Mitochondrial oxidative DNA damage in experimental autoimmune uveitis

Abstract

Purpose: In experimental autoimmune uveitis (EAU), recent work has demonstrated that retinal damage involves oxidative stress early in uveitis, before macrophage cellular infiltration. The purpose of this study was to determine whether oxidative mitochondrial DNA damage occurs early in EAU, before leukocyte infiltration.

Methods: Lewis rats were immunized with S-antigen mixed with complete Freund adjuvant (CFA) to induce EAU. Nonimmunized animals and animals injected with CFA served as controls. Animals were killed on days 3, 4, 7, and 12 after immunization. Damage to mitochondrial DNA and nuclear DNA was assessed using a novel long quantitative polymerase chain reaction technique. TUNEL staining to detect apoptosis and immunohistochemical detection of leukocyte infiltration in EAU retinas were also performed at these times.

Results: Mitochondrial DNA damage occurred early in EAU, from day 4 to day 12. In the early phase of EAU (days 4-7), there was no inflammatory cell infiltration. On day 12 inflammatory cells infiltrated the retina and uvea. Nuclear DNA damage occurred later in EAU at day 12. Neither mitochondrial nor nuclear DNA damage was detected in the controls. TUNEL-positive staining for apoptosis was detected only at day 12 in EAU retina.

Conclusions: Oxidative mitochondrial DNA damage begins at day 4 in EAU, supporting the view that oxidative stress selectively occurs in the mitochondria in the early phase of EAU, before leukocyte infiltration. Such oxidative damage in the mitochondria may be the initial event leading to retinal degeneration in EAU.