1. The glycolysis of peritoneal macrophages in septic mice is enhanced.
We utilized the GSE249975 dataset to perform clustering analysis on the scRNA-seq results of peritoneal lavage fluid (Fig. 1A, left). Five major immune cell populations were identified (Fig. 1A, right). Deeply, the cells were primarily categorized into neutrophils (Cxcl2, Ccl3, Cstdc4), macrophages (Pt4, Alox15, Lyz2), B cells (Igkc, Ighm, Cd79a), lymphocytes (Ms4a4b, Ccl5, Cma1), and dendritic cells (Ccr7, Satb1, Ncl) (Fig. 1B). Given the significant role of peritoneal macrophages in sepsis, we extracted the macrophage subpopulation for further analysis. By comparing the CLP group with the control group, we identified 2706 differentially expressed genes (Fig. 1C). Subsequent GSEA analysis revealed the activation of the innate immune system, glycolysis, and glucose metabolism pathways in peritoneal macrophages of the CLP mice (Fig. 1D).
2. Pim1 was upregulated in the peritoneal macrophage with the LPS treatment
Next, using the GSE234930 dataset, we analyzed the RNA-seq results of peritoneal macrophages treated with LPS. Setting the criteria at logFC ≥ 2 and p < 0.05, we identified 1765 differentially expressed genes (Fig. 2A). By intersecting these genes with the top 100 differentially expressed genes from the scRNA-seq data, we narrowed down to 32 representative genes (Fig. 2B). The KEGG analysis of these genes revealed enrichment in signaling pathways such as cytokine-cytokine receptor interaction, Jak-STAT, MAPK, NF-κB, TNF, NOD-like receptor, and Toll-like receptor signaling pathways (Fig. 2C). Moreover, There was an upregulation of M1 polarization markers (Il1b, Nos2, Il6, Trl2, Cd86), and an increase in the expression of essential genes involved in glycolysis (Hk2, Pfkp, Dld, Minpp1) in LPS-treated peritoneal macrophages (Fig. 2D, E). Notably, Pim1 is one of the 32 representative genes, and its expression was elevated following LPS treatment (Fig. 2F). Furthermore, immune infiltration analysis indicated a close association between high expression of Pim1 in peritoneal macrophages and T cell follicular helper and mast cell activation (Fig. 2G), all of these results suggested that Pim1 could play a crucial role in driving the M1 polarization of peritoneal macrophages and inducing glycolysis in sepsis.
3. Knockout of Pim1 alleviated inflammation and inhibited glycolysis
To further investigate the role of Pim1 in macrophage, we analyzed the dataset GSE195582 of bone marrow-derived macrophage (BMDM) with Pim1 knockout. Under the LPS-treated condition, setting the criteria at logFC\(\:\ge\:\)1.5 and p-value<0.01, the knockout of Pim1 resulted in changes in the expression of 318 genes (Fig. 3A). GO enrichment analysis was conducted on the differential expressed genes. In terms of Biological Processes (BP), the results showed that the knockout of Pim1 upregulated positive regulation of the mitotic cell cycle and positive regulation of chromosome separation while inhibiting the ERK1 and ERK2 cascade, leukocyte chemotaxis, and monocyte chemotaxis. For Cellular Components (CC), the knockout of Pim1 upregulated microtubule-associated complex and protein-DNA complex, while inhibiting the expression of plasma lipoprotein particle, lipoprotein particle, and protein-lipid complex. In Molecular Function (MF), the knockout of Pim1 upregulated single-stranded DNA binding and microtubule binding, while inhibiting the expression of cytokine activity and chemokine activity (Fig. 3B). Furthermore, the KEGG enrichment analysis results indicated that the knockout of Pim1 affected the signaling transduction of numerous pathways, such as the TNF, PPAR, p53, HIF-1, and FoxO signaling pathways. It also directly regulated the metabolism of steroid, pyrimidine, amino acid, glutathione, and cholesterol (Fig. 3C). Most importantly, we observed that the knockout of Pim1 led to the inhibition of LPS-induced glycolysis in macrophages, with a significant downregulation in the expression of glycolysis-related genes Pfkl, Pgm2, Hk2, Acss2, and Aldh2 (Fig. 3D). Consequently, this resulted in a decrease in the M1 polarization of macrophages, accompanied by reduced expression of Il1a, Il1b, Nos2, Cd86, and Cxcl9 (Fig. 3E).
