Influence of injured podocytes on glomerular maturation in neonatal mice

Objective To study the effect of injured podocytes on glomerular maturation and its underlying mechanism in neonatal mice.Methods Single i.p.injection with puromycin aminonucleoside (PA,0.1 mg/g BW) was given to ICR neonatal mice at day 1 after birth (1 dpp). Littermates injected with normal saline (NS) were used as control.Animals were examined for urine protein,blood pressure,kidney weight/body weight (KW/BW),renal histology at 2,4,8,12, 30,60 and 90 dpp (n=6～9 for each group).Immunohistochemistry and quantitative RT-PCR were performed to examine the expression of WT-1,CD31,VEGF,Flk-1,Ang-1,Ang-2,Tie-1 and Tie-2.Results Mice with PA injection had lower kidney weight and body weight at all time points as well as lower KW/BW at 4,8,12 dpp when compared with NS controls.Electron microscopy revealed nearly complete foot process effacement and segmental microvillous transformation as early as 1 day after PA injection.PA-injected kidneys showed fewer capillary loops and decreased maturation index as well as less CD31-positive endothelium in cortical glomeruli at 12 dpp. Glomerular mesangial injury and developing glomerulosclerosis along with proteinuria were noted in PA-injected kidneys starting from 30 dpp.Significantly increased systolic blood pressure was detected at 60 dpp in PA mice.Compared with NS injection,PA injection significantly induced decreased mRNA expression of Flk-1 and Tie-2 as well as increased expression of Ang-1,without obvious changes of VEGF at 2 dpp.Conclusions Podocytes in neonatal kidney of ICR mice are susceptible to PA. Such podocyte injury can alter the expression of VEGF and angiopoietin system in glomeruli,leading to abnormal development of glomerular capillaries,and subsequent proteinuria,hypertension and glomerulosclerosis.