Rat and model
75 healthy adult male Sprague–Dawley rats weighing 230-320g were purchased from Animal Core Facility of Nanjing Medical University. All experiments were carried out under the Guide for the Care and Use of Laboratory Animals published by NIH and approved by the Experimental Animal Ethics Committee of Nanjing Drum Tower, approved number: 2020AE02015. All animal studies are reported in compliance with the ARRIVE guidelines [13, 23].
The endovascular perforation SAH model was performed as previously described [16, 17, 35]. The endovascular perforation surgery was performed by the same experimenter (X.G.). Briefly, rats were anaesthetized by isoflurane inhalation (RWD Life Science, Shenzhen) firstly. After sharpness and blunt separation, a marked 6 − 0 filament was inserted to the middle cerebral artery (MCA) through the internal carotid artery (ICA). We punctured the bifurcation of the anterior and middle cerebral arteries in SAH group. In sham group, the filament was pulled out without puncturing the artery.
The neurological score was blindly evaluated by two independent observers using a Modified Garcia scale score 24 h post-SAH [21, 35]. Rats with a Modified Garcia scale score ≤ 6 or ≥ 15 were excluded to prevent the interference of dying models and failure SAH models.
Primary neuron culture
For neuron culture, the cortex was obtained from rats at embryonic day 13–15 as we previously reported [16, 17, 35]. In brief, after removing leptomeninges, cerebral cortex was digested with Trypsin. Then we used fetal bovine serum to stop the digestion and repeated triturated the neuron suspension. After filtration and centrifugation, the remaining neurons were seeded in poly-D-lysine-coated plates with neurobasal medium and incubated at 37℃ and 5% CO2. The medium contained 0.5mM GlutaMax (Gibco Company, USA) and 2% B27 supplement (Gibco Company, USA). We would replace the medium at 4 h、3 d、5 d and 7 d following seeding. For the in vitro SAH model, neurons were treated with hemoglobin (Hb, Sigma, USA) at a concentration of 25uM for 24 h. Primary neurons were randomly assigned to different groups.
Patient population
Patients with SAH were recruited from the Department of Neurosurgery of the Nanjing Drum Tower Hospital between April 2020 and April 2021. A diagnosis of severe SAH required a positive cranial CT scan and bloody cerebrospinal fluid. For all SAH subjects, the inclusion criteria were:
(1) patient age between 16 and 70 years,
(2) signed consent from the subject or next of kin,
(3) a Hunt-Hess grade of 1 or 2.
The exclusion criteria were:
(1) failure to meet the inclusion criteria or unfit for the experiment as determined by the responsible doctor,
(2) presence of severe cardiac insufficiency, renal dysfunction, diabetes or other systemic diseases,
(3) a history of traumatic brain injury, severe cerebral edema or hydrocephaly.
As a control group, knee arthritis subjects who needed surgery were recruited. For control subjects, the inclusion criteria were:
(1) patient age between 16 and 70 years,
(2) no current or pre-existing brain injuries, neurological diseases, or bleeding disorders, and subjects who needed surgery for knee arthritis,
(3) signed consent from the subject or next of kin.
Ultimately, 34 patients with SAH and 6 controls were included. Patient demographics are shown in Table 1. The study was approved by the Ethics Committee of Drum Tower Hospital (No. 2020-041-01) and registered in the Chinese Clinical Trial Registry (ChiCTR2100042986). Written informed consent was obtained from each participant.
