Fructose Promotes Colorectal Cancer Growth by Modulating Tumor-Associated Macrophage Polarization

Introduction

In recent years, fructose intake has dramatically increased worldwide and is closely associated with obesity and metabolic syndrome, both of which are recognized risk factors for cancer development. Although previous studies have shown that fructose promotes tumor cell proliferation and metastasis through its metabolism, its specific role in the tumor immune microenvironment has not yet been fully elucidated. Tumor-Associated Macrophages (TAMs) have dual roles in the immune microenvironment of colorectal cancer, potentially inhibiting tumor growth through pro-inflammatory M1-like polarization or promoting tumor growth through immunosuppressive M2-like polarization. This study, carried out by research teams from the Institute of Biophysics, Chinese Academy of Sciences, Wenzhou Medical University, **** General Hospital, and other institutions, primarily explores the role of fructose in regulating the polarization of TAMs and elucidates how fructose promotes colorectal cancer progression by inhibiting M1-like TAM polarization.

Research Background and Objective

As fructose intake increases, recent research has gradually revealed the potential role of fructose in promoting tumor growth. However, most studies have focused on the direct effects of fructose on tumor cells, while its effects on TAMs in the tumor immune microenvironment remain unclear. This study aims to uncover the mechanistic impact of fructose on TAM polarization in colorectal cancer to further elucidate its role in tumor immune regulation.

Research Methods

Overview of Study Process

1. Establishment of Animal Models: The study used murine models of colorectal cancer, including a spontaneous adenoma model (APCmin/+ mice) and an ectopic tumor model, to explore the effects of fructose on the tumor microenvironment and tumor growth.
2. Effects of Fructose on TAM Polarization: The proportions of immune cells infiltrating the tumor were analyzed by fluorescent flow cytometry, focusing on changes in M1-like and M2-like TAM proportions, and the distribution of M1-like TAMs was detected through immunofluorescence staining.
3. In Vitro Macrophage Induction: An in vitro bone marrow-derived macrophage (BMDM) induction system was constructed, with BMDMs cultured in glucose or fructose media, to compare the direct inhibitory effect of fructose on M1-like TAM polarization.
4. Key Molecular Mechanism Analysis: Immunoprecipitation and mass spectrometry analyses were utilized to reveal how fructose regulates the interaction between Hexokinase 2 (HK2) and Inositol 1,4,5-Trisphosphate Receptor Type 3 (ITPR3), affecting macrophage calcium ion flow.
5. Verification of the Role of Transporter GLUT5: Conditional GLUT5 knockout mice were generated using gene knockout techniques to verify that fructose is transported through GLUT5 and acts on macrophage polarization.

Main Experimental Steps and Analysis

1. Promotion of Colorectal Cancer Growth by Fructose in Mice: Using a mouse model with 25% high fructose corn syrup (HFCS), it was found that long-term fructose consumption significantly increased the proportion of M1-like TAMs in colorectal cancer tumors without causing obesity or metabolic syndrome.
2. Effects of Fructose on Gut Microbiota: The impact of fructose intake on the gut microbiome was analyzed through 16S rDNA sequencing, revealing significant changes in the abundance of certain bacterial species in the HFCS mouse group.
3. Inhibitory Effect of Fructose on M1-like TAM Polarization: Flow cytometry analysis showed that HFCS treatment significantly reduced the proportion of M1-like TAMs in the colorectal cancer model, indicating an inhibitory effect of fructose on TAM polarization.
4. In Vitro Fructose Treatment of Bone Marrow-Derived Macrophages: Treatment of BMDMs with 6mM fructose significantly inhibited the expression of pro-inflammatory factors (such as IL-1β, TNF-α, IL-6), without significantly affecting M2-like macrophages.
5. Validation of GLUT5 Transporter Role: Experiments with GLUT5 knockout mice and in vitro tests confirmed that fructose enters macrophages via GLUT5, affecting TAM polarization.
6. Interaction Between HK2 and ITPR3: Immunoprecipitation experiments indicated that fructose promotes the interaction between HK2 and ITPR3, inhibiting the transfer of calcium ions from the endoplasmic reticulum to mitochondria, a process that suppresses M1-like TAM polarization.

Research Results

1. Fructose Promotes Tumor Growth by Inhibiting M1-like TAM Polarization: The HFCS mouse model showed that fructose significantly reduces the proportion of M1-like TAMs in tumors and increases the number of large adenomas, suggesting that fructose may promote tumor growth by inhibiting the anti-tumor effects of M1-like macrophages.
2. Direct Inhibition of TAM Polarization by Fructose: In the in vitro BMDM induction system, fructose treatment significantly inhibited the expression of pro-inflammatory factors in M1-like TAMs without affecting M2-like TAM marker expression.
3. Mechanisms of HK2 and ITPR3 Interaction: The interaction between HK2 and ITPR3 results in blocked intracellular calcium ion transmission, inhibiting the activation of MAPK and STAT1 signaling pathways, thus suppressing M1-like TAM polarization.
4. Fructose Transport Depends on GLUT5: The GLUT5 knockout mouse model indicates that GLUT5 is key for fructose entry into macrophages and its regulatory effect on polarization.
5. Clinical Correlation Analysis: Analysis of single-cell RNA sequencing data from immune cells infiltrating colorectal cancer patients’ tumors showed that high GLUT5 expression in TAMs is significantly associated with poor clinical outcomes in advanced colorectal cancer.

Research Significance and Value

This study is the first to reveal the key role of fructose as a signaling molecule, rather than a metabolite, in regulating macrophage polarization and the tumor immune microenvironment. Fructose promotes the interaction between HK2 and ITPR3, inhibiting M1-like TAM polarization and thus fostering a more supportive immune environment for tumor growth. The high expression of GLUT5 in macrophages also suggests the potential clinical application of GLUT5 as a biomarker for colorectal cancer progression.

This study not only theoretically enriches the understanding of fructose’s role in tumor progression mechanisms but also suggests potential clinical intervention strategies, such as targeting GLUT5 or blocking the HK2-ITPR3 interaction, which may improve the clinical treatment outcomes of colorectal cancer. Furthermore, the research provides important insights for investigating fructose’s role in other cancer types, with broad application prospects.