Transcellular biosynthesis contributes to the production of leukotrienes during inflammatory responses in vivo - PubMed (original) (raw)

Transcellular biosynthesis contributes to the production of leukotrienes during inflammatory responses in vivo

Jean-Etienne Fabre et al. J Clin Invest. 2002 May.

Abstract

Leukotrienes are lipid mediators that evoke primarily proinflammatory responses by activating receptors present on virtually all cells. The production of leukotrienes is tightly regulated, and expression of 5-lipoxygenase, the enzyme required for the first step in leukotriene synthesis, is generally restricted to leukocytes. Arachidonic acid released from the cell membrane of activated leukocytes is rapidly converted to LTA(4) by 5-lipoxygenase. LTA(4) is further metabolized to either LTC(4) or LTB(4) by the enzyme LTC(4) synthase or LTA(4) hydrolase, respectively. Unlike 5-lipoxygenase, these enzymes are expressed in most tissues. This observation previously has led to the suggestion that LTA(4) produced by leukocytes may, in some cases, be delivered to other cell types before being converted into LTC(4) or LTB(4). While in vitro studies indicate that this process, termed transcellular biosynthesis, can lead to the production of leukotrienes, it has not been possible to determine the significance of this pathway in vivo. Using a series of bone marrow chimeras generated from 5-lipoxygenase- and LTA(4) hydrolase-deficient mice, we show here that transcellular biosynthesis contributes to the production of leukotrienes in vivo and that leukotrienes produced by this pathway are sufficient to contribute significantly to the physiological changes that characterize an ongoing inflammatory response.

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Figures

Figure 1

In vitro LTB4 production by leukocytes stimulated with A23187. Leukocytes were isolated from peritoneal lavage fluid of mice in which acute peritonitis had been induced by injection of zymosan A. The 5-Lo–/– and Lta4-h–/– leukocytes do not produce significant amounts of LTB4 in response to stimulation with A23187. In contrast, similar treatment of a mixture of these two cell populations resulted in a significant increase in LTB4 production. This graph shows data averaged from three separate experiments. *P < 0.01.

Figure 2

Description of the experiments. Chimeric mice are generated by exposing mice to a lethal dose of ionizing radiation with subsequent injection of donor bone marrow. The following chimeras were generated: wild-type mice receiving wild-type marrow (WT→WT), 5-Lo–/– mice receiving wild-type marrow (WT→5-LO), 5-Lo–/– mice receiving 5-Lo–/– marrow (5-LO→5-LO), and 5-Lo–/– mice receiving Lta4-h–/– marrow (LTA4-H→5-LO). The callout illustration shows the expected interaction between neutrophils of donor origin (top) and the cells of recipient origin (bottom) that will lead to LTB4 production. Labels in the illustration refer to the donors and to the recipients, respectively (donor genotype→recipient genotype). WT, wild-type mice; LTA4-H, LTA4-H–deficient mice; 5-LO, 5-LO–deficient mice; AA, arachidonic acid.

Figure 3

Efficiency of bone marrow transplantation. (a) Survival curve obtained after irradiation and reconstitution with marrow from various genotypes. Symbols refer to the donors and to the recipients, respectively (donor genotype→recipient genotype). WT, wild-type mice; LTA4-H, LTA4-H–deficient mice; 5-LO, 5-LO–deficient mice. (b) PCR detection of the Y chromosome in total DNA extracted from blood of female mice transplanted with marrow from male donors. Lane 1 shows expression of the Y chromosome as a 340-bp band detected in blood from a male control. Lane 2 was loaded with DNA from a nontransplanted female. Other lanes were loaded with DNA from transplanted females.

Figure 4

Transcellular biosynthesis in vivo. (a) Zymosan A–induced peritoneal inflammation. LTB4 production was measured in the peritoneal lavage fluid. Loss of 5-LO expression impairs LTB4 production in response to zymosan A stimulation (5-LO→5-LO). In contrast, the presence of leukocytes expressing 5-LO, but unable to produce LTB4 (LTA4-H→5-LO), results in LTB4 production. *P < 0.05. WT, wild-type; 5-LO, 5-LO–deficient mice; LTA4-H, LTA4-H–deficient mice. The transplanted groups are identified as donor→recipient genotypes. Results are presented as numerical values in Table 1. (b) Acute cutaneous inflammatory responses to AA. Mice received Evans blue dye and indomethacin immediately before topical application of AA. At 1 hour after the treatment, the inflamed tissue was biopsied, weighed, and the serum exudate present in the tissue was determined. The white bars represent the difference in optical densities (Δ OD) between the ear treated with AA and the ear treated with vehicle (acetone) alone. The black bars represent the difference in ear-disc weights (Δ ear weight) between the AA-treated ear and the vehicle-treated ear for each mouse. While loss of 5-LO or LTA4-H attenuated the inflammatory response to AA, the response was significantly increased in mice in which the reconstituted immune cells express 5-LO, but are unable to produce LTB4 (LTA4-H→5LO). This graph combines data from two separate experiments. Statistical significance is indicated only for the transplanted groups for clarity. *P < 0.05. WT, wild-type; 5-LO, 5-LO–deficient mice; LTA4-H, LTA4-H–deficient mice. Results are presented as numerical values in Table 1.

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Transcellular biosynthesis contributes to the production of leukotrienes during inflammatory responses in vivo - PubMed (original) (raw)