Exploration of glyoxals' level changes in endoplasmic reticulum during ferroptosis by a photocaged fluorescent probe

Both ferroptosis and elevated glyoxals (e.g. methylglyoxal and glyoxal), are associated with endoplasmic reticulum stress, but their correlations, in particular, how level of glyoxals changes in endoplasmic reticulum during ferroptosis remains unclear. In this work, a new photoactivatable fluorescent probe Photo-ER-GOS was developed to study level changes of glyoxals in endoplasmic reticulum during ferroptosis via in situ photodecaging and fluorescence detection, avoiding potential interference from glyoxals in cytosol. The probe contains a photolabile nitrobenzyloxymethyl group functioned both as the reactivity blocking group and the fluorescence quenching group, which linked to the guanidino group of NAP-DCP-3, , the active endoplasmic reticulum-targeting fluorescent probe for glyoxals previously developed in our lab. It was found that the level of glyoxals in endoplasmic reticulum increases significantly during erastin-induced ferroptosis in RAW 264.7 cells via comparison of relative fluorescence intensity increases. The endoplasmic reticulum glyoxal level increase was also confirmed by the Ultra Performance Liquid Chromatography-Mass Spectrum studies. In contrast, no significant change of level of glyoxals in endoplasmic reticulum was found in staurosporine-induced apoptosis, suggesting that upregulated glyoxals in endoplasmic reticulum may be a previously overlooked characteristic of ferroptosis. Erastin-induced level increase of glyoxals was also found in zebrafish. The caged probe Photo-ER-GOS thus provides a useful chemical tool to study GOS levels changes in endoplasmic reticulum.