Transcriptional and Cell Cycle Alterations Distinguish Aging of Primary Human Adipose-Derived Stem Cells from Fibroblasts
Xiaoyin Shan, Ph.D., Cleresia Roberts, BS, Eunji Kim, BS, Ariana Brenner, BS, Greg Grant, Ph.D., Ivona Percec, MD, Ph.D.
University Of Pennsylvania School of Medicine, Philadelphia, PA, USA.
PURPOSE: Adult stem cells play a critical role in the maintenance of health and the prevention of aging. The regenerative therapeutic potential of stem cells with low cellular turnover, such as adipose-derived stem cells (ASC), is increasingly recognized. Yet, technical limitations have limited the study of aging in slowly replicating primary human stem cells, and thus the mechanism remains poorly understood. Here, we employ ASCs as a model system to elucidate mechanisms of aging.
METHODS: Subcutaneous abdominal tissue was obtained from healthy patients of various ages (25-74) undergoing abdominoplasty. ASCs were isolated via standard collagenase protocols. Dermal fibroblasts were isolated from human skin specimens obtained from healthy patients of various ages (25-64). Transcriptional and chromatin accessibility profiles were examined using RNA-seq technology. ASCs and fibroblasts were isolated from healthy individuals of various ages (25-74) undergoing abdominoplasty. Nascent protein synthesis and protein post-translational modification were examined using op-puromycin incorporation and Western blot. Cell cycle progression of ASCs and fibroblasts were analyzed using flow cytometry.
RESULTS: RNA-seq analysis indicated that aging ASCs displayed more stable transcriptome than age-matched fibroblasts. However, limited transcriptional modifications were observed in aging ASCs, revealing more active cell cycle and translation initiation related gene transcription compared to aging fibroblasts. Accordingly, we also detected increased nascent protein synthesis in aging ASCs, concurrent with decreased inhibitory phosphorylation at ser-51 of eIF2-alfa. Older ASCs, but not fibroblasts, further demonstrate a shortened G1 phase, in accordance with the increased protein synthesis.
CONCLUSIONS: In the fifth decade of life, ASCs begin to demonstrate subtle age-dependent functional and molecular changes. We demonstrate that despite aging, primary human ASCs are able to maintain stable transcription network globally. However, in limited pathways, we discovered altered gene expressions. Specifically, genes involved in cell cycle regulation and translation initiation were up-regulated in aging ASCs but not in fibroblasts. Accordingly, we also detected a shortened G1 phase in cell cycle and an increase in nascent protein synthesis in ASCs from older patients. The shortened G1 phase may reflect an organismal attempt to meet the increased demands of tissue and organ preservation during aging. Furthermore, our data reveals a critical role for cell cycle control in early human stem cell aging and offers insights for developing novel therapeutic avenues for the prevention and treatment of aging-related diseases.
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