Tight junction proteins expression and modulation in immune cells and multiple sclerosis

The tight junction proteins (TJPs) are major determinants of endothelial cells comprising physiological vascular barriers such as the blood–brain barrier, but little is known about their expression and role in immune cells. In this study we assessed TJP expression in human leukocyte subsets, their induction by immune activation and modulation associated with autoimmune disease states and therapies. A consistent expression of TJP complexes was detected in peripheral blood leukocytes (PBLs), predominantly in B and T lymphocytes and monocytes, whereas the in vitro application of various immune cell activators led to an increase of claudin 1 levels, yet not of claudin 5. Claudins 1 and 5 levels were elevated in PBLs of multiple sclerosis (MS) patients in relapse, relative to patients in remission, healthy controls and patients with other neurological disorders. Interestingly, claudin 1 protein levels were elevated also in PBLs of patients with type 1 diabetes (T1D). Following glucocorticoid treatment of MS patients in relapse, RNA levels of JAM3 and CLDN5 and claudin 5 protein levels in PBLs decreased. Furthermore, a correlation between CLDN5 pre‐treatment levels and clinical response phenotype to interferon‐β therapy was detected. Our findings indicate that higher levels of leukocyte claudins are associated with immune activation and specifically, increased levels of claudin 5 are associated with MS disease activity. This study highlights a potential role of leukocyte TJPs in physiological states, and autoimmunity and suggests they should be further evaluated as biomarkers for aberrant immune activity and response to therapy in immune‐mediated diseases such as MS.     

Effects of palmitate on astrocyte amino acid contents

The effects of palmitate on intracellular and extracellular amino acid concentrations of cultured astrocytes was studied. Exposure of astrocytes to either 0.72 mM or 0.36 mM palmitate was associated with a significant reduction in the intracellular pool of glutamine and taurine. In contrast, the intracellular concentration of histidine, glycine, citrulline, isoleucine and leucine were increased in the presence of 0.72 mM palmitate. Comparable changes in the extracellular amino acid pool were not observed. The data suggest that palmitic acid, which accumulates in the brain during periods of anoxia, alters the metabolism of several amino acids in cultured astrocytes. These changes may be of significance in terms of the pathophysiology of a stress such as anoxia.Special issue dedicated to Dr. Elling Kvamme     

Characterization of the Calcium-release Channel/Ryanodine Receptor from Zebrafish Skeletal Muscle

Calcium (Ca²⁺)-mediated signaling is fueled by two sources for Ca²⁺: Ca²⁺ can enter through Ca²⁺ channels located in the plasma membrane and can also be released from intracellular stores. In the present study the intracellular Ca²⁺ release channel/ryanodine receptor (RyR) from zebrafish skeletal muscle was characterized. Two RyR isoforms could be identified using immunoblotting and single-channel recordings. Biophysical properties as well as the regulation by modulators of RyR, ryanodine, ruthenium red and caffeine, were measured. Comparison with other RyRs showed that the zebrafish RyRs have features observed with all RyRs described to date and thus, can serve as a model system in future genetic and physiological studies. However, some differences in the biophysical properties were observed. The slope conductance for both isoforms was higher than that of the mammalian RyR type 1 (RyR1) measured with divalent ions. Also, inhibition by millimolar Ca²⁺ concentrations of the RyR isoform that is inhibited by high Ca²⁺ concentrations (teleost α RyR isoform) was attenuated when compared to mammalian RyRs. Due to the widespread expression of RyR these findings have important implications for the interpretation of the role of the RyR in Ca²⁺ signaling when comparing zebrafish with mammalian physiology, especially when analyzing mutations underlying physiological changes in zebrafish. Received: 15 February 2001/Revised: 1 June 2001     

Reef fish community structure on coastal islands of the southeastern Brazil: the influence of exposure and benthic cover

Patterns of community structure in the marine environment are strongly influenced by population relationships to biotic and physical gradients. The aim of this work is to explore the relationships of tropical rocky reef fish assemblages to wave exposure and benthic coverage in a gradient of distance from the coast. The study was conducted on the Guarapari Islands, southeastern Brazilian coast. Fish were sampled by underwater visual census (166 transects) and benthic cover was estimated with quadrats (223 replicates). Two main kinds of habitats were found to be derived from the close interrelation between exposure and benthic coverage: (1) exposed areas subjected to major hydrodynamic forcing, and (2) sheltered or moderately exposed areas. The first group is associated with mid-water schooling species like planktivorous labrids and Chromis, piscivorous Caranx, as well as gregarious omnivores like Abudefduf and Diplodus. In terms of benthic composition, macroalgae and encrusting calcareous algae prevail in this high-energy habitat. The second group is characterized by site-attached and reef associated species like territorial pomacentrids, invertebrate feeders such as Halichoeres poeyi and Chaetodon striatus, and small cryptobenthic fishes (e.g. blenniids and labrisomids). Turf algae, zoanthids and massive corals dominate this environment. Environmental plasticity is also common with some genera showing high abundances in all habitats (e.g. Holocentrus, Haemulon, Acanthurus). Examples of the coupling of food availability and fish abundance were found. Planktivores, territorial herbivores, macroalgae browsers and spongivores were positively related with the abundance of their preferred food items along the exposure gradient. Within-family analyses of Pomacentridae and Labridae showed that niche partitioning is likely occurring and seems to be mediated by swimming ‘ability’ and associated feeding performance.