We studied 28 patients who required kidney biopsy for acquired proteinuric diseases (diabetic glomerulosclerosis, 9 cases; IgA nephropathy, 10 cases; minimal change disease, 5 cases; membranous nephropathy, 5 cases). We also studied 10 cases of diabetic microalbuminuria and 9 healthy controls. The mRNA expressions of nephrin (NephRNA), podocin (PodRNA) and synaptopodin (SynRNA) in urinary sediment were measured by real time quantitative PCR. After recruitment, all patients were followed for at least 12 months.
There were significant differences in the NephRNA and PodRNA in the urinary sediment between diagnosis groups (p < 0.005). On the other hand, SynRNA was only marginally significant between diagnosis groups (p < 0.05). Although statistically significant, the degree of proteinuria had only modest correlations with the urinary expression of nephrin. After a median follow up for 23 months, there was a significant correlation between the rate of decline in renal function and NephRNA (r = 0.559, p = 0.001) and PodRNA (r = 0.530, p = 0.002), but not SynRNA (r = 0.054, p = NS). The correlation remained statistically significant after multivariate analysis to adjust for the degree of proteinuria and initial renal function.
Urinary mRNA expression of podocyte markers, such as nephrin and podocin, are significantly different between proteinuric disease categories. Further, NephRNA and PodRNA correlated with the rate of decline in renal function. Our results suggest that urinary podocyte gene expression may be a useful non-invasive tool which provides additional information for the management of proteinuric diseases.