ALBERT

Description: Bone morphogenetic proteins 2 and 4 (BMP2/4) are essential for osteoblast differentiation and osteogenesis. Generation of a BMP2/4 dual knock out ( ko/ko ) osteoblastic cell line is a valuable asset for studying effects of BMP2/4 on skeletal development. In this study, our goal was to create immortalized mouse deleted BMP2/4 osteoblasts by infecting adenoviruses with Cre recombinase and green fluorescent protein genes into immortalized murine floxed BMP2/4 osteoblasts. Transduced BMP2/4 ko/ko cells were verified by green immunofluorescence and PCR. BMP2/4 ko/ko osteoblasts exhibited small size, slow cell proliferation rate and cell growth was arrested in G1 and G2 phases. Expression of bone-relate genes was reduced in the BMP2/4 ko/ko cells, resulting in delay of cell differentiation and mineralization. Importantly, extracellular matrix remodeling was impaired in the BMP2/4 ko/ko osteoblasts as reflected by decreased Mmp-2 and Mmp-9 expressions. Cell differentiation and mineralization were rescued by exogenous BMP2 and/or BMP4. Therefore, we for the first time described establishment of an immortalized deleted BMP2/4 osteoblast line useful for study of mechanisms in regulating osteoblast lineages. This article is protected by copyright. All rights reserved

Description: The extent to which atmospheric nitrogen (N) deposition reflects land use differences and biogenic vs. fossil fuel reactive N sources remains unclear, yet represents a critical uncertainty in ecosystem N budgets. We compared N concentrations and isotopes in precipitation-event bulk (wet + dry) deposition across nearby valleys in northern Utah with contrasting land use (highly urban vs. intensive agriculture/low-density urban). We predicted greater nitrate (NO 3 - ) vs. ammonium (NH 4 + ) and higher δ 15 N of NO 3 - and NH 4 + in urban valley sites. Contrary to expectations, annual N deposition (3.5–5.1 kg N ha -1 y -1 ) and inorganic N concentrations were similar within and between valleys. Significant summertime decreases in δ 15 N of NO 3 - possibly reflected increasing biogenic emissions in the agricultural valley. Organic N was a relatively minor component of deposition (~13%). Nearby paired wildland sites had similar bulk deposition N concentrations as the urban and agricultural sites. Weighted bulk deposition δ 15 N was similar to natural ecosystems (-0.6 ± 0.7‰). Fine atmospheric particulate matter (PM 2.5 ) had consistently high values of bulk δ 15 N (15.6 ± 1.4‰), δ 15 N in NH 4 + (22.5 ± 1.6‰), and NO 3 - (8.8 ± 0.7‰), consistent with equilibrium fractionation with gaseous species. δ 15 N in bulk deposition NH 4 + varied by more than 40‰, and spatial variation in δ 15 N within storms exceeded 10‰. Sporadically high values of δ 15 N were thus consistent with increased particulate N contributions as well as potential N source variation. Despite large differences in reactive N sources, urban and agricultural landscapes are not always strongly reflected in the composition and fluxes of local N deposition—an important consideration for regional-scale ecosystem models.

Description: Climate variability affects the capacity of the biosphere to assimilate and store important elements, such as nitrogen and carbon. Here we present biogeochemical evidence from the sediments of tropical Lake Titicaca indicating that large hydrologic changes in response to global glacial cycles during the Quaternary were accompanied by major shifts in ecosystem state. During prolonged glacial intervals, lake level was high and the lake was in a stable nitrogen-limited state. In contrast, during warm dry interglacials lake level fell and rates of nitrogen concentrations increased by a factor of 4–12, resulting in a fivefold to 24-fold increase in organic carbon concentrations in the sediments due to increased primary productivity. Observed periods of increased primary productivity were also associated with an apparent increase in denitrification. However, the net accumulation of nitrogen during interglacial intervals indicates that increased nitrogen supply exceeded nitrogen losses due to denitrification, thereby causing increases in primary productivity. Although primary productivity in tropical ecosystems, especially freshwater ecosystems, tends to be nitrogen limited, our results indicate that climate variability may lead to changes in nitrogen availability and thus changes in primary productivity. Therefore some tropical ecosystems may shift between a stable state of nitrogen limitation and a stable state of nitrogen saturation in response to varying climatic conditions.

Description: A reasonable representation of crop phenology and biophysical processes in land surface models is necessary to accurately simulate energy, water and carbon budgets at the field, regional, and global scales. However, the evaluation of crop models that can be coupled to earth system models is relatively rare. Here, we evaluated two such models (CLM4-Crop and CLM3.5-CornSoy), both implemented within the Community Land Model (CLM) framework, at two AmeriFlux corn-soybean sites to assess their ability to simulate phenology, energy, and carbon fluxes. Our results indicated that the accuracy of net ecosystem exchange and gross primary production simulations was intimately connected to the phenology simulations. The CLM4-Crop model consistently overestimated early growing season leaf area index, causing an overestimation of gross primary production, to such an extent that the model simulated a carbon sink instead of the measured carbon source for corn. The CLM3.5-CornSoy simulated LAI, energy, and carbon fluxes showed stronger correlations with observations compared to CLM4-Crop. Net radiation was biased high in both models and was especially pronounced for soybeans. This was primarily caused by the positive LAI bias, which led to a positive net long wave radiation bias. CLM4-Crop underestimated soil water content during mid-growing season in all soil layers at the two sites, which caused unrealistic water stress, especially for soybean. Future work regarding the mechanisms that drive early growing season phenology and soil water dynamics are needed to better represent crops including their net radiation balance, energy partitioning, and carbon cycle processes.

