{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n Tear lipocalin (LCN1) is a multifunctional, highly abundant protein in the tear film that plays a critical role in maintaining ocular surface homeostasis. Its large and flexible ligand‐binding pocket enables LCN1 to function as a “master lipid sponge” by selectively binding and sequestering a variety of hydrophobic molecules—including lipids (such as ceramides), vitamins, and steroid hormones—to prevent excess or aberrant lipids from disrupting epithelial wetting and tear film stability."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}]}, {"type": "t", "text": " Structural studies further reveal that pH‐dependent conformational changes in key loop regions of LCN1 facilitate dynamic ligand accommodation and release, underscoring its versatility as a lipid carrier."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}, {"type": "fg_f", "ref": "2"}, {"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": " In addition to its binding functions, LCN1 exhibits extracellular endonuclease activity that helps to degrade extracellular DNA—thereby reducing pro‐inflammatory triggers in the tear film."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "6"}]}, {"type": "t", "text": " Its interactions with the lipocalin‐1–interacting membrane receptor (LIMR) further suggest a role in mediating cellular uptake and turnover of the protein, contributing to the dynamic regulation of the tear film."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}]}, {"type": "t", "text": " Altered LCN1 expression and deposition have been associated with ocular surface disorders such as dry eye syndrome and keratitis, and its levels on contact lenses vary with material type—highlighting its potential utility as a diagnostic biomarker."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "9"}]}, {"type": "t", "text": " Moreover, the detection of LCN1 in non‐exocrine tissues (for example, in human pituitary corticotrophs) suggests that its functions may extend beyond the ocular surface into broader roles in cellular homeostasis and immune regulation."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "11"}]}, {"type": "t", "text": " Collectively, these studies emphasize the importance of LCN1 as a versatile lipid‐binding, regulatory, and protective protein that is central to tear film integrity and ocular surface defense.\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Roy Karnati, Diane E Laurie, Gordon W Laurie "}, {"type": "b", "children": [{"type": "t", "text": "Lacritin and the tear proteome as natural replacement therapy for dry eye."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Exp Eye Res (2013)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1016/j.exer.2013.05.020"}], "href": "https://doi.org/10.1016/j.exer.2013.05.020"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "23769845"}], "href": "https://pubmed.ncbi.nlm.nih.gov/23769845"}]}, {"type": "r", "ref": 2, "children": [{"type": "t", "text": "Oktay K Gasymov, Adil R Abduragimov, Taleh N Yusifov, et al. 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