Background
Cerebral palsy (CP) is defined as a group of permanent movement and posture disorders that results in restricted activity due to non-progressive disturbances that occur early in brain development [
1,
2]. Although it is recognized that various physiological and cognitive symptoms are associated with the disease, chronic pain has been a subject of clinical and empirical concern in recent years [
3,
4]. The obstruction in diagnosing the syndrome stems from its different classifications, for the reason that CP can be defined by anatomical brain damage in the cerebral cortex, extrapyramidal system, pyramidal tract, or cerebellum [
5]. Routine therapies for CP include orthomorphia, neurotomy, physical therapy, language training, motor function training, and intramuscular injections of botulinum toxin A [
6]. Stem cell transplantation is suggested to be a new and promising treatment for CP [
7]. Nevertheless, this procedure is still at the preliminary stage of investigation and no clinical trial results have been published so far [
8,
9].
Several types of stem cells are reported to be candidates for treating CP, including olfactory ensheathing cells, human embryonic neural stem cells, umbilical mesenchymal stem cells (MSCs), as well as bone marrow mesenchymal stem cells (BMSCs) [
10,
11]. Autologous MSCs may be a good source of cells, which have been introduced for the treatment of CP due to their roles in tissue repair together with the regulation of immunological processes [
12]. In addition, accumulating studies have indicated that human BMSCs show neural phenotypes, which is capable of differentiating into neural stem cell (NSC)-like cells in vitro [
13‐
15]. Based on which, we hypothesized that BMSCs could be used as a novel treatment for the patients with CP. X-linked inhibitor of apoptosis protein (XIAP) is the most effective inhibitor of natural apoptosis through inhibiting the initiator (e.g. caspase-9) and effector (e.g. caspase-3 and -7) caspases along with inhibiting caspase-independent cell death [
16,
17]. It is reported that the regulation of XIAP may be a promising neuroprotective strategy for treating acute and chronic neurodegenerative disorders [
18]. Furthermore, a study has shown that combining XIAP with MSC-delivered soluble tumor necrosis factor-related apoptosis inducing ligand (sTRAIL) contributed to the regression of primary tumors without lacking of metastases [
19]. Saito et al. have demonstrated that XIAP plays an significant role in the control of the death of apoptotic neuronal cells after transient focal cerebral ischemia [
20]. Furthermore, XIAP is of great importance in the apoptosis resistance of HL-60 cells when co-cultured with BMSCs through direct cell contact, and the inhibition of XIAP provides a new strategy for treating acute myeloid leukemia [
21]. Therefore, we conducted this study to investigate the effects of adenovirus-mediated XIAP modification of BMSCs on brain injury in rats with CP.
Materials and methods
Ethics statement
The study was approved by the animal ethics committee in The First Affiliated of Zhengzhou University (approval number: 2019-KY-220). All animal work was conducted to relieve their pain according to relevant national and international guidelines.
Experimental animals
A total of 73 Sprague–Dawley (SD) rats in clear grade (regardless of gender, aging 7 days and weighting 20 ± 5 g) were purchased from Beijing Vital River Laboratory Animal Technology Co., Ltd. (Beijing, China). The rats had free access to eating and drinking in a room with 12 h day/night cycle, temperature of (23–25) °C, humidity of 45–60% as well as regular disinfection and ventilation.
Culture and identification of BMSCs in rats
One rat was euthanized by cervical dislocation, and immersed in 75% ethanol for 5 min. The tibia and femur were separated in aseptic condition, and the muscle and fibrous tissues were removed. The marrow cavity was washed several times in DMEM/DF12 medium (Gibco, Grand Island, NY, USA) with a 1 mL injector, until the marrow cavity became white and bright. The cells were suspended and inoculated into a culture flask with the concentration of 1 × 106 cells/mL and incubated in an incubator at 37 °C with 5% CO2 for 3 days. When the adherent cells reached 80–90% confluence, the culture medium was removed. The cells were detached with 0.25% trypsin at room temperature and sub-cultured in the ratio of 1:2. Afterwards, the culture process was repeated every 2 to 3 days, when the cell confluence reached 80–90%, the sub-culture process was repeated.
The cultured and amplified rat’s BMSCs at passage 3 were detached with 2.5 mL trypsin, then washed with PBS containing 10 g/L bovine serum albumin (BSA). The cells were suspended for preparing the single cell suspension at a density of 2 × 105 cells/mL. The cells were added with rabbit anti-mouse CD29, CD44, CD34 and CD4 (each 5 μL) and homotypic control flow antibody and incubated at room temperature in dark for 15–20 min. The cells were detected by a flow cytometer (Becton, Dickinson and Company, Franklin Lake, New Jersey, USA).
