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

Abstract

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.