Academic Background

Liver regeneration is a complex biological process involving the coordinated action of various cell types and signaling pathways. Following partial liver resection, the remaining liver tissue restores its function and mass through a series of precisely regulated cell proliferation and immune responses. Although extensive research has been conducted on the mechanisms of liver regeneration, the specific roles of certain cell types in this process remain incompletely understood. Myeloid-Derived Suppressor Cells (MDSCs) are a heterogeneous population of immature myeloid cells known to play immunomodulatory roles in processes such as cancer and wound healing. However, the specific functions of MDSCs in liver regeneration, particularly their impact on hepatocyte proliferation and immune modulation, have not been fully elucidated.

This study aims to investigate the role of granulocytic MDSCs (G-MDSCs) in hepatocyte proliferation and immune modulation during liver regeneration. Through gene expression profiling, cell culture experiments, and mass cytometry (CyTOF), the researchers revealed the critical role of G-MDSCs in the early stages of liver regeneration, particularly their regulation of hepatocyte proliferation and intrahepatic immune cell composition.

Source of the Paper

This paper was co-authored by Ido Nachmany, Shir Nevo, Sarit Edelheit, Avital Sarusi-Portuguez, Gilgi Friedlander, Tomer-Meir Salame, Vera Pavlov, Oran Yakubovsky, and Niv Pencovich. These authors are affiliated with institutions such as Sheba Medical Center and Weizmann Institute of Science. The paper was published in 2024 in the journal Genes & Immunity, titled Myeloid derived suppressor cells mediate hepatocyte proliferation and immune suppression during liver regeneration following resection.

Research Process and Results

1. Liver Resection and G-MDSC Depletion

The researchers first performed two-thirds liver resection (hepatectomy, Hx) in mice to simulate the liver regeneration process. To study the role of G-MDSCs, they depleted CD11b+Ly6G+ G-MDSCs in mice using an anti-Gr1 antibody. Control mice were injected with a non-targeting IgG antibody.

2. Isolation of Hepatocytes and Non-Parenchymal Cells

Following surgery, the researchers isolated hepatocytes and non-parenchymal cells using a two-step perfusion method. Hepatocytes were used for subsequent gene expression analysis, while non-parenchymal cells were analyzed for immune cell composition using flow cytometry.

3. Gene Expression Profiling

Using RNA sequencing, the researchers compared the gene expression changes in hepatocytes between G-MDSC-depleted mice and control mice during liver regeneration. The results showed that G-MDSC depletion significantly disrupted the transcriptional progression of hepatocytes, particularly on postoperative day 2 (POD2), where hepatocytes exhibited substantial changes in gene expression. Compared to the control group, G-MDSC-depleted mice showed 3174 differentially expressed genes in hepatocytes on POD2, with 1244 genes downregulated and 1930 genes upregulated.

4. Cell Culture Experiments

To verify the direct effect of G-MDSCs on hepatocyte proliferation, the researchers co-cultured HepG2 hepatocytes with G-MDSCs isolated from regenerating livers. The results showed that the number of hepatocytes in co-culture was significantly higher than in mono-cultured HepG2 cells. Additionally, the researchers found that G-MDSCs upregulated amphiregulin (AREG) during regeneration, and AREG-treated HepG2 cells also exhibited increased proliferation.

5. Mass Cytometry (CyTOF) Analysis

Using CyTOF, the researchers analyzed the impact of G-MDSC depletion on the immune cell composition within regenerating livers. The results showed that G-MDSC depletion led to an increase in the proportions of natural killer cells (NK cells) and activated T cells, while the proportions of monocytes and neutrophils also changed. These results indicate that G-MDSCs play an important role in regulating the immune cell composition during liver regeneration.

Research Conclusions

This study revealed the critical role of G-MDSCs in the early stages of liver regeneration. G-MDSCs ensure the smooth progression of liver regeneration by promoting hepatocyte proliferation and modulating intrahepatic immune responses. Specifically, G-MDSCs directly promote hepatocyte proliferation by upregulating growth factors such as AREG. At the same time, G-MDSCs maintain immune balance during liver regeneration by regulating the proportions of NK cells and T cells.

Research Highlights

1. Multifaceted Role of G-MDSCs in Liver Regeneration: This study is the first to comprehensively reveal the dual role of G-MDSCs in hepatocyte proliferation and immune modulation during liver regeneration.
2. Key Role of AREG: The study found that G-MDSCs directly promote hepatocyte proliferation by upregulating AREG, providing new insights into the molecular mechanisms of liver regeneration.
3. Regulation of Immune Cell Composition: Using CyTOF, the researchers demonstrated that G-MDSCs play a significant role in regulating the immune cell composition during liver regeneration, particularly the modulation of NK cells and T cells.

Research Significance

This study not only deepens our understanding of the mechanisms of liver regeneration but also provides new directions for the treatment of liver regeneration disorders. By modulating the function of G-MDSCs, it may be possible to promote liver regeneration, particularly in clinical scenarios such as liver resection and transplantation. Additionally, this study offers potential therapeutic targets for other liver regeneration-related diseases, such as drug-induced liver injury and alcoholic hepatitis.

Other Valuable Information

The RNA sequencing data from this study have been uploaded to the NCBI Gene Expression Omnibus (GEO) database under the accession number GSE277186, available for further analysis and validation by other researchers.

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Through this study, we have gained a deeper understanding of the role of G-MDSCs in liver regeneration and provided new directions for future clinical treatments.