1.1 ISO alleviated Pathological Liver Injury Induced by LPS/D-GalN-Treated in Mice
Acute liver failure was induced in mice by intraperitoneally co-administering LPS (30 mg/kg, Sigma, USA) and D-galactosamine (600mg/kg, Sigma, USA), while maintaining control with an equal amount of PBS. As revealed by gross morphology, the massive hepatic injury was apparent after 4~6 h; and there are a lot of visible necrosis areas, inflammatory cell infiltration and congestion in the liver tissue with hematoxylin and eosin (H&E) staining (Figure 1A). Interestingly, after pretreating the ALF mice with ISO (10mg/kg) for 1 hour, we observed significant enhancements in the liver's pathology, characterized by reduced hyperemia and swelling, as well as decreased hepatocellular necrosis (Figure 1B). Likewise, pre-treated ISO can reduce the elevation of the serum concentrations of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) caused by LPS/D-GalN in ALF mice (Figure 1C). The aforementioned findings suggest that ISO demonstrates a defensive effect against mortality and liver damage induced by LPS/D-GalN. After injecting LPS/D-GalN, we proceeded to compare the survival rates of mice that received ISO treatment with those that did not receive ISO treatment. As anticipated, the injection of LPS/D-GalN led to complete mortality within 12 hours, however, prior administration of ISO can reduce the mortality rate in ALF mice (Figure 1D). Additionally, we endeavored to investigate the impact of ISO on the production of inflammatory cytokines induced by LPS/D-GalN. The expressions of hepatic TNF-α mRNA were significantly higher in mice stimulated with LPS/D-GalN compared to control mice. In contrast, the levels of TNF-α, IL-6, and IL1-β mRNAs decreased noticeably after ISO treatment (Figures 1E, p<0.05). In general, the findings indicate that the ALF mouse model created in this research using LPS/D-GalN was beneficial, and ISO demonstrates a protective effect against the liver damage caused by LPS/D-GalN.
1.2 Validations of Filtering and Quality Control for Proteomic Data in the Liver Samples
Our subsequent attention was directed towards investigating the safeguarding mechanism of ISO against liver injury induced by LPS/D-GalN. According to a previous investigation, the results indicated that the usual receptors of ISO, including both α- and β-adrenergic receptors, were predominantly present in liver cells that are not parenchymal[5]. We next mainly investigated whether ISO plays a role among the stromal cells. Proteins extracted from non-parenchymal cells of mouse liver tissues were isolated in the control group, as well as in the LPS/D-GalN and ISO+ LPS/D-GalN groups. TMT labelling proteomics approach was conducted to identify the protein expression pattern.
In order to achieve accurate analysis outcomes, the spectrogram, peptide, and protein identification were set with an accuracy FDR of 1% to obtain high-quality results (Figure 2). A grand total of 320,737 spectrums were generated through the process of mass spectrometry analysis. There was a total of 56,779 spectrums that aligned with the protein, and the spectrograms were utilized at a rate of 17.7%. Spectrogram analysis successfully identified a grand total of 18,297 peptides, with a remarkable count of 17,696 being distinct peptide segments. In the end, a total of 3,914 proteins were identified, with 3,840 being measurable (Figure S1A). Figure S1B–F illustrates the verification of data quality control, including the examination of protein coverage distribution, distribution of peptide length, distribution of peptide number, and distribution of protein molecular weight. The majority of proteins have a coverage of less than 30% (Figure S1B), while the mainly peptides are found within the range of 6 to 20 amino acids (Figure S1C). According to the illustration in Figure S1E, themajority of proteins are represented by two or more peptides. When quantifying, it is advantageous for enhancing the precision and reliability of quantitative outcomes to get a protein that corresponds to multiple specific peptides (or multiple spectrograms). Overall, this data confirms that the outcomes of filtering the data in the serum samples adhere to the quality control standards.
Principal component analysis (PCA) result shows that the data within the group were spatially clustered (Fig. S1F). It displays clear differences of protein expression pattern between the treated and control groups. The PCA results could annotated 80% components in each sample. The analysis of Pearson correlation coefficients showed a strong correlation in protein expression profiles within the same group (Con group: 0.79–0.80, ALF group: 0.93–0.94, ISO group: 0.82-0.83), but a weak correlation was observed among samples from different groups (–0.76–0.51; Fig. 2H). Overall, he findings indicated that the quantitative reproducibility of both isolated liver total protein samples is satisfactory.