When the cells in the culture dish reached 80–90% confluence, the cells were seeded to the six-well plate, and cultured in the incubator. After reaching 70% cell confluence, the original culture medium was removed and then cultured in osteogenic differentiation medium (2 mL/well, Guangzhou Saiye Biotechnology Co., Ltd., Guangzhou, Guangdong, China). The liquid was changed once every 3 days, five times in total. After abandoning the original culture medium, the cells were fixed with 10% neutral formaldehyde solution, stained with 1 mL alizarin red S (Cyagen Biosciences, Santa Clara, CA, USA) for 5 min. The staining was observed under the microscope.
When the cells in the culture dish reached 80–90% confluence, the cells were inoculated to the six-well plate, and cultured in the incubator. After reaching 100% cell confluence, the original culture medium was removed and then cultured in adipose induced differentiation medium (2 mL/well, Guangzhou Saiye Biotechnology Co., Ltd., Guangzhou, Guangdong, China). After 3 days, the medium was replaced by growth medium and then changed into adipose induced differentiation medium after 24 h. The above two medium were used alternately, with a total of three to five times exchange. The cells were fully cultured for about a week, in which the medium solution was changed every 3 days. After abandoning the original culture medium, the cells were fixed with 10% neutral formaldehyde solution, stained with 1 mL Oil red o solution (Cyagen Biosciences, Santa Clara, CA, USA) for 30 min. The staining was observed under the microscope.
BMSCs transfected with adenovirus expression vector Ad-XIAP-green fluorescent protein (GFP)
BMSCs was inoculated in a 24-well plate at the density of 1.5 × 105 cells/well and cultured for 24 h. The Ad-XIAP-GFP virus solution with the multiplicity of infection (MOI) of 100, 200 and 400 were transferred into the BMSCs. After 12 h, the solution was changed and the complete culture medium was added for further culture. The expression of GFP in BMSCs transfected with Ad-XIAP/GFP was observed by a fluorescence microscope to determine the MOI. In order to verify the transfection efficiency, the cells which were infected with the MOI of Ad-XIAP/GFP and Ad-GFP on the 3rd day and the untreated cells were detected by reverse transcription quantitative polymerase chain reaction (RT-qPCR) and western blot analysis to detect the expression of XIAP mRNA and protein in cells. The BMSCs that successfully infected the recombinant adenoviral vector carrying the XIAP gene (Ad-GFP-XIAP) were named XIAP-BMSCs. BMSCs infected with empty vector virus (Ad-GFP) were named NC-BMSCs, and uninfected BMSCs were named as blank. Both Ad-GFP-XIAP and Ad-GFP expression vectors were constructed and identified by Shanghai Sangon Bioengineering Co., Ltd. (Shanghai, China).
Establishment of a rat model of CP
The rats were numbered according to their body weight and 12 rats were randomly selected as a sham group. The rat model of CP was established by ligating the left common carotid artery and anoxia for 2 h [
22] in the remaining 60 rats. The anesthetized rats were intraperitoneally injected with 1% pentobarbital sodium for anesthesia. The experimental rats were in supine on the surgical plate, fixed their limbs and heads, and disinfected with iodophor before the neck. The left common carotid artery was found in the triangle area at the junction of the inner side of the sternocleidomastoid and the anterior part of the neck, and the incision was sutured with a No. 0 wire. The experimental rats were immediately placed in an anoxic chamber at 37 °C. The mixture of 8% oxygen and 92% nitrogen was continuously filled with the flow rate of 1 L/min for 2 h. The whole process of anoxia was continuously monitored by an oxygen meter. In the sham group, the common carotid artery was isolated, and no ligation was performed without hypoxia treatment.
Experimental grouping and treatment
The successfully-modeled rats were divided into 5 groups, 12 rats in each group: CP group (establish a rat model of ischemic and anoxic CP without other treatment), CP + PBS group (on the 3rd day after modeling, stereotactic injection of 2 μL PBS into the left lateral ventricle of CP rats), CP + BMSCs group (on the 3rd day after modeling, stereotactic injection of 2 μL BMSCs into the left lateral ventricle of CP rats), CP + NC-BMSCs group (on the 3rd day after modeling, stereotactic injection of 2 μL NC-BMSCs into the left lateral ventricle of CP rats), and CP + XIAP-BMSCs group (on the 3rd day after modeling, stereotactic injection of 2 μL XIAP-BMSCs into the left lateral ventricle of CP rats). The rats in the CP + PBS group, CP + BMSCs group, CP + NC-BMSCs group and CP + XIAP-BMSCs group were fixed on the stereotactic locator on the 3rd day after modeling. The scalp sagittal incision was made under aseptic operation, and 2 μL PBS, BMSCs, NC-BMSCs and XIAP-BMSCs (about 5 × 105 BMSCs) were injected into the left ventricle via a microinjector.
