High glucose and advanced glycosylated end-products affect the expression of alpha-actinin-4 in glomerular epithelial cells

To investigate the molecular basis for the phenotypic alterations of glomerular epithelial cells (GEpC, podocytes), involving cytoskeletal changes especially on alpha-actinin-4 as a candidate regulating the barrier to protein filtration and the podocyte actin cytoskeleton.

To examine the effects of glucose and advanced glycosylated end-products (AGE) on alpha-actinin-4, the author cultured rat GEpC on AGE- or BSA-coated plates under normal (5 mmol) and high glucose (30 mmol) conditions and examined the distribution of alpha-actinin by confocal microscope and measured the change in alpha-actinin-4 production by western blotting and reverse transcription-polymerase chain reaction.

Confocal microscopy indicated that alpha-actinin-4 moved from the peripheral cytoplasm to inner actin filament complexes in the presence of AGE and high glucose. These changes might be related to the fusion of microvilli of cell surface examined by electron microscopy. In western blot analysis, AGE significantly decreased the amount of alpha-actinin by 28.1%. Furthermore, the combination of high glucose and AGE decreased the amount of alpha-actinin more significantly by 53.6% compared with that of the control. The mRNA expression for alpha-actinin-4 was not changed with high glucose or AGE-coated surfaces; however, when added, the combination of high glucose and AGE significantly decreased the expression of alpha-actinin-4 mRNA by 15.7% compared with that of the control.

The author suggests that both high glucose and AGE (either individually or in combination) induce the cytoplasmic translocation and the combination suppresses the production of alpha-actinin-4 at the transcriptional level with post-translational modification and these in vitro changes may explain the cytoskeletal changes of GEpC in diabetic conditions.