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      High-Resolution Ultrastructural Comparison of Renal Glomerular and Tubular Basement Membranes


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          Background/Aims: Glomerular basement membranes (GBM) and tubular basement membranes (TBM) consist of a fine meshwork composed mainly of type IV collagen. Each segment of tubules has specialized physiologic functions, and thus we investigated the ultrastructure of various basement membranes in rat kidneys. Methods: Since purifying basement membranes from different tubule segments is technically challenging, we employed tissue negative staining rather than conventional negative staining to compare the ultrastructures of proximal and distal TBM and GBM in normal rats. We also assessed the distribution of extracellular matrix components including type IV collagen, laminin, heparan sulfate proteoglycan, and fibronectin in the basement membranes by immunohistochemistry. Results: TBM and GBM of normal rats showed a fine meshwork structure consisting of fibrils forming small round to oval pores. Short- and long-pore diameters in proximal tubules were 3.3 ± 0.5 and 3.9 ± 0.6 nm, respectively, and in distal tubules 3.5 ± 0.7 and 4.3 ± 0.8 nm, respectively. For GBM the respective diameters were 2.5 ± 0.5 and 3.0 ± 0.5 nm. Immunohistochemical analysis showed no significant difference in distribution of extracellular matrix components between proximal and distal TBM. However, immunofluorescence scores of α1 chain of type IV collagen, fibronectin, and laminin were higher in the TBM than in the GBM. On the other hand, heparan sulfate proteoglycan was higher in the GBM. Conclusion: Ultrastructural differences in renal basement membranes may be related to differences in physiologic function in each segment.

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          Accumulation of N σ -(Carboxy-methyl)lysine and Changes inGlomerular Extracellular MatrixComponents in Otsuka Long-EvansTokushima Fatty Rat:A Model of Spontaneous NIDDM

          Increases in extracellular matrix (ECM) and changes in its components have been documented in the glomeruli of diabetic nephropathy. Advanced glycation end products formed by glycoxidation have been shown to induce the synthesis of ECM components and transforming growth factor beta (TGF-β), suggesting that advanced glycation end products may be involved in the etiology of imbalance of ECM components in diabetic glomerulosclerosis. The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is an inbred strain that spontaneously develops non-insulin-dependent diabetes mellitus which progresses to diabetic glomerulosclerosis. N Ε -(carboxymethyl)lysine (CML) is known to be formed by glycoxidation. To clarify the involvement of glycoxidation in diabetic nephropathy, we examined the localization of CML, ECM components, and TGF-β 1 in the glomeruli of OLETF rats. The amounts of α 3 (IV) collagen, type VI collagen, and fibronectin were significantly increased in the glomeruli of OLETF rats, whereas the heparan sulfate proteoglycan levels were decreased. After 6 months of age, CML levels were significantly increased in the mesangial area of the glomeruli in these animals. The overexpression of TGF-β 1 preceded the increase in glomerular ECM components. The present study demonstrated that the accumulation of CML precedes the changes of glomerular ECM components in the glomeruli during the course of diabetic nephropathy, suggesting that glycoxidation may be one of the major causes of diabetic glomerulosclerosis.

            Author and article information

            Am J Nephrol
            American Journal of Nephrology
            S. Karger AG
            December 1999
            26 November 1999
            : 19
            : 6
            : 686-693
            aDepartment of Medicine III and bCentral Research Laboratory, Okayama University Medical School, Okayama, Japan
            13543 Am J Nephrol 1999;19:686–693
            © 1999 S. Karger AG, Basel

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            Page count
            Figures: 5, References: 36, Pages: 8
            Self URI (application/pdf): https://www.karger.com/Article/Pdf/13543
            Self URI (text/html): https://www.karger.com/Article/FullText/13543
            Self URI (journal page): https://www.karger.com/SubjectArea/Nephrology
            Laboratory Investigation

            Cardiovascular Medicine,Nephrology
            Glomerular basement membrane,Tissue negative staining,Renal ultrastructure,Tubular basement membrane


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