements have been detected in the background of Fig 9, affecting all lanes. In addition, unusually straight horizontal and vertical discrepancies appear to cut the signal of each band presented in this figure. The original western blot data provided by the corresponding author did not match the figure as presented in the article and did not explain the appearance of the repetitive elements and other discrepancies observed in the figure.
- In Fig 10, the background between the top of the blot and the 43 kDa marker in lane 1 appears similar to the background of the same area in lane 2, lane 3 and lane 4, and the background between 34 kDa marker and the bottom of the blot in lane 1 appears similar to the background of the same area in lane 2, lane 3, and lane 4. In addition, there appear to be unusually straight horizontal and vertical lines surrounding the band presented in lane 1. The original western blot data provided by the corresponding author did not match the figure as presented in the article and did not explain the similarities observed in the background of the separate lanes and other discrepancies observed in the figure.
- Black rectangular squares have been detected in Fig 14C and Fig 14J that obscure the signal present in the underlying areas of these panels. The corresponding author provide underlying data for these panels, however the data provided for Fig 14C did not match the published panel, and the data provided for Fig 14J only partially matched the published panel not including the region of concern.
In light of the concerns affecting multiple figure panels that question the integrity of these data, the PLOS ONE Editors retract this article.
MY, SoL, and HL did not agree with the retraction. MS, YZ, WaW, ZH, DT, ShL, XW, and WeW either did not respond or could not be reached.
2 Nov 2020: The PLOS ONE Editors (2020) Retraction: Conversion of human umbilical cord mesenchymal stem cells in Wharton’s jelly to dopamine neurons mediated by the Lmx1a and Neurturin In Vitro: Potential therapeutic application for Parkinson’s disease in a rhesus monkey model. PLOS ONE 15(11): e0242032. https://doi.org/10.1371/journal.pone.0242032 View retraction
Figures
Abstract
hUC-MSCs hold great promise in vitro neuronal differentiation and therapy for neurodegenerative disorders including Parkinson’s disease. Recent studies provided that Lmx1α play an important role in the midbrain dopamine cells differentiation. Neurturin is desired candidate gene for providing a neuroprotective to DA neurons. In this study, we investigated a novel neuronal differentiation strategy in vitro with Lmx1α and NTN. We transferred these two genes to hUC-MSCs by recombinant adenovirus combined with Lmx1α regulatory factor and other inductor to improve the efficiency of inducing. Then those induced cells were implanted into the striatum and substantia nigra of MPTP lesioned hemi-parkinsonian rhesus monkeys. Monkeys were monitored by using behavioral test for six months after implantation. The result showed that cells isolated from the umbilical cord were negative for CD45, CD34 and HLA-DR, but were positive for CD44, CD49d, CD29. After those cells were infected with recombinant adenovirus, RT-PCR result shows that both Lmx1α and NTN genes were transcribed in hUC-MSCs. We also observed that the exogenous were highly expressed in hUC-MSCs from immunofluorescence and western blot. Experiments in vitro have proved that secretion NTN could maintain the survival of rat fetal midbrain dopaminergic neurons. After hUC-MSCs were induced with endogenous and exogenous factors, the mature neurons specific gene TH, Pitx3 was transcripted and the neurons specific protein TH, β-tubulinIII, NSE, Nestin, MAP-2 was expressed in those differentiated cells. In addition, the PD monkeys, transplanted with the induced cells demonstrated the animals’ symptoms amelioration by the behavioral measures. Further more, pathological and immunohistochemistry data showed that there were neuronal-like cells survived in the right brain of those PD monkeys, which may play a role as dopaminergic neurons. The findings from this study may help us to better understand the inside mechanisms of PD pathogenesis and may also help developing effective therapy for Parkinson’s disease.
Citation: Yan M, Sun M, Zhou Y, Wang W, He Z, Tang D, et al. (2013) Conversion of Human Umbilical Cord Mesenchymal Stem Cells in Wharton’s Jelly to Dopamine Neurons Mediated by the Lmx1a and Neurturin In Vitro: Potential Therapeutic Application for Parkinson’s Disease in a Rhesus Monkey Model. PLoS ONE 8(5): e64000. https://doi.org/10.1371/journal.pone.0064000
Editor: Aditya Bhushan Pant, Indian Institute of Toxicology Research, India
Received: January 14, 2013; Accepted: April 8, 2013; Published: May 28, 2013
Copyright: © 2013 Yan et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This research was financially supported by the Research Fund for Doctor Innovation of Beijing Union Medical College (2011-1001-32); Science and Technology Project of Yunnan Province (2012AE001, 2007C0012Z); National Natural Science Foundation of China (30971003). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Introduction
Parkinson disease (PD) is a neurodegenerative disorder in the elderly whose symptoms of tremor, rigidity, bradykinesia and postural instability are caused primarily by the degeneration of dopamine (DA) neurons in the substantia nigra [1], [2], [3].
The current existence therapies mostly confined to relieve symptoms but not fundamentally restore the lesion side function and loss of efficacy with disease progression [4]. Therefore, a therapy, which is safe and the functional recovery of the nigrostriatal system, is critical in clinical treatment of PD.
