ABSTRACT
Members of the cyclic-AMP response-element binding protein (CREB) transcription factor family regulate the expression of genes needed for long-term memory formation. Loss of Notch impairs long-term, but not short-term, memory in flies and mammals. We investigated if the Notch-1 (N1) exerts an effect on CREB-dependent gene transcription. We observed that N1 inhibits CREB mediated activation of cyclic-AMP response element (CRE) containing promoters in a γ-secretase-dependent manner. We went on to find that the γ-cleaved N1 intracellular domain (N1ICD) sequesters nuclear CREB1α, inhibits cAMP/PKA-mediated neurite outgrowth and represses the expression of specific CREB regulated genes associated with learning and memory in primary cortical neurons. Similar transcriptional effects were observed with the N2ICD, N3ICD and N4ICDs. Together, these observations indicate that the effects of Notch on learning and memory are, at least in part, via an effect on CREB-regulated gene expression.
Subject(s)
Cyclic AMP Response Element-Binding Protein/metabolism , Receptor, Notch1/metabolism , Amyloid Precursor Protein Secretases/metabolism , Animals , Cells, Cultured , Colforsin/pharmacology , Cyclic AMP/pharmacology , Cyclic AMP Response Element-Binding Protein/genetics , Cyclic AMP-Dependent Protein Kinases/metabolism , Embryo, Mammalian/cytology , Embryo, Mammalian/drug effects , Embryo, Mammalian/metabolism , Female , HEK293 Cells , Humans , Memory, Long-Term/physiology , Mice , Mice, Inbred C57BL , Neurites/physiology , Neurons/cytology , Neurons/metabolism , Protein Isoforms/chemistry , Protein Isoforms/genetics , Protein Isoforms/metabolism , Protein Structure, Tertiary , Rats , Receptor, Notch1/chemistry , Receptor, Notch1/genetics , Transcription, Genetic/drug effectsABSTRACT
Diagnosis of the progressive neurodegenerative disorder Alzheimer's disease (AD) can only definitively be made postmortem. The most promising AD biomarkers identified to date are found in cerebrospinal fluid (CSF). Among these, one of the most interesting candidates is transthyretin (TTR), the carrier of thyroxine and retinol, which also binds with amyloid-ß (Aß), and it has been suggested that it protects against Aß deposition. A biomarker detectable in plasma would have great diagnostic value and could be of use for determining disease progression and the monitoring of therapeutic efficacy due to its greater accessibility over CSF-based markers. We aimed to validate TTR as a prognostic marker in AD and to determine its relation with cognitive measures. We examined the plasma protein levels of TTR in 90 people with late-onset AD and 50 age-matched non-demented controls (NDC) by immunoblotting and found lower plasma TTR levels in AD compared to NDC (p = 0.004). We then quantified plasma TTR by enzyme-linked immunosorbent assays in a larger independent cohort (n = 270) including subjects with mild to severe AD. Plasma TTR levels were significantly lower in AD cases with rapid cognitive decline and with severe cognitive impairment. Regression analyses showed plasma TTR levels also predicted cognitive decline over the ensuing 6 months. These data indicate that plasma TTR is a strong candidate AD biomarker that should be included in the development of blood based biomarker panels for disease diagnosis and also suggests that plasma TTR is a marker of disease severity and progression.
Subject(s)
Alzheimer Disease/blood , Prealbumin/metabolism , Aged , Aged, 80 and over , Alzheimer Disease/complications , Alzheimer Disease/genetics , Apolipoproteins E , Biomarkers/blood , Case-Control Studies , Cognition Disorders/blood , Cognition Disorders/etiology , Cognition Disorders/genetics , Enzyme-Linked Immunosorbent Assay , Female , Follow-Up Studies , Humans , Linear Models , Male , Mental Status Schedule , White PeopleABSTRACT
BACKGROUND: Impaired insulin signalling is increasingly thought to contribute to Alzheimer's disease (AD). The ε4 isoform of the APOE gene is the greatest genetic risk factor for sporadic, late onset AD, and is also associated with risk for type 2 diabetes mellitus (T2DM). Neuropathological studies reported the highest number of AD lesions in brain tissue of ε4 diabetic patients. However other studies assessing AD pathology amongst the diabetic population have produced conflicting reports and have failed to show an increase in AD-related pathology in diabetic brain. The thiazolidinediones (TZDs), peroxisome proliferator-activated receptor gamma agonists, are peripheral insulin sensitisers used to treat T2DM. The TZD, pioglitazone, improved memory and cognitive functions in mild to moderate AD patients. Since it is not yet clear how apoE isoforms influence the development of T2DM and its progression to AD, we investigated amyloid beta and tau pathology in APOE knockout mice, carrying human APOEε3 or ε4 transgenes after diet-induced insulin resistance with and without pioglitazone treatment. METHODS: Male APOE knockout, APOEε3-transgenic and APOEε4-transgenic mice, together with background strain C57BL6 mice were kept on a high fat diet (HFD) or low fat diet (LFD) for 32 weeks, or were all fed HFD for 32 weeks and during the final 3 weeks animals were treated with pioglitazone or vehicle. RESULTS: All HFD animals developed hyperglycaemia with elevated plasma insulin. Tau phosphorylation was reduced at 3 epitopes (Ser396, Ser202/Thr205 and Thr231) in all HFD, compared to LFD, animals independent of APOE genotype. The introduction of pioglitazone to HFD animals led to a significant reduction in tau phosphorylation at the Ser202/Thr205 epitope in APOEε3 animals only. We found no changes in APP processing however the levels of soluble amyloid beta 40 was reduced in APOE knockout animals treated with pioglitazone.
