Transient non-integrative expression of nuclear reprogramming factors promotes multifaceted amelioration of aging in human cells

[Jackb23]

“Aging is characterized by a gradual loss of function occurring at the molecular, cellular, tissue and organismal levels. At the chromatin level, aging associates with progressive accumulation of epigenetic errors that eventually lead to aberrant gene regulation, stem cell exhaustion, senescence, and deregulated cell/tissue homeostasis. Nuclear reprogramming to pluripotency can revert both the age and the identity of any cell to that of an embryonic cell. Recent evidence shows that transient reprogramming can ameliorate age-associated hallmarks and extend lifespan in progeroid mice. However, it is unknown how this form of rejuvenation would apply to naturally aged human cells. Here we show that transient expression of nuclear reprogramming factors, mediated by expression of mRNAs, promotes a rapid and broad amelioration of cellular aging, including resetting of epigenetic clock, reduction of the inflammatory profile in chondrocytes, and restoration of youthful regenerative response to aged, human muscle stem cells, in each case without abolishing cellular identity.”

“ In terms of energy metabolism, aged cells display decreased mitochondrial activity, accumulation of reactive oxygen species (ROS), and deregulated nutrient sensing2,16,17. We therefore tested the effects of treatment on aged cells by measuring mitochondria membrane potential, mitochondrial ROS, and levels of Sirtuin1 protein (SIRT1) in the cells. Transient reprogramming increased mitochondria membrane potential in both cell types (Fig. 2g), while it decreased mitochondrial ROS (Fig. 2h) and increased SIRT1 protein levels in fibroblasts, similar to young cells (Supplementary Fig. 8). Senescence-associated beta-galactosidase staining showed a significant reduction in the number of senescent cells in aged endothelial cells but not in fibroblasts (Supplementary Fig. 8). This decrease was accompanied by a decrease in pro-inflammatory senescence-associated secretory phenotype cytokines again in endothelial cells and not in fibroblasts (Fig. 2i and Supplementary Fig. 8)16,18,19. Last, in neither cell type did telomere length, measured by quantitative fluorescence in situ hybridization2,20, show significant extension with treatment (Supplementary Fig. 8), suggesting that the cells did not dedifferentiate into a stem-like state in which telomerase activity would be reactivated, and in agreement with previous reports where activation of TERT was observed at later stages of nuclear reprogramming21.”

https://www.nature.com/articles/s41467-020-15174-3

 

[Jackb23]

“ Treatment showed a significant reduction in intracellular mRNA levels of RANKL and iNOS2, as well as in levels of inflammatory factors secreted by the cells (Fig. 3b–d). In addition, we observed increased cell proliferation (Fig. 3e), increased ATP production (Fig. 3f), and decreased oxidative stress as revealed by reduced mitochondrial ROS and elevated RNA levels of antioxidant SOD2 (Fig. 3g, h), a gene that has been shown to be downregulated in OA23. Finally, when we checked for retention of cellular identity, we observed that the treatment did not affect the expression level of SOX9 (a transcription factor core to chondrocyte identity and function) and significantly increased the level of expression of COL2A1 (the primary collagen in articular cartilage) (qRT-PCR in Fig 3i, j), suggesting retention of chrondrogenic cell identity. Together, these results show that transient expression of OSKMLN can promote a partial reversal of gene expression and cellular physiology in aged OA chondrocytes toward a healthier, more youthful state, suggesting a potential new therapeutic strategy to ameliorate the OA disease process.”