Schematic summarizing the effect of marrow adiposity on hematopoiesis. Aging or obesity associated increase in marrow adiposity leads to elevated secretion of G-CSF, M-CSF, and GM-CSF, which subsequently results in elevated myelopoiesis (mediated by neutrophil elastase) and suppressed lymphopoiesis (mediated by IL-1). Marrow adipocytes can also secrete RANKL, which can prompt monocyte-macrophage progenitors towards osteoclasts. Osteoblasts then attract osteoclasts towards mineralized bone surfaces to initiate bone resorption, which can impair bone remodeling and bone health. [G-CSF – granulocyte colony stimulating factor, M-CSF – macrophage colony stimulating factor, GM-CSF – granulocyte macrophage colony stimulating factor, RANKL – receptor activator of nuclear factor kappa-B ligand, IL-1 – interleukin 1, HSC – hematopoietic stem cell, MSC – mesenchymal stem cell]