Yong Sun Kim

Redox metals and oxidative abnormalities in human prion diseases

Prion diseases are characterized by the accumulation of diffuse and aggregated plaques of protease-resistant prion protein (PrP) in the brains of affected individuals and animals. Whereas prion diseases in animals appear to be almost exclusively transmitted by infection, human prion diseases most often occur sporadically and, to a lesser extent, by inheritance or infection. In the sporadic cases (sporadic Creutzfeld-Jakob disease, sCJD), PrP-containing plaques are infrequent, whereas in transmitted (variant CJD) and inherited (Gerstmann-Straussler-Scheinker Syndrome) cases, plaques are a usual feature. In the current study, representative cases from each of the classes of human prion disease were analyzed for the presence of markers of oxidative damage that have been found in other neurodegenerative diseases. Interestingly, we found that the pattern of deposition of PrP, amyloid-β, and redox active metals was distinct for the various prion diseases. Whereas 8-hydroxyguanosine has been shown to be increased in sCJD, and inducible NOS is increased in scrapie-infected mice, well-studied markers of oxidative damage that accumulate in the lesions of other neurodegenerative diseases (such as Alzheimer’s disease, progressive supranuclear palsy, and Parkinson’s disease), such as heme oxygenase-1 and lipid peroxidation, were not found around PrP deposits or in vulnerable neurons. These findings suggest an important distinction in prion-related oxidative stress, indicating that different neurodegenerative pathways are involved in different prion diseases.

Expression of inducible nitric oxide synthase in the brains of scrapie-infected mice

The neuronal cell damage caused by inducible nitric oxide synthase (iNOS) in brain has been reported to be associated, at least in part, with many neurodegenerative diseases including Alzheimers disease. We recently observed vacuolation and astrocytosis in the brains of ME7 scrapie strain-infected C57BL mice. To investigate if these phenomena might have a relationship to iNOS, the level of iNOS expression was measured immunohistochemically and molecular biologically in the brains of scrapie-infected C57BL mice. The number and size of astrocytes were increased and immunoreactivity of glial fibrillary acidic protein (GFAP) was significantly enhanced. iNOS immunoreactivity was observed in the astrocytes of the scrapie-infected group, but not in the control group. iNOS mRNA levels were increased in scrapie-infected mice compared to the levels in non-infected mice of the same age. Our results suggest that iNOS induction in reactive astrocytes is a part of the neurodegenerative mechanisms in scrapie infection.

Aluminum induced reversible change in permeability of the blood-brain barrier to [14C]sucrose

To determine whether aluminum alters the permeability of the blood-brain barrier (BBB), 4 groups of rats were given an intraperitoneal injection of aluminum chloride, aluminum lactate, aluminum hydroxide or physiological saline. Two hours later, [14C]sucrose was injected, and brain radioactivity was measured from 5 different brain regions. The permeability capillary surface area (PA) was calculated by the dual compartment model (plasma-brain) proposed by Rapoport et al. The PAs for [14C]sucrose were significantly elevated in all brain regions of the animals injected with the aluminum chloride or aluminum lactate. However, the aluminum hydroxide group showed no BBB permeability change. In the second experiment, the reversibility of the aluminum induced BBB change was examined. PA was determined at 2, 4 or 24 h after exposure to aluminum lactate. Significant permeability changes were observed at 2 and 4 h after aluminum. However, the difference disappeared by 24 h. These findings indicate that exposure to a high level of aluminum alters the function of BBB in the rat and the aluminum induced BBB change is reversible. An increase in the blood aluminum level and time after exposure appear to be important factors associated with the BBB permeability change. Implications of the results are discussed in terms of aluminums potential action on the endothelial cells.

Alterations of c-fos gene methylation in the processes of aging and tumorigenesis in human liver

The state of DNA methylation in the c-fos gene was examined in human livers of different ages, cirrhosis and hepatocellular carcinoma. The degree of methylation in the intron 1 to exon 4 region increased with age, whereas all of the 10 cirrhosis samples revealed a decrease in methylation when compared to normal livers of similar ages. The 11 hepatocellular carcinomas showed varied alterations suggesting that the alteration of the c-fos gene methylation is related to aging as well as to early-step of hepatocarcinogenesis.

