Proteomics-based identification of differentially-expressed proteins including galectin-1 in the blood plasma of type 2 diabetic patients.

Type 2 diabetes (T2D) is a very heterogeneous and multifactorial disease. The pathophysiology of T2D is presumed to occur with an alteration in the levels of plasma proteins. To identify these differentially expressed proteins, plasma samples from normal and T2D humans were subjected to two-dimensional gel electrophoresis, quantitative densitometry, and mass spectrometry. Up to 200 protein spots were visible on each gel, of which 57 appeared modulated in diabetic individuals. Subsequently, 31 spots with > or =2-fold change in their expression were analyzed by MALDI-TOF mass spectrometry leading to the identification of 11 proteins with average sequence coverage of approximately 38%. The expression of apolipoprotein A-I was reduced by 4.2-fold, and galectin-1 was increased 4.8 times in diabetic samples. Induction of galectin-1 in T2D samples was confirmed by ELISA. In addition, the dose-dependent treatment of rat L6 skeletal muscle cells with glucose resulted in an upregulation of galectin-1. These data implicate the association of galectin-1 with the pathophysiology of diabetes and identify galectin-1 as a novel diagnostic marker protein in T2D patients.