Earlier renal fibrosis aggravates acute kidney injury induced by ischemia reperfusion in mice

Objective To investigate the influence of earlier renal fibrosis on ischemia and reperfusion induced acute kidney injury. Methods Male C57BL/6 mice at eight to twelve weeks old age were divided into 4 groups randomly: (1)Sham (n=3); (2)Unilateral ureter obstruction (UUO, n=6): UUO for 3 days (UUO3d, n=3) and UUO for 5 days (UUO5d, n=3); (3)Ischemia and reperfusion (IR, n=7): bilateral kidney ischemia for 40 minutes followed by 24 hours of reperfusion; (4)UUO for 3 days plus IR (UUO3d+IR, n=6): bilateral kidney ischemia after UUO 2 days for 40 minutes followed by 24 hours of reperfusion, and the real time for UUO was 3 days. Pathologic analysis for acute or chronic injury was performed on paraffin embedded kidney sections with hematoxylin and eosin (HE) or Masson staining. Apoptosis was detected by immunohistochemistry(IHC) and Western blotting with anti-caspase-3 antibody, and proliferation was observed by IHC with anti-ki67 antibody. Results On kidney sections with HE or Masson staining, it showed that the chronic kidney lesions and fibrosis got more severe as time of UUO prolonged from 3 days to 5 days; the area of matrix deposition increased in UUO5d and UUO3d mice significantly compared to Sham mice (P<0.05) and was smaller in UUO3d mice compared with UUO5d mice obviously (P<0.05). Acute kidney injury could be observed in UUO3d+IR mice, such as massive inflammatory cells infiltration, tubules dilation, brush border disappearance, tubular epithelial cells vacuolar degeneration, necrosis, casting formation, coexisting with chronic lesions: thinner cortex, broadened interstitial space, and increased blue stained matrix. Acute kidney injury score in UUO3d+IR mice was higher than that in IR mice significantly (P<0.05), and serum creatinine level increased significantly in UUO3d+IR mice compared to Sham mice (P<0.05). Caspase-3 expression increased and ki67 positive tubular cells decreased in UUO3d+IR mice than those in IR mice obviously (P<0.05). Conclusion Earlier renal fibrosis aggravates acute kidney injury induced by ischemia reperfusion in mice through increasing apoptosis and decreasing proliferation of tubular epithelial cells. Key words: Fibrosis; Kidney tubular necrosis, acute; Reperfusion injury; Ureteral obstruction