Leptin modulates the survival of autoreactive CD4+ T cells through the nutrient/energy-sensing mammalian target of rapamycin signaling pathway

Chronic inflammation can associate with autoreactive immune responses, including CD4(+) T cell responses to self-Ags. In this paper, we show that the adipocyte-derived proinflammatory hormone leptin can affect the survival and proliferation of autoreactive CD4(+) T cells in experimental autoimmune encephalomyelitis, an animal model of human multiple sclerosis. We found that myelin olygodendrocyte glycoprotein peptide 35-55 (MOG(35-55))-specific CD4(+) T cells from C57BL/6J wild-type mice could not transfer experimental autoimmune encephalomyelitis into leptin-deficient ob/ob mice. Such a finding was associated with a reduced proliferation of the transferred MOG(35-55)-reactive CD4(+) T cells, which had a reduced degradation of the cyclin-dependent kinase inhibitor p27(kip1) and ERK1/2 phosphorylation. The transferred cells displayed reduced Th1/Th17 responses and reduced delayed-type hypersensitivity. Moreover, MOG(35-55)-reactive CD4(+) T cells in ob/ob mice underwent apoptosis that associated with a downmodulation of Bcl-2. Similar results were observed in transgenic AND-TCR- mice carrying a TCR specific for the pigeon cytochrome c 88-104 peptide. These molecular events reveal a reduced activity of the nutrient/energy-sensing AKT/mammalian target of rapamycin pathway, which can be restored in vivo by exogenous leptin replacement. These results may help to explain a link between chronic inflammation and autoimmune T cell reactivity.     

A simple fluorogenic method for determination of acid ceramidase activity and diagnosis of Farber disease

Acid ceramidase (aCDase) is one of several enzymes responsible for ceramide degradation within mammalian cells. As such, aCDase regulates the intracellular levels of the bioactive lipid ceramide. An inherited deficiency of aCDase activity results in Farber disease (FD), also called lipogranulomatosis, which is characterized by ceramide accumulation in the tissues of patients. Diagnosis of FD is confirmed by demonstration of a deficient aCDase activity and the subsequent storage of ceramide. Existing methods include extremely complex assays, many of them using radiolabeled compounds. Therefore, the aCDase assay and the in vitro enzymatic diagnosis of FD are still performed in only a very limited number of specialized laboratories. Here, the new fluorogenic substrate Rbm14-12 was synthesized and characterized as a new tool to determine aCDase activity. The resulting optimized assay was performed in 96-well plates, and different fibroblast and lymphoid cell lines derived from FD patients and controls were tested to measure aCDase activity. As a result, the activity in cells of FD patients was found to be very low or even null. This new fluorogenic method offers a very easy and rapid way for specific and accurate determination of aCDase activity and, consequently, for diagnosis of FD.     

Protein N-Homocysteinylation Induces the Formation of Toxic Amyloid-Like Protofibrils

Previous works reported that a mild increase in homocysteine level is a risk factor for cardiovascular and neurodegenerative diseases in humans. Homocysteine thiolactone is a cyclic thioester, most of which is produced by an error-editing function of methionyl-tRNA synthetase, causing in vivo post-translational protein modifications by reacting with the ?-amino group of lysine residues. In cells, the rate of homocysteine thiolactone synthesis is strictly dependent on the levels of the precursor metabolite, homocysteine. In this work, using bovine serum albumin as a model, we investigated the impact of N-homocysteinylation on protein conformation as well as its cellular actions. Previous works demonstrated that protein N-homocysteinylation causes enzyme inactivation, protein aggregation, and precipitation. In addition, in the last few years, several pieces of evidence have indicated that protein unfolding and aggregation are crucial events leading to the formation of amyloid fibrils associated with a wide range of human pathologies. For the first time, our results reveal how the low level of protein N-homocysteinylation can induce mild conformational changes leading to the formation of native-like aggregates evolving over time, producing amyloid-like structures. Taking into account the fact that in humans about 70% of circulating homocysteine is N-linked to blood proteins such as serum albumin and hemoglobin, the results reported in this article could have pathophysiological relevance and could contribute to clarify the mechanisms underlying some pathological consequences described in patients affected by hyperhomocysteinemia.     

Discharge and the response of biofilms to metal exposure in Mediterranean rivers

The expected response of fluvial biofilms to the environment and metal pollution prevailing under different discharge conditions was investigated. The relationship between inter-annual hydrological variability and metal concentration in water and sediments was explored in Mediterranean rivers (Catalonia, NE Spain) affected by low but chronic metal pollution, using monitoring data provided by the Catalan Water Agency (ACA). During the period investigated (2000–2006), metal pollution was characterized by low water concentrations and high concentrations in sediments. The most consistent pattern was observed for sediment cadmium (Cd) concentrations, showing a positive relationship with annual discharge, reaching values of environmental concern (above ecotoxicological benchmarks). A different pattern was observed for Cu, Zn, and As increasing with flow in some sites and decreasing in others. While Cd seems to proceed from diffuse sources being washed by surface runoff, Zn, Pb, and As may proceed from either diffuse or point-sources in the different river sites investigated. The relevance of diffuse metal pollution in the area of study indicates that polluted landfills runoff might be an important source of metals causing repetitive pulses of high metal concentration in the receiving water courses. The experimental results presented demonstrate that metal effects in fluvial biofilms may be accumulative, increasing the toxicity after repetitive pulse exposures. Since draughts and extreme rain events are expected to increase at higher latitudes due to global change, the sources of metal pollution, its final concentration and potential effects on the fluvial ecosystem may also change following the patterns expected for human-impacted Mediterranean rivers.     

