Monitoring dynamic changes of glutathione redox state in subcellular compartments of human cells - an approach based on rxYFP biosensor

The kinetic and spatial separation of redox systems renders redox biology studies a particularly challenging field. Genetically encoded biosensors including the glutathione-specific redox-sensitive yellow fluorescent protein (rxYFP) provide an alternative way to overcome the limitations of conventional glutathione/glutathione disulfide (GSH/GSSG) redox measurements. In this study, the plasmids expressing respectively cytosol-, nucleus-, and mitochondrial matrix- targeted rxYFP were created and introduced to human cervical carcinoma (HeLa) cells. The rxYFP redox states were monitored by direct assessment of the oxidized to reduced rxYFP ratio via redox protein extraction, redox Western blot and signal quantification. RxYFP proteins expressed in the cytosol, nucleus or mitochondrial matrix of HeLa cells were responsive to the intracellular redox state changes induced by reducing as well as oxidizing agents. Compartment-targeted rxYFP sensors were able to detect different steady-state redox conditions between the cytosol, nucleus and mitochondrial matrix. Furthermore, rxYFP sensors were able to sense dynamic and compartment-specific redox changes caused by 100µM hydrogen peroxide (H2O2). Mitochondrial matrix-targeted rxYFP displayed a greater dynamics of oxidation in response to a H2O2 challenge than the cytosol- and nucleus-targeted sensors, largely due to a more alkaline local pH environment. Our data provide direct evidence that mitochondrial glutathione redox state is maintained and regulated independently from that of the cytosol and nucleus. Complementary to existing redox sensors and conventional redox measurements, compartment-targeted rxYFP sensors provide a novel tool for examining mammalian cell redox homeostasis, permitting high resolution readout of steady glutathione state and dynamics of redox changes.