Effects of mouse and human lipocalin homologues 24p3/lcn2 and neutrophil gelatinase-associated lipocalin on gastrointestinal mucosal integrity and repair.

BACKGROUND & AIMS: The lipocalin superfamily, including the mouse and human homologues 24p3/lcn2 and neutrophil gelatinase-associated lipocalin, show great functional diversity including roles in olfaction, transportation, and prostaglandin synthesis in mammals. Their potential role in maintaining gastrointestinal mucosal integrity and repair is, however, unclear. METHODS: Changes in 24p3/lcn2 expression in the mouse gut in response to various noxious agents were examined using Northern blot, in situ hybridization, and immunohistochemistry. Effects of recombinant 24p3/lcn2 on proliferation ([3H]-thymidine uptake), and restitution (cell-wounding migration) were assessed using human colonic HT29 and HCT116 cells. In addition, the effects of recombinant 24p3/lcn2 on the amount of gastric damage were assessed in rats treated with indomethacin (20 mg/kg) and restraint. RESULTS: Marked up-regulation of expression of 24p3/lcn2 was seen throughout the gut in response to indomethacin or dextran sodium sulfate treatment. Expression was increased particularly in the surface epithelial cells and infiltrating inflammatory cells. Proliferation and restitution assays in the presence of recombinant wild-type sequence neutrophil gelatinase-associated lipocalin, wild-type cys(98)-24p3/lcn2, and mutant ala98-24p3/lcn2 showed that all 3 peptides caused a 3- to 4-fold increase in promigratory activity (P < .01 vs control) but did not influence proliferation. The administration of wild-type cys98-, or mutant ala98-24p3/lcn2 (25 and 50 microg/kg/h, respectively), given via the subcutaneous route, both caused similar reductions in the rat gastric damage model (60% reduction at highest dose, P < .01 vs control), although oral administration was ineffective. CONCLUSIONS: 24p3/lcn2 facilitates mucosal regeneration by promoting cell migration.

Tissue involution and the acute phase response.

After their roles in reproduction are completed, the mass of the uterus and the mammary gland decrease rapidly by the process of involution that involves an ordered series of events including apoptosis, neutrophil entry, the release of degradative enzymes, and phagocytosis of cellular debris. The acute phase proteins are produced by the liver and other tissues in response to inflammation or a toxic challenge. Uterocalin (SIP24/24p3) is one of these proteins. During involution, the mammary gland and uterus express high levels of uterocalin that reach an average of 0.2-0.5% of the total extractable protein at its peak. Uterocalin and its orthologues have been demonstrated in vitro to (1). bind certain fatty acids and (2). specifically induce apoptosis in neutrophils and other leukocytes. The period of uterocalin expression during involution is consistent with the hypothesis that one of its physiological roles is to induce apoptosis of invading neutrophils and delay the entry of neutrophils into the tissue until the second phase of involution. Interestingly, it has been shown that uterocalin expression remains higher in primiparous gland than in virgin glands after the pregnant glands have completely involuted. This observation and the known protective effect of early pregnancy on later development of breast cancer suggest that the ability of uterocalin to induce apoptosis in neutrophils might also decrease oxidative and carcinogenic activity in the gland and result in a lower mutation rate and thus a lower probability of cancer in the primiparous gland.

High expression in involuting reproductive tissues of uterocalin/24p3, a lipocalin and acute phase protein.

During reproduction the mass and number of cells in the uterus and the mammary gland increase rapidly and then diminish more rapidly after their reproductive functions are completed. The diminishment of tissue mass, known as involution, involves an ordered series of events that includes apoptosis of resident cells, neutrophil invasion, the release of degradative enzymes and phagocytosis of cellular debris. Local signals are believed to regulate the progression of involution in each tissue. Here we show that the mammary gland and uterus express high levels of uterocalin, a protein that specifically induces apoptosis in neutrophils and other leucocytes. In the mammary gland, uterocalin expression is induced by weaning. In both tissues, uterocalin is expressed at extremely high levels such that it constitutes an average of 0.2-0.5% of the total extractable protein at its peak. Epithelial cells in the uterus and mammary gland produce uterocalin. In each case, the protein is secreted into the tissue lumen, with mammary-derived uterocalin being found in the milk. The period of highest uterocalin expression in vivo is consistent with the hypothesis that one of its physiological roles is to induce apoptosis of infiltrating neutrophils and thereby delay the entry of neutrophils into the tissue. It is proposed that the role of uterocalin during involution is to provide a window of time during which resident cells are protected from the degradative enzymes, free radicals and other secreted products of activated phagocytes to allow these cells to prepare to survive the processes of involution.