Pathogenic ACVR1R206H activation by Activin A-induced receptor clustering and autophosphorylation.

Fibrodysplasia ossificans progressiva (FOP) and diffuse intrinsic pontine glioma (DIPG) are debilitating diseases that share causal mutations in ACVR1, a TGF-ß family type I receptor. ACVR1R206H is a frequent mutation in both diseases. Pathogenic signaling via the SMAD1/5 pathway is mediated by Activin A, but how the mutation triggers aberrant signaling is not known. We show that ACVR1 is essential for Activin A-mediated SMAD1/5 phosphorylation and is activated by two distinct mechanisms. Wild-type ACVR1 is activated by the Activin type I receptors, ACVR1B/C. In contrast, ACVR1R206H activation does not require upstream kinases, but is predominantly activated via Activin A-dependent receptor clustering, which induces its auto-activation. We use optogenetics and live-imaging approaches to demonstrate Activin A-induced receptor clustering and show it requires the type II receptors ACVR2A/B. Our data provide molecular mechanistic insight into the pathogenesis of FOP and DIPG by linking the causal activating genetic mutation to disrupted signaling.

[Copeptin - a novel biomarker for perioperative homeostasis disorders]. / Kopeptyna ­ nowy biomarker zaburzen homeostazy w okresie okolooperacyjnym.

Recently there has been an increasing amount of research on copeptin as a novel biomarker for stress response and homeostasis disorders in a wide spectrum of morbidities. Copeptin is a stable and easily measured surrogate marker of arginine vasopressin and is increasingly included as a part of routine patient assessment tests in selected clinical scenarios. Such tests are also performed in the perioperative period, in which complication risk assessment is of exceptional importance. This review is an attempt to appraise up to date publications on use of copeptin as a biomarker.

Copeptin (CTproAVP) - A Biomarker of a Circulatory Impairment in Liver Transplant Recipients? A Prospective, Observational Study.

BACKGROUND: Copeptin, an easily measured and stable surrogate marker of arginine vasopressin, is a biomarker of a homeostasis disorder and a circulatory impairment in a wide spectrum of morbidities. The aim of this study was to evaluate the potential of copeptin as a biomarker of a circulatory impairment in patients undergoing liver transplantation (LT). METHODS: This was a prospective, observational study. Blood samples were obtained from 38 patients undergoing LT. Serum copeptin level was measured by means of a sandwich immunoassay pre-, intra-, and postoperatively up to 21 days after the operation. RESULTS: The mean concentration of copeptin remained in the range of values slightly below 1000 pg/mL during the analyzed observation period and remained higher than the values observed in healthy individuals. Intraoperative and immediately postoperative copeptin levels did not correlate with hemodynamic parameters. There was also no correlation between preoperative copeptin levels (C1) and preoperative Model for End-Stage Liver Disease scores, serum creatinine levels, plasma transaminase levels, international normalized ratio, or hematocrit (Spearman ρ, P > .05). CONCLUSIONS: Preoperative copeptin levels are elevated in most LT recipients and remain elevated for 21 days after surgery. There was no correlation between the concentration of copeptin and the Model for End-Stage Liver Disease-Sodium score or the cause of a hepatic failure. It cannot be concluded that copeptin is a biomarker of a circulatory impairment in patients with transplanted liver in the perioperative period. The secretion of vasopressin, as measured by copeptin concentration during and after LT, requires further study.

Human BDNF/TrkB variants impair hippocampal synaptogenesis and associate with neurobehavioural abnormalities.

Brain-derived neurotrophic factor (BDNF) signals through its high affinity receptor Tropomyosin receptor kinase-B (TrkB) to regulate neuronal development, synapse formation and plasticity. In rodents, genetic disruption of Bdnf and TrkB leads to weight gain and a spectrum of neurobehavioural phenotypes. Here, we functionally characterised a de novo missense variant in BDNF and seven rare variants in TrkB identified in a large cohort of people with severe, childhood-onset obesity. In cells, the E183K BDNF variant resulted in impaired processing and secretion of the mature peptide. Multiple variants in the kinase domain and one variant in the extracellular domain of TrkB led to a loss of function through multiple signalling pathways, impaired neurite outgrowth and dominantly inhibited glutamatergic synaptogenesis in hippocampal neurons. BDNF/TrkB variant carriers exhibited learning difficulties, impaired memory, hyperactivity, stereotyped and sometimes, maladaptive behaviours. In conclusion, human loss of function BDNF/TrkB variants that impair hippocampal synaptogenesis may contribute to a spectrum of neurobehavioural disorders.

Lst4, the yeast Fnip1/2 orthologue, is a DENN-family protein.

The folliculin/Fnip complex has been demonstrated to play a crucial role in the mechanisms underlying Birt-Hogg-Dubé (BHD) syndrome, a rare inherited cancer syndrome. Lst4 has been previously proposed to be the Fnip1/2 orthologue in yeast and therefore a member of the DENN family. In order to confirm this, we solved the crystal structure of the N-terminal region of Lst4 from Kluyveromyces lactis and show it contains a longin domain, the first domain of the full DENN module. Furthermore, we demonstrate that Lst4 through its DENN domain interacts with Lst7, the yeast folliculin orthologue. Like its human counterpart, the Lst7/Lst4 complex relocates to the vacuolar membrane in response to nutrient starvation, most notably in carbon starvation. Finally, we express and purify the recombinant Lst7/Lst4 complex and show that it exists as a 1 : 1 heterodimer in solution. This work confirms the membership of Lst4 and the Fnip proteins in the DENN family, and provides a basis for using the Lst7/Lst4 complex to understand the molecular function of folliculin and its role in the pathogenesis of BHD syndrome.