Since only HSCs are widely used, but all other celluar therapy with SCs are experimental. In the search for a renewable source of dopamine-producing, human fetal brain tissue [5], embryonic stem cells [6], and neural SCs/progenitors [7] have been investigated. However, technical and ethical difficulties limited the application of this therapy [8], [9]. During the last few years isolations of adult mesenchymal stem cell from different sources have been reported [10], [11], [12]. The MCSs derived from umbilical cord tissue have low immunogenicity and contain few immune cells. Previously studys demonstrated that human umbilical cord mesenchymal stem cells (hUC-MSCs) could be induced to differentiate into neuron-like cells. Sarugaser et al. [13] and Karahuseyinoglu et al. [14] showed the isolation, culturing and differentiation behavior of human perivascular umbilical cells and obtained osteogenic nodules. Datta et al. [15], Fu et al. [16] and weiss et al. [17] demonstrated the differentiation capacity of hUC-MSCs into dopaminergic neurons and better than bone marrow derived MSCs.
The LIM homeobox transcription factors 1 alpha (Lmx1α) is sufficient and required to trigger midbrain dopamine (mDA) neurons differentiation. It is accepted by most research that fully compatible dopaminergic differentiation requires extrinsic cues provided by signaling molecules such as sonic hedgeho (SHH) and the fibroblast growth factor (FGF-8) [18], [19], [20]. Ran Brazilay et al. [21] reported that Lmx1α forced expression, together with extrinsic signaling molecule is sufficient to produce cells that expressed high level of TH, the rate-limiting enzyme in dopamine synthesis, and secreted significantly higher levels of dopamine.
Neurturin (NTN) is a potent trophic factor for dopaminergic neurons. NTN enhances dopaminergic neurons survival, prevents the loss of damaged nigral dopamine neurons in an animal model of PD and restores the neuronal micro-environment in vivo [22], [23].
We hypothesized that hUC-MSCs infected with adenoviral vectors expressing Lmx1α and NTN and cultured in chemical micro-environment could be transdifferentiated to undertake neuronal differentiation pathways. In this study, we examed the effects of promoting the differentiation potential and trophic effects on endogenous neural stem cells by continuous NTN and nutritional factors secretion in the transplanted neural-like cells.
Materials and Methods
Collection and use of human umbilical cord was approved by the Ethics Committee of the Institute of Medical Biology (YISHENGLUNZI [2011] 16), and was provided following caesarian section with written informed consent.
The recombinant adenoviruses Ad-NTN and Ad-Lmx1α were provided by the Laboratory of Molecular Biology at the Institute of Medical Biology of the Chinese Academy of Medical Sciences.
Ethics Statement
All animal experimental procedures were carried out in strict accordance with the National Institute of Health Guidelines for the Care and Use of Laboratory Animals. The animal experiments were approved by the Ethics Committee of Animal Care & Welfare, Institute of Medical Biology, CAMS (Permit Number: SYXK (dian)2010-0007), in accordance with the animal ethics guidelines of Chinese National Health and Medical Research Council (NHMRC) and the Office of Laboratory Animal Management of Yunnan Province, China. Non-human primates were kept in a single cage and bred according to the guidelines of the Experimental Animals Ethics Committee of Institute of Medical Biology Chinese Academy of Medical Sciences (Permit Number SCXK-2005-0005). We injected penicillin to monkeys for diminishing inflammation after surgery. Rhesus monkeys were euthanized by an overdose of injection anaesthetic (sodium pentobarbital, 10 mg/kg). All efforts were made to minimize the number of animals used and their suffering. [24].
The rats we were obtained from Institute of Medical Biology of Chinese Academy of Medical Sciences. After the experiments rats were euthanized by dislocation of cervical vertebra; fetuses were euthanized by decapitation.
Isolation and Expansion of hUC-MSCs
Human umbilical cords were obtained from healthy full-term caesarian section births and aseptically store at 4°C PBS containing 1% antibiotics of penicillin and streptomycin. The cord was rinsed several times to drained blood from vessels and cords. Then cut it into 2–3 cm length and rinsed again. Umbilical arteries and veins were removed, and the remaining tissues were transferred to a sterile container and were dicied into small fragments in the PBS. The explants were transferred to flask contain minimum essential medium (α-MEM) along with 15% fetal bovine serum (FBS) and incubated at 37°C in a humidified atmosphere containing 5% CO2. The medium was replaced every five days. The cells were reached 60%–70% confluence then transferred it to 6-well plates supplemented with 20 µM BrdU. After 48 h incubation, the cells were rinsed with PBS and fixed with 2% paraformaldehyde/0.2% Trinton-X 100/PBS for 30 min at 4°C and then treated with pre-cooled methanol for 10 min at 4°C. The cells were rinsed with PBS, subsequently treated with 2 M hydrogen chloride (HCl) for 20 min at 37°C and rinsed with PBS. Then the sample blocked with 2% bovine serum albumin (BSA) in PBS for 30 min at 37°C. Cells were incubated overnight at 4°C with the primary antibody (anti-BrdU mouse monoclonal antibodiy, ZSGB-BIO ORIGENE, diluted in 1∶50). The next day, cells were rinsed with PBS, then incubated with secondary antibody diluted in 2% BSA/0.2 Tween-20/PBS for 30 min at 37°C and counterstained DAPI (4′, 6-Diamidino-2-Phenylindole Dihydrochloride, Sigma-Aldrich) for 2 min at room temperature. The testing cells were observed under fluorescence microscope.