4. Pim1 regulated RAW264.7 glycolysis under LPS treatment
Given the critical role of Pim1 in regulating glycolysis, we used sh-RNA to knock down Pim1 expression in LPS-treated RAW264.7 cells (Fig. 4A, B). The results showed that the shPim1 could inhibit LPS-induced glycolysis in macrophages, leading to reduced glucose uptake (Fig. 4C), and decreased lactate production within the cells (Fig. 4D). Furthermore, in macrophages with Pim1 knocked out, the mRNA expression levels of glycolysis-related genes were also downregulated (Figure E). Flow cytometry analysis also revealed that the M1 polarization response of LPS-induced macrophages was also suppressed by the knockout of Pim1 (Fig. 4F).
5. c-Myc was regulated by Pim1 and affected M1 macrophage polarization
To uncover the potential regulatory mechanism by which Pim1 modulates macrophage polarization, bioinformatics was employed to predict the proteins that interact with Pim1 in the present study. Many proteins that interacted with pim1 were exhibited in Fig. 5A (https://cn.string-db.org), such as Myc, Il6, Socs1, Edc3 and so on. As an important transcription factor regulating glycolysis, expression of Myc increased in peritoneal macrophages treated with LPS and was regulated by Pim1 (Fig. 5B). The Co-IP experiment indicated that Pim1 had a relationship with c-Myc in the macrophages (Fig. 5C). As the most widely functional subtype[21], we further investigated the role of c-Myc. Western blot results showed that LPS could induce an increase in c-Myc expression and phosphorylation levels, which could be reversed by knocking out Pim1 (Fig. 5D). qPCR results also demonstrated a significant downregulation of c-Myc mRNA level after Pim1 knockout (Fig. 5E). Subsequently, we used si-RNA to inhibit c-Myc expression in RAW264.7 cells (Fig. 5F, G), and the results showed that inhibiting C-Myc expression also led to significant suppression of cellular glycolysis, resulting in reduced glucose uptake and lactate production (Fig. 5H, I). Similarly, the expression of glycolysis-related genes was decreased (Fig. 5J); and the trend of M1 polarization in macrophages was weakened either (Fig. 5K).
6. c-Myc affected the transcriptional efficiency of glycolysis-related genes
Supplement experiments confirmed that overexpression of Pim1 can upregulate c-Myc expression (Fig. 6A, B). The increase in glycolysis caused by overexpression of Pim1 can be reversed by si-c-Myc (Fig. 6C, D), accompanied by changes in glycolysis-related genes and the trend of M1 polarization in macrophages (Fig. 6E, F). We predicted the possible binding site of C-Myc in the promoter region of the target genes (Fig. 6G). Further validation using ChIP assay confirmed that LPS could promote the binding of c-Myc to the promoter region of glycolysis-related genes, while sh-Pim1 inhibited the efficiency of the binding to the gene promoter regions (Fig. 6H).
7. Pharmacological inhibition of Pim1 suppressed the function of peritoneal macrophage in sepsis
Given the regulatory role of Pim1 in peritoneal macrophage in sepsis, we established a mouse model of CLP and used the Pim1 inhibitor SMI-4a. The survival curve of mice showed that inhibition of Pim1 could effectively prolong the survival time of mice (Fig. 7A), and the Tnf-α and Il6 in intraperitoneal lavage fluid were reduced (Figure B, C). The M1 polarization in peritoneal macrophage was decreased either (Fig. 7D). In addition, under the condition of Pim1 inhibitor, the lung injury of CLP mice was improved obviously (Fig. 7E).