TLDc proteins: Stress-responsive nexus regulators of redox signaling, V-ATPase dynamics, and organellar crosstalk in neurodegeneration

Abstract

Many age-related neurodegenerative disorders are marked by progressive defects in cellular energy metabolism and protein homeostasis that converge on mitochondrial and lysosomal dysfunction. TLDc domain-containing proteins, such as OXR1, NCOA7, and related family members, have emerged as crucial modulators of organellar physiology and cellular stress responses. Growing evidence indicates that TLDc proteins physically interact with vacuolar ATPases (V-ATPases) to modulate their assembly and catalytic activity, linking TLDc function directly to the maintenance of lysosomal and Golgi lumen pH. This organellar pH homeostasis, in turn, is fundamental to intracellular iron handling and metabolic regulation, processes essential for mitochondrial bioenergetics, lysosomal functions, and cellular viability. Lysosomes maintain an acidic lumen via V-ATPase proton pumping, counterbalanced by specific ion channels, including TMEM175. This acidic environment is required for ferric iron reduction and subsequent release into the cytosol; when acidification fails, cells develop cytosolic iron deficiency, mitochondrial defects, pseudohypoxia via HIF-1α activation, and inflammation. Conversely, iron flux from lysosomes to mitochondria depends on acidic conditions and direct organelle contact, as exemplified by BDH2-driven siderophore transport, a V-ATPase-dependent but not TLDc-regulated process, which supports mitochondrial bioenergetics and sustains lysosomal acidity. Iron and pH dysregulation synergize to drive ferroptosis, lipid peroxidation, and neurotoxicity. Emerging studies link lysosomal deacidification and iron dyshomeostasis to the pathogenesis of major neurodegenerative diseases. These mechanisms collectively shape neuronal resilience, survival, and aging trajectories. This review integrates recent insights into how TLDc proteins coordinate organellar pH regulation and iron homeostasis and discusses how disruption of these interconnected pathways contributes to age-related neurodegeneration.