Previous analyses of gene expression in a mouse model of Huntington's disease (R6/2) indicated that an N-terminal fragment of mutant huntingtin causes downregulation of striatal signaling genes and particularly those normally induced by cAMP and retinoic acid. The present study expands the regional and temporal scope of this previous work by assessing whether similar changes occur in other brain regions affected in Huntington's disease and other polyglutamine diseases and by discerning whether gene expression changes precede the appearance of disease signs. Oligonucleotide microarrays were employed to survey the expression of approximately 11,000 mRNAs in the cerebral cortex, cerebellum and striatum of symptomatic R6/2 mice. The number and nature of gene expression changes were similar among these three regions, influenced as expected by regional differences in baseline gene expression. Time-course studies revealed that mRNA changes could only reliably be detected after 4 weeks of age, coincident with development of early pathologic and behavioral changes in these animals. In addition, we discovered that skeletal muscle is also a target of polyglutamine-related perturbations in gene expression, showing changes in mRNAs that are dysregulated in brain and also muscle-specific mRNAs. The complete dataset is available at www.neumetrix.info.

Inflammation is a significant component of chronic neurodegenerative diseases. Cyclooxygenase-2 (COX-2) is expressed in activated microglial cells and appears to be an important source of prostaglandins during inflammatory conditions. To investigate the effect of curcumin on COX-2 gene expression in microglial cells, we treated lipopolysaccharide (LPS)-challenged BV2 microglial cells with various concentrations of curcumin. Curcumin significantly inhibited LPS-mediated induction of COX-2 expression in both mRNA and protein levels in a concentration-dependent manner. COX-2 enzyme activity was also inhibited in accordance with mRNA and protein levels. Furthermore, curcumin markedly inhibited LPS-induced nuclear factor kB (NF-kB) and activator protein 1 (AP-1) DNA bindings. These data suggest that curcumin suppresses LPS-induced COX-2 gene expression by inhibiting NF-k B and AP-1 DNA bindings in BV2 microglial cells.

To quantitatively measure tau aggregation in situ, we established a cell model system using a split green fluorescence protein (GFP) complementation assay. In this assay the more aggregated the protein of interest the lower the GFP fluorescence. Tau microtubule-binding domain constructs, whose aggregation characteristics have been described previously (Khlistunova et al. 2006), were used to validate the assay. The aggregation-prone construct exhibited the lowest GFP intensity whereas the aggregation-resistant construct showed the highest GFP intensity. To examine the role of glycogen synthase kinase 3b (GSK3b) activity and caspase 3 cleavage on tau aggregation, GFP complementation of full length (T4), caspase-cleaved (T4C3), and pseudophosphorylated at S396/S404 (T4-2EC) tau was examined in the presence of an active or a kinase-dead GSK3b. Extensive phosphorylation of T4 by GSK3b resulted in increased GFP intensity. T4C3 showed neither efficient phosphorylation nor a significant GFP intensity change by GSK3b. The GFP intensity of T4-2EC was significantly reduced by GSK3b accompanying its presence in the sarkosyl-insoluble fraction, thus demonstrating that T4-2EC was partitioning into aggregates. This indicates that if the majority of tau is phosphorylated at S396/S404, in combination with increased GSK3b activity, tau aggregation is favored. These data demonstrate that split GFP complementation may be a valuable approach to determine the aggregation process in living cells.