Inhibition of annexin A7 suppresses senescence-associated heterochromatin foci formation and senescence through the AMPK/mTOR pathway in human dermal fibroblasts.

Senescence-associated heterochromatin foci (SAHF) is often used as a biological marker for senescent cells, but the regulation of its formation process is unclear. To find a new modulator of SAHF, we screened our chemical small molecules and found 7-amino-2,3,4,5-tetrahedrobenzo[b][1,4] oxazepin-3-ol (ABO) that was identified as an inhibitor of annexin A7 GTPase (ANXA7) dramatically suppressed the aggregation of heterochromatin protein (HP1γ), an indicator of SAHF. To understand its action mechanism, we first observed the changes in the karyoplasmic ratio of ANXA7 because HP1γ mainly located in the nucleus. The results showed that ABO elevated the protein level of ANXA7 in the nucleus. Therefore, we raised a hypothesis that ANXA7 interacted with HP1γ and regulated its phosphorylation, which is closely related to the formation of SAHF. The co-immunoprecipitation and Western blot experiment results showed that ANXA7 had no direct interaction with HP1γ, however, the phosphorylation of HP1γ was increased by ABO, which suggested that ANXA7 indirectly regulated HP1γ phosphorylation. Then, based on our previous discovery of ANXA7 interacting with AMP-activated protein kinase (AMPK), we investigated the effect of the AMPK/mammalian target of rapamycin (mTOR) signaling pathway on ABO-increased phosphorylation of HP1γ. We found that ABO decreased AMPK phosphorylation and increased the phosphorylation level and activity of mTOR. In the presence of an AMPK activator or mTOR inhibitor, ABO could not increase HP1γ phosphorylation. As a result, ABO inhibited the senescence of human dermal fibroblasts (HDFs). In this study, we found that ANXA7 was a new regulator of SAHF, it could regulate the formation of SAHF through the AMPK/mTOR pathway. The data suggested that ABO could be used as a powerful tool to inhibit the replicative senescence of HDFs.