Rapamycin increases lifespan only in female flies. We found higher baseline autophagy in the gut in males, and showed that gut cell sexual identity dictates basal autophagy, gut health and lifespan and their responses to rapamycin. Rapamycin treatment increased histone protein levels in gut, and this altered expression of specific autophagy genes. Remarkably, brief rapamycin treatment induced long-term elevated autophagy in gut, which increased gut health and extended lifespan. Because lithium did not extend lifespan in mice (Aim 2), we discontinued work with it. We instead showed that rigosertib extends fly lifespan. Trametinib reduced gut dysplasia in aged flies, and also markedly reduced inflammation during ageing. However, reduced inflammation seems not to be causal for increased lifespan, and we are continuing work on the exact mechanisms at work.
We found remarkably persistent effects of earlier treatment with rapamycin on gut health in middle-aged mice. We have discovered that lifespan is also extended by earlier treatment, as much as a year after the drug has been withdrawn. Intermittent treatment with the drug also extends lifespan, although less than chronic treatment, but with fewer side-effects. Trametinib extended lifespan in both female and male mice, with the health and pathology data currently under analysis. The effects of RAS pathway activity on ageing are thus conserved in mice. Although it extended fly lifespan, rigosertib did not extend mouse lifespan at the dose tested.
This part was carried out in collaboration with Prof. Eline Slagboom (Leiden University Medical Center), and was the highest risk part of the project. The Leiden team identified protein altering variants in genes from the Ras Mek Erk pathway in long lived subjects from the LLS and their long-lived siblings, after whole-genome sequencing and stringent filtering and validation by Sanger sequencing. We generated cell lines harboring these variants and assessed resulting functional changes. A cell line harboring a variant in Nf1 shows significantly decreased p-Erk/Erk ratio, decreased protein and gene expression levels of Nf1 and decreased ER stress resistance in response to tunicamycin. A variant in Raf1 showed the opposite, i.e. a significantly increased p-Erk/Erk ratio, with increased protein and gene expression levels of Raf1 and increased ER stress resistance in response to tunicamycin. We are following up these findings in transgenic flies and mice.
