NADPH oxidase expression in active multiple sclerosis lesions in relation to oxidative tissue damage and mitochondrial injury

Abstract

Multiple sclerosis is a chronic inflammatory disease of the central nervous system, associated with demyelination and neurodegeneration. The mechanisms of tissue injury are poorly understood, but recent data suggest that mitochondrial injury may play an important role in this process. Mitochondrial injury can be triggered by reactive oxygen and nitric oxide species, and we recently provided evidence for oxidative damage of oligodendrocytes and dystrophic axons in early stages of active multiple sclerosis lesions. In this study, we identified potential sources of reactive oxygen and nitrogen species through gene expression in carefully staged and dissected lesion areas and by immunohistochemical analysis of protein expression. Genome-wide microarrays confirmed mitochondrial injury in active multiple sclerosis lesions, which may serve as an important source of reactive oxygen species. In addition, we found differences in the gene expression levels of various nicotinamide adenine dinucleotide phosphate oxidase subunits between initial multiple sclerosis lesions and control white matter. These results were confirmed at the protein level by means of immunohistochemistry, showing upregulation of the subunits gp91phox, p22phox, p47phox, nicotinamide adenine dinucleotide phosphate oxidase 1 and nicotinamide adenine dinucleotide phosphate oxidase organizer 1 in activated microglia in classical active as well as slowly expanding lesions. The subunits gp91phox and p22phox were constitutively expressed in microglia and were upregulated in the initial lesion. In contrast, p47phox, nicotinamide adenine dinucleotide phosphate oxidase 1 and nicotinamide adenine dinucleotide phosphate oxidase organizer 1 expression were more restricted to the zone of initial damage or to lesions from patients with acute or early relapsing/remitting multiple sclerosis. Double labelling showed co-expression of the nicotinamide adenine dinucleotide phosphate oxidase subunits in activated microglia and infiltrated macrophages, suggesting the assembly of functional complexes. Our data suggest that the inflammation-associated oxidative burst in activated microglia and macrophages plays an important role in demyelination and free radical-mediated tissue injury in the pathogenesis of multiple sclerosis.

Elucidating the Molecular Basis of Multiple Sclerosis and Understanding the Disease Pathophysiology

“…Effectively, this implies that uptake of myelin debris converts macrophages from a pro-inflammatory to an anti-inflammatory status. To an extent, this concurs with earlier findings of both subpopulations of macrophage/microglia in active lesion sites [96].…”

Oxidative injury in multiple sclerosis cerebellar grey matter

“…The enzymes responsible for the generation of ROS have been detected in tissue derived from patients with MS and experimental models of CNS inflammation. NADPH oxidase is responsible for the generation of superoxide ions and is highly expressed in activated microglia and infiltrating macrophages within MS lesions (Fischer et al, 2012). In addition, expression of iNOS, which is responsible for the generation of nitric oxide, is up-regulated in microglia and macrophages in acute and chronic lesions and has been linked to acute axonal injury (Bagasra et al, 1995;Diaz-Sanchez et al, 2006;Hill et al, 2004;Liu et al, 2001).…”

Exploring the origins of grey matter damage in multiple sclerosis

“…A role for inflammation in mitochondrial dysfunction is suggested by post-mortem studies showing that reactive oxygen species (ROS) produced by activated microglia and macrophages can induce mitochondrial dysfunction not only in the white matter 120 , but also in the grey matter lesions 104 . Several lines of evidence have led to the hypothesis that mitochondrial injury is a primary phenomenon in multiple sclerosis 121 .…”