Central role of guanylyl cyclase in natriuretic peptide signaling in hypertension and metabolic syndrome

Studied for nearly 30 years for its ability to control many parameters, such as vascular smooth muscle cell relaxation, heart fibrosis, and kidney function, the natriuretic peptide (NP) system is now considered to be a key element in several other major metabolic pathways. After stimulation by NPs, natriuretic peptide receptors (NPR) convert GTP to the second messenger cGMP. In addition to its vasodilatory effects and natriuretic and diuretic functions, cGMP has been positively associated with fat cell function, apoptosis, and NPR expression/activity modulation. The NP system is also closely linked to metabolic syndrome (MetS) progression and obesity control. A new era is now on its way targeting the NP system to not only treat high blood pressure, but to also assist in the fight against the obesity pandemic. Here, we summarize recent data on the role of NPs in hypertension and MetS.     

Thigmomorphogenesis in Solanum lycopersicum: Morphological and biochemical responses in stem after mechanical stimulation

The activation of the phenylpropanoid pathway in plants by environmental stimuli is one of the most universal biochemical stress responses known. In tomato plant, rubbing applied to a young internode inhibit elongation of the rubbed internode and his neighboring one. These morphological changes were correlated with an increase in lignification enzyme activities, phenylalanine ammonia-lyase (PAL), cinnamyl alcohol dehydrogenase (CAD) and peroxidases (POD), 24 hours after rubbing of the forth internode. Furthermore, a decrease in indole-3-acetic acid (IAA) content was detected in the rubbed internode and the upper one. Taken together, our results suggest that decrease in rubbed internode length is a consequence of IAA oxidation, increases in enzyme activities (PAL, CAD and POD), and cell wall rigidification associated with induction of lignification process.Key words: Mechanical stimulation, PAL, CAD, POD, IAAIn their environment, plants are constantly submitted to several stimuli such as wind, rain and wounding. The growth response of plants to such stimuli was termed thigmomorphogenesis and was observed in a wide range of plants.^1–3 The most common thigmomorphogenetic response is a retardation of tissue elongation accompanied by an increase in thickness.⁴ The plant response to mechanical perturbation is mainly restricted to the young developing internode, since no influence can be detected when the internode has reached its final length.^5,6 These plant growth modifications, which characterize thigmomorphogenesis, are related to biochemical events associated with lignification process⁷ and ethylene production.^8,9In tomato plant the length of internodes 4 (N4) and 5 (N5) was measured 14 days after rubbing of the fourth internode. Results reported in Figure 1 show that rubbing led to a significant reduction of elongation of the stressed internode (N4) (decrease of N4 length from 4.3 cm in the control plant to 2.9 in the rubbed one). This effect was not limited to the rubbed area but affected also the elongation of the neighboring internodes (N5) that were shorter in rubbed plants than in control ones.Open in a separate windowFigure 1Internode lengths of control and rubbed plants measured 14 day after mechanical stress applied to the fourth internode. Standard errors are indicated by vertical bars.Results reported in Figure 2 show an increase in PAL activity in both internodes N4 and N5, 24 hours after mechanical stress application as compared with corresponding controls. CAD activity was also investigated in N4 and N5, 24 h after rubbing of the fourth internode. Results presented in Figure 3 show that mechanical stress application induces a strong increase of CAD activity in the rubbed internode N4 (5.3 nkatal μg-1 protein) with an approximately two-fold increase when compared to control tomato internodes (2.3 nkatal μg-1 protein). Further, CAD activity in N5 was also increased in the rubbed internode (5.538 nkatal μg-1 protein) as compared with the control one (3.256 nkatal μg-1 protein).Open in a separate windowFigure 2PAL activity of internode 4, and 5 in control and rubbed plants 24 h after rubbing of the fourth internode. Standard errors are indicated by vertical bars.Open in a separate windowFigure 3CAD activity of internode 4, and 5 in control and rubbed plants 24 h after rubbing of the fourth internode. Standard errors are indicated by vertical bars.Syringaldazine (S-POD) and gaïacol (G-POD) peroxidase activities were measured in tomato N4 and N5. Results reported in Figure 4 show an increase in soluble peroxidase activity with both substrates in the rubbed internode N4 as compared with control plant. Enhancement in peroxidase activities in N4 was more pronounced with gaïacol (80.7 U) as an electron donor than syringaldazine (33.8 U). Similar results were observed in internode 5 as compared with control one (Fig. 4).Open in a separate windowFigure 4(A) Syringaldazine-POD (Syr-POD) activity of internode 4 and 5 in control and rubbed plants 24 h after rubbing of the fourth internode. Standard errors are indicated by vertical bars. (B) Gaiacol-POD (G-POD) activity of internode 4 and 5 in control and rubbed plants 24 h after rubbing of the fourth internode. Standard errors are indicated by vertical bars.IAA was quantified in control and rubbed plant internodes 24 h after rubbing of the fourth internode. Results reported in figure 5 show that in control sample and as expected, the content of IAA was found to be higher in the younger internode (N5) as compared to the older one (N4). Rubbing led to a significant decrease in IAA levels in N4 (5.06 nmol g⁻¹ MF⁻¹) as compared with corresponding controls (7.27 nmol g⁻¹ MF⁻¹). Similar results were observed in internode 5, where IAA content was reduced from 16.52 nmol g⁻¹ MF⁻¹ in control internode to 12.35 nmol g⁻¹ MF⁻¹ in the rubbed internode (Fig. 5).Open in a separate windowFigure 5IAA Level of internode 4 and 5 in control and rubbed plants 24 h after rubbing of the fourth internode. Standard errors are indicated by vertical bars.The results reported here establish an evident correlation between growth limitation of the rubbed internode and their degree of lignification, the increase in lignification enzymes activities and auxin degradation after mechanical stress application.Auxin seems to be involved in thigmomorphogenesis.¹⁰ It was proposed that MIS (Mechanically-induced stress) has opposite effects on auxin levels in the two species studied to date, Phaseolus vulgaris¹⁰ and Bryonia dioica.^11,12 Auxin level as measured by bioassay, increased in Phaseolus vulgaris following rubbing of the stem.¹⁰ It was proposed that a build up of auxin may result from the reduced polar transport of IAA at the rubbed internode, causing a build up of IAA in the stem tissue. Exogenous IAA did not reverse the MIS inhibition of growth in Phaseolus vulgaris and high levels of IAA retarded growth in non-stressed plants.¹⁰ Thus, retardation of extension growth in Phaseolus vulgaris may have been caused by high levels of endogenous auxin and the increase in stem diameter by increased ethylene production.⁴ However, ethylene increases radial growth only if auxin is present.¹³Boyer¹¹ reported a decrease in auxinlike activity in Bryonia dioica following MIS and this was confirmed in the same species by Hofinger et al.¹² who reported a decrease in IAA using gas chromatography-mass spectrometry. Auxin catabolism was accompanied with changes in both soluble and ionically bound cell wall basic peroxidases¹⁴ and the appearance of an additional peroxidase. This can suggest that in Bryonia, auxin catabolism is hastened by mechanical stimulated peroxidase. In addition, Boyer et al.¹⁵ reported that lithium pre-treatment prevents both thigmomorphogenesis and appearance of specific cathodic isoperoxidase in Bryonia plants subjected to MIS. This is give further credence to the possibility that the peroxidase-auxin system is involved in Bryonia thigmomorphogenesis. In addition, ethylene increases peroxidase activity which reduces the auxin content in the tissue to a level low enough not to support normal growth. We have evidence that decrease of auxin level contribute to mechanism leading to tomato internode inhibition subjected to mechanical stress.Growth inhibition has been suggested to be the result of tissues lignification.⁶ As the initial enzyme in the monolignol biosynthesis pathway, PAL has a direct influence on lignin accumulation.¹⁶ The characteristics of lignin differ among cell wall tissues and plant organs.¹⁷ It comprises polyphenolic polymers derived from the oxidative polymerization of different monolignols, including p-coumaryl, coniferyl and sinapyl alcohols via a side pathway of phenylalanine metabolism leading to lignin synthesis.¹⁸ The increase in lignin content in the rubbed tomato internode could be a response mechanism to mechanical damage caused by rubbing.³ It is known that plants create a natural barrier that includes lignin and suberin synthesis, components directly linked to support systems.^19,20The increase in lignin content of rubbed tomato internode³ is paralleled by a rise in CAD activity and whilst such direct proportionality between CAD activity and lignin accumulation does not always agree with the results in the literature, it clearly is responding in ways similar to those of the other enzymes in the pathway.²¹Mechanical stress-induced membrane depolarization would generate different species of free radicals and peroxides, which in turn initiate lipid peroxidation.²² The degradation of cell membranes is suggested to bring about rapid changes in ionic flux, especially release of K⁺ which would result in an enhanced endogenous Ca/K ratio and in leakage of solutes, among them electron donors such as ascorbic acid and phenolic substances. The increased intracellular relative calcium level activated secretion of basic peroxidases²³ into the free space where, in association with the electron donors and may be with the circulating IAA, they eliminate the peroxides, and facilitated binding of basic peroxidases to membrane structures allowing a role as 1-aminocyclopropane-1-carboxylic acid (ACC)-oxidases. The resulting IAA and ACC oxidase-mediated changes in ethylene production²⁴ would further induce (this time through the protein synthesis machinery) an increase in activity of phenylalanine ammonia-lyase and peroxidases. The resulting lignification and cell wall rigidification determines the growth response of tomato internode to the mechanical stress.     

Nitrogen fluxes from treefrogs to tank epiphytic bromeliads: an isotopic and physiological approach

Diverse invertebrate and vertebrate species live in association with plants of the large Neotropical family Bromeliaceae. Although previous studies have assumed that debris of associated organisms improves plant nutrition, so far little evidence supports this assumption. In this study we used isotopic (¹⁵N) and physiological methods to investigate if the treefrog Scinax hayii, which uses the tank epiphytic bromeliad Vriesea bituminosa as a diurnal shelter, contributes to host plant nutrition. In the field, bromeliads with frogs had higher stable N isotopic composition (δ¹⁵N) values than those without frogs. Similar results were obtained from a controlled greenhouse experiment. Linear mixing models showed that frog feces and dead termites used to simulate insects that eventually fall inside the bromeliad tank contributed, respectively, 27.7% (±0.07 SE) and 49.6% (±0.50 SE) of the total N of V. bituminosa. Net photosynthetic rate was higher in plants that received feces and termites than in controls; however, this effect was only detected in the rainy, but not in the dry season. These results demonstrate for the first time that vertebrates contribute to bromeliad nutrition, and that this benefit is seasonally restricted. Since amphibian–bromeliad associations occur in diverse habitats in South and Central America, this mechanism for deriving nutrients may be important in bromeliad systems throughout the Neotropics.     

Both caffeoyl Coenzyme A 3-<Emphasis Type="Italic">O</Emphasis>-methyltransferase 1 and caffeic acid <Emphasis Type="Italic">O</Emphasis>-methyltransferase 1 are involved in redundant functions for lignin,flavonoids and sinapoyl malate biosynthesis in Arabidopsis

Two methylation steps are necessary for the biosynthesis of monolignols, the lignin precursors. Caffeic acid O-methyltransferase (COMT) O-methylates at the C5 position of the phenolic ring. COMT is responsible for the biosynthesis of sinapyl alcohol, the precursor of syringyl lignin units. The O-methylation at the C3 position of the phenolic ring involves the Caffeoyl CoA 3-O-methyltransferase (CCoAOMT). The CCoAOMT 1 gene (At4g34050) is believed to encode the enzyme responsible for the first O-methylation in Arabidopsis thaliana. A CCoAOMT1 promoter-GUS fusion and immunolocalization experiments revealed that this gene is strongly and exclusively expressed in the vascular tissues of stems and roots. An Arabidopsis T-DNA null mutant named ccomt 1 was identified and characterised. The mutant stems are slightly smaller than wild-type stems in short-day growth conditions and has collapsed xylem elements. The lignin content of the stem is low and the S/G ratio is high mainly due to fewer G units. These results suggest that this O-methyltransferase is involved in G-unit biosynthesis but does not act alone to perform this step in monolignol biosynthesis. To determine which O-methyltransferase assists CCoAOMT 1, a comt 1 ccomt1 double mutant was generated and studied. The development of comt 1 ccomt1 is arrested at the plantlet stage in our growth conditions. Lignins of these plantlets are mainly composed of p-hydroxyphenyl units. Moreover, the double mutant does not synthesize sinapoyl malate, a soluble phenolic. These results suggest that CCoAOMT 1 and COMT 1 act together to methylate the C3 position of the phenolic ring of monolignols in Arabidopsis. In addition, they are both involved in the formation of sinapoyl malate and isorhamnetin.     

Effects of high-intensity training on MCT1, MCT4, and NBC expressions in rat skeletal muscles: influence of chronic metabolic alkalosis

This study investigated the effects of high-intensity training, with or without induced metabolic alkalosis, on lactate transporter (MCT1 and MCT4) and sodium bicarbonate cotransporter (NBC) content in rat skeletal muscles. Male Wistar rats performed high-intensity training on a treadmill 5 times/wk for 5 wk, receiving either sodium bicarbonate (ALK-T) or a placebo (PLA-T) prior to each training session, and were compared with a group of control rats (CON). MCT1, MCT4, and NBC content was measured by Western blotting in soleus and extensor digitorum longus (EDL) skeletal muscles. Citrate synthase (CS) and phosphofructokinase (PFK) activities and muscle buffer capacity (betam) were also evaluated. Following training, CS and PFK activities were significantly higher in the soleus only (P < 0.05), whereas betam was significantly higher in both soleus and EDL (P < 0.05). MCT1 (PLA-T: 30%; ALK-T: 23%) and NBC contents (PLA-T: 85%; ALK-T: 60%) increased significantly only in the soleus following training (P < 0.01). MCT4 content in the soleus was significantly greater in ALK-T (115%) but not PLA-T compared with CON. There was no significant change in protein content in the EDL. Finally, NBC content was related only to MCT1 content in soleus (r = 0.50, P < 0.01). In conclusion, these results suggest that MCT1, MCT4, and NBC undergo fiber-specific adaptive changes in response to high-intensity training and that induced alkalosis has a positive effect on training-induced changes in MCT4 content. The correlation between MCT1 and NBC expression suggests that lactate transport may be facilitated by NBC in oxidative skeletal muscle, which may in turn favor better muscle pH regulation.     

Newly identified biologically active and proteolysis-resistant VEGF-A isoform VEGF111 is induced by genotoxic agents

Ultraviolet B and genotoxic drugs induce the expression of a vascular endothelial growth factor A (VEGF-A) splice variant (VEGF111) encoded by exons 1–4 and 8 in many cultured cells. Although not detected in a series of normal human and mouse tissue, VEGF111 expression is induced in MCF-7 xenografts in nude mice upon treatment by camptothecin. The skipping of exons that contain proteolytic cleavage sites and extracellular matrix–binding domains makes VEGF111 diffusible and resistant to proteolysis. Recombinant VEGF111 activates VEGF receptor 2 (VEGF-R2) and extracellularly regulated kinase 1/2 in human umbilical vascular endothelial cells and porcine aortic endothelial cells expressing VEGF-R2. The mitogenic and chemotactic activity and VEGF111's ability to promote vascular network formation during embyonic stem cell differentiation are similar to those of VEGF121 and 165. Tumors in nude mice formed by HEK293 cells expressing VEGF111 develop a more widespread network of numerous small vessels in the peritumoral tissue than those expressing other isoforms. Its potent angiogenic activity and remarkable resistance to proteolysis makes VEGF111 a potential adverse factor during chemotherapy but a beneficial therapeutic tool for ischemic diseases.     

Hammering,mauling, and kissing: stereotyped courtship behavior in <Emphasis Type="Italic">Cardiocondyla</Emphasis> ants

Sex appears to be a rather prosaic and casual event in the life of most social Hymenoptera. In contrast, mating in the ant genus Cardiocondyla is regularly preceded by a prolonged and stereotypic courtship display. Pummeling the head of the female with mandibles and / or antennae and vibrations of the gaster, presumably stridulation, are essential parts of male courtship. The overall structure of the mating pattern is conserved throughout species and between winged and wingless, “ergatoid” males, but exhibits species-specific idiosyncrasies. For example, C. elegans males regularly end the interaction with a female with a short mouth-to-mouth contact. Variation in the duration of the precopulatory phase and the copulation itself might reflect different degrees of inter- and intrasexual selection. More information on the dynamics of sperm transfer and the risk and intensity of sperm competition are needed to better understand the evolution of the complex mating behavior in this genus. Received 15 December 2006; revised 25 June 2007; accepted 11 September 2007.