ABSTRACT
Albuminuria in diabetic nephropathy is due to endothelial dysfunction, a loss of negative charges in the basement membrane, and changes a of the slit-membrane diaphragm composition. We have recently shown that protein kinase C alpha (PKCalpha)-deficient mice are protected against the development of albuminuria under diabetic conditions. We here tested the hypothesis that PKCalpha mediates the hyperglycemia-induced downregulation of the slit-diaphragm protein nephrin. After 8 weeks of streptozotocin (STZ)-induced hyperglycemia the expression of glomerular nephrin was significantly reduced. In contrast, other slit-diaphragm proteins such as podocin and CD2AP were unaltered in diabetic state. In PKCalpha-/- mice, hyperglycemia-induced downregulation of nephrin was prevented. Podocin and CD2AP remained unchanged. In addition, the nephrin messenger RNA expression was also reduced in hyperglycemic wild-type mice but remained unaltered in PKCalpha-/- mice. We postulate that the underlying mechanism of the hyperglycemia-induced regulation of various proteins of the glomerular filtration barrier is a PKCalpha-dependent regulation of the Wilms' Tumor Suppressor (WT1) which previously has been shown to act as a direct transcription factor on the nephrin promoter. Our data suggest that PKCalpha activation may be an important intracellular signaling pathway in the regulation of nephrin expression and glomerular albumin permeability in the diabetic state.
Subject(s)
Diabetic Nephropathies/metabolism , Membrane Proteins/metabolism , Protein Kinase C-alpha/genetics , Protein Kinase C-alpha/metabolism , Signal Transduction/physiology , Adaptor Proteins, Signal Transducing/genetics , Adaptor Proteins, Signal Transducing/metabolism , Albuminuria/etiology , Albuminuria/metabolism , Animals , Cytoskeletal Proteins/genetics , Cytoskeletal Proteins/metabolism , Diabetes Mellitus, Experimental/metabolism , Diabetes Mellitus, Experimental/physiopathology , Diabetic Nephropathies/physiopathology , Gene Expression Regulation/physiology , Humans , Hyperglycemia , Intracellular Signaling Peptides and Proteins/genetics , Intracellular Signaling Peptides and Proteins/metabolism , Kidney Glomerulus/metabolism , Male , Membrane Proteins/genetics , Mice , Mice, Knockout , RNA, Messenger/genetics , RNA, Messenger/metabolism , WT1 Proteins/genetics , WT1 Proteins/metabolismABSTRACT
When nephrin, the protein product of NPHS1, was cloned, it was proposed to be specific for the kidney glomerular podocytes. Recently, however, new reports have emerged verifying additional nephrin expression sites, particularly the insulin-producing beta cells of the pancreas, as well as the central nervous system. In this study, we demonstrate nephrin expression in lymphoid tissues, specifically the tonsil, adenoid and lymph node. Nephrin mRNA expression levels were 4-fold higher in tonsils and adenoids than in thymus or B lymphocytes, and 20-fold higher than in T lymphocytes or monocytes, as shown by quantitative RT-PCR analysis. Anti-nephrin antibodies recognised a specific 165-kDa band in lysates of tonsil and adenoid. In immunofluorescence and immunohistochemichal stainings of adenoid and lymph node sections, nephrin-positive cells were detected in the germinal centres of the lymphoid follicles in a staining pattern typical for interdigitating cells. These results indicate a definite and additional presence of nephrin in lymphoid tissue.
