Original Research: Potential of urinary nephrin as a biomarker reflecting podocyte dysfunction in various kidney disease models.

Urinary nephrin is a potential non-invasive biomarker of disease. To date, however, most studies of urinary nephrin have been conducted in animal models of diabetic nephropathy, and correlations between urinary nephrin-to-creatinine ratio and other parameters have yet to be evaluated in animal models or patients of kidney disease with podocyte dysfunction. We hypothesized that urinary nephrin-to-creatinine ratio can be up-regulated and is negatively correlated with renal nephrin mRNA levels in animal models of kidney disease, and that increased urinary nephrin-to-creatinine ratio levels are attenuated following administration of glucocorticoids. In the present study, renal nephrin mRNA, urinary nephrin-to-creatinine ratio, urinary protein-to-creatinine ratio, and creatinine clearance ratio were measured in animal models of adriamycin nephropathy, puromycin aminonucleoside nephropathy, anti-glomerular basement membrane glomerulonephritis, and 5/6 nephrectomy. The effects of prednisolone on urinary nephrin-to-creatinine ratio and other parameters in puromycin aminonucleoside (single injection) nephropathy rats were also investigated. In all models tested, urinary nephrin-to-creatinine ratio and urinary protein-to-creatinine ratio increased, while renal nephrin mRNA and creatinine clearance ratio decreased. Urinary nephrin-to-creatinine ratio exhibited a significant negative correlation with renal nephrin mRNA in almost all models, as well as a significant positive correlation with urinary protein-to-creatinine ratio and a significant negative correlation with creatinine clearance ratio. Urinary protein-to-creatinine ratio exhibited a significant negative correlation with renal nephrin mRNA. Following the administration of prednisolone to puromycin aminonucleoside (single injection) nephropathy rats, urinary nephrin-to-creatinine ratio was significantly suppressed and exhibited a significant positive correlation with urinary protein-to-creatinine ratio. In addition, the decrease in number of glomerular Wilms tumor antigen-1-positive cells was attenuated, and urinary nephrin-to-creatinine ratio exhibited a significant negative correlation in these cells. In conclusion, these results suggest that urinary nephrin-to-creatinine ratio level is a useful and reliable biomarker for predicting the amelioration of podocyte dysfunction by candidate drugs in various kidney disease models with podocyte dysfunction. This suggestion will also be validated in a clinical setting in future studies.

Damaged DNA-binding protein 2 accelerates UV-damaged DNA repair in human corneal endothelium.

PURPOSE: To determine damaged DNA-binding protein 2-gene expression levels in vitro and ex vivo, and the degree of DNA repair in damaged DNA-binding protein 2-overexpressing cultured human corneal endothelium after ultraviolet irradiation. METHODS: Constitutive damaged DNA-binding protein 2-gene expression levels in various human tissues were determined by semi-quantitative reverse transcription-polymerase chain reactions. The dynamics of nucleotide excision repair-related gene expression in cultured human corneal endothelium were investigated in a ribonuclease protection assay after ultraviolet-irradiation. The effect of damaged DNA-binding protein 2 on DNA repair was studied after ultraviolet-irradiation in cultured human corneal endothelium infected with adenovirus carrying damaged DNA-binding protein 2. RESULTS: Human corneal endothelium and epithelium in the donor cornea had the highest constitutive damaged DNA-binding protein 2-gene expression of the various human tissues studied. Gene expression level dynamics associated with nucleotide excision repair factors after ultraviolet-irradiation showed that the increase in the rate of damaged DNA-binding protein 2-gene expression in cultured human corneal endothelium was highest of the nucleotide excision repair-related genes studied. An in vivo DNA repair assay showed that DNA repair efficiency in damaged DNA-binding protein 2-overexpressing cultured human corneal endothelium after ultraviolet-irradiation was significantly improved as compared with that in the control human corneal endothelium. CONCLUSION: The human corneal endothelium abundantly expresses the damaged DNA-binding protein 2-gene that is produced efficiently on ultraviolet exposure. This overexpressed damaged DNA-binding protein 2 in the human corneal endothelium contributes to the protection system against DNA damage after ultraviolet-irradiation. Our findings show a critical role for damaged DNA-binding protein 2 in DNA repair to maintain the human corneal endothelium function.