FORPRION

BAVARIAN RESEARCH ASSOCIATION PRIONS

Wü 1 Pathogenesis of Prion Diseases IV

Oxidative stress in the brain at early preclinical stages of mouse scrapie Oxidative stress has been shown to be involved in the pathogenesis of neurodegenerative diseases including prion diseases. Although a growing body of evidence suggests direct involvement of oxidative stress in the pathogenesis of prion diseases, it is still not clear whether oxidative stress is a causative early event in these conditions or a secondary phenomenon commonly found in the progression of neurodegenerative diseases. Using a mouse scrapie model, we assessed oxidative stress in the brain at various stages of the disease progression and observed significantly increased concentration of lipid peroxidation markers, malondialdehyde and 4-hydroxyalkenals, and mRNA level of an oxidative stress response enzyme, heme oxygenase-1 (HO-1), at early preclinical stages of scrapie. The changes preceded dramatic synaptic loss demonstrated by immunohistochemical staining of a synaptic protein, synaptophysin. These findings imply that the brain undergoes oxidative stress even from an early stage of prion invasion into the brain. Given the well-known deleterious effects of reactive oxygen species-mediated damage in the brain, it is considered that the oxidative stress at the preclinical stage of prion disease may predispose the brain to neurodegenerative mechanisms that characterize the disease. Unaltered susceptibility to scrapie in serotonin transporter deficient mice The serotonergic system has been hypothesized to play an important role in prion diseases. Specifically, hyperactivity of the serotonergic system in prion diseases is suggested by an increase in the turnover rate of the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) in human and experimental prion diseases. The 5-HT transporter (5-HTT) determines the duration of serotonergic neurotransmission by way of reuptake of 5-HT from the extracellular space. 5-HTT availability is reduced in brains of patients with the human prion disease familial fatal insomnia. To further clarify a possible role of the 5-HTT in prion diseases we investigated whether mice lacking the 5-HTT display an altered susceptibility to experimental scrapie infection. Surprisingly, 5-HTT knockout mice developed mouse scrapie in a time course similar to wildtype control mice with accumulation of the pathological prion protein, PrPSc and with the typical pathological hallmarks of the disease. These findings argue against a major role of the 5-HTT in the pathogenesis of prion diseases in mice. Beta-amyloid plaque formation and prion infection in an adult primary brain cell long-term culture model Primary neuronal cell cultures are obtained mostly from embryos or neonatal animals because of the technical difficulty of culturing neuronal cells isolated from adults. However, to assist our understanding of molecular and cellular changes occurring at different developmental and aging stages throughout life and their contribution to the pathogenesis of age-related disorders, an in vitro model prepared with adult animal cells would more closely represent the physiological conditions of interest. Further, to explore slow progressive changes, long-term culture of the cells is required. By combining and comparing various conditions for cell dissociation and culture, we found that a mixed population of brain cells isolated from adult mice can be cultured for several months under optimized conditions. We applied this novel cell culture system to various models of progressive neurodegenerative diseases. After longterm culture of adult primary brain cells prepared from Alzheimer’s disease and prion disease mouse models, we observed beta-amyloid plaque formation and prion infection in cell cultures in vitro. This new model would be a useful tool for studying a wide range of agerelated disorders of the central nervous system.