Justicidin A Reduces β-Amyloid via Inhibiting Endocytosis of β-Amyloid Precursor Protein

β-amyloid precursor protein (APP) can be cleaved by α-, and γ-secretase at plasma membrane producing soluble ectodomain fragment (sAPPα). Alternatively, following endocytosis, APP is cleaved by β-, and γ-secretase at early endosomes generating β-amyloid (Aβ), the main culprit in Alzheimer's disease (AD). Thus, APP endocytosis is critical for Aβ production. Recently, we reported that Monsonia angustifolia, the indigenous vegetables consumed in Tanzania, improved cognitive function and decreased Aβ production. In this study, we examined the underlying mechanism of justicidin A, the active compound of M. angustifolia, on Aβ production. We found that justicidin A reduced endocytosis of APP, increasing sAPPα level, while decreasing Aβ level in HeLa cells overexpressing human APP with the Swedish mutation. The effect of justicidin A on Aβ production was blocked by endocytosis inhibitors, indicating that the decreased APP endocytosis by justicidin A is the underlying mechanism. Thus, justicidin A, the active compound of M. angustifolia, may be a novel agent for AD treatment.

Activation of transient receptor potential melastatin 7 (TRPM7) channel increases basal autophagy and reduces amyloid β-peptide

Cerebral accumulation of amyloid β-peptide (Aβ), which is produced from amyloid precursor protein (APP), is the primary cause of Alzheimer's disease (AD). Autophagy recycles cellular components and digests intracellular components including Aβ. The Ca²⁺- and Mg²⁺-permeable transient receptor potential melastatin 7 (TRPM7) channel underlies the constitutive Ca²⁺ influx in some cells. Since we already reported that TRPM7 channel-mediated Ca²⁺ influx regulates basal autophagy, we hypothesize that the activation of TRPM7 channel could increase basal autophagy and consequently decrease Aβ. In this study, we showed that naltriben (NTB), a specific TRPM7 channel activator, induced Ca²⁺ influx and activated autophagic signaling in neuroblastoma SH-SY5Y cells. NTB also promoted co-localization of LC3 and APP, and reduced Aβ. Furthermore, we found that an early-onset familial AD-associated presenilin1 ΔE9 (PS1 ΔE9) mutant cells had attenuated basal autophagy. NTB was able to recover autophagy and decrease Aβ in PS1 ΔE9 cells. Our results show that the activating TRPM7 channel may prevent AD-related Aβ neuropathology via modulating Ca²⁺-regulated basal autophagy.

O-GlcNAcylation promotes non-amyloidogenic processing of amyloid-β protein precursor via inhibition of endocytosis from the plasma membrane

Amyloid-β protein precursor (AβPP) is transported to the plasma membrane, where it is sequentially cleaved by α-secretase and γ-secretase. This is called non-amyloidogenic pathway since it precludes the production of amyloid-β (Aβ), the main culprit of Alzheimer's disease (AD). Alternatively, once AβPP undergoes clathrin-dependent endocytosis, it can be sequentially cleaved by β-secretase and γ-secretase at endosomes, producing Aβ (amyloidogenic pathway). β-N-acetylglucosamine (GlcNAc) can be attached to serine/threonine residues of the target proteins. This novel type of O-linked glycosylation is called O-GlcNAcylation mediated by O-GlcNAc transferase (OGT). The removal of GlcNAc is mediated by O-GlcNAcase (OGN). Recently, it is shown that O-GlcNAcylation of AβPP increases the non-amyloidogenic pathway. To investigate the regulatory role for O-GlcNAcylation in AβPP processing, we first tested the effects of inhibitor for OGN, PUGNAc, on AβPP metabolism in HeLa cells stably transfected with Swedish mutant form of AβPP. Increasing O-GlcNAcylated AβPP level increased α-secretase product while decreased β-secretase products. We found that PUGNAc increased the trafficking rate of AβPP from the trans-Golgi network to the plasma membrane, and selectively decreased the endocytosis rate of AβPP. These events may contribute to the increased AβPP level in the plasma membrane by PUGNAc. Inhibiting clathrin-dependent endocytosis prevented the effect of PUGNAc on Aβ, suggesting that the effect of PUGNAc was mainly mediated by decreasing AβPP endocytosis. These results strongly indicate that O-GlcNAcylation promotes the plasma membrane localization of AβPP, which enhances the non-amyloidogenic processing of AβPP. Thus, O-GlcNAcylation of AβPP can be a potential therapeutic strategy for AD.

