{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n Apolipoprotein O (APOO) is a multifunctional protein that exists in distinct forms and displays both intracellular and secreted roles. A mitochondrial isoform of APOO, originally identified as MIC26, is integrated into the inner membrane as a bona fide subunit of the mitochondrial contact site and cristae organizing system (MICOS) complex. This isoform is key to maintaining crista junction formation, proper mitochondrial membrane architecture, and cardiolipin metabolism; its dysregulation leads to mitochondrial fragmentation, impaired respiration, and increased reactive oxygen species production."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n In parallel, circulating forms of APOO have been implicated in cardiovascular pathology. For instance, elevated APOO levels have been reported in acute coronary syndrome, where plasma APOO acts as an independent inflammatory predictor."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "2"}]}, {"type": "t", "text": " Moreover, cardiac-specific studies indicate that overexpression of APOO in the heart can promote mitochondrial uncoupling and enhance fatty acid metabolism, thereby triggering increased reactive oxygen species production, lipoapoptosis, and ultimately contributing to cardiomyopathy in diabetic conditions."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "3"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Additional work in hepatic systems reveals that APOO overexpression perturbs lipid metabolism by altering the expression of key lipid regulatory genes, disrupting mitochondrial ultrastructure and membrane potential, and thereby linking APOO function to non‐alcoholic fatty liver disease progression."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": " Complementary experiments in liver-derived cells have further shown that modulation of APOO expression influences genes involved in fatty acid metabolism and inflammation, suggesting that APOO may act as a mediator between lipid handling and inflammatory responses."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n In addition to its metabolic functions, APOO has also emerged as a candidate gene in studies of neuropsychiatric outcomes, being associated with an increased risk of suicidal ideation during antidepressant treatment; however, the mechanistic underpinnings of this association remain to be fully elucidated."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "6"}]}, {"type": "t", "text": " Finally, molecular cloning and characterization studies have facilitated the generation of recombinant fusion proteins, providing essential tools to further dissect the protein’s structure–function relationships"}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}]}, {"type": "t", "text": ", while regulatory studies indicate that APOO expression may be modulated by microRNAs in pathological contexts such as alcoholic fatty liver."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "8"}]}, {"type": "t", "text": "\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Sebastian Koob, Miguel Barrera, Ruchika Anand, et al. 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