Phospholipase D1 is associated with amyloid precursor protein in Alzheimer's disease

Amyloid precursor protein (APP) is a widely expressed transmembrane protein of unknown function that is involved in the pathogenesis of Alzheimers disease (AD). We investigated the involvement of phospholipase D (PLD) in the pathophysiology of AD. We showed dramatic upregulation of PLD1 immunoreactivity in reactive astroglial cells in brain tissue sections from authentic AD patients. Expression and activity of PLD1 were up-regulated in brain tissues from AD patients, especially caveolae membrane fraction, compared with those of control brains. Interestingly, PLD1 physically interacts and colocalizes with APP and caveolin-3. We found that APP was associated with the pleckstrin homology domain of PLD1, and the amyloid region of APP interacted with PLD. Elevated expression of APP stimulated PLD activity in human astroglioma cells. These results suggest that up-regulation of PLD might have a role in the neuronal pathology associated with AD.

Control of neurite outgrowth by RhoA inactivation

J. Neurochem. (2012) 120, 684–698.

Genetic Studies in Human Prion Diseases

Human prion diseases are fatal neurodegenerative disorders that are characterized by spongiform changes, astrogliosis, and the accumulation of an abnormal prion protein (PrPSc). Approximately 10%-15% of human prion diseases are familial variants that are caused by pathogenic mutations in the prion protein gene (PRNP). Point mutations or the insertions of one or more copies of a 24 bp repeat are associated with familial human prion diseases including familial Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome, and fatal familial insomnia. These mutations vary significantly in frequency between countries. Here, we compare the frequency of PRNP mutations between European countries and East Asians. Associations between single nucleotide polymorphisms (SNPs) of several candidate genes including PRNP and CJD have been reported. The SNP of PRNP at codon 129 has been shown to be associated with sporadic, iatrogenic, and variant CJD. The SNPs of several genes other than PRNP have been showed contradictory results. Case-control studies and genome-wide association studies have also been performed to identify candidate genes correlated with variant and/or sporadic CJD. This review provides a general overview of the genetic mutations and polymorphisms that have been analyzed in association with human prion diseases to date. Graphical Abstract

Alteration of iron regulatory proteins (IRP1 and IRP2) and ferritin in the brains of scrapie-infected mice

Considerable evidence suggests that oxidative stress may be involved in the pathogenesis of Transmissible Spongiform Encephalopathies (TSEs). To investigate the involvement of iron metabolism in TSEs, we examined the expression levels of iron regulatory proteins (IRPs), ferritins, and binding activities of IRPs to iron-responsive element (IRE) in scrapie-infected mice. We found that the IRPs-IRE-binding activities and ferritins were increased in the astrocytes of hippocampus and cerebral cortex in the brains of scrapie-infected mice. These results suggest that alteration of iron metabolism contributes to development of neurodegeneration and that some protective mechanisms against iron-induced oxidative damage may occur during the pathogenesis of TSEs.

Incubation periods and histopathological changes in mice injected stereotaxically in different brain areas with the 87V scrapie strain

SummaryAfter stereotaxic injection into five different brain areas (cortex, caudate nucleus, substantia nigra, thalamus and cerebellum) of IM mice with the 87V scrapie strain, the cerebellum had the shortes incubation period. The vacuolation pattern was similar regardless of the area injected with extensive vacuolation in the thalamus, mesencephalon and hypothalamus. The pattern of amyloid plaques differed markedly depending on the area injected. In particular, no plaques were seen anywhere in the brain after injection into intact cerebellum, whereas injection into the four cerebral areas yielded plaques in the forebrain but not in the cerebellum. The incubation period after injection into bisected cerebella was much longer than after injection into intact cerebella. Mice injected on one side of bisected cerebellum had amyloid plaques in the forebrain but not in the cerebellum. There is a discussion of the finding that, although no plaques and virtually no vacuolation were seen in the cerebellum, the shortest incubation period occurred after injection into intact cerebellum.

Increased expression of CaM kinase II alpha in the brains of scrapie-infected mice

We investigated the distribution of calcium/calmodulin-dependent protein kinase II (CaM kinase II) in the brains of mice infected with ME7 scrapie strain. CaM kinase II is an enzyme that plays a major role in the regulation of long-term potentiation, a form of synaptic plasticity associated with learning and memory. Immunoreactivity of CaM kinase II alpha, measured by Western blot, increased markedly in scrapie-infected brains compared with control brains. Immunohistochemically, CaM kinase II alpha immunoreactivity was upregulated in the cerebral cortex and hippocampal CA1 area of scrapie-positive mice infected with ME7 scrapie strain. This result implies that this enzyme is associated with aberrant function of synaptic transmission and LTP of the pyramidal neurons in the hippocampal CA1 area of mice infected with ME7 scrapie strain.