CD40 Enhances Sphingolipids in Orbital Fibroblasts: Potential Role of Sphingosine-1-Phosphate in Inflammatory T-Cell Migration in Graves' Orbitopathy

Abstract

PURPOSE. Graves' orbitopathy (GO) is an autoimmune orbital disorder associated with Graves' disease caused by thyrotropin receptor autoantibodies. Orbital fibroblasts (OFs) and CD40 play a key role in disease pathogenesis. The bioactive lipid sphingosine-1-phosphate (S1P) has been implicated in promoting adipogenesis, fibrosis, and inflammation in OFs. We investigated the role of CD40 signaling in inducing S1P activity in orbital inflammation. METHODS. OFs and T cells were derived from GO patients and healthy control (Ctl) persons. S1P abundance in orbital tissues was evaluated by immunofluorescence. OFs were stimulated with CD40 ligand and S1P levels were determined by ELISA. Further, activities of acid sphingomyelinase (ASM), acid ceramidase, and sphingosine kinase were measured by ultraperformance liquid chromatography. Sphingosine and ceramide contents were analyzed by mass spectrometry. Finally, the role for S1P in T-cell attraction was investigated by T-cell migration assays. RESULTS. GO orbital tissue showed elevated amounts of S1P as compared to control samples. Stimulation of CD40 induced S1P expression in GO-derived OFs, while Ctl-OFs remained unaffected. A significant increase of ASM and sphingosine kinase activities, as well as lipid formation, was observed in GO-derived OFs. Migration assay of T cells in the presence of SphK inhibitor revealed that S1P released by GO-OFs attracted T cells for migration. CONCLUSIONS. The results demonstrated that CD40 ligand stimulates GO fibroblast to produce S1P, which is a driving force for T-cell migration. The results support the use of S1P receptor signaling modulators in GO management.

Elusive Roles of the Different Ceramidases in Human Health, Pathophysiology, and Tissue Regeneration

“…Ceramidases are expressed in epithelial cells and fibroblasts and may be involved in their response through S1P [ 12 , 103 , 113 ]. However, only a limited number of studies have demonstrated the effects of these enzymes in tissue regeneration and healing.…”

Lessons from mouse models of Graves’ disease

“…Besides the proliferative stimulation of the orbital fibroblasts, inflammatory cytokines are released which act to recruit additional immune and inflammatory cells to the orbit [11,12]. The CD40 expression of orbital fibroblasts allows direct interaction with infiltrating T cells with potential additional cytokine release [13]. Since the inflammatory/proliferative processes take place in a bony limited space-the orbit-tissue hypoxia contributes to the pathogenic mechanisms depending on the grade of compression which is caused by the tissue volume changes [14].…”

“…Another recent in vitro study suggested that sphingosine-1-phosphate (S1P) signaling is involved in orbitopathy [13]. In a follow-up study the immune modulatory potential of S1P receptor antagonist fingolimod (FTY720) was explored in a murine model for Graves' disease [33].…”

Update endokrine Orbitopathie

“…Neben der proliferativen Stimulation der Orbitafibroblasten wird auch eine ganze Reihe von inflammatorischen Zytokinen freigesetzt, die zur Infiltration von Immunzellen in die Orbita führen [9,10]. Die CD40-Expression von Orbitafibroblasten erlaubt eine direkte Interaktion mit den infiltrierenden T-Zellen, was die Potenzierung der Zytokin-Freisetzung zur Folge hat [11]. Da sich die entzündliche Gewebevermehrung bei der endokrinen Orbitopathie in einem knöchern begrenzten Raumder Orbitaabspielt, trägt auch eine Gewebehypoxie je nach Ausprägung des Kompressionseffekts zum Entzündungsgeschehen bei [12].…”