Characterization of the endosteal niche in myeloproliferative neoplasms associated to the Jak2V617F mutation

Author(s)

Talita Perez Sanches

• Document type: Master's Dissertation
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2020-09-16

Examining board members

Lorena Lôbo de Figueiredo Pontes; Gil Cunha de Santis; Virginia Mara de Deus Wagatsuma

• Advisor: Lorena Lôbo de Figueiredo Pontes

Abstract

Myeloproliferative neoplasms (MPN) originate from molecular changes at the hematopoietic stem cells (HSC) level, but changes in the bone marrow niche may also contribute to the functional regulation of neoplastic and normal residual stem cells, and thus participate in the pathophysiology of the disease. Although MPN are well described, the contribution of the microenvironment to the disease has not been fully studied. Therefore, it is our goal to study how the cells from the bone marrow microenvironment contribute to the disease. We believe that MPN are initiated not only by intrinsic HSC defects but also by its regulation by an abnormal niche, that provides proliferative support to myelopoiesis. Therefore, we aimed to phenotypically characterize cells that support the hematopoietic niche located at the endosteum (endothelial cells, osteoblasts and mesenchymal stromal cells) by the use of a murine transgenic knockin model of conditional heterozygous expression of the Jak2V617F mutation. For that, cells from the bone marrow niche of Jak2wt (controls) and Jak2VF (animals with Jak2V617F-associated MPN) were obtained by bone digestion and characterized by immunophenotyping of the total bone marrow. After exclusion of hematopoietic cells, the niche cells were identified as endothelial cells (EC, CD31+/Sca1+), mesenchymal stromal cells (MSC, CD31-/Sca-1+/CD51+) and osteoblasts (OB, CD31-/Sca1-/CD51+). Our results showed that it was possible to establish the methods for isolation of a pure population of mesenchimal stromal cells in the Jak2V617F transgenic model. In addition, we observed a decreased frequency of osteoblasts in the Jak2VF animals when compared to Jak2wt controls. It is possible that the numeric deficiency of osteoblasts results in functional abnormalities of the niche that may favor the expansion or maintenance of the neoplastic stem cells. It is also plausible that neoplastic stem cells exert a suppressive effect on the niche cells, thus reducing specific subpopulations of the endosteum, a site of important interactions between stem cells and the microenvironment of the bone marrow. Such hypotheses generated by our study deserve to be further explored by future functional studies. (AU)

• FAPESP's process: 17/15484-4 - Characterization of the bone marrow endosteal niche in JAK2-mutated myeloproliferative neoplasms
• Grantee: Talita Perez Sanches
• Support Opportunities: Scholarships in Brazil - Master