PEGylation and purification of PEGylated PDZ (PEG-WT PDZ) and PEGylated mut PDZ (PEG-mut PDZ).

(a) Peptides were synthesized with fluorescein isothiocyanate (FITC) and entered Tat region (italicized amino acids) for cell penetration based on the first PDZ domain sequence (A, upper panel), and 25GG26 was changed to 25AA26 for the mutant PDZ peptide (mut PDZ peptide; lower panel). (b) Size exclusion chromatography for isolation of PEG-WT PDZ or PEG-mut PDZ from the mixture of WT PDZ or mut PDZ reacted with m-PEG-succinimidyl succinate (MW 5000). (c) SDS-PAGE analysis for visualization of PEGylated products. Samples were run on SDS-PAGE and then illuminated at λex = 480 nm to obtain in-gel fluorescence.

The inhibitory effect of PDZ peptide on LPS-induced systemic inflammatory responses in vivo

(a) Comparison of body weight change after administration of LPS or both LPS and PDZ peptide. The body weight was measured for the duration of LPS administration (5 days). LPS administration (10 mg/kg/30 μL) into the peritoneum of mice that were injected 4 hrs prior with either the wild-type (WT) PDZ peptide or the mutant PDZ peptide (7.5 mg/kg/30 μL, i.v.). (b) After 5 days, the IL-6, IL-8, and TNF-α concentrations in the plasma were measured using specific ELISAs. (c) To examine lung pathology, BALF was harvested. The IL-6, IL-8, and TNF-α concentrations in the BALF were measured using specific ELISAs. *p < 0.05 compared with saline-treated mice; **p < 0.05 compared with LPS-treated mice; ***p < 0.05 compared with LPS- and WT PDZ peptide-treated mice.

Plasma biochemical measurements in LPS-administrated mice.

The effects of PDZ peptide on LPS-induced damage markers in plasma

Five days after LPS administration (10 mg/kg/30 μL) into the peritoneum of mice that were injected with either the wild-type (WT) PDZ peptide or the mutant PDZ peptide (mPDZ peptide; 7.5 mg/kg/30 μL, i.v.) 4 h previously. The blood samples were centrifuged, and the plasma was harvested. The ALT, AST, BUN, and creatinine levels were analyzed (n = 5).

The effects of PDZ peptide on liver, kidney, and lung injuries in LPS-administered mice

LPS administration (10 mg/kg/30 μL) into the peritoneum of mice injected 4 hrs prior with either the wild-type (WT) PDZ peptide or the mutant PDZ peptide (7.5 mg/kg/30 μL, i.v.). After administration for 5 days, the liver (a), kidney (b), and lung (c) were harvested. Both hematoxylin and eosin (H&E) and iba-1 staining were performed on the tissue sections from the treated mice (×400). Indicated scale bars were 20 μm. (d) After the kidneys were harvested, tissue lysates were used for MTT assay. (e) After mitochondria from the kidneys was isolated, the mitochondria lysates were used for ROS measurement. *p < 0.05 compared with saline-treated mice; **p < 0.05 compared with LPS-treated mice; ***p < 0.05 compared with LPS- and WT PDZ peptide-treated mice. All data shown are representative of three independent experiments.

Gating strategy used in flow cytometry to determine the populations of immune cells in mice administered LPS and PDZ peptides

Five days after LPS administration (10 mg/kg/30 μL) into the peritoneum of mice that were injected 4 hrs prior with either the wild-type (WT) PDZ peptide or the mutant PDZ peptide (7.5 mg/kg/30 μL, i.v.). After administration for 5 days, spleens were harvested. (a, c) Subpopulations of either immature or mature neutrophils were identified as CXCR2-Ly6Glo/+ (immature) and CXCR2+Ly6G+ (mature). (b, d) Data for each neutrophil phenotype are displayed as the percentages of neutrophil (CD11b+Gr-1+) in CD45+ cells and the exact number of immature- and mature-neutrophil counted per 104 total neutrophil cells. (e, f) Flow cytometry of monocyte (CD11b+F4/80int) and macrophage (CD11b+F4/80+) expression in CD45+ cells is shown. Data for each cell phenotype are displayed as the percentages of monocyte and macrophage in CD45+ cells and the exact number of monocyte and macrophage counted per 104 total single cells. (g) Subpopulations of two types of macrophages were identified as CD86+F4/80+ (M1) and CD206+F4/80+ (M2) in CD45+ cells. (h, i) Data for each cell phenotype are displayed as the percentages of M1- and M2-macrophages in CD45+ cells and the exact number of M1- and M2- macrophages counted per 104 total single cells. (j) The M1/M2 ratio was calculated based on the percentage of F4/80+CD86+ cells and F4/80+CD206+ cells in CD45+ cells. *p < 0.05 compared with saline-treated mice; **p < 0.05 compared with LPS-treated mice; ***p < 0.05 compared with LPS- and WT PDZ peptide-treated mice. All data shown are representative of three independent experiments.

Comparison of mRNA expression in PDZ-treated BEAS-2B cells.

BEAS-2B cells were treated with wild-type PDZ or mutant PDZ peptide for 24 h and then incubated with LPS for 2 h, after which RNA sequencing analysis was performed. (a) Hierarchical clustering of DEGs in LPS vs control; WT PDZ+LPS vs Control; mut PDZ+LPS vs Control; WT PDZ+LPS vs LPS; and mut PDZ+LPS vs LPS. Up- and downregulated genes were shown in red and blue color, respectively. The 51 overlapping genes from 4 gene categories were selected and the heatmap was generated using fold change values. (b) Significant genes were selected using Gene category chat (Fold change value of 2.00 and normalized data (log2) value of 4.00). (c) protein–protein interaction network was constructed using the STRING database. In the network, genes serve as nodes and edges serve as protein–protein associations. Line thickness of the network edge indicated the strength of data support.

PDZ peptide dramatically increases M2 marker proteins to regulate M1/M2 polarization via NF-κB signaling and ROS production.

(a, c, e, g) The cells were treated with LPS in a time-dependent manner. After treatment with WT PDZ and mutant PDZ, the cells were treated with LPS for 4 hrs (b, d, f) or 1 hr (h). The mitochondria morphology was stained using MitoTracker® Green FM and visualized (a, b). The mitochondria fission was stained using phospho-Drp1 antibody and visualized (c, d). The phospho-specific and total antibodies were assessed by Western blot analysis. β-actin was used as a loading control (e, f). The lysates were prepared for qPCR for the expression of M1 and M2 marker proteins (g, h). *p < 0.05 compared with control; **p < 0.05 compared with LPS treatment; ***p < 0.05 compared with WT PDZ-treated transfectants. All of the data shown are representative of three independent experiments. (i) A graphic abstract illustrating that PDZ peptide of ZO-1 protein inhibits LPS-induced systemic inflammation by regulating the activation of NF-κB signaling pathways, ROS production, and M1/M2 polarization.