Professor Barbara Zieger, MD, MME (Master of Medical Education)
Head, Section for Hemostaseology
E: barbara.zieger@uniklinik-freiburg.de
T: +49 761 270 43000
F: +49 761 270 45820
Medical Center – University of Freiburg
Center for Pediatrics
Division of Pediatric Hematology and Oncology
Section for Hemostaseology
Mathildenstr.1
79106 Freiburg
Germany
Regulation of hemostasis is a key element of a healthy life. Inherited or acquired disorders of hemostasis can lead to increased bleeding and prolonged wound healing. Our research focuses on biochemical and molecular genetic characterization of inherited platelet disorders (IPDs), inherited von Willebrand disease and acquired von Willebrand syndrome to assess patients’ risk profiles and to optimize therapy. Additionally, we have identified several novel disease-causing variants in various inherited platelet disorders. Our work also comprises basic research on murine and human septins (GTP-binding proteins) which are part of the cellular cytoskeleton and which seem to be involved in secretion and membrane processes. Our aim is to understand the impact of septins in platelet function and human disease.
TEAM
- Doris Böckelmann (PhD)
- Katharina Neubauer (PhD)
- Anja Kahle (Technican)
- Jessica Heinze (Technician)
- Anna Seeliger (MD student)
Former lab members
- Kirstin Sandrock-Lang (PhD)
- Ingrid Bartsch (PhD)
- Susanne Bläser (PhD)
RESEARCH THEMES
In many patients who present with severe bleeding symptoms, the cause remains unclarified for many years and the patients suffer significantly from the symptoms and the associated complications (re-operation, inflammation, wound healing disorders). We have established innovative methods to investigate primary hemostasis disorders, including aggregometry, flow cytometry of platelets, vWF multimeric analyses and high-throughput sequencing. For molecular genetic analysis, we have established a panel-based next generation sequencing (NGS) approach, comprising 95 genes associated with IPDs and von Willebrand disease. Included in the panel are genes coding for human septins which assemble into cytoskeletal filaments and are involved in multiple processes (i.e. platelet and membrane processes).
CURRENT PROJECTS
Biochemical and molecular genetic characterization (NGS) of patients with inherited defects of the primary hemostasis (platelet disorders and von Willebrand disease)
Inherited platelet disorders (IPDs) comprise a highly heterogeneous group of disorders affecting platelet number and function. IPDs are phenotypically and biochemically highly diverse. The extent of bleeding symptoms (hematoma, gastrointestinal bleeding, menorrhagia, intracranial bleeding) can vary widely. After trauma or surgical intervention, life-threatening bleeding can occur leading to reoperations or even resuscitation. IPDs may be syndromic or associated with risk to develop malignant disorders. The precise clinical and biochemical characterization and identification of the molecular genetic defect of the inherited platelet disorder are important for stratifying the patients’ risk profile and for personalized therapeutic options. Many patients also suffer from von Willebrand disease and extensive bleeding complications. Therefore, a comprehensive phenotypical and molecular genetic characterization of these patients is elementary to provide adequate therapy. To identify the molecular genetic defect of primary hemostasis defects we use next generation sequencing (gene panel and whole exome).
Phenotypical and biochemical platelet characterization of a patient with Glanzmann thrombasthenia (Cesari et al., J Blood Transfusions Dis. 2019; 2(1): 36-39).
Acquired von Willebrand syndrome and thrombocytopathy in patients with Ventricular Assist Device (VAD), Extracorporeal Life Support (ECLS) or Extracorporeal Membrane Oxygenation (ECMO)
Severe bleeding symptoms are one of the main complications in patients with VAD, ECLS or ECMO. Our working group identified for the first time Acquired von Willebrand syndrome (AvWS) as the main cause of these bleeding symptoms and published these results for large cohorts with VAD, ECLS or ECMO. In addition, we identified thrombocytopathy (platelet secretion defect) in these patients. AvWS and thrombocytopathy seem to be due to the increased shear stress caused by these devices leading to hemolysis and activation of primary and secondary hemostasis. Identifying these acquired disorders leads to improved diagnostic and therapeutical algorithms and better clinical outcome. In addition, these results may help to develop devices which will lead to less shear stress.
Von Willebrand factor (vWF) multimeric analysis (ECLS: loss of high molecular weight multimers) and ratio of vWF:collagen binding activity/vWF:antigen pre, during and post ECMO (Heilmann et al., Intensive care medicine. 2012; 38(1):62-8; Kalbhenn et al., J Heart Lung Transplant. 2018; 37(8):985-91.
