Dynamics of Aß42 reduction in plasma, CSF and brain of rats treated with the γ-secretase modulator, GSM-10h.

BACKGROUND: Allosteric modulation of γ-secretase is an attractive therapeutic approach for the treatment of Alzheimer's disease. We recently identified a novel γ-secretase modulator, GSM-10h, which effectively lowers Aß42 production in cells and in amyloid precursor protein transgenic mice. OBJECTIVE: Here, we describe the in vivo characterization of GSM-10h in a model of endogenous Aß production. METHODS: Rats were administered orally with GSM-10h, and the effect on Aß levels in peripheral and central compartments was determined. In addition, the effect of GSM-10h on Notch processing was assessed. RESULTS: Acute administration of GSM-10h to rats causes a dose-dependent decrease in the level of Aß42 in plasma, CSF and brain, with little effect on the level of Aß40 in these compartments. The magnitude of Aß42 lowering in the CSF and brain was further enhanced upon sub-chronic administration of GSM-10h. No deleterious effect on Notch processing was evident in either of these studies. To further explore the dynamics of Aß42 reduction in peripheral and CNS compartments, a time course study was conducted. In all compartments, the decrease in Aß42 was greatest at 6 h after administration of GSM-10h. This decrease in Aß42 was maintained for 9-15 h, after which time Aß42 levels returned to baseline levels. Encouragingly, no rebound in Aß42 levels beyond baseline levels was observed. CONCLUSIONS: These findings support the γ-secretase modulator profile of GSM-10h, and highlight the utility of the rat for assessing the pre-clinical efficacy of γ-secretase modulators.

TASTPM mice expressing amyloid precursor protein and presenilin-1 mutant transgenes are sensitive to γ-secretase modulation and amyloid-ß42 lowering by GSM-10h.

BACKGROUND: Cleavage of the amyloid precursor protein (APP) by ß-site APP-cleaving enzyme and γ-secretase results in the generation of amyloid-ß (Aß) peptides that aggregate and deposit as senile plaques in brains of Alzheimer disease patients. Due to the fundamental role γ-secretase plays in the proteolysis of a number of proteins including Notch, pharmacological inhibition of γ-secretase has been associated with mechanism-based toxicities. Therefore, efforts have focussed on the modulation of γ-secretase activity to selectively decrease levels of Aß42 peptide while avoiding deleterious activity on Notch processing. OBJECTIVE: Here, we describe the in vitro and in vivo characterisation of a novel γ-secretase modulator, GSM-10h, and investigate the potential for shorter Aß peptides to induce neurotoxicity in rat primary cortical neurons. METHODS: The effect of GSM-10h on Aß levels was investigated in SH-SY5Y cells expressing mutant APP and in TASTPM mice expressing APP and presenilin-1 mutant transgenes. The effect of GSM-10h on Notch processing was also determined. RESULTS: In cells, GSM-10h decreased levels of Aß42 while concomitantly increasing levels of Aß38 in the absence of effects on Aß40 levels. In TASTPM mice, GSM-10h effectively lowered brain Aß42 and increased brain Aß38, with no effect on Notch signalling. Unlike Aß42, which causes neuronal cell death, neither Aß37 nor Aß38 were neurotoxic. CONCLUSIONS: These findings confirm GSM-10h exhibits the profile of a γ-secretase modulator. In addition, TASTPM mice are shown to be responsive to treatment with a γ-secretase modulator, thereby highlighting the utility of this bitransgenic mouse model in drug discovery efforts focussed on the development of γ-secretase modulators.

Development of an autocrine neuregulin signaling loop with malignant transformation of human breast epithelial cells.

Neuregulin (NRG) is a heparin-binding factor that activates members of the epidermal growth factor family of tyrosine kinase receptors including erbB2 that is overexpressed in more aggressive types of breast cancer. The exact role that NRG plays in breast cancer is complicated by the fact that NRG has been shown to have both proliferative and antiproliferative effects, depending on the breast cancer cell line used. Using an isogenic series of breast epithelial cell lines (MCF10A) ranging from benign to malignant, we found that the actions of NRG changed from antiproliferative to proliferative as the cells progress to cancer. This correlated with a progressive inability of NRG to down-regulate a group of proliferation genes identified previously using cDNA microarrays. As the cells progress to malignancy, they expressed higher levels of erbB2 and lower levels of erbB3 and secreted high levels of NRG into the culture media, resulting in high basal levels of erbB receptor phosphorylation. Disruption of this autocrine signaling loop by blocking ligand-induced receptor activation inhibited cancer cell proliferation. These results demonstrate that the transition of MCF10A cells from normal to premalignant to malignant correlates with the development of a constitutively active autocrine NRG signaling loop that promotes cell proliferation and suggest that disrupting this autocrine loop may provide an important therapeutic measure to control breast cancer cell growth.

