Effects of High Glucose and Advanced Glycosylation Endproducts (AGE) on the alpha-actinin-4 Expressed by Glomerular Epithelial Cells (GEpC)

Ha, Tae Sun

Abstract

BACKGROUND
Regardless of the underlying diagnosis, the proteinuric condition demonstrates ultrastructural changes in GEpC with retraction and effacement of the highly specialized interdigitating podocyte foot processes. I examined the molecular basis for this alteration of the podocyte phenotype, involving cytoskeletal changes especially on alpha-actinin-4 as a candidate regulating the modulation of pathogenic changes in the barrier to protein filtration and regulation of the podocyte actin cytoskeleton. METHODS: To investigate whether high glucose and AGE induce podocyte cytoskeletal changes, we cultured rat GEpC under normal (5 mM) or high glucose (30 mM) and AGE- or BSA-added conditions and examined the distribution of alpha-actinin-4 by confocal microscope and measured the change of alpha-actinin-4 production by Western blotting and RT-PCR. RESULTS: I found that alpha-actinin-4 moved from peripheral cytoplasm to inner actin filaments complexes in the condition of AGE and high glucose by confocal microscopy. In Western blotting, administration of high glucose or AGE decreased the alpha-actinin-4 productions by 22.3% (p>0.05) and 28.1% (p<0.05), respectively. Furthermore, both high glucose and AGE decreased the amount of alpha-actinin-4 more significantly by 53.6% compared to those of control (p<0.01). S uch changes could not be seen by osmotic control. The expression of mRNA for alpha- actinin-4 were not changed in condition of high glucose or AGE-coated surface, however, both high glucose and AGE significantly decreased the expression of alpha-actinin-4 mRNA by 15.7% compared to those of control. CONCLUSION: I could suggest that both high glucose and AGE induce the cytoplasmic translocation and suppress the production of alpha-actinin-4 at transcriptional level and these changes may explain the cytoskeletal changes of GEpC in diabetic conditions.