Loss of mitofusin 2 links beta‐amyloid‐mediated mitochondrial fragmentation and Cdk5‐induced oxidative stress in neuron cells

Mitochondrial dysfunction is implicated in age‐related degenerative disorders such as Alzheimer's disease (AD). Maintenance of mitochondrial dynamics is essential for regulating mitochondrial function. Aβ oligomers (AβOs), the typical cause of AD, lead to mitochondrial dysfunction and neuronal loss. AβOs have been shown to induce mitochondrial fragmentation, and their inhibition suppresses mitochondrial dysfunction and neuronal cell death. Oxidative stress is one of the earliest hallmarks of AD. Cyclin‐dependent kinase 5 (Cdk5) may cause oxidative stress by disrupting the antioxidant system, including Prx2. Cdk5 is also regarded as a modulator of mitochondrial fission; however, a precise mechanistic link between Cdk5 and mitochondrial dynamics is lacking. We estimated mitochondrial morphology and alterations in mitochondrial morphology‐related proteins in Neuro‐2a (N2a) cells stably expressing the Swedish mutation of amyloid precursor protein (APP), which is known to increase AβO production. We demonstrated that mitochondrial fragmentation by AβOs accompanies reduced mitofusin 1 and 2 (Mfn1/2) levels. Interestingly, the Cdk5 pathway, including phosphorylation of the Prx2‐related oxidative stress, has been shown to regulate Mfn1 and Mfn2 levels. Furthermore, Mfn2, but not Mfn1, over‐expression significantly inhibits the AβO‐mediated cell death pathway. Therefore, these results indicate that AβO‐mediated oxidative stress triggers mitochondrial fragmentation via decreased Mfn2 expression by activating Cdk5‐induced Prx2 phosphorylation.

     

Ursodeoxycholic Acid (UDCA) Exerts Anti-Atherogenic Effects by Inhibiting Endoplasmic Reticulum (ER) Stress Induced by Disturbed Flow

Disturbed blood flow with low-oscillatory shear stress (OSS) is a predominant atherogenic factor leading to dysfunctional endothelial cells (ECs). Recently, it was found that disturbed flow can directly induce endoplasmic reticulum (ER) stress in ECs, thereby playing a critical role in the development and progression of atherosclerosis. Ursodeoxycholic acid (UDCA), a naturally occurring bile acid, has long been used to treat chronic cholestatic liver disease and is known to alleviate endoplasmic reticulum (ER) stress at the cellular level. However, its role in atherosclerosis remains unexplored. In this study, we demonstrated the anti-atherogenic activity of UDCA via inhibition of disturbed flow-induced ER stress in atherosclerosis. UDCA effectively reduced ER stress, resulting in a reduction in expression of X-box binding protein-1 (XBP-1) and CEBP-homologous protein (CHOP) in ECs. UDCA also inhibits the disturbed flow-induced inflammatory responses such as increases in adhesion molecules, monocyte adhesion to ECs, and apoptosis of ECs. In a mouse model of disturbed flow-induced atherosclerosis, UDCA inhibits atheromatous plaque formation through the alleviation of ER stress and a decrease in adhesion molecules. Taken together, our results revealed that UDCA exerts anti-atherogenic activity in disturbed flow-induced atherosclerosis by inhibiting ER stress and the inflammatory response. This study suggests that UDCA may be a therapeutic agent for prevention or treatment of atherosclerosis.     

