RRC ID 65341
Author Furuta Y, Pena-Ramos O, Li Z, Chiao L, Zhou Z.
Title Calcium ions trigger the exposure of phosphatidylserine on the surface of necrotic cells.
Journal PLoS Genet
Abstract Intracellular Ca2+ level is under strict regulation through calcium channels and storage pools including the endoplasmic reticulum (ER). Mutations in certain ion channel subunits, which cause mis-regulated Ca2+ influx, induce the excitotoxic necrosis of neurons. In the nematode Caenorhabditis elegans, dominant mutations in the DEG/ENaC sodium channel subunit MEC-4 induce six mechanosensory (touch) neurons to undergo excitotoxic necrosis. These necrotic neurons are subsequently engulfed and digested by neighboring hypodermal cells. We previously reported that necrotic touch neurons actively expose phosphatidylserine (PS), an "eat-me" signal, to attract engulfing cells. However, the upstream signal that triggers PS externalization remained elusive. Here we report that a robust and transient increase of cytoplasmic Ca2+ level occurs prior to the exposure of PS on necrotic touch neurons. Inhibiting the release of Ca2+ from the ER, either pharmacologically or genetically, specifically impairs PS exposure on necrotic but not apoptotic cells. On the contrary, inhibiting the reuptake of cytoplasmic Ca2+ into the ER induces ectopic necrosis and PS exposure. Remarkably, PS exposure occurs independently of other necrosis events. Furthermore, unlike in mutants of DEG/ENaC channels, in dominant mutants of deg-3 and trp-4, which encode Ca2+ channels, PS exposure on necrotic neurons does not rely on the ER Ca2+ pool. Our findings indicate that high levels of cytoplasmic Ca2+ are necessary and sufficient for PS exposure. They further reveal two Ca2+-dependent, necrosis-specific pathways that promote PS exposure, a "two-step" pathway initiated by a modest influx of Ca2+ and further boosted by the release of Ca2+ from the ER, and another, ER-independent, pathway. Moreover, we found that ANOH-1, the worm homolog of mammalian phospholipid scramblase TMEM16F, is necessary for efficient PS exposure in thapsgargin-treated worms and trp-4 mutants, like in mec-4 mutants. We propose that both the ER-mediated and ER-independent Ca2+ pathways promote PS externalization through activating ANOH-1.
Volume 17(2)
Pages e1009066
Published 2021-2-1
DOI 10.1371/journal.pgen.1009066
PMID 33571185
PMC PMC7904182
MeSH Animals Animals, Genetically Modified Apoptosis / genetics Caenorhabditis elegans / drug effects Caenorhabditis elegans / genetics Caenorhabditis elegans / metabolism* Caenorhabditis elegans Proteins / genetics Caenorhabditis elegans Proteins / metabolism Calcium / metabolism* Cytoplasm / metabolism Dantrolene / pharmacology Degenerin Sodium Channels / genetics Degenerin Sodium Channels / metabolism Endoplasmic Reticulum / drug effects Endoplasmic Reticulum / genetics Endoplasmic Reticulum / metabolism* Enzyme Inhibitors / pharmacology Membrane Proteins / genetics Membrane Proteins / metabolism Muscle Relaxants, Central / pharmacology Necrosis / genetics Necrosis / metabolism Neurons / drug effects Neurons / metabolism* Neurons / pathology Phosphatidylserines / metabolism* Phospholipid Transfer Proteins / genetics Phospholipid Transfer Proteins / metabolism Sodium Channels / genetics Sodium Channels / metabolism TRPC Cation Channels / genetics TRPC Cation Channels / metabolism Thapsigargin / pharmacology
C.elegans tm4762