Tomomichi Watanabe

FBL2 Regulates Amyloid Precursor Protein (APP) Metabolism by Promoting Ubiquitination-Dependent APP Degradation and Inhibition of APP Endocytosis

The ubiquitin–proteasome pathway is a major protein degradation pathway whose dysfunction is now widely accepted as a cause of neurodegenerative diseases, including Alzheimers disease. Here we demonstrate that the F-box and leucine rich repeat protein2 (FBL2), a component of the E3 ubiquitin ligase complex, regulates amyloid precursor protein (APP) metabolism through APP ubiquitination. FBL2 overexpression decreased the amount of secreted amyloid β (Aβ) peptides and sAPPβ, whereas FBL2 mRNA knockdown by siRNA increased these levels. FBL2 overexpression also decreased the amount of intracellular Aβ in Neuro2a cells stably expressing APP with Swedish mutation. FBL2 bound with APP specifically at its C-terminal fragment (CTF), which promoted APP/CTF ubiquitination. FBL2 overexpression also accelerated APP proteasome-dependent degradation and decreased APP protein localization in lipid rafts by inhibiting endocytosis. These effects were not observed in an F-box-deleted FBL2 mutant that does not participate in the E3 ubiquitin ligase complex. Furthermore, a reduced insoluble Aβ and Aβ plaque burden was observed in the hippocampus of 7-month-old FBL2 transgenic mice crossed with double-transgenic mice harboring APPswe and PS1M146V transgenes. These findings indicate that FBL2 is a novel and dual regulator of APP metabolism through FBL2-dependent ubiquitination of APP.

Discovery of novel 5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-a]pyridine derivatives as γ-secretase modulators.

Novel 5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-a]pyridine derivatives were designed, synthesized, and evaluated as γ-secretase modulators (GSMs). An optimization study of this series resulted in the identification of (R)-11j, which showed a potent Aβ42-lowering effect, high bioavailability and good blood-brain barrier permeability in mice. Oral administration of (R)-11j significantly reduced brain Aβ42 in mice at a dose of 10 mg/kg.

Pharmacological properties of a novel and potent γ-secretase modulator as a therapeutic option for the treatment of Alzheimer’s disease

Previous studies of γ-secretase inhibitors (GSIs) and Notch-sparing GSIs have shown reduced amyloid-β (Aβ) peptide levels but increased Notch-related and -unrelated adverse effects. In this study, we examined the effects of compound-1 on Aβ processing and cognitive function and assessed Notch-related and -unrelated adverse effects. Compound-1 reduced Aβ40 and Aβ42 levels but inversely increased Aβ37 in Neuro2a cells, leading to no net changes in total Aβ levels, indicating that compound-1 is a γ-secretase modulator (GSM). In time-course experiments, compound-1 reduced Aβ40 and Aβ42 levels in tris-soluble fractions, with peak reduction at approximately 3h after oral administration in C57BL mice. Moreover, at >1mg/kg, compound-1 dose dependently reduced Aβ40 and Aβ42 levels in Tg2576 mice. Chronic treatment with compound-1 in Tg2576 mice for 4 months significantly reduced both soluble and insoluble Aβ42 levels and ameliorated cognitive impairments, even after drug withdrawal for 10 days following oral administration for 2 months. In contrast with compound-1, at 100-fold higher doses (100mg/kg), the GSI LY450139 decreased HES1 mRNA expression in thymus tissues and increased the intensity of periodic acid-Schiff (PAS)-positive areas in the intestine. Moreover, the Notch-sparing GSI BMS708163 led to amyloid precursor protein (APP)-β-C-terminal fragment accumulation in mouse primary neurons. BMS708163 significantly hampered cognitive function in normal mice 1 month after administration, whereas compound-1 significantly improved cognitive function. Taken together, the present novel and orally active GSM is a promising molecule for the treatment of pathologies associated with Aβ42 and Aβ40.

Neuronal Expression of F-Box and Leucine-Rich-Repeat Protein 2 Decreases over Braak Stages in the Brains of Alzheimer’s Disease Patients

Background: The dysfunction of protein degradation through the ubiquitin-proteasome system is now widely accepted as one of the causes of Alzheimer’s disease (AD), the pathological hallmarks of which are abnormal protein accumulation such as senile plaques and neurofibrillary tangles in the brain. Objective: To examine the expression of F-box and leucine-rich-repeat protein 2 (FBL2), a member of the ubiquitin-protein ligase complex expected to be involved in the ubiquitin-proteasome system. Methods and Results: We investigated the expression profile of FBL2 in the brains of AD patients by quantitative PCR and immunohistochemical analysis. In healthy subjects, the FBL2 mRNA level was very high in the brain when compared to other tissues. FBL2 immunoreactivities were detected in somata and dendrites in the neurons, but not detected in astrocytes or microglia. The FBL2 mRNA level decreased progressively in the brains of AD patients over Braak stages; this was more prominent in the temporal cortex (known to be a vulnerable region) than in the frontal cortex. Interestingly, the decrease was more severe in AD patients carrying the apolipoprotein E4 allele. The FBL2 IR also decreased over Braak stages, and was hardly detected at Braak stage 5 in both NeuN-positive and EAAC1-positive glutamatergic neurons. Conclusion: These results suggest that the involvement of the reduction of FBL2 level is related to AD progression.

