Insulin-driven translational capacity is impaired in primary fibroblasts of Prader Willi.

Prader-Willi (PW) syndrome is a rare genetic disorder characterized by hypothalamic-pituitary abnormalities and severe hypotonia, hyperphagia, behavioural and psychiatric problems. Absence of satiety leads to severe obesity and frequently to diabetes. Furthermore, adult patients suffer from a severe loss of muscle mass, which severely impacts their quality of life. The mechanisms underlying alterations in muscle growth in PW remain to be clarified. In this study we explored the hypothesis that, in PW cells, alterations of protein synthesis are determined by dysfunctions in the promotion of cell growth. In order to study the molecular changes leading to dysfunction in protein translation, primary fibroblasts derived from four PW patients and five control subjects were used to study the insulin-mediated signaling pathway implicated in the control of protein synthesis by immunoblotting. Here we present, for the first time, evidences that the protein translation response to insulin is impaired in PW fibroblasts. Insulin alone has a major upregulatory effect on protein kinase B (AKT), glycogen synthase kinase (GSK3beta), while phosphorylation of p70S6K1 protein elongation factor controlled by mammalian target of rapamycin complex I (mTORC1) is reduced. In addition, we provide data that the response to insulin in PW cells can be restored by previous treatment with the amino acid L-Leucine (L-Leu). Our experiments in primary cell cultures demonstrate an impairment of insulin signaling that can be rescued by supplementation with the branched aminoacid L-Leu, indicating a possible therapeutic approach for alleviating muscle mass loss in PW patients.

Nuclear GSK-3ß segregation in desmoid-type fibromatosis.

AIMS: Desmoid-type fibromatosis (DF) is a rare benign myofibroblastic neoplasm of the connective tissue that is unable to metastasize but is associated with a high local recurrence rate. Nuclear ß-catenin is the most commonly used histological marker of DF; however, clinical and biological predictive markers guiding the treatment and follow-up of DF are still lacking. Normally, ß-catenin is regulated by the cytoplasmic multiprotein complex of adenomatous polyposis coli (APC), axin, casein kinase 1α (CK1α), and glycogen synthase kinase 3ß (GSK-3ß); this phosphorylates and degrades ß-catenin, which would otherwise translocate to the nucleus. The aim of this study was to analyse the expression and localization of the ß-catenin-protein complex of the Wnt pathway in cells isolated from DF patients. METHODS AND RESULTS: We isolated cells from biopsies of DF patients, and demonstrated, by immunofluorescence and immunoblot analyses, that it is almost exclusively nuclear GSK-3ß that colocalizes and interacts with ß-catenin. The nuclear translocation of ß-catenin and GSK-3ß is not correlated with CTNNB1 mutations. In DF samples, the multiprotein complex is disrupted, as the cytoplasmic localization of APC and axin makes interaction with the nuclear ß-catenin and GSK-3ß impossible. CONCLUSIONS: Our data suggest that GSK-3ß is an additional DF marker with an important role in the aetiopathogenesis of this entity.