The Role of Megakaryocytes in Breast Cancer Metastasis to Bone
Menée à l'aide de modèles murins de cancer du sein, cette étude met en évidence le rôle joué par les mégacaryocytes pour prévenir le développement de métastases osseuses
Little is known about how megakaryocytes affect metastasis apart from serving as the source of platelets. We noted an increase in the number of megakaryocytes in the femurs of metastases-bearing athymic mice four weeks following intracardiac inoculation of MDA-MB-231 human breast cancer cells. How did the megakaryocytes relate to the metastases? Did megakaryocytes prepare a niche or did they increase in response to metastases? To test these possibilities, we examined two models of experimental metastasis, intracardiac inoculation of human MDA-MB-231 into athymic mice, and intramammary injection of mouse tumor cells, 4T1.2 (metastatic) or 67NR (non-metastatic) in BALB/c mice. In both models, metastatic, but not primary tumor growth was associated with increased megakaryopoiesis. At 4 weeks post injection, megakaryocytes increased ~ two-fold in the bone marrow of mice with MDA-MB-231 bone metastasis. BALB/c mice injected orthotopically with murine 4T1.2 cells showed extramedullary hematopoiesis resulting in a four-fold increase in megakaryocytes in the spleen. These findings led us to speculate that a reduction in megakaryocytes would result in reduced metastasis. Thrombopoietin knockout mice exhibited a 90% decrease in megakaryocytes compared to wild type mice. Nonetheless, they developed more aggressive metastasis than wild type. We also found with human clinical samples, an increase in megakaryocytes in the bone marrow of 75% (6/8) of patients with metastatic breast cancer compared to age and gender matched controls. The data suggested that the increase in megakaryocytes occurs in response to metastatic cells in the bone, and that megakaryocytes are in some measure protective against metastases.