Stepping closer to treating Alzheimer's disease patients with BACE1 inhibitor drugs.
ABSTRACT: Alzheimer's disease (AD) is the most common age-dependent neurodegenerative disease which impairs cognitive function and gradually causes patients to be unable to lead normal daily lives. While the etiology of AD remains an enigma, excessive accumulation of ?-amyloid peptide (A?) is widely believed to induce pathological changes and cause dementia in brains of AD patients. BACE1 was discovered to initiate the cleavage of amyloid precursor protein (APP) at the ?-secretase site. Only after this cleavage does ?-secretase further cleave the BACE1-cleaved C-terminal APP fragment to release A?. Hence, blocking BACE1 proteolytic activity will suppress A? generation. Due to the linkage of A? to the potential cause of AD, extensive discovery and development efforts have been directed towards potent BACE1 inhibitors for AD therapy. With the recent breakthrough in developing brain-penetrable BACE1 inhibitors, targeting amyloid deposition-mediated pathology for AD therapy has now become more practical. This review will summarize various strategies that have successfully led to the discovery of BACE1 drugs, such as MK8931, AZD-3293, JNJ-54861911, E2609 and CNP520. These drugs are currently in clinical trials and their updated states will be discussed. With the promise of reducing A? generation and deposition with no alarming safety concerns, the amyloid cascade hypothesis in AD therapy may finally become validated.
Project description:Amyloid-beta (Abeta) the primary component of the senile plaques found in Alzheimer's disease (AD) is generated by the rate-limiting cleavage of amyloid precursor protein (APP) by beta-secretase followed by gamma-secretase cleavage. Identification of the primary beta-secretase gene, BACE1, provides a unique opportunity to examine the role this unique aspartyl protease plays in altering Abeta metabolism and deposition that occurs in AD. The current experiments seek to examine how modulating beta-secretase expression and activity alters APP processing and Abeta metabolism in vivo. Genomic-based BACE1 transgenic mice were generated that overexpress human BACE1 mRNA and protein. The highest expressing BACE1 transgenic line was mated to transgenic mice containing human APP transgenes. Our biochemical and histochemical studies demonstrate that mice overexpressing both BACE1 and APP show specific alterations in APP processing and age-dependent Abeta deposition. We observed elevated levels of Abeta isoforms as well as significant increases of Abeta deposits in these double transgenic animals. In particular, the double transgenics exhibited a unique cortical deposition profile, which is consistent with a significant increase of BACE1 expression in the cortex relative to other brain regions. Elevated BACE1 expression coupled with increased deposition provides functional evidence for beta-secretase as a primary effector in regional amyloid deposition in the AD brain. Our studies demonstrate, for the first time, that modulation of BACE1 activity may play a significant role in AD pathogenesis in vivo.
Project description:Deposition of amyloid-? protein (A?) to form neuritic plaques is the characteristic neuropathology of Alzheimer's disease (AD). A? is generated from amyloid precursor protein (APP) by ?- and ?-secretase cleavages. BACE1 is the ?-secretase and its inhibition induces severe side effects, whereas its homolog BACE2 normally suppresses A? by cleaving APP/A? at the ?-site (Phe20) within the A? domain. Here, we report that BACE2 also processes APP at the ? site, and the juxtamembrane helix (JH) of APP inhibits its ?-secretase activity, enabling BACE2 to cleave nascent APP and aggravate AD symptoms. JH-disrupting mutations and clusterin binding to JH triggered BACE2-mediated ?-cleavage. Both BACE2 and clusterin were elevated in aged mouse brains, and enhanced ?-cleavage during aging. Therefore, BACE2 contributes to AD pathogenesis as a conditional ?-secretase and could be a preventive and therapeutic target for AD without the side effects of BACE1 inhibition.
Project description:Deposition of amyloid ? protein (A?) to form neuritic plaques in the brain is the pathological hallmark of Alzheimer's disease (AD). A? is generated from sequential cleavages of the ?-amyloid precursor protein (APP) by the ?- and ?-secretases, and ?-site APP-cleaving enzyme 1 (BACE1) is the ?-secretase essential for A? generation. Previous studies have indicated that glycogen synthase kinase 3 (GSK3) may play a role in APP processing by modulating ?-secretase activity, thereby facilitating A? production. There are two highly conserved isoforms of GSK3: GSK3? and GSK3?. We now report that specific inhibition of GSK3?, but not GSK3?, reduced BACE1-mediated cleavage of APP and A? production by decreasing BACE1 gene transcription and expression. The regulation of BACE1 gene expression by GSK3? was dependent on NF-?B signaling. Inhibition of GSK3 signaling markedly reduced A? deposition and neuritic plaque formation, and rescued memory deficits in the double transgenic AD model mice. These data provide evidence for regulation of BACE1 expression and AD pathogenesis by GSK3? and that inhibition of GSK3 signaling can reduce A? neuropathology and alleviate memory deficits in AD model mice. Our study suggests that interventions that specifically target the ?-isoform of GSK3 may be a safe and effective approach for treating AD.
