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The Role of Proteoglycans in Glomerular Physiology and Pathophysiology
Author(s) -
Ebefors Kerstin,
Khramova Alina,
Nyström Jenny
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.09398
Subject(s) - albumin , mannitol , renal function , pathophysiology , medicine , glycocalyx , chemistry , diabetes mellitus , proteinuria , endocrinology , kidney , biochemistry
Background Diabetic kidney disease (DKD) is the leading cause of renal failure in the world. Diabetes is associated with damage to the endothelial glycocalyx (eGCX), the layer of proteoglycans (PGs) and other negatively charged molecules covering the glomerular endothelial capillaries. The eGCX restrain the flow of charged molecules, such as albumin, over the filtration barrier in the kidney. Loss of the glomerular eGCX leads to proteinuria without other visible damage to the filtration barrier, but the detailed structure and composition is still largely unknown. The aim of this study was to gain new knowledge about the composition and role of the EGCX in health and DKD. Methods The negatively charged PGs in the eGCX was eluted from rat kidneys using 1 M NaCl solution (high salt, HS). In addition 1 M mannitol was used as osmotic control (HO) and 0.15 M NaCl to mimic physiological salt concentrations (NS). Solutions were introduced intra‐arterially to rat kidneys under anesthesia in vivo. Venous effluent was analyzed using mass spectrometry. Fractional clearance of albumin and GFR was measured. Electron microscopy (EM) was used to investigate morphological changes. Expression of PGs and PG related genes in glomeruli from patients with DKD was investigated using deep sequencing data from a Swedish DKD cohort (DKD, n=19, controls; pre‐transplant biopsies, n=20). Results We identified 15 PGs in the eluate from rats. PGs were found in highest yields in the HS samples. EM demonstrated that the eGCX thickness was significantly reduced in the HS rats −28% (p<0.05) compared to NS. Rats perfused with HS had increased fractional clearance of albumin and reduced GFR, compared to NS and HO, 10 minutes after perfusion. In glomeruli from patients with DKD 12 PGs were found to be significantly regulated, and 4 of these PGs were also identified in the eGCX eluates from rats. There was an overall decrease in expression of enzymes responsible for building up PG side chains, as well as an increase in proteins involved in PG degradation. Conclusion The eGCX itself represents a dynamic structure with significant molecular turnover. In our study, we identified several PGs novel to the glomerular eGCX. We show that loss of eGCX leads to proteinuria and reduced GFR, strongly supporting that the eGCX is important for preventing proteinuria. In glomeruli from patients with DKD we found significant alterations in the gene expression of PGs and the enzymes regulating their composition. Further investigation is needed to clarify in detail when and how these alterations appear in DKD.