Metformin sensitizes insulin signaling through AMPK-mediated PTEN down-regulation in preadipocyte 3T3-L1 cells

Insulin resistance is the primary cause responsible for type 2 diabetes. Phosphatase and tensin homolog (PTEN) plays a negative role in insulin signaling and its inhibition improves insulin sensitivity. Metformin is a widely used insulin-sensitizing drug; however, the mechanism by which metformin acts is poorly understood. To gain insight into the role of PTEN, we examined the effect of metformin on PTEN expression. Metformin suppressed the expression of PTEN in an AMP-activated protein kinase (AMPK)-dependent manner in preadipocyte 3T3-L1 cells. Knock-down of PTEN potentiated the increase in insulin-mediated phosphorylation of Akt/ERK. Metformin also increased the phosphorylation of c-Jun N-terminal kinase (JNK)-c-Jun and mammalian target of rapamycin (mTOR)-p70S6 kinase pathways. Both pharmacologic inhibition and knock-down of AMPK blocked metformin-induced phosphorylation of JNK and mTOR. Knock-down of AMPK recovered the metformin-induced PTEN down-regulation, suggesting the involvement of AMPK in PTEN regulation. PTEN promoter activity was suppressed by metformin and inhibition of mTOR and JNK by pharmacologic inhibitors blocked metformin-induced PTEN promoter activity suppression. These findings provide evidence for a novel role of AMPK on PTEN expression and thus suggest a possible mechanism by which metformin may contribute to its beneficial effects on insulin signaling.     

A hybrid peptide derived from cecropin-A and magainin-2 inhibits osteoclast differentiation

The adult skeleton is in a dynamic state, being continually broken down and reformed by the coordinated actions of osteoclasts and osteoblasts. Increased osteoclast activity may contribute to the development of osteoporosis. Therefore, the intervention of osteoclast-mediated bone resorption is considered as an effective therapeutic approach in the treatment of osteoporosis. In the course of searching for agents that inhibit osteoclast differentiation and activation, we found that a novel hybrid peptide P1 derived from cecropin-A and magainin-2 reduced osteoclast differentiation in various osteoclast culture systems. As this peptide had no cytotoxicity on various cultures of primary cells and established cell lines, its inhibitory effect on osteoclastogenesis was not due to general cytotoxicity. The effects of P1 on osteoclasts appear to be mediated through the inhibition of NF-kappaB and JNK activation induced by the osteoclastogenic cytokine, receptor activator of NF-kappaB ligand (RANKL). These results provide an evidence for the potential usefulness of P1 for the treatment of bone-resorbing diseases.     

Structural characterization of a new N‐substituted pantothenamide bound to pantothenate kinases from Klebsiella pneumoniae and Staphylococcus aureus

Pantothenate kinase (PanK) is the rate‐limiting enzyme in Coenzyme A biosynthesis, catalyzing the ATP‐dependent phosphorylation of pantothenate. We solved the co‐crystal structures of PanKs from Staphylococcus aureus (SaPanK) and Klebsiella pneumonia (KpPanK) with N‐[2‐(1,3‐benzodioxol‐5‐yl)ethyl] pantothenamide (N354‐Pan). Two different N354‐Pan conformers interact with polar/nonpolar mixed residues in SaPanK and aromatic residues in KpPanK. Additionally, phosphorylated N354‐Pan is found at the closed active site of SaPanK but not at the open active site of KpPanK, suggesting an exchange of the phosphorylated product with a new N354‐Pan only in KpPanK. Together, pantothenamides conformational flexibility and binding pocket are two key considerations for selective compound design. Proteins 2014; 82:1542–1548. © 2014 Wiley Periodicals, Inc.     

Structure of the hypothetical protein Ton 1535 from Thermococcus onnurineus NA1 reveals unique structural properties by a left‐handed helical turn in normal α‐solenoid protein

The crystal structure of Ton1535, a hypothetical protein from Thermococcus onnurineus NA1, was determined at 2.3 Å resolution. With two antiparallel α‐helices in a helix‐turn‐helix motif as a repeating unit, Ton1535 consists of right‐handed coiled N‐ and C‐terminal regions that are stacked together using helix bundles containing a left‐handed helical turn. One left‐handed helical turn in the right‐handed coiled structure produces two unique structural properties. One is the presence of separated concave grooves rather than one continuous concave groove, and the other is the contribution of α‐helices on the convex surfaces of the N‐terminal region to the extended surface of the concave groove of the C‐terminal region and vice versa. Proteins 2014; 82:1072–1078. © 2013 Wiley Periodicals, Inc.     

