HLA class I expression on human platelets is highly variable and correlates with distinct allele group frequencies.

BACKGROUND: Human leukocyte antigen (HLA) class I molecules are expressed on platelets and can represent a source of alloimmunization in recipients of platelet transfusions. HLA mismatch between donors and recipients may be associated with the induction of anti-HLA antibodies, which can culminate in refractoriness to platelet transfusions. In the present study we analyzed HLA allele group frequencies and HLA expression levels on human platelets from blood donors. MATERIALS AND METHODS: Platelet-rich plasma was collected from 139 donors to monitor platelet HLA class I expression by flow cytometry. DNA from donors with high and low platelet HLA expression was used in the genotype studies. Frequencies of large and normal-sized platelet subpopulations were determined and HLA class I expression was studied. Mean platelet volume (MPV) and platelet large-cell ratio (P-LCR) were analyzed in both groups of donors. RESULTS: The analysis showed variable platelet HLA class I expression with significant differences among donors. HLA class I allele group frequencies in donors with high and low platelet HLA expression showed distinctive genotypic features strictly related to expression level. The main allele groups found in samples with high platelet HLA class I expression were HLA-A*02, -A*68, -B*15, -B*49, and -C*03. Platelet HLA class I expression did not change over time or during freezing-thawing cycles. The analysis of platelet subpopulations showed a statistically significant higher expression of HLA class I molecules on large platelets than on normal-sized platelets. Moreover, donors with high HLA class I expression showed a higher frequency of large platelets (p<0.0001). The analysis of P-LCR in both groups of donors showed a statistically significant difference (p<0.05) within high HLA-expressing donors. DISCUSSION: Our data suggest an allele-dependent expression of HLA class I molecules on human platelets with distinct HLA allele group frequencies and different platelet subpopulation frequencies among blood donors.

Identification and characterization of three novel mutations in the CASQ1 gene in four patients with tubular aggregate myopathy.

Here, we report the identification of three novel missense mutations in the calsequestrin-1 (CASQ1) gene in four patients with tubular aggregate myopathy. These CASQ1 mutations affect conserved amino acids in position 44 (p.(Asp44Asn)), 103 (p.(Gly103Asp)), and 385 (p.(Ile385Thr)). Functional studies, based on turbidity and dynamic light scattering measurements at increasing Ca2+ concentrations, showed a reduced Ca2+ -dependent aggregation for the CASQ1 protein containing p.Asp44Asn and p.Gly103Asp mutations and a slight increase in Ca2+ -dependent aggregation for the p.Ile385Thr. Accordingly, limited trypsin proteolysis assay showed that p.Asp44Asn and p.Gly103Asp were more susceptible to trypsin cleavage in the presence of Ca2+ in comparison with WT and p.Ile385Thr. Analysis of single muscle fibers of a patient carrying the p.Gly103Asp mutation showed a significant reduction in response to caffeine stimulation, compared with normal control fibers. Expression of CASQ1 mutations in eukaryotic cells revealed a reduced ability of all these CASQ1 mutants to store Ca2+ and a reduced inhibitory effect of p.Ile385Thr and p.Asp44Asn on store operated Ca2+ entry. These results widen the spectrum of skeletal muscle diseases associated with CASQ1 and indicate that these mutations affect properties critical for correct Ca2+ handling in skeletal muscle fibers.

Organization of junctional sarcoplasmic reticulum proteins in skeletal muscle fibers.

The sarcoplasmic reticulum (SR) of striated muscles is specialized for releasing Ca(2+) following sarcolemma depolarization in order to activate muscle contraction. To this end, the SR forms a network of longitudinal tubules and cisternae that surrounds the myofibrils and, at the same time, participates to the assembly of the triadic junctional membrane complexes formed by the close apposition of one t-tubule, originated from the sarcolemma, and two SR terminal cisternae. Advancements in understanding the molecular basis of the SR structural organization have identified an interaction between sAnk1, a transmembrane protein located on the longitudinal SR (l-SR) tubules, and obscurin, a myofibrillar protein. The direct interaction between these two proteins results in molecular contacts that have the overall effect to stabilize the l-SR tubules along myofibrils in skeletal muscle fibers. Less known is the structural organization of the sites in the SR that are specialized for Ca(2+) release and are positioned at the junctional SR (j-SR), i.e. the region of the terminal cisternae that faces the t-tubule at triads. At the j-SR, several trans-membrane proteins like triadin, junctin, or intra-luminal SR proteins like calsequestrin, are assembled together with the ryanodine receptor, the SR Ca(2+) release channel, into a macromolecular complex specialized in releasing Ca(2+). At triads, the 12 nm-wide gap between the t-tubule and the j-SR allows the ryanodine receptor on the j-SR to be functionally coupled with the voltage-gated L-type calcium channel on the t-tubule in order to allow the transduction of the voltage-induced signal into Ca(2+) release through the ryanodine receptor channels. The muscle-specific junctophilin isoforms (JPH1 and JPH2) are anchored to the j-SR with a trans-membrane segment present at the C-terminus and are capable to bind the sarcolemma with a series of phospholipid-binding motifs localized at the N-terminus. Accordingly, through this dual interaction, JPH1 and JPH2 are responsible for the assembly of the triadic junctional membrane complexes. Recent data indicate that junctophilins seem also to interact with other proteins of the excitation-contraction machinery, suggesting that they may contribute to hold excitation-contraction coupling proteins to the sites where the j-SR is being organized.

Las anticipaciones de futuro de jóvenes en situación de vulnerabilidad socio-educativa / The anticipations of future of young people in situation of socio-educational vulnerability

En un contexto cambiante y complejo, caracterizado por la precariedad y la vulnerabilidad existe una importante desigualdad en las trayectorias educativas y laborales de los jóvenes, según el sector social y el circuito educativo de pertenencia. Este artículo presenta la investigación Las anticipaciones de futuro de Jóvenes en situación de vulnerabilidad Socio-educativa (subsidiado por UBACyT, Programación 2010-2012), en la que nos proponemos estudiar de qué manera perciben, qué sentido le atribuyen y cómo se proyectan en el futuro jóvenes en situación de vulnerabilidad socio-educativa, focalizando en la incidencia de sus trayectorias familiares, sociales, laborales y educativas. Para ello, se trabajará desde una metodología cualitativa, realizando entrevistas en profundidad.

In a changing and complex context, characterized by instability and vulnerability, there is a signiicant disparity in education and employment pathways for young people, according to the social sector and the educational circuit of belonging. This article exposes the research The anticipations of future of young people in situation of socio-educational vulnerability (subsidized by UBACyT, programming 2010-2012), in which we aim to study the meanings that young people in situation of socio-educational vulnerability give to the future. We are also interested in how they perceive and project their future, considering the impact of their social, working and educational paths. Thus, we will work with a qualitative methodology by indepth interviewing.