Flow Cytometry
To stain the hUC-MSCs, the cells were lifted with 0.125% trypsin. The digested cells were washed with PBS and resuspended into a single cell suspension at a concentration of 106/mL. The suspension cells were stained with the following labeled antibody: CD45-PerCP, CD34-PE, CD49d-PE, CD29-PE, CD44-PE and HLA-DR-FITC (BD Pharmingen), incubated in the dark for 30 min at room temperature and then analyzed by means of a FACSCalibur (BD Biosciences).
Transmission Electron Microscopy
The hUC-MSCs were detached with 0.125% trypsin and fixed in 2.5% glutaraldehyde in PBS for 2 h. Cells were rinsed with 0.1 M PBS and fixed in 1% osmic acid fixative for 3 h at 4°C. Cells underwent sequential dehydration for 15 min in 50%, 70% and 90% ethanol, a 1∶1 mixture of 90% ethanol and 90% acetone and then 90% acetone. The above steps were all operated at 4°C. Cells were washed with 100% acetone at room temperature for three times. Cells were embedded in epoxy resin, and cut it into 50–60 nm slices. The slices were double stained with 3% uranyl acetate-lead citrate and observed under TEM at 80 kV.
Adipogenic Differentiation Potential
hUC-MSCs were transferred to 6-well plates(1×105 cells per well) with cover slips cultured with MEM-α containing 15% FBS. When the cells reached 90% confluence, the medium was replaced with high-glucose Dulbecco’s Modified Eagle’s Medium(H-DMEM) containing 10% FBS, 1 µM dexamethasone (ENZO), 10 µg/mL insulin and 0.5 mM 3-isobuty-1-methylxanthine (Sigma). Four days later, the medium was replaced with H-DMEM containing 10% FBS and 200 µM indomethacin (Sigma-Aldrich). After four days inducing, the medium was replaced with H-DMEM containing 10% FBS, 1 µM dexamethasone, 10 µg/mL insulin, 0.5 mM 3-isobuty-1-methylxanthine and 200 µM indomethacin. The medium was replaced every four days. After 21 days of adipogenic stimulation, cells were rinsed with PBS, fixed in 4% paraformaldehyde at room temperature and incubated for 30 min with oil red O to stain lipid vacuoles and treated with hematoxylin (Beytime) to stain nuclei.
Osteogenic Differentiation Potential
hUC-MSCs were transferred to 6-well plates(1×105 cells per well) with cover slips cultured with MEM-α containing 15% FBS. When the cells reached 60%–70% confluence, the medium was replaced with H-DMEM containing 10% FBS, 10 nM dexamethasone, 10 mM β-glycerophosphate disodium salt hydrate and 150 µM L-ascorbic acid-2-phosphate (Sigma-Aldrich). Medium was changed every four days. After 21 days of osteogenic stimulation, cells were rinsed with PBS, fixed in 4% paraformaldehyde at room temperature and incubated for 30 min with alizarin red to stain calcium nodules. Alkaline phosphatase (ALP) activity was assayed by means of the GENMED alkaline phosphatase activity staining kit (GENMED Scientifics, Inc.).
RT-PCR Analysis of the Transcription of the NTN and Lmx1α in hUC-MSCs
hUC-MSCs were transferred to a flask (1×106 cells per well) and adenovirus was added in culture medium at multiplicity of infection (MOI, the appropriate dose for the virus between the number of infected cells and the virus titer) of 5 for 48 h. Total RNA was extracted from control cells and treated cells (Ad-NGFpreNTN and Ad-Lmx1α infected) with the use of the RNA extraction kit (OMEGA) as described by the supplier. RNA was reverse-transcribed with the use of M-MuLV reverse transcriptase in a 20 µL volume containing 0.2 µg Oligo (dT), 400 µmol/L dNTP and buffers supplied by the manufacture. With the above cDNA (1 µg) as a template, the sequences were used in the Polymerase chain reaction (PCR) was showed in Table 1.
Immunofluorescence Detected the Expression of NTN and Lmx1α hUC-MSCs
hUC-MSCs were transferred to 6-well plates (1×105 cells per well) with cover slips and adenovirus (Ad-NGFpreproNTN, Ad-Lmx1α) was added in culture medium at MOI of 5 for 48 h. The cells were rinsed with PBS and fixed with 2% paraformaldehyde containing 0.2% Triton X-100 at 4°C for 30 min, Subsequently fixed with precooled methanol for 10 min at 4°C. After washing with PBS, samples were incubated with antibodies (NTN: Mouse Anti-Human Neurturin Monoclonal Antibody,R&D,1∶100; Lmx1α: Rabbit Anti-Human Lmx1α Monoclonal Antibody,Santa Cruz,1∶50) for 90 min at 37°C. Then rinsed the cells and incubated with the secondary antibody(NTN: FITC Labeled Rabbit Anti-Mouse IgG Secondary Antibody,KPL,1∶250; Lmx1α: anti-rabbit IgG-DylightTM549, RockLand immunochemicals, 1∶3000) for 30 min at 37°C. The cells were observed under a fluorescence microscope. hUC-MSCs without any treated were as control group.
