Increased SHP-1 protein expression by high glucose levels reduces nephrin phosphorylation in podocytes.
Nephrin, a critical podocyte membrane component that is reduced in diabetic nephropathy, has been shown to activate phosphotyrosine signaling pathways in human podocytes. Nephrin signaling is important to reduce cell death induced by apoptotic stimuli. We have shown previously that high glucose level exposure and diabetes increased the expression of SHP-1, causing podocyte apoptosis. SHP-1 possesses two Src homology 2 domains that serve as docking elements to dephosphorylate tyrosine residues of target proteins. However, it remains unknown whether SHP-1 interacts with nephrin and whether its elevated expression affects the nephrin phosphorylation state in diabetes. Here we show that human podocytes exposed to high glucose levels exhibited elevated expression of SHP-1, which was associated with nephrin. Coexpression of nephrin-CD16 and SHP-1 reduced nephrin tyrosine phosphorylation in transfected human embryonic kidney 293 cells. A single tyrosine-to-phenylalanine mutation revealed that rat nephrin Tyr(1127) and Tyr(1152) are required to allow SHP-1 interaction with nephrin. Overexpression of dominant negative SHP-1 in human podocytes prevented high glucose-induced reduction of nephrin phosphorylation. In vivo, immunoblot analysis demonstrated that nephrin expression and phosphorylation were decreased in glomeruli of type 1 diabetic Akita mice (Ins2(+/C96Y)) compared with control littermate mice (Ins2(+/+)), and this was associated with elevated SHP-1 and cleaved caspase-3 expression. Furthermore, immunofluorescence analysis indicated increased colocalization of SHP-1 with nephrin in diabetic mice compared with control littermates. In conclusion, our results demonstrate that high glucose exposure increases SHP-1 interaction with nephrin, causing decreased nephrin phosphorylation, which may, in turn, contribute to diabetic nephropathy.
['Denhez|Benoit|B|', 'Lizotte|Farah|F|', 'Guimond|Marie-Odile|MO|', 'Jones|Nina|N|', 'Takano|Tomoko|T|', 'Geraldes|Pedro|P|']
D000818:Animals D053148:Caspase 3 D002460:Cell Line D003922:Diabetes Mellitus, Type 1 D003928:Diabetic Nephropathies D004195:Disease Models, Animal D058851:GPI-Linked Proteins D005786:Gene Expression Regulation D005947:Glucose D057809:HEK293 Cells D006801:Humans D007328:Insulin D007678:Kidney Glomerulus D008565:Membrane Proteins D051379:Mice D008822:Mice, Transgenic D010766:Phosphorylation D019000:Phosphotyrosine D050199:Podocytes D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6 D051381:Rats D017452:Receptors, IgG D015398:Signal Transduction
Nephrin Podocyte Diabetes Phosphotyrosine Nephrology Protein-Tyrosine Phosphatase (Tyrosine Phosphatase) Src Homology 2 domain (SH2 domain)