Table 1
Summary of demographic data in patients with SAH
Case No. | Age (years) | Gender | Hyper- tension | Aneurysm | Days after hemorrhage (d) | Initial GCS | Initial Hunt-Hess | Initial GOS | GOS (after 3 months) |
1 | 63 | F | 1 | 1 | 1 | 15 | 3 | 5 | 5 |
2 | 72 | F | 1 | 1 | 1 | 15 | 1 | 5 | 5 |
3 | 54 | M | 0 | 1 | 1 | 3 | 4 | 1 | 1 |
4 | 75 | F | 0 | 1 | 1 | 8 | 4 | 3 | 3 |
5 | 65 | F | 1 | 1 | 1 | 15 | 2 | 4 | 5 |
6 | 69 | F | 1 | 0 | 1 | 15 | 2 | 5 | 5 |
7 | 69 | F | 0 | 1 | 1 | 15 | 3 | 5 | 5 |
8 | 48 | M | 0 | 1 | 1 | 14 | 3 | 3 | 4 |
9 | 64 | M | 1 | 1 | 2 | 14 | 3 | 4 | 5 |
10 | 76 | M | 0 | 1 | 2 | 7 | 4 | 3 | 5 |
11 | 40 | F | 1 | 1 | 2 | 15 | 3 | 3 | 5 |
12 | 50 | F | 0 | 1 | 2 | 9 | 4 | 3 | 5 |
13 | 62 | F | 1 | 1 | 2 | 5 | 4 | 1 | 1 |
14 | 49 | F | 0 | 1 | 2 | 12 | 3 | 4 | 5 |
15 | 56 | F | 1 | 0 | 2 | 15 | 1 | 4 | 5 |
16 | 66 | F | 1 | 1 | 2 | 5 | 3 | 5 | 5 |
17 | 63 | M | 0 | 0 | 2 | 14 | 2 | 5 | 5 |
18 | 55 | M | 1 | 1 | 2 | 15 | 1 | 5 | 5 |
19 | 45 | M | 1 | 1 | 2 | 15 | 3 | 5 | 5 |
20 | 63 | M | 1 | 0 | 2 | 15 | 2 | 5 | 5 |
21 | 73 | F | 1 | 1 | 2 | 14 | 3 | 3 | 3 |
22 | 45 | F | 1 | 1 | 2 | 15 | 2 | 5 | 5 |
23 | 47 | F | 0 | 1 | 3 | 15 | 2 | 4 | 4 |
24 | 49 | M | 0 | 1 | 3 | 15 | 2 | 4 | 5 |
25 | 53 | M | 0 | 0 | 3 | 15 | 2 | 4 | 5 |
26 | 54 | F | 0 | 1 | 3 | 15 | 2 | 4 | 5 |
27 | 72 | F | 0 | 1 | 3 | 14 | 1 | 4 | 5 |
28 | 55 | M | 0 | 1 | 3 | 15 | 2 | 4 | 5 |
29 | 63 | F | 1 | 1 | 3 | 15 | 3 | 4 | 5 |
30 | 68 | M | 1 | 1 | 3 | 14 | 3 | 4 | 5 |
31 | 57 | F | 1 | 1 | 3 | 14 | 2 | 4 | 5 |
32 | 65 | F | 1 | 1 | 3 | 14 | 2 | 3 | 5 |
33 | 57 | F | 1 | 1 | 3 | 15 | 1 | 4 | 5 |
34 | 52 | M | 1 | 1 | 3 | 15 | 1 | 5 | 5 |
d = days; GCS = Glasgow Coma Scale; GOS = Glasgow outcome scale
lines of Hypertension and Aneurysm: 0 = No; 1 = yes
F = female; M = male
Sample collection
Cerebrospinal fluid (CSF) samples were collected within 72 h after SAH following the consensus protocol for the standardization of cerebrospinal fluid
collection [37]. The posterior cerebrospinal fluid was retained as samples and centrifuged at 2000 g for 15 minutes at 4°C to pellet cellular bodies and debris. All samples were stored at -80℃.
Experimental design
The main experimental protocols are described as follows (Fig. 1):
Experiment 1
To examine the expression variation of PDKs and PDH in rat brain after SAH, a total of 50 rats were randomly assigned to six groups: sham (n = 5), 6 h post-SAH (n = 9), 24 h post-SAH (n = 9), 2 days post-SAH (n = 9), 3 days post-SAH (n = 9) and 7 days post-SAH (n = 9). Five rats from each group were sacrificed randomly for WB and qPCR. In stage 2, 15 rats were randomly allocated into two groups: the sham group (n = 6) and the SAH group (2 days) (n = 9). Six rats from each group were selected randomly for immunofluorescence staining.
Experiment 2
To examine the expression variation of PDKs and PDH in cultured neurons after Hb stimulation, Hb from bovine erythrocytes (Sigma, USA) was dissolved in complete culture medium at a concentration of 25 µmol/L. Cultured neurons were randomly assigned to six groups (the control group and Hb groups (1 h, 3 h, 6 h, 12 h, 24 h) (n = 5 each)) for WB and five groups (the control group and Hb groups (1 h, 4 h, 12 h, 24 h) (n = 5 each)) for qPCR. Finally, the control group and 12 h post-Hb group were used for immunofluorescence staining and TUNEL staining.
