Faculty Bibliography

An increasing body of evidence suggests that soluble assemblies of amyloid beta-protein (Abeta) play an important role in the initiation of Alzheimer disease (AD). In vitro studies have found that synthetic Abeta can form soluble aggregates through self-assembly, but this process requires Abeta concentrations 100- to 1000-fold greater than physiological levels. Tissue transglutaminase (TGase) has been implicated in neurodegeneration and can cross-link Abeta. Here we show that TGase induces rapid aggregation of Abeta within 0.5-30 min, which was not observed with chemical cross-linkers. Both Abeta40 and Abeta42 are good substrates for TGase but show different aggregation patterns. Guinea pig and human TGase induced similar Abeta aggregation patterns, and oligomerization was observed with Abeta40 concentrations as low as 50 nm. The formed Abeta40 species range from 5 to 6 nm spheres to curvilinear structures of the same width, but up to 100 nm in length, that resemble the previously described self-assembled Abeta protofibrils. TGase-induced Abeta40 assemblies are resistant to a 1-h incubation with either neprilysin or insulin degrading enzyme, whereas the monomer is rapidly degraded by both proteases. In support of these species being pathological, TGase-induced Abeta40 assemblies (100 nm) inhibited long term potentiation recorded in the CA1 region of mouse hippocampus slices. Our data suggest that TGase can contribute to AD by initiating Abeta oligomerization and aggregation at physiological levels, by reducing the clearance of Abeta due to the generation of protease-resistant Abeta species, and by forming Abeta assemblies that inhibit processes involved in memory and learning. Our data suggest that TGase might constitute a specific therapeutic target for slowing or blocking the progression of AD.

Tert-butyl hydroperoxide (t-BHP), an analog of hydroperoxide, induced characteristic changes of senescence in human diploid fibroblasts WI-38 cells. It was reported that ginsenoside Rg1, an active ingredient of ginseng, ameliorated learning deficits in aged rats. The present study was aimed to investigate whether ginsenoside Rg1 can delay the premature senescence of WI-38 cells induced by t-BHP and to explore the underlying molecular mechanisms. First, Rg1 pretreatment markedly reversed senescent morphological changes in WI-38 cells induced by t-BHP. Second, t-BHP treatment alone resulted in an increase in the protein levels of P16 and P21, and a decline in intracellular adenosine 5'-triphosphate (ATP) level and mitochondrial complex IV activity. Ginsenoside Rg1 pretreatment had significant effects of attenuating these changes. These data indicate that ginsenoside Rg1 has an anti-aging effect on t-BHP-induced premature senescence in WI-38 cells. This effect may be mediated by regulating cell cycle proteins and enhancing mitochondrial functioning.

Following intraparenchymal injection of the dopamine (DA) neurotoxin 6-hydroxydopamine, we previously demonstrated passage of fluoresceinisothiocyanate-labeled albumin (FITC-LA) from blood into the substantia nigra (SN) and striatum suggesting damage to the blood-brain barrier (BBB). The factors contributing to the BBB leakage could have included neuroinflammation, loss of DA neuron control of barrier function, or a combination of both. In order to determine which factor(s) was responsible, we assessed BBB integrity using the FITC-LA technique in wild-type (WT), tumor necrosis factor alpha (TNF-alpha) knockout (KO), and minocycline (an inhibitor of microglia activation) treated mice 72 h following treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Compared with WT mice, TNF-alpha KO mice treated with MPTP showed reduced FITC-LA leakage, decreased numbers of activated microglia, and reduced proinflammatory cytokines (TNF-alpha and interleukin 1beta) associated with significant MPTP-induced DA neuron loss. In contrast, minocycline treated animals did not exhibit significant MPTP-induced DA neuron loss although their FITC-LA leakage, numbers of activated microglia, and MPTP-induced cytokines were markedly attenuated. Since both TNF-alpha KO and minocycline treatment attenuated MPTP-induced BBB dysfunction, microglial activation, and cytokine increases, but had differential effects on DA neuron loss, it appears that neuroinflammation and not DA neuron loss was responsible for disrupting the blood-brain barrier integrity.