Glutaminase inhibition is correlated with an increase in phospholipid unsaturation, a potential cellular adaptation to pH fluctuations

The ability of cells to adapt to stress is fundamental for the maintenance of cellular homeostasis. In this study, we identified a possible adaptation mechanism to pH fluctuations while investigating the role of glutamine metabolism in Drosophila S2 cells. Inhibition of glutaminase (GLS), an enzyme that catalyzes the deamination of glutamine to glutamate, yielding ammonia, has been correlated with an increase in monounsaturated fatty acid (MUFA) content in membrane phospholipids. GLS inhibition–linked lipid remodeling was driven by the selective promotion of MUFA-rich phospholipid biosynthesis and was reversed by the addition of basic compounds such as ammonia, a byproduct of the GLS reaction, or NaOH, but not by glutamate-derived metabolites. Furthermore, lowering the pH of culture medium with HCl or reducing intracellular pH through the inhibition of the Na⁺/H⁺ exchanger resulted in lipid composition changes similar to those observed in GLS-inhibited cells. This suggests that pH changes govern membrane lipid unsaturation and that cellular acidification itself promotes the accumulation of MUFA-rich phospholipids. Notably, cells with higher MUFA levels exhibited higher intracellular pH than those with lower MUFA levels. Taken together, these findings indicate that cells respond to pH fluctuations by adjusting membrane lipid unsaturation to maintain cellular pH homeostasis.