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Ultrastructural alterations in the sialic acid distribution in minimal change disease and membranous
Abstract:
Kidney biopsy specimens from patients with minimal change disease and membranous glomerulonephritis were embedded in glycolmethacrylate and stained with phosphotungstic acid (PTA) at low pH. Biopsy specimens from patients without proteinuria served as a control. The PTA staining at low pH on glycolmethacrylate sections was used to study the changes in the sialic acid content of the lamina rara externa of the glomerular basement membrane. This method also gives a clear picture of the changes occurring at the epithelial cell coat and these alterations have implications on the distribution of the negative charges. In minimal change disease no alterations could be observed in the sialic acid content of the lamina rara externa. But the luminal epithelial cell coat showed obvious changes in conjunction with extensive foot process widening. In membranous glomerulonephritis with heavy deposits the staining of the lamina rara externa became almost completely negative and the foot process architecture was strongly affected. Obvious defects at the luminal epithelial cell coat, as observed in minimal change disease, were also found regularly. The alterations at the epithelial cell coat are tentatively related to the selective proteinuria reported in minimal change disease. In addition the non-selective proteinuria observed in non-minimal glomerulopathies, may find its origin in the absence of sialic acid molecules from the lamina rara externa.
Insights
Phosphotungstic acid staining revealed altered sialic acid in kidney disease. Minimal change disease showed epithelial cell coat changes, while membranous glomerulonephritis exhibited significant lamina rara externa alterations, impacting proteinuria.
Area of Science:
- Nephrology
- Biochemistry
- Pathology
Background:
- Proteinuria is a key indicator of kidney disease.
- Sialic acid in the glomerular basement membrane plays a role in kidney function.
- Understanding charge distribution is crucial for diagnosing kidney pathologies.
Purpose of the Study:
- To investigate alterations in sialic acid content within the glomerular basement membrane.
- To correlate these changes with proteinuria in minimal change disease and membranous glomerulonephritis.
- To examine the impact on the epithelial cell coat and negative charge distribution.
Main Methods:
- Kidney biopsy specimens from patients with minimal change disease, membranous glomerulonephritis, and controls were used.
- Specimens were embedded in glycolmethacrylate and stained with phosphotungstic acid (PTA) at low pH.
- PTA staining assessed sialic acid content in the lamina rara externa and epithelial cell coat.
Main Results:
- Minimal change disease showed no change in lamina rara externa sialic acid but significant epithelial cell coat alterations and foot process widening.
- Membranous glomerulonephritis displayed a near-complete loss of lamina rara externa staining and severe foot process damage.
- Defects in the epithelial cell coat were consistently observed in both disease groups.
Conclusions:
- Epithelial cell coat alterations in minimal change disease may explain selective proteinuria.
- Loss of sialic acid from the lamina rara externa in membranous glomerulonephritis could contribute to non-selective proteinuria.
- PTA staining at low pH is a valuable method for assessing sialic acid distribution in glomerular diseases.