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

Abstract

Mesenchymal stem cells (MSCs) hold considerable promise in tissue engineering (TE). However, their poor survival when exogenously administered limits their therapeutic potential. Previous studies from our group demonstrated that lack of glucose (glc) (but not of oxygen) is fatal to human MSCs because it serves as a pro-survival and pro-angiogenic molecule for human MSCs (hMSCs) upon transplantation. However, which energy-providing pathways MSCs use to metabolize glc upon transplantation? Are there alternative energetic nutrients to replace glc? And most importantly, do hMSCs possess significant intracellular glc reserves for ensuring their survival upon transplantation? These remain open questions at the forefront of TE based-therapies. In this study, we established for the first time that the in vivo environment experienced by hMSCs is best reflected by near-anoxia (0.1% O ) rather than hypoxia (1%-5% O ) in vitro. Under these near-anoxia conditions, hMSCs rely almost exclusively on glc through anerobic glycolysis for ATP production and are unable to use either exogenous glutamine, serine, or pyruvate as energy substrates. Most importantly, hMSCs are unable to adapt their metabolism to the lack of exogenous glc, possess a very limited internal stock of glc and virtually no ATP reserves. This lack of downregulation of energy turnover as a function of exogenous glc level results in a rapid depletion of hMSC energy reserves that explains their poor survival rate. These new insights prompt for the development of glc-releasing scaffolds to overcome this roadblock plaguing the field of TE based-therapies. Stem Cells 2018;36:363-376.

Mesenchymal stem cells: Cell therapy and regeneration potential

“…Cheng, Zhang, & Jiang, 2015;X. B. Liu, Chen, et al, 2012;Moya et al, 2018;J. Zhang, Jia, et al, 2013) Xenofree isolation and culturing (Bakopoulou et al, 2017;Gottipamula et al, 2013;Laitinen et al, 2016;Swamynathan et al, 2014) Abbreviation: MSC, mesenchymal stromal/stem cell.…”

Cryopreserved H2 O2 -preconditioned human adipose-derived stem cells exhibit fast post-thaw recovery and enhanced bioactivity against oxidative stress

“…In relation to this, HC016 cells had a higher survival rate than control ASCs when submitted to adverse environments that might be present in pathologic conditions. One of them consisting of extreme oxidative stress conditions (two consecutive oxidative cycles in total serum depletion), and the other the combination of oxidative stress, total serum depletion, and lower levels of glucose (considered one of the key nutrients for MSCs; Deschepper et al, ; Moya et al, ). This improvement in cell survival might be very beneficial for cell therapy considering that MSC functions are seriously affected by oxidative stress and nutrient deprivation, impairing their self‐renewal, differentiation capacity, and proliferation (Denu & Hematti, ).…”

“…From this perspective, we have found that our HC016 cells showed lower basal mitochondrial activity than their corresponding control ASCs. Further, numerous authors have demonstrated that when mitochondrial oxidative phosphorylation is down‐regulated, cell energy demands are ensured by activating glycolysis, as observed in hypoxia when oxygen is too limiting to support oxidative phosphorylation (Estrada et al, ; Kim, Tchernyshyov, Semenza, & Dang, ; Moya et al, ; Papandreou, Cairns, Fontana, Lim, & Denko, ). Therefore, we analysed expression levels of PFKFB4 and PDK1—key enzymes in regulation of glycolysis (Kumar et al, )—and observed that HC016 cells are able to up‐regulate their expression in response to oxidative stress.…”

“…Another important challenge that cells face when administered to injured tissue is the harmful pro‐inflammatory microenvironment, characterized by extreme conditions of oxidative stress due to the presence of high levels of reactive oxygen species (ROS), a low pH, low oxygen tension, and nutrient deprivation (Baldari et al, ; Lee, Choi, Cha, & Hwang, ; Moya et al, ). This harsh environment together with impaired functionality of cryopreserved cells could account for the poor engraftment and survival of transplanted cells (Copland & Galipeau, ; Phinney et al, ).…”

Hydrogel mechanical properties are more important than osteoinductive growth factors for bone formation with MSC spheroids

“…[1] Among other tissues, MSCs have been used clinically to promote bone repair in the craniofacial region. [2] However, high rates of cell death upon transplantation have limited the effectiveness of such therapies [3,4], motivating the need for alternative approaches to utilize these multipotent cells. The therapeutic efficacy of MSCs can be increased through their formation into spheroids, three-dimensional aggregates of cells.…”