Yoo-Hun Suh

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder resulting in cognitive decline or dementia, the number of patients with AD is continuously increasing. Although a lot of great progress has been made in research and development of AD therapeutics, there is no fundamental cure for this disease yet. This study demonstrated the memory-improving effects of Cuban policosanol (PCO) in 5xFAD mice, which is an animal model of AD. Following 4-months of treatment with PCO in 5xFAD mice, we found that the number of amyloid plaques decreased in the brain compared to the vehicle-treated 5xFAD mice. Long-term PCO treatment in 5xFAD mice resulted in the reduction of gliosis and abnormal inflammatory cytokines level (interleukin [IL]-1β, IL-6, and tumor necrosis factor [TNF]-α) in the cortex and hippocampus. Levels of lipid peroxide (4-hydroxynonenal [4-HNE]) and superoxide dismutase (SOD1 and SOD2) levels were also recoverd in the brains of PCO-treated 5xFAD mice. Notably, PCO administration reduced memory deficits in the passive avoidance test, as well as synaptic loss (PSD-95, synaptophysin) in 5xFAD mice. Collectively, we identified the potential effects of PCO as a useful supplement to delay or prevent AD progression by inhibiting the formation of Aβ plaques in the brain.

We previously demonstrated that dehydroevodiamine•HCl (DHED), which was purified from Evodia rutaecarpa Bentham (Rutaceae), has beneficial effects on memory impairment and neuronal damage in three disease models. To investigate the preventive action of DHED in Alzheimer's disease (AD), a progressive neurodegenerative disorder characterized by memory decline, amyloid-β (Aβ) protein-containing neuritic plaques and neurofibrillary tangles, in this study, we proposed that DHED may be therapeutically effective against the memory impairment and disease-related neurochemical changes that occur in Tg2576 (Tg) mice. DHED (0.5 mg/kg) was intraperitoneally administered to 7-month-old Tg and wild type mice for 4 months. In passive avoidance and water maze tests, DHED improved memory impairment of Tg mice after 4 months of administration. DHED also reduced cortical levels of soluble Aβ40, soluble Aβ42 and total Aβ peptides in the Tg mice. Additionally, we investigated whether DHED may be a β-secretase inhibitor that affects the production of Aβ related to the formation of neuritic plaques. DHED directly inhibited β-secretase activity in a concentrationdependent manner. The concentration required for 50 % enzyme inhibition (IC50) was 40.96 μM, and DHED may act as a competitive inhibitor of β-secretase. Moreover, DHED interacted strongly with BACE1 (β-secretase 2QP8), as demonstrated in the analysis of the binding mode of DHED in the active site of human BACE1. In conclusion, DHED may exhibit therapeutic effects for AD as a β-secretase inhibitor.

Neuregulin-1 (NRG-1) is a ligand of the epidermal growth factor receptor (erbB), and its interaction involves activation of the glutamatergic N-methyl-Daspartate receptor, which increases the expression of the β2 subunit of the γ- aminobutyric acid receptor and subunits of the nicotinic acetylcholine receptor. In the dentate gyrus of 14-month-old Tg2576 mice, NRG-1 was strongly expressed compared with age-matched controls. The supernatant of oligomeric amyloid β peptide (Aβ42)-treated glial cells enhanced the Aβ42;-induced cytotoxic effects, but the expression of Fas ligand and tumor necrosis factor-related apoptosis-inducing ligand in microglial cells was not changed upon cytotoxic treatment. This suggests that the oligomeric form of Aβ42 toxicity is not related to apoptosis, which is mediated by cell-to-cell interaction. During the 24-h incubation, the secretion of the soluble form of NRG-1 was increased, but interleukin 6 secretion was not changed. Further, soluble NRG-1 increased Aβ42-induced toxicity. In conclusion, soluble NRG-1 significantly enhanced oligomeric Aβ42-induced toxicity through the activation of endoplasmic reticulum stress by the increase of a phospho-translation initiation factor 2 alpha (p-eIF2α).

α‐Synuclein oligomers can induce neurotoxicity and are implicated in Parkinson's disease etiology and disease progression. Many studies have reported α‐synuclein oligomerization by dopamine (DA) and transition metal ions, but few studies provide insight into joint influences of DA and Cu²⁺. In this study, DA and Cu²⁺ were coadministered aerobically to measure α‐synuclein oligomerization under these conditions. In the presence of oxygen, DA induced α‐synuclein oligomerization in a dose‐dependent manner. Cu^+/2+ did not effect oligomerization in such a manner in the presence of DA. By electrophoresis, Cu²⁺ was found easily to induce oligomerization with DA. This implies that oligomerization invoked by DA is reversible in the presence of Cu²⁺, which appears to be mediated by noncovalent bond interactions. In the absence of oxygen, DA induced less oligomerization of α‐synuclein, whereas DA/Cu²⁺ induced aerobic‐level amounts of oligomers, suggesting that DA/Cu²⁺ induces oligomerization independent of oxygen concentration. Radical species were detected through electron paramagnetic resonance (EPR) spectroscopic analysis arising from coincubation of DA/Cu²⁺ with α‐synuclein. Redox reactions induced by DA/Cu²⁺ were observed in multimer regions of α‐synuclein oligomers through NBT assay. Cellular toxicity results confirm that, for normal and hypoxic conditions, copper or DA/Cu²⁺ can induce cell death, which may arise from copper redox chemistry. From these results, we propose that DA and DA/Cu²⁺ induce different mechanisms of α‐synuclein oligomerization, cross‐linking with noncovalent (or reversible covalent) bonding vs. likely radical‐mediated covalent modification.