Crystal structure of folliculin reveals a hidDENN function in genetically inherited renal cancer.

Mutations in the renal tumour suppressor protein, folliculin, lead to proliferative skin lesions, lung complications and renal cell carcinoma. Folliculin has been reported to interact with AMP-activated kinase, a key component of the mammalian target of rapamycin pathway. Most cancer-causing mutations lead to a carboxy-terminal truncation of folliculin, pointing to a functional importance of this domain in tumour suppression. We present here the crystal structure of folliculin carboxy-terminal domain and demonstrate that it is distantly related to differentially expressed in normal cells and neoplasia (DENN) domain proteins, a family of Rab guanine nucleotide exchange factors (GEFs). Using biochemical analysis, we show that folliculin has GEF activity, indicating that folliculin is probably a distantly related member of this class of Rab GEFs.

Unexpected fatal right ventricular rupture during liver transplantation: case report.

BACKGROUND: The pulmonary artery catheter provides most hemodynamic informations, which are necessary for the patient monitoring during liver transplantation. However, its application may be associated with complications. CASE REPORT: Authors present a case of unexpected right ventricular rupture during liver transplantation in a 53-year-old male, with end-stage liver disease secondary to hepatitis C virus and alcohol abuse. The most likely cause of this complication was myocardial scarification of right ventricle during introducer sheath inserting. There was six hours period between vessel cannulation and the first signs of heart failure, which occurred in the final anhepatic phase. Attempts to surgical repair of damaged heart wall failed and the patient died. CONCLUSIONS: Based on the present case analysis we suggest to restrict the introduction depth of dilatator and possibly shorten it 2-3 cm by the manufacturer. We should also note that time elapsed from the vessel cannulation to cardiac tamponade first signs does not preclude this procedure as a cause of this fatal complications.

Thoracic epidural analgesia in anaesthesia for liver transplantation: the 10-year experience of a single centre.

BACKGROUND: Improvements in operating techniques, methods of anaesthesia and postoperative care in liver transplantation (LT) contribute to better outcomes. In order to restrict postoperative mechanical ventilation, a thoracic epidural analgesia (TEA) has been performed in our centre since 2000. In this report we present our 10-year experience of using TEA as a component of LT anaesthesia. MATERIAL/METHODS: TEA was performed, by anaesthetists experienced in this method, on patients qualified for LT, who consented and met inclusion criteria: INR<1.5, APTT<45s and platelets >70 G/L. Since 2008 the decision to insert an epidural catheter has been additionally supported by thromboelastometry. We assessed extubation time, frequency of complications of TEA and undesired accidents. RESULTS: From 279 patients undergoing LT, TEA was performed on 67 (24%), and from these 56 (84%) were extubated in the operating theatre. There were 5 cases of unsatisfactory thoracic epidural analgesia. Only 1 epidural catheter was removed accidentally, on the 2nd postoperative day. None of the complications of TEA were observed in the TEA group. CONCLUSIONS: Based on our observations, it can be assumed that TEA done by experienced an anaesthetist is a safe component of anaesthesia in selected groups of patients undergoing LT, and allows for early extubation.

The use of thromboelastometry in the assessment of hemostasis during orthotopic liver transplantation reduces the demand for blood products.

BACKGROUND: Bleeding due to fibrinolysis is a serious intraoperative complication during orthotopic liver transplantation (OLT). For a number of years aprotinin was used to minimize risk of this complication. This drug was however banned in 2007 and substituted with other antifibrinolytics. The aim of the study was to assess the potential of intraoperative thromboelastometry to evaluate hemostasis and channelize antifibrinolytic therapy. MATERIAL/METHODS: Since ban on aprotinin, 39 patients underwent OLT in our center with no monitoring of fibrinolysis (NMF). Severe disturbances of hemostasis assessed clinically only as a need for blood and blood products transfusion and were treated with transfusion of fresh frozen plasma only. In 2008 we started to use thromboelastometry (ROTEM group, n=39), which allowed for targeted treatment of hyperfibrinolysis with tranexamic acid. RESULTS: The need for blood transfusion in ROTEM group was insignificantly a lower than in NMF group (4.1±4.76 vs 5.53±4.89 units, p=0.2). Patients from ROTEM group required also less plasma transfusions (10.01±7.47 vs 13.15±6.62, p=0.06). Severe fibrinolysis was found in 3 patients from ROTEM group (7.7%) and was treated with tranexamic acid. CONCLUSIONS: Thromboelastometry provides an immediate diagnosis of fibrinolysis, justifies implementation of targeted treatment and confirms effectiveness of the therapy. In a larger study group it can also result in significant minimization of blood products transfusion during OLT.