Energy metabolism and aging pathways in human stem cell reprogramming and differentiation

We are interested in the role of energy metabolism and aging in human stem cell reprogramming and differentiation. In the past year, we have successfully reprogrammed cells from young and old human donors. We have examined the metabolic profiles of young and old donor cells using ultra-high throughput approaches. Remarkably, we observed differences in the metabolism of old cells compared to young cells, specifically in protein metabolism. We observed similar metabolic differences between the cells of young and old donors in mice, suggesting a conserved phenomenon. Interestingly, there was a greater variability in the ability of cells from old donors to reprogram efficiently - some old cells reprogrammed as well or even better than young cells, but some also reprogrammed more poorly, so the range was much more variable. We are currently investigating the molecular basis for this interesting difference in variability of reprogramming as individuals get older. In the past year, we have also started to examine the role of a central 'fuel-gauge' in the cells, the energy-sensing protein kinase named AMPK. We have generated sophisticated tools to probe the role of AMPK in the reprogramming of human cells into induced-pluripotent stem cells and in the differentiation of these induced pluripotent stem cells in specific cell types, specifically neurons and cardiomyocytes. We have also identified novel substrates of AMPK that could be particularly important in relaying the action of this central fuel gauge for stem cell function. In the next year, we plan to investigate the interaction between age and metabolism for the function and quality of stem cells generated from donors of young and old ages.

In the past year, we examined the importance of metabolic pathways in human induced pluripotent stem cells. We first focused on an energy-gauge, the energy-sensing protein kinase called AMP-dependent protein kinase (AMPK). We found that this energy-sensing protein is expressed in human stem cells and that it gets activated upon nutrient deprivation. We were also able to model human mutations in this pathway in these stem cells. Finally, we were able to identify novel substrates of AMPK in human cells and to verify that they were indeed targeted by AMPK in human stem cells. Together, these data indicate that energy-sensing pathway are highly active in human stem cells and could be very important for the generation, quality, and differentiation of these cells into specific cell types such as cardiac cells. Another portion of our program is to develop novel methodology to analyze in an unbiased manner the metabolism of human stem cells with the goal to improve their function and ability to differentiate into cardiac or neuronal cells. In the past year, we have optimized new approaches that can detect in a very sensitive and unbiased manner different types of metabolites in cells, in particular lipid metabolites. As low energy leads to lipid utilization by cells, understanding lipid metabolism will be a key step in understanding stem cell function and quality. Together, our analysis should give insight into the metabolism of stem cells, which could improve their generation, quality, and ability to differentiate into specialized cells for regenerative medicine.

The goal of this project was to test how metabolism impacts human induced pluripotent stem cells (iPSCs). A key metabolic-sensing protein is called AMP-dependent protein kinase (AMPK): it has been called the “energy gauge” of cells. During the past years, we showed that the metabolism-sensing AMPK is highly expressed in human iPSCs and that it becomes activated upon nutrient deprivation. There are humans harboring mutations in their AMPK gene, and these mutations lead to diseases, notably major brain and heart malfunctions. Using genome-engineering, we were able to model these human mutations in AMPK in human iPSCs. This is important because it allows to model the “disease in a dish” and to determine the cellular and molecular causes for these disorders. Finally, we were able to find novel substrates of AMPK in human cells (some of them are also substrates in iPSCs). Collectively, our results show that metabolism pathways are highly regulated in human stem cells and could play critical role for the quality and derivation of these cells into cardiac cells or neurons. Our other goal was to use a more global, unbiased approaches and pioneer novel technology to analyze the metabolism of human stem cells with the goal to improve their generation and derivation into cardiac or neuronal cells. We have now optimized cutting-edge technology that can identified a series of lipid metabolites, which was not possible before. As AMPK activation (and low energy in general) leads to lipid utilization by cells, probing lipid metabolism is critical in improving stem cell function and quality. Out work should provide new knowledge on the metabolism of stem cells and improve the generation and derivation of human iPSCs into specialized cells for personalized regenerative medicine.