Western Blotting Detection of Lmx1α Expression and Mature NTN Secretion
Adenovirus (Ad-NGFpreproNTN, Ad-Lmx1α) was added at MOI of 5 for 48 h. The condition medium and cells were harvested after adenovirus infection. The normal cells were as control group. These samples were separated by SDS-PAGE (12% gel) and transferred to PVDF membranes.
The membranes were blocked at 37°C for 2 h with nonfat milk in PBS. Membranes were incubated with primary antibodies (NTN:Goat Anti-Human Neurturin Polyclonal Antibody,R&D,1∶250; Lmx1α: Rabbit Anti-Human Lmx1α Monoclonal Antibody,Santa Cruz,1∶50) for 2 h at 37°C, after washed three times the membranes were incubated for 2 h at 37°C with approximate horseradish peroxidase (HRP) conjugated secondary antibodies (NTN: Rabbit anti-Goat IgG Secondary antibody,KPL,1∶2000; Lmx1α: Goat anti-Rabbit IgG Secondary antibody,KPL,1∶2000). After washing, blots were visualized using DAB chromogenic reagent. The molecular weight of the analyzed proteins was estimated using PageRuler Prest Protein Ladder (Therom).
ELISA Detection of the Extracellular Secretion of NTN by hUC-MSCs
The medium was collected after hUC-MSCs infected with Ad-NGFpreproNTN at 24 h, 48 h, 72 h and 96 h. Control group was normal hUC-MSCs culture medium. The 96-well palte was incubated with coating buffer overnight at 4°C. The samples were washed three times with PBS-T (containing 0.5% Tween-20) and blocked with 3% BSA in PBS-T for 2 h at 37°C. After washing, each sample was incubated with primary antibody (Goat Anti-Human Neurturin Polyclonal Antibody, R&D, 1∶2000) for 1 h at 37°C. Then the plate was rinsed three times and incubated again with secondary antibody (Rabbit anti-Goat IgG Secondary antibody, KPL, 1∶2500) for 1 h at 37°C. The samples were visualized using TMB (3, 3′, 5, 5′-Tetramethylbenzidine) for 15 min at room temperature. The results of densitometry measurement were statically analyzed by student’s t test.
The Bioassay of the Neurons Survival Promoting Activity of NTN
Sprague Dawley (SD) rats that had been pregnant for 14 days were sacrificed by dislocation of cervical vertebra. The abdominal cavity was opened under aseptic conditions and put the uterus in a sterile dish containing precooled Hank’s Balanced Salt Solution (HBSS). Then removed the fetal rats carefully and opened the cranial cavity with forceps and the entire brain was dissected after clearing the meninges and blood vessels. The ventral midbrain area was removed and cut into pieces in precooled HBSS solution. The pieces were digested with 0.125% trypsin for 20 min before adding culture medium to terminate the digestion. Cells were dispersed by repeated pipetting. Digested cells were added to 6-well plates coated with poly-L-lysine with coverglasses, followed by incubation at 37°C with 5% CO for 24 h. The culture medium was together with the condition mediun and Neural Basal plus B27 seurm free supplements. The control group was supplemented with the culture supernatant from control hUC-MSCs. The DA neurons were incubated and the medium was replaced by half ervery three days. After 21day’s observation, immunohistochemisty was performanced to assay the DA neuros.
Differentiation of hUC-MSC into Dopaminergic Neurons Like Cells
To differentiated hUC-MSCs into a dopaminergic neurons like cells in vitro, hUC-MSCs were transferred to 6-well plates with cover slips (1×105 cells per well). hUC-MSCs were infected with Ad-NGFpreproNTN at MOI of 6 for 24 h. Subsequently the cells were infected with Ad-Lmx1α at MOI of 5 for 24 h. Then, the medium was replaced with neuronal pre-induction medium, consisting of MEM-α (20% FBS) medium with a cocktail of bFGF (Millpore) and β-mercaptoethanol (Sigma-Aldrich). Cells were induced for 24 h and replaced with neuronal induction medium, containing MEM-α (15% FBS) medium with a cocktail of bFGF, β-mercaptoethanol, SHH (R&D), FGF-8(R&D), RA (Sigma-Aldrich). Seven days later, the medium was replaced with the final induction medium, consisting of MEM-α (5% FBS) medium with a cocktail of bFGF, β-mercaptoethanol, SHH, FGF-8, RA. The neuronal indction medium was replaced every seven days. As a control, hUC-MSCs were also cultured with growth medium alone, without added adenovirus or induction medium.
Real-time PCR analysis.
Total RNA was isolated with the use of the RNA extraction kits (OMEGA) as described by the supplier. RNA was reverse-transcribed with the use of M-MuLV reverse transcriptase in a 20 µL volume containing 0.2 µg Oligo (dT), 400 µmol/L dNTP and buffers supplied by the manufacture. With the above cDNA (1 µg) as a template, real-time PCR was performed with the use of SsoFast™ EvaGreen Supermix (Bio-Rad) and run on a CFX96™ real-time system instrument and software (Bio-Rad). Sequences of the primers are show in Table 1. The mRNA level relative to that of β-actin was calculated.