The affinity ratio--its pivotal role in gold nanoparticle-based competitive colorimetric aptasensor

We present an important role of the ratio of affinities in unmodified gold nanoparticles-based colorimetric aptasensor reactions. An affinity ratio, representing the competitive interactions among aptamers, targets, and unmodified gold nanoparticles (umAuNPs), was found to be an important factor for the sensitivity (the performance), where the affinity ratio is the affinity of the aptamer to targets divided by the affinity to umAuNPs (K(dAuNP)/K(dTarget)). In this study, the five different aptamers having different affinity ratios to both umAuNPs and targets are used, and the degree of color change is well correlated with its affinity ratio. This result is verified by using a tetracycline binding aptamer (TBA) showing different affinities to its three derivatives, tetracycline, oxytetracycline and doxycycline. Based on this model, the sensitivity of umAuNPs based colorimetric detection for ibuprofen can be enhanced simply through reducing the ibuprofen binding aptamer's affinity to umAuNP by using bis (p-sulfonatophenyl) phenylphosphine as an AuNP-capping ligand, instead of using the citrate. As a result, a clear color change is observed even at a 20-fold less amount of ibuprofen. This study presents that the performance (detection sensitivity) of umAuNPs-based colorimetric aptasensors could be improved by simply adjusting the affinity ratio of the aptamers to targets and umAuNPs, without knowing the conformational changes of aptamers upon the target binding or needing any modification of aptamer sequences.     

RNA interference of pheromone biosynthesis-activating neuropeptide receptor suppresses mating behavior by inhibiting sex pheromone production in Plutella xylostella (L.)

Sex pheromone production is regulated by pheromone biosynthesis-activating neuropeptide (PBAN) in many lepidopteran species. We cloned a PBAN receptor (Plx-PBANr) gene from the female pheromone gland of the diamondback moth, Plutella xylostella (L.). Plx-PBANr encodes 338 amino acids and has conserved structural motifs implicating in promoting G protein coupling and tyrosine-based sorting signaling along with seven transmembrane domains, indicating a typical G protein-coupled receptor. The expression of Plx-PBANr was found only in the pheromone gland of female adults among examined tissues and developmental stages. Heterologous expression in human uterus cervical cancer cells revealed that Plx-PBANr induced significant calcium elevation when challenged with Plx-PBAN. Female P. xylostella injected with double-stranded RNA specific to Plx-PBANr showed suppression of the receptor gene expression and exhibited significant reduction in pheromone biosynthesis, which resulted in loss of male attractiveness. Taken together, the identified PBAN receptor is functional in PBAN signaling via calcium secondary messenger, which leads to activation of pheromone biosynthesis and male attraction.     

Synthesis and evaluation of cytotoxic effects of hanultarin and its derivatives

One of the known cytotoxic lignans is (-)-1-O-feruloyl-secoisolariciresinol designated as hanultarin, which was isolated from the seeds of Trichosanthes kirilowii. In this Letter, we described the first synthesis of 1-O-feruloyl-secoisolariciresinol, 1,4-O-diferuloyl-secoisolariceresinol and their analogues. The cytotoxicities of these compounds were evaluated against several cancer cell lines. Interestingly, we found that the feruloyl diester derivative of secoisolariciresinol was the most active cytotoxic compound against all the cancer cells tested in this experiment. The IC(50) values of the1,4-O-diferuloyl-secoisolariceresinol were in the range of 7.1-9.8μM except one cell line. In considering that both ferulic acid and secoisolariciresinol are commonly found in many plants and have no cytotoxicity, this finding is remarkable in that simple covalent bonds between the ferulic acid and secoisolariciresinol cause a cytotoxic effect.     

C<Subscript>6</Subscript>-ceramide enhances phagocytic activity of Kupffer cells through the production of endogenous ceramides

Ceramide has been suggested to be not only a tumorsuppressive lipid but also a regulator of phagocytosis. We examined whether exogenous cell-permeable C₆-ceramide enhances the phagocytic activity of Kupffer cells (KCs) and affects the level of cellular ceramides. Rat KCs were isolated by collagenase digestion and differential centrifugation, using Percoll system. Phagocytic activity was measured by FACS analysis after incubating KCs with fluorescence-conjugated latex beads, and the level of cellular ceramide was analyzed by liquid chromatography tandem-mass spectrometry (LC-MS/MS). In this study we found that permeable C₆-ceramide increases the cellular levels of endogenous ceramides via a sphingosine-recycling pathway leading to enhanced phagocytosis by KCs.