5-Azacytidine Protects Against Kidney Aging by Inhibiting FHL2 Expression

Background: DNA methylation levels of several genes are reported to be associated with physiological age in humans, which can serve as predictors of aging. Four-and-a-half LIM domains protein 2 (FHL2) is one of the top predictive genes of aging. However, the potential role and mechanism of FHL2 in renal aging remains to be elucidated. Methods: Three mouse models of renal aging were used: natural aging, D-galactose (D-gal) induced-accelerated aging, and streptozotocin-induced diabetic kidney disease (DKD). Cellular senescence of cultured primary renal tubular epithelial cells (TECs) from mice was induced by D-gal or high glucose (HG). 5-azacytidine (5-Aza) was used to inhibit DNA methylation. Results: Reduced Representation Bisulfite Sequencing analysis revealed that FHL2 gene body contains a differentially methylated region with seven CpG sites, and the methylation level in the kidney of 24-month-old mice was markedly higher than that of 2-month-old mice. The expression of FHL2 mRNA and protein was induced in a time-dependent manner during renal aging both in vivo and in vitro. The upregulation of FHL2 expression and cellular senescence induced by D-gal was substantially inhibited by 5-Aza. In DKD mice, insulin alone was not sufficient to suppress the increase in FHL2 expression and cellular senescence, while 5-Aza or 5-Aza combined with insulin had a significant inhibitory effect on it. In cultured TECs, after 24 hours of stimulation with HG, the upregulation of FHL2 expression and cellular senescence was not restrained by switching to normal glucose for 24 hours. However, the addition of 5-Aza when HG was replaced with normal glucose for 24 hours notably impeded FHL2 induction and cellular senescence. Conversely, overexpression of FHL2 in TECs counteracted the anti-aging effect of 5-Aza both in vivo and in vitro. Conclusion: These results indicate that the increased expression of FHL2 in renal aging relates to hypermethylation of CpG sites located within FHL2 gene body region. 5-Aza ameliorates cellular senescence in TECs by inhibiting FHL2 methylation level and the subsequent upregulation of FHL2 expression, which contributes to impeding renal aging. 5-Aza may also be beneficial for improving HG-induced metabolic memory. Funding: Government Support – Non-U.S.