Immunofluorescence staining.
For immunofluorescence staining, the induced cells were fixed with 2% paraformaldehyde containing 0.2% Triton X-100 for 30 min at 4°C. They were then fixed with pre-cooled methanol for 10 min at 4°C and subsequently blocked with 2% BSA in PBS for 30 min at 37°C. Cells were incubated with the following specific primary antibodies diluted in PBS: TH (Rabbit anti-Human TH,Millipore,1∶1000), NSE (Rabbit anti-Human/Monkey neuron-specific enolase,Thermo Fisher Scientific,60 µL/mL), Nestin (Anti-Nestin,miliipore,1∶200), β-tubulinIII (Anti-Tubulin, beta III isoform, C-terminus,millipore, 1∶100)and MAP-2 (Rabbit anti-human microtubule-associated protein 2,Cell Signaling Technology, 1∶50). The next day, the cells were washed and appropriate secondary antibodies including anti-mouse IgG, FITC (KPL) and anti rabbit IgG, FITC (Chemicon) were incubated for 30 min at 37°C. The negative controls were processed identically to the test sample.
Animal Model Study
Establishment of a semi-parkinsonian animal model.
Monkeys were anesthetized with hydrochloric acidulated ketamine (10 mg/kg) for inducement and sodium pentobarbital (20 mg/kg) for maintenance. The right carotid artery was exposed by surgery, and the common carotid artery was injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP-HCL,GBICO, 0.6 mg/kg), while the external carotid artery was being blocked.
Stereotaxic surgery.
Nine hemiparkinsonism monkeys were selected and randomly divided into three groups: the test group, which was injected with induced cells, the control group, which was injected with HBSS and the normal group. Before the stereotaxic injection, magnetic resonance imaging (MRI) was conducted to locate the target sites (caudate nucleus, putamen and substantia nigra). All test monkeys were injected by the same parameters (CA: AP = 27 mm, ML = −5.5 mm and DV = 21 mm; PU: AP = 22 mm, ML = −11.5 mm and DV = 25 mm; and SN: AP = 9 mm, ML = −5 mm and DV = 33.5 mm) [25]. After anesthesia with hydrochloric acidulated ketamine and sodium pentobarbital was given, monkeys were fixed in a surgical frame. The cells culture medium was added BrdU to label the hUC-MSCs. The injection dosage was 107 per pore. For the control group, the HBSS injection dosage was 50 µL.
Behavioral analysis by the parkinson’s disease rating scale.
Parkinsonian behavior was evaluated by Kordower et al. [23], with modifications (Table 2) including tremor, grait, hypokinesia, balance and so forth. The evaluation was conducted 3 times per week. An average score was calculated and ayalyzed by means of the student’s t test.
R-(−) apomorphine-induced rotation.
A characteristic of the hemiparkinsonian state is rotation induced by R-(−) apomorphine (2 mg/kg, GBICO), a dopamine agonist. The induced rotations were examined after administration of the cell therapies to evaluate the recovery of DA neurons on the lesioned sides. The number of rotations of each animal was recorded and analyzed by means of the student’s t test.
Histological evaluation of recovery.
About six months after treatment, the monkeys were sacrificed with the method of euthanasia. Brains were removed and fixed with paraformaldehyde for seven days. The tissues were sectioned in paraffin (7 µm) by a sliding microtome.The sections were incubated with the primary antibody mouse anti-monkey TH (1∶2000) and mouse anti-BrdU (1∶50), followed by treatment with HRP-labeled secondary antibodies.
Grafted cells, which were labeled with BrdU, were detected in the right side substantia nigra of cell therapy monkeys (Fig. 20 C) and the left side had no significantly staining (Fig. 20 D). In the HBSS group there were not significantly staining in the left side (Fig. 20 A) and the lesion side (Fig. 20 B).
Results
Characteriztion of Cultured hUC-MSCs
About 3×106 hUC-MSCs were collected from 20 cm of umbilical cord. Seven days after isolation, hUC-MSCs adhered and displayed a fibroblast-like appearance. Ten days later, they started to proliferate rapidly and reached 80% confluence within 2–3 weeks (Fig. 1 A). The cells isolation in vitro was stabled through 7 passages (Fig. 1 B). An amplification index assay indicated that 90% of DAPI-positive cells were BrdU positive (Fig. 2 A, B), confirming the capacity of hUC-MSCs for self-proliferation.
(A) Morphology of hUC-MSCs primary cultured for 20 days. Scale bar: 40 µm. (B) Morphology of hUC-MSCs cultured at the 7th generation. Scale bar: 100 µm.
(A) hUC-MSCs counterstain with BrdU. (B) hUC-MSCs counterstain with DAPI. Scale bar: 100 µm.
Flow Cytometry
FACS analysis demonstrated that hUC-MSCs were stained positive for CD29, CD44 and CD49d but negative for CD45, CD34 and HLA-DR. The CD45 negative cells (Fig. 3 A), 82.76% were CD29+HLA-DR (Fig. 3 C), 81.25% were CD49d+HLA-DR (Fig. 3 D), 66.75% were CD44+HLA-DR (Fig. 3 B) and 99.38% were CD34+HLA-DR (Fig. 3 E).
