Integrative scRNA-seq Analysis Illuminates LUAD Progression: Contrasting Primary and Metastatic Landscapes with TCGA Insights

Abstract

Lung adenocarcinoma (LUAD) is the most prevalent form of lung cancer and is a significant contributor to cancer-related deaths globally. This cancer type displays extensive diversity and complex characteristics at molecular and cellular levels. Furthermore, LUAD frequently spreads to remote organs, including lymph nodes and the brain, complicating diagnosis, prognosis, and treatment processes. Its progression is a complex and multifaceted process that involves dynamic changes in gene expression patterns, cell identity, and the activation of critical pathways. This comprehensive study utilised single-cell RNA sequencing (scRNA-seq) technology to unveil the complex cellular heterogeneity within primary lung adenocarcinomas and their metastatic sites. This meticulous analysis led to several key findings. The differential gene expression analysis results revealed a striking diversity in gene expression patterns among various cell types within the primary tumour microenvironment. This heterogeneity underscores the specialised roles of distinct cell types in supporting or contributing to tumour growth and maintenance. Conversely, a consistent stemness signature emerged in metastatic samples, suggesting a potential activation of the epithelial-to-mesenchymal transition (EMT), a critical step in cancer metastasis. Our findings shed light on the dynamic changes in gene expression profiles during cancer progression. Gene set enrichment analysis highlighted the significance of several biological pathways in cancer initiation and progression. In primary tumours, the Epithelial-Mesenchymal Transition (EMT) pathway emerged as a central player, emphasising its role in cancer initiation. Other pathways, such as Androgen Response, Adipogenesis, and Coagulation, were also identified, potentially contributing to later-stage tumour growth. Pathways like UV Response Dn and Apical Junction appeared to act as safeguards against uncontrolled cell growth. The p53 Pathway has somehow complex role depending on the specific environment. In metastatic samples, pathways associated with EMT, TNF-alpha Signalling, and IL-2/STAT5 Signalling exhibited high significance, reflecting their importance in promoting tumour growth, metastasis, and immune evasion. Additionally, pathways linked to hypoxia and apoptosis were also found to be actively involved in metastatic processes. By comparing our results with The Cancer Genome Atlas (TCGA) data, we identified two previously unreported genes, ADGRL2 and 2 ERO1A, with potential roles in cancer progression. ADGRL2 emerged as a stem-cellspecific negative regulator, while ERO1A was associated with poor prognosis in various cancer types and linked to metastasis and the epithelial-to-mesenchymal transition (EMT). Our study offers valuable insights into the intricate processes of cancer progression, emphasising the role of EMT and identifying potential therapeutic targets. It provides a broader context for understanding cancer biology and paves the way for personalised cancer treatments. While acknowledging the study's limitations, including sample size and the need for experimental validation, this research sets the stage for future investigations to explore the identified genes and pathways further, potentially revolutionising cancer diagnosis and treatment.