1.3 Identification of differentially expressed proteins between the ISO treated or non-treated ALF and control mice
A 1.2-fold change cut-off with an adjust p-value < 0.01 was set for volcano plot to filter DEPs in each comparison (Figure 2A). Significant expression among different comparisons was observed in a total of 1587 proteins. As compared to the control group, there were 34 upregulated and 17 downregulated differential proteins displayed in LPS/D-GalN treated mice. Similar number of of DEPs (375 upregulated and 268 down-regulated) was observed when compared the LPS/D-GalN injected group to ISO+ LPS/D-GalN treated group. However, a lower number of DEPs (375 upregulated and 268 down-regulated) was obtained in the comparison of ISO+ LPS/D-GalN with control group (Figure 2A and 2B). Further analyzing the characteristics of DEPs, venn diagram showed 64.1% DEPs were common between LPS/D-GalN vs. Con and LPS/D-GalN vs.ISO+ LPS/D-GalN comparisons (Figure 2C). Afterwards, the distinct proteins were organized into a hierarchical cluster and displayed in an expression heatmap (Fig. 2D). The clustering results showed a closer relationship of ISO+LPS/D-GalN to control group, indicating that the protein expression patterns in ISO+LPS/D-GalN and control group were similar. In contrast, the clustering heatmap exhibited a clear distinction of ISO+LPS/D-GalN from LPS/D-GalN group, denoting that the expression patterns of differential proteins in drug used and healthy groups were quite different from those in the disease group (Fig. 2D). Furthermore, we ranked proteins according to the fold changes and found top 20 upregulated and downregulated proteins were similarly expressed between the comparisons of AFL vs. Con (Figure 2E) and ALF vs. ISO (Figure 2F), including upregulated Zg16, Dmtn, Mrpl24, Pglyrp2, Cpa1, Amy2 and Serpini2 proteins, and downregulated Nmral1, Atp5f1d, H2bc3, Sf3a2, Abhd11, Nedd8, U2af1, Nfu1 proteins. Among them, Amy2, Pglyrp2, and Cpa1 were particularly ranked top 20 in downregulated proteins between the comparison of ISO and Con group (Figure 2G).
1.4 Functional enrichment analysis of the screened DEPs
For each comparison, GSEA, GO, and KEGG pathway enrichment analysis were conducted to classify the annotated proteins and ascertain their functions. The GSEA results presented in Figure 3A showed the proteins were positively enriched in heme metabolism (Figure 3B), interferon gamma response (Figure 3C), TNFA signaling pathway, and fatty acid metabolism pathway in the comparisons of ALF vs. Control group. Heme metabolism, interferon gamma response, fatty acid metabolism (Figure 3E) and adipogenesis (Figure 3F) pathway were also enriched in the comparisons of ALF vs. ISO group (Figure 3D). Coagulation (Figure 3H), complement, and MTORC1 signaling pathway were enriched in in the comparisons of ISO vs. Con group (Figure 3G).
To visualize the effect of ISO on anti-ALF, hierarchical cluster analysis was performed with the 3095 DEPs. We computed five hierarchical clusters the detect the changes of DEPs, three of which were exhibited closed characteristics to the healthy status (Figure 3D, Figure 4 A-E). The clustered DEPs were subjected to GO enrichment analysis in order to examine their functions. Cluster 1 majorly contained the upregulated proteins in ALF group, of which were enriched in proteolysis, cytoplasm, proteasome complex and protein binding GO terms (Figure 4F). According to the KEGG pathway analysis, it was found that the cluster 1 proteins were enriched in coronavirus disease, prion disease and phagosome terms (Figure 5A). Cluster 4 proteins were involved in the GO terms of lipid metabolism, fatty acid metabolism, mitochondrion, endoplasmic reticulum, and oxidoreductase activity, and KEGG terms of metabolic pathways (Figure 4G and 5B). Cluster 5 proteins mainly participated in the lipid metabolic process, membrane component, oxidoreductase activity, and PPAR signaling pathway (Figure 4H and 5C).
