TRPM2-mediated rise in mitochondrial Zn2+ promotes palmitate-induced mitochondrial fission and pancreatic β-cell death in rodents

Rise in plasma free fatty acids (FFAs) represents a major risk factor for obesity-induced type 2 diabetes. Saturated FFAs cause a progressive decline in insulin secretion by promoting pancreatic β-cell death through increased production of reactive oxygen species (ROS). Recent studies have demonstrated that palmitate (a C16-FFA)-induced rise in ROS causes β-cell death by triggering mitochondrial fragmentation, but the underlying mechanisms are unclear. Using the INS1-832/13 β-cell line, here we demonstrate that palmitate generates the ROS required for mitochondrial fission by activating NOX (NADPH oxidase)-2. More importantly, we show that chemical inhibition, RNAi-mediated silencing and knockout of ROS-sensitive TRPM (transient receptor potential melastatin)-2 channels prevent palmitate-induced mitochondrial fission. Although TRPM2 activation affects the intracellular dynamics of Ca2+ and Zn2+, chelation of Zn2+ alone was sufficient to prevent mitochondrial fission. Consistent with the role of Zn2+, palmitate caused a rise in mitochondrial Zn2+, leading to Zn2+-dependent mitochondrial recruitment of Drp-1 (a protein that catalyses mitochondrial fission) and loss of mitochondrial membrane potential. In agreement with the previous reports, Ca2+ caused Drp-1 recruitment, but it failed to induce mitochondrial fission in the absence of Zn2+. These results indicate a novel role for Zn2+ in mitochondrial dynamics. Inhibition or knockout of TRPM2 channels in mouse islets and RNAi-mediated silencing of TRPM2 expression in human islets prevented FFA/cytokine-induced β-cell death, findings that are consistent with the role of abnormal mitochondrial fission in cell death. To conclude, our results reveal a novel, potentially druggable signalling pathway for FFA-induced β-cell death. The cascade involves NOX-2-dependent production of ROS, activation of TRPM2 channels, rise in mitochondrial Zn2+, Drp-1 recruitment and abnormal mitochondrial fission

Prion protein facilitates uptake of zinc into neuronal cells

Zinc is released into the synaptic cleft upon exocytotic stimuli, although the mechanism for its reuptake into neurons is unresolved. Here we show that the cellular prion protein enhances the uptake of zinc into neuronal cells. This prion-protein-mediated zinc influx requires the octapeptide repeats and amino-terminal polybasic region in the prion protein, but not its endocytosis. Selective antagonists of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors block the prion protein-mediated zinc uptake, and the prion protein co-immunoprecipitates with both GluA1 and GluA2 AMPA receptor subunits. Zinc-sensitive intracellular tyrosine phosphatase activity is decreased in cells expressing prion protein and increased in the brains of prion-protein-null mice, providing evidence of a physiological consequence of this process. Prion protein-mediated zinc uptake is ablated in cells expressing familial associated mutants of the protein and in prion-infected cells. These data suggest that alterations in the cellular prion protein-mediated zinc uptake may contribute to neurodegeneration in prion and other neurodegenerative diseases

Changes in nasal specific IgE to mites after periods of allergen exposure-avoidance: a comparison with serum levels

Variations of serum and nasal specific IgE to Dermatophagoides pteronyssinus (Der p) during alternate periods of antigen avoidance-exposure have been evaluated with an open design in a group of allergic children with asthma and rhinitis at the residential house Istituto Pio XII (Misurina, BL, Italy), at 1756 m, in the Italian Dolomites. A method based on direct incubation of allergen coupled substrate on the nasal mucosa has been employed to evaluate the levels of nasal IgE. Serum specific IgE decreased respectively from (median) 117-89.3 kU/l (P < 0.001) during an initial period of 3 months of allergen avoidance and from 88.2 to 78.4 kU/l (P < 0.0002) during a subsequent period of allergen avoidance. No significant increase in serum specific IgE was, in contrast, observed during two periods, 22 and 9 days, of antigen exposure, changing respectively from 89.3 to 88.2 and from 78.4 to 89.1 kU/l. In contrast, nasal IgE has been significantly influenced by the alternate periods of antigen exposure-avoidance, showing a decrease from 19.75 to 4.01 kU/l (P < 0.0001) after the initial period of avoidance, followed by an increase to 9.95 kU/l (P < 0.0001) after 22 days of exposure. A significant decrease to a value of 2.37 kU/l (P < 0.0001) was also observed during the subsequent period of avoidance, followed again by an increase to 7.87 kU/l (P < 0.002) after 9 days of exposure. The evaluation of the kinetics of changes in nasal specific IgE revealed a significant decrease (P < 0.01) as soon as antigen avoidance was implemented for 3 days.(ABSTRACT TRUNCATED AT 250 WORDS

Measurement of nasal IgE in an epidemiological study: assessment of its diagnostic value in respiratory allergy

Specific questionnaire and skin prick test (SPT) are the most used methods in epidemiological studies on respiratory allergy. SPT, however, can be positive in many subjects without evidence of any allergic disease. Nasal IgE determination has been suggested by some authors as a valuable diagnostic method, which may overcome this lack of specificity. OBJECTIVE: The aim of this study was to evaluate sensitivity and specificity of nasal specific IgE for the seven most common inhalant allergens in order to verify its reliability as a screening test. METHODS: 126 children, involved in an epidemiological study on prevalence of respiratory allergic disease, were evaluated. All children were assessed with a specific questionnaire, SPT and nasal specific IgE. Nasal specific IgE were determined with a previously described method modified for screening purposes, in order to test seven allergens at the same time. When discordant results were obtained between questionnaire, SPT and nasal IgE, an allergen specific nasal challenge (ASNC) was performed and nasal tryptase was also determined before and after challenge. RESULTS: The questionnaire was positive for respiratory allergy in 28/126 children. SPT was positive in 21 of the 28 children, but also in 5/10 children with atopic dermatitis (AD), and in 12/88 children without allergic symptoms. Nasal IgE were positive in 22/28 and also in 2/10 with AD. Nasal challenge and tryptase confirmed the negativity of nasal IgE in 12/17 children with positive SPT but totally negative for allergic respiratory disease. Moreover nasal IgE was found to be positive to dermatophagoides in one of seven children with negative SPT despite a clinical history suggestive for mite respiratory allergy. In this patient and in 2 of the 5 children with AD the positive nasal IgE to mites was confirmed by a positive ASNC and tryptase. CONCLUSIONS: Nasal IgE have shown a specificity significantly higher than SPT (98% vs. 83%) and a good sensibility. This screening test may also be useful to detect the beginning of upper airways sensitization in patients with AD