Microglial activation in multiple system atrophy: a potential role for NF-kappaB/rel proteins

Microglial activation is a prominent feature of affected brain areas in multiple system atrophy. Microglia express proinflammatory peptides, which may be a result of activation of nuclear factor-KB. We investigated the nuclear presence of RelA, the 65 kDa subunit of the NF-KB/RelA family in striatum and brain stem of patients with multiple system atrophy. Affected brain areas of patients with multiple system atrophy showed a marked immunoreactivity for nuclear Rel A p65, which was almost exclusively localized in activated microglia. Interestingly nuclear translocation of Rel A was not detected in striatal tissue of controls and Parkinson disease patients. Thus, NF-kappaB/Rel A complexes may play a role in mediating microglial activation in multiple system atrophy.     

Photo-oxidative stress down-modulates the activity of nuclear factor-kappaB via involvement of caspase-1, leading to apoptosis of photoreceptor cells

The mechanisms of photoreceptor cell death via apoptosis, in retinal dystrophies, are largely not understood. In the present report we show that visible light exposure of mouse cultured 661W photoreceptor cells at 4.5 milliwatt/cm2 caused a significant increase in oxidative damage of 661W cells, leading to apoptosis of these cells. These cells show constitutive expression of nuclear factor-kappaB (NF-kappaB), and light exposure of photoreceptor cells results in lowering of NF-kappaB levels in both the nuclear and cytosolic fractions in a time-dependent manner. Immunoblot analysis of IkappaBalpha and p50, and p65 (RelA) subunits of NF-kappaB, suggested that photo-oxidative stress results in their depletion. Immunocytochemical studies using antibody to RelA subunit of NF-kappaB further revealed the presence of this subunit constitutively both in the nucleus and cytoplasm of the 661W cells. Upon exposure to photo-oxidative stress, a depletion of the cytoplasmic and nuclear RelA subunit was observed. The depletion of NF-kappaB appears to be mediated through involvement of caspase-1. Furthermore, transfection of these cells with a dominant negative mutant IkappaBalpha greatly enhanced the kinetics of down modulation of NF-kappaB, resulting in a faster photo-oxidative stress-induced apoptosis. Taken together, these studies show that the presence of NF-kappaB RelA subunit in the nucleus is essential for protection of photoreceptor cells against apoptosis mediated by an oxidative pathway.     

Chronic human immunodeficiency virus type 1 infection of myeloid cells disrupts the autoregulatory control of the NF-kappaB/Rel pathway via enhanced IkappaBalpha degradation

Productive human immunodeficiency virus type 1 (HIV-1) infection causes sustained NF-kappaB DNA-binding activity in chronically infected monocytic cells. A direct temporal correlation exists between HIV infection and the appearance of NF-kappaB DNA-binding activity in myelomonoblastic PLB-985 cells. To examine the molecular basis of constitutive NF-kappaB DNA-binding activity in HIV1 -infected cells, we analyzed the phosphorylation and turnover of IkappaBalpha protein, the activity of the double-stranded RNA-dependent protein kinase (PKR) and the intracellular levels of NF-kappaB subunits in the PLB-985 and U937 myeloid cell models. HIV-1 infection resulted in constitutive, low-level expression of type 1 interferon (IFN) at the mRNA level. Constitutive PKR activity was also detected in HIV-1-infected cells as a result of low-level IFN production, since the addition of anti-IFN-alpha/beta antibody to the cells decreased PKR expression. Furthermore, the analysis of IkappaBalpha turnover demonstrated an increased degradation of IkappaBalpha in HIV-1-infected cells that may account for the constitutive DNA binding activity. A dramatic increase in the intracellular levels of NF-kappaB subunits c-Rel and NF-kappaB2 p100 and a moderate increase in NF-kappaB2 p52 and RelA(p65) were detected in HIV-1-infected cells, whereas NF-kappaB1 p105/p50 levels were not altered relative to the levels in uninfected cells. We suggest that HIV-1 infection of myeloid cells induces IFN production and PKR activity, which in turn contribute to enhanced IkappaBalpha phosphorylation and subsequent degradation. Nuclear translocation of NF-kappaB subunits may ultimately increase the intracellular pool of NF-kappaB/IkappaBalpha by an autoregulatory mechanism. Enhanced turnover of IkappaBalpha and the accumulation of NF-kappaB/Rel proteins may contribute to the chronically activated state of HIV-1-infected cells.     

Late-onset chronic inflammatory encephalopathy in immune-competent and severe combined immune-deficient (SCID) mice with astrocyte-targeted expression of tumor necrosis factor

To examine the role of tumor necrosis factor (TNF)-alpha in the pathogenesis of degenerative disorders of the central nervous system (CNS), transgenic mice were developed in which expression of murine TNF-alpha was targeted to astrocytes using a glial fibrillary acidic protein (GFAP)-TNF-alpha fusion gene. In two independent GFAP-TNFalpha transgenic lines (termed GT-8 or GT-2) adult (>4 months of age) animals developed a progressive ataxia (GT-8) or total paralysis affecting the lower body (GT-2). Symptomatic mice had prominent meningoencephalitis (GT-8) or encephalomyelitis (GT-2) in which large numbers of B cells and CD4+ and CD8+ T cells accumulated at predominantly perivascular sites. The majority of these lymphocytes displayed a memory cell phenotype (CD44high, CD62Llow, CD25-) and expressed an early activation marker (CD69). Parenchymal lesions contained mostly CD45+ high, MHC class II+, and Mac-1+ cells of the macrophage microglial lineage with lower numbers of neutrophils and few CD4+ and CD8+ T cells. Cerebral expression of the cellular adhesion molecules ICAM-1, VCAM-1, and MAdCAM as well as a number of alpha- and beta-chemokines was induced or upregulated and preceded the development of inflammation, suggesting an important signaling role for these molecules in the CNS leukocyte migration. Degenerative changes in the CNS of the GFAP-TNFalpha mice paralleled the development of the inflammatory lesions and included primary and secondary demyelination and neurodegeneration. Disease exacerbation with more extensive inflammatory lesions that contained activated cells of the macrophage/microglial lineage occurred in GFAP-TNFalpha mice with severe combined immune deficiency. Thus, persistent astrocyte expression of murine TNF-alpha in the CNS induces a late-onset chronic inflammatory encephalopathy in which macrophage/microglial cells but not lymphocytes play a central role in mediating injury.