Farnesoid X receptor: A “homeostat” for hepatic nutrient metabolism

The Farnesoid X receptor (FXR) is a nuclear receptor activated by bile acids (BAs). BAs are amphipathic molecules that serve as fat solubilizers in the intestine under postprandial conditions. In the post-absorptive state, BAs bind FXR in the hepatocytes, which in turn provides feedback signals on BA synthesis and transport and regulates lipid, glucose and amino acid metabolism. Therefore, FXR acts as a homeostat of all three classes of nutrients, fats, sugars and proteins. Here we re-analyze the function of FXR in the perspective of nutritional metabolism, and discuss the role of FXR in liver energy homeostasis in postprandial, post-absorptive and fasting/starvation states.FXR, by regulating nutritional metabolism, represses autophagy in conditions of nutrient abundance, and controls the metabolic needs of proliferative cells. In addition, FXR regulates inflammation via direct effects and via its impact on nutrient metabolism. These functions indicate that FXR is an attractive therapeutic target for liver diseases.     

Comparative analysis of photosynthetic and respiratory parameters in the psychrophilic unicellular green alga <Emphasis Type="Italic">Koliella antarctica</Emphasis>, cultured in indoor and outdoor photo-bioreactors

Effect of temperatures and illumination of temperate winter on photosynthesis and respiration was studied in the psychrophilic microalgae, Koliella antarctica (Trebouxiophyceae). Outdoor and indoor algal cultures were compared. Photosynthetic as well as respiration rates increased as light and temperature increased, until 35 °C, more in outdoor than in indoor cells, in agreement with the calculated Q₁₀ values. K. antarctica showed important strategy mechanisms of adaption to the several temperature and light conditions. These significant photo-acclimation and thermo-acclimation abilities make it possible to cultivate Koliella for different uses, under less expensive outdoor conditions. Therefore, K. antarctica shows important strategy mechanisms of adaption to various temperature and light conditions; moreover, by varying the culture conditions, it is possible to modulate and optimize the growth and accordingly the biomass production. This is a very interesting point since it has been proved that this microalga is a promising potential source of functional ingredients, such as polyunsaturated fatty acids and carotenoids, suitable for industrial purposes.     

MicroRNAs in durum wheat seedlings under chronic and short-term nitrogen stress

Nitrogen is an essential macronutrient for plant growth and reproduction. In durum wheat, an appropriate nitrogen soil availability is essential for an optimal seed development. miRNAs contribute to the environmental change adaptation of plants through the regulation of important genes involved in stress processes. In this work, nitrogen stress response was evaluated in durum wheat seedlings of Ciccio and Svevo cultivars. Eight small RNA libraries from leaves and roots of chronically stressed plants were sequenced to detect conserved and novel miRNAs. A total of 294 miRNAs were identified, 7 of which were described here for the first time. The expression level of selected miRNAs and target genes was analyzed by qPCR in seedlings subjected to chronic (Ciccio and Svevo, leaves and roots) or short-term (Svevo roots) stress conditions. Some miRNAs showed an immediate stress response, and their level of expression was either maintained or returned to a basal level during a long-term stress. Other miRNAs showed a gradual up- or downregulation during the short-term stress. The newly identified miRNA ttu-novel-106 showed an immediate strongly downregulation after nitrogen stress, which was negatively correlated with the expression of MYB-A, its putative target gene. PHO2 gene was significantly upregulated after 24–48-h stress, corresponding to a downregulation of miR399b. Ttu-miR399b putative binding sites in the 5′ UTR region of the Svevo PHO2 gene were identified in the A and B genomes. Both MYB-A and PHO2 genes were validated for their cleavage site using 5′ RACE assay.     

Stimulation of carrot somatic embryogenesis by proline and serine

Serine and proline, when added in a wide range of concentrations to Daucus carota cultures during pre-growth in the presence of 2,4-D(2,4-dichlorophenoxyacetic acid), extended in time and quantity the mitotic divisions and stimulated significantly the number of embryos regenerated when the hormone subsequently was omitted from the medium. A specific effect of these amino acids on regeneration is suggested, since proline (as hydroxyproline) and serine are the two major constituents of the cell wall glycoprotein, extensin, which thus may have a morphoregulatory function. The significant role of the conditions during pregrowth of the cultures in the presence of hormone is underlined by the effect of hydroxyproline and D-proline which also stimulate embryogenesis, but alter markedly the development of the embryos.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - 6-BAP 6-benzylaminopurine - Pro proline - Ser serine - Ala alanine - Glu glutamic acid - Leu leucine - Hyp Hydroxyproline - FC fusicoccin     

Evidence for two transport systems for nitrate in the acidophilic thermophilic alga Cyanidium caldarium

In the unicellular non-vacuolate red alga Cyanidium caldarium nitrate uptake occurs through two specific permease systems which, on the basis of kinetic constants can be defined as low affinity system and high affinity system. The high affinity system is saturated at very low nitrate concentrations (<1 M), whereas the low affinity system is saturated only at high nitrate concentrations (K _m=0.45±0.10 mM). The low affinity system is present in cells growing under conditions of nitrogen limitation as well as in cells growing in excess nitrate. In contrast, the high affinity system is present only in cells growing under conditions of nitrogen limitation. The high affinity system works only at acid pH and is inactive at neutral pH. The low affinity system is active both at acid and at neutral pH.     

