Net nitrogen mineralization in soils under six indigenous tree species,an abandoned pasture and a secondary forest in the atlantic lowlands of costa rica

Nitrogen mineralization, nitrification potentials, pH, total N, C, extractable P and cations were measured in soils under 4-year-old, mono-specific stands of six fast-growing, native tree species, an abandoned pasture, and a 20-year-old secondary forest, as part of a study on the use of indigenous tree species for rehabilitation of soil fertility on degraded pastures at the La Selva Biological Station in the Atlantic humid lowlands of Costa Rica. Soil net nitrification potential rates were higher under two N-fixing, leguminous species,Stryphnodendron microstachyum Poepp. et Endl. (1.1–1.9 mg kg^–1 day^–1) andDalbergia tucurensis Donn. Smith (0.7–1.5 mg kg^–1 day^–1), than under the non-N-fixing trees in the plantation,Vochysia guatemalesis Don. Sm.,Vochysia ferruginea Mart,Dipteryx panamensis (Pittier) Record and Mell andHyeronima alchorneoides Fr. Allemao (0.2–0.8 mg kg^–1 day^–1). Values under the N-fixing trees were comparable to those found in secondary forest. There were no statistically significant differences in soil total N or in other nurtients between the species. Results of pH measurements done before and after incubation did not show any clear evidence of a pH drop attributable to nitrification.     

Identification of a novel mechanism for LFA-1 organization during NK cytolytic response

The elimination of transformed and viral infected cells by natural killer (NK) cells requires a specialized junction between NK and target cells, denominated immunological synapse (IS). After initial recognition, the IS enables the directed secretion of lytic granules content into the susceptible target cell. The lymphocyte function-associated antigen (LFA)-1 regulates NK effector function by enabling NK-IS assembly and maturation. The pathways underlying LFA-1 accumulation at the IS in NK cells remained uncharacterized. A kinase anchoring protein 350 (AKAP350) is a centrosome/Golgi-associated protein, which, in T cells, participates in LFA-1 activation by mechanisms that have not been elucidated. We first evaluated AKAP350 participation in NK cytolytic activity. Our results showed that the decrease in AKAP350 levels by RNA interference (AKAP350KD) inhibited NK-YTS cytolytic activity, without affecting conjugate formation. The impairment of NK effector function in AKAP350KD cells correlated with decreased LFA-1 clustering and defective IS maturation. AKAP350KD cells that were exclusively activated via LFA-1 showed impaired LFA-1 organization and deficient lytic granule translocation as well. In NK AKAP350KD cells, activation signaling through Vav1 was preserved up to 10 min of interaction with target cells, but significantly decreased afterwards. Experiments in YTS and in ex vivo NK cells identified an intracellular pool of LFA-1, which partially associated with the Golgi apparatus and, upon NK activation, redistributed to the IS in an AKAP350-dependent manner. The analysis of Golgi organization indicated that the decrease in AKAP350 expression led to the disruption of the Golgi integrity in NK cells. Alteration of Golgi function by BFA treatment or AKAP350 delocalization from this organelle also led to impaired LFA-1 localization at the IS. Therefore, this study characterizes AKAP350 participation in the modulation of NK effector function, revealing the existence of a Golgi-dependent trafficking pathway for LFA-1, which is relevant for LFA-1 organization at NK-lytic IS.     

Selection of synthetic proteins to modulate the human frataxin function

Frataxin is a kinetic activator of the mitochondrial supercomplex for iron-sulfur cluster assembly. Low frataxin expression or a decrease in its functionality results in Friedreich's Ataxia (FRDA). With the aim of creating new molecular tools to study this metabolic pathway, and ultimately, to explore new therapeutic strategies, we have investigated the possibility of obtaining small proteins exhibiting a high affinity for frataxin. In this study, we applied the ribosome display approach, using human frataxin as the target. We focused on Affi_224, one of the proteins that we were able to select after five rounds of selection. We have studied the interaction between both proteins and discussed some applications of this specific molecular tutor, concerning the modulation of the supercomplex activity. Affi_224 and frataxin showed a K_D value in the nanomolar range, as judged by surface plasmon resonance analysis. Most likely, it binds to the frataxin acidic ridge, as suggested by the analysis of chemical shift perturbations (nuclear magnetic resonance) and computational simulations. Affi_224 was able to increase Cys NFS1 desulfurase activation exerted by the FRDA frataxin variant G130V. Importantly, Affi_224 interacts with frataxin in a human cellular model. Our results suggest quaternary addition may be a new tool to modulate frataxin function in vivo. Nevertheless, more functional experiments under physiological conditions should be carried out to evaluate Affi_224 effectiveness in FRDA cell models.     

Variation in trophic resources in female South American sea lions at a small geographic scale

Difference among colonies in the population structure of otariids can be driven by philopatry and/or by specializations in the foraging ecology of females. In northern Patagonia, the South American sea lion (SASL) shows some degree of spatial genetic structure among colonies from north and south zones. This study aims to explore the isotopic niche of SASL females in the last period of the pregnancy from different colonies of northern Patagonia and to consider whether the fine scale genetic spatial structuring is potentially related to variation in trophic resources. Stable isotope analysis was performed on 101 skin samples of newborn pups in 10 colonies, as a proxy for the feeding ecology of their mothers. Differences among colonies in the metrics studied revealed the plasticity of the species and support individual trophic specialization of SASL females at a small geographic scale. Also, significant differences were found in all isotopic metrics between the north and south zones. Several hypotheses were proposed to explain the differences in SASL females' isotope values (e.g., use of different foraging areas or prey, isotopic baseline variation). Nonetheless, further research is needed to better understand the relation between fine scale genetic structuring and the foraging ecology of SASL females.     

