Effects of elevated pCO2 on the metabolism of a temperate rhodolith Lithothamnion corallioides grown under different temperatures

Coralline algae are considered among the most sensitive species to near future ocean acidification. We tested the effects of elevated pCO₂ on the metabolism of the free‐living coralline alga Lithothamnion corallioides (“maerl”) and the interactions with changes in temperature. Specimens were collected in North Brittany (France) and grown for 3 months at pCO₂ of 380 (ambient pCO₂), 550, 750, and 1000 μatm (elevated pCO₂) and at successive temperatures of 10°C (ambient temperature in winter), 16°C (ambient temperature in summer), and 19°C (ambient temperature in summer +3°C). At each temperature, gross primary production, respiration (oxygen flux), and calcification (alkalinity flux) rates were assessed in the light and dark. Pigments were determined by HPLC. Chl a, carotene, and zeaxanthin were the three major pigments found in L. corallioides thalli. Elevated pCO₂ did not affect pigment content while temperature slightly decreased zeaxanthin and carotene content at 10°C. Gross production was not affected by temperature but was significantly affected by pCO₂ with an increase between 380 and 550 μatm. Light, dark, and diel (24 h) calcification rates strongly decreased with increasing pCO₂ regardless of the temperature. Although elevated pCO₂ only slightly affected gross production in L. corallioides, diel net calcification was reduced by up to 80% under the 1,000 μatm treatment. Our findings suggested that near future levels of CO₂ will have profound consequences for carbon and carbonate budgets in rhodolith beds and for the sustainability of these habitats.     

Analysis of the growth of Chlorella cultures using electronically measured cell-volume distribution data

Cell-number density and cell-volume distribution data were obtained from cultures of Chlorella fusca var. vacuolata Shihira & Krauss growing under both continuous and periodic illumination. Mean, median and modal cell-volumes were calculated from the cell-volume distributions and a high correlation shown between mean and median values, whilst mean and modal values did not correlate well. It was concluded that where the computation necessary for deriving mean cell-volumes was not practicable, the median cell-volume was the next most useful statistic.

Synchrony indices of discontinuously illuminated cultures gave similar values when based on change in cell-number and change in mean cell-volume. Cultures under continuous illumination showed synchronous divisions at the beginning of growth. These divisions gave high values of a synchrony index based on change in cell-number, but low values of an index based on change in mean cell-volume. It was concluded that mean cell-volume data are more sensitive to the occurrence of unbalanced growth than analysis of cell-number data.     

Effects of β1 →4 Linked Galactooligosaccharides on Use of Magnesium and Calcification of the Kidney and Heart in Rats Fed Excess Dietary Phosphorus and Calcium

Magnesium deficiency was induced in male Wistar rats by adding an excess of phosphorus and calcium to the diet (1.195 g of phosphorus and 1.04g of calcium/100g of diet). Feeding of these animals with a diet containing β1→4 linked galactooligosaccharides (4′-GOS) (5g of 4′-GOS/100g of diet) increased the apparent magnesium absorption ratios and the concentrations of magnesium in the serum and femur, and reduced accumulation of calcium in the kidney and heart. We speculate that the use of magnesium increased by feeding 4′-GOS to a limited extent prevented the lower magnesium status and the severity of calcification of the kidney and heart caused by excess dietary phosphorus and calcium.     

Chronic senolytic treatment alleviates established vasomotor dysfunction in aged or atherosclerotic mice

While reports suggest a single dose of senolytics may improve vasomotor function, the structural and functional impact of long‐term senolytic treatment is unknown. To determine whether long‐term senolytic treatment improves vasomotor function, vascular stiffness, and intimal plaque size and composition in aged or hypercholesterolemic mice with established disease. Senolytic treatment (intermittent treatment with Dasatinib + Quercetin via oral gavage) resulted in significant reductions in senescent cell markers (TAF⁺ cells) in the medial layer of aorta from aged and hypercholesterolemic mice, but not in intimal atherosclerotic plaques. While senolytic treatment significantly improved vasomotor function (isolated organ chamber baths) in both groups of mice, this was due to increases in nitric oxide bioavailability in aged mice and increases in sensitivity to NO donors in hypercholesterolemic mice. Genetic clearance of senescent cells in aged normocholesterolemic INK‐ATTAC mice phenocopied changes elicited by D+Q. Senolytics tended to reduce aortic calcification (alizarin red) and osteogenic signaling (qRT–PCR, immunohistochemistry) in aged mice, but both were significantly reduced by senolytic treatment in hypercholesterolemic mice. Intimal plaque fibrosis (picrosirius red) was not changed appreciably by chronic senolytic treatment. This is the first study to demonstrate that chronic clearance of senescent cells improves established vascular phenotypes associated with aging and chronic hypercholesterolemia, and may be a viable therapeutic intervention to reduce morbidity and mortality from cardiovascular diseases.     

