P0105THE ROLE OF PROTEOGLYCANS IN GLOMERULAR PHYSIOLOGY AND PATHOPHYSIOLOGY

Abstract Background and Aims Damage to the filtration barrier in the kidney may result in proteinuria, a hallmark of kidney disease. The glomerular filtration barrier consist of 3 layers: the endothelial cells with their endothelial surface layer (ESL), the glomerular basement membrane and podocytes. The ESL is rich in negatively charged molecules, such as proteoglycans (PGs). The negatively charged molecules restrain the flow of charged molecules, as albumin, over the barrier. Loss of ESL has been shown to lead to proteinuria without damage to the other structures of the filtration barrier. In order to gain further knowledge about the function and composition of the glomerular ESL we eluted the glomerular ESL from rats and analyzed the PG content as well as the effect of loss of the ESL on the function of the glomerular filtration. Method The basic principles of ion exchange chromatography were applied in this study. In order to elute highly negatively charged proteoglycans of the ESL, we used 1 M NaCl solution (HS). 1 M mannitol (HO) was included to evaluate osmotic effects. A control fraction was eluted with normal saline solution (0,15 M NaCl) (NS). Solutions were introduced intraarterially to rat kidneys under anesthesia in vivo. Venous effluent was collected and analyzed using proteomics and mass spectrometry. Fractional clearance of albumin was measured as well as GFR. Electron microscopy (EM) was used to investigate changes to the filtration barrier and the thickness of the glomerular ESL. Immunohistochemistry was used to confirm the presence of identified PGs in human tissue. Results We identified 15 PGs and PG candidates in ESL as well as hyaluronan. The most abundant PGs were lumican, glypican-1, syndecan-4, perlecan, podocan, decorin, serglycan, agrin and biglycan. In general, PGs were found in in all HS, NS and HO fractions, but in higher yields in the HS samples. EM demonstrated that the glomerular ESL thickness was significantly reduced in HS perfused rats – 28% (p<0.05) compared to rats perfused with NS. Rats perfused with HS also had increased fractional clearance of albumin compared to NS and HO, and a large reduction of GFR 10 minutes after perfusion. Conclusion The ESL itself represents a dynamic structure with significant molecular turnover and is formed by PGs, glycosaminoglycans, glycoproteins and soluble proteins. In our study, we identified several PGs in the glomerular endothelial ESL. We show that loss of ESL leads to increased albumin fractional clearance and reduction in GFR after perfusion, strongly suggesting that the ESL is important for preventing proteinuria. Characterizing the composition of the glomerular ESL is therefore of great importance, and can give new possible targets for treatment of proteinuria.