Dislodgement effect of natural semiochemicals released by disturbed triatomines: a possible alternative monitoring tool

The quick detection of domestic and peridomestic triatomines in their environments becomes difficult without the use of dislodgement substances that flush them out from their shelters. At present, tetramethrin 0.2% is being widely used in control programs. Although it is an efficient dislodging agent, its toxicity might affect the health of captured triatomines, of other insects and, to a lesser extent, of other animals, including humans. Here, we tested if semiochemicals released by disturbed adults of Triatoma infestans and/or Rhodnius prolixus can make larvae of the same species exit from their refuges. In a walking olfactometer we found that: 1) larvae of T. infestans were repelled by the odors released by disturbed adults of their own species and of R. prolixus, 2) larvae of R. prolixus did not change their behavior in the presence of odors released by adults of both species, and 3) activity levels were not modulated by these odors in any of both species. Besides, in pseudo‐natural conditions we found an increased flushing‐out activity of larvae of T. infestans when their shelters were sprayed with isobutyric acid or 3‐pentanol, and of larvae of R. prolixus when sprayed with 3‐methyl1butanol. We succeeded in this work to dislodge larvae of triatomines from artificial shelters using natural volatile compounds, allowing the capture of live bugs for further investigations (e.g., xenodiagnosis or genetic studies) and favoring ecological aspects (e.g., minimizing environmental insecticide‐contamination and non‐targeted mortality).     

The immunogenicity to the first anti-TNF therapy determines the outcome of switching to a second anti-TNF therapy in spondyloarthritis patients

Introduction

Anti-TNF drugs have proven to be effective against spondyloarthritis (SpA), although 30% of patients fail to respond or experience adverse events leading to treatment discontinuation. In rheumatoid arthritis, the presence of anti-drug antibodies (ADA) against the first TNF inhibitor influences the outcome after switching. Our aim was to assess whether the response to a second anti-TNF drug is related to the previous development of ADA to the first anti-TNF drug SpA patients.

Methods

Forty-two SpA patients began a second anti-TNF drug after failing to respond to the first anti-TNF therapy. Clinical activity was assessed by the Ankylosing Spondylitis Disease Activity Score (ASDAS) at baseline (at the beginning of the first and second anti-TNF therapy) and at 6 months after switching. The drug and ADA levels were measured by ELISA before each administration.

Results

All patients were treated with anti-TNF drugs and mainly due to inefficacy were switched to a second anti-TNF drug. Eleven of 42 (26.2%) developed ADA during the first biologic treatment. At baseline, no differences in ASDAS were found in patients with or without ADA to the first anti-TNF drug (3.52 ± 1.03 without ADA vs. 3.14 ± 0.95 with ADA, p = 0.399) and to the second anti-TNF drug (3.36 ± 0.94 without ADA vs. 3.09 ± 0.91 with ADA, p = 0.466). At 6 months after switching, patients with previous ADA had lower disease activity (1.62 ± 0.93 with ADA vs. 2.79 ± 1.01 without ADA, p = 0.002) and most patients without ADA had high disease activity state by the ASDAS (25 out of 31 (80.6%) without ADA vs. 3 out of 11 (27.3%) with ADA, p = 0.002).

Conclusions

In SpA the failure to respond to the first anti-TNF drug due to the presence of ADA predicts a better clinical response to a second anti-TNF drug.     

Phosphatidate phosphatase,a key regulator of lipid homeostasis

Yeast Pah1p phosphatidate phosphatase (PAP) catalyzes the penultimate step in the synthesis of triacylglycerol. PAP plays a crucial role in lipid homeostasis by controlling the relative proportions of its substrate phosphatidate and its product diacylglycerol. The cellular amounts of these lipid intermediates influence the synthesis of triacylglycerol and the pathways by which membrane phospholipids are synthesized. Physiological functions affected by PAP activity include phospholipid synthesis gene expression, nuclear/endoplasmic reticulum membrane growth, lipid droplet formation, and vacuole homeostasis and fusion. Yeast lacking Pah1p PAP activity are acutely sensitive to fatty acid-induced toxicity and exhibit respiratory deficiency. PAP is distinguished in its cellular location, catalytic mechanism, and physiological functions from Dpp1p and Lpp1p lipid phosphate phosphatases that utilize a variety of substrates that include phosphatidate. Phosphorylation/dephosphorylation is a major mechanism by which Pah1p PAP activity is regulated. Pah1p is phosphorylated by cytosolic-associated Pho85p–Pho80p, Cdc28p-cyclin B, and protein kinase A and is dephosphorylated by the endoplasmic reticulum-associated Nem1p–Spo7p phosphatase. The dephosphorylation of Pah1p stimulates PAP activity and facilitates the association with the membrane/phosphatidate allowing for its reaction and triacylglycerol synthesis. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.