P16INK4a Deletion Ameliorated Renal Tubulointerstitial Injury in a Stress-induced Premature Senescence Model of Bmi-1 Deficiency

To determine whether p16(INK4a) deletion ameliorated renal tubulointerstitial injury by inhibiting a senescence-associated secretory phenotype (SASP) in Bmi-1-deficient (Bmi-1(-/-)) mice, renal phenotypes were compared among 5-week-old Bmi-1 and p16(INK4a) double-knockout, and Bmi-1(-/-) and wild-type mice. Fifth-passage renal interstitial fibroblasts (RIFs) from the three groups were analyzed for senescence and proliferation. The effect of Bmi-1 deficiency on epithelial-to-mesenchymal transition (EMT) was examined in Bmi-1-knockdown human renal proximal tubular epithelial (HK2) cells, which were treated with concentrated conditioned medium (CM) from the fifth-passage renal interstitial fibroblasts (RIFs) of above three group mice or with exogenous TGF-beta 1. Our results demonstrated that p16(INK4a) deletion largely rescued renal aging phenotypes caused by Bmi-1 deficiency, including impaired renal structure and function, decreased proliferation, increased apoptosis, senescence and SASP, DNA damage, NF-kappa B and TGF-beta 1/Smad signal activation, inflammatory cell infiltration, and tubulointerstitial fibrosis and tubular atrophy. P16(INK4a) deletion also promoted proliferation, reduced senescence and SASP of RIFs and subsequently inhibited EMT of Bmi-1-knockdown HK2 cells. TGF-beta 1 further induced the EMT of Bmi-1-knockdown HK2 cells. Thus, p16(INK4)a positive senescent cells would be a therapeutic target for preventing renal tubulointerstitial injury.