[Paper Review] Probing leukemia cells behavior under starvation

Simone Scalise, Giorgio Gosti+3 more|arXiv (Cornell University)|Aug 17, 2024

Liver Disease Diagnosis and Treatment4 citations

TL;DR

This study investigates how leukemia cells (Jurkat T-cells) adapt to serum starvation using live-cell fluorescence and flow cytometry combined with a quantitative model. It reveals that cells retain memory of prior serum-rich conditions for up to one generation before adapting their growth and division rates, maintaining a sizer-like division strategy, while non-proliferating cells exhibit asymmetric partitioning of older mitochondria.

ABSTRACT

The ability of a cancer cell population to achieve heterogeneity in their phenotype distributions offers advantages in tumor invasiveness and drug resistance. Studying the mechanisms behind such observed heterogeneity in mammalian cells presents challenges due for instance to the prolonged proliferation times compared to widely studied unicellular organisms like bacteria and yeast. Here, we studied the response of leukemia cell populations to serum starvation via a protocol, we recently developed, that makes use of live cell fluorescence and flow cytometry in combination with a quantitative analytical model to follow the population proliferation while monitoring the dynamics of its phenotype distributions. We found that upon switching between a serum-rich to a serum-poor media, leukemia cells (i) maintain a memory of the previous environment up to one generation even in the presence of severe medium-depletion, before (ii) adapting their growth and division rates to the novel environment while preserving a sizer-like division strategy. Finally, looking at the mitochondria content of the proliferating vs non-proliferating cells, we found that the latter is characterized by a higher number of older mitochondria, suggesting a possible functional role of the observed asymmetric partitioning of (aged) mitochondria in leukemia cells.

Motivation & Objective

• To understand how leukemia cell populations dynamically adapt to serum starvation at the phenotypic and population level.
• To investigate whether cells retain memory of prior environmental conditions during nutrient transition.
• To determine if the division strategy (e.g., sizer, timer, or adder) is preserved under starvation conditions.
• To explore the role of mitochondrial age and asymmetry in proliferation fate decisions in leukemic cells.

Proposed method

• Employed flow cytometry with carboxyfluorescein diacetate succinimidyl ester (CFSE) dye dilution to track cell generations over time.
• Used forward scatter (FSC) as a proxy for cell size to correlate size with division dynamics.
• Applied a Gaussian Mixture Model (GMM) with the Expectation-Maximization (EM) algorithm to identify generation-specific fluorescence clusters.
• Developed a stochastic Gillespie simulation model to validate the theoretical growth and division dynamics.
• Formulated a minimal theoretical model to quantify growth and division rates as power functions of cell size.
• Integrated experimental data with mathematical modeling to infer population-level proliferation statistics.

Experimental results

Research questions

• RQ1 How do leukemia cells respond to progressive serum starvation in terms of proliferation dynamics?
• RQ2 Do cells retain a memory of prior serum-rich conditions during transition to starvation?
• RQ3 Is the division strategy (e.g., sizer, timer, adder) preserved under serum-deprived conditions?
• RQ4 What is the relationship between mitochondrial age and cell fate (proliferating vs. non-proliferating) in starved conditions?
• RQ5 How does the phenotypic distribution of the population evolve during nutrient transition?

Key findings

• Leukemia cells maintain a memory of prior serum-rich conditions for up to one generation after switching to serum-poor media.
• Cells adapt their growth and division rates to the new environment in a serum-dependent manner, preserving a sizer-like division strategy.
• The duration of the memory effect is inversely proportional to the difference between the initial and final serum concentrations.
• Non-proliferating cells exhibit a higher proportion of older mitochondria compared to proliferating cells, indicating asymmetric partitioning of aged mitochondria.
• The experimental protocol successfully stratifies the population by generation using dye dilution and FSC, enabling quantitative analysis of proliferation dynamics.
• Theoretical modeling and Gillespie simulations confirm that the observed proliferation curves are consistent with size-dependent growth and division rates.