Fatty Acid Metabolism is Associated with Immune Microenvironment Variation in Bladder Cancer, and FN1 May Mediate PD-L1 Expression through the IL6-STAT3 Pathway

Research Article

Austin J Nutr Metab. 2023; 10(1): 1130.

Fatty Acid Metabolism is Associated with Immune Microenvironment Variation in Bladder Cancer, and FN1 May Mediate PD-L1 Expression through the IL6-STAT3 Pathway

Kexin Bai2#; Kai Zhao1#; Zhonglei Deng1#; Jingyuan Tang1; Qiang Song2*; Yan Xu1*; Jie Han1*

¹Department of Urology, Jiangsu Province Hospital of Chinese Medicine, Affiliated Hospital of Nanjing University of Chinese Medicine, Nanjing 210029, PR China

²Department of Urology, The First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, PR China

*Corresponding author: Yan Xu & Jie Han Department of Urology, Jiangsu Province Hospital of Chinese Medicine, Affiliated Hospital of Nanjing University of Chinese Medicine, Nanjing 210029, PR China;

Qiang Song, Department of Urology, The First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, PR China. Tel: +86 25 86528546; Fax: +86 25 86528546 Email:qiangsong121@163.com; xuyan3615@sina.com; 867262505@qq.com

#These authors contributed equally to this work.

Received: October 12, 2023 Accepted: November 15, 2023 Published: November 22, 2023

Abstract

Background: Fatty acid metabolism plays an important role in many biological activities, such as cell membrane formation, energy storage, and signal molecule generation in tumorigenesis. Lipid metabolism affects the progression and treatment of Bladder Cancer (BLCA). Therefore, it is imperative to explore the function and prognostic value of lipid metabolism-related genes in BLCA patients.

Methods: In this study, we collected gene expression profiles and clinical information in The Cancer Genome Map (TCGA) database and two independent Group on Earth Observations (GEO) datasets. Gene interaction information was obtained from ENCORI database. Based on these databases, we analyzed the expression patterns of genes and proteins involved in fatty acid metabolism and their matching clinicopathological features. Further, the gene for fatty acid metabolism, FN1, was screened for cellular function science experiments to validate our findings.

Results: Analysis in the TCGA database identified 310 fatty acid metabolism-related mRNAs, 91 of which were differentially expressed in BLCA patients. Based on the correlation of Differentially Expressed Genes (DGEs) with patient characteristics, we developed a clinical prognostic correlation model and validated the accuracy of the model based on information from the GEO database. Survival analysis and clinical correlation analysis showed that elevated FN1 levels were highly correlated with shorter survival, higher staging, higher grading, and lower infiltration of immune cells in BLCA. Furthermore, we experimentally verified that FN1 can activate the IL6 -JAK - STAT3 pathway and further promote PD-L1 expression, which would serve as a potential factor for immune escape in bladder cancer. Finally, our experimental results were consistent with the bioinformatics analysis.

Keywords: Bladder cancer; Fatty acid metabolism; Immunotherapy; fn1

Abbreviations: BLCA: Bladder Cancer; FA: Fatty Acids; TCGA: The Cancer Genome Map; GEO: Group on Earth Observations; GO: Gene Ontology; KEGG: Kyoto Encyclopedia of genes and genomes

Background

BLCA is one of the most common malignant tumors, particularly in the middle-aged and elderly [1]. Although a variety of treatment methods have been developed in recent years, such as surgery, chemotherapy, and targeted therapy, most patients relapse after treatment, resulting in high medical costs and low quality of life [2]. In addition, BLCA is a disease with relatively high treatment cost, which causes a considerable disease burden to individuals and society [3]. Therefore, it is very important to explore new therapeutic targets and develop new prognostic models in BLCA [4].

Metabolic disorder is one of the characteristics of cancer [5]. Lipid metabolism reprogramming is one of the most significant metabolic changes observed in cancer cells and has attached more and more attention [6]. Fatty Acids (FA) are required for energy storage, membrane proliferation and signal molecule generation [7]. FA are important components of lipid metabolism, and their accumulation can meet the needs of lipid synthesis signal molecules and membranes [8]. Therapies targeting deregulated fatty acids in cancer may slow tumor growth and have synergistic effects with immune checkpoint inhibitors [9]. More than this, the prognostic value of fatty acid metabolism-related genes and their relationship with BLCA immunotherapy remain largely unknown. The gene set related to fatty acid metabolism in BLCA has not been systematically studied. Therefore, we think it is necessary to further explore the mechanism of fatty-acid metabolism genes involved in the tumorigenesis and development of BLCA.

In this study, we comprehensively evaluated the metabolic pattern of fatty acids by analyzing the genomic information of 433 BLCA samples. Combining the TCGA database and two independent GEO datasets, we analyzed the sequencing data of BLCA and constructed a fatty acid prognostic risk score model. The prognostic risk score model can independently predict the survival outcome of BLCA patients. We investigated the relationship between the prognostic risk score model and the characteristics of TME cell infiltration. Prognostic risk scoring model can effectively distinguish whether patients are sensitive to BLCA immunotherapy. Therefore, fatty acid metabolism is crucial in forming individual TME characteristics. We found that FN1 was significantly high expressed in tumor tissues of BLCA patients compared with tumor-adjacent tissue. In addition, the results of clinical correlation analysis showed that the expression of FN1 was related to the clinical stage, tumor invasion, and immune invasion of BLCA patients. By further exploring the possible molecular mechanism of FN1 in BLCA, we found that it is involved in immune escape. Recently, increasingly people pay attention to the role of CD8+T cells in tumor immunity [10-13]. Our analysis results indicate that FN1 may participate in tumor immune checkpoint blocking (PD-L1 and CTLA4). Finally, we detected the expression of FN1 in BLCA tissue samples and verified its potential significance. These findings provide a new perspective for exploring the metabolic mechanism and treatment of BLCA.

Methods

Data Collection and Processing

TCGA database (https://portal.gdc.cancer.gov/) was used to obtain transcriptome analysis data of BLCA tumors and tumor-adjacent tissue. Then, 19 normal samples and 433 BLCA samples were obtained. At the same time, the clinical information of the samples was obtained from TCGA database, and other BLCA related datasets were downloaded from GEO database (https://www.ncbi.nlm.nih.gov/geo/). The overview design of this study is displayed (Figure 1). We used the annotation platform to convert the entrez gene ID of each sample into the corresponding gene symbol. If the same entrez gene ID is targeted by multiple probes, the average value is used. We also downloaded the matched clinical and survival data from the TCGA queue, including gender, age, pathological stage, AJCC-TNM classification (TNM) stage, and prognosis information. Finally, 412 BLCA samples were included to form a training set of TCGA data. The original readings of the above data are processed and standardized in R software.