Mechanism of cellular senescence in acute kidney injury that leads to chronic kidney disease in elderly mice

Abstract

Objective To investigate the mechanism of cellular senescence in ischemia reperfusion injury (IRI)-induced acute kidney injury (AKI) that leads to chronic kidney disease (CKD) in elderly mice. Methods An acute kidney injury model was established in C57Bl/6 male mice at ages 8-10 weeks (young group) or 20-24 months (old group) by bilateral IRI. The animals were randomly divided into 4 groups as follows: Young-Sham (n=8), Old-Sham (n=8), Young-IRI (n=8), and Old-IRI groups (n=8). All mice were weighted, and their blood was collected from the tail vein at days 1, 3, and 7 after surgery. The mice were killed on day 14 after surgery, and their kidneys were harvested for further analysis. Serum was used for the creatinine test. The changes of the renal tissue morphology and pathology were assessed using hematoxylin-eosin staining and sirius red staining. Immunofluorescence staining of collagen Ⅰ, F4/80, phosphor-histone H3 (p-HH3), and Ki67 were performed to determine the stage of the collagen deposit, macrophage filtration, and cell cycle G2/M arrest. The collagen Ⅰ expression was analyzed using western blot. The expression levels of TNF-α, IL-6, TGF-β, and collagenⅠ were determined using real-time PCR. Results Compared with that in the sham group, the serum creatinine levels in both Young-IRI and Old-IRI groups were obviously increased. The Young-IRI group recovered completely on day 7. The Old-IRI group had higher creatinine levels than the Young-IRI group at each time point. Morphology and pathology analyses revealed that acute injury was repaired in the Young-IRI group, but slight inflammatory cell filtration and collagen deposition were observed in the Old-Sham and Old-IRI groups, respectively. Immunofluorescence staining revealed some F4/80-positive macrophage filtration, collagenⅠdeposition, and p-HH3 and Ki67 double-positive nuclear tubular epithelial cells in the Old-Sham group, but considerably more positive results were found in the Old-IRI group. Western blot analysis revealed that collagenⅠ expression level was higher in the Old-IRI group than in the Young-IRI group (P<0.01) and in the Old-Sham group than in the Young-Sham group (P<0.05). Real-time PCR demonstrated that the mRNA expression levels of cytokines and fibrosis markers, including of TNF-α, IL-6, TGF-β, and collagenⅠ, in the Old-Sham and Old-IRI groups were increased as compared with those in the Young-Sham and Young-IRI groups (P<0.05). Conclusions The levels of kidney inflammation, fibrosis, and cell-cycle arrest are lower in the old mice. After IRI injury, a sustained and ongoing inflammatory reaction is involved and more cells are arrested in the cell cycle G2/M, which inhibit renal repair and promote fibrosis progression. Key words: Reperfusion injury; Cell aging; Inflammation; Cell cycle arrest; Chronic kidney disease