| 1. |
- Fager Ferrari, Marcus, et al.
(författare)
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Evaluation of the Sialidase Inhibitor Oseltamivir in GNE-associated Thrombocytopenia
- 2021
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Ingår i: Research and practice in thrombosis and haemostasis. - 2475-0379. ; 5:S2, s. 644-645
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Konferensbidrag (refereegranskat)abstract
- Background: GNE encodes UDP-N-acetyl-glucosamine-2-epimerase/N-acetylmannosamine kinase, the rate limiting enzyme of sialic acid biosynthesis. Biallelic variants in GNE have recently been associated with severe isolated macrothrombocytopenia, attributed to an increased clearance of desialylated platelets. Interestingly, treatment with the sialidase inhibitor oseltamivir has been reported to increase platelet counts in conditions such as immune thrombocytopenia (ITP) and influenza. We present a case of a 17-year-old boy (the proband) with severe congenital macrothrombocytopenia (platelet counts < 10 x 109/L). Whole genome sequencing revealed two previously undescribed compound heterozygous variants in GNE (c.416_426del, p.Ile139Argfs*4 and c.1352G>A, p.Arg451Gln). The proband was otherwise healthy, with no signs of GNE myopathy. Aims: To investigate the consequences of the identified variants in GNE and evaluate the effect of oseltamivir in GNE-associated thrombocytopenia. Methods: Sialylation of platelets, granulocytes, lymphocytes and monocytes was determined by flow cytometry in the proband and healthy controls (n = 5), using Sambucus nigra lectin (SNA) and Maackia amurensis lectin II (MAL II). Platelet sialylation was reassessed in the proband following treatment with oseltamivir (75 mg twice daily, off-label use). Informed consent was obtained from all participants. The study was approved by the regional ethical committee. Results: Sialylation of platelets and leukocytes was markedly decreased in the proband compared with the healthy controls, consistent with a deleterious effect of the compound heterozygous variants in GNE (Figure 1). Platelet sialylation was persistently decreased after 18 days of treatment with oseltamivir, and no clinically significant elevation of the platelet counts could be observed (Figure 1, Figure 2).
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| 2. |
- Smolag Klosowska, Karolina
(författare)
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Cancer and autoimmunity: two sides of the same coin. Complement system proteins in the regulation of immune responses.
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Factor H is an inhibitor of the complement system, essential for controlling the alternative pathway and also playing a crucial role in various cellular functions. In this thesis, we identified new intriguing functions of FH as a survival factor for primary human monocytes, promoting their differentiation into immunosuppressive macrophages. We showed that FH is expressed by human breast cancer cells, and that the expression correlates with the presence of immunosuppressive macrophages in the cancer microenvironment, breast cancer recurrence, and severity of the disease. Following this finding, we showed that FH also increases the survival of regulatory T-cells, which is mediated via the binding of FH to the inducible co-stimulator on the surface of the cells. This phenomenon seems to play a role in glioma, an aggressive type of brain tumors, where FH expression positively correlates with the occurrence of regulatory T-cells and a worse prognosis for the patients. In contrast to this detrimental role in cancer, FH was shown to play a beneficial role in the silent removal of apoptotic cells and their remnants. This process is of central importance in the pathogenesis of systemic lupus erythematosus, a severe autoimmune disease. Moreover, we confirmed that a different complement protein, C4d, which is the final cleavage fragment of C4, can be a valuable biomarker to measure the activity of this disease. The loss of sialic acid, an important FH ligand, and diminished binding of FH on platelets and other immune cells was furthermore associated with decreased protection against complement attack in a patient suffering from congenital thrombocytopenia. Altogether this thesis aimed to explore the dual role of complement proteins in cancer and autoimmunity.
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| 3. |
- Smolag Klosowska, Karolina, et al.
(författare)
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Severe Congenital Thrombocytopenia Characterized by Decreased Platelet Sialylation and Moderate Complement Activation Caused by Novel Compound Heterozygous Variants in GNE
- 2021
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Ingår i: Frontiers in Immunology. - : Frontiers Media SA. - 1664-3224. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Background: Hereditary thrombocytopenias constitute a genetically heterogeneouscause of increased bleeding. We report a case of a 17-year-old boy suffering fromsevere macrothrombocytopenia throughout his life. Whole genome sequencing revealed the presence of two compound heterozygous variants in GNE encoding the enzyme UDP-N-acetyl-glucosamine-2-epimerase/N-acetylmannosamine kinase, crucial for sialic acid biosynthesis. Sialic acid is required for normal platelet life span, and biallelic variants in GNE have previously been associated with isolated macrothrombocytopenia. Furthermore, sialic acid constitutes a key ligand for complement factor H (FH), an important inhibitor of the complement system, protecting host cells fromindiscriminate attack.Methods: Sialic acid expression and FH binding to platelets and leukocytes wasevaluated by flow cytometry. The binding of FH to erythrocytes was assessed indirectlyby measuring the rate of complement mediated hemolysis. Complement activation wasdetermined by measuring levels of C3bBbP (alternative pathway), C4d (classical/lectinpathway) and soluble terminal complement complex assays.Results: The proband exhibited markedly decreased expression of sialic acid on platelets and leukocytes. Consequently, the binding of FH was strongly reduced and moderate activation of the alternative and classical/lectin complement pathways was observed, together with an increased rate of erythrocyte lysis.Conclusion: We report two previously undescribed variants in GNE causing severecongenital macrothrombocytopenia in a compound heterozygous state, as aconsequence of decreased platelet sialylation. The decreased sialylation of platelets, leukocytes and erythrocytes affects the binding of FH, leading to moderate complement activation and increased hemolysis.
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