Mitochondrial and metabolic alterations are an early adaptation for pre-neoplastic cells during tumour initiation in a zebrafish model

Abstract

Altered metabolism is a well-defined characteristic of established cancers. Metabolic changes have been observed in various pathways, including glycolysis, oxidative phosphorylation, lipid metabolism and amino acid metabolism. Alterations can also be seen in cancer cell mitochondria, where many of these metabolic processes take place. Mitochondrial fission above normal levels has been shown to be important for the proliferation of transformed cells. While these phenotypes are described in established cancers, their role in tumour initiation and development is less well understood. The aim of this project is to begin to describe the metabolic phenotype of developing pre-neoplastic cells (PNCs) and investigate how metabolic adaptations may act synergistically with host inflammatory responses to regulate the developing tumour microenvironment at the very earliest stages of tumour initiation. Recently, the zebrafish (D. rerio) has become an important and dynamic model for in vivo investigations. Our group has used the genetic tractability and in vivo imaging potential of zebrafish to develop a novel model in which tumour development can be monitored in real time. This model allows for precise spatial and temporal induction of epithelial cellular transformation in larval zebrafish, giving rise to mosaic PNCs which can be monitored in vivo as they develop over time. Early work for this project involved characterisation of this model under the control of the superficial skin epithelial layer specific keratin 4 promoter driven human HRASG12V induced PNC initiation. The project then began to define the metabolic phenotype for human HRASG12V driven PNCs at the earliest stages of development. Data reveal that PNCs acquire a hyper-fragmented mitochondrial phenotype, which appears to be associated with altered mitochondrial function and enhanced proliferative capacity. Interestingly, while PNC bearing embryos display enhanced glycolytic flux, PNCs themselves do not show such alterations in glycolytic intermediates or end-products. This suggests that complex metabolic adaptations are taking place at early stages of PNC development and that broad spectrum, unbiased approaches are required to fully understand the complexity of metabolic adaptations in PNCs. Here, I present data which point to an altered metabolic phenotype in PNCs during tumour initiation and development. These findings, as well as a number of new tools and techniques developed during the project, will help to enhance our understanding of cancer initiation and development and provides a basis for further studies of PNC metabolism and cross-talk with the developing PNC niche.