Description: Thymosin beta-4 (Tβ4) is a ubiquitous protein with many properties relating to cell proliferation and differentiation that promotes wound healing and modulates inflammatory mediators. However, the role of Tβ4 in cardiomyocyte hypertrophy is currently unknown. The purpose of this study was to determine the cardio-protective effect of Tβ4 in angiotensin II (Ang II)-induced cardiomyocytes growth. Neonatal rat ventricular cardiomyocytes (NRVM) were pretreated with Tβ4 followed by Ang II stimulation. Cell size, hypertrophy marker gene expression and Wnt signaling components, β-catenin and Wnt-induced secreted protein-1 (WISP-1) were evaluated by quantitative real-time PCR, Western blotting and fluorescent microscopy. Pre-treatment of Tβ4 resulted in reduction of cell size, hypertrophy marker genes and Wnt-associated gene expression and protein levels; induced by Ang II in cardiomyocytes. WISP-1 was overexpressed in NRVM and, the effect of Tβ4 in Ang II-induced cardiomyocytes growth was evaluated. WISP-1 overexpression promoted cardiomyocytes growth and was reversed by pretreatment with Tβ4. This is the first report which demonstrates that Tβ4 targets Wnt/WISP-1 to protect Ang II-induced cardiomyocyte growth. This article is protected by copyright. All rights reserved

Description: Accurately simulating gross primary productivity (GPP) in terrestrial ecosystem models is critical because errors in simulated GPP propagate through the model to introduce additional errors in simulated biomass and other fluxes. We evaluated simulated, daily average GPP from 26 models against estimated GPP at 39 eddy covariance flux tower sites across the United States and Canada. None of the models in this study match estimated GPP within observed uncertainty. On average, models overestimate GPP in winter, spring, and fall, and underestimate GPP in summer. Models overpredicted GPP under dry conditions and for temperatures below 0°C. Improvements in simulated soil moisture and ecosystem response to drought or humidity stress will improve simulated GPP under dry conditions. Adding a low-temperature response to shut down GPP for temperatures below 0°C will reduce the positive bias in winter, spring, and fall and improve simulated phenology. The negative bias in summer and poor overall performance resulted from mismatches between simulated and observed light use efficiency (LUE). Improving simulated GPP requires better leaf-to-canopy scaling and better values of model parameters that control the maximum potential GPP, such as εmax (LUE), Vcmax (unstressed Rubisco catalytic capacity) or Jmax (the maximum electron transport rate).

Description: We have previously shown that retinoic acid (RA) has protective effects on high glucose (HG)-induced cardiomyocyte apoptosis. To further elucidate the molecular mechanisms of RA effects, we determined the interaction between nuclear factor (NF)-κB and RA signaling. HG induced a sustained phosphorylation of IKK/IκBα and transcriptional activation of NF-κB in cardiomyocytes. Activated NF-κB signaling has an important role in HG-induced cardiomyocyte apoptosis and gene expression of interleukin-6 (IL-6), tumor necrosis factor (TNF)-α and monocyte chemoattractant protein-1 (MCP-1). All-trans RA (ATRA) and LGD1069, through activation of RAR/RXR-mediated signaling, inhibited the HG-mediated effects in cardiomyocytes. The inhibitory effect of RA on NF-κB activation was mediated through inhibition of IKK/IκBα phosphorylation. ATRA and LGD1069 treatment promoted protein phosphatase 2A (PP2A) activity, which was significantly suppressed by HG stimulation. The RA effects on IKK and IκBα were blocked by okadaic acid or silencing the expression of PP2Ac-subunit, indicating that the inhibitory effect of RA on NF-κB is regulated through activation of PP2A and subsequent dephosphorylation of IKK/IκBα. Moreover, ATRA and LGD1069 reversed the decreased PP2A activity and inhibited the activation of IKK/IκBα and gene expression of MCP-1, IL-6 and TNF-α in the hearts of Zucker diabetic fatty rats. In summary, our findings suggest that the suppressed activation of PP2A contributed to sustained activation of NF-κB in HG-stimulated cardiomyocytes; and that the protective effect of RA on hyperglycemia-induced cardiomyocyte apoptosis and inflammatory responses is partially regulated through activation of PP2A and suppression of NF-κB-mediated signaling and downstream targets. J. Cell. Physiol. © 2012 Wiley Periodicals, Inc.

