S296: il-1β signalling induces, and baricitinib alleviates neu1-mediated megakaryocyte desialylation in immune thrombocytopenia

Background: Neuraminidase 1 (NEU1)-mediated platelet and megakaryocyte (MK) desialylation has been implicated in immune thrombocytopenia (ITP). Surface desialylation leads to abnormal MK distribution (reduced localization adjacent to the vascular niche) and impaired thrombopoiesis in ITP bone marrow (BM). However, the mechanisms of NEU1 regulation remains poorly understood. Our group previously reported abnormal interleukin-1β (IL-1β) signalling (Haematologica, 2019) and the impaired distribution of MKs (Blood Advances, 2019) in ITP. Exogeneous IL-1β could activate the JAK/STAT pathway via an interferon (IFN)-β autocrine loop in hematopoietic cells. IFN-β autocrine or paracrine signalling has been associated with abnormal MK distribution subsequent to viral infection. Moreover, the major histocompatibility complex (MHC), in which the human NEU1 gene is located, could be remodelled and transcriptionally upregulated by STATs. Therefore, IL-1β-induced IFN signalling might modulate NEU1-mediated MK desialylation through the JAK/STAT pathway. Aims: To explore whether IL-1β signalling could regulate NEU1 expression through the JAK/STAT pathway in ITP-BM, and to investigate the potential of baricitinib in alleviating NEU1-mediated desialylation and impaired thrombopoiesis. Methods: Peripheral blood mononuclear cells (PBMC) were isolated from 5 patients with steroid-resistant or relapse ITP and 5 healthy donors for single-cell transcriptome analysis. BM CD34+ cells were isolated from ITP patients and healthy control subjects and cultured for differentiation into MKs in cell medium supplemented with thrombopoietin. The active mouse model of ITP was established as previously described (Blood, 2015). Baricitinib (Selleckchem, S2851) was administrated at 3mg/kg or 10mg/kg for 14 days since model establishment. Platelet counts, NEU1 expression, MK desialylation and distribution were measured and compared between the treatment and control groups. Results: MKs from ITP-PBMC showed upregulated expression of IL-1β and type I IFN response genes (e.g. IKBKG, IFITM3) by single-cell RNA sequencing. Immunohistochemistry indicated higher IL-1β and IFN-β levels in ITP-BM. ITP-MKs and IL-1β-treated control MKs exhibited upregulated mRNA transcription and increased surface expression of NEU1, as well as enhanced surface desialylation measured by flow cytometry. Immunofluorescence confirmed the translocation of NEU1 to the plasma membrane in control MKs subsequent to IL-1β treatment. Increased IL-1R1 expression and STAT2 phosphorylation were observed in ITP-MKs compared with control MKs. Exogenous IL-1β induced STAT2 phosphorylation in control MKs. JAK blockade by pyridone 6 suppressed STAT2 phosphorylation and reduced NEU1 expression. After IL-1β treatment, IFN-β was detected in the cell supernatants, indicating IFN-β secretion by stimulated MKs. In vitro baricitinib treatment of ITP-MKs inhibited STAT2 phosphorylation, reduced the surface expression of NEU1, and alleviated surface desialylation. In vivo administration of baricitinib completely rescued the induced thrombocytopenia in ITP murine model (no significant differences compared with healthy controls). BM immunofluorescence verified the abnormal MK distribution and upregulated NEU1, IL-1R1, and IFN-β expression in ITP murine model, which were also alleviated by baricitinib treatment.Summary/Conclusion: IL-1β signalling may induce JAK/STAT activation to promote NEU1-mediated desialylation in ITP-MKs, leading to impaired platelet production. Baricitinib has the potential to alleviate NEU1-mediated desialylation and improve thrombopoiesis. Keywords: Idiopathic thombocytopenic purpura (ITP), Janus Kinase inhibitor, Megakaryocyte, IL-1