Project description:The ?-site APP cleaving enzyme 1 (BACE1) is an important target for causing Alzheimer's disease (AD), due to the brain deposition peptide amyloid beta (A?) require cleavages of amyloid precursor protein (APP) by BACE1 and ?-secretase, but treatments of AD still have side effect in recent therapy. This study utilizes the world largest traditional Chinese medicine (TCM) database and database screening to provide potential BACE1 inhibited compound. Molecular dynamics (MD) simulation was carried out to observe the dynamics structure after ligand binding. We found that Triptofordin B1 has less toxicity than pyrimidine analogue, which has more potent binding affinity with BACE1. For trajectory analysis, all conformations are tending to be stable during 5000 ps simulation time. In dynamic protein validation, the residues of binding region are still stable after MD simulation. For snapshot comparison, we found that Triptofordin B1 could reduce the binding cavity; the results reveal that Triptofordin B1 could bind to BACE1 and better than control, which could be used as potential lead drug to design novel BACE1 inhibitor for AD therapy.
Project description:Amyloid plaques, composed of the amyloid beta-protein (Abeta), are hallmark neuropathological lesions in Alzheimer disease (AD) brain. Abeta fulfills a central role in AD pathogenesis, and reduction of Abeta levels should prove beneficial for AD treatment. Abeta generation is initiated by proteolysis of amyloid precursor protein (APP) by the beta-secretase enzyme BACE1. Bace1 knockout (Bace1(-/-)) mice have validated BACE1 as the authentic beta-secretase in vivo. BACE1 is essential for Abeta generation and represents a suitable drug target for AD therapy, especially because this enzyme is up-regulated in AD. However, although initial data indicated that Bace1(-/-) mice lack an overt phenotype, the BACE1-mediated processing of APP and other substrates may be important for specific biological processes. In this minireview, topics range from the initial identification of BACE1 to the fundamental knowledge gaps that remain in our understanding of this protease. We address pertinent questions such as putative causes of BACE1 elevation in AD and discuss why, nine years since the identification of BACE1, treatments that address the underlying pathological mechanisms of AD are still lacking.
Project description:?-Secretase, an age-dependent asparagine protease, cleaves both amyloid precursor protein (APP) and Tau and is required for amyloid plaque and neurofibrillary tangle pathologies in Alzheimer's disease (AD). However, whether ?-secretase activation is sufficient to trigger AD pathogenesis remains unknown. Here we show that the fragments of ?-secretase-cleavage, APP (586-695) and Tau(1-368), additively drive AD pathogenesis and cognitive dysfunctions. Tau(1-368) strongly augments BACE1 expression and A? generation in the presence of APP. The Tau(1-368) fragment is more robust than full-length Tau in binding active STAT1, a BACE1 transcription factor, and promotes its nuclear translocation, upregulating BACE1 and A? production. Notably, A?-activated SGK1 or JAK2 kinase phosphorylates STAT1 and induces its association with Tau(1-368). Inhibition of these kinases diminishes stimulatory effect of Tau(1-368). Knockout of STAT1 abolishes AD pathologies induced by ?-secretase-generated APP and Tau fragments. Thus, we show that Tau may not only be a downstream effector of A? in the amyloid hypothesis, but also act as a driving force for A?, when cleaved by ?-secretase.
