We discovered a new 16.5 kDa molecular (lipophilin) that is a prominent component of normal human tears. Lipophilin molecules are heterodimers whole subunits are linked covalently by 3 intramolecular cystine disulfide bonds. Our preliminary sequences and structure data suggest that lipophilin is homologous to prostatein, a steroid-binding protein secrete by the rate prostate gland. The larger subunit of lipophilin also shows strong homology to certain other steroid-binding and PLA2-inhibitory proteins (mammaglobin, uteroglobin and human CC-10) that are secreted by mammary, uterine, and lung epithelial cells. We have assembled an experienced, multi-disciplinary group of co-investigators to determine the structural and functional properties of lipophilin. Both a consideration of its homologues and the considerable concentration of lipophilin in tears suggest that I may play a crucial role with respect to the nutritional lubricating and anti-inflammatory needs of the cornea and conjunctiva.
The Specific Aims are: 1) To determine the complete amino acid sequences of both lipophilin components; define how their cysteines pair, and if the heterodimers associate non0covalently into tetramers. 2) To clone each lipophilin component from a lacrimal gland cDNA library; determine if any non-ocular tissues express lipophilin-related peptides; and identify the chromosomal locations of the genes for both lipophilin components. 3) To identify sites of lipophilin storage in the lacrimal gland and other tissues by immunohistochemistry. 4) To establish an ELISA assay for lipophilin and measure its concentration in the tears of normal men and women. 5) To examine the ability of human tear lipophilin to bind biologically significant lipids, including retinoids, selected steroid hormones and phospholipids; to identify endogenous lipids and to examine its ability to inhibit the Type II secretory phospholipase A2 found in normal human tears. The long-term objectives for this research are to learn how lipophilin contributes to corneal and conjuctival health, and to explore its potential for creating new diagnostic and therapeutic modalities.
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