Experiment 3
To examine the levels of PDK4 and pyruvate in the CSF of patients with SAH, CSF samples were collected from 34 SAH patients and 6 controls for ELISA.
Western blot
The brains were removed and the basal cortex tissues were collected and washed. Neurons cultured in six-well plated were washed with phosphate-buffered saline (PBS). Cortex tissues and neurons were lysed with RIPA buffer (Thermo Scientific, USA) with protease inhibitor (Roche, Switzerland) and phosphatase inhibitor (Thermo Fisher Scientific). A bicinchoninic acid protein assay kit (Beyotime, China) was used to quantified the amounts of protein. The same amount of protein was resolved by SDA-PAGE (EpiZyme Scientific) and transferred to polyvinylidene difluoride membranes (Millipore, USA). We used 2% BSA to block the membranes for 2 h at room temperature. After incubation with diluted primary antibody overnight at 4 ℃, the membranes were washed 3 times for 10 min with PBS and Tween 20. The antibodies were as follows: anti-PDK1 (1:1000, 3820, Cell Signaling Technology), anti-PDK2 (1:1000, 68164, Abcam), anti-PDK3 (1:1000, 154549, Abcam), anti-PDK4 (1:1000, 89295, Abcam), anti-PDH (1:1000, 3205, Cell Signaling Technology), anti- phospho-PDH(S293) (1:1000, 177461, Abcam), anti-ASK1 (1:1000, 45178, Abcam), anti-phospho-ASK1 (Thr845) (1:1000, 3765, Cell Signaling Technology), anti-P38 (1:1000, 9212, Cell Signaling Technology), anti- phospho-P38 (Thr180/Tyr182) (1:1000, 9211, Cell Signaling Technology), anti-BAX (1:1000, 2772, Cell Signaling Technology), anti- BCL2 (1:1000, 32124, Abcam), anti-caspase3 (1:1000, 9662, Cell Signaling Technology), anti-cleaved-caspase3 (Asp175) (1:1000, 9664, Cell Signaling Technology) and anti-GAPDH (1:5000, AP0066, Bioworld). The membranes were incubated with horseradish peroxidase (HRP)-conjugated secondary antibody (Bioworld) for 1 h at room temperature. Finally, the bands were detected by Immobilon Western Chemiluminescent HRP Substrate (Millipore Sigma, Burlington, MA, USA). Images were analyzed with ImageJ software (National Institutes of Health, Bethesda, MD, USA) and normalized against GAPDH.
Real-time PCR
The total RNA of basal cortex tissues and neurons was extracted by TRIzol reagent (Invitrogen, USA) according to the manufacturer’s instructions. cDNA was reverse transcribed from mRNA with a reverse transcription mix (Vazyme, Nanjing) after removal of genomic DNA. qPCR was performed using a PCR system (Applied Biosystems, United States) with a SYBER Green mix (Roche, Switzerland). The primers used in qPCR are listed in Table 2. The results were analyzed with the 2 − ΔΔCt method and normalized against GAPDH too.
