Glomerular filtration is normal in the absence of both agrin and perlecan-heparan sulfate from the glomerular basement membrane.
BACKGROUND
For several decades, it has been thought that the glomerular basement membrane (GBM) provides a charge-selective barrier for glomerular filtration. However, recent evidence has presented challenges to this concept: selective removal of heparan sulfate (HS) moieties that impart a negative charge to the GBM causes little if any increase in proteinuria. Removal of agrin, the major GBM HS-proteoglycan (HSPG), from the GBM causes a profound reduction in the glomerular anionic charge without changing the excretion of a negatively charged tracer. Perlecan is another HSPG present in the GBM, as well as in the mesangium and Bowman's capsule, that could potentially contribute to a charge barrier in the absence of agrin.


METHODS
Here we studied the nature of the glomerular filtration barrier to albumin in mice lacking the HS chains of perlecan either alone or in combination with podocyte-specific loss of agrin.


RESULTS
The results show significant reductions in anionic sites within the GBM in perlecan-HS and in perlecan-HS/agrin double mutants. Podocyte and overall glomerular architecture were normal, and renal function was normal up to 15 months of age with no measurable proteinuria. Moreover, excretion of a negatively charged Ficoll tracer was unchanged as compared to control mice.


CONCLUSIONS
These findings cast further doubt upon a critical role for the GBM in charge selectivity.
Goldberg
Seth
S
Renal Division, Department of Internal Medicine, Washington University School of Medicine, St Louis, MO 63110, USA.
Harvey
Scott J
SJ
Cunningham
Jeanette
J
Tryggvason
Karl
K
Miner
Jeffrey H
JH
D018171:Agrin / Q000235:genetics / Q000502:physiology*; D000818:Animals; D050533:Glomerular Basement Membrane / Q000502:physiology*; D019812:Heparan Sulfate Proteoglycans / Q000235:genetics / Q000502:physiology*; D051379:Mice; D009154:Mutation
D018171:Agrin; D019812:Heparan Sulfate Proteoglycans; C071927:perlecan