HIV-1 gp120-induced lysosomal stress responses are controlled by TRPML1 redox sensors.

BACKGROUND

Increased lysosomal stress responses (LSR) are commonly implicated in the pathogenesis of neurodegenerative disorders including HIV-1-associated neurocognitive disorders (HAND). The HIV-1 envelope glycoprotein gp120 causes LSR, increases levels of ferrous iron (Fe2+) in the cytosol and in mitochondria, disrupts the reactive species interactome (RSI), and increases neural cell death.

METHODS

Using SH-SY5Y human neuroblastoma and U87MG human astrocytoma cells treated with gp120 and pharmacological modulators, we evaluated redox signaling and LSR by redox-sensitive fluorescent probes, spinning-disk confocal microscopy, flow cytometry, Western blotting, and immunostaining.

RESULTS

Here, we report that TRPML1, an endolysosome redox-sensitive cation channel, is mechanistically involved in gp120-induced neurotoxicity. TRPML1 was activated by gp120-induced increases in cytosolic reactive oxygen species (ROS) and resulted in release of Fe2+ from endolysosomes in levels sufficient to increase cytosolic levels of Fe2+ and ROS as well as decrease levels of hydrogen sulfide (H2S). Reduced glutathione normally buffers intracellular Fe2+, but gp120 decreased endolysosome glutathione levels and disrupted this regulatory control mechanism thereby promoting TRPML1-mediated Fe2+ efflux from endolysosomes. TRPML1 redox activation led to changes to the RSI in endolysosomes including increased ROS, lipid peroxidation, nitric oxide, and sulfane sulfur as well as decreased H2S. These changes were accompanied by increased cysteine oxidation of luminal proteins and endolysosome deacidification. Pharmacological inhibition of TRPML1 or knocking down expression levels of TRPML prevented these effects.

CONCLUSION

Our findings suggest that TRPML1 redox activation controls gp120-induced endolysosome dysfunction and iron/redox imbalance, and further implicates TRPML1 in the pathogenesis of HAND.