Proteomic Identification and Immunolocalization of Increased Renal Calbindin-D28k Expression in OVE26 Diabetic Mice

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Abstract
Diabetic nephropathy is a common diabetic complication that is associated with alterations in the expression of several renal proteins and abnormal calcium homeostasis. We performed proteomic analysis to screen for global changes of renal protein expression in diabetic kidney. Proteins extracted from the whole kidney of 120-day-old OVE26 (a transgenic model of Type 1 diabetes) and FVB (non-diabetic background strain) mice were separated by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) and visualized by SYPRO Ruby staining (n = 5 in each group). Quantitative intensity analysis revealed 41 differentially expressed proteins, of which 30 were identified by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) followed by peptide mass fingerprinting. One of the altered proteins with the greatest magnitude of change was the calcium-binding protein, calbindin-D28k, whose expression was increased 6.7-fold in diabetic kidney. We confirmed the increase in calbindin-D28k expression in diabetic kidney by Western blot analysis. Immunohistochemical study demonstrated that calbindin-D28k expression was markedly increased in tubular epithelial cells of distal convoluted tubules (DCT), collecting ducts (CD), and proximal convoluted tubules (PCT) in diabetic kidney. Calbindin-D28k plays a critical role in maintaining calcium homeostasis. The elevation in renal calbindin-D28k expression in our model may indicate a compensatory mechanism to overcome hypercalciuria in diabetes.