Structural insights on ligand recognition at the human leukotriene B4 receptor 1

The leukotriene B4 receptor 1 (BLT1) regulates the recruitment and chemotaxis of different cell types and plays a role in the pathophysiology of infectious, allergic, metabolic, and tumorigenic human diseases. Here we present a crystal structure of human BLT1 (hBLT1) in complex with a selective antagonist MK-D-046, developed for the treatment of type 2 diabetes and other inflammatory conditions. Comprehensive analysis of the structure and structure-activity relationship data, reinforced by site-directed mutagenesis and docking studies, reveals molecular determinants of ligand binding and selectivity toward different BLT receptor subtypes and across species. The structure helps to identify a putative membrane-buried ligand access channel as well as potential receptor binding modes of endogenous agonists. These structural insights of hBLT1 enrich our understanding of its ligand recognition and open up future avenues in structure-based drug design.

Expression of leukotriene B4 receptor 1 defines functionally distinct DCs that control allergic skin inflammation

Leukotriene B4 (LTB4) receptor 1 (BLT1) is a chemotactic G protein-coupled receptor expressed by leukocytes, such as granulocytes, macrophages, and activated T cells. Although there is growing evidence that BLT1 plays crucial roles in immune responses, its role in dendritic cells remains largely unknown. Here, we identified novel DC subsets defined by the expression of BLT1, namely, BLT1hi and BLT1lo DCs. We also found that BLT1hi and BLT1lo DCs differentially migrated toward LTB4 and CCL21, a lymph node-homing chemoattractant, respectively. By generating LTB4-producing enzyme LTA4H knockout mice and CD11c promoter-driven Cre recombinase-expressing BLT1 conditional knockout (BLT1 cKO) mice, we showed that the migration of BLT1hi DCs exacerbated allergic contact dermatitis. Comprehensive transcriptome analysis revealed that BLT1hi DCs preferentially induced Th1 differentiation by upregulating IL-12p35 expression, whereas BLT1lo DCs accelerated T cell proliferation by producing IL-2. Collectively, the data reveal an unexpected role for BLT1 as a novel DC subset marker and provide novel insights into the role of the LTB4-BLT1 axis in the spatiotemporal regulation of distinct DC subsets.

Chemoreactome analysis of 7-hydroxymatairesinol, 17-estradiol, phytoestrogen β-sitosterol and epigallocatechin-3-gallate

The results of the evaluation of 7-hydroximatairesinol (7-HMR) properties in comparison with control molecules (17-estradiol, phytoestrogen β-sytostirol, epigallocatechin-3-gallate) are presented. The results of chemoreactomic modeling allowed to formulate the molecular mechanisms of 7-HMR pharmacological effects for anti-inflammatory (inhibition of 5-lipoxygenase, matrix metalloproteinase MMR2, mitogen-activated kinase p38-alpha, leukotriene-b4 receptor, prostacyclin receptor), antitumor (antioxidant effect due to inhibition of hemoxygenase-2, inhibition of cyclin dependent kinases 3 and 4, epidermis growth factor, protein mTOR), vasodilator (inhibition of adrenoreceptors and renin), antibacterial and antiviral (inhibition of viral proteases 3C) properties of 7-HMR molecule.

Expression of the leukotriene B4 receptor, LTB4R, is perturbed in the blood of patients with Crohn’s Disease.

first-line treatment which includes the 5-aminosalicylate drug mesalamine and steroids (2, 3). Both of these drugs are thought to have physiologically pleiotropic functions but it is still not understood how these drugs exert their therapeutic function in CD (4,5). Deciphering their mechanism of action can be facilitated by a basic understanding of the relevant therapeutic targets in patients with Crohn’s Disease, and can assist in determining which patients will benefit from first-line treatment with mesalamine versus top-down treatment with biologics (6) which are more beneficial but also more costly and associated with an increased risk of development of non-Hodgkin’s and hepatosplenic T-cell lymphomas (7, 8, 9). Transcriptome analysis to understand how gene expression differs in the tissues of patients with Crohn’s Disease can facilitate this understanding. We found, using two published datasets (10, 11), that the leukotriene B4 receptor, LTB4R (12, 13), was among the genes whose expression was most different when comparing blood from patients with Crohn’s Disease with blood from healthy, non-affected subjects. Interestingly, while LTB4R was also a differentially expressed gene in CD4+ CD25+ regulatory T-cells from patients with Crohn’s Disease, in Treg it was expressed at significantly lower levels compared to non-affected subjects as opposed to whole blood where it was expressed at significantly higher levels. This is the first report documenting differential expression of LTB4R in the hematopoietic tissues of patients with Crohn’s Disease.