Energy metabolism and aging pathways in human stem cell reprogramming and differentiation
The discovery that human skin cells can be reprogrammed into stem cells holds great promise for therapies for degenerative diseases. As many patients in need of regenerative medicine therapies are middle-aged or older, identifying strategies to improve the reprogramming efficiency and quality of cells from aging donors will be crucial in harnessing the full potential of stem cells for therapies. Our idea is that mechanisms that regulate aging, particularly those related to energy metabolism, can be used to enhance stem cell function, particularly when cells come from older individuals.
To test this idea, we will analyze the importance of a central energy metabolism gauge in cells termed AMPK in the reprogramming of human skin cells into stem cells. Systematic analysis of metabolic pathways in stem cells and their progeny will give fundamental clues into the mechanisms connecting energy metabolism, aging, and stem cell function. This knowledge will help overcome road-blocks in reprogramming and differentiation into specific lineages, a crucial step in achieving therapeutic tissue replacement. These studies will also increase the pool of drug-targetable molecules that can be used to improve the quality of stem cells for therapies.
Embryonic stem cells hold the promise of treatments and cures for human diseases and conditions that affect millions of people. In particular, neurodegenerative diseases linked with age are affecting increasing number of patients. Thus, one strategy would be to replace degenerating cells in patients with stem cells. However, these approaches will only be possible when the mechanisms controlling the generation of these stem cells and their capacity to produce their functional progeny are better understood in young and old patients.
We propose to study the mode of action of metabolism and aging regulators in human cell reprogramming. The AMPK pathway plays major role in metabolism and aging. Metabolic pathways are a major target for the development of therapeutic strategies that may benefit a wide range of patients. However, the mechanisms by which metabolic pathways regulate stem cells are still poorly understood, hampering the development of such strategies. We believe that the results of our experiments will be ultimately translated into novel strategies to cure age-dependent diseases such as neurodegenerative diseases, stroke, diabetes and heart diseases in aging patients.
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.