Nitrate reductase and glutamine synthetase activities,nitrate and ammonia assimilation,in the unicellular alga Cyanidium caldarium

Nitrogen-limited continuous cultures of Cyanidium caldarium contained induced levels of glutamine synthetase and nitrate reductase when either nitrate or ammonia was the sole nitrogen source. Nitrate reductase occurred in a catalytically active form. In the presence of excess ammonia, glutamine synthetase and nitrate reductase were repressed, the latter enzyme completely. In the presence of excess nitrate, intermediate levels of glutamine synthetase activity occurred. Nitrate reductase was derepressed but occurred up to 60% in a catalytically inactive form.Cell suspensions of C. caldarium from nitrate- or ammonialimited cultures assimilated either ammonia or nitrate immediately when provided with these nutrients. In these types of cells, as well as in cells grown with excess nitrate, the rate of ammonia assimilation was 2.5-fold higher than the rate of nitrate assimilation. It is proposed that the reduced rate at which nitrate was assimilated as compared to ammonia might be due to regulatory mechanisms which operate at the level of nitrate reductase activity.     

Effect of darkness and CO2 starvation on NH4+ and NO3− assimilation in the unicellular alga Cyanidium caldarium

Cyanidium caldarium (Tilden) Geitler, a non-vacuolate unicellular alga, resuspended in medium flushed with air enriched with 5% CO₂, assimilated NH₄⁺ at high rates both in the light and in the dark. The assimilation of NO₃⁻, by contrast, was inhibited by 63% in the dark. In cell suspensions flushed with CO₂-free air, NH₄⁺ assimilation decreased with time both in the light and in the dark and ceased almost completely after 90 min. The addition of CO₂ completely restored the capacity of the alga to assimilate NH₄⁺. NO₃⁻ assimilation, by contrast, was 33% higher in the absence of CO₂ and was linear with time. It is suggested that NO₃⁻ and NH₄⁺ metabolism in C. caldarium are differently controlled in response to the light and carbon conditions of the cell.     

The lipopeptides Pal-Lys-Lys-NH(2) and Pal-Lys-Lys soaking alone and in combination with intraperitoneal vancomycin prevent vascular graft biofilm in a subcutaneous rat pouch model of staphylococcal infection

Staphylococcal infections are often associated with the use of implantable medical devices. Such infections are difficult to treat because of biofilm resistance to antibiotics and are common causes of morbidity and mortality. Graft infections were established in the back subcutaneous tissue of adult male Wistar rats by implantation of Dacron prostheses followed by topical inoculation with 2x10(7) colony-forming units of bacterial strains. The study included a control group, a contaminated group that did not receive any antibiotic prophylaxis and five contaminated groups that received intraperitoneal vancomycin, Pal-Lys-Lys-NH(2) and Pal-Lys-Lys-soacked graft, and vancomycin plus Pal-Lys-Lys-NH(2) or Pal-Lys-Lys-soacked graft, respectively. The infection was evaluated by using sonication and quantitative agar culture. Moreover, an in vitro antibiotic susceptibility assay for Staphylococcus aureus biofilms was performed to elucidate the same activity. When tested alone, vancomycin and lipopeptides showed comparable efficacies. All combinations showed efficacies significantly higher than that of each single compound. Vancomycin combined to Pal-Lys-Lys-NH(2) exerted the strongest anti-staphylococcal efficacies. The in vitro studies showed, that MIC and MBC values for vancomycin were lower in presence of lipopeptides. They reduce the bacterial load and to enhance the effect of vancomycin in the prevention of vascular graft staphylococcal infections.     

Filamin A is mutated in X-linked chronic idiopathic intestinal pseudo-obstruction with central nervous system involvement

We have previously reported that an X-linked recessive form of chronic idiopathic intestinal pseudo-obstruction (CIIPX) maps to Xq28. To select candidate genes for the disease, we analyzed the expression in murine fetal brain and intestine of 56 genes from the critical region. We selected and sequenced seven genes and found that one affected male from a large CIIPX-affected kindred bears a 2-bp deletion in exon 2 of the FLNA gene that is present at the heterozygous state in the carrier females of the family. The frameshift mutation is located between two close methionines at the filamin N terminus and is predicted to produce a protein truncated shortly after the first predicted methionine. Loss-of-function FLNA mutations have been associated with X-linked dominant nodular ventricular heterotopia (PVNH), a central nervous system (CNS) migration defect that presents with seizures in females and lethality in males. Notably, the affected male bearing the FLNA deletion had signs of CNS involvement and potentially has PVNH. To understand how the severe frameshift mutation we found can explain the CIIPX phenotype and its X-linked recessive inheritance, we transiently expressed both the wild- type and mutant filamin in cell culture and found that filamin translation can start from either of the two initial methionines in these conditions. Therefore, translation of a normal shorter filamin can occur in vitro from the second methionine downstream of the 2-bp insertion we found. We confirmed this, demonstrating that the filamin protein is present in the patient's lymphoblastoid cell line that shows abnormal cytoskeletal actin organization compared with normal lymphoblasts. We conclude that the filamin N terminal region between the initial two methionines is crucial for proper enteric neuron development.