Advanced glycation end product (AGE) accumulation on Bruch's membrane: links to age-related RPE dysfunction.

PURPOSE: Advanced glycation end products (AGEs) accumulate during aging and have been observed in postmortem eyes within the retinal pigment epithelium (RPE), Bruch's membrane, and subcellular deposits (drusen). AGEs have been associated with age-related dysfunction of the RPE-in particular with development and progression to age-related macular degeneration (AMD). In the present study the impact of AGEs at the RPE-Bruch's membrane interface was evaluated, to establish how these modifications may contribute to age-related disease. METHODS: AGEs on Bruch's membrane were evaluated using immunohistochemistry. A clinically relevant in vitro model of substrate AGE accumulation was established to mimic Bruch's membrane ageing. Responses of ARPE-19 growing on AGE-modified basement membrane (AGE-BM) for 1 month were investigated by using a microarray approach and validated by quantitative (q)RT-PCR. In addition to identified AGE-related mRNA alterations, lysosomal enzyme activity and lipofuscin accumulation were also studied in ARPE-19 grown on AGE-BM. RESULTS: Autofluorescent and glycolaldehyde-derived AGEs were observed in clinical specimens on Bruch's membrane and choroidal extracellular matrix. In vitro analysis identified a range of dysregulated mRNAs in ARPE-19 exposed to AGE-BM. Altered ARPE-19 degradative enzyme mRNA expression was observed on exposure to AGE-BM. AGE-BM caused a significant reduction in cathepsin-D activity in ARPE-19 (P

Age-dependent accumulation of lipofuscin in perivascular and subretinal microglia in experimental mice

Fundus autofluorescence (AF) imaging by confocal scanning laser ophthalmoscopy has been widely used by ophthalmologists in the diagnosis/monitoring of various retinal disorders. It is believed that fundus AF is derived from lipofuscin in retinal pigment epithelial (RPE) cells; however, direct clinicopathological correlation has not been possible in humans. We examined fundus AF by confocal scanning laser ophthalmoscopy and confocal microscopy in normal C57BL/6 mice of different ages. Increasingly strong AF signals were observed with age in the neuroretina and subretinal/RPE layer by confocal scanning laser ophthalmoscopy. Unlike fundus AF detected in normal human subjects, mouse fundus AF appeared as discrete foci distributed throughout the retina. Most of the AF signals in the neuroretina were distributed around retinal vessels. Confocal microscopy of retinal and choroid/RPE flat mounts demonstrated that most of the AF signals were derived from Iba-1+ perivascular and subretinal microglia. An age-dependent accumulation of Iba-1+ microglia at the subretinal space was observed. Lipofuscin granules were detected in large numbers in subretinal microglia by electron microscopy. The number of AF+ microglia and the amount of AF granules/cell increased with age. AF granules/lipofuscin were also observed in RPE cells in mice older than 12 months, but the number of AF+ RPE cells was very low (1.48 mm-2 and 5.02 mm-2 for 12 and 24 months, respectively) compared to the number of AF+ microglial cells (20.63 mm-2 and 76.36 mm-2 for 6 and 24 months, respectively). The fluorescence emission fingerprints of AF granules in subretinal microglia were the same as those in RPE cells. Our observation suggests that perivascular and subretinal microglia are the main cells producing lipofuscin in normal aged mouse retina and are responsible for in vivo fundus AF. Microglia may play an important role in retinal aging and age-related retinal diseases.

