Abstract
The role of stem cells in normal and neoplastic hematopoiesis is well established. However, neither normal nor neoplastic hematopoietic stem cells (HSCs) develop in isolation and accumulating evidence indicates that a critical developmental role is played by the perivascular "niche." The cellular, humoral, and cell surface contacts that provide the proper environment for HSC survival, proliferation, and differentiation are becoming increasingly better understood. A number of studies have established that endothelial cells (ECs), several types of perivascular stromal cells, and megakaryocytes (MKs) provide several cell surface and secreted molecules required for HSC development. Accumulating evidence also indicates that the normal stem cell niche is altered in patients with hematological neoplasms and that the "neoplastic niche" plays an important role in promoting malignant and suppressing normal blood cell development in such patients. To explore this concept in the myeloproliferative neoplasms (MPNs), we employed a murine model to determine the effects of Jak2V(617)F, an oncogene found in a majority of such patients, in marrow ECs and MKs and their effect on promoting neoplastic and suppressing normal hematopoiesis. We found that Jak2V(617)F has profound effects on both cell types, which together are critical for the growth advantage and radioresistance shown by Jak2V(617)F-bearing HSCs. Such findings should provide new approaches to the treatment of patients with MPNs.