Evaluation of nerve function injury
Neurobehavioral assessment of rats was conducted at 3 weeks after modeling.
Morris water maze test: The rats facing the water wall were placed in water several times from 4 water entry points to record the time when they found the hidden platform under the water surface, namely the escape latency.
Suspension test: The rat forelegs grabbed the 0.5 cm glass rod and observed the time of falling: < 10 s was 1 point, 10–30 s was 2 points, 31–119 s was 3 points, 2–5 min was 4 points, > 5 min was 5 points.
Slope test: The rats were placed on a 45° slope to observe the turning time.
Open field test: The covered box with length and width of 36 cm was divided into 9 equal size lattices at the bottom of the box, and then to record the activity of rats. More than 1/2 of the body part of the rat entered the adjacent grid was 1 point, and the hind limb of the rat stood was 1 point. The sum of the two points was the total score.
Hematoxylin–eosin (HE) staining
After the neurological deficit score was finished, 8 rats were taken from each group, and the brain was removed from the neck, and then the brain tissue was quickly separated on the ice. The brain tissue of 4 rats was placed in a prelabeled cryopreservation tube and rapidly put into liquid nitrogen, and then transferred to − 80 °C for the detection of RT-qPCR and western blot analysis. In addition, the brain tissues of 4 rats in each group were fixed in 4% paraformaldehyde for 24 h, dehydrated, embedded, and sliced with the thickness of 4 μm, which were used for HE staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining and immunohistochemical staining.
According to the isometric random method, each group of rats was randomly selected with five slices of brain tissue. The slices were dewaxed with xylene for 20 min, and hydrated with 100%, 95%, 80% and 70% for 5 min, respectively, stained with hematoxylin (Beijing Solarbio Science & Technology Co., Ltd., Beijing, China) for 4 min, differentiated with hydrochloric acid alcohol and washed with running water for 5 min. Next, the slices were stained with eosin (Beijing Solarbio Science & Technology Co., Ltd., Beijing, China) for 3 min, followed by gradient alcohol dehydration, xylene clearance, and sealing with neutral gum. Tissue staining was observed under an optical microscope (DSX100, Olympus, Tokyo, Japan).
TUNEL staining
According to the isometric random method, 5 slices of brain tissue were randomly selected from each rat in each group and immersed in 200 mL 0.1 mol/L sodium citrate buffer solution for 5 min under microwave heating, and then poured into 80 mL distilled water immediately. Next, the tissues were added with TUNEL solution ((Boster Biological Technology, Ltd., Wuhan, China) and reacted at 37 °C for 1 h. After that, the tissues were supplemented with converter-POD and reacted at 37 °C for 1 h. Lastly, the tissues were counterstained with hematoxylin, followed by gradient alcohol dehydration, xylene clearance, and sealing with neutral gum. The positive cells in the left brain region were counted when the brown granules were stained. Apoptotic index (AI) = the number of positive cells/the total number of cells × 100%.
Immunohistochemical staining
Five slices of brain tissue were randomly selected from each rat in each group and rinsed with PBS for three times, each time for 10 min, fixed with 4% 1-phosphofructaldolase (PFA) for 10 min, and rinsed with PBS for three times, each time for 5 min. After sealing with 5% goat serum, the tissues were added with primary antibody, glial fibrillary acidic protein (GFAP) (1:200, Abcam, Cambridge, MA, USA) and incubated at 37 °C for 2 h. Next, the tissues were rinsed with PBS for three times, each time for 10 min, supplemented with S-P compound and incubated at 37 °C for 30 min. Afterwards, the tissues were rinsed with PBS for three times, each time for 10 min, supplemented with 0.05% diaminobenzidine (DAB) solution, followed by alcohol dehydration, xylene clearance, and sealing with neutral gum. Under the same exposure condition, the images were analyzed by software Image-Pro Plus 6.0 (Media Cybernetics, Rockville, Maryland, USA), and 5 fields of vision were randomly selected to count the average number of positive cells of GFAP.
