Jong-Sung Park

Alzheimer’s disease and Notch signaling

Cleavage of the amyloid precursor protein (APP) by gamma-secretase generates a neurotoxic amyloid beta-peptide (Abeta) that is thought to be associated with the neurodegeneration observed in Alzheimers disease (AD) patients. Presenilin is the catalytic member of the gamma-secretase proteolytic complex and mutations in presenilins are the major cause of early-onset familial Alzheimers disease. In addition to APP, gamma-secretase substrates include Notch1 homologues, Notch ligands Delta and Jagged, and additional type I membrane proteins, raising concerns about mechanism-based toxicities that might arise as a consequence of inhibiting gamma-secretase. Notch signaling is involved in tumorigenesis as well as in determining the fates of neural and nonneural cells during development and in adults. Alterations in proteolysis of the Notch by gamma-secretase could be involved in the pathogenesis of AD. Inconsistently, several recent observations have indicated that enhanced Notch signaling and expression could be instrumental in neurodegeneration in AD. Therefore, detailed and precise study of Notch signaling in AD is important for elucidating diverse mechanisms of pathogenesis and potentially for treating and preventing Alzheimers disease.

Evidence that γ-secretase mediates oxidative stress-induced β-secretase expression in Alzheimer's disease

Beta-secretase (BACE1), an enzyme responsible for the production of amyloid beta-peptide (Abeta), is increased by oxidative stress and is elevated in the brains of patients with sporadic Alzheimers disease (AD). Here, we show that oxidative stress fails to induce BACE1 expression in presenilin-1 (gamma-secretase)-deficient cells and in normal cells treated with gamma-secretase inhibitors. Oxidative stress-induced beta-secretase activity and sAPPbeta levels were suppressed by gamma-secretase inhibitors. Levels of gamma- and beta-secretase activities were greater in brain tissue samples from AD patients compared to non-demented control subjects, and the elevated BACE1 level in the brains of 3xTgAD mice was reduced by treatment with a gamma-secretase inhibitor. Our findings suggest that gamma-secretase mediates oxidative stress-induced expression of BACE1 resulting in excessive Abeta production in AD.

Evidence that γ-Secretase-Mediated Notch Signaling Induces Neuronal Cell Death via the Nuclear Factor-κB-Bcl-2-Interacting Mediator of Cell Death Pathway in Ischemic Stroke

Notch-1 (Notch) is a cell surface receptor that regulates cell-fate decisions in the developing nervous system, and it may also have roles in synaptic plasticity in the adult brain. Binding of its ligands results in the proteolytic cleavage of Notch by the γ-secretase enzyme complex, thereby causing the release of a Notch intracellular domain (NICD) that translocates to the nucleus, in which it regulates transcription. Here we show that activation of Notch modulates ischemic neuronal cell death in vitro and in vivo. Specifically, our findings from the use of Notch-1 siRNA or the overexpression of NICD indicate that Notch activation contributes to cell death. Using modified NICD, we demonstrate an apoptosis-inducing function of NICD in both the nucleus and the cytosol. NICD transfection-induced cell death was reduced by blockade of calcium signaling, caspase activation, and Janus kinase signaling. Inhibition of the Notch-activating enzyme, γ-secretase, protected against ischemic neuronal cell death by targeting an apoptotic protease, cleaved caspase-3, nuclear factor-κB (NF-κB), and the pro-death BH3-only protein, Bcl-2-interacting mediator of cell death (Bim). Treatment of mice with a γ-secretase inhibitor, compound E, reduced infarct size and improved functional outcome in a model of focal ischemic stroke. Furthermore, γ-secretase inhibition reduced NICD, p-p65, and Bim levels in vivo. These findings suggest that Notch signaling endangers neurons after ischemic stroke by modulating the NF-κB, pro-death protein Bim, and caspase pathways.

Oxidative lipid modification of nicastrin enhances amyloidogenic γ-secretase activity in Alzheimer's disease.