Electrochemical Oxidation of Hydrogen Sulfide at Platinum Electrodes in Room Temperature Ionic Liquids: Evidence for Significant Accumulation of H2S at the Pt/1-Butyl-3-methylimidazolium Trifluoromethylsulfonate Interface

Electrochemical oxidation of hydrogen sulfide gas (H2S) has been studied at a platinum microelectrode (10 mu m diameter) in five room temperature ionic liquids (RTILs): [C(4)mim][OTf], [C(4)dmim][NTf2], [C(4)mim][PF6],. [C(6)mim][FAP], and [P-14,P-6,P-6,P-6][FAP] (where [C-n mim](+) = 1-alkyl-3-methylimidazolium, [C(n)dmim](+) = 1-alkyl-2,3-dimethylimidazolium, [P-14,P-6,P-6,P-6](+) = tris(p-hexyl)-tetradecylphosphonium, [OTf](-) = trifluoromethlysulfonate, [NTf2](-) = bis(trifluoromethylsulfonyl)imide, [PF6](-) = hexafluorophosphate, and [FAP](-) = trifluorotris(pentafluoroethyl)phosphate). In four of the RTILs ([C(4)dmim][NTf2], [C(4)mim][PF6], [C(6)mim][FAP], and [P-14,P-6,P-6,P-6][FAP]), no clear oxidative signal was observed. In [C(4)mim][OTf], a chemically irreversible oxidation peak was observed on the oxidative sweep with no signal seen on the reverse scan. The oxidative signal showed an adsorptive stripping peak type followed by near steady-state limiting current behavior. Potential step chronoamperometry was carried out on the reductive wave, giving a diffusion coefficient and solubility of 1.6 x 10(-11) m(2) s(-1) and 7 mM, respectively (at 25 degrees C). Using these data, we modeled the oxidation signal kinetically, assuming adsorption preceded oxidation and that adsorption was approximately Langmuirian. The oxidation step was described by an electrochemically fully irreversible Tafel law/Butler-Volmer formalism. Modeling indicated a substantial buildup of H2S in the double layer in excess of the coverage that would be expected for a monolayer of chemisorbed H2S, reflecting high solubility of the gas in [C(4)mim][OTf] and possible attractive interactions with the [OTf](-) anions accumulated at the electrode at potentials positive of the potential of zero charge. Solute enrichment of the double layer in the solution adjacent to the electrode appears a novel feature of RTIL electrochemistry.

Intracellular accumulation of polyphosphate by the yeast Candida humicola G-1 in response to acid pH

Cells of a newly isolated environmental strain of Candida humicola accumulated 10-fold more polyphosphate (polyP), during active growth, when grown in complete glucose-mineral salts medium at pH 5.5 than when grown at pH 7.5. Neither phosphate starvation, nutrient limitation, nor anaerobiosis was required to induce polyP formation. An increase in intracellular polyP was accompanied by a 4.5-fold increase in phosphate uptake from the medium and sixfold-higher levels of cellular polyphosphate kinase activity. This novel accumulation of polyP by C. humicola G-1 in response to acid pH provides further evidence as to the importance of polyP in the physiological adaptation of microbial cells during growth and development and in their response to environmental stresses.

Erythrocytosis-associated HIF-2alpha mutations demonstrate a critical role for residues C-terminal to the hydroxylacceptor proline.

Abstract A classic physiologic response to hypoxia in humans is the up-regulation of the ERYTHROPOIETIN (EPO) gene, which is the central regulator of red blood cell mass. The EPO gene, in turn, is activated by hypoxia inducible factor (HIF). HIF is a transcription factor consisting of an alpha subunit (HIF-alpha) and a beta subunit (HIF-beta). Under normoxic conditions, prolyl hydroxylase domain protein (PHD, also known as HIF prolyl hydroxylase and egg laying-defective nine protein) site specifically hydroxylates HIF-alpha in a conserved LXXLAP motif (where underlining indicates the hydroxylacceptor proline). This provides a recognition motif for the von Hippel Lindau protein, a component of an E3 ubiquitin ligase complex that targets hydroxylated HIF-alpha for degradation. Under hypoxic conditions, this inherently oxygen-dependent modification is arrested, thereby stabilizing HIF-alpha and allowing it to activate the EPO gene. We previously identified and characterized an erythrocytosis-associated HIF2A mutation, G537W. More recently, we reported two additional erythrocytosis-associated HIF2A mutations, G537R and M535V. Here, we describe the functional characterization of these two mutants as well as a third novel erythrocytosis-associated mutation, P534L. These mutations affect residues C-terminal to the LXXLAP motif. We find that all result in impaired degradation and thus aberrant stabilization of HIF-2alpha. However, each exhibits a distinct profile with respect to their effects on PHD2 binding and von Hippel Lindau interaction. These findings reinforce the importance of HIF-2alpha in human EPO regulation, demonstrate heterogeneity of functional defects arising from these mutations, and point to a critical role for residues C-terminal to the LXXLAP motif in HIF-alpha.