Transmission electron microscope observation
The remaining 4 rats in each group were anesthetized by intraperitoneal injection of 1% pentobarbital sodium after neurobehavioral evaluation. The heart was exposed by opening the chest, and the left ventricle was inserted into the ascending aorta by cutting the left ventricle into the ascending aorta and fixed with hemostatic forceps. The abdominal aorta was clamped with hemostatic forceps. The right atrium was cut open and 50 mL normal saline containing 12.5 U/L heparin sodium was quickly infused. After the blood was washed out, 2% glutaraldehyde was perfused with 100–150 mL glutaraldehyde. About 1 mm3 ischemic brain tissue mass was fixed with 4% glutaraldehyde for 4 h and 1% osmium acid for 2 h, followed by gradient ethanol dehydration, epoxy resin 618 embedding as well as uranium acetate and lead citrate electron staining. The brain cells were observed under a JEM-1400Plus electron microscope (JEOL, Tokyo, Japan).
RT-qPCR
The Trizol one-step method (Invitrogen, Carlsbad, CA, USA) was implemented to extract the total RNA in brain tissues and BMSCs. The complementary DNA (cDNA) was obtained by avian myeloblastosis virus (AMV) reverse transcriptase after obtaining l μg RNA. SYBR Green was used for qPCR, and glyceraldehyde phosphate dehydrogenase (GAPDH) was selected as an internal control. PCR primer was designed and synthesized by Invitrogen (Carlsbad, CA, USA) (Table
1). RT-qPCR instrument (ABI 7500, ABI, Foster City, CA, USA) was used for detection. The 2
−ΔΔCt method was used to analyze the ratio relation of target gene expression between the experimental group and the control group. The experiment was repeated in triplicate.
XIAP | F: 5′-CCCTTGGGAACAGCATGCTA-3′ |
R: 5′-AATCCAGCACCACAGTAGGC-3′ |
GFAP | F: 5′-AGGCCTAGGCATCTGGAAGA-3′ |
R: 5′-ATCCTTCTGAGGCCCTCCAT-3′ |
GAPDH | F: 5′-CAGCCGCATCTTCTTGTGC-3′ |
R: 5′-GGTAACCAGGCGTCCGATA-3′ |
Western blot analysis
The proteins from brain tissues and BMSCs were extracted and the protein concentrations were determined referring to the instructions of the bicinchoninic acid assay (Boster Biological Technology, Ltd., Wuhan, China). After the proteins were separated by 10% sodium dodecyl sulfate polyacrylamide gel electrophoresis (Boster Biological Technology, Ltd., Wuhan, China), they were transferred to a nitrocellulose membrane using the wet transfer method. Subsequently, the protein samples were transferred to polyvinylidene fluoride membrane and blocked with 5% BSA for 1 h. Afterwards, the membranes were added with the primary antibodies to XIAP (1: 1000, ab229050), cleaved caspase-3 (1:500, ab49822), Bax (1:1000, ab53154), Bcl-2 (1:1000, ab196495) and β-actin (1:1000, ab8227). All these antibodies were purchased from (Abcam, Cambridge, MA, USA) and incubated at 4 °C overnight. The membranes were then rinsed with TBST for 3 times, each time for 10 min. The corresponding IgG secondary antibody labeled by horseradish peroxidase (1: 2000, ab6721, Abcam, Cambridge, MA, USA) were incubated for 2 h at room temperature so as to wash the membranes for 3 times, each time for 10 min. After DAB coloration, a gel imager was used for photographing (Gel Doc XR, Bio-Rad, Hercules, CA, USA). The gray value analysis of target band was analyzed by Image J software (National Institutes of Health, Bethesda, Maryland, USA).
Enzyme-linked immunosorbent assay (ELISA)
The brain tissue was thawed at room temperature and weighed it accurately. The content of acetylcholine (Ach) and the activity of acetylcholinesterase (AchE) in the homogenate of rat brain tissue were determined by ELISA kit (Nanjing Jiancheng Institute of Bioengineering, Nanjing, Jiangsu, China) after homogenization in tissue lysate.
Statistical analysis
All statistical analyses were performed using the SPSS 21.0 software (IBM SPSS, Inc., Chicago, IL, USA). The data were normally distributed by Kolmogorov–Smirnov test. The measurement data were expressed as mean ± standard deviation. The t test was used for the comparison between the two groups, and one-way analysis of variance (ANOVA) was used for the comparison among multiple groups. Fisher’s least significant difference t test (LSD-t) was used for pairwise comparisons after ANOVA analysis. P values ≤ 0.05 were considered statistically significant.
