Metformin inhibits nuclear egress of chromatin fragments in senescence and aging

Abstract

Chronic inflammation is a hallmark of aging and contributes to many age-associated diseases. Metabolic intervention is a strategy to modulate inflammation. However, the connection between inflammation and metabolism during aging remains poorly understood. A mechanism driving chronic inflammation involves cytoplasmic chromatin fragments (CCFs), which appear in senescent cells and aged tissues, activating the cGAS-STING pathway. The size of the CCFs exceeds the capacity of the nuclear pore complex, raising the question of how chromatin fragments enter the cytoplasm. Here, we report that chromatin fragments exit the nucleus via nuclear egress, a membrane trafficking process at the nuclear envelope that shuttles large complexes from the nucleus to the cytoplasm. Inactivating critical nuclear egress ESCRT-III or Torsin proteins results in accumulation of chromatin fragments at the nuclear membrane, thereby impairing the activation of cGAS-STING and senescence-associated inflammation. Notably, nuclear egress of CCFs is inhibited by glucose limitation or metformin treatment. This is due to AMPK phosphorylation and autophagic degradation of the ESCRT-III component, ALIX. Metformin treatment in naturally aged mice downregulates ALIX protein and blocks cGAS activation and chronic inflammation in the small intestine. Together, our study defines a central mechanism linking nutrient sensing and chronic inflammation, two distinct hallmarks of aging, and suggests a new approach to suppress age-associated inflammation by targeting the nuclear egress of chromatin fragments.