Assessing coral bleaching and recovery with a colour reference card in Watamu Marine Park,Kenya

With this study we estimated the changes in colour, bleaching and mortality of coral colonies from February to December 2007, using the colour reference card method. The study was developed in the Watamu Marine Park lagoon (Kenya), bridging the local summer when seawater temperatures were highest and coral bleaching risk was at its maximum. Seven coral genera were selected, and their colour recorded using a colour reference card (Coral Watch card). Seven different scenarios of bleaching and mortality were observed, varying among the coral genera and between two species in the genus Pocillopora. Twenty percent of the colonies bleached, of which 50% died. Only 15% of the coral that did not bleach died. Branching genera had a higher bleaching incidence than massive and sub-massive genera. Pocillopora showed the highest bleaching susceptibility, followed by Acropora, and the highest level of mortality. Of the two species of Pocillopora considered in this study, P. eydouxi showed higher bleaching and mortality levels, while P. verrucosa bleached less and experienced only partial mortality. Our results evidenced different patterns of coral bleaching and mortality which were easily and clearly detected with the colour card method during both bleaching and a post-bleaching events.     

Salt intake and depletion increase circulating levels of endogenous ouabain in normal men

High-salt diets elevate circulating Na+ pump inhibitors, vascular resistance, and blood pressure. Ouabain induces a form of hypertension mediated via the alpha2-Na+ pump isoform and the calcium influx mode of the vascular sodium calcium exchanger (NCX). Whereas elevated levels of an endogenous ouabain (EO) and NCX have been implicated in salt-sensitive hypertension, acute changes in sodium balance do not affect plasma EO. This study investigated the impact of longer-term alterations in sodium balance on the circulating levels and renal clearance of EO in normal humans. Thirteen normal men consumed a normal diet, high-salt diet, and hydrochlorothiazide (HCTZ), each for 5-day periods to alter sodium balance. EO and other humoral and urinary variables were determined daily. On a normal diet, urinary sodium excretion (140 +/- 16 meq/day), plasma EO (0.43 +/- 0.08 nmol/l) and urinary EO excretion (1.04 +/- 0.13 nmol/day) were at steady state. On the 3rd day of a high-salt diet, urine sodium excretion (315 +/- 28 meq/day), plasma EO (5.8 +/- 2.2 nmol/l), and the urinary EO excretion (1.69 +/- 0.27 nmol/day) were significantly increased, while plasma renin activity and aldosterone levels were suppressed. The salt-evoked increase in plasma EO was greater in older individuals, in subjects whose baseline circulating EO was higher, and in those with low renal clearance. During HCTZ, body weight decreased and plasma renin activity, aldosterone, and EO (1.71 +/- 0.77 nmol/l) rose, while urinary EO excretion remained within the normal range (1.44 +/- 0.31 nmol/day). Blood pressure fell in one subject during HCTZ. HPLC of the plasma extracts showed one primary peak of EO immunoreactivity with a retention time equivalent to ouabain. High-salt diets and HCTZ raise plasma EO by stimulating EO secretion, and a J-shaped curve relates sodium balance and EO in healthy men. Under normal dietary conditions, approximately 98% of the filtered load of EO is reabsorbed by the kidney, and differences in the circulating levels of EO are strongly influenced by secretion and urinary excretion of EO. The dramatic impact of high-salt diets on plasma EO is consistent with its proposed role as a humoral vasoconstrictor that links salt intake with vascular function in hypertension.     

Adrenergic origin of very low-frequency blood pressure oscillations in the unanesthetized rat

Spectral analysis of cardiovascular signals has been extensively used to investigate circulatory homeostatic mechanisms. However, the nature of very low-frequency (VLF) fluctuations remains unclear. Because we previously observed enhanced VLF fluctuations in blood pressure (BP) in the sympathectomized rat (a model characterized by markedly increased plasma epinephrine levels), the aims of our study were to assess whether the genesis of VLF fluctuations in BP depends on circulating catecholamines and to determine which adrenergic receptor(s) and which membrane ion channel(s) are involved. We used continuous intra-arterial BP recordings from unanesthetized unrestrained rats to compute the power of VLF fluctuations in BP in the intact condition, during acute ganglionic blockade with hexamethonium, and after restoration of BP levels by infusion (in addition to hexamethonium) of adrenergic agonists (epinephrine, norepinephrine, and clonidine) or nonadrenergic vasoconstrictors (vasopressin). Effects of infusion of specific adrenergic receptor blockers (propranolol, prazosin, and yohimbine) with hexamethonium and catecholamines and infusion of various membrane ion channel blockers on VLF fluctuations in BP were also evaluated. Our results are as follows. 1) Ganglionic blockade drastically reduced BP levels and VLF fluctuations. 2) All vasoconstrictors restored BP levels, but only adrenergic vasoconstrictors generated striking VLF fluctuations in BP. 3) Catecholamine-induced fluctuations were abolished by alpha2-, but not alpha1- or beta-, adrenergic receptor blockade and by Ba2+-sensitive K+ channel or L-type Ca2+ channel, but not by other ion channel, blockers. We conclude that, in the conscious, unrestrained ganglion-blocked rat, catecholamine infusion generates VLF fluctuations in BP through stimulation of alpha2-receptors and activation of Ba2+-sensitive K+ channels. These fluctuations may have (patho)physiological relevance under conditions of disrupted circulatory homeostasis.