The cells were stained with antibodies against CD29, CD49d, CD44, CD45, CD34 and HLA-DR.
Ultrastructural of hUC-MSCs
The hUC-MSCs were sphere-like (Fig. 4 A), and the surface of the cells membrane had many microvilli-like protrusions (Fig. 4 C). Cells had a large nuclear-cytoplasmic ratio, and the nuclei were oval or irregular with nuclear fussion (Fig. 4 D). The nuclear outer membrane was visibled and contained ribosomes (Fig. 4 E). The heterochromatin was distributed around the nucleus, which contained greater amount of enchromatin (Fig. 4 B), rough endoplasmic (Fig. 4 C) and concentration mitochondria (Fig. 4 F). The result indicated that hUC-MSCs were primitive, metabolically active and poorly differentiated.
Differentiation Capacity and Plasticity of hUC-MSCs
In vitro differentiation into adipogenic cells.
Adipocytic phenotypes in induced hUC-MSCs were first signaled by the appearance multisized, most cells became round or cuboid and retracted their cellular extensions during induction, although a few retained their fusiform shape. After 5 days of adipogenic differentiation, tiny intracytoplasmic droplets could be observed. After 21 days adipogenic differentiation, most cultivation cells were became larger and the number of lipid droplets in cytoplasm increased (Fig. 5 A). The effectiveness of differentiation was assessed by histochemical staining. In the adipogenic differentiated cells, red stained intracellular vacuoles (Fig. 5 C). Control hUC-MSCs were only visibly stained with hematoxylin (Fig. 5 B).
(A) The lipid droplet of cells cultured in adipogenic medium for 21 days. (B) Staining was not observed in control hUC-MSCs cultured in growth medium. (C) Oil red O staining of the lipid droplet of cells cultured in adipogenic medium. Scale bar: 100 µm.
In vitro differentiation into osteogenic cells.
After osteogenic induction, most cells became proximity to each other (Fig. 6 A, D). After 21days induction, alizarin red stained obvious calcium deposits (Fig. 6 B), whereas noninduced cells did not exhibit any calcium deposits (Fig. 6 C). ALP activity revealed blue-black stained in induced cells (Fig. 6 E), whereas non induced cells did not exibit any ALP activity (Fig. 6 F).
(A, D) Morphology of hUC-MSCs cultured in osteogenic medium for 21 days. (B, E) In vitro differentiation of hUC-MSCs into osteoblasts, were shown by positive alizarin red (B) and ALP staining (E) of calcified extracellular matrix. (C, F) Staining was not observed in control hUC-MSCs cultured in growth medium. Scale bar: 100 µm.
Transcription of NTN and Lmx1α in hUC-MSCs after Recombinant Adenoviruses
After infected with Ad-NGFpreproNTN and Ad-Lmx1α for 48 h, the RT-PCR results shown that NTN and Lmx1α were transcripted in the cells infected with adenoviruses, but they were not transcripted in the control hUC-MSCs (Fig. 7).
Lane 1, the PCR product of Lmx1α in Ad-Lmx1α infected hUC-MSCs. Lane 2, the PCR product of β-actin in Ad-Lmx1α infected hUC-MSCs. Lane 3, the product of NTN in Ad-NGFpreproNTN infected hUC-MSCs. Lane 4, the product of β-actin in Ad-NGFpreproNTN infected hUC-MSCs. Lane 5, the product of Lmx1α in control hUC-MSCs. Lane 6, the product of NTN in control hUC-MSCs. Lane 7, the product of β-actin in control hUC-MSCs, DNA marker DL,2000.
Identification of NTN and Lmx1α Protein Expression in hUC-MSCs and the Secretion of NTN
Immunofluorescence results showed that NTN and Lmx1α proteins were expressed at high level in infected hUC-MSCs: NTN was expressed in the cytoplasm (Fig. 8 C), whereas Lmx1α was expressed in the nucleus (Fig. 8 A). These two proteins were not detected in control hUC-MSCs (Fig. 8 B, D).
(A) The expression of Lmx1α in hUC-MSCs infected with Ad-Lmx1α. (B) The expression of Lmx1α in control hUC-MSCs. (C) The expression of NTN in hUC-MSC infected with Ad-NGFpreproNTN. (D) The expression of NTN in control hUC-MSCs. Scale bar: 100 µm.
From WB result we found that the band with a strong signal appearing in the membrane at approximately 12 kDa which characterized as NTN was observed in cytoplasm and culture medium (24 kDa was dimmer of mature NTN) (Fig. 9). However, the expression of Lmx1α was only be detected in cytoplasm (36 kDa) (Fig. 10). The expression of these two proteins was not detected in control group.
Lane 1, was loaded with the cell lysis infected with Ad-NGFpreproNTN. Lane 2, was loaded with the medium harvested from Ad-NGFpreproNTN infection. Lane 3, was loaded with the cell lysis from control hUC-MSCs. Lane 4, was loaded with the medium from control hUC-MSCs.
Lane 1, was loaded with the cell lysis infected with Ad-Lmx1α. Lane 2, was loaded with the medium infected with Ad-Lmx1α. Lane 3, was loaded with the cell lysis from control hUC-MSCs. Lane 4, was loaded with the medium from control hUC-MSCs.
