Mathematical modelling of phenotypic plasticity and conversion to a stem-cell state under hypoxia.

Andrew Dhawan,Stephen Hu,Seyed Ali Madani Tonekaboni,Sendurai A Mani,Joseph H Taube,Mohammad Kohandel,Nathalie Sphyris

doi:10.1038/srep18074

Abstract

Hypoxia, or oxygen deficiency, is known to be associated with breast tumour progression, resistance to conventional therapies and poor clinical prognosis. The epithelial-mesenchymal transition (EMT) is a process that confers invasive and migratory capabilities as well as stem cell properties to carcinoma cells thus promoting metastatic progression. In this work, we examined the impact of hypoxia on EMT-associated cancer stem cell (CSC) properties, by culturing transformed human mammary epithelial cells under normoxic and hypoxic conditions, and applying in silico mathematical modelling to simulate the impact of hypoxia on the acquisition of CSC attributes and the transitions between differentiated and stem-like states. Our results indicate that both the heterogeneity and the plasticity of the transformed cell population are enhanced by exposure to hypoxia, resulting in a shift towards a more stem-like population with increased EMT features. Our findings are further reinforced by gene expression analyses demonstrating the upregulation of EMT-related genes, as well as genes associated with therapy resistance, in hypoxic cells compared to normoxic counterparts. In conclusion, we demonstrate that mathematical modelling can be used to simulate the role of hypoxia as a key contributor to the plasticity and heterogeneity of transformed human mammary epithelial cells.

Highlights

Hypoxia, or oxygen deficiency, is known to be associated with breast tumour progression, resistance to conventional therapies and poor clinical prognosis
In order to profile hypoxia-induced changes in epithelial-mesenchymal transition (EMT)-related gene expression and cancer stem cell (CSC) properties, we cultured Ras-transformed immortalized human mammary epithelial cells (HMLER) under normoxic (20% O2, 5% CO2) or hypoxic (1% O2, 5% CO2) conditions
While we expected to observe a rapid transition to a mesenchymal phenotype within 24 hours[12], we observed instead that exposure to hypoxia for up to six days was not sufficient to alter the ‘cobblestone-like’ epithelial growth pattern of the rounded HMLER cells to the elongated, spindle-shaped morphology associated with mesenchymal cells and cells that have undergone EMT

Summary

Introduction

Oxygen deficiency, is known to be associated with breast tumour progression, resistance to conventional therapies and poor clinical prognosis. Regard, hypoxia has been implicated in the induction of a process, known as the epithelial-mesenchymal transition (EMT), that has been shown to confer intrinsic migratory and invasive capabilities as well as stem cell properties to carcinoma cells, enhancing their metastatic potential[2,5,6]. Upon undergoing EMT, epithelial cells typically acquire a less differentiated mesenchymal morphology characterised by loss of the epithelial marker E-cadherin and apico-basal polarity, expression of mesenchymal genes, acquisition of enhanced intrinsic migratory and invasive capabilities, and a reduced proliferation rate. These features are clinically relevant prognostic factors, and have been shown to correlate with increased metastasis and drug resistance[7,8]

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