Inducible Disruption Of Endothelial Hyaluronan Synthase-2 Expression In Adult Mice Reveals A Direct Involvement Of Glomerular Endothelial Surface Hyaluronan In Development Of Albuminuria And Renal Injury

We demonstrated that infusion with hyaluronidase of C57Bl/6 mice for 4 wks to chronically reduce EC surface hyaluronan expression resulted in glomerular albumin passage and podocyte injury. However, with systemic hyaluronan degradation it precludes definitive conclusions on cellular-specific effects. Here we investigated the hypothesis that it is specifically the structure and integrity of the glomerular EC glycocalyx that determines whether or not albumin passage across the capillary wall occurs, and subsequently protects against development of kidney injury. To this end, we generated a conditional EC specific hyaluronan synthase2-knock out (HAS2–KO) mouse model. 8 Week old B6.VECad-creERT2.has2f/f.Rosa26-tdTomato were injected i.p. for 5 consecutive days with 2mg/0.2μL tamoxifen (control B6.VECad-creERT2.Rosa26-tdTomato) to induce an endothelial specific deletion of has2. Compared to ctrl, these mice show that 4 wks after induction, weