Inverse Agonistic Action of 3-Iodothyronamine at the Human Trace Amine-Associated Receptor 5

ObjectiveApplication of 3-iodothyronamine (3-T₁AM) results in decreased body temperature and body weight in rodents. The trace amine-associated receptor (TAAR) 1, a family A G protein-coupled receptor, is a target of 3-T₁AM. However, 3-T₁AM effects still persist in mTaar1 knockout mice, which suggest so far unknown further receptor targets that are of physiological relevance. TAAR5 is a highly conserved TAAR subtype among mammals and we here tested TAAR5 as a potential 3-T₁AM target. First, we investigated mouse Taar5 (mTaar5) expression in several brain regions of the mouse in comparison to mTaar1. Secondly, to unravel the full spectrum of signaling capacities, we examined the distinct G_s-, G_i/o-, G_12/13-, G_q/11- and MAP kinase-mediated signaling pathways of mouse and human TAAR5 under ligand-independent conditions and after application of 3-T₁AM. We found overlapping localization of mTaar1 and mTaar5 in the amygdala and ventromedial hypothalamus of the mouse brain. Second, the murine and human TAAR5 (hTAAR5) display significant basal activity in the G_q/11 pathway but show differences in the basal activity in G_s and MAP kinase signaling. In contrast to mTaar5, 3-T₁AM application at hTAAR5 resulted in significant reduction in basal IP₃ formation and MAP kinase signaling. In conclusion, our data suggest that the human TAAR5 is a target for 3-T₁AM, exhibiting inhibitory effects on IP₃ formation and MAP kinase signaling pathways, but does not mediate G_s signaling effects as observed for TAAR1. This study also indicates differences between TAAR5 orthologs with respect to their signaling profile. In consequence, 3-T₁AM-mediated effects may differ between rodents and humans.     

Local chromatin microenvironment determines DNMT activity: from DNA methyltransferase to DNA demethylase or DNA dehydroxymethylase

Insights on active DNA demethylation disproved the original assumption that DNA methylation is a stable epigenetic modification. Interestingly, mammalian DNA methyltransferases 3A and 3B (DNMT-3A and -3B) have also been reported to induce active DNA demethylation, in addition to their well-known function in catalyzing methylation. In situations of extremely low levels of S-adenosyl methionine (SAM), DNMT-3A and -3B might demethylate C-5 methyl cytosine (5mC) via deamination to thymine, which is subsequently replaced by an unmodified cytosine through the base excision repair (BER) pathway. Alternatively, 5mC when converted to 5- hydroxymethylcytosine (5hmC) by TET enzymes, might be further modified to an unmodified cytosine by DNMT-3A and -3B under oxidized redox conditions, although exact pathways are yet to be elucidated. Interestingly, even direct conversion of 5mC to cytosine might be catalyzed by DNMTs. Here, we summarize the evidence on the DNA dehydroxymethylase and demethylase activity of DNMT-3A and -3B. Although physiological relevance needs to be demonstrated, the current indications on the 5mC- and 5hmC-modifying activities of de novo DNA C-5 methyltransferases shed a new light on these enzymes. Despite the extreme circumstances required for such unexpected reactions to occur, we here put forward that the chromatin microenvironment can be locally exposed to extreme conditions, and hypothesize that such waves of extremes allow enzymes to act in differential ways.     

Biochemical characterization and structure–function relationship of two plant NCS2 proteins,the nucleobase transporters NAT3 and NAT12 from Arabidopsis thaliana

Nucleobase ascorbate transporters (NATs), also known as Nucleobase:Cation-Symporter 2 (NCS2) proteins, belong to an evolutionary widespread family of transport proteins with members in nearly all domains of life. We present the biochemical characterization of two NAT proteins, NAT3 and NAT12 from Arabidopsis thaliana after their heterologous expression in Escherichia coli UraA knockout mutants. Both proteins were shown to transport adenine, guanine and uracil with high affinities. The apparent K_M values were determined with 10.12 μM, 4.85 μM and 19.95 μM, respectively for NAT3 and 1.74 μM, 2.44 μM and 29.83 μM, respectively for NAT12. Competition studies with the three substrates suggest hypoxanthine as a further substrate of both transporters. Furthermore, the transport of nucleobases was markedly inhibited by low concentrations of a proton uncoupler indicating that NAT3 and NAT12 act as proton–nucleobase symporters. Transient expression studies of NAT-GFP fusion constructs revealed a localization of both proteins in the plasma membrane. Based on the structural information of the uracil permease UraA from E. coli, a three-dimensional experimentally validated homology model of NAT12 was created. The NAT12 structural model is composed of 14 TM segments and divided into two inverted repeats of TM1–7 and TM8–14. Docking studies and mutational analyses identified residues involved in NAT12 nucleobase binding including Ser-247, Phe-248, Asp-461, Thr-507 and Thr-508. This is the first study to provide insight into the structure–function of plant NAT proteins, which reveals differences from the other members of the NCS2 protein family.     

C-type natriuretic peptide (CNP) signal peptide fragments are present in the human circulation

Background

Signal peptides may be novel biomarkers in cardiovascular diseases.

Methods

We developed a novel immunoassay to the signal peptide of preproCNP (CNPsp) and used this to document circulating venous concentrations of CNPsp in normal healthy volunteers (n = 109), regional plasma CNPsp concentrations in patients undergoing clinically indicated catheterisation (n = 24) and temporal CNPsp concentrations in patients with ST-elevation myocardial infarction (STEMI) <4 h after symptom onset (n = 8). The structure/sequence of circulating CNPsp was confirmed by tandem mass spectrometry (MS/MS).

Results

In normal human plasma, CNPsp was detectable at levels higher than NT-proCNP (74 ± 17 vs. 20 ± 5.5 pmol/L). There was no correlation between NTproCNP and CNPsp, but plasma concentrations of sibling signal peptides – CNPsp and BNPsp – were strongly correlated (r = 0.532, P < 0.001). In patients undergoing catheterisation, there were significant arterio-venous step-ups in CNPsp concentrations across the heart (P < 0.01) and kidney (P < 0.01). Arterial concentrations of CNPsp significantly correlated with heart rate (r = 0.446, P < 0.05). In STEMI patients, plasma concentrations of CNPsp showed a biphasic elevation pattern between 6 and 12 h after symptom onset, with 12 h values significantly elevated (∼3-fold) compared with levels at presentation (P < 0.05). MS/MS verified circulating CNPsp to be preproCNP(14–23) and preproCNP(16–23) peptides.

Conclusions

This is the first report of a circulating preproCNP derived signal peptide. Given the clear cardiac and renal secretion profiles of CNPsp and its response in STEMI patients, further studies on potential biological functions and biomarker applications of CNPsp in cardiovascular disease are warranted.     

Proteome and radioimmunoassay analyses of pituitary hormones and proteins in response to feed restriction of dairy cows

The hypothalamic-pituitary system controls homeostasis during feed energy reduction. In order to examine which pituitary proteins and hormone variants are potentially associated with metabolic adaptation, pituitary glands from ad libitum and energy restrictively fed dairy cows were characterized using RIA and 2-DE followed by MALDI-TOF-MS. We found 64 different spots of regulatory hormones: growth hormone (44), preprolactin (16), luteinizing hormone (LH) (1), thyrotropin (1), proopiomelanocortin (1) and its cleavage product lipotropin (1), but none of these did significantly differ between feeding groups. Quantification of total pituitary LH and prolactin concentrations by RIA confirmed the results obtained by proteome analysis. Also, feed energy restriction provoked increasing non-esterified fatty acid, decreasing prolactin, but unaltered glucose, LH and growth hormone plasma concentrations. Energy restriction decreased the expression of glial fibrillary acidic protein, triosephosphate isomerase, purine-rich element-binding protein A and elongation factor Tu, whereas it increased expression of proline synthetase co-transcribed homolog, peroxiredoxin III, β-tubulin and annexin A5 which is involved in the hormone secretion process. Our results indicate that in response to feed energy restriction the pituitary reservoir of all posttranslationally modified hormone forms remains constant. Changing plasma hormone concentrations are likely attributed to a regulated releasing process from the gland into the blood.     