A global perspective of the hub DEPs in various comparisons, particularly those related to response mechanisms, was obtained by constructing a PPI network. MODE was used to modularly and deeply observe the important DEPs from each clustered proteins of heatmap in the Cytoscape software. Within the most enriched model in the Cluster 1 of DEPs, the top 10 hub proteins were presented in Figure 5D. The upregulation of Mapk14 and Caspase 3 were playing essential roles in the Clustered 1 PPI network. Subunits of respiratory complex, including Uqcrc1, Uqcrc2, Uqcrh, Ndufs7, and Ndufs3 proteins were verified as the top 10 hub DEPs in the downregulated proteins of Clustered 4 in ALF groups (Figure 5E). Besides, the lower protein abundances of immune-inflammatory proteins, including B2m, Fas, Thy1 and Fas in Cytoplasm were detected as the top 10 in the Cluster 5 DEPs in ALF mice (Figure 5F), indicating that a large amount of pro-inflammatory components were depleted during inflammation. Nevertheless, the network requires verification, but it narrowed the pool of protein–protein interactions that potentially contributing to the collaboration and synchronization of their roles in non-parenchymal liver cells during the response to LPS/D-Galn induced ALF.
1.5 Confirmation of DEPs for Macrophage Markers in Mice Liver
Since macrophages were the key nonparenchymal cells contributing to inflammatory progress of ALF, we strove to figure out the characteristics of macrophages in the isolated nonparenchymal cells. Firstly, 29 macrophage related markers were selected and presented in the Figure 6A. According to the proteomic results, the expression levels of Nup85, St6gal1, Myo9b, Mapk14, Marco, Mtus1, Thbs1, Sbno2, Casp1, C5, Ddt, Csf1r, Cd44, Aif1, Casp8, Pde2a, Syk, Mrc1, Itgb2, Mif, Itgb3 and Myo18a proteins were upregulated in LPS/D-GalN treated liver tissues compared to healthy group, while the rest proteins of Fcgr2, Slc7a2, C5ar1, Apob, Cd74, Hmgb1 and Ptprj were significantly upregulated in ISO intervention group compared to the non-ISO ALF group. qRT-PCR was confirmed to verify the reliability of the above 29 DEPs for markers of macrophage (Figure S2). Consistently, the transcript levels of Mapk14, Marco, Mtus1, Thbs1, Sbno2, Casp1, C5, Ddt, Csf1r, Cd44, Aif1, Casp8, Pde2a, Syk, and Mrc1were upregulated under LPS/D-GalN treatment compared with the group injected with ISO. Aligning with the findings from the proteomic analysis, the expression level of Apob, Cd74, Hmgb1 and Ptprj coding genes were differently downregulated following with the LPS/D-GalN treatment compared with the ISO group. Nevertheless, the expression levels of the remaining genes contradicted the findings of the proteomic analysis, probably attributed to the influence of post-translational modification procedures. Next, we imputed these macrophage related markers into STRING database and found they were belonged to macrophage migration inhibitory factor receptor complex, caspase complex and HGB1 complex in the cell compartment category, macrophage cell line in the tissue category, and inflammatory signal pathways (Figure 6B). Therefore, we conducted the IHC assay to identify the classic protein markers of M1 and M2 phenotype of macrophage in liver tissues. According to the staining results, the markers of M1 macrophage, iNOS (Figure 6C) was presented more significant in the nonparenchymal cells of ALF liver tissues, while the markers of M2 macrophage, ARG-1 was visualized more significantly in the nonparenchymal cells of ALF liver tissues under the treatment of ISO (Figure 6D). Furthermore, we conducted Western-Blotting assay to investigate the protein expression level of the several hub DEPs (Caspase 8, Caspase3, and Caspase1) in NPCs, and found these proteins were reduced in ISO treated ALF mice (Figure 6F).
1.6 ISO Suppressed inflammatory cytokines in THP-1 cell, probably via the Inhibition of p38 MAPK Signaling in THP-1 cell.
To further verify the proteomic results regarding whether ISO could affect inflammation mechanism through macrophage, we conducted Western-Blotting assay to investigate the protein expression level of the several hub genes (NF-kB, and Mapk14) in vitro THP-1 cell line. Although LPS induction markedly upregulated TNF-α, and IL-6 mRNA (P<0.05) excluding IL-10, after 1h in THP-1 cells, the expression of these cytokine expressions had an available diminish after ISO treatment (P< 0.05) (Figures 7A–C). The activation of THP-1 cells was detected using flow cytometry, which showed a significant increase in the population of CD14+CD40+ macrophages (representing M1 phenotype) in the LPS treated group, but was significantly reduced by ISO (Figure 7D-G). Furthermore, we explored whether the MAPK signaling pathway enriched in our results of KEGG enrichment participated in this process. We found that Mapk14 (p38 MAPK), and NF-kB (p65) was significantly activated after LPS administration (Figure 7D, 7E), but was inhibited by ISO. Collectively, the administration of ISO effectively reduced the elevations of inflammatory cytokines, likely by activating the p38 MAPK and NF-kB pathways.