The activities of CDK5 and p35 are thought to be important in the pathogenesis of neurodegenerative diseases, including Alzheimer’s disease (AD). We studied the effect of p35 deletion in Tg2576 mice, which is an AD animal model. To obtain the desired mice, we crossed p35^-/- with Tg2576 mice. The resulting p35^-/-/Tg2576 (KO/Tg) mice displayed higher mortality rates and exhibited impaired spatial learning and memory at 6 months of age. Using immunohistochemical and biochemical approaches, we observed a reduction in the expression of pre- and post-synaptic markers such as NMDAR1, synaptophysin and GluR1. In addition, the intensity of MAP-2-positive dendrites extending from neuronal cell bodies was significantly decreased in KO/Tg mice compared with KO/WT and WT/Tg mice. We also detected increased neuronal cell death in the hippocampus, along with thinned and collapsed morphological changes in the alveus region and a dramatic increase in the number of microglial cells. Microglial infiltration in the hippocampus could result in the increased secretion of the soluble high mobility group box-1 protein (HMGB-1). The secretion of HMGB-1 is increased by Aβ, and secretion of HMGB-1 promotes neuronal cell death. Moreover, we found that HMGB-1 secretion induced by Aβ in KO/Tg mice gave rise to ER-mediated cell death. In summary, during the stages of KO/Tg mice model, the microglial infiltration and secretion of soluble HMGB-1 were significantly increased in the hippocampus. These conditions promote neuronal death, synaptic destruction and behavioral deficits.

Background: S100A9 protein (myeloid-related protein MRP14, also referred to as calgranulin B) is a reliable marker of inflammation, an important proinflammatory factor of innate immunity and acts as an additional antimicrobial peptide in the innate immune system. Evidence indicates that S100A9 contributes to Alzheimer’s disease (AD) pathology, although the precise mechanisms are not clear.Methods: We were interested to study the mechanisms of S100A9 release upon Aβ1-42 stimulation, the potential roles of extracellular S100A9 depletion in Aβ-induced cytotoxicity, and the interaction with innate immune response in THP-1 monocytic cells that have been challenged with mostly Aβ1-42 monomers instead of oligomers. We used protein preparation, Ca²⁺influx fluorescence imaging, MTT assay, siRNA knockdown, colony forming units (CFUs) assay and western blotting techniques to perform our study.Results: Aβ1-42 monomers elicited a marked decrease of S100A9 release into the cell culture supernatant in a dose-dependent manner in human THP-1 monocytes. This reduction of S100A9 release was accompanied by an increase of intracellular Ca²⁺level. Aβ1-42-mediated decrease of S100A9 release was not associated with Aβ1-42-induced cytotoxicity as measured by MTT reduction assay. This observation was confirmed with the recombinant S100A9, which had little effect on Aβ1-42-induced cytotoxicity. Moreover, depletion of S100A9 with siRNA did not significantly evoke the cell toxicity. On the other hand, Aβ1-42-induced extracellular S100A9 depletion resulted in decreased antimicrobial activity of the culture supernatant after Aβ1-42 stimulation. Immunodepletion of S100A9 with anti-S100A9 also decreased the antimicrobial peptide activity of the vehicle treated culture supernatant. Consistently, the recombinant S100A9 clearly elicited the antimicrobial peptide activityin vitro,confirming the observed antimicrobial activity of S100A9 in the culture supernatant.Conclusion: Collectively, our findings suggest that the mostly monomeric form of Aβ1-42 negatively regulates the innate immune system by down-regulating the secretion of S100A9, which is likely a main mediator of antimicrobial activity in the conditioned media of human THP-1 monocytes.

Alzheimer’s disease (AD) is characterized by the accumulation of amyloid plaques and neurofibrillary tangles accompanied by cognitive dysfunction. The aim of the present study was to elucidate preventive and therapeutic potential of stem cells for AD. Among stem cells, autologous human adipose-derived stem cells (hASCs) elicit no immune rejection responses, tumorigenesis, or ethical problems. We found that intravenously transplanted hASCs passed through the BBB and migrated into the brain. The learning, memory and pathology in an AD mouse model (Tg2576) mice greatly improved for at least 4 months after intravenous injection of hASC. The number of amyloid plaques and Aβ levels decreased significantly in the brains of hASC-injected Tg mice compared to those of Tg-sham mice. Here, we first report that intravenously or intracerebrally transplanted hASCs significantly rescues memory deficit and neuropathology, in the brains of Tg mice by up-regulating IL-10 and VEGF and be a possible use for the prevention and treatment of AD.