Aminoindan and hydroxyaminoindan, metabolites of rasagiline and ladostigil, respectively, exert neuroprotective properties in vitro

The anti-Parkinson, selective irreversible monoamine oxidase B inhibitor drug, rasagiline (Azilect), recently approved by the US Food and Drug Administration, has been shown to possess neuroprotective-neurorescue activities in in vitro and in vivo models. Recent preliminary studies indicated the potential neuroprotective effect of the major metabolite of rasagiline, 1-(R)-aminoindan. In the current study, the neuroprotective properties of 1-(R)-aminoindan were assessed employing a cytotoxic model of human neuroblastoma SK-N-SH cells in high-density culture-induced neuronal death. We show that aminoindan (0.1-1 mumol/L) significantly reduced the apoptosis-associated phosphorylated protein, H2A.X (Ser139), decreased the cleavage of caspase 9 and caspase 3, while increasing the anti-apoptotic proteins, Bcl-2 and Bcl-xl. Protein kinase C (PKC) inhibitor, GF109203X, prevented the neuroprotection, indicating the involvement of PKC in aminoindan-induced cell survival. Aminoindan markedly elevated pPKC(pan) and specifically that of the pro-survival PKC isoform, PKCepsilon. Additionally, hydroxyaminoindan, a metabolite of a novel bifunctional drug, ladostigil [(N-propargyl-(3R) aminoindan-5yl)-ethyl methyl carbamate], combining cholinesterase and monoamine oxidase inhibitor activity, exerted similar neuroprotective properties. Aminoindan and hydroxyaminoindan also protected rat pheochromacytoma PC-12 cells against the neurotoxin, 6-hydroxydopamine. Our findings suggest that both metabolites may contribute to the overall neuroprotective activity of their respective parent compounds, further implicating rasagiline and ladostigil as potentially valuable drugs for treatment of a wide variety of neurodegenerative disorders of aging.     

Admixture mapping of an allele affecting interleukin 6 soluble receptor and interleukin 6 levels

Circulating levels of inflammatory markers can predict cardiovascular disease risk. To identify genes influencing the levels of these markers, we genotyped 1,343 single-nucleotide polymorphisms (SNPs) in 1,184 African Americans from the Health, Aging and Body Composition (Health ABC) Study. Using admixture mapping, we found a significant association of interleukin 6 soluble receptor (IL-6 SR) with European ancestry on chromosome 1 (LOD 4.59), in a region that includes the gene for this receptor (IL-6R). Genotyping 19 SNPs showed that the effect is largely explained by an allele at 4% frequency in West Africans and at 35% frequency in European Americans, first described as associated with IL-6 SR in a Japanese cohort. We replicate this association (P<1.0x10-12) and also demonstrate a new association with circulating levels of a different molecule, IL-6 (P<3.4x10-5). After replication in 1,674 European Americans from Health ABC, the combined result is even more significant: P<1.0x10-12 for IL-6 SR, and P<2.0x10-9 for IL-6. These results also serve as an important proof of principle, showing that admixture mapping can not only coarsely localize but can also fine map a phenotypically important variant.     

Interaction with MEK causes nuclear export and downregulation of peroxisome proliferator-activated receptor gamma

The mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) cascade plays a central role in intracellular signaling by many extracellular stimuli. One target of the ERK cascade is peroxisome proliferator-activated receptor gamma (PPARgamma), a nuclear receptor that promotes differentiation and apoptosis. It was previously demonstrated that PPARgamma activity is attenuated upon mitogenic stimulation due to phosphorylation of its Ser84 by ERKs. Here we show that stimulation by tetradecanoyl phorbol acetate (TPA) attenuates PPARgamma's activity in a MEK-dependent manner, even when Ser84 is mutated to Ala. To elucidate the mechanism of attenuation, we found that PPARgamma directly interacts with MEKs, which are the activators of ERKs, but not with ERKs themselves, both in vivo and in vitro. This interaction is facilitated by MEKs' phosphorylation and is mediated by the basic D domain of MEK1 and the AF2 domain of PPARgamma. Immunofluorescence microscopy and subcellular fractionation revealed that MEK1 exports PPARgamma from the nucleus, and this finding was supported by small interfering RNA knockdown of MEK1 and use of a cell-permeable interaction-blocking peptide, which prevented TPA-induced export of PPARgamma from the nucleus. Thus, we show here a novel mode of downregulation of PPARgamma by its MEK-dependent redistribution from the nucleus to the cytosol. This unanticipated role for the stimulation-induced nuclear shuttling of MEKs shows that MEKs can regulate additional signaling components besides the ERK cascade.     

Potential for Mercury Reduction by Microbes in the High Arctic

The contamination of polar regions due to the global distribution of anthropogenic pollutants is of great concern because it leads to the bioaccumulation of toxic substances, methylmercury among them, in Arctic food chains. Here we present the first evidence that microbes in the high Arctic possess and express diverse merA genes, which specify the reduction of ionic mercury [Hg(II)] to the volatile elemental form [Hg(0)]. The sampled microbial biomass, collected from microbial mats in a coastal lagoon and from the surface of marine macroalgae, was comprised of bacteria that were most closely related to psychrophiles that had previously been described in polar environments. We used a kinetic redox model, taking into consideration photoredox reactions as well as mer-mediated reduction, to assess if the potential for Hg(II) reduction by Arctic microbes can affect the toxicity and environmental mobility of mercury in the high Arctic. Results suggested that mer-mediated Hg(II) reduction could account for most of the Hg(0) that is produced in high Arctic waters. At the surface, with only 5% metabolically active cells, up to 68% of the mercury pool was resolved by the model as biogenic Hg(0). At a greater depth, because of incident light attenuation, the significance of photoredox transformations declined and merA-mediated activity could account for up to 90% of Hg(0) production. These findings highlight the importance of microbial redox transformations in the biogeochemical cycling, and thus the toxicity and mobility, of mercury in polar regions.     

