Minimal Change Disease Is Associated With Endothelial Glycocalyx Degradation and Endothelial Activation

Research background: unknown role of endothelial cells in MCD and glomerular filtration barrier

Minimal change disease (MCD) is the most common type of nephrotic syndrome in children but its overall pathogenesis has been poorly understood. Unlike some other types of kidney diseases, MCD doesn’t show infiltrating cells or immune complex cells in the glomeruli.

MCD has been thought of as a disorder related to podocytes, the specialized epithelial cells that cover the outer surfaces of glomerular capillaries in the kidney. It is currently believed that one or more substances circulating in the bloodstream might directly damage podocytes.

However, podocytes are not the only important components of the glomerular filtration barrier critical in preventing proteinuria. The glomerular endothelium, including its inner layer coated with glycocalyx, is also needed to maintain a proper barrier. In other conditions associated with proteinuria, investigators studied injury to the endothelium, but it has not previously been thoroughly investigated in MCD.

This study, led by pediatric nephrology researchers at Children’s Colorado, sought to test the hypothesis that MCD involves injury both to the glomerular endothelium and to endothelium in blood vessels throughout the body.

Research methods: analysis of endothelial biomarkers in human samples from people with MCD

Study participants:

• 45 children with nephrotic syndrome (at disease onset or relapse) and 30 pediatric controls
• 21 adults with MCD relapse and 8 adult controls

Blood samples were analyzed by ELISA and mass spectrometry for:

• Markers of endothelial glycocalyx damage
• Endothelial activation

Kidney biopsy specimens from 11 adults in relapse from MCD and five controls were evaluated for the presence of a protein used as an indicator of endothelial activation.

Investigators also used a previously existing line of human glomerular endothelial cells in cell culture. To these cells, researchers added serum samples from five children with active nephrotic syndrome and five pediatric controls. After incubation, western blot was performed to assess for endothelial activation.  

Research results: markers of endothelial degradation are elevated in MCD

Key findings from blood analyses:

• Syndecan-1, a component of the endothelial glycocalyx, was significantly higher in the blood of children with MCD with active disease compared to controls and to patients in remission, indicating endothelial glycocalyx damage.
• Heparan sulfate, the most common glycosaminoglycan in the glycocalyx, was significantly increased in the blood of children with active MCD compared to controls.
• MMP-2, an enzyme that breaks down the glycocalyx, was significantly increased in children with active MCD compared to controls, and levels remained somewhat higher than controls during remission.
• Both syndecan-1 and heparan sulfate were higher in adults having a relapse of MCD compared to controls.
• In children with MCD with active disease, thrombomodulin and von Willebrand factor were increased, and endothelial cells release in response to vascular injury.
• Children in remission with MCD had higher von Willebrand factor compared to healthy children.
• In adults with MCD in relapse, thrombomodulin was significantly higher than in controls.

Notable additional findings include:

• Patients with MCD in relapse had higher amounts of thrombomodulin and nitric oxide (another endothelial activation marker) in their glomeruli (as noted by gene expression).
• By immunofluorescence of kidney tissue from adults with MCD in relapse, caveolin-1, a marker of endothelial activation, was increased compared to controls.
• When cultured glomerular endothelial cells were exposed to serum from children with active MCD, it dramatically increased the amount of thrombomodulin they produced compared to controls.

Research discussion and conclusion: alterations to the systemic and kidney glomeruli endothelium play a role in MCD

• Markers consistent with injury to the glycocalyx coating the endothelium
• Suggests markers originated from the endothelial cells in blood vessels throughout the body
  • Findings previously associated with serious conditions such as sepsis and preeclampsia
• Some markers may persist elevated during remission in some patients (at lower levels than during relapse).

The study provides evidence that MCD is not simply a disorder of podocytes and demonstrated that MCD involves alterations to the endothelium, systemically and locally (glomerulus). Importantly, sera from patients with nephrotic syndrome directly activate glomerular endothelial cells.

This study suggests that glomerular endothelial cells may play an important role in the pathogenesis of childhood nephrotic syndrome and MCD.