Fig 1: Representative confocal images of double-labeling immunofluorescence of BDNF (green) and TrkB/p75 (red) in SH-SY5Y cells. The merged images include BDNF (green), TrkB/p75 (red), nucleus (blue), and the BDNF-TrkB/p75 complex (yellow). (A) Double-IF images of control group. (B) Double-IF images of BDNF group. (C,D) Double-IF images of Aβ42M and Aβ42O groups with or without IG3/BCP/CA/EGCG/HT6, respectively. The first and second rows in (A–D) represent TrkB and p75 groups, respectively. Scale bar = 20 μm.
Fig 2: Differential effects of Aβ42M and Aβ42O on BDNF-supported neural cell survival. Viability of SH-SY5Y (A) and HT22 (B) cells in the presence of anti-BDNF antibody (Ab), BDNF, and Aβ42M/Aβ42O with and without CA and IG3 for 2 h at 37 °C quantified by MTT assay. The viability of the blank control group was defined as 100%. Symbol ⊕ indicates addition after being pre-incubated for 0.5 h at 4 °C. Symbols *, #, §, and ◊ indicate significant differences between the experimental and control groups, between BDNF alone and other groups, between Ab alone and other groups, and between Aβ42O alone and other groups, respectively. */#/§/◊ p < 0.05, **/##/§§ p < 0.01, and ***/###/§§§/◊◊◊ p < 0.001.
Fig 3: Detection of BDNF bound to TrkB and p75 by Western blot analysis after Co-IP. Co-IP was conducted using anti-TrkB and anti-p75 antibodies, with rabbit IgG serving as a negative control. BDNF bound to TrkB and p75 was detected using an anti-BDNF antibody. The symbols indicating groups in Figure 5 correspond to those listed in Table 3. The letters a through q indicate the corresponding groups. WCL: whole-cell lysate samples; SFC: supernatants from Co-IP; Co-IP: Co-IP beads. SFC and Co-IP samples were prepared from equal amounts of WCL within the same group, while the WCL samples were obtained from lysates of initial cells equivalent to those of the control groups. The symbol 0.5× indicates that half of the sample size was used. An arrow in subgroup e indicates that the WCL sample in the p75 group is the same as that in the TrkB group.
Fig 4: Schematic illustration of the different effects of Aβ42M (A) and Aβ42O (B) on BDNF and the modulatory roles of BOs and CAs therein.
Fig 5: Molecular docking models of BDNF to Aβ42M, Aβ42 trimer, and the extracellular binding domain of TrkB. (A) Docking models of BDNF to Aβ42M chain and Aβ42 trimer (peptide chains were marked with symbols a, b, and c, respectively), showing the intermolecular hydrogen bonds (dashed lines) between BDNF’s (lines) and the Aβ42 trimer’s (stick) amino acid residues. (i) main amino acid residues involved in the interaction between BDNF and Aβ42; (ii,iii) docking model of BDNF with Aβ42; (iv,v) docking model of BDNF with Aβ42 trimer. (B) Docking models of BDNF to the extracellular binding domain (EBD) of TrkB (i,ii) and the crystal structure of NT4-TrkB complex downloaded from PDB (ID: 1HCF) (iii,iv). N or C: N or C terminus of Aβ42 chain.
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