Nitrogen biofiltration capacities and photosynthetic activity of Pyropia yezoensis Ueda (Bangiales,Rhodophyta): groundwork to validate its potential in integrated multi-trophic aquaculture (IMTA)

Porphyra spp. (currently Porphyra and Pyropia) are major sources of seafood globally. In this study, we investigated the effects of ammonium concentration, water temperature, and thallus stocking density on N-ammonium uptake rate (NUR), tissue nutrients content, N–NH₄ ⁺ filtration efficiency (NUE: nitrogen uptake efficiency %) of Pyropia yezoensis at a laboratory scale and in a mesoscale to evaluate the potential of this species as a biofilter. Additionally, photosynthetic activity was examined using Diving-PAM fluorometer to evaluate the health status. At a laboratory scale, the NUR and tissue nitrogen (N) content of P. yezoensis increased with increasing NH₄ ⁺ concentrations in the medium. The NUR at thallus stocking densities of 5 and 10 g fresh weight (FW) L^–1 were significantly higher than that at 20 g FW L^–1. Effective quantum yield (? F/F’ _m ) and tissue N content was significantly higher at all stocking densities than that at the beginning of experiment. The NUE was over 90 % at 10 and 17 °C, while all thalli cultured at 25 °C died after 5 days. In a mesoscale, the NUE at a thallus stocking density of 10.0 g FW L^–1 was significantly higher than that at a stocking density of 5.0 g FW L^–1. No differences in the NUE occurred between 10 °C and 17 °C. Photosynthetic activity (?F/F’_m and rETR_max) of P. yezoensis at optimal culture condition (10–12 °C and 10 g FW L^–1) increased over time through the experiment. This indicates that thallus was healthy during culture and chlorophyll a fluorescence can be as a monitoring tool for evaluating the physiological status of seaweeds in an integrated multi-trophic aquaculture.     

An amphipathic polypeptide derived from poly‐γ‐glutamic acid for the stabilization of membrane proteins

Difficulties in the extraction of membrane proteins from cell membrane and their solubilization in native conformations have hindered their structural and biochemical analysis. To overcome these difficulties, an amphipathic polypeptide was synthesized by the conjugation of octyl and glucosyl groups to the carboxyl groups of poly‐γ‐glutamic acid (PGA). This polymer, called amphipathic PGA (APG), self‐assembles as mono‐disperse oligomers consisted of 4–5 monomers. APG shows significantly low value of critical micelle concentration and stabilization activity toward membrane proteins. Most of the sodium dodecyl sulfate (SDS)‐solubilized membrane proteins from Escherichia coli remain soluble state in the presence of APG even after the removal of SDS. In addition, APG stabilizes purified 7 transmembrane proteins such as bacteriorhodopsin and human endothelin receptor Type A (ET_A) in their active conformations. Furthermore, ET_A in complex with APG is readily inserted into liposomes without disrupting the integrity of liposomes. These properties of APG can be applied to overcome the difficulties in the stabilization and reconstitution of membrane proteins.     

PEP-1-PEA-15 protects against toxin-induced neuronal damage in a mouse model of Parkinson's disease

Background

PEA-15 is abundantly expressed in both neurons and astrocytes throughout the brain. It is a multifunctional protein with the ability to increase cell survival via anti-apoptotic and anti-proliferative properties. However, the function of PEA-15 in neuronal diseases such as Parkinson's disease (PD) remains unclear. In this study, we investigated the protective effects of PEA-15 on neuronal damage induced by MPP⁺ in neuroblastoma SH-SY5Y and BV2 microglia cells and in a MPTP-induced PD mouse model using cell-permeable PEP-1-PEA-15.

Methods

PEP-1-PEA-15 was purified using affinity chromatography. Cell viability and DNA fragmentation were examined by MTT assay and TUNEL staining. Dopaminergic neuronal cell death in the animal model was examined by immunohistochemistry.

Results

PEP-1-PEA-15 transduced into the SH-SY5Y and BV2 cells in a time- and dose-dependent manner. Transduced PEP-1-PEA-15 protected against MPP⁺-induced toxicity by inhibiting intracellular ROS levels and DNA fragmentation. Further, it enhanced the expression levels of Bcl-2 and caspase-3 while reducing the expression levels of Bax and cleaved caspase-3. We found that PEP-1-PEA-15 transduced into the substantia nigra and prevented dopaminergic neuronal cell death in a MPTP-induced PD mouse. Also, we showed the neuroprotective effects in the model by demonstrating that treatment with PEP-1-PEA-15 ameliorated MPTP-induced behavioral dysfunctions and increased dopamine levels in the striatum.

Conclusions

PEP-1-PEA-15 can efficiently transduce into cells and protects against neurotoxin-induced neuronal cell death in vitro and in vivo.

General significance

These results demonstrate the potential for PEP-1-PEA-15 to provide a new strategy for protein therapy treatment of a variety of neurodegenerative diseases including PD.