Accumulation of tau induced in neurites by microglial proinflammatory mediators.

Aggregated fibrillary microtubule-associated protein tau is the major component of neurofibrillary tangles in Alzheimer's disease. The exact molecular mechanism of tau aggregation is unknown. Microglial cell activation and migration toward amyloid-beta plaques precede the appearance of dysmorphic neurites and formation of neurofibrillary tangles. Here, we analyzed the accumulation of tau at a distance range of expected spontaneous aggregation by fluorescence lifetime-based Förster resonance energy transfer in cultured primary murine neurons cotransfected with the human tau gene tagged to the green fluorescent protein variants Citrine (tau-Citrine) and Cerulean (tau-Cerulean). No spontaneous accumulation of cotransfected tau-Citrine and tau-Cerulean was detected in untreated neurons. Coculture of neurons with activated microglia induced aggregation of tau in neurites. Treatment of neurons with tumor necrosis factor-alpha (TNF-alpha) stimulated reactive oxygen species generation and resulted in the accumulation of tau-Citrine and tau-Cerulean in neurites, which was inhibited by neutralization of TNF and the free radical inhibitor 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox). These data demonstrate that activated microglia and the microglial-derived proinflammatory cytokine TNF can induce accumulation of the aggregation-prone tau molecules in neurites via reactive oxygen species.

Wild-type Cu/Zn superoxide dismutase (SOD1) does not facilitate, but impedes the formation of protein aggregates of amyotrophic lateral sclerosis causing mutant SOD1.

Aggregation of Cu/Zn superoxide dismutase (SOD1) is a hallmark of a subset of familial amyotrophic lateral sclerosis (ALS) cases. The expression of wild-type SOD1 [SOD(hWT)] surprisingly exacerbates the phenotype of mutant SOD1 in vivo. Here we studied whether SOD1(hWT) may affect mutant SOD1 aggregation by employing fluorescence microscopy techniques combined with lifetime-based Förster resonance energy transfer (FRET). Only a very minor fraction of SOD1(hWT) was observed in aggregates induced by mutant SOD1(G37R), SOD1(G85R) or SOD1(G93C). Quite in contrast, co-expression of SOD(hWT) reduced the amount of mutant SOD1 in the aggregate fraction. Furthermore, we did not detect endogenous mouse SOD1 in aggregates formed by mutant SOD1 in two distinct mutant SOD1 mouse lines. The hypothesis that SOD1(WT) is able to keep mutant SOD1 variants in a soluble state is supported by the increased presence of heterodimers upon SOD1(hWT) co-expression. Therefore we propose that SOD1(WT) contributes to disease by heterodimerization with mutant SOD1 forms.

Unloading kinesin transported cargoes from the tubulin track via the inflammatory c-Jun N-terminal kinase pathway.

Axonal transport of mitochondria and synaptic vesicle precursors via kinesin motor proteins is essential to keep integrity of axons and synapses. Disturbance of axonal transport is an early sign of neuroinflammatory and neurodegenerative diseases. Treatment of cultured neurons by the inflammatory cytokine tumor necrosis factor-alpha (TNF) stimulated phosphorylation of c-Jun N-terminal kinase (JNK) in neurites. TNF treatment induced dissociation of the heavy chain kinesin family-5B (KIF5B) protein from tubulin in axons but not cell bodies as determined by lifetime-based Förster resonance energy transfer (FRET) analysis. Dissociation of KIF5B from tubulin after TNF treatment was dependent on JNK activity. Furthermore, TNF inhibited axonal transport of mitochondria and synaptophysin by reducing the mobile fraction via JNK. Thus, TNF produced by activated glial cells in inflammatory or degenerative neurological diseases acts on neurites by acting on the kinesin-tubulin complex and inhibits axonal mitochondria and synaptophysin transport via JNK.

Deletion of BGL2 results in an increased chitin level in the cell wall of Saccharomyces cerevisiae.

It is shown that the deletion of BGL2 gene leads to increase in chitin content in the cell wall of Saccharomyces cerevisiae. A part of the additional chitin can be removed from the bgl2Delta cell wall by alkali or trypsin treatment. Chitin synthase 1 (Chs1) activity was increased by 60 % in bgl2Delta mutant. No increase in chitin synthase 3 (Chs3) activity in bgl2Delta cells was observed, while they became more sensitive to Nikkomycin Z. The chitin level in the cell walls of a strain lacking both BGL2 and CHS3 genes was higher than that in chs3Delta and lower than that in bgl2Delta strains. Together these data indicate that the deletion of BGL2 results in the accumulation and abnormal incorporation of chitin into the cell wall of S. cerevisiae, and both Chs1 and Chs3 take part in a response to BGL2 deletion in S. cerevisiae cells.