Open AccessDefective c‐Mpl signaling in the syndrome of thrombocytopenia with absent radii
Author(s) -
Ballmaier Matthias,
Schulze Harald,
Cremer Malte,
Strauss Gabriele,
Welte Karl,
Folman Claudia C.
Publication year - 1998
Publication title -
stem cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.159
H-Index - 229
eISSN - 1549-4918
pISSN - 1066-5099
DOI - 10.1002/stem.5530160720
Subject(s) - thrombopoietin , megakaryocytopoiesis , platelet , biology , phosphorylation , tyrosine phosphorylation , megakaryocyte , stimulation , medicine , signal transduction , recombinant dna , tar (computing) , thrombopoiesis , endocrinology , tyrosine , immunology , haematopoiesis , microbiology and biotechnology , biochemistry , stem cell , gene , computer science , programming language
Thrombocytopenia with absent radii (TAR) syndrome is a rare congenital defect with severe hypomegakaryocytic thrombocytopenia and bilateral radial aplasia. To elucidate a possible relationship between thrombocytopenia in TAR and defects in the thrombopoietin (TPO)/c‐Mpl system, we examined TPO activity in sera from six patients and in vitro reactivity of the patients' platelets to recombinant human TPO. We found elevated TPO serum levels in all patients, excluding a TPO production defect as a pathomechanism for the thrombocytopenia. In contrast to healthy controls, however, platelets of TAR patients failed to respond to recombinant TPO as measured by testing TPO synergism to suboptimal concentration of platelet activators. Most interestingly, TPO‐induced tyrosine phosphorylation of platelet proteins was completely absent (four out of five) or markedly decreased (one out of five). More detailed investigations of the signal cascades of c‐Mpl demonstrated the absence of Jak2 phosphorylation after TPO stimulation in a TAR patient's platelets. A defect in the early events of c‐Mpl signal transduction might be the reason for impaired megakaryocytopoiesis in TAR syndrome.