Accumulation of knowledge and accumulation of capital in early ‘theories’ of growth and development

This paper argues that prior to Adam Smith economic progress was largely conceived as being based on the accumulation of knowledge. The development by Turgot and Smith of a concept of capital that subsumed other factors contributing to development led their followers to focus on capital to the neglect of the independent role of knowledge. The paper demonstrates that this paradigmatic shift was identified and challenged by Bentham, Hodgskin and Rae who argued for the independent role of innovation but without lasting impact. © The Author 2009. Published by Oxford University Press on behalf of the Cambridge Political Economy Society. All rights reserved.

Migration, human capital accumulation and economic development

We study how the possibility of migration changes the composition of human capital in sending countries, and how this affects development. In our model, growth is driven by productivity growth, which occurs via imitation or innovation. Both activities use the same types of skilled labour as input, albeit with different intensities. Heterogenous agents accumulate skills in response to economic incentives. Migration distorts these incentives, and the accumulation of human capital. This slows down, or even hinders, economic development. The effect is stronger, the farther away the country is from the technological frontier. (C) 2008 Elsevier B.V. All rights reserved.

Carbon accumulation in peatlands of West Siberia over the last 2000 years

We use a network of cores from 77 peatland sites to determine controls on peat C content and peat C accumulation over the last 2000 years (since 2 ka) across Russia's West Siberian Lowland (WSL), the world's largest wetland region. Our results show a significant influence of fossil plant composition on peat C content, with peats dominated by Sphagnum having a lower C content. Radiocarbon-derived C accumulation since 2 ka at 23 sites is highly variable from site to site, but displays a significant N–S trend of decreasing accumulation at higher latitudes. Northern WSL peatlands show relatively small C accumulation of 7 to 35 kg C m-2 since 2 ka. In contrast, peatlands south of 60°N show larger accumulation of 42 to 88 kg C m-2. Carbon accumulation since 2 ka varies significantly with modern mean annual air temperature, with maximum C accumulation found between -1 and 0°C. Rates of apparent C accumulation since 2 ka show no significant relationship to long-term Holocene averages based on total C accumulation. A GIS-based extrapolation of our site data suggests that a substantial amount (~40%) of total WSL peat C has accumulated since 2 ka, with much of this accumulation south of 60°N. The large peatlands in the southern WSL may be an important component of the Eurasian terrestrial C sink, and future warming could result in a shift northward in long-term WSL C sequestration.

Spatial characterization of salt accumulation in early stage limestone weathering using probe permeametry

This research characterizes the weathering of natural building stone using an unsteady-state portable probe permeameter. Variations between the permeability properties of fresh rock and the same rocks after the early stages of a salt weathering simulation are used to examine the effects of salt accumulation on spatial variations in surface rock permeability properties in two limestones from Spain. The Fraga and Tudela limestones are from the Ebro basin and are of Miocene age. Both stone types figure largely in the architectural heritage of Spain and, in common with many other building limestones, they are prone to physical damage from salt crystallization in pore spaces. To examine feedbacks associated with salt accumulation during the early stages of this weathering process, samples of the two stone types were subjected to simulated salt weathering under laboratory conditions using magnesium sulphate and sodium chloride at concentrations of 5% and 15%. Permeability mapping and statistical analysis (aspatial statistics and spatial prediction) before and after salt accumulation are used to assess changes in the spatial variability of permeability and to correlate these changes with salt movement, porosity change, potential rock deterioration and textural characteristics. Statistical analyses of small-scale permeability measurements are used to evaluate the drivers for decay and hence aid the prediction of the weathering behaviour of the two limestones.