Metabolic adjustments are necessary for the initiation, proliferation, and spread of cancer cells. Although mitochondria have been shown to move to cancer cells from their microenvironment, the metabolic consequences of this phenomenon have yet to be fully elucidated. Here, we report that multiple myeloma cells use mitochondrial-based metabolism as well as glycolysis when located within the bone marrow microenvironment. The reliance of multiple myeloma cells on oxidative phosphorylation was caused by intercellular mitochondrial transfer to multiple myeloma cells from neighboring nonmalignant bone marrow stromal cells. This mitochondrial transfer occurred through tumor-derived tunneling nanotubes (TNT).Moreover, shRNA-mediated knockdown of CD38 inhibits mitochondrial transfer and TNT formation in vitro and blocks mitochondrial transfer and improves animal survival in vivo. This study describes a potential treatment strategy to inhibit mitochondrial transfer for clinical benefit and scientifically expands the understanding of the functional effects of mitochondrial transfer on tumor metabolism.Significance: Multiple myeloma relies on both oxidative phosphorylation and glycolysis following acquisition of mitochondria from its bone marrow microenvironment.

Hematopoietic stem cells (HSCs) undergo rapid expansion in response to stress stimuli. Here we investigate the bioenergetic processes which facilitate the HSC expansion in response to infection. We find that infection by Gram-negative bacteria drives an increase in mitochondrial mass in mammalian HSCs, which results in a metabolic transition from glycolysis toward oxidative phosphorylation. The initial increase in mitochondrial mass occurs as a result of mitochondrial transfer from the bone marrow stromal cells (BMSCs) to HSCs through a reactive oxygen species (ROS)-dependent mechanism. Mechanistically, ROS-induced oxidative stress regulates the opening of connexin channels in a system mediated by phosphoinositide 3-kinase (PI3K) activation, which allows the mitochondria to transfer from BMSCs into HSCs. Moreover, mitochondria transfer from BMSCs into HSCs, in the response to bacterial infection, occurs before the HSCs activate their own transcriptional program for mitochondrial biogenesis. Our discovery demonstrates that mitochondrial transfer from the bone marrow microenvironment to HSCs is an early physiologic event in the mammalian response to acute bacterial infection and results in bioenergetic changes which underpin emergency granulopoiesis.