As one of the most common gastrointestinal malignancies, CRC also has a high mortality rate. In recent years, the survival rate of colorectal cancer patients has improved significantly compared to the previous period with the continuous refinement of therapeutic treatments, including surgery, radiotherapy methods and immunotherapy [14]. The exact molecular mechanisms underlying the developmental progression of CRC have not been clearly reported, although an increasing number of relevant studies are now emerging. The ability to treat advanced stages of tumors has therefore been limited. Therefore, by taking a deeper look into the key genes and pathways involved in the reprogramming of CRC glutamine metabolism, the aim is to explore potential biomarkers and biological targets that could contribute to the development of more effective screening, diagnostic and therapeutic strategies.
Cancer cells have higher energy requirements and biosynthetic needs for growth and metabolism. As early as a century ago, the Voorburg effect, a landmark discovery, emerged, which showed that under aerobic conditions, cancer cells rely primarily on aerobic glycolytic enzymes to break down glycosylated glucose to generate triphosphate and lactate, unlike most somatic cells that maintain their functions by synthesizing triphosphates through oxidative phosphorylation [15]. Increasing evidence suggests that the metabolic reprogramming process of cancer cells is a complex process used to achieve the desired metabolic state for the survival, growth and proliferation processes of cancer cells. Dysregulation of many oncogenes has been found to be a key process in the metabolism of tumor cells, contributing to the alteration of metabolic manifestations that are beneficial for growth, and thus metabolic reprogramming is considered to be a characteristic manifestation of cancer development, which is essential for tumor growth and progression [16, 17]. The process of reorganization of glutamine metabolism is a common metabolic alteration in the progression of cancer cell growth, and it ranks only below glucose metabolism in importance[18].
Glutamine is an essential amino acid in the body, and it has been shown to be an essential trophic factor for lymphocyte proliferation, macrophage phagocytic and secretory activity, cytokine survival, and neutrophil bacterial killing[19]. Compared to other amino acids, glutamine has long been recognized as playing a unique role in the metabolism of proliferating cells[20]. As early as 1960, it was reported that an increase in glutaminase activity was found to be strongly associated with tumor growth rate [21, 22].
There is increasing evidence that the expression level of glutamine metabolism-related genes in tumor cells not only reflects the growth and proliferation process of tumor cells but also serves as a predictive indicator for the prognosis of tumor patients. It has been shown in relevant literature that the expression and abnormal alteration of GMRGs have a essential relationship with the prognosis of many malignant tumors, such as bladder cancer [11], neuroblastoma[23, 24], ovarian cancer[25], lung adenocarcinoma[26] and hepatocellular carcinoma[27–29]. However, the molecular mechanism of glutamine metabolism-related genes on the regulation of colorectal cancer progression and the prognosis prediction of patients have not been further expressed for the time being. Therefore, finding relevant genetic markers for reprogramming glutamine metabolism is expected to improve the long-term survival of CRC patients.
In this study, we obtained gene expression and clinically relevant data from TCGA-CRC and GEO databases. A risk-prognostic model based on four genes (ADIPOQ, VEGFA, TIMP1 and MMP3) was constructed by grouping 1057 colorectal tumor samples and incorporating the expression differences of genes related to glutamine metabolism. Firstly, according to the expression level of GMRG, we divided CRC patients into cluster1 and cluster2 groups and related immune function enrichment analysis. In addition, four genes, ADIPOQ, VEGFA, TIMP1, and MMP3, were analyzed by univariate, multivariate, and lasso regression analyses, and the associated risk-prognostic models were constructed. Moreover, combined with the risk score model we constructed and clinical indicators, glutamine metabolism-related genes were significantly associated with immune infiltration, cell mutation, and functional enrichment in colorectal cancer. We analysed the mutation rates of 15 common somatic genes between different risk grouping subtypes and found more significant differences in APC and P53 mutations. Studies have shown that immune infiltration and immune scores play a particularly critical role in TME and in predicting the prognosis of patients with tumors[30, 31]. This study showed that the patients of CRC in the high-risk group usually have higher immune infiltration and richer immune-related pathways, suggesting that our constructed risk scoring model for GMRGs can differentiate the degree of immune infiltration in patients. Finally, more consistent and meaningful results were obtained in the skewed-neck validation of the GEO dataset GSE 39582. In addition, TMB analyses showed that patients in the high-risk group usually had a poorer prognosis than those in the low-risk group, whereas patients in the low-risk group subtype with lower mutation loads had the most favourable prognosis in the tumor mutation load analysis. Finally, we constructed column-line diagrams that can have an accurate prognosis for colorectal cancer patients. Thus, the model based on the four GMRG risk characteristics in this study may be capable of effectively predicting the prognostic level of CRC patients.
Immunosuppression is significantly associated with the progression of malignant tumors, and in tumor cells there are different mechanisms to evade immune surveillance. Tumor microenvironment (TME) plays an important role in cancer development and progression[17, 32, 33]. Immunosuppression has a detrimental effect on the treatment of malignant tumors. In tumor tissues, tumor cells can have a suppressive outcome on the function of immune cells through competitive consumption of nutrients. At the same time, metabolites produced in tumor tissues likewise have a modulating effect on immune cell function.[34]. Immune infiltrating cells play a key role in the process of tumor development and are mainly composed of dendritic cells, macrophages, natural killer cells, T cells and B cells. [35]. In this study, we found that the glutamine metabolism-related gene TIMP1 showed significantly high expression in CRC samples and higher expression in cluster2 compared to cluster1.TIMP1 family members are natural inhibitors of matrix metalloproteinases (MMPS) including MMP1. It has been shown that TIMP1 has a significant correlation to colorectal carcinogenesis and metastasis and is a potential cancer prognostic biomarker [36, 37]. This is consistent with our findings that TIMP1 can affect the the prognosis of CRC patients,which was considersd as an independent factor.In addition, tissue microarray verified that ADIPOQ was expressed at high levels in colorectal cancer paracellular tissues.
According to the fact that glutamine metabolism plays an important role in tumor cell and immune cell function, it is possible to promote the prognosis of tumor patients by interfering with the process of glutamine metabolism and thereby altering the processes of tumor growth, proliferation, and metastasis. Tumor-associated macrophages are an important component of immune cells in tumor necrotic tissue, and metabolic reprogramming of macrophages creates associated functional subtypes[38]. In the present study, the low-risk group was characterised by a higher infiltration of M2 macrophages compared with the high-risk group, suggesting that glutamine metabolism and synthesis are essential for maintaining the function of M2[39].
However, there are still some unavoidable limitations of this study. First, Our data were obtained from open public databases, which may lead to a certain case selection bias. Second, only database analysis was applied in this study, and relevant biological experiments were not perfected, which should be followed by relevant clinical validation to prove the validity of the study. Finally, more animal experiments or clinical studies should be conducted to clarify the exact role of glutamine metabolism-related gene regulation in CRC patients.