The mitochondrial Ca2+ uptake regulator, MICU1, is involved in cold stress-induced ferroptosis.

Ferroptosis has recently attracted much interest because of its relevance to human diseases such as cancer and ischemia-reperfusion injury. We have reported that prolonged severe cold stress induces lipid peroxidation-dependent ferroptosis, but the upstream mechanism remains unknown. Here, using genome-wide CRISPR screening, we found that a mitochondrial Ca2+ uptake regulator, mitochondrial calcium uptake 1 (MICU1), is required for generating lipid peroxide and subsequent ferroptosis under cold stress. Furthermore, the gatekeeping activity of MICU1 through mitochondrial calcium uniporter (MCU) is suggested to be indispensable for cold stress-induced ferroptosis. MICU1 is required for mitochondrial Ca2+ increase, hyperpolarization of the mitochondrial membrane potential (MMP), and subsequent lipid peroxidation under cold stress. Collectively, these findings suggest that the MICU1-dependent mitochondrial Ca2+ homeostasis-MMP hyperpolarization axis is involved in cold stress-induced lipid peroxidation and ferroptosis.

A Novel Lens for Cell Volume Regulation: Liquid-Liquid Phase Separation.

Cells are constantly exposed to the risk of volume perturbation under physiological conditions. The increase or decrease in cell volume accompanies intracellular changes in cell membrane tension, ionic strength/concentration and macromolecular crowding. To avoid deleterious consequences caused by cell volume perturbation, cells have volume recovery systems that regulate osmotic water flow by transporting ions and organic osmolytes across the cell membrane. Thus far, a number of biomolecules have been reported to regulate cell volume. However, the question of how cells sense volume change and modulate volume regulatory systems is not fully understood. Recently, the existence and significance of phaseseparated biomolecular condensates have been revealed in numerous physiological events, including cell volume perturbation. In this review, we summarize the current understanding of cell volume-sensing mechanisms, introduce recent studies on biomolecular condensates induced by cell volume change and discuss how biomolecular condensates contribute to cell volume sensing and cell volume maintenance. In addition to previous studies of biochemistry, molecular biology and cell biology, a phase separation perspective will allow us to understand the complicated volume regulatory systems of cells.