All the procedures using animals were approved by the University of Wisconsin Research Animal Resources and Care Committee, conducted in compliance with the “Animal Research: Reporting of In Vivo Experiments (ARRIVE)” guidelines and cared in accordance with the Guide for the Care and Use of Laboratory Animals, U.S. Department of Health and Human Services Publication Number. 86 − 23 (revised) (Percie du Sert et al. 2020). Animals were randomly divided into experimental groups. The outcome measures were evaluated by an investigator blinded to study groups.
Focal ischemia
Adult, male, C57BL/6J, C57BL/6N-Snca tm1Mjff/J (SNCA knockout; α-Syn−/−) and B6.129X1-Mapttm1Hnd/J (Tau knockout; Tau−/−) and corresponding wild-type controls (12 weeks, 27 ± 2 g,) were obtained from Jackson Labs USA. Transient focal ischemia was induced by intraluminal middle cerebral artery occlusion (MCAO) using silicon-coated monofilament (6 − 0, Doccol Corporation USA) under isoflurane anesthesia followed by 12h or 24h of reperfusion (Chelluboina et al. 2021; Chokkalla et al. 2019; Kim et al. 2016; Kim et al. 2018; Mehta et al. 2017; Mehta et al. 2022; Kim et al. 2021). Sham-operated animals were used as control. The body temperature during surgery was maintained at 37.0 ± 0.5°C with a heating blanket. Regional cerebral blood flow (rCBF) and physiological parameters (pH, PaO2, PaCO2, hemoglobin, and blood glucose) were monitored. For the inclusion and exclusion criteria, mice subjected to transient MCAO that showed no signs of neurologic deficits during reperfusion or those that showed signs of hemorrhage during imaging or after euthanasia were excluded (Kim et al. 2018).
GSK-3β inhibitor administration
A cell-permeable GSK-3β Inhibitor VIII, CAS 487021-52-3 (Cat # 361549; Calbiochem USA) that regulates the biological activity of GSK-3β by phosphorylation and dephosphorylation at different residues and prevents Tau phosphorylation at a GSK-3β-specific site was injected (4 mg/kg dissolved in 5 mg/ml of DMSO and supplemented with 0.9% sterile NaCl; IV) at 30 min of reperfusion following transient MCAO. Mice in the control group received an equal volume of vehicle (Venna et al. 2015).
Co-immunoprecipitation (Co-IP): The protein-protein interaction between α-Syn, Tau, and GSK-3β was analyzed using Co-IP Assay (Cat. # ab206996; Abcam USA) as described previously (Kim et al. 2021). Briefly, the ipsilateral peri-infarct cortex was homogenized in a non-denaturing lysis buffer containing a cocktail of protease and phosphatase inhibitors. The homogenate was centrifuged (10,000g; 5 min at 4°C) and 300 µg protein equivalent of the supernatant was incubated overnight at 4°C with antibodies against α-Syn or GSK-3β (each at 1:50; Cell Signaling Technology USA) and with 25 µl of protein A/G Sepharose beads slurry (1h at 4°C). The precipitated protein complex was eluted, washed in buffer, incubated (5 min at 80°C) with NuPAGE LDS Sample Buffer (Cat. # NP0008; Life Technologies USA) and immunoblotted to evaluate the protein-protein interaction. Rabbit IgG was used as a control.
Western blotting: Ipsilateral peri-infarct cortex was homogenized in T-PER Tissue Protein Extraction Reagent (Cat. # 78510; Life Technologies USA) supplemented with a cocktail of protease and phosphatase inhibitors. Homogenates were centrifuged (10,000g for 10 min at 4°C) and 40 µg protein equivalents were electrophoresed, transferred to nitrocellulose membranes, and probed with antibodies against α-Syn, Tau, p-Tau, GSK-3β, p-GSK-3β (S9) and GAPDH (each at 1:1,000; Cell Signaling Technology USA), followed by HRP-conjugated (1:3,000) or IRDye Infrared Fluorescent Dye-conjugated (1:20,000; LI-COR) anti-rabbit or anti-mouse antibodies. Protein bands were detected using enhanced chemiluminescence or scanned with a NIR spectrum (between 680 and 800 nm) using a Li-COR Odyssey analyzer and the band intensity was quantitated with Image Studio software (LI-COR Biotechnology USA).
Infarct volume assessment
Infarct size was assessed with T2-MRI (4.7T small animal system scanner; Agilent Technologies USA). Briefly, mice were anesthetized with isoflurane and 8–10 coronal brain slices at 1.0 mm thickness and 20 × 20 mm2 fields were scanned under isoflurane anesthesia as described previously (Chelluboina et al. 2021). The respiration rate was monitored during the imaging. The Infarct size was computed blindly, and total infarct volume was configured by numeric integration of data from serial coronal sections factoring-in sectional intervals and corrected for edema using NIH ImageJ software with an FDF plugin as described before (Chelluboina et al. 2021; Kim et al. 2018; Mehta et al. 2022; Mehta et al. 2015).