Aberrant expression and localization of the RAP1 shelterin protein contribute to age-related phenotypes

Abstract

Short telomeres induce a DNA damage response (DDR) that evokes apoptosis and senescence in human cells. An extant question is the contribution of telomere dysfunction-induced DDR to the phenotypes observed in aging and telomere biology disorders. One candidate is RAP1, a telomere-associated protein that also controls transcription at extratelomeric regions. To distinguish these roles, we generated a knockin mouse carrying a mutated Rap1, which was incapable of binding telomeres and did not result in eroded telomeres or a DDR. Primary Rap1 knockin embryonic fibroblasts showed decreased RAP1 expression and re-localization away from telomeres, with an increased cytosolic distribution akin to that observed in human fibroblasts undergoing telomere erosion. Rap1 knockin mice were viable, but exhibited transcriptomic alterations, proinflammatory cytokine/chemokine signaling, reduced lifespan, and decreased healthspan with increased body weight/fasting blood glucose levels, spontaneous tumor incidence, and behavioral deficits. Taken together, our data present mechanisms distinct from telomere-induced DDR that underlie age-related phenotypes. Author summary As we age, special structures at the ends of our chromosomes, known as telomeres, gradually get shorter. Critically short telomeres activate pathways that disrupt cell division and function or induce cell death. We sought to address the extent to which, as telomeres shorten, telomeric proteins might relocate to other regions of the cell and thus alter cellular function through a telomere-independent mechanism. We chose to focus on the telomere-associated protein, RAP1, since RAP1 is primarily a telomeric protein, but is also found in other regions of the cell where it affects gene expression. To determine the effects of RAP1 distal to telomeres, we generated a Rap1 mutant mouse model in which RAP1 does not localize at telomeres. Cells derived from this model showed decreased RAP1 expression and increased distribution of RAP1 in the cytosol, similar to that observed in human fibroblasts undergoing telomere attrition. Rap1 mutant mice exhibited changes in gene expression, inflammation, glucose metabolism, behavior, and decreased lifespan and healthspan. These findings support two important functional roles for RAP1, telomeric and extratelomeric, and suggests that both these respective functions may be integral to aging phenotypes.