Cationized ferritin binding to anionic surfaces in normal and aminonucleoside nephrotic kidneys

Area of Science:

• Nephrology
• Cell Biology
• Biochemistry

Background:

• The kidney glomerulus filtration barrier involves complex interactions between anionic sites on cell surfaces and circulating molecules.
• Understanding these interactions is crucial for diagnosing and treating kidney diseases, particularly those affecting the glomerular filtration barrier.

Purpose of the Study:

• To investigate the distribution and effects of polycationized ferritin (PCF) on anionic sites of normal and puromycin aminonucleoside nephrotic (PAN) kidney cells using an in vitro model.
• To elucidate the dynamic binding and cellular uptake mechanisms of PCF in kidney epithelial cells.

Main Methods:

• In vitro incubation of isolated glomeruli with varying concentrations of PCF.
• Microscopic analysis of PCF distribution and cellular structural changes.
• Assessment of PCF binding inhibition using specific enzyme and protein treatments (neuraminidase, protamine sulfate).
• Evaluation of PCF effects under conditions altering cellular dynamics (cytochalasin B, low temperatures).

Main Results:

• PCF preferentially binds to microvilli on glomerular podocytes at low concentrations and forms layers at higher concentrations.
• Short-term PCF exposure does not impede filtration slits, but longer exposure leads to slit narrowing and foot process junctions.
• PCF accumulates in the lamina rara externa (LRE) of the glomerular basement membrane, a process inhibited by cytochalasin B or low temperatures.
• PCF shedding occurs from free surfaces, but not microvilli tips, within an hour.
• Neuraminidase or protamine sulfate pretreatment significantly reduces PCF binding.
• PAN glomeruli show patchy PCF distribution, and high PCF concentrations bind to parietal epithelial surfaces and basal laminae.

Conclusions:

• Polycationized ferritin (PCF) binding to anionic sites on kidney cells alters podocyte morphology and glomerular basement membrane structure.
• Cellular uptake mechanisms, including caveolae and pinosomes, are involved in PCF internalization.
• The observed structural changes and PCF accumulation are sensitive to cellular metabolic state and cytoskeletal integrity.
• These findings provide a model for understanding macromolecule-cell interactions in kidney filtration and disease.