{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n Cytochrome P450 2U1 (CYP2U1) is an atypical, evolutionarily conserved enzyme that is predominantly expressed in extrahepatic tissues, especially in the brain and thymus."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}]}, {"type": "t", "text": " It catalyzes the regioselective ω- and ω–1 hydroxylation of long‐chain fatty acids such as arachidonic acid, converting it into bioactive metabolites (notably the 19‐ and 20‐hydroxyeicosatetraenoic acids), and is also capable of oxidizing related substrates including docosahexaenoic acid and N‐arachidonoylserotonin."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "2"}, {"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": " Through these reactions, CYP2U1 is implicated in modulating lipid signaling pathways that play roles in neuronal function and cellular homeostasis.\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Beyond its involvement in endogenous fatty acid metabolism, altered CYP2U1 activity has been associated with a spectrum of neurodegenerative phenotypes. Genetic mutations in CYP2U1 underlie spastic paraplegia type 56 (SPG56), a disorder characterized by progressive lower limb spasticity and a range of complex clinical features including pigmentary degenerative maculopathy and, in some cases, cognitive and motor regression."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "6", "end_ref": "10"}]}, {"type": "t", "text": " Functional studies of missense variants have demonstrated that loss of enzymatic activity—stemming from disrupted heme binding or protein destabilization—is central to the disease mechanism."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}, {"type": "fg_f", "ref": "11"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Moreover, CYP2U1 expression appears to be subject to regulatory influences and environmental modulation. Its mRNA levels can be affected by oxidative stress pathways—for instance, Nrf2 activation reduces CYP2U1 expression"}, {"type": "fg", "children": [{"type": "fg_f", "ref": "12"}]}, {"type": "t", "text": "—and its expression in brain regions such as the prefrontal cortex and amygdala is modulated by alcohol and tobacco exposure."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "13"}]}, {"type": "t", "text": " Additionally, cell signaling events, including those induced by glutamate, further regulate CYP2U1 expression and may alter the local production of hydroxylated arachidonic acid derivatives, thereby linking neuronal activity to lipid mediator synthesis."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "14"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Structural investigations reveal that CYP2U1 possesses unique extended regions in its amino‐terminal domain, which may facilitate its distinctive substrate interactions and membrane associations, ultimately influencing substrate recruitment and metabolic regioselectivity."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "15"}, {"type": "fg_f", "ref": "11"}]}, {"type": "t", "text": " Finally, studies in non‐human species, such as in the red-crowned crane, have begun to elucidate its broader physiological roles in xenobiotic and endogenous lipid metabolism across taxa."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "16"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n In summary, CYP2U1 is emerging as a critical enzyme at the interface of fatty acid signaling and neural function. Its ability to generate specific hydroxylated lipid mediators positions it as an important regulator of neurophysiology, while loss‐of‐function mutations contribute to neurodegenerative disorders such as SPG56. The enzyme also shows responsiveness to environmental and cellular signals, underlining its potential significance in both health and disease."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}, {"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": "\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Ramzi Shawahna, Yasuo Uchida, Xavier Declèves, et al. 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