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Background: Adipose tissue is uniquely suited for the study of the onset of normal human aging, a poorly understood, but highly critical biological process in human health and disease. Though adipose tissue and its resident adipose derived stem cells have garnered great interest for translational and regenerative therapies, such therapeutic benefits may be limited by molecular changes triggered by the onset of aging. The goal of is this study is twofold: first to demonstrate molecular modifications that occur at the onset of human adipose tissue aging, and further, to argue that some of these modifications may serve as critical biomarkers for the onset of aging.
Methods: Subcutaneous abdominal tissue was obtained from healthy patients undergoing elective abdominoplasty. Patient age ranged from 26 to 76 years old. Adipocytes (AD) and stromal vascular fractions (SVF) were isolated and analyzed for age-associated changes in a series of 30 molecular markers via qRT-PCR, Western Blot, Southern Blot, and immunoprecipitation analyses. Adipose-derived stem cells (ASC) were analyzed via immunofluorescence staining and standard differentiation protocols. Data were analyzed in three age categories: age greater than 50 versus less than 50, less than 40 versus greater than 40 or greater than 50 versus less than 40. Statistical data was analyzed via linear regression analysis.
Results: p16 and p21 demonstrated significant increases with aging in AD, while EEF1A1 showed significant decreases with aging in SVF. Immunoprecipitation experiments showed significant increases in H3K9ac and H3K18ac in SVF, and in H3K56ac in SVF and AD. Seven of the 30 marks investigated demonstrated statistically different changes with advancing age, suggesting that they may serve as biomarkers of adipose aging. As confirmation that the tissues investigated are undergoing the onset of aging, immunoflorescence staining demonstrated stronger SA-B-gal, p14ARF, and p16INK4a and weaker LMNB1 signal in ASCs from older patients, without senescence-associated heterochromatin foci (SAHFs) formation. Finally, as additional evidence that the fourth decade is critical in the onset of adipose tissue aging and more significantly, correlates with functional deficits, we demonstrated changes in the efficiency of adipocyte-derived stem cell differentiation into the adipocyte and osteocyte lineages in ASCs from patients above 40 years.
Conclusions: Significant age-dependent molecular changes can be detected in both AD and SVF starting in the fourth decade of life. We propose that the molecular marks with significant differences in older patients may serve as biomarkers of adipose tissue aging. Our data further suggest that changes in chromatin conformation and gene accessibility occur during the onset of human aging and that epigenetic changes specifically may serve as the most robust biomarkers. The confirmation of a set of parameters that could determine the "biological age" of adipose tissue could have a significant impact on the treatment and prevention of human aging, biobanking, and more specifically, on adipose tissue- and stem cell-based regenerative therapies that may be limited by molecular changes triggered by the onset of aging.