Abstract
Abstract: :
Purpose: Optic neuritis is one of the most common features of multiple sclerosis (MS), an autoimmune disorder of the central nervous system. The infiltration of auto–reactive T cells and macrophages is thought to lead to demyelination and axonal degeneration and glial cell death in optic nerve and death of retinal ganglion cells (RGCs), resulting in visual impairment. Previously, we have demonstrated that the calcium–activated neutral protease calpain is upregulated in both infiltrating immune cells and in resident glial cells of the optic nerve (ON) in experimental allergic encephalomyelitis (EAE), an animal model of MS and optic neuritis. Since calpain plays a role in T cell activation and migration, we hypothesize that treatment with the calpain inhibitor SJA 6017 will block the infiltration of immune cells into the ON, which should therefore decrease damage to axons and RGCs and restore retinal function. Methods: EAE was induced in Lewis rats by a subcutaneous injection of Complete Freund’s Adjuvant plus guinea pig spinal cord (200 mg/ml) and myelin basic protein (280 µg/ml) followed two hours later by an intraperitoneal (ip) injection of pertussis toxin (20 µg/ml). On days 4 and 8 post–EAE induction, rats received an ip injection of SJA6017 (3mg/kg) or vehicle control. On day 11 post–EAE induction, single–flash electroretinograms (ERGs) were performed to test retinal function. Then animals were sacrificed and ON samples were collected for immunohistochemical (IH) analysis of calpain expression in immune cells. Results: A– and b–wave ERG amplitudes were almost completely abolished in EAE rats, as compared to controls, indicating that retinal function wass greatly reduced. Treatment with SJA6017 significantly (p<0.05) restored a– and b–wave amplitudes by ∼100 and ∼60%, respectively. IH analysis demonstrated increased staining of OX42+ (macrophages) and IFNγ+ (T cells) cells in ON of EAE rats, suggesting increased immune cell infiltration. Calpain expression was increased in OX42+ and IFNγ+ cells, as well as other cells in EAE and SJA treatment decreased calpain expression and blocked immune cell infiltration in EAE ON. Conclusions: These experiments suggest that treatment with calpain inhibitors will decrease loss of retinal function by blocking increased calpain expression and immune cell infiltration in EAE, thus offering a novel approach to treating optic neuritis in MS patients.
Keywords: autoimmune disease • inflammation