Aging activates latent enhancers that can be reversed with exercise

Aging profoundly alters the genome's regulatory landscape, but the properties of age-acquired enhancers, including how they are selected and sustained in aged animals are unclear. We used single-cell multiomics in the mouse heart to identify age-responsive cis-regulatory elements and endurance exercise to understand which of these elements can be attenuated. Aging increased AP-1 engagement at more than 100,000 regulatory loci across cardiac cell types. Exercise opposed most of these gains. Despite low endogenous accessibility, age-gained enhancer sequences drove reporter activity comparable to stable elements, revealing substantial latent transcriptional potential. Local sequence features distinguished responsiveness to aging and exercise. Reporter perturbations implicated sequence outside the AP-1 core, and mutagenesis localized informative positions to dispersed segments of dynamic enhancers. These enhancers were IL-1-sensitive and were preferentially responsive to neutralization of the cytokine in vivo. AP-1 inhibition further opposed age-associated transcription. Together, these findings support a model in which aging engages latent cell-type specific enhancers that are sustained in an active state by ongoing trans signaling. Aging therefore changes the deployment of existing regulatory information, while the acquired activity remains responsive to changes in signaling even in old age.