Quiescence Preconditioned Human Multipotent Stromal Cells Adopt a Metabolic Profile Favorable for Enhanced Survival under Ischemia

Abstract

A major impediment to the development of therapies with mesenchymal stem cells/multipotent stromal cells (MSC) is the poor survival and engraftment of MSCs at the site of injury. We hypothesized that lowering the energetic demand of MSCs by driving them into a quiescent state would enhance their survival under ischemic conditions. Human MSCs (hMSCs) were induced into quiescence by serum deprivation (SD) for 48 hours. Such preconditioned cells (SDhMSCs) exhibited reduced nucleotide and protein syntheses compared to unpreconditioned hMSCs. SD-hMSCs sustained their viability and their ATP levels upon exposure to severe, continuous, near-anoxia (0.1% O 2 ) and total glucose depletion for up to 14 consecutive days in vitro, as they maintained their hMSC multipotential capabilities upon reperfusion. Most importantly, SD-hMSCs showed enhanced viability in vivo for the first week postimplantation in mice. Quiescence preconditioning modified the energy-metabolic profile of hMSCs: it suppressed energysensing mTOR signaling, stimulated autophagy, promoted a shift in bioenergetic metabolism from oxidative phosphorylation to glycolysis and upregulated the expression of gluconeogenic enzymes, such as PEPCK. Since the presence of pyruvate in cell culture media was critical for SD-hMSC survival under ischemic conditions, we speculate that these cells may utilize some steps of gluconeogenesis to overcome metabolic stress. These findings support that SD preconditioning causes a protective metabolic adaptation that might be taken advantage of to improve hMSC survival in ischemic environments. STEM CELLS 2017;35:181-196 SIGNIFICANCE STATEMENTPoor survival of grafted cells at the injury site is the major impediment for developing successful cell based therapies. While some studies have focused on improving cell survival upon implantation, most of them have failed to address the critical issue of long term cell survival postimplantation thus drastically reducing the potential benefit of these therapies. In this study, we demonstrated that cellular quiescence preconditioning is a simple, safe, yet very efficient solution for enhancing cell survival in ischemia that may be applicable not only for adult stem cells (hMSC) but also other cell types.

Human Mesenchymal Stem Cell Failure to Adapt to Glucose Shortage and Rapidly Use Intracellular Energy Reserves Through Glycolysis Explains Poor Cell Survival After Implantation

“…Although it was out of the scope of this study to explore in detail the role of autophagy in hMSCs, we observed that inhibition of autophagy had a deleterious impact on hMSC survival under near‐anoxia independently of the presence of exogenous glc (Supporting Information Fig. S1) confirming that maintenance of a high autophagic activity is crucial for hMSC survival under near anoxia .…”

“…For both the analyses of HIF‐1α and LDH‐A expression and the assessment of the TCA activity (via the MTT assay) in vivo, 10 6 hMSCs were loaded in 100 µl fibrin hydrogels and implanted subcutaneously in nude mice as described previously . For assessment of hMSC viability, ATP contents and glycolytic reserves in vivo, 2 × 10 5 hMSCs were loaded in a “closed system” consisting in a fibrin hydrogel (200 µl) placed in diffusion chambers (membrane filters with 0.45 µm diameter pores; Millipore, France) as described previously in Moya et al . The diffusion chambers were then implanted subcutaneously in mice.…”

Human myogenic reserve cells are quiescent stem cells that contribute to muscle regeneration after intramuscular transplantation in immunodeficient mice

“…Quiescent MRC may adopt a metabolic profile favorable to their survival and increase their autophagy as demonstrated recently for quiescent preconditioned mesenchymal stem cell 48 . As such, initial quiescence may favor myogenic stem cell survival after transplantation in an ischemic environment.…”

Survival/Adaptation of Bone Marrow-Derived Mesenchymal Stem Cells After Long-Term Starvation Through Selective Processes

“…It can be converted to lactate by lactate dehydrogenase or to acetyl‐CoA to enter the Cori and Krebs cycles as well as the gluconeogenesis pathway. Moya et al also showed that no or minimal lactate was detected under induced ischemic conditions. In the conditions used in this study, high amounts of lactate were present throughout the entire starvation period also implicating the involvement of gluconeogenesis and thus glycolysis.…”