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.     

The Ras/Erk pathway induces primitive endoderm but prevents parietal endoderm differentiation of F9 embryonal carcinoma cells

The formation of parietal endoderm (PE) is one of the first differentiation processes during mouse development and can be studied in vitro using F9 embryonal carcinoma (EC) cells. Treatment of F9 EC cells with retinoic acid (RA) induces differentiation toward primitive endoderm (PrE), while differentiation toward PE is induced by subsequent addition of parathyroid hormone (PTH) or PTH-related peptide (PTHrP). The signal transduction mechanisms involved in this two-step process are largely unclear. We show that the RA-induced differentiation toward PrE is accompanied by a sustained increase in Ras activity and that ectopic expression of oncogenic Ha-Ras is sufficient to induce PrE differentiation. Ras activity subsequently decreases upon PTH-induced differentiation toward PE. This is a necessary event, since expression of oncogenic Ha-Ras in PrE-like cells prevents PTH-induced PE differentiation. Expression of active PKA in PrE-like F9 cells mimics PTH-induced PE differentiation and is again prevented by oncogenic Ha-Ras. The effect of oncogenic Ras on both differentiation steps is abolished by the MEK inhibitor PD98059 and can be mimicked by constitutively active forms of Raf and MEK. In conclusion, our data suggest that activation of the Ras/Erk is sufficient to induce differentiation to PrE and to prevent subsequent differentiation toward PE. Activation of PKA down-regulates Ras activity, resulting in disappearance of this blockade and transmission of signal(s) triggering PE differentiation.     

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.