Sphingosine-1-Phosphate Agonists Increase Macrophage Homing, Lymphocyte Contacts, and Endothelial Junctional Complex Formation in Murine Lymph Nodes

Abstract

The sphingosine-1-phosphate (S1P) receptor agonist, phosphorylated FTY720 (FTY-P), causes lymphopenia, lymphocyte sequestration in mesenteric lymph nodes (MLNs), and immunosuppression. Using multiple techniques to analyze MLN cells harvested from mice treated with S1P receptor agonists, we saw a redistribution of lymphocytes out of nodal sinuses and an expansion of follicles. Although changes in circulating monocytes were not observed with overnight exposure to FTY720, we saw a significant increase in S1P receptor 1 (S1P1)-expressing CD68+ macrophages in subcapsular sinuses of FTY-P-treated MLNs. This was confirmed by quantitative analysis of F4/80+ cells in MLN suspensions. The sinus volume and number of S1P1-positive cells within sinuses were also increased by FTY-P. High endothelial venules and lymphatic endothelium expressed high levels of S1P1, and treatment with FTY-P resulted in intense staining and colocalization of CD31, β-catenin, and zona occludens 1 in junctions between sinus cells. Transmission electron microscopy showed that FTY-P greatly reduced lymphocyte microvilli and increased cell-cell contacts in the parenchyma. Immunoelectron microscopy revealed that intranodal lymphocytes lacked surface expression of S1P1, whereas S1P1 was evident on the surface and within the cytoplasm of macrophages, endothelial cells, and stromal cells. This subcellular pattern of intranodal receptor distribution was unchanged by treatment with FTY-P. We conclude that S1P1 agonists have profound effects on macrophages and endothelial cells, in addition to inducing lymphopenia.

Circulating Monocytes Are Reduced by Sphingosine-1-Phosphate Receptor Modulators Independently of S1P3

“…However, an effect on circulating monocytes has not been reported. Moreover, FTY720 has been shown to increase the number of macrophages in mesenteric lymph nodes, suggesting that S1P receptors may be important for monocyte egress from lymph nodes in a manner similar to lymphocytes (20). However, it is not clear whether this is a direct or indirect effect on either the numbers or trafficking of circulating monocytes.…”

Sphingosine-1-Phosphate Metabolism and Intestinal Tumorigenesis: Lipid Signaling Strikes Again

“…In fact, interactions between S1P, SK and various catenin family members have been described. [79][80][81][82][83] A recent study demonstrated that Sphk1, the major enzyme necessary for synthesizing S1P, is required for enlargement of Min mouse adenomas, since Min mice that do not express this enzyme develop only small adenomas, in contrast to the significant number of large adenomas that developed in Min mice with intact Sphk1 expression. 84 Importantly, both S1P and sphingosine levels were high in Min mouse polyps compared to normal adjacent tissues, indicating that sphingolipid metabolism is abnormal in the neoplastic tissue.…”

Sphingosine-1–Phosphate, FTY720, and Sphingosine-1–Phosphate Receptors in the Pathobiology of Acute Lung Injury

“…Further, in a recent multiple sclerosis clinical trial, FTY720 increased rates of dyspnea and decreased lung function (lowered forced expiratory volume in 1 second) (88), perhaps mediated through mechanisms similar to those seen in the S1P-induced contraction of bronchial smooth muscle in mice (67). Importantly, FTY720-P induced the ubiquitination and proteasomal degradation of S1P 1 in cultured ECs (84) and HEK293 cells (89). Prolonged exposure to FTY720 resulted in the down-regulation of the EC surface expression of S1P 1 and decreased responses to S1P (90).…”

“…However, although FTY720 increased the expression of protein phosphatase 2A, it did not alter FTY720-induced barrier enhancement (83). FTY720 also up-regulated the expression of EC junctional proteins b-catenin and zonula occludens protein 1 (ZO-1) (71), and it promoted adherens junction assembly (84). However, ECs treated with specific siRNAs against claudin-5 or ZO-1/ZO-2 did not alter FTY720-induced barrier enhancement, suggesting that adherens junction or tight junction proteins are not involved in FTY720-induced barrier enhancement (83).…”