Accuracy of cDNA microarray methods to detect small gene expression changes induced by neuregulin on breast epithelial cells.

BACKGROUND: cDNA microarrays are a powerful means to screen for biologically relevant gene expression changes, but are often limited by their ability to detect small changes accurately due to "noise" from random and systematic errors. While experimental designs and statistical analysis methods have been proposed to reduce these errors, few studies have tested their accuracy and ability to identify small, but biologically important, changes. Here, we have compared two cDNA microarray experimental design methods with northern blot confirmation to reveal changes in gene expression that could contribute to the early antiproliferative effects of neuregulin on MCF10AT human breast epithelial cells. RESULTS: We performed parallel experiments on identical samples using a dye-swap design with ANOVA and an experimental design that excludes systematic biases by "correcting" experimental/control hybridization ratios with control/control hybridizations on a spot-by-spot basis. We refer to this approach as the "control correction method" (CCM). Using replicate arrays, we identified a decrease in proliferation genes and an increase in differentiation genes. Using an arbitrary cut-off of 1.7-fold and p values <0.05, we identified a total of 32 differentially expressed genes, 9 with the dye-swap method, 18 with the CCM, and 5 genes with both methods. 23 of these 32 genes were subsequently verified by northern blotting. Most of these were <2-fold changes. While the dye-swap method (using either ANOVA or Bayesian analysis) detected a smaller number of genes (14-16) compared to the CCM (46), it was more accurate (89-92% vs. 75%). Compared to the northern blot results, for most genes, the microarray results underestimated the fold change, implicating the importance of detecting these small changes. CONCLUSIONS: We validated two experimental design paradigms for cDNA microarray experiments capable of detecting small (<2-fold) changes in gene expression with excellent fidelity that revealed potentially important genes associated with the anti-proliferative effects of neuregulin on MCF10AT breast epithelial cells.

A behavioural characterisation of the FVB/N mouse strain.

The use of transgenic models in scientific research has made an enormous contribution to our understanding of the causes and symptoms of many diseases, including neurodegenerative conditions such as Alzheimer's Disease (AD) and Parkinson's Disease (PD). In the creation of transgenic models of neurodegenerative disease, effects of the background strain of the animal on the resulting genotype must be taken into consideration. This is particularly true for behavioural studies in which the background strain of the mouse may mask the phenotype of the genetic manipulation. Here, the behaviour of two mouse strains used in transgenic models, FVB/N and C57BL6/J, were compared. Studies of circadian wheel activity, cognition and aggression revealed considerable phenotypic differences between strains. These data also indicate that the FVB/N strain is not appropriate as a background strain in the behavioural assessment of transgenic mouse models.

A common pattern of persistent gene activation in human neocortical epileptic foci.

Epilepsy is a disease of recurrent seizures that can develop after a wide range of brain insults. Although surgical resection of focal regions of seizure onset can result in clinical improvement, the molecular mechanisms that produce and maintain focal hyperexcitability are not understood. Here, we demonstrate a regional, persistent induction of a common group of genes in human epileptic neocortex in 17 patients with neocortical epilepsy, regardless of the underlying pathology. This relatively small group of common genes, identified using complementary DNA microarrays and confirmed with quantitative reverse transcription polymerase chain reaction and immunostaining, include the immediate early gene transcription factors EGR-1, EGR-2, and c-fos, with roles in learning and memory, and signaling genes such as the dual-specificity kinase/phosphatase MKP-3. Maximal expression of these genes was observed in neurons in neocortical layers II through IV. These neurons also showed persistent cyclic adenosine monophosphate response element binding protein (CREB) activation and nuclear translocation of EGR-2 and c-fos proteins. In two patients, local interictal epileptiform discharge frequencies correlated precisely with the expression of these genes, suggesting that these genes either are directly modulated by the degree of epileptic activity or help sustain ongoing epileptic activity. The identification of a common set of genes and the persistent activation of CREB signaling in human epileptic foci provide a clinically relevant set of biological markers with potential importance for developing future diagnostic and therapeutic options in human epilepsy.