Stromal interactions in pleural mesothelioma
Pleural mesothelioma (PM) is a devastating malignancy primarily related to past asbestos exposure. There are no curative options, and 1-year survival stands currently at just 40%. The genomic landscape in mesothelioma is dominated by loss of function of tumour suppressor genes rather than targetable oncogenes. It is a stromal rich malignancy with cancer cell nuclei frequently accounting for less than 25% of all tumour nuclei. The remainder are largely comprised of stromal cells, the roles of which have been relatively neglected by existing studies. Of particular interest are the cancer-associated fibroblasts (CAF) whose interactions with cancer cells modulates the tumour microenvironment. The rarity of mesothelioma is a challenge to studying its biology since fresh tissue is not reliably available for experimentation. In this thesis, I sought to understand the composition of the tumour stroma in PM to identify interactions between the tumour stroma and malignant mesothelial cells. I generated a single cell transcriptomic dataset from both fresh tissue for single-cell RNA-sequencing, and isolated nuclei from frozen samples for single nuclei RNA-sequencing. Following rigorous quality control, I retained 268,089 cells and nuclei across asbestos exposed benign and malignant pleura. I characterised the heterogenous populations of mesothelial cells identifying various states of trans-differentiation, and discovered a previously unexplored malignant mesenchymal cell population within sarcomatoid PM. I identified key gene regulatory networks that govern the identity of these cells and use in situ hybridisation to spatially localise gene biomarkers specific to distinct states of mesothelial cell trans-differentiation. I then explored CAF heterogeneity revealing both universal and pleura-specific fibroblast subtypes, including a population of myofibroblasts unique to sarcomatoid PM that upregulate genes in Hedgehog signalling pathways. This work advances our understanding of how PM may evolve across histological subtypes and highlights signalling pathways that could be targeted for future therapeutic benefit.
Mesothelioma, Pleural biology, Asbestos, Single-cell transcriptomics
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