BRIEF REPORT |
Correspondence to: Bernhard Redl, Institut für Molekularbiologie, Universität Innsbruck, Fritz Pregl Str. 3, A-6020 Innsbruck, Austria. E-mail: bernhard.redl@uibk.ac.at
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Summary |
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Lipocalin-1 (Lcn-1), a member of the lipocalin superfamily that binds a broad array of different chemical classes of lipophilic ligands, is believed to act as a physiological scavenger of potentially harmful lipophilic molecules. Thus far, it was thought to be produced exclusively by a number of exocrine glands and tissues, including lachrymal and lingual glands, prostate, secretory glands of the tracheobronchial tract, and sweat glands. Using Northern blotting analysis, we were able to demonstrate Lcn-1 expression by the human pituitary gland. Moreover, double immunolabeling with antibodies against Lcn-1 and pituitary gland hormones and detection with fluorophore-conjugated secondary antibodies revealed that Lcn-1 is specifically produced by corticotrophs, clearly indicating that its distribution is not restricted to exocrine tissues. (J Histochem Cytochem 50:433435, 2002)
Key Words: lipocalin, pituitary gland, immunohistochemistry, adenohypophysis, corticotrophs
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Introduction |
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LIPOCALINS are members of an expanding superfamily of typically small secretory proteins characterized by their ability to bind hydrophobic ligands and their common structure, consisting of a single eight-stranded antiparallel ß-sheet, which forms a hydrogen-bonded ß-barrel enclosing an internal ligand binding site (
Human Lcn-1 (also called tear lipocalin or von Ebner's gland protein) is known to bind an unusual large variety of lipophilic molecules of different chemical classes, including fatty acids, fatty alcohols, phospholipids, glycolipids, and cholesterol, retinol, and lipid peroxidation products such as isoprostanes, arachidonic acid and metabolites of arachidonic acid (
This study presents the first evidence that Lcn-1 is also produced by endocrine organs, because we were able to localize Lcn-1-producing cells in human pituitary gland, which were further identified as corticotrophs.
In a first step we examined expression of Lcn-1 by Northern blotting analysis using an Lcn-1-specific cDNA probe (
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Samples for immunohistochemical analysis were obtained from autopsies of two male donors and one female donor aged 65, 71, and 74 years, respectively, all of whom died of cardiac failure. Preliminary immunohistochemical investigations on sections (4 µm) of formalin-fixed and paraffin-embedded human pituitary glands, using an Lcn-1-specific antiserum, indicated production of Lcn-1 in the anterior lobe (adenohypophysis) of the glands (data not shown). In a next step, double labeling immunohistochemical experiments were performed to identify the exact localization of Lcn-1 within the specific cell populations of the anterior pituitary gland. For this purpose, cryostat sections (20 µm) of paraformaldehyde (4% in PBS)-fixed tissues were rinsed in 50 mM Tris-HCl-buffered saline, pH 7.2 (TBS), 0,4% Triton X-100. After incubation with 10% normal horse serum (Dakopatts; Copenhagen, Denmark), the free-floating sections were incubated with a polyclonal primary rabbit anti-Lcn-1 (
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Expression of a lipid scavenger, such as Lcn-1, by cells of the pituitary gland is novel but not fully unexpected, because potential ligands of Lcn-1 are known to induce various effects in the pituitary gland, such as the modulation of hormone secretion and the activation or inhibition of ion channels (
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Acknowledgments |
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Supported by the Austrian Science Fund (FWF) grant P12628 (to BR) and P13652 (to PB).
We would like to thank F. Marx for helpful discussions on preparing the manuscript, and G. Sperk and A. Wieselthaler for technical advice.
Received for publication July 23, 2001; accepted October 31, 2001.
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