A) Epigenetic state of the chromosomes (e.g.， DNA methylation and histone acetylation) and microRNAs (miRNA) DNA methylation correlates with age.
B ) Histone acetylation is regulated by many enzymes including SIRT 1， a protein that has marked effects on aging and the response to dietary restriction.
C) miRNAs are a very large group of noncoding lengths of RNA (18-25 nucleotides) that inhibit translation of multiple different mRNAs through binding their 3’ untranslated regions (UTRs).
The expression of miRNAs usually decreases with aging and is altered in some age-related diseases.
■ Specific miRNAs linked with aging pathways include miR-21 (associated with target of rapamycin pathway) and miR-1 (associated with insulin/insulin-like growth factor 1 pathway).