Discovery of novel 5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-a]pyridine derivatives as γ-secretase modulators (Part 2).

γ-Secretase modulators (GSMs), which lower pathogenic amyloid beta (Aβ) without affecting the production of total Aβ or Notch signal, have emerged as a potential therapeutic agent for Alzheimers disease (AD). A novel series of 5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-a]pyridine derivatives was discovered and characterized as GSMs. Optimization of substituents at the 8-position of the core scaffold using ligand-lipophilicity efficiency (LLE) as a drug-likeness guideline led to identification of various types of high-LLE GSMs. Phenoxy compound (R)-17 exhibited especially high LLE as well as potent in vivo Aβ42-lowering effect by single administration. Furthermore, multiple oral administration of (R)-17 significantly reduced soluble and insoluble brain Aβ42, and ameliorated cognitive deficit in novel object recognition test (NORT) using Tg2576 mice as an AD model.

Design and synthesis of piperazine derivatives as a novel class of γ-secretase modulators that selectively lower Aβ42 production

Novel piperazine derivatives as γ-secretase modulators (GSMs) were prepared and tested for their ability to selectively lower Aβ₄₂ production. Lead compound 3, with selective Aβ₄₂-lowering activity, was modified by replacing its imidazolylphenyl moiety with an oxazolylphenyl moiety. Optimization of the urea group significantly improved mouse microsomal stability, while retaining both activity and selectivity. These efforts led to the successful identification of an orally available and brain-penetrant GSM, 6j, which selectively reduced brain Aβ₄₂ in mice.

Single administration of a novel γ-secretase modulator ameliorates cognitive dysfunction in aged C57BL/6J mice.

Mutations in presenilin 1 (PS1) and presenilin 2 (PS2) are known to cause early onset of Alzheimers disease (AD). These proteins comprise the catalytic domain of γ-secretase, which catalyzes the cleavage of β-amyloid (Aβ) from amyloid precursor protein (APP). In recent reports, PS1 and PS2 were linked to the modulation of intracellular calcium ion (Ca(2+)) dynamics, a key regulator of synaptic function. Ca(2+) dysregulation and synaptic dysfunction are leading hypothesis of cognitive dysfunctions during aging and AD progression. Accordingly, manipulations of presenilins by small molecules may have therapeutic potential for the treatment of cognitive dysfunction. In an accompanying report, we showed that chronic treatment with compound-1, a novel γ-secretase modulator (GSM), reduced Aβ production and ameliorated cognitive dysfunction in Tg2576 APP transgenic mice. Accordingly, in the present study we showed that single oral administration of compound-1 at 1 and 3mg/kg ameliorated cognitive dysfunction in aged non-transgenic mice. Moreover, compound-1 enhanced synaptic plasticity in hippocampal slices from aged C57BL/6J mice and increased messenger RNA (mRNA) expression of the immediate early gene c-fos, which has been shown to be related to synaptic plasticity in vivo. Finally, compound-1 modulated Ca(2+) signals through PS1 in mouse embryonic fibroblast cells. Taken together, compound-1 ameliorates both Aβ pathology and age-related cognitive dysfunctions. Hence, compound-1 may have potential as an early intervention for the cognitive declines that are commonly diagnosed in aged subjects, such as mild cognitive impairment (MCI) and prodromal AD.

Pharmacologic properties of compound-1, a novel and orally active γ-secretase modulator, as a therapeutic option for the treatment of Alzheimer's disease

compounds in which the anionic terminus interacted with the cationic “H” residues of Ab and the cationic terminus interacted with the anionic “E” residue of Ab were identified. Although the standard alpha amino acids showed no capacity to inhibit Ab aggregation, a number of atypical amino acids including b-alanine, 2aminoethanesulfonic acid, and L-phosphoserine demonstrated varying capacities to inhibit the oligomerization and aggregation of Ab. These predictions were verified using in vitro assays, including the kinetic Thioflavin T [ThT] aggregation assay, to demonstrate the capacity of these compounds to inhibit misfolding. Conclusions: Searching for an “endogenous anti-AD compound” represents an unexplored concept. Our in silico and in vitro studies suggest that compounds endogenous to the human brain, including several zwitterionic small molecules, can inhibit pathological protein misfolding of Ab. The value of a novel in silico screening assay to identify bioactive endogenous agents within brain has also been demonstrated.