Description: Lakes within fluvial networks may affect dissolved organic matter (DOM) dynamics in streams by dampening spring DOM snowmelt flushing responses and/or by increasing summer DOM production. We assessed the temporal variability of dissolved organic carbon (DOC) concentration and DOM characteristics (specific ultraviolet absorbance (SUVA254); DOC:dissolved organic nitrogen (DOC:DON)), as well as DOC export in seven paired lake inflows and outflows in the Sawtooth Mountain lake district, Idaho. We hypothesized that lakes would decrease stream DOM temporal variability and increase DOM export as a result of autotrophic production. We correlated DOM variability with landscape factors to evaluate potential drivers of DOM temporal patterns (measured as coefficient of variation). Coefficients of variation were 40–90% higher in lake inflows than outflows for DOC concentrations, characteristics, and DOC:DON. Increases in DOC concentrations on the ascending limb of the snowmelt hydrograph were greater in lake inflows than outflows, and on average mean DOC flux occurred 5.4 days earlier in the inflows than for the outflows. During base flow, mean outflow DOC concentrations were 1.7 times greater than inflows, and six outflows had higher annual export than inflows. Combined, these results illustrate that lakes alter the magnitude, timing and temporal variation of DOM concentration and characteristics exported from subalpine watersheds. This buffering effect results from a seasonal shift in the balance between hydrological versus biological controls on DOC dynamics, where lakes act as a sink during the spring when hydrologic controls dominate watershed DOM transport and act as a DOM source during summer.

Description: The oxygen isotope of water (18O-H2O) and carbon dioxide (18O-CO2) is an important signal of global change and can provide constraints on the coupled carbon-water cycle. Here, simultaneous observations of 18O-H2O (liquid and vapor phases) and 18O-CO2 were used to investigate the relation between canopy leaf water 18O enrichment, 18O-CO2 photosynthetic discrimination (18Δ), isotope disequilibrium (Deq), and the biophysical factors that control their temporal variability in a C4 (Zea mays L.) ecosystem. Data and analyses are presented from a 74 day experiment conducted in Minnesota during summer 2009. Eddy covariance observations indicate that the oxygen isotope composition of C4 evapotranspiration (δE) ranged from about −20‰ (VSMOW scale) in the early morning to −5‰ after midday. These values were used to estimate the isotope composition at the sites of leaf water evaporation (δL,e) assuming non-steady-state conditions and revealed a strong diurnal pattern ranging from about −5‰ in the early morning to +10‰ after midday. With the addition of net ecosystem CO2 exchange measurements and carbonic anhydrase (CA) assays, we derived canopy-scale 18Δ. These estimates typically varied from 11.3 to 27.5‰ (VPDB scale) and were shown to vary significantly depending on the steady state or non-steady-state assumptions related to leaf water enrichment. We demonstrate that the impact of turbulence on kinetic fractionation and steady state assumptions result in larger estimates of 18Δ and Deq. Further, the results indicate that both leaf-scale and canopy-scale CO2 hydration efficiency may be substantially lower than that previously reported for laboratory conditions. These results may have important implications for interpreting variations in atmospheric 18O-CO2 and constraining regional carbon budgets based on the oxygen isotope tracer approach.

Description: Biogeochemical reactions associated with stream nitrogen cycling, such as nitrification and denitrification, can be strongly controlled by water and solute residence times in the hyporheic zone (HZ). We used a whole-stream steady state 15N-labeled nitrate (15NO3−) and conservative tracer (Cl−) addition to investigate the spatial and temporal physiochemical conditions controlling the denitrification dynamics in the HZ of an upland agricultural stream. We measured solute concentrations (15NO3−, 15N2 (g), as well as NO3−, NH3, DOC, DO, Cl−), and hydraulic transport parameters (head, flow rates, flow paths, and residence time distributions) of the reach and along HZ flow paths of an instrumented gravel bar. HZ exchange was observed across the entire gravel bar (i.e., in all wells) with flow path lengths up to 4.2 m and corresponding median residence times greater than 28.5 h. The HZ transitioned from a net nitrification environment at its head (short residence times) to a net denitrification environment at its tail (long residence times). NO3− increased at short residence times from 0.32 to 0.54 mg-N L−1 until a threshold of 6.9 h and then consistently decreased from 0.54 to 0.03 mg-N L−1. Along these same flow paths, declines were seen in DO (from 8.31 to 0.59 mg-O2 L−1) and DOC (from 3.0 to 1.7 mg-C L−1). The rates of the DO and DOC removal and net nitrification were greatest during short residence times, while the rate of denitrification was greatest at long residence times. 15NO3− tracing confirmed that a fraction of the NO3− removal was via denitrification as 15N2 was produced across the entire gravel bar HZ. Production of 15N2 across all observed flow paths and residence times indicated that denitrification microsites are present even where nitrification was the net outcome. These findings demonstrate that the HZ is an active nitrogen sink in this system and that the distinction between net nitrification and denitrification in the HZ is a function of residence time and exhibits threshold behavior. Consequently, incorporation of HZ exchange and water residence time characterizations will improve mechanistic predictions of nitrogen cycling in streams.