Ethics
All animal procedures were approved by the Institute of Animal Care and Use Committee at Kaohsiung Chang Gung Memorial Hospital (Affidavit of Approval of Animal Use Protocol No. 2019062504) and performed in accordance with the Guide for the Care and Use of Laboratory Animals.
Animals were housed in an Association for Assessment and Accreditation of Laboratory Animal Care International (AAALAC; Frederick, MD, USA)-approved animal facility in our hospital with controlled temperature and light cycles (24 oC and 12/12 light cycle).
Animal model of acute traumatic spinal cord injury
Pathogen-free, adult-male Sprague-Dawley (SD) rats (n=40) weighing 300-325 g (Charles River Technology, BioLASCO Taiwan Co. Ltd., Taiwan) were utilized in the present study. Animals were anesthetized by inhalational 2.0% isoflurane and placed in prone position on a warming pad at 37 °C for laminectomy. Sham-operated control (SC) animals underwent opening the skin and muscle layers only, while acute TSCI groups received acute TSCI procedure. The step-by-step procedure for creating an animal model of acute TSCI is listed below:
- The rats were anesthetized by inhalation of 2.0 % isoflurane, then placed in prone position on a warming pad at 37 °C to secure the head and shave the back hair.
- Skin incision was carried out at the T10~T12 levels, subperiosteal dissection of the paraspinal muscle, and then a laminectomy was performed at T10 to T12 to expose the spinal cord.
- A modified aneurysm clip was used to create an impact-compression injury of the spinal cord. The clip was left for compressing the spinal cord for 30 seconds prior to be removed by the operator.
- After induction of the aforementioned TSCI, the muscles were sutured using 3–0 vicryl suture (Ethicon, Somerville, NJ) and the skin/muscle layers were finally closed with Michel clips.
- The animals recovered from anaesthesia in a portable animal intensive care unit (ThermoCare®) for 24 hours, then were allowed to recover in a cage. Bladders were expressed 3 times daily until spontaneous voiding occurred, and any hematuria or urinary tract infection was treated with ampicillin (100 mg/kg by subcutaneous administration twice daily for 5 days).
- Post-op wound care and the motor/sensory neurologic function assessment were performed consistently.
- Walking feature and neurological status were recorded by days 1, 3, 7, 14, 28, 35, 42 and 49 after TSCI procedure.
Animal grouping
The animals (n=40) were equally categorized into group 1 [sham-operated control (only open the skin and muscle layer of spinal cord area)], group 2 (acute TSCI), group 3 [TSCI + HBO (1.5h per day for 14 consecutive days with the first time point at 3h after the acute TSCI procedure), group 4 [TSCI + ADMSCs (1.2 x 106 cells/per time) by intravenous injection at 3h and days 1 and 2 after acute TSCI procedure] and group 5 (TSCI + HBO + ADMSCs), respectively. Animals in each group were euthanized by day 49 after TSCI procedure and the spinal cord specimen in each animal was harvested for individual study.
Isolation of adipose tissue for culturing mesenchymal stem cells
For preparation of allogenic ADMSCs, additional 12 rats were utilized in the present study. The procedure and protocol have been clearly described in our previous reports [24, 25]. Briefly, rats in groups 4 and 5 were anesthetized with inhalational 2.0% isoflurane 14 days before TSCI procedure for harvesting the adipose tissue surrounding the epididymis. The tissue was then be cut into < 1 mm3 pieces using a pair of sharp, sterile surgical scissors. Sterile saline (37˚C) was added to the homogenized adipose tissue in a ratio of 3:1 (saline: adipose tissue) by volume, followed by the addition of stock collagenase solution to a final concentration of 0.5 U/mL. The cells obtained were placed to the rocker for incubation. The contents of the flask were transferred to 50 mL tubes after digestion, followed by centrifugation at 600 g for 5 minutes at room temperature. The flow-through was pipetted to a 40 mm filter into a new 50 mL conical tube. The tubes were centrifuged for a third time at 600 g for 5 minutes at room temperature. The cells were resuspended in saline again. Isolated ADMSCs were cultured in a 100 mm diameter dish with 10 mL DMEM culture medium containing 10% FBS for 14 days.
Basso, Beattie, Bresnahan (BBB) functional scale for assessment of the locomotor capacity of rats after acute TSCI
The animals were followed for 7 weeks (i.e., 49 days) after acute TSCI procedure. The procedure and protocol of BBB scale were based on the previous reports [31, 32]. In detail, after the aforementioned period each rat was placed in an 80 x 80 x 30 cm3 clear box lined with a blue non-slippery material and stimulated to move freely. Their movement was video-recorded. Identical copies of the edited videos were given to two independent evaluators who were blinded with regards to the degree of injury severity. Each evaluator made a determination of the locomotor capacity of the rats using the BBB functional scale. Finally, the parameters in each rat were calculated by averaging scores collected from these two evaluators.