ELISA Detection of NTN Secretion
The student’s t test compared the means of OD450 between the conditional medium and the control medium, there were significant difference between these two groups (Fig. 11).The expression of NTN at 48 h was higher than 24 h, 72 h and 96 h. These results indicated that NTN be secreted into the culture medium.
Identification the Bioactivity of NTN
Isolated neuronal cells were strong light refraction and slender axons. These cells were co-cultured with B27 and conditional medium. Cells in the experimental group were treated with NTN-conditioned medium were alived after 21 days cultured, according to observations, these cells exhibited neuronal morphology and the survival rate was 80% (Fig. 12 B). In contrast, a large number of cells in the control group were shrunk, and there were few surviving cells with intact morphology after 21 days cultured (Fig. 12 A). Immunohistochemistry showed TH expressed in the treated group, suggesting that the surviving cells were dopaminergic neurons (Fig. 12 C).
(A) The neurons cultured in neural basal (2% B27) alone. Neurons are most dead. (B, C) the neurons cultured in neural basal (2% B27) and NTN condition medium (1∶1). The result of TH immunohistochemistry reveals some neurons are alive and grow well. Scale bar: 100 µm.
Identification of Inducing hUC-MSCs
Real-time PCR detected the neuron-specific genes.
After 21 days induction, the transcriptional levels of TH, Msx-1, Nestin, MAP-2, Lmx1β, Foxα2, Pitx3, DAT, β-tubulin III, Nurrl and EN1 were significantly upregulated. The upregulation of TH suggested the cells had been induced to dopaminergic neurons. Nestin is a marker that is specifically expressed in neuronal precursor cells, and these results showed that the transcription of nestin was significantly reduced on the 21st day induction, suggested the induced cells were going to differentiate into mature neurons. It is also worth mentioned that the NSE transcription level was similar between cells before and after induction, suggesting that genes were expressed highly in uninduced cells. The statistical analysis (student’s t test) revealed significant difference in the transcriptional levels of 11 genes (TH, Msx-1, nestin, MAP-2, Lmx1β, Foxα2, Pitx3, DAT, β-tubulin III, Nurrl and EN1) between cells induced for 21 days and normal cells, and between cells induced for 21 days and cells induced for 7 days (Fig. 13).
Transcription of neural-specific genes like TH, Msx-1, Nestin, MAP-2, Lmx1β, Foxα2, Pitx3, DAT, β-tubulin III, Nurrl, EN1 and NES was analyzed by real-time PCR. All samples were normalized with β-actin (* p<0.05 compared with non-induecd cells; # p<0.05 compared with cells induced for 7 days).
Immunofluorescence detection of neuron-specific protein expression.
After seven days induction, immunofluorescence was able to detect expression of the neuronal precursor cell-specific protein nestin (Fig. 14 F) but not the expression of proteins specific for mature neurons (Fig. 14 G, H, I, J). After 21 days of induction, the immunofluorescence results revealed the expression of proteins specific for mature neurons, including NSE (Fig. 15 F), MAP-2 (Fig. 15 H), β-tubulinIII (Fig. 15 G) and the dopaminergic neuron-specific antigen TH (Fig. 15 J), whereas the nestin expression level was significantly decreased (Fig. 15 I). The expression of these mature proteins was not detected in the control group (Fig. 15 A, B, C, D; Fig. 14 A, B, C, D, E).
Scale bar: 100 µm.
Scale bar: 100 µm.
Effect of Induced hUC-MSCs in Parkinsonian Rhesus Monkeys
Behavioral evaluation.
We found that all monkeys who were lesioned by MPTP displayed acute symptoms with reduced motor movements and facial expressions. After the administration of therapeutic cells, instant behavior restorations were observed in cell therapy group. One weeks after therapy, the monkeys injected with cells not only made more vigorous movements, but also show good balance ability and had no handicap in the motor movements in this entire experiment cours. However, the monkeys in the control group displayed no significant behaviors recovery expressed as reduced movement, loss of facial expression and holding the cage for balance.
One week after surgery, behavior changes were evaluated by the UPDRS. The evaluation was conducted three times a week and last for six months (Fig. 16 A). Significant difference was observed in behavior rating scores between cell therapy group and HBSS control group. (Fig. 16 B).
(A) Evaluation of the behavior restoration of the normal group, HBSS group and cell transplanted therapy group (n = 3). (B) Comparison of the behavior recovery rating score between the HBSS group and cell therapy group. (n = 3, * p<0.05 compared with cell therapy group; # p<0.05 compared with cell therapy group).
Effect of Apomorphine-induced rotation.
Apomorphine was injected from the fourth week after the model was established, and the results were shown in Fig. 17 A. The rotation rate of the experimental animals in the cell transplantation group was reduced to 16 turns/min in the fourth week, whereas that of the HBSS group was increased to 34 turns/min. Following five months therapy, the cell therapy group animals could control their rotation behavior and stop rotation in 10 min. The final rotation rate in cell therapy group was 5 turns/min. In HBSS group, the animals could not control their rotaion behavior and the final rating was 40 turns/min. There was significant difference in rotation rating scores between cell therapy group and HBSS group (Fig. 17 B).