Cholesterol regulates HERG K+ channel activation by increasing phospholipase C β1 expression

Human ether-a-go-go-related gene (HERG) K(+) channel underlies the rapidly activating delayed rectifier K(+) conductance (IKr) during normal cardiac repolarization. Also, it may regulate excitability in many neuronal cells. Recently, we showed that enrichment of cell membrane with cholesterol inhibits HERG channels by reducing the levels of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] due to the activation of phospholipase C (PLC). In this study, we further explored the effect of cholesterol enrichment on HERG channel kinetics. When membrane cholesterol level was mildly increased in human embryonic kidney (HEK) 293 cells expressing HERG channel, the inactivation and deactivation kinetics of HERG current were not affected, but the activation rate was significantly decelerated at all voltages tested. The application of PtdIns(4,5)P2 or inhibitor for PLC prevented the effect of cholesterol enrichment, while the presence of antibody against PtdIns(4,5)P2 in pipette solution mimicked the effect of cholesterol enrichment. These results indicate that the effect of cholesterol enrichment on HERG channel is due to the depletion of PtdIns(4,5)P2. We also found that cholesterol enrichment significantly increases the expression of β1 and β3 isoforms of PLC (PLCβ1, PLCβ3) in the membrane. Since the effects of cholesterol enrichment on HERG channel were prevented by inhibiting transcription or by inhibiting PLCβ1 expression, we conclude that increased PLCβ1 expression leads to the deceleration of HERG channel activation rate via downregulation of PtdIns(4,5)P2. These results confirm a crosstalk between two plasma membrane-enriched lipids, cholesterol and PtdIns(4,5)P2, in the regulation of HERG channels.

Increasing Membrane Cholesterol Level Increases the Amyloidogenic Peptide by Enhancing the Expression of Phospholipase C

Cerebral elevation of 42-residue amyloid β-peptide (Aβ42) triggers neuronal dysfunction in Alzheimer's disease (AD). Even though a number of cholesterol modulating agents have been shown to affect Aβ generation, the role of cholesterol in the pathogenesis of AD is not clear yet. Recently, we have shown that increased membrane cholesterol levels downregulates phosphatidylinositol 4,5-bisphosphate (PIP2) via activation of phospholipase C (PLC). In this study, we tested whether membrane cholesterol levels may affect the Aβ42 production via changing PIP2 levels. Increasing membrane cholesterol levels decreased PIP2 and increased secreted Aβ42. Supplying PIP2, by using a PIP2-carrier system, blocked the effect of cholesterol on Aβ42. We also found that cholesterol increased the expressions of β1 and β3 PLC isoforms (PLCβ1, PLCβ3). Silencing the expression of PLCβ1 prevented the effects of cholesterol on PIP2 levels as well as on Aβ42 production, suggesting that increased membrane cholesterol levels increased secreted Aβ42 by downregulating PIP2 via enhancing the expression of PLCβ1. Thus, cholesterol metabolism may be linked to Aβ42 levels via PLCβ1 expression and subsequent changes in PIP2 metabolism.

Modulation of transient receptor potential melastatin related 7 channel by presenilins

Presenilins (PS1 and PS2) are multifunctional proteins involved in a diverse array of molecular and cellular functions, including proteolysis, development, neurogenesis, synaptic plasticity, ion channel regulation and phospholipid metabolism. Mutations in presenilin genes are responsible for the majority of Familial Alzheimer disease (FAD). Consequently, FAD-associated mutations in genes encoding PS1 or PS2 lead to several key cellular phenotypes, including alterations in proteolysis of β-amyloid precursor protein (APP) and Ca(2+) entry. The mechanism underlying presenilin (PS)-mediated modulation of Ca(2+) entry remains to be determined. Our previous studies showed that the PS-dependent down-regulation of phosphatidylinositol-4,5-bisphosphate (PIP2) is attributable to the observed Ca(2+) deficits. In this study, we attempted to identify the ion channel that is subject to the PIP2 and PS-dependent modulation. We found that Ca(2+) or Zn(2+) entry via the transient receptor potential melastatin 7 (TRPM7) channel was attenuated by the presence of FAD-associated PS1 mutants, such as ΔE9 and L286V. TRPM7 has been implicated in Mg(2+) homeostasis and embryonic development. The intracellular delivery of PIP2 restored TRPM7-mediated Ca(2+) influx, indicating that the observed deficits in Ca(2+) entry are due to downregulation of PIP2. Conversely, PS1 and PS2 deficiency, previously shown to upregulate PIP2 levels, potentiated TRPM7-mediated Ca(2+) influx. PS-dependent changes in Ca(2+) influx could be neutralized by a TRPM7 channel blocker. Collectively, these results indicate that TRPM7 may underlie the Ca(2+) entry deficits observed in FAD-associated PS mutants and suggest that the normal function of PS involves regulation of TRPM7 through a PIP2-dependent mechanism.