The cause of elevated level of amyloid β‐peptide (Aβ42) in common late‐onset sporadic [Alzheimer’s disease (AD)] has not been established. Here, we show that the membrane lipid peroxidation product 4‐hydroxynonenal (HNE) is associated with amyloid and neurodegenerative pathologies in AD and that it enhances γ‐secretase activity and Aβ42 production in neurons. The γ‐secretase substrate receptor, nicastrin, was found to be modified by HNE in cultured neurons and in brain specimens from patients with AD, in which HNE–nicastrin levels were found to be correlated with increased γ‐secretase activity and Aβ plaque burden. Furthermore, HNE modification of nicastrin enhanced its binding to the γ‐secretase substrate, amyloid precursor protein (APP) C99. In addition, the stimulation of γ‐secretase activity and Aβ42 production by HNE were blocked by an HNE‐scavenging histidine analog in a 3xTgAD mouse model of AD. These findings suggest a specific molecular mechanism by which oxidative stress increases Aβ42 production in AD and identify HNE as a novel therapeutic target upstream of the γ‐secretase cleavage of APP.

Inhibition of Notch signalling ameliorates experimental inflammatory arthritis

Objective To test the hypothesis that Notch signalling plays a role in the pathogenesis of rheumatoid arthritis (RA) and to determine whether pharmacological inhibition of Notch signalling with γ-secretase inhibitors can ameliorate the RA disease process in an animal model. Methods Collagen-induced arthritis was induced in C57BL/6 or Notch antisense transgenic mice by immunisation with chicken type II collagen (CII). C57BL/6 mice were administered with different doses of inhibitors of γ-secretase, an enzyme required for Notch activation, at disease onset or after onset of symptoms. Severity of arthritis was monitored by clinical and histological scores, and in vivo non-invasive near-infrared fluorescence (NIRF) images. Micro-CT was used to confirm joint destruction. The levels of CII antibodies and cytokines in serum were determined by ELISA and bead-based cytokine assay. The expression levels of cytokines were studied by quantitative PCR in rheumatoid synovial fibroblasts. Results The data show that Notch signalling stimulates synoviocytes and accelerates their production of proinflammatory cytokines and immune responses involving the upregulation of IgG1 and IgG2a. Pharmacological inhibition of γ-secretase and antisense-mediated knockdown of Notch attenuates the severity of inflammatory arthritis, including arthritis indices, paw thickness, tissue damage and neutrophil infiltration, and reduces the levels of active NF-κB, ICAM-1, proinflammatory cytokines and matrix metalloproteinase-3 activity in the mouse model of RA. Conclusions These results suggest that Notch is involved in the pathogenesis of RA and that inhibition of Notch signalling is a novel approach for treating RA.

Pin1 promotes neuronal death in stroke by stabilizing Notch intracellular domain

Stroke is a leading cause of mortality and disability. The peptidyl‐prolyl cis/trans isomerase Pin1 regulates factors involved in cell growth. Recent evidence has shown that Pin1 plays a major role in apoptosis. However, the role of Pin1 in ischemic stroke remains to be investigated.

Hyaluronan nanoparticles bearing γ-secretase inhibitor: in vivo therapeutic effects on rheumatoid arthritis.

γ-Secretase inhibitors which prevent Notch activation are emerging as potent therapeutics for various inflammatory diseases, including ischemic stroke and rheumatoid arthritis. However, their indiscriminate distribution in the body causes serious side effects after systemic administration, since Notch proteins are ubiquitous receptors that play an important role in cellular functions such as differentiation, proliferation, and apoptosis. In this study, hyaluronan nanoparticles (HA-NPs) bearing a γ-secretase inhibitor (DAPT) were prepared as potential therapeutics for rheumatoid arthritis. In vivo biodistribution of the DAPT-loaded HA-NPs (DNPs), labeled with near-infrared dye, were observed using a non-invasive optical imaging system after systemic administration to a collagen-induced arthritis (CIA) mouse model. The results demonstrated that DNPs were effectively accumulated at the inflamed joint of the CIA mice. From the in vivo therapeutic efficacy tests, DNPs (1mg DAPT/kg) significantly attenuated the severity of RA induction compared to DAPT alone (2mg/kg), which was judged from clinical scores, tissue damage, and neutrophil infiltration. In addition, DNPs dramatically reduced the production of pro-inflammatory cytokines (TNF-α, IFN-γ, MCP-1, and IL-6, -12, -17) and collagen-specific auto-antibodies (IgG1 and IgG2a) in the serum of the CIA mice. These results suggest that DNPs have potential as therapeutics for rheumatoid arthritis.

