Advanced glycation end products inhibit Na(+) K(+) ATPase in proximal tubule epithelial cells: Role of cytosolic phospholipase A(2)alpha and phosphatidylinositol 4-phosphate 5-kinase gamma.

摘要

Chronic hyperglycaemia during diabetes leads to non-enzymatic glycation of proteins to form advanced glycation end products (AGEs) that contribute to nephropathy. In diabetes, renal Na(+) K(+) ATPase (NKA) activity is downregulated and phosphoinositide metabolism is upregulated. We examined the effects of AGEs on NKA activity in porcine LLC-PK1 and human HK2 proximal tubule epithelial cells. AGE-BSA increased cellular phosphoinositol 4,5 bisphosphate (PIP2) production as determined by immunofluorescence microscopy and thin layer chromatography. AGE-BSA (40muM) induced (3)H-arachidonic acid release and reactive oxygen species (ROS) production via cytosolic phospholipase A(2)(cPLA(2)) activation. Within minutes, AGE-BSA significantly inhibited NKA surface expression and activity in a dose- and time-dependent manner as determined by immunofluorescence staining and [(86)Rb(+)] uptake, respectively, suggesting AGEs inhibit NKA by stimulating its endocytosis. The AGE-BSA-induced decrease in cell surface NKA was reversed by a cPLA(2)alpha inhibitor, neomycin, a PIP2 inhibitor, and PP2, a Src inhibitor. AGE-BSA increased binding of NKA to the alpha-adaptin but not beta2- or mu2-adaptin subunits of the AP-2 clathrin pit adaptor complex. Transfection of HK2 cells with PIP5Kgamma siRNA prevented AGE-BSA inhibition of NKA activity. AGEs may stimulate PIP5Kgamma to increase PIP2 production, which may enhance AP-2 localisation to clathrin pits, increase clathrin pit formation, enhance NKA cargo recognition by AP-2 and/or stimulate cPLA(2)alpha activity. These results suggest AGEs modulate arachidonic acid and phosphoinositide metabolism to inhibit NKA via clathrin-mediated endocytosis. Elucidation of new intracellular AGE signaling pathways may lead to improved therapies for diabetic nephropathy.