Deficiency in the anti‐aging gene Klotho promotes aortic valve fibrosis through AMPKα‐mediated activation of RUNX2

Fibrotic aortic valve disease (FAVD) is an important cause of aortic stenosis, yet currently there is no effective treatment for FAVD due to its unknown etiology. The purpose of this study was to investigate whether deficiency in the anti‐aging Klotho gene (KL) promotes high‐fat‐diet‐induced FAVD and to explore the underlying molecular mechanism. Heterozygous Klotho‐deficient (KL^+/?) mice and WT littermates were fed with a high‐fat diet (HFD) or normal diet for 13 weeks, followed by treatment with the AMPKα activator (AICAR) for an additional 2 weeks. A HFD caused a greater increase in collagen levels in the aortic valves of KL^+/? mice than of WT mice, indicating that Klotho deficiency promotes HFD‐induced aortic valve fibrosis (AVF). AMPKα activity (pAMPKα) was decreased, while protein expression of collagen I and RUNX2 was increased in the aortic valves of KL^+/? mice fed with a HFD. Treatment with AICAR markedly attenuated HFD‐induced AVF in KL^+/? mice. AICAR not only abolished the downregulation of pAMPKα but also eliminated the upregulation of collagen I and RUNX2 in the aortic valves of KL^+/? mice fed with HFD. In cultured porcine aortic valve interstitial cells, Klotho‐deficient serum plus cholesterol increased RUNX2 and collagen I protein expression, which were attenuated by activation of AMPKα by AICAR. Interestingly, silencing of RUNX2 abolished the stimulatory effect of Klotho deficiency on cholesterol‐induced upregulation of matrix proteins, including collagen I and osteocalcin. In conclusion, Klotho gene deficiency promotes HFD‐induced fibrosis in aortic valves, likely through the AMPKα–RUNX2 pathway.     

Mechanical robustness of the calcareous tubeworm Hydroides elegans: warming mitigates the adverse effects of ocean acidification

Development of antifouling strategies requires knowledge of how fouling organisms would respond to climate change associated environmental stressors. Here, a calcareous tube built by the tubeworm, Hydroides elegans, was used as an example to evaluate the individual and interactive effects of ocean acidification (OA), warming and reduced salinity on the mechanical properties of a tube. Tubeworms produce a mechanically weaker tube with less resistance to simulated predator attack under OA (pH 7.8). Warming (29°C) increased tube volume, tube mineral density and the tube’s resistance to a simulated predatory attack. A weakening effect by OA did not make the removal of tubeworms easier except for the earliest stage, in which warming had the least effect. Reduced salinity (27 psu) did not affect tubes. This study showed that both mechanical analysis and computational modeling can be integrated with biofouling research to provide insights into how fouling communities might develop in future ocean conditions.     

Three-dimensional macro-scale assessment of regional and temporal wall shear stress characteristics on aortic valve leaflets

The aortic valve (AV) achieves unidirectional blood flow between the left ventricle and the aorta. Although hemodynamic stresses have been shown to regulate valvular biology, the native wall shear stress (WSS) experienced by AV leaflets remains largely unknown. The objective of this study was to quantify computationally the macro-scale leaflet WSS environment using fluid–structure interaction modeling. An arbitrary Lagrangian–Eulerian approach was implemented to predict valvular flow and leaflet dynamics in a three-dimensional AV geometry subjected to physiologic transvalvular pressure. Local WSS characteristics were quantified in terms of temporal shear magnitude (TSM), oscillatory shear index (OSI) and temporal shear gradient (TSG). The dominant radial WSS predicted on the leaflets exhibited high amplitude and unidirectionality on the ventricularis (TSM>7.50 dyn/cm², OSI < 0.17, TSG>325.54 dyn/cm² s) but low amplitude and bidirectionality on the fibrosa (TSM < 2.73 dyn/cm², OSI>0.38, TSG < 191.17 dyn/cm² s). The radial WSS component computed in the leaflet base, belly and tip demonstrated strong regional variability (ventricularis TSM: 7.50–22.32 dyn/cm², fibrosa TSM: 1.26–2.73 dyn/cm²). While the circumferential WSS exhibited similar spatially dependent magnitude (ventricularis TSM: 1.41–3.40 dyn/cm², fibrosa TSM: 0.42–0.76 dyn/cm²) and side-specific amplitude (ventricularis TSG: 101.73–184.43 dyn/cm² s, fibrosa TSG: 41.92–54.10 dyn/cm² s), its temporal variations were consistently bidirectional (OSI>0.25). This study provides new insights into the role played by leaflet–blood flow interactions in valvular function and critical hemodynamic stress data for the assessment of the hemodynamic theory of AV disease.