Abstract
Purpose :
Autoimmune uveitis is a sight-threatening disease characterized by intraocular inflammation, which is usually accompanied with Th17 cells-associated systemic autoimmune disorders such as Behcet's disease. Thus, the role of Th17 cells in autoimmune uveitis and the novel treatments targeting Th17 cells are needed. GHRH, synthesized in the hypothalamus, controls the secretion of growth hormone in the pituitary. GHRH receptor (GHRHR) is also expressed in ocular tissues and T cells. We hypothesize that GHRH promotes autoimmune uveitis by regulating Th17 cell differentiation.
Methods :
Ghrhr lit/lit mice (n=28) with non-functional GHRHR, were immunized with IRBP to induce autoimmune experimental uveitis (EAU). 21 days after immunization, EAU was assessed based on clinical examinations of cSLO, OCT and ERG. Eyeballs were collected for histology staining. Th17 cells isolated from spleen (SP), eye-draining lymph nodes (LNs) and eyes were evaluated for their activation, apoptosis and gene expression. GHRH agonist and antagonist were applied to wild-type (WT) mice (n=15 per group) immunized with IRBP to verify the role of GHRHR. CD4+ T cells from IRBP-immunized WT and Ghrhr lit/lit mice were differentiated into Th17 cells in vitro following adoptive transfer into naïve recipient mice (n=8 per group) to determine the effect of GHRHR in the differentiation of pathogenic Th17 cells to induce EAU.
Results :
Compared with WT mice, Ghrhr lit/lit mice have lower disease score (p<0.0001), decreased fold change of retina-choroidal thickness (RCT) (p<0.0001), higher amplitudes of b-wave in photopic and scotopic ERG (p<0.001). Ghrhr lit/lit mice have fewer CD4+ IL-17a+ T cells in the SP (p<0.05), LNs (p<0.05) and eye (p<0.001). Gene expression of Il17a, Il17f, Il22 and Csf2 is downregulated, while Il10 is upregulated. Compared with WT EAU mice treated with DMSO, mice treated with GHRH agonist have higher disease score (p<0.05), increased fold change of RCT (P<0.05) and increased Th17 cells (p<0.05), while EAU mice treated with GHRH antagonist have lower disease score (P<0.01), decreased fold change of RCT (P<0.001) and decreased Th17 cells (P<0.01).
Conclusions :
Our results indicate that GHRH signaling is required in Th17-mediated autoimmune uveitis. GHRH signaling promotes EAU by increasing pathogenic Th17 cells, and Th17-lineage proinflammatory cytokines, but does not alter T cell activation and apoptosis.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.