Selenium attenuates Aβ production and Aβ-induced neuronal death

The objective of the present study was to examine the role of selenium in the metabolism of A beta and in A beta-induced neuronal death. Selenium treatment significantly reduced A beta 40, A beta 42, and sAPP beta production by reducing A beta producing beta-secretase and gamma-secretase activities. The lipid peroxidation product 4-Hydroxynonenal (HNE)-induced transcription of beta-secretase (BACE1) was blocked by selenium. Finally, our data show that selenium protects against HNE and A beta-mediated toxicity in primary cultured neurons. The present study suggests that selenium may be able to salvage the neuronal degeneration of Alzheimers disease, thereby limiting beta-amyloid production and neuronal death.

Neuropep-1 ameliorates learning and memory deficits in an Alzheimer's disease mouse model, increases brain-derived neurotrophic factor expression in the brain, and causes reduction of amyloid beta plaques.

Alzheimers disease (AD) is a neurodegenerative disease characterized by amyloid beta (Aβ) deposits, hyperphosphorylated tau deposition, and cognitive dysfunction. Abnormalities in the expression of brain-derived neurotrophic factor (BDNF), which plays an important role in learning and memory formation, have been reported in the brains of AD patients. A BDNF modulating peptide (Neuropep-1) was previously identified by positional-scanning synthetic peptide combinatorial library. Here we examine the neuroprotective effects of Neuropep-1 on several inxa0vitro neurotoxic insults, and triple-transgenic AD mouse model (3xTg-AD). Neuropep-1 protects cultured neurons against oligomeric Aβ1-42, 1-methyl-4-phenylpyridinium, and glutamate-induced neuronal cell death. Neuropep-1 injection also significantly rescues the spatial learning and memory deficits of 3xTg-AD mice compared with vehicle-treated control group. Neuropep-1 treatment markedly increases hippocampal and cortical BDNF levels. Furthermore, we found that Neuropep-1-injected 3xTg-AD mice exhibit dramatically reduced Aβ plaque deposition and Aβ levels without affecting tau pathology. Neuropep-1 treatment does not alter the expression or activity of full-length amyloid precursor protein, α-, β-, or γ-secretase, but levels of insulin degrading enzyme, an Aβ degrading enzyme, were increased. These findings suggest Neuropep-1 may be a therapeutic candidate for the treatment of AD.

Secretases as therapeutic targets for Alzheimer's disease.

Accumulation of amyloid-β (Aβ) is widely accepted as the key instigator of Alzheimers disease (AD). The proposed mechanism is that accumulation of Aβ results in inflammatory responses, oxidative damages, neurofibrillary tangles and, subsequently, neuronal/synaptic dysfunction and neuronal loss. Given the critical role of Aβ in the disease process, the proteases that produce this peptide are obvious targets. The goal would be to develop drugs that can inhibit the activity of these targets. Protease inhibitors have proved very effective for treating other disorders such as AIDS and hypertension. Mutations in APP (amyloid-β precursor protein), which flanks the Aβ sequence, cause early-onset familial AD, and evidence has pointed to the APP-to-Aβ conversion as a possible therapeutic target. Therapies aimed at modifying Aβ-related processes aim higher up the cascade and are therefore more likely to be able to alter the progression of the disease. However, it is not yet fully known whether the increases in Aβ levels are merely a result of earlier events that were already causing the disease.