Preliminary studies have shown that bone marrow transplants from young mice into old mice prevent sarcopenia.178,179 Macrophages present in muscle repair have been shown to secrete nicotinamide phosphoribosyltransferase (NAMPT) to stimulate muscle stem cells and promote myoblast proliferation.180 Because NAMPT has been shown to inhibit senescence in endothelial progenitor cells via SIRT1 regulation,181 the study suggests that macrophages, by producing NAMPT, may prevent/inhibit cellular senescence and the corresponding SASP and therefore positively regulate muscle regeneration. The gene discussed is SIRT1; the disease is sarcopenia.