The Impact of Rapamycin and Metformin on Genome Organization and Function in Normal Human Fibroblasts

Abstract

For decades, dietary restriction (DR) has been documented to extend health and lifespan across numerous model organisms. Two compounds, rapamycin (an immuno-suppressant) and metformin (a drug used to treat type II diabetes) have been proposed to mimic these health and lifespan benefits. Interestingly, DR, rapamycin and metformin result in the inhibition of the mammalian target of rapamycin (mTOR), a major nutrient sensing and signalling hub in the cell. The unexpected side-effect of this inhibition is the proposed extension in both health and lifespan in cell cultures and organisms. Despite the impact of inhibiting mTOR being well established at the biochemical level, the impact of mTOR inhibition on genome function (gene expression) and organization (organization of the genome in three-dimensional space) is poorly understood. Normal human fibroblasts were grown in culture and treated with either rapamycin or metformin for 120 h. It was established that with both treatments applied individually, population doubling times increased with no evidence of cell death; however, cellular morphology was divergent, with rapamycin-treated fibroblasts reminiscent of quiescence, whilst metformin-treated fibroblasts still exhibited the morphology of proliferating cells. Analysis of chromosome territory positioning revealed similar re-location of chromosomes 18 and 10 whilst RNA sequencing analyses demonstrated divergent transcript profiles. In particular, transcripts changing significantly in response to rapamycin treatment were enriched for the cytokine-cytokine receptor interaction pathway, whilst genes changing significantly in response to metformin were enriched in the AP-1 transcription factor pathway. Chromatin immuno-precipitation analyses revealed STAT5A/B as a potential mediator of rapamycin-mediated changes in gene expression. Together, these data demonstrated that although rapamycin and metformin are potential mimetics of DR, they elicit differential changes in gene expression and function through divergent mechanisms. Finally, these findings indicate that there are multiple targets for treatments which could result in increased health and lifespan in humans.