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Blood Adv. 2018 Mar 13;2(5):534-548. doi: 10.1182/bloodadvances.2017013599.

Sipa1 deficiency-induced bone marrow niche alterations lead to the initiation of myeloproliferative neoplasm.

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Center for Hematology and Regenerative Medicine, Department of Medicine, Karolinska University Hospital, and.
Division of Experimental Cancer Medicine, Department of Laboratory Medicine, Karolinska Institute, Stockholm, Sweden.
Clinical Research Center, Karolinska University Hospital Huddinge, Stockholm, Sweden.
Integrated Cardio Metabolic Centre, Department of Medicine, Karolinska University Hospital, Karolinska Institute, Stockholm, Sweden.
Department of Oncology and Pathology, Karolinska University Hospital, Karolinska Institute, Solna, Sweden.
Department of Immunology and Cell Biology, Graduate School of Biostudies, Kyoto University, Kyoto, Japan.
Center for Regenerative Medicine, Massachusetts General Hospital, Boston, MA.
Harvard Stem Cell Institute, Cambridge, MA.
Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden; and.
Division of Molecular Hematology, Lund University, Lund, Sweden.


Mutations of signal-induced proliferation-associated gene 1 (SIPA1), a RAP1 GTPase-activating protein, were reported in patients with juvenile myelomonocytic leukemia, a childhood myelodysplastic/myeloproliferative neoplasm (MDS/MPN). Sipa1 deficiency in mice leads to the development of age-dependent MPN. However, Sipa1 expression in bone marrow (BM) microenvironment and its effect on the pathogenesis of MPN remain unclear. We here report that Sipa1 is expressed in human and mouse BM stromal cells and downregulated in these cells from patients with MPN or MDS/MPN at diagnosis. By using the Sipa1-/- MPN mouse model, we find that Sipa1 deletion causes phenotypic and functional alterations of BM mesenchymal stem and progenitor cells prior to the initiation of the MPN. Importantly, the altered Sipa1-/- BM niche is required for the development of MDS/MPN following transplantation of normal hematopoietic cells. RNA sequencing reveals an enhanced inflammatory cytokine signaling and dysregulated Dicer1, Kitl, Angptl1, Cxcl12, and Thpo in the Sipa1-/- BM cellular niches. Our data suggest that Sipa1 expression in the BM niche is critical for maintaining BM niche homeostasis. Moreover, Sipa1 loss-induced BM niche alterations likely enable evolution of clonal hematopoiesis to the hematological malignancies. Therefore, restoring Sipa1 expression or modulating the altered signaling pathways involved might offer therapeutic potential for MPN.

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