Habitat fragmentation may not matter to species diversity

Conservation biologists worry that fragmenting a bloc of natural habitat might reduce its species diversity. However, they also recognize the difficulty and importance of isolating the effect of fragmentation from that of simple loss of area. Using two different methods (species-area curve and Fisher's alpha index of diversity) to analyse the species diversities of plants, tenebrionid beetles and carabid beetles in a highly fragmented Mediterranean scrub landscape, we decoupled the effect of degree of fragmentation from that of area loss. In this system, fragmentation by itself seems not to have influenced the number of species. Our results, obtained at the scale of hectares, agree with similar results at island and continent scales.     

Chlorophyllase is a rate-limiting enzyme in chlorophyll catabolism and is posttranslationally regulated

Chlorophyll is a central player in harvesting light energy for photosynthesis, yet the rate-limiting steps of chlorophyll catabolism and the regulation of the catabolic enzymes remain unresolved. To study the role and regulation of chlorophyllase (Chlase), the first enzyme of the chlorophyll catabolic pathway, we expressed precursor and mature versions of citrus (Citrus sinensis) Chlase in two heterologous plant systems: (1) squash (Cucurbita pepo) plants using a viral vector expression system; and (2) transiently transformed tobacco (Nicotiana tabacum) protoplasts. Expression of full-length citrus Chlase resulted in limited chlorophyll breakdown in protoplasts and no visible leaf phenotype in whole plants, whereas expression of a Chlase version lacking the N-terminal 21 amino acids (ChlaseDeltaN), which corresponds to the mature protein, led to extensive chlorophyll breakdown in both tobacco protoplasts and squash leaves. ChlaseDeltaN-expressing squash leaves displayed a dramatic chlorotic phenotype in plants grown under low-intensity light, whereas under natural light a lesion-mimic phenotype occurred, which was demonstrated to follow the accumulation of chlorophyllide, a photodynamic chlorophyll breakdown product. Full-length and mature citrus Chlase versions were localized to the chloroplast membrane fraction in expressing tobacco protoplasts, where processing of the N-terminal 21 amino acids appears to occur. Results obtained in both plant systems suggest that Chlase functions as a rate-limiting enzyme in chlorophyll catabolism controlled via posttranslational regulation.     

A computational proposal for designing structured RNA pools for in vitro selection of RNAs

Although in vitro selection technology is a versatile experimental tool for discovering novel synthetic RNA molecules, finding complex RNA molecules is difficult because most RNAs identified from random sequence pools are simple motifs, consistent with recent computational analysis of such sequence pools. Thus, enriching in vitro selection pools with complex structures could increase the probability of discovering novel RNAs. Here we develop an approach for engineering sequence pools that links RNA sequence space regions with corresponding structural distributions via a "mixing matrix" approach combined with a graph theory analysis. We define five classes of mixing matrices motivated by covariance mutations in RNA; these constructs define nucleotide transition rates and are applied to chosen starting sequences to yield specific nonrandom pools. We examine the coverage of sequence space as a function of the mixing matrix and starting sequence via clustering analysis. We show that, in contrast to random sequences, which are associated only with a local region of sequence space, our designed pools, including a structured pool for GTP aptamers, can target specific motifs. It follows that experimental synthesis of designed pools can benefit from using optimized starting sequences, mixing matrices, and pool fractions associated with each of our constructed pools as a guide. Automation of our approach could provide practical tools for pool design applications for in vitro selection of RNAs and related problems.     

RagPools: RNA-As-Graph-Pools--a web server for assisting the design of structured RNA pools for in vitro selection

SUMMARY: Our RNA-As-Graph-Pools (RagPools) web server offers a theoretical companion tool for RNA in vitro selection and related problems. Specifically, it suggests how to construct RNA sequence/structure pools with user-specified properties and assists in analyzing resulting distributions. This utility follows our recently developed approach for engineering sequence pools that links RNA sequence space regions with corresponding structural distributions via a 'mixing matrix' approach combined with a graph theory analysis of RNA secondary-structure space; the mixing matrix specifies nucleotide transition rates, and graph theory links sequences to simple graphical objects representing RNA motifs. The companion RagPools web server ('Designer' component) provides optimized starting sequences, mixing matrices and associated weights in response to a user-specified target pool structure distribution. In addition, RagPools ('Analyzer' component) analyzes the motif distribution of pools generated from user-specified starting sequences and mixing matrices. Thus, RagPools serves as a guide to researchers who aim to synthesize RNA pools with desired properties and/or experiment in silico with various designs by our approach. AVAILABILITY: The web server is accessible on the web at http://rubin2.biomath.nyu.edu