Water metabolism in T cells

Cell growth is a central process for life and a basic principle in biology. While the biosynthesis and acquisition of dry biomass are well characterized, the way cells regulate their wet mass remains incompletely understood. To study cellular water homeostasis we developed a novel method, Cold Aqua Trap – Isotope Ratio Mass Spectrometry (CAT-IRMS), which allows analyzing the isotope composition of intracellular water. Applying CAT-IRMS on T cells we found no significant difference in water uptake rate between naïve, quiescent cells and stimulated growing cells. In contrast, we discovered that post-activation glycolysis-coupled de-novo water biosynthesis accounts for a substantial portion of the volume gained by stimulated T cells. Thus, during their early growth process, T cells gain wet mass as a byproduct of metabolism. Our study shed light on the way cells regulate their wet mass, and therefore, lays the foundations for better understanding of how cells determine what size to grow to before dividing.