Hyperbaric oxygen (HBO) therapy
The procedure and protocol of HBO therapy were based on a recent report [30]. Briefly, to induce tissue-level hyperoxia, SD rats were subjected to HBO administration in an animal tabletop chamber (Piersol-Dive, model 4934) with the animals exposed to 100% oxygen at 2.4 atmospheres absolute (ATA) for 90 minutes one session for 14 consecutive days.
Western blot analysis
The spinal cord from the rats of the sham control and experimental groups were harvested as previously described [36]. Equal amounts (50 µg) of protein extracts were loaded and separated by SDS-PAGE using 8-12% acrylamide gradients. After electrophoresis, the separated proteins were transferred electrophoretically to a polyvinylidene difluoride (PVDF) membrane (Amersham Biosciences). Nonspecific sites were blocked by incubation of the membrane in blocking buffer [5% nonfat dry milk in T-TBS (TBS containing 0.05% Tween 20)] overnight. The membranes were incubated with the indicated primary antibodies [NADPH oxidase (NOX)-1 (1: 2000, Sigma), NOX-2 (1:750, Sigma), toll like receptor (TLR)-4 (1:1000, Novus Biologicals), myelin and lymphocyte (MAL) (1:1000, Invitrogen Antibodies), myeloid differentiation primary response 88 (MyD88) (1:2000, Abcam), TNF receptor associated factor (TRAF) 6 (1:1000, Abcam), IκB kinase α (IKK-α) (1:1000, Abcam), IKK-ß (1:1000, Cell Signaling), interleukin (IL)-1β (1:1000, Cell Signaling), tumor necrosis factor (TNF)-α (1:1000, Cell Signaling), nuclear factor (NF)-κB (1:600, Abcam), substance p (1:1000, Invitrogen Antibodies), PI3K (1:1000, Cell Signaling), phosphorylated (p)-AKT (1:1000, Cell Signaling), p-m-TOR (1:1000, Cell Signaling), Nav 1.3 (1:200, Alomone Labs), Nav 1.8 (1:2000, Abcam), Nav 1.9 (1:200, Alomone Labs) and actin (1:10000, Millipore)] for 1 hour at room temperature. Horseradish peroxidase-conjugated anti-rabbit immunoglobulin IgG (1:2000, Cell Signaling) was used as the secondary antibody for one hour incubation at room temperature. The washing procedure was repeated eight times within an hour, and immunoreactive bands were visualized by enhanced chemiluminescence (ECL; Amersham Biosciences) after exposure to Biomax L film (Kodak). For quantification, ECL signals were digitized using Labwork software (UVP).
Immunofluorescent (IF) staining
IF staining proceeded as we previously reported [36]. Rehydrated paraffin sections were first treated with 3% H2O2 for 30 minutes and incubated with Immuno-Block reagent (BioSB, Santa Barbara, CA, USA) for 30 minutes at room temperature. Sections were then incubated with primary antibodies specifically against CD68 (1:500, Abcam), glial fibrillary acidic protein (GFAP) (1:500, Dako), γ-H2AX (1:1000, Abcam), p-JNK (1:500, R&B systems), p-ERK (1:200, Abcam), p-p38 (1:500, Gene Tex), NF-200 (7.5mg, Abcam), Nav1.3 (1:100, GeneTex), Nav1.8, Nav1.9 (1:100, GeneTex) and peripherin (1:1000, Abcam). Sections incubated with irrelevant antibodies served as controls. Three sections of DRG specimens were analysed in each rat. For quantification, three randomly selected high-power fields (HPFs) were analysed per section. The mean number of positively stained cells per HPF for each animal was determined across all nine HPFs.
Histological quantification of spinal cord injured area
The H.E. stain was used for identifying the area of spinal cord injury. The spinal cord specimens were sectioned at 4 µm for light microscopy for each animal. Three spinal cord sections from each rat were analyzed and three randomly selected high-power fields (HPFs; 10x) were examined in each section.The integrated area (µm2) of spinal cord injury on each section was calculated using the Image Tool 3 (IT3) image analysis software (University of Texas, Health Science Center, San Antonio, UTHSCSA; Image Tool for Windows, Version 3.0, USA). Three randomly selected HPFs (10x) were analyzed in each section. After assessment of the number of pixels in each injured area per HPF, the numbers of pixels obtained from three HPFs were summed. The procedure was repeated in two other sections for each animal. The mean pixel number per HPF for each animal was then calculated by summing up all pixel numbers and divided by 9. The mean integrated area (µm2) (i.e., the morphological destructive area) of per HPF was obtained using a conversion factor of 19.24 (1 µm2 corresponded to 19.24 pixels).
Statistical Analysis
Quantitative data were expressed as mean ± SD. Statistical analysis was adequately performed by one way ANOVA followed by Bonferroni multiple-comparison post hoc test. Statistical analysis was performed using SAS statistical software for Windows version 8.2 (SAS institute, Cary, NC, USA). A probability value <0.05 was considered statistically significant.