Septins
Septins (SEPTs) are a family of filamentous GTPases, which have been described for the first time in the context of septum formation in yeast cells. So far, 13 mammalian septins have been published to form heteropolymeric complexes with other septins, actin filaments, microtubules, cellular membranes, and/or diverse proteins. Thus, they function as multimodular scaffolds that can recruit components of several signaling pathways and exert diverse functions in a cell type-specific manner. There is more and more evidence that links dysregulated septins to diseases, including neurological diseases or cancer. Originally, our group cloned four septins (SEPT4, SEPT5, SEPT8, SEPT11) and investigated septin expression and septin interaction with other proteins. We have identified the first patient with a deletion in the SEPT5 gene and severe bleeding symptoms due to a platelet secretion defect. Unrecognized platelet dysfunction can lead to severe perioperative bleeding complications, making research regarding the precise mechanisms of septins in platelets of great importance. We identified a platelet secretion defect for a pathogenic variant in the SEPT9 and SEPT6 gene using “next generation sequencing” (NGS) in patients. In a knockout mouse model, we demonstrated that Sept8 plays an essential role in platelet function. Loss of Sept8 in mice led to a reduction in platelet activation (integrin αIIbβ3), α-granule secretion, aggregation, spreading, pro-coagulant activity, and thrombin generation. Sept4-deficient platelets do not show the marked platelet dysfunction described for Sept8, but they do exhibit an enhanced procoagulant or apoptotic state after activation compared with controls. These different platelet phenotypes in the Sept4- and Sept8-knockout mouse models demonstrate that the analysis of each of the individual septins is essential. For platelets, there is currently no functional data for 10 of the 13 septins available. Currently, we investigate the role of septins (Sept2, 6, 7, and 9) in platelet function using knockout mouse models and patients with septin defects (including superresolution- and electron microscopy, proteome analyses and flow cytometry). We perform NGS-screening of patients with thrombocytopathies/-penias for different septin variants, in particular those with cytoskeletal defects or platelet secretory disorders. Analysis of genetically modified mice and patients with septin defects will provide fundamental insights into the relevance of septins in platelets, particularly for cytoskeletal reorganization, granule degranulation, and spreading of filo/lamellipodia. Since the secretion processes in platelets and endothelial cells appear to be similar, we investigate the role of septins in these cell types in our mouse models as well. The knowledge gained in this work will lead to a better understanding of the functional mechanisms of septins in platelets and endothelial cells.
Immunohistochemical staining of SEPT2, β-tubulin, and F-actin in activated human platelets.
COLLABORATIONS, CO-OPERATIONS AND NETWORKS
- Johan Heemskerk (PhD), CARIM, Maastricht, Netherlands
- Albert Sickmann (PhD), isas, Dortmund, Germany
- Kerstin Jurk (PhD), Mainz, Germany
- Axel Schlagenhauf (PhD), Medizinische Universität Graz, Graz, Austria
- Willem Ouwehand (PhD), Cambridge, United Kingdom
- Anna Pavlova (MD, PhD), Universitätsklinikum Bonn, Bonn, Germany
SELECTED RECENT PUBLICATIONS
- Fernandez DI, Provenzale I, Canault M, Fels S, Lenz A, Andresen F, Krumpel A, Dupuis A, Heemskerk JWM, Boeckelmann D, Zieger BMH. High-throughput microfluidic blood testing to phenotype genetically linked platelet disorders: an aid to diagnosis. Blood Adv. 2023. doi: 10.1182/bloodadvances.2023009860
- Zieger B, Schneider D, Brixius SJ, Scherer C, Buchwald A, Trummer G, Czerny M, Beyersdorf F, Busch HJ, Benk C, Pooth JS. Development of an in-vitro model for extracorporeal blood pumps to study the effects of artificial pulsatility on human blood. Front Med (Lausanne). 2023;10:1237002. doi: 10.3389/fmed.2023.1237002
- Boeckelmann D, Wolter M, Neubauer K, Sobotta F, Lenz A, Glonnegger H, Kasmann-Kellner B, Mann J, Ehl S, Zieger B. Hermansky-Pudlak Syndrome: Identification of Novel Variants in the Genes HPS3, HPS5, and DTNBP1 (HPS-7). Front Pharmacol. 2021;12:786937. doi: 10.3389/fphar.2021.786937
- Neubauer K, Jurk K, Petermann V, Kumm E, Zieger B. Impaired Platelet Function in Sept8-Deficient Mice In Vitro. Thromb Haemost. 2021;121(4):484-494. doi: 10.1055/s-0040-1718733
- Neubauer K, Boeckelmann D, Koehler U, Kracht J, Kirschner J, Pendziwiat M, Zieger B. Hereditary neuralgic amyotrophy in childhood caused by duplication within the SEPT9 gene: A family study. Cytoskeleton (Hoboken). 2019;76(1):131-136. doi: 10.1002/cm.21479
Complete list of publications: https://pubmed.ncbi.nlm.nih.gov/?term=zieger+b
FUNDING
DFG funding „Characterization of murine and human and human septins and their interaction partners” 2024-2027 (ZI 486/8-3; project number 347212107)