Exploring the mechanistic effects of life extending treatments on the mTOR network : a combined computational and experimental approach

Abstract

Nitrogen containing bisphosphonates (N-BPs) such as Zoledronate are currently used to treat osteoporosis and act by disrupting the actions of osteoclasts responsible for bone resorbption by inhibiting prenylation. There is a growing body of evidence that these drugs have broader benefits including a reduction of mortality in patients treated with Zoledronate that exceeds the expected benefits conferred from reduced fracture risk alone. Further observations support a role for Zoledronate in longevity. Levels of cellular damage were reduced in a Hutchinson-Gilford progeroid mice model treated with a combination of Zoledronate and Statins. Interestingly, recent evidence that treatment of Zoledronate extends the lifespan of MSCs via inhibition of the mTOR pathway similarly to calorie restriction. We apply an integrative systems modelling approach informed with data generated using Reverse Phase Protein Arrays to perform an in depth analysis of the response of the mTOR network to three life extending treatments. The hypothesis we test concerns the overlapping response we expect between Zoledronate and starvation-restimulation, whereas we would expect both MRC5 cells and MSC’s to respond differently to Rapamycin treatment. We show that a single model topology is capable of reproducing the data produced by RPPA for three separate life extending treatments in both MRC5 fibroblasts and MSCs. We identify that the activation of the AMPK-mTOR signalling axis is of primary importance in response to both nutrient deprivation and Zoledronate treatment. Furthermore we identify that the regulation of the mTOR network in response to these treatments occurs through two distinct mechanisms. In addition we demonstrate that in response to Rapamycin withdrawal it is the P70S6K negative feedback loop that is of primary importance with regards to mTOR regulation. This work demonstrates the power of an integrative modelling-experimental approach and suggests that life extending treatments act through distinct mechanisms affecting similar sections of the mTOR network.