Oxidative stress in the cerebellum of the spastic Han-Wistar (sHW) mutant rat, a model of Ataxic Neurodegeneration

Abstract

Neurodegeneration is the progressive breakdown of neurons resulting in impairment of cognitive functions and motor abilities, and has been attributed to such neurological diseases as Alzheimer's, Parkinson's, Huntington's, amyotrophic lateral sclerosis (ALS), and, important in this study, ataxia. Oxidative and nitrosative stress occurs when the damaging action of the reactive oxygen species (ROS) and reactive nitrogen species (RNS) targets key cellular molecules such as proteins, DNA, and RNA. This phenomenon is usually kept in check by the body's natural antioxidant defense system. However, under certain biomolecular or environmental factors, this defense system can be overwhelmed and shuts down, leading to a degenerative state. Growing data from experimental models and human brain studies suggest that oxidative stress plays an important role in degeneration in neurologic diseases. To determine whether ROS or RNS is occurring in the brains of patients suffering from neurodegenerative diseases, various oxidative stress markers have been utilized, including 8-hydroxydeoxyguanosine (8-OHdG) formed during DNA damage, and nitrotyrosine (NT) a marker of oxidative damage to proteins. My project utilized the mutant spastic Han-Wistar (sHW) rat, an acknowledged model of ataxia. Previous morphological examination of mutant animals indicated progressive losses of cerebellar Purkinje cells correlated with ataxia-like symptoms. Immunohistochemical analyses of expression of 8-OHdG showed increased staining intensity in the Purkinje cells of 55 day old mutant rats compared to littermate controls; while expression of NT was not seen in either mutant or normal siblings. Cerebellar sagittal sections of 50-55 day old mutant and normal sHW rats were stained with 8-OHdG antibody. The sections showed uniform distribution of 8-OHdG in both normal and mutant cerebellums but the mutant sHW rat displayed significantly higher staining compared to normal sHW rats. Specifically, mutant sHW rats showed much greater staining intensity within the Purkinje cells and within the deep cerebellar nuclei. Cerebellar sagittal sections were stained with NT antibody from 50-55 day old mutant and normal sHW rats. The immunohistochemistry staining of NT in the cerebellum showed very light, yet similar staining intensities within both the normal and mutant Purkinje cells. My findings suggest that sHW rat Purkinje cells undergo oxidative stress at the level of DNA only.