Discussion
The neonatal mortality rate was decreased due to the improvements in perinatal emergency medicine, while the incidence of premature CP and hypoxic ischemic encephalopathy has increased over time [
6]. Routine rehabilitation treatment for CP is unable to improve the motor function of those patients who with moderate-to-severe chronic CP [
24,
25]. Previously, MSCs have been considered as an important experimental tumor therapy based on their intrinsic anticancer properties or integrated with the expression of therapeutic transgenes [
19]. In this present study, we aim to investigate the effects of lentivirus-mediated XIAP modification of BMSCs on brain injury in rats with CP. Collectively, the results of this study highlights that BMSCs modified by XIAP can inhibit the apoptosis of brain nerve cells and the activation of astrocytes and increase the activity of AchE, so as to lower the CP caused by cerebral ischemia and hypoxia in rats.
Both cell type and cell modifications play a role in affecting the cells homing after intravascular delivery [
26]. The application of BMSCs is particularly promising for the reason that they home to both the injured tissue or secrete factors that induce brain repair [
27]. It has been demonstrated that cellular engineering, cell culture conditions as well as cell surface modifications may also regulate cells’ migratory behavior and immunomodulatory properties and further improve their therapeutic potential [
28,
29]. Experiments have revealed that transplanted NSCs show strong plasticity, which is able to integrate with host cells and also become functional substituting nerve cells by establishing a stable synaptic connection [
30‐
32]. At the same time, NSCs may generate neurotrophic factors that promote the recovery of impaired tissues in the damaged brain region [
33‐
35]. As previously reported, MSCs utilized in the model of experimental stroke have elevated the functional recovery of neurological deficits resulted from cerebral ischemia [
27]. Besides, another study suggested that MSC transplantation may improve the functional recovery of patients with stroke patients in the absence of adverse side effects [
36]. Consistent with these findings, we found that BMSCs is helpful for the treatment of CP to some extent.
In addition, our study also demonstrated that BMSCs modified by XIAP improved the neurobehavioral situation, decreased content of Ach and increased activity of AchE, attenuated brain pathological injury, inhibited apoptosis of brain nerve cells and the activation of astrocytes in CP rats. Several studies have elucidated that in an animal model of cerebral hypoxic-ischemic injury, apoptosis is known as a delayed process of neuronal cell death [
37,
38]. The upregulation of XIAP suppresses ischemic damage in the hippocampus and also recovers neurologic function of adult rat after global ischemia [
39]. Wang et al. have stated that the activities of caspase-3 and -9 were virtually abolished; and relative to wild-type mice after hypoxicischemic injury, and XIAP neonatal transgenic mice exhibited decreased tissue loss [
40]. In line with the results in our study, neuronal XIAP expression is increased in both developing brain of human and rat after ischemic injury [
17]. Meanwhile, overexpression of XIAP in the penumbra of subacute infarcts has been suggested to play a role in the suppression of both caspase-dependent and -independent apoptosis in the position of ischemic developing brain [
41‐
43]. Furthermore, it has been revealed that PI3K/Akt/XIAP axis is implicated in the apoptosis resistance of HL-60 cells in the condition of co-culturing with BMSCs through direct cell contact, and the inhibition of PI3K/Akt/XIAP axis may provide a promising therapeutic strategy for the treatment of acute myeloid leukemia [
21]. All these aforementioned confirmed the important binding role of XIAP and BMSCs.
XIAP is a major member of the family of endogenous inhibitors of apoptosis (IAPs), which achieves anti-apoptosis by inhibiting different caspases in vitro and in vivo [
44]. XIAP is the strongest caspase inhibitor in the IAP family [
45]. Ischemic brain injury is a frequent and critical disease of the nervous system. Cerebral ischemia is often accompanied by a large number of neuronal apoptosis, which is closely related to the caspase family. Eberhardt et al. have found that XIAP gene was transfected into rat brain substantia nigra cells by adenovirus in an mitochondrial permeability transition pore-induced animal model of Parkinson’s disease. To some extent, up-regulation of XIAP can reduce the death of substantia nigra cells and protect dopamine neurons [
46]. Simons and Wagenknecht have found that increased expression of XIAP in cerebellar granule cells and glial cells can reduce the damage of such nerve cells. It is speculated that XIAP may have strong anti-apoptotic effect in the central nervous system [
47,
48]. BMSCs not only participate in the repair of neurological function of ischemic brain injury, but also serve as a carrier for gene therapy of cerebral ischemia, while whether overexpression of XIAP in BMSCs can prevent apoptosis in vitro remains to be unearthed, which could be verified in future study if condition permitting (Additional file
1).
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