[show abstract][hide abstract] ABSTRACT: We have previously outlined functional interactions, including feedback cycles, between several of the gene products implicated in the pathogenesis of Alzheimer's disease. A number of Alzheimer-related stressors induce neuronal expression of apolipoprotein E (ApoE), β-amyloid precursor protein (βAPP), and fragments of the latter such as amyloid β-peptide (Aβ) and secreted APP (sAPP). These stressors include interleukin-1 (IL-1)-mediated neuroinflammation and glutamate-mediated excitotoxicity. Such circumstances are especially powerful when they transpire in the context of an APOE ε4 allele.
Semi-quantitative immunofluorescence imaging was used to analyze rat brains implanted with IL-1β slow-release pellets, sham pellets, or no pellets. Primary neuronal or NT2 cell cultures were treated with IL-1β, glutamate, Aβ, or sAPP; relative levels of ApoE mRNA and protein were measured by RT-PCR, qRT-PCR, and western immunoblot analysis. Cultures were also treated with inhibitors of multi-lineage kinases--in particular MAPK-p38 (SB203580), ERK (U0126), or JNK (SP600125)--prior to exposure of cultures to IL-1β, Aβ, sAPP, or glutamate.
Immunofluorescence of tissue sections from pellet-implanted rats showed that IL-1β induces expression of βAPP, IL-1α, and ApoE; the latter was confirmed by western blot analysis. These protein changes were mirrored by increases in their mRNAs, as well as in those encoding IL-1β, IL-1β-converting enzyme (ICE), and tumor necrosis factor (TNF). IL-1β also increased ApoE expression in neuronal cultures. It stimulated release of sAPP and glutamate in these cultures too, and both of these agents--as well as Aβ--stimulated ApoE expression themselves, suggesting that they may contribute to the effect of IL-1β on ApoE levels. Inhibitors of MAPK-p38, ERK, and JNK inhibited ApoE induction by all these agents except glutamate, which was sensitive only to inhibitors of ERK and JNK.
Conditions of glial activation and hyperexcitation can elevate proinflammatory cytokines, ApoE, glutamate, βAPP, and its secreted fragments. Because each of these factors promotes glial activation and neuronal hyperexcitation, these relationships have the potential to sustain self-propagating neurodegenerative cycles that could culminate in a progressive neurodegenerative disorder such as Alzheimer's disease.
Journal of Neuroinflammation 12/2011; 8:175. · 4.35 Impact Factor
[show abstract][hide abstract] ABSTRACT: S100β has been implicated in the formation of dystrophic neurites, overexpressing β-amyloid precursor protein (βAPP), in the β-amyloid plaques of Alzheimer's disease. We assessed the effects of S100β on cell viability of, neurite outgrowth from, and βAPP expression by neurons in primary cultures from fetal rat cortex. S100β (1–10 ng/ml) enhanced neuronal viability (as assessed by increased mitochondrial activity and decreased lactic acid dehydrogenase release) and promoted neurite outgrowth. Higher levels of S100β (100 ng/ml, but not 1 µg/ml) produced qualitatively similar, but less marked, effects. S100β also induced increased neuronal expression of the microtubule-associated protein MAP2, an effect that is consistent with trophic effects of S100β on neurite outgrowth. S100β (10 and 100 ng/ml) induced graded increases in neuronal expression of βAPP and of βAPP mRNA. These results support our previous suggestion that excessive expression of S100β by activated, plaque-associated astrocytes in Alzheimer's disease contributes to the appearance of dystrophic neurites overexpressing βAPP in diffuse amyloid deposits, and thus to the conversion of these deposits into the diagnostic neuritic β-amyloid plaques.
[show abstract][hide abstract] ABSTRACT: We surveyed several human cell lines for production of α- and β-human chorionic gonadotropin (hCG) under a variety of conditions
known to induce gene expression α- and β-hCG subunits were monitored in culture media by specific radioimmunoassays and were
shown to be quite sensitive to serum refeeding and growth state of all cell types studied. The permanent line JEG-3 secreted
both α- and β-subunits whereas HeLa cells secreted only the α-subunit. Production of both subunits was augmented in these
permanent cell lines, for each growth state, by pretreating cells with 5-azacytidine; in contrast, spontaneous β-hCG production
by normal human fibroblasts (four of six strains) was only rarely increased after 5-azacytidine treatment, and more often
was suppressed by 30 to 40%. Three of five strains from inherited chromosomal breakage syndromes produced immunoassayable
β-hCG spontaneously, two of which increased secretion upon treatment with either UV or mitomycin C. Surprisingly, one normal
cell strain of fetal origin was induced to secrete α-hCG, but not β-hCG, after UV irradiation. JEG-3 and HeLa cells produced
detectable cognate mRNA for α- or β-hCG subunits or both by Northern and S1 nuclease protection analyses, whereas such transcripts
from untransformed human fibroblasts were consistently below detectable levels. Quantitation of β-hCG mRNA by RNA:RNA annealing
kinetics indicates that even the fibroblast strain producing the highest secreted β-hCG levels contained cognate mRNAs at
only ∼0.1 copy per cell. We conclude that hCG expression in human fibroblasts is strongly repressed at the transcriptional
level, although a variety of conditions (growth state, serum refeeding, cell senescence, or DNA damage) can affect the level
of “leaky” expression, at least in some responding fraction of cells.