(A) The apomorphine-induced revolution of the experimental animals in the therapy group and HBSS group. (B) Statistical illustration of the cycle per minute the monkeys revolved, induced by apomporphine (n = 3, * p<0.05 compared with cell therapy group; # p<0.05 compared with cell therapy group).
Histological assessment.
In HBSS group, TH positive neurons in the lesioned substantia nigra side were more or less lost (Fig. 18 A). However, there were many TH positive cells in the left side (Fig. 18 B). Moreover, we have examined histopathological section of substantia nigra by HE staining (Fig. 19 A, B), the results were the same as TH immunohistochemical. However, the cell therapy group has a greater color reactive area and intensity compared to HBSS group, which indicated that the neuroprotection effect from NTN delivered by Ad-NTN has protected the DA neurons which were lesioned by MPTP (Fig. 18 C, D). The HE staining results were also showed in the right substantia nigra have a small number of neurons (Fig. 19 C) but were fewer than the left side (Fig. 19 D). The surviving neurons on the right side show normal morphology and only a few showed pyknosis.
Scale bar: 100 µm.
Scale bar: 100 µm.
Scale bar: 100 µm.
Discussion
It has been reported that the human umbilical cord contained abundant of MSCs [13], [26], [27], [28]. Different culture methods were used to guide cells to express neuronal phenotypes [16], [17], endothelial phenotypes of myocardial cells markers [29], [30].The facts explained that these cells have multi-differentiation potential. The current methods used for the isolation of hUC-MSCs mainly include the enzyme digestion and the tissue explant adherent. The enzyme digestion has the advantage of rapid isolation, but the enzyme system may degrade the outer leaflet of the cell membrane, and damage cells if improper control of time. So we utilized the tissue explant adherent method to isolate hUC-MSCs. The hUC-MSCs obtained in this study showed similar to previous reports: including cell morphology, immunophenotype, cell proliferative and differentiation potential.
Studies have suggested that stem cells could be induced and played a role as engineered cells to release neurotrophic factors, providing neuronal protection and promote self-healing [31], [32]. Cells therapy is undoubtedly the most promsing therapeutic approach for PD. The aim of this study was to replace lost neurons and restore the net work of striatal dopaminergic nerve terminals in PD. So we focused on inducing the hUC-MSCs into dopaminergic neurons. After inducing, Real-time PCR results showed that the transcriptional level of the Msx1 gene was upregulated after inducing. The Msx1 and Lmx1α genes were played important roles in the midbrain dopaminergic neurons during embryonic development, the upregulation of Msx1 expression resulted in a transcriptional cascade, leading to the induced cells into mature dopaminergic neurons expressing Pitx3 and TH. In the present studies, NTN secreted by hUC-MSCs was abled to enhance dopaminergic neurons survival and play a nutritive role in sensory neurons. In other words, NTN was abled to prevent the deterioration of induced neurons derived from hUC-MSCs.
Lmx1α is presumed to be the first expressed intrinsic dopaminergic determinant. We hypothesized the expression of endogenous transcription factors (upregulation of Lmx1α and NTN genes) could activate the SHH/Lmx1α pathways involved in neuronal development. It has also been reported that transplated cells to substantia nigra and striatum together can enhance recovery in PD model [33]. So we choose to transplant induced cells into the substantia nigra, the caudate nucleus and putamen to alleviate the symptoms of PD.
The animal experiment results indicated that the obvious behavioral recovery was not observed in HBSS control group. The symptoms of control monkeys get worsen. The symptoms in cell therapy animals were gradually alleviated. TH immunohistochemistry results also demonstrated that there were surviving neurons in the lesioned side substantia nigra of the cell therapy group and there were no significant difference between the caudate nucleus and the putamen. These results were the same as PD clinically pathological changes. In this study, the grafted cells which were labeled with BrdU were detected in the right side of substantia nigra. These results were also indicated that the transplanted cells were survival; on the one hand, transplanted neural-like cells are capable of replacing lost neurons and restoring the lost net work of striatal dopaminergic nerve terminals in PD. On the other hand, transplanted neural-like cells are capable of promoting the differentiation potential and providing trophic effects on endogenous neural stem cells probably through their continuous NTN and nutritional factors secretion. The furtuer secretion of NTN by induced DA neurons could provide neurons nutritional protection on the cells differentiated by induced cells and neural stem cells and form a virtuous circle.
Conclusions
In this study, we induced hUC-MSCs into neuron-like cells in vitro that are able to secret dopamine. In addition, we transplanted those cells into the brains of PD monkeys. These neuron-like cells could perform the physiological functions of dopaminergic neurons and may play a therapeutic role to ameliorate the symptoms of PD. We believe the results from this study would provide the basis for developing novel cell therapy for PD in future.
Acknowledgments
We are grateful to Huaisheng Shi and Jinyuan Wu for assistance with image capture during the expriments.
Author Contributions
Conceived and designed the experiments: HL. Performed the experiments: MY YZ Wanpu Wang XW S. Li. Analyzed the data: MY MS. Contributed reagents/materials/analysis tools: Wenju Wang ZH S. Lu DT. Wrote the paper: MY.
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