Varying Ti-6Al-4V surface roughness induces different early morphologic and molecular responses in MG63 osteoblast-like cells

Osteoblast response to Ti implants depends not only on the chemistry of the implant but also on the physical properties of the implant surface, such as microtopography and roughness. This study was undertaken to examine early changes in cell morphology and gene expression during the early phase of osteoblast interaction with titanium alloy (Ti-6Al-4V) surfaces of two different roughnesses. MG63 osteoblast-like cells were cultured for 2, 6, 24, and 72 h on smooth (Ra=0.18+/-0.03 microm) and rough (Ra=2.95+/-0.23 microm) Ti-6Al-4V surfaces. Changes in cell proliferation were assessed by measuring cell number after 72 h in culture. Morphological characteristics were observed by scanning electron microscopy after 2, 6, and 24 h of culture. Changes in gene expression for extracellular signal-regulated kinase 2 (Erk2), type I collagen (alpha2[I] collagen), phospholipase C-gamma2 (Plc-gamma2), and beta-actin were measured by RT-PCR after 6 and 24 h in culture. Cell number was significantly higher on the smooth surface. In scanning electron micrographs, cells on smooth Ti-6Al-4V were spherical and raised up from the surface after 2 h in culture. In contrast, cells on the rough surface adopted an irregular, elongated shape that spanned across pits in the surface. At 24 h, cells on the smooth surface had flattened, become elongate, and covered the surface. In contrast, cells on the rough surface appeared more differentiated in shape and the margins of the cells were irregular, with many processes extending out, following the contour of the surface. Of the genes examined, only Erk2 and beta-actin showed a change in expression with surface roughness. Both genes were upregulated (p<0.05) on the rough surface at 6 h. These results indicate that Ti-6Al-4V surface roughness affects osteoblast proliferation, morphology, and gene expression, and that these effects can be measured after periods as short as 2-6 h.

Identification of Acanthocephala discovered in changran-pickles and myungran-pickles

To identify acanthocephala found in 'Changran-pickles' and 'Myungran-pickles' each organ was measured in permanent slides. In the present report, the results obtained were as follows: 1. Morphology of male worms: Worms possessed 18-19 longitudinal rows, with 4 hooks per row, which became smaller towards the base of proboscis. Each worm contained two testis and six cement glands arranged linearly. Body 22.0 by 0.8-0.6 mm and 15.0 by 0.6-0.4 mm, proboscis 284.8 by 227.6 micro m and 524.9 by 151.4 micro m, proboscis sheath 1570.7 by 72.7 micro m and 751.9 by 280.4 micro m, lemnisci length 2566.7 and 1085.6, testis 2202.9-1860.5 by 737.0-575.7 micro m and 1033.8-981.1 by 463.1-351.6 micro m, cement glands 940.2 by 441.2 micro m and 610.0 by 369.1 micro m. 2. Morphology of female worms: Worms possessed 14-18 longitudinal rows, with 6-10 hooks per row and become smaller toward the base of proboscis. Each worm contained an uterine bell and uterus in the posterior portion and the eggs filled the body cavity. Body, approximately 14.0 - 51.0 mm by 0.7-0.5 - 2.2-1.4 mm, proboscis 466.1-268.9 micro m by 259.9-252.0 micro m, proboscis sheath 1550.7-506.0 by 298.8-231.1 micro m, lemnisci length 1325.7-473.1 micro m, eggs approximately 112.4 by 28.5 micro m - 51.7 by 14.0 micro m. In this present study, the acanthocephala collected in 'Changran-pickles' and 'Myungran-pickles' were identified as Echinorhynchus gadi by morphological features.