Hunting differentially affects mixed-sex and bachelor-herds in a gregarious ungulate, the impala (Aepyceros melampus: Bovidae)

We investigated herd-sizes and herd-compositions of Impala ( Aepyceros melampus ) inside a protected area [Lake Mburo National Park (LMNP) in western Uganda] and the unprotected adjacent ranchland [the Ankole Ranching Scheme (ARS)]. Impala experience intense hunting and poaching in the study area, and poaching is especially strong on the ARS. We found evidence for changes in overall group-sizes in both mixed-sex and pure bachelor herds between areas in and outside LMNP. Mixed-sex herds strongly decreased in size outside the National Park, but bachelor herds even slightly increased in size. While the group-composition of mixed-sex herds was very similar in areas in and outside LMNP, bachelor herds comprised more yearlings and subadult males on the ARS. Our study suggests that effects of hunting and other human nuisance may differ between herd types: mixed herds probably decrease in size because females are more strongly hunted. Around LMNP, impala are usually hunted using nets and spears, thereby increasing the hunters' chance of being injured. Poachers therefore prefer hornless females (and their calves), as it is less dangerous to handle net-caught females than males. As a result, males are less hunted, but increased vigilance and, therefore, reduced aggression among the members of a bachelor herd, may account for the observed increase in herd sizes and changes in group-compositions.     

Regulation and function of xanthophyll cycle-dependent photoprotection in algae

The xanthophyll cycle represents one of the important photoprotection mechanisms in plant cells. In the present review, we summarize current knowledge about the violaxanthin cycle of vascular plants, green and brown algae, and the diadinoxanthin cycle of the algal classes Bacillariophyceae, Xanthophyceae, Haptophyceae, and Dinophyceae. We address the biochemistry of the xanthophyll cycle enzymes with a special focus on protein structure, co-substrate requirements and regulation of enzyme activity. We present recent ideas regarding the structural basis of xanthophyll cycle-dependent photoprotection, including different models for the mechanism of non-photochemical quenching of chlorophyll a fluorescence. In a dedicated chapter, we also describe the unique violaxanthin antheraxanthin cycle of the Prasinophyceae, together with its implication for the mechanism of xanthophyll cycle-dependent heat dissipation. The interaction between the diadinoxanthin cycle and alternative electron flow pathways in the chloroplasts of diatoms is an additional topic of this review, and in the last chapter we cover aspects of the importance of xanthophyll cycle-dependent photoprotection for different algal species in their natural environments.     

Macronutrient balancing in free‐ranging populations of moose

At northern latitudes, large spatial and temporal variation in the nutritional composition of available foods poses challenges to wild herbivores trying to satisfy their nutrient requirements. Studies conducted in mostly captive settings have shown that animals from a variety of taxonomic groups deal with this challenge by adjusting the amounts and proportions of available food combinations to achieve a target nutrient balance. In this study, we used proportions‐based nutritional geometry to analyze the nutritional composition of rumen samples collected in winter from 481 moose (Alces alces) in southern Sweden and examine whether free‐ranging moose show comparable patterns of nutrient balancing. Our main hypothesis was that wild moose actively regulate their rumen nutrient composition to offset ecologically imposed variation in the nutritional composition of available foods. To test this, we assessed the macronutritional composition (protein, carbohydrates, and lipids) of rumen contents and commonly eaten foods, including supplementary feed, across populations with contrasting winter diets, spanning an area of approximately 10,000 km². Our results suggest that moose balanced the macronutrient composition of their rumen, with the rumen contents having consistently similar proportional relationship between protein and nonstructural carbohydrates, despite differences in available (and eaten) foods. Furthermore, we found that rumen macronutrient balance was tightly related to ingested levels of dietary fiber (cellulose and hemicellulose), such that the greater the fiber content, the less protein was present in the rumen compared with nonstructural carbohydrates. Our results also suggest that moose benefit from access to a greater variety of trees, shrubs, herbs, and grasses, which provides them with a larger nutritional space to maneuver within. Our findings provide novel theoretical insights into a model species for ungulate nutritional ecology, while also generating data of direct relevance to wildlife and forest management, such as silvicultural or supplementary feeding practices.