ABSTRACT
Experimental autoimmune encephalomyelitis (EAE) is a common rodent model for multiple sclerosis (MS). Yet, the long-term consequences for retina and optic nerve (ON) are unknown. C57BL/6 mice were immunized with an encephalitogenic peptide (MOG35-55) and the controls received the carriers or PBS. Clinical symptoms started at day 8, peaked at day 14, and were prevalent until day 60. They correlated with infiltration and demyelination of the ON. In MOG-immunized animals more microglia cells in the ONs and retinas were detected at day 60. Additionally, retinal ganglion cell (RGC) loss was combined with an increased macroglia response. At this late stage, an increased number of microglia was associated with axonal damage in the ON and in the retina with RGC loss. Whether glial activation contributes to repair mechanisms or adversely affects the number of RGCs is currently unclear.
Subject(s)
Encephalomyelitis, Autoimmune, Experimental/pathology , Microglia/physiology , Optic Nerve/pathology , Retina/pathology , Analysis of Variance , Animals , Axons/drug effects , Axons/pathology , Calcium-Binding Proteins/metabolism , Central Nervous System Stimulants/toxicity , Disease Models, Animal , Encephalomyelitis, Autoimmune, Experimental/chemically induced , Freund's Adjuvant/toxicity , Glial Fibrillary Acidic Protein/metabolism , Mice , Mice, Inbred C57BL , Microfilament Proteins/metabolism , Microglia/drug effects , Myelin-Oligodendrocyte Glycoprotein/toxicity , Optic Nerve/drug effects , Peptide Fragments/toxicity , Picrotoxin/toxicity , Protein Kinase C-alpha/metabolism , Retina/drug effects , Transcription Factor Brn-3A/metabolism , Vimentin/metabolismABSTRACT
BACKGROUND: Multiple sclerosis (MS) is often accompanied by optic nerve inflammation. And some patients experience permanent vision loss. We examined if the grade of optic nerve infiltration and demyelination affects the severity of clinical signs in an experimental autoimmune encephalomyelitis (EAE) model. The loss of retinal ganglion cells (RGC) and alterations in glia activity were also investigated. METHODS: C57BL/6 mice were immunized with peptide MOG35-55 in complete Freund's adjuvant (CFA) and controls received PBS in CFA. Then 23 days post immunization eyes were prepared for flatmounts and stained with Nissl to evaluated neuronal density. Clinical EAE symptoms as well as cell infiltration and demyelination in the optic nerve were examined. Retinal sections were stained with hematoxylin and eosin and silver stain. Immunohistochemistry was used to label RGCs (Brn-3a), apoptotic cells (caspase 3), macroglia (glial fibrillary acidic protein (GFAP)), microglia (Iba1), macrophages (F 4/80) and interleukin-6 (IL-6) secretion. RESULTS: EAE symptoms started at day 8 and peaked at day 15. Cell infiltrations (P = 0.0047) and demyelination (P = 0.0018) of EAE nerves correlated with the clinical score (r > 0.8). EAE led to a significant loss of RGCs (P< 0.0001). Significantly more caspase 3+ cells were noted in these animals (P = 0.0222). They showed an increased expression of GFAP (P< 0.0002) and a higher number of microglial cells (P< 0.0001). Also more macrophages and IL-6 secretion were observed in EAE mice. CONCLUSIONS: MOG immunization leads to optic neuritis and RGC loss. EAE severity is related to the severity of optic nerve inflammation and demyelination. EAE not only affects activation of apoptotic signals, but also causes a glial response in the retina.
