11 research outputs found
Chloride transport-driven alveolar fluid secretion is a major contributor to cardiogenic lung edema.
Alveolar fluid clearance driven by active epithelial Na(+) and secondary Cl(-) absorption counteracts edema formation in the intact lung. Recently, we showed that impairment of alveolar fluid clearance because of inhibition of epithelial Na(+) channels (ENaCs) promotes cardiogenic lung edema. Concomitantly, we observed a reversal of alveolar fluid clearance, suggesting that reversed transepithelial ion transport may promote lung edema by driving active alveolar fluid secretion. We, therefore, hypothesized that alveolar ion and fluid secretion may constitute a pathomechanism in lung edema and aimed to identify underlying molecular pathways. In isolated perfused lungs, alveolar fluid clearance and secretion were determined by a double-indicator dilution technique. Transepithelial Cl(-) secretion and alveolar Cl(-) influx were quantified by radionuclide tracing and alveolar Cl(-) imaging, respectively. Elevated hydrostatic pressure induced ouabain-sensitive alveolar fluid secretion that coincided with transepithelial Cl(-) secretion and alveolar Cl(-) influx. Inhibition of either cystic fibrosis transmembrane conductance regulator (CFTR) or Na(+)-K(+)-Cl(-) cotransporters (NKCC) blocked alveolar fluid secretion, and lungs of CFTR(-/-) mice were protected from hydrostatic edema. Inhibition of ENaC by amiloride reproduced alveolar fluid and Cl(-) secretion that were again CFTR-, NKCC-, and Na(+)-K(+)-ATPase-dependent. Our findings show a reversal of transepithelial Cl(-) and fluid flux from absorptive to secretory mode at hydrostatic stress. Alveolar Cl(-) and fluid secretion are triggered by ENaC inhibition and mediated by NKCC and CFTR. Our results characterize an innovative mechanism of cardiogenic edema formation and identify NKCC1 as a unique therapeutic target in cardiogenic lung edema
FKBP (FK506 Binding Protein)
In the 70s, after a decade from the purification of cyclosporine, a selective immunosuppressant
agent and potent tool in transplantation medicine, a novel molecule was purified from bacteria
Streptomyces tsukubaensis. This molecule, called FK506, showed the same selective
immunosuppressant action as cyclosporine but was 10 to 100 fold more potent.
In an attempt to clarify the molecular mechanism through which the new drug exerted such a
selective effect on T-cells activation, two laboratories identified the cytosolic receptor for FK506.
This so-called FK506 binding protein (FKBP) was purified from bovine thymus, human spleen, and
Jurkat T-cell line. The isolated FKBP had an approximate molecular mass of 14 kDa and showed
an isomerase activity similar to the recently purified cyclosporine-binding protein, cyclophilin, but, it
was inhibited by FK506 and rapamycin but not cyclosporine. The
subsequent cloning of FKBP gene revealed that FKBP and cyclophilin had dissimilar sequences in
spite of their common enzymatic activity. The identified FKBP gene encoded for a protein of 108
aminoacids with a relative molecular mass of 11,819. For this reason, the progenitor of this
nascent class of proteins was later known as FKBP12.
The subsequent studies showed that FKBP12 was just a member of a ubiquitous and evolutionarily
conserved sub-family of proteins which differ from each other in their molecular weight and
structure. All FKBPs share a highly conserved domain, termed âFK-12 like domainâ, capable of
binding to FK506 and exerting isomerase properties, i.e. interconversion from cis-to-trans and
trans-to-cis of peptide bonds involving proline, on protein substrates.
A schematic historical background of the 17 FKBPs so far identified is shown. A general
overview of FKBP structure, function and eventually associated disease is given in this
monograph, with the order of proteins following the chronology of discovery