The uORF-containing thrombopoietin mRNA escapes nonsense-mediated decay (NMD)

Platelet production is induced by the cytokine thrombopoietin (TPO). It is physiologically critical that TPO expression is tightly regulated, because lack of TPO causes life-threatening thrombocytopenia while an excess of TPO results in thrombocytosis. The plasma concentration of TPO is controlled by a negative feedback loop involving receptor-mediated uptake of TPO by platelets. Furthermore, TPO biosynthesis is limited by upstream open reading frames (uORFs) that curtail the translation of the TPO mRNA. uORFs are suggested to activate RNA degradation by nonsense-mediated decay (NMD) in a number of physiological transcripts. Here, we determine whether NMD affects TPO expression. We show that reporter mRNAs bearing the seventh TPO uORF escape NMD. Importantly, endogenously expressed TPO mRNA from HuH7 cells is unaffected by abrogation of NMD by RNAi. Thus, regulation of TPO expression is independent of NMD, implying that mRNAs bearing uORFs cannot generally be considered to represent NMD targets

Fibrodysplasia Ossificans Progressiva: what have we achieved and where are we now? follow-up to the 2015 Lorentz Workshop

Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare progressive genetic disease effecting one in a million individuals. During their life, patients with FOP progressively develop bone in the soft tissues resulting in increasing immobility and early death. A mutation in the ACVR1 gene was identified as the causative mutation of FOP in 2006. After this, the pathophysiology of FOP has been further elucidated through the efforts of research groups worldwide. In 2015, a workshop was held to gather these groups and discuss the new challenges in FOP research. Here we present an overview and update on these topics

Thrombocytosis in children and adolescents—classification, diagnostic approach, and clinical management

Secondary thrombocytosis is a frequent secondary finding in childhood infection and inflammation. Primary hereditary thrombocytosis may be caused by germline mutations within the genes encoding key regulators of thrombopoiesis, i.e., thrombopoietin (THPO) and its receptor c-MPL (MPL) or the receptor's effector kinase Januskinase2 (JAK2). Furthermore, somatic mutations in JAK2, MPL, and in the gene-encoding calreticulin (CALR) have been described to act as driver mutations within the so-called Philadelphia-negative myeloproliferative neoplasms (MPNs), namely essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF). Increasing knowledge on the molecular mechanisms and on the clinical complications of these diseases is reflected by the WHO diagnostic criteria and European LeukemiaNet (ELN) recommendations on the management of adult MPN. However, data on childhood thrombocytosis are rare, and no consensus guidelines for pediatric thrombocytosis exist. Current literature has highlighted differences in the epidemiology and molecular pathogenesis of childhood thrombocytosis as compared to adults. Furthermore, age-dependent complications and pharmacological specificities suggest that recommendations tailored to the pediatric population are necessary in clinical practice. Here we summarize literature on classification, diagnostics, and clinical management of childhood thrombocytosis

Protocol paper: a multi-center, double-blinded, randomized, 6-month, placebo-controlled study followed by 12-month open label extension to evaluate the safety and efficacy of Saracatinib in Fibrodysplasia Ossificans Progressiva (STOPFOP)

BACKGROUND: Fibrodysplasia Ossificans Progressiva (FOP) is a genetic, progressive and devastating disease characterized by severe heterotopic ossification (HO), loss of mobility and early death. There are no FDA approved medications. The STOPFOP team identified AZD0530 (saracatinib) as a potent inhibitor of the ALK2/ACVR1-kinase which is the causative gene for this rare bone disease. AZD0530 was proven to prevent HO formation in FOP mouse models. The STOPFOP trial investigates the repositioning of AZD0530, originally developed for ovarian cancer treatment, to treat patients with FOP. METHODS: The STOPFOP trial is a phase 2a study. It is designed as a European, multicentre, 6-month double blind randomized controlled trial of AZD0530 versus placebo, followed by a 12-month trial comparing open-label extended AZD0530 treatment with natural history data as a control. Enrollment will include 20 FOP patients, aged 18-65 years, with the classic FOP mutation (ALK2 R206H). The primary endpoint is objective change in heterotopic bone volume measured by low-dose whole-body computer tomography (CT) in the RCT phase. Secondary endpoints include 18F NaF PET activity and patient reported outcome measures. DISCUSSION: Clinical trials in rare diseases with limited study populations pose unique challenges. An ideal solution for limiting risks in early clinical studies is drug repositioning - using existing clinical molecules for new disease indications. Using existing assets may also allow a more fluid transition into clinical practice. With positive study outcome, AZD0530 may provide a therapy for FOP that can be rapidly progressed due to the availability of existing safety data from 28 registered clinical trials with AZD0530 involving over 600 patients. TRIAL REGISTRATION: EudraCT, 2019-003324-20. Registered 16 October 2019, https://www.clinicaltrialsregister.eu/ctr-search/trial/2019-003324-20/NL . CLINICALTRIALS: gov , NCT04307953 . Registered 13 March 2020