Two-dimensional electrophoretic profiling of normal human kidney: differential protein expression in glomerulus, cortex and medulla

Abstract

The diverse functions of the kidney are fundamentally fulfilled by the nephron, the functional unit of the kidney. The nephron consists of several functionally and structurally different segments, which spans the kidney from the cortex through the medulla. The functional specialization along the nephron and specific localization of the different segments should be reflected in the protein expression profiles of distinct anatomical compartments of the kidney. We performed a two-dimensional gel electrophoresis (2-DE)-based, quantitative, proteomic analysis to identify proteins differentially expressed in the cortex, medulla, and glomeruli purified from cortex of normal human kidney. The protein extracts of the three compartments obtained from 4 normal subjects were separated on 2-DE gels, and analyzed by using a 2-DE gel image analysis software. We detected 1,810 valid protein spots in the glomerulus, 1,758 in the cortex, and 1,275 spots in the medulla. Statistical analysis by one-way ANOVA followed by Tukey's post-hoc test revealed that 616 protein spots were differentially expressed in the glomeruli, 582 in the cortex, and 469 in the medulla. Among these protein spots, spots expressing in considerably higher relative amounts in one of the three compartments were selected and subjected to identification by peptide mass fingerprinting method with a MALDI-TOF mass spectrometer, which led to identification 19 protein spots preferentially expressed in the glomerulus, 35 in the cortex, and 21 in the medulla. The distinct protein expression profiles in different kidney compartments may serve as a resource for further study of physiology and pathophysiology of the human kidney.