Feedback loops between DNMT1 and autophagy as well as senescence promotes organ aging and canities

Alternations of DNA methylation occur in aging, which is regulated by DNA methyltransferases (DNMTs). In this study, we show that even though the transcription of DNMT1, the only enzyme that maintains DNA methylation in the mammalian genome, is reported to be decreased in an age-dependent manner, the decrease of Dnmt1 mRNA does not result in a decrease of its protein. Instead, DNMT1 protein is increased in aged mouse tissues, which is responsible for the methylation of genes related to macroautophagy/autophagy, senescence repression, and melanin synthesis and transport in aged organs, resulting in a decline of autophagy, an increase of senescence in those organs, and a decrease in melanin production in hair follicles (canities) in response to ionizing radiation (IR). Genetic deletion and inhibition of DNMT1 can reverse these processes. The interaction of DNMT1 with ATG7 through its CXXC domain is essential for its degradation, and treatment with senolytics also downregulates DNMT1 in aged organs, supporting two feedback loops between them.Abbreviations: 4-OHT, 4-hydroxytamoxifen; ChIP, chromatinimmunoprecipitation; D, dasatinib; D-gal, D-galactose; DCT/Trp-2, dopachrometautomerase; DMRs, differentially methylated regions; DNAm, DNA methylation; DNMTs,DNA methyltransferases; DSBs, double-stranded breaks; ETO, etoposide; GST, glutathione-S-transferase; HEK293T,human embryonic kidney 293T; HEM, human epidermal melanocytes; Hydr, hydralazine;IP, immunoprecipitation; IR,  ionizingradiation; KIF1A, kinesin family member 1A; M, methylated; MmIMCD3,mouse inner-medullary collecting duct 3; MITF, melanocyte inducingtranscription factor; MSP, methylation specific PCR; NCBI, national center for biotechnologyinformation; N-me, N-methyladenosine; PBMCs, peripheral blood mononuclear cells;Pro, proliferating; Q, quercetin; Rapa, rapamycin; RRBS, reduced representationbisulfite sequencing; RT, reverse transcription; SA-GLB1/β-Gal, senescence-associatedgalactosidase beta 1; SASP, senescence-associated secretory phenotype; Sen, senescent; SNP, single nucleotidepolymorphism; TYR, tyrosinase; TYRP1/Trp-1, tyrosinase related protein 1; UHRF1,ubiquitin like with PHD and ring finger domains 1; UM, unmethylated; UTR, untranslatedregion; WGBS, whole-genome bisulfite sequencing.