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.