Dysregulated dopamine (DA) signaling and redox homeostasis contributes to multiple neuropsychiatric and neurodegenerative disorders. Polymorphisms that influence the activity of catechol-O-methyltransferase (COMT), an enzyme critical for degrading DA in the dorsolateral prefrontal cortex, have been implicated in behavioral and neuropsychiatric alterations associated with schizophrenia (SCZ). Adverse neuropsychiatric effects have also been reported in Parkinson's disease (PD) patients administered COMT inhibitors in combination with other DA-enhancing therapies. COMT exists as two isoforms: a soluble short isoform (S-COMT) and a membrane-bound long isoform (MB-COMT). These variants differ in their N-terminal domains, with MB-COMT being the predominant brain isoform. Here, unbiased proteomic and biochemical analyses show that genetic loss of MB-COMT disrupts DA signaling and perturbs pathways governing synaptic and mitochondrial function, iron and copper homeostasis, and redox balance. Limited proteolysis mass spectrometry (LiP-MS) further revealed that MB-COMT deficiency triggers widespread protein structural alterations, a molecular event commonly occurring in neurodegenerative conditions but not as well studied in neuropsychiatric diseases. Our results show that MB-COMT is a molecular hub that connects multiple cellular pathways whose differential dysregulation underlies the pathophysiology of complex neuropsychiatric diseases such as SCZ. Thus, MB-COMT is identified as a key regulator of brain DA biology, loss of which activates cellular stress response pathways, revealing potential targets for therapeutic intervention.
S. Tripathi, Suwarna Chakraborty, Neil B. Wood et al.· Proceedings of the National...· 0 citations
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.
Mohammad Sajid Ghufran, Priyanka Soni, Bobby Thomas· Redox Biology· 0 citations
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