Table 2
polymerase chain reaction (PCR) primer sequences
Target gene | Forward (5' to 3') | Reverse (5' to 3') |
PDK1 | GTTCAGTACTTTTTGGATCGGTTC | TCGACTACATCACAGTTTGGATTT |
PDK2 | TGGACCGCTTCTACCTCAG | TCTTTCACCACATCAGACACG |
PDK3 | TGACCTAGGTGGTGGAGTCCCA | ACCAAATCCAGCCAAGGGAGCA |
PDK4 | GAACACCCCTTCCGTCCAGCT | TGTGCCATCGTAGGGACCACA |
BAX | GACACCTGAGCTGACCTTGG | GAGGAAGTCCAGTGTCCAGC |
BCL2 | TATGATAACCGGGAGATCGTGATC | GTGCAGATGCCGGTTCAGGTACTC |
GAPDH | TGTGAAGCTCATTTCCTGGTA | TTACTCCTTGGAGGCCATGT |
Immunofluorescence staining
Brain tissue was postfixed in 4% paraformaldehyde, dehydrated with sucrose solution and sliced to 10 um. Cultured neurons were fixed with 4% paraformaldehyde. Then they were permeabilized with 0.3% Triton X-100, and blocked with immunostaining blocking solution (Epizyme, Shanghai). After incubation with diluted primary antibody overnight at 4 ℃, the membranes were washed 3 times for 10 min with PBS and Tween 20. The antibodies were as follows: anti-PDK4 (1:200, 89295, Abcam), anti-NeuN (1:200, 26975-1-AP, Proteintech), anti-Iba1(1:200, 5076, Abcam), anti-GFAP(1:200, 4648, Abcam). The next day, they were incubated with corresponding secondary antibodies: anti-rabbit Alex Fluor 488-conjugated secondary antibody (1:200, A11008, Invitrogen), anti-rabbit Alexa Fluor 594-conjugated secondary antibody (1:200, A32754, Invitrogen), anti-mice Alexa Fluor 594-conjugated secondary antibody (1:200, A32740, Invitrogen), anti-mice Alexa Fluor 488-conjugated secondary antibody (1:200, A32723, Invitrogen). Immunofluorescence images were captured using the microscope (ZEISS, HB050, Germany) and analyzed with ImageJ.
Enzyme Linked Immunosorbent Assay
The levels of PDK4 were determined by an ELISA kit (abx252933, Abbexa) according to the manufacturer’s instruction. In brief, CSF and standard samples were loaded in to the 96-well plate incubated with PDK4 antibody. After incubation of detection reagent A and B, the TMB substrate and stop solution were added to every well. Finally, the results were detected at OD 450 nm in a microplate reader (Tecan, Switzerland). The levels of PDK4 were calculated according to the standard curve.
Pyruvate assay
The levels of pyruvate were detected by a pyruvate assay kit (#K609-100, Biovision, USA) according to the manufacturer's instructions. Briefly, after brain tissue and cultured neurons were extracted, samples were homogenized. Subsequently, the supernatant was collected after centrifugation at 10000 x g for 10 min at 4°C. Finally, the fluorescence was detected at an Ex/Em of 435/590 nm in a microplate reader (Tecan, Switzerland). A preliminary experiment in which color (OD 570 nm) was used to calculate the results was essential to determine the appropriate loading volume. The pyruvate contents were calculated according to the manufacturer’s instructions.
Terminal deoxynucleotidyl transferase–mediated dUTP nick end labeling
TUNEL staining was performed on frozen brain sections and cultured neurons with a TUNEL detection kit (Beyotime, China) according to the manufacturer’s instructions. After incubation with a primary antibody against NeuN (1:200, 26975-1-AP, Proteintech) at 4 ℃ overnight, the TUNEL reaction mixture were loaded into every section for 1 h at 37 ℃. The images were captured using the microscope (ZEISS, HB050, Germany) and analyzed with ImageJ.
Modified Garcia scale
We used the Modified Garcia scale to assess the functional defects at 1 days post-SAH by two observers who were blind to groups [35, 43]. It contains 6 tests covering spontaneous activity and movement of the four limbs, forepaw outstretching, climbing, body proprioception, and response to whisker stimulation.
Statistical analysis
Glasgow Coma Scale (GCS) scores 1–3 days after SAH were categorized as severe (GCS score < 12) or mild (GCS score 12–15) injury for each subject.
Hunt-Hess Scale scores obtained 1–3 days after SAH were used to assess neurological impairment. The subjects were divided into two groups: those with Hunt-Hess scores of 1–2 and those with Hunt-Hess scores of 3–4.
Glasgow Outcome Scale (GOS) scores at 3 months were compared with those at 1–3 days after SAH to sort subjects into an improved group and an unchanged group for ease of presentation and interpretation of results. Subjects whose initial GOS scores and GOS scores after 3 months were both 5 were excluded.
Statistical analysis was performed using Prism 8.01 (GraphPad Software, USA). Two -tailed unpaired Student’s t-test was used to compare two experimental groups after normality and lognormality tests were satisfied. One-way ANOVA followed by Tukey’s test was performed to assess differences between more than two groups. Two-way ANOVA was used to assess the interaction effects of treatments and time courses. P < 0.05 was considered statistically significant. All data are expressed as the means ± SD.