Project description:As only symptomatic treatments are now available for Alzheimer's disease (AD), safe and effective mechanism-based therapies remain a great unmet need for patients with this neurodegenerative disease. Although gamma-secretase and BACE1 [beta-site beta-amyloid (Abeta) precursor protein (APP) cleaving enzyme 1] are well-recognized therapeutic targets for AD, untoward side effects associated with strong inhibition or reductions in amounts of these aspartyl proteases have raised concerns regarding their therapeutic potential. Although moderate decreases of either gamma-secretase or BACE1 are not associated with mechanism-based toxicities, they provide only modest benefits in reducing Abeta in the brains of APPswe/PS1DeltaE9 mice. Because the processing of APP to generate Abeta requires both gamma-secretase and BACE1, it is possible that moderate reductions of both enzymes would provide additive and significant protection against Abeta amyloidosis. Here, we test this hypothesis and assess the value of this novel anti-amyloid combination therapy in mutant mice. We demonstrate that genetic reductions of both BACE1 and gamma-secretase additively attenuate the amyloid burden and ameliorate cognitive deficits occurring in aged APPswe/PS1DeltaE9 animals. No evidence of mechanism-based toxicities was associated with such decreases in amounts of both enzymes. Thus, we propose that targeting both gamma-secretase and BACE1 may be an effective and safe treatment strategy for AD.
Project description:Toxic aggregated amyloid-? accumulation is a key pathogenic event in Alzheimer's disease (AD), which derives from amyloid precursor protein (APP) through sequential cleavage by BACE1 (?-site APP cleavage enzyme 1) and ?-secretase. Small interfering RNAs (siRNAs) show great promise for AD therapy by specific silencing of BACE1. However, lack of effective siRNA brain delivery approaches limits this strategy. Here, we developed a glycosylated "triple-interaction" stabilized polymeric siRNA nanomedicine (Gal-NP@siRNA) to target BACE1 in APP/PS1 transgenic AD mouse model. Gal-NP@siRNA exhibits superior blood stability and can efficiently penetrate the blood-brain barrier (BBB) via glycemia-controlled glucose transporter-1 (Glut1)-mediated transport, thereby ensuring that siRNAs decrease BACE1 expression and modify relative pathways. Noticeably, Gal-NP@siBACE1 administration restored the deterioration of cognitive capacity in AD mice without notable side effects. This "Trojan horse" strategy supports the utility of RNA interference therapy in neurodegenerative diseases.
Project description:The molecular mechanism underlying the pathogenesis of the majority of cases of sporadic Alzheimer's disease (AD) is unknown. A history of stroke was found to be associated with development of some AD cases, especially in the presence of vascular risk factors. Reduced cerebral perfusion is a common vascular component among AD risk factors, and hypoxia is a direct consequence of hypoperfusion. Previously we showed that expression of the beta-site beta-amyloid precursor protein (APP) cleavage enzyme 1 (BACE1) gene BACE1 is tightly controlled at both the transcriptional and translational levels and that increased BACE1 maturation contributes to the AD pathogenesis in Down's syndrome. Here we have identified a functional hypoxia-responsive element in the BACE1 gene promoter. Hypoxia up-regulated beta-secretase cleavage of APP and amyloid-beta protein (Abeta) production by increasing BACE1 gene transcription and expression both in vitro and in vivo. Hypoxia treatment markedly increased Abeta deposition and neuritic plaque formation and potentiated the memory deficit in Swedish mutant APP transgenic mice. Taken together, our results clearly demonstrate that hypoxia can facilitate AD pathogenesis, and they provide a molecular mechanism linking vascular factors to AD. Our study suggests that interventions to improve cerebral perfusion may benefit AD patients.
Project description:Amyloid-? (A?) peptide plays an essential role in the pathogenesis of Alzheimer's disease (AD) and is generated from amyloid-? precursor protein (APP) through sequential proteolytic cleavages by ?-site APP cleaving enzyme 1 (BACE1) and ?-secretase. Trafficking dysregulation of APP, BACE1, and ?-secretase may affect A? generation and disease pathogenesis. Sorting nexin 15 (SNX15) is known to regulate protein trafficking. Here, we report that SNX15 is abundantly expressed in mouse neurons and astrocytes. In addition, we show that although not affecting the protein levels of APP, BACE1, and ?-secretase components and the activity of BACE1 and ?-secretase, overexpression and downregulation of SNX15 reduce and promote A? production, respectively. Furthermore, we find that overexpression of SNX15 increases APP protein levels in cell surface through accelerating APP recycling, whereas downregulation of SNX15 has an opposite effect. Finally, we show that exogenous expression of human SNX15 in the hippocampal dentate gyrus by adeno-associated virus (AAV) infection can significantly reduce A? pathology in the hippocampus and improve short-term working memory in the APPswe/PSEN1dE9 double transgenic AD model mice. Together, our results suggest that SNX15 regulates the recycling of APP to cell surface and, thus, its processing for A? generation.