Slit2 Modulates the Inflammatory Phenotype of Orbit-Infiltrating Fibrocytes in Graves’ Disease

Abstract

Human CD34 fibrocytes, circulating monocyte lineage progenitor cells, have recently been implicated in thyroid-associated ophthalmopathy (TAO), the ocular manifestation of Graves' disease (GD). Fibrocytes express constitutive MHC class II (MHC-2) and, surprisingly, thyroglobulin (Tg) and functional thyrotropin (TSH) receptor (TSHR). Underlying expression of these thyroid proteins is the autoimmune regulator protein (AIRE). Fibrocytes respond robustly to TSH and thyroid-stimulating Igs by generating extremely high levels of inflammatory cytokines, such as IL-6. In TAO, they appear to infiltrate the orbit, where they transition to CD34 orbital fibroblasts (OF). There, they coexist with CD34 OF as a mixed fibroblast population (GD-OF). In contrast to fibrocytes, GD-OF express vanishingly low levels of MHC-2, Tg, TSHR, and AIRE. Further, the amplitude of IL-6 induction by TSH in GD-OF is substantially lower. The molecular basis for this divergence between fibrocytes and CD34 OF remains uncertain. In this article, we report that Slit2, an axon guidance glycoprotein, is constitutively expressed by the CD34 OF subset of GD-OF. Culture conditioned medium (CM) generated by incubating with GD-OF and CD34 OF substantially reduces levels of MHC-2, Tg, TSHR, and AIRE in fibrocytes. Expression can be restored by specifically depleting CM of Slit2. The effects of CD34 OF CM are mimicked by recombinant human Slit2. TSH induces Slit2 levels in GD-OF by enhancing both Slit2 gene transcription and mRNA stability. These findings suggest that Slit2 represents a TSH-inducible factor within the TAO orbit that can modulate the inflammatory phenotype of CD34 OF and therefore may determine the activity and severity of the disease.

Reflections on Thyroid Autoimmunity: A Personal Overview from the Past into the Future

“…Remarkably, contrary to the need for development of antigen-specific therapy for GO, an ever-growing number of non-specific immune-related and signal transduction molecules are being proposed as potential targets for therapy in GO. Indeed, one laboratory in the past 4 years has published data on the following molecules described to be of interest in this regard; IL-1R antagonist, IL-6, IL-8, IL-12, IL-23/IL-17, TNF alpha, Slit2, CXCL-12/CXCR4, Pen-traxin-3, PTEN, AIRE, PCP-1, and p53 [101][102][103][104][105][106][107][108]. The modified Bill Clinton campaign slogan mentioned above deserves repeating.…”

SLIT2 Overexpression in Periodontitis Intensifies Inflammation and Alveolar Bone Loss, Possibly via the Activation of MAPK Pathway

“…SLIT2 is aberrantly expressed in various cancers and plays a role in the regulation of cancer cell apoptosis, cancer metastasis, tumor-associated inflammation, and tumor progression ( Wang et al, 2003 , 2008 ; Schmid et al, 2007 ; Avci et al, 2008 ; Yang et al, 2010 ; Zhou et al, 2011 ; Chang et al, 2015 ; Liu et al, 2018 ). Moreover, the SLIT2 has been reported to aberrantly regulate the inflammation in different inflammatory diseases and cell types ( Zhao et al, 2014 ; Zhou et al, 2017 ; Fernando et al, 2018 ). SLIT2 is a secreted protein that binds to Roundabout (ROBO) receptors, i.e., ROBO1, ROBO2, ROBO3, and ROBO4.…”

Mechanisms That Underly T Cell Immunity in Graves’ Orbitopathy

“…Moreover, T cell immunoglobulin domain and mucin domain 3, which restrains cytokine production in effector T cells except Th2 cells, is down-regulated in peripheral Th1 and Th17 cells in GO patients ( 123 , 124 ). Slit2 from residential CD34 - OFs might inhibit production of IL-6 from GO CD34 + OFs, thereby ameliorating orbital inflammation and repressing Th17 cell differentiation ( 125 ). These findings offer new insights to explore novel approaches for therapy of GO.…”