Transcellular biosynthesis of cysteinyl leukotrienes in vivo during mouse peritoneal inflammation

Abstract

Leukotrienes (LTs) are lipid mediators of inflammation formed by enzymatic oxidation of arachidonic acid. One intriguing aspect of LT production is transcellular biosynthesis: cells expressing 5-lipoxygenase (5LO) form LTA4 and transfer it to cells expressing LTA4 hydrolase (LTA4H) or LTC4 synthase (LTC4S) to produce LTB4 or LTC4. This process has been demonstrated in vivo for LTB4, but not for cysteinyl LTs (cysLTs). We examined transcellular cysLT synthesis during zymosan-induced peritonitis, using bone marrow transplants with transgenic mice deficient in key enzymes of LT synthesis and analyzing all eicosanoids by liquid chromatography/ tandem mass spectrometry. WT mice time-dependently produced LTB4 and cysLTs (LTC4, LTD4, and LTE4). 5LO ؊/؊ mice were incapable of producing LTs. WT bone marrow cells restored this biosynthetic ability, but 5LO ؊/؊ bone marrow did not rescue LT synthesis in irradiated WT mice, demonstrating that bone marrow-derived cells are the ultimate source of all LTs in this model. Total levels of 5LO-derived products were comparable in LTA4H ؊/؊ and WT mice, but were reduced in LTC4S ؊/؊ animals. No differences in prostaglandin production were observed between these transgenic or chimeric mice. Bone marrow cells from LTA 4H ؊/؊ or LTC4S ؊/؊ mice injected into 5LO ؊/؊ mice restored the ability to synthesize LTB4 and cysLTs, providing unequivocal evidence of efficient transcellular biosynthesis of cysLTs. These results highlight the potential relevance of transcellular exchange of LTA 4 for the synthesis of LTs mediating biological activities during inflammatory events in vivo. chimeric mice ͉ leukotriene B4 ͉ mass spectrometry ͉ leukotriene E4 ͉ 5-lipoxygenase

Regulation and Function of Epithelial Secreted Phospholipase A2 Group X in Asthma

“…The epithelium is often overlooked as a regulator of eicosanoids, because the terminal synthetic enzymes for the major eicosanoids implicated in asthma are predominantly expressed in leukocytes; however, structural cells serve as an important source of AA via transcellular metabolism (51). We found that sPLA 2 -X serves as a key regulator of AA release in mTECs and that the PLa2g10 knockout had a larger effect on AA release than inhibition of cPLA 2 a, which is generally believed to be the dominant regulator of AA release in epithelial cells (52).…”

Placenta Growth Factor-induced Early Growth Response 1 (Egr-1) Regulates Hypoxia-inducible Factor-1α (HIF-1α) in Endothelial Cells

“…However, they express LTA 4 hydrolase and LTC 4 synthetase enzymes, which can generate LTB 4 and LTC 4 , respectively, from exogenous LTA 4 . In addition, other studies have identified the transcellular mode of cysteinyl-LT biosynthesis (8,52) by uptake of LTA 4 , which is secreted from neighboring activated peripheral blood leukocytes after their adhesion to vascular endothelium (53). Consequently, a direct role of endothelial cells as an independent source of LT has not been widely accepted.…”

Identification of GPR99 Protein as a Potential Third Cysteinyl Leukotriene Receptor with a Preference for Leukotriene E4 Ligand

“…LTE 4 , the most abundant cys-LT at sites of inflammation due to its stability (7,8), was only a weak agonist for the CysLT 1 R and CysLT 2 R in studies with transfectants (3, 4), suggesting that it might lack agonist activity. In contrast, pretreatment with LTE 4 , but not LTC 4 or LTD 4 , enhanced the response of guinea pig trachea (9) or human bronchial smooth muscle to histamine (10).…”

“…The type 1 cys-LT receptor (CysLT 1 R) is the high affinity receptor for LTD 4 , whereas the type 2 receptor (CysLT 2 R) can bind both LTC 4 and LTD 4 with one-log less affinity than that of CysLT 1 R for LTD 4 in transfected cells (3, 4). The cys-LTs are mediators of bronchial asthma on the basis of their potent bronchoconstrictive activity via the CysLT 1 R in pharmacologic studies and the clinical effectiveness of CysLT 1 R antagonists (5, 6).LTE 4 , the most abundant cys-LT at sites of inflammation due to its stability (7,8), was only a weak agonist for the CysLT 1 R and CysLT 2 R in studies with transfectants (3, 4), suggesting that it might lack agonist activity. In contrast, pretreatment with LTE 4 , but not LTC 4 or LTD 4 , enhanced the response of guinea pig trachea (9) or human bronchial smooth muscle to histamine (10).…”