This study was approved by the Ethics Committee of Zhangjiakou First Hospital (approval No. 2024-KY-18). All participants were informed of the study objectives and potential risks and provided written informed consent before enrollment. Venous blood samples were collected from healthy controls during routine physical examinations and from patients with SCI immediately after hospital admission. Laboratory measurements were performed by the hospital clinical laboratory. The research tools used in this protocol are listed in the Table of Materials.
1. Subjects
A total of 75 patients with SCI were recruited from Zhangjiakou First Hospital between January 2023 and January 2025. The inclusion criteria were SCI confirmed by computed tomography (CT) or magnetic resonance imaging (MRI) and a time from injury to hospital admission of ≤ 12 h. The exclusion criteria were a history of spinal cord or brain trauma or surgery within the previous 6 months; severe cardiovascular disease, including myocardial infarction or arrhythmia; pregnancy or lactation; and malignant tumors, impaired liver or kidney function, severe cerebrovascular disease, or infectious diseases.
According to the American Spinal Injury Association (ASIA) neurological classification standards26, 75 patients with SCI were classified into the normal neurological function (n = 21), incomplete SCI (n = 36), and complete SCI (n = 18) groups. The distribution of injury sites was as follows: cervical, 36.0%; thoracic, 30.7%; and lumbar, 33.3%. 30 healthy individuals matched to the study population were randomly recruited to serve as the control group. Baseline clinical information was collected for all participants. The inclusion criteria for healthy individuals were no history of spinal cord or brain trauma, surgery, or neurological disorders; no history of chronic inflammatory diseases, autoimmune disorders, or malignancies; no severe cardiovascular, hepatic, or renal disease; no acute or chronic infection within the previous 4 weeks; no pregnancy or lactation; and age and sex matched to the SCI group.
The Functional Independence Measure (FIM) was used to assess functional independence in daily activities. The maximum FIM score is 126. Tactile sensation, acmesthesia, and motor scores were used to evaluate sensory and motor function. The maximum tactile sensation and acmesthesia scores were 112, and the maximum motor score was 100. Lower scores indicate more severe neurological impairment.
2. Cell culture, model construction, and transfection
Immortalized mouse microglial BV2 cells were obtained from the Cell Resource Center of the Shanghai Institute of Biotechnology. Cells were cultured in high-glucose Dulbecco's Modified Eagle Medium (DMEM) supplemented with 10% fetal bovine serum (FBS), penicillin (100 U/mL), and streptomycin (100 U/mL). Cells were maintained at 37 °C in a humidified incubator containing 5% CO₂.
For model construction, BV2 cells were stimulated with 0, 10, 20, 50, 100, 150, or 200 ng/mL lipopolysaccharide (LPS) for 24 h. The optimal LPS concentration was selected based on the experimental results.
For transfection, BV2 cells were seeded in 6-well plates and transfected once they reached the appropriate confluence. A transfection reagent was used at 1.5 µL/well according to the manufacturer’s instructions. After 6 h, the culture medium was replaced with fresh medium, and the cells were cultured for an additional 24 h. The LINC00707 knockdown construct, corresponding negative control, miR-145-5p oligonucleotide, and corresponding control oligonucleotide were each used at a concentration of 50 nM per well. All transfection experiments were independently repeated at least 5 times, with 3 parallel replicates per independent experiment. Data were statistically analyzed using the results of at least 5 independent experiments.
3. ELISA
The culture supernatants of transfected and LPS-stimulated BV2 cells were harvested by centrifugation at 12,000 × g for 10 min, and the levels of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α) were measured using the corresponding ELISA kits. Briefly, the assay was performed by sequentially incubating with a biotinylated antibody, an HRP-streptavidin conjugate, and a TMB substrate according to the manufacturer's instructions. Absorbance was recorded at 450 nm using a microplate reader. Cytokine levels were determined from standard curves. Each sample was measured in triplicate, and 6 independent experiments were performed.
4. ROS measurement
Intracellular ROS levels in LPS-stimulated BV2 cells were measured using a reactive oxygen species assay kit. Briefly, cells were incubated with 10 µmol/L DCFH-DA at 37 °C for 20 min. After incubation, the supernatant was discarded, and the cells were washed 3 times with phosphate-buffered saline (PBS) to remove excess extracellular probe. Fluorescence intensity was measured using a microplate reader at excitation and emission wavelengths of 488 nm and 525 nm, respectively. Relative ROS levels were calculated based on fluorescence intensity. All samples were analyzed in triplicate, and the entire experiment was independently repeated at least 5 times.
5. Detection of malondialdehyde, superoxide dismutase, and glutathione
Treated BV2 cells were collected, and cell homogenates were prepared. Samples were centrifuged at 12,000 × g for 10 min at 4 °C to obtain the supernatant. Commercial detection kits for malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione (GSH) were used according to the manufacturer's instructions to determine their levels in the cell supernatants. All samples were analyzed in triplicate, and the entire experiment was independently repeated at least 5 times.
6. Dual-luciferase reporter assay
The 3' untranslated region (3' UTR) fragments of LINC00707 and TRAF6 containing the predicted miR-145-5p binding sites, together with the corresponding mutant sequences, were cloned into the pmirGLO luciferase reporter vector to generate wild-type (WT-LINC00707 and WT-TRAF6) and mutant (MUT-LINC00707 and MUT-TRAF6) reporter constructs. BV2 cells were co-transfected with the reporter constructs and miR-145-5p oligonucleotides and cultured for 24 h. The cells were then collected, and firefly and Renilla luciferase activities were measured using a microplate reader.
7. RT-qPCR
Total RNA was extracted using an RNA extraction reagent. RNA quality was assessed using the OD₂₆₀/OD₂₈₀ ratio, with values between 1.8 and 2.0 considered acceptable. Approximately 1 µg of total RNA was reverse transcribed into cDNA using a reverse transcription kit. Gene expression was quantified by RT-qPCR using a SYBR Green PCR master mix. Reverse transcription was performed at 42 °C for 15 min, followed by reverse transcriptase inactivation at 95 °C for 3 min. The synthesized cDNA was stored at −20 °C until analysis. Quantitative real-time PCR was performed using pre-denaturation at 95 °C for 1 min, followed by 40 cycles of denaturation at 95 °C for 5 s and annealing and extension at 60 °C for 15 s. Fluorescence signals were collected at the end of each annealing and extension step. Melting curve analysis was performed at 95 °C for 15 s, followed by 60 °C for 1 min. Relative expression levels were calculated using the 2⁻ΔΔCt method. GAPDH or 5S was used as the internal reference for gene expression normalization. The primer sequences were as follows: LINC00707, forward 5'-CCAACAGGGTATCAGAATTCTC-3' and reverse 5'-TGCTGACAATAGCCATTAGG-3'; miR-145-5p, forward 5'-GCCGAGGTCCAGTTTTCCCA-3' and reverse 5'-CTCAACTGGTGTCGTGGA-3'; TRAF6, forward 5'-ATTACAACTGAGGTGCTTCT-3' and reverse 5'-GCATCTGGTTCTGTTATAGGA-3'; GAPDH, forward 5'-ATCCCATCACCATCTTCCAGG-3' and reverse 5'-CGCCCCACTTGATTTTGG-3'; and 5S, forward 5'-TCGTCTGATCTCGGAAGCTAA-3' and reverse 5'-AAGCCTACAGCACCCGGTAT-3'.
8. Statistical analysis
Statistical analyses were performed using statistical software. The normality of the data distribution was assessed using the Shapiro-Wilk test, with P > 0.05 indicating a normal distribution. Normally distributed data were presented as the mean ± SD, whereas non-normally distributed data were presented as the median (P25, P75). For continuous variables with a normal distribution, comparisons between 2 groups were performed using Student's t-test, and comparisons among multiple groups were performed using one-way ANOVA followed by Tukey's post hoc test. For non-normally distributed data, the Mann-Whitney U test was used for 2-group comparisons, and the Kruskal-Wallis test was used for multiple-group comparisons. The chi-square test was used to analyze categorical variables between groups. Univariate and multivariate logistic regression analyses were used to evaluate clinical factors associated with LINC00707 expression. Continuous variables were dichotomized at the cohort median (high-value group = 1; low-value group = 0). Variables with P < 0.05 in the univariate logistic regression analysis were entered into the multivariate logistic regression analysis. Results were presented as odds ratios (ORs) with 95% confidence intervals (CIs), where OR > 1 indicated a positive association and OR < 1 indicated a negative association. All cell phenotype experiments included at least 4 independent biological replicates, with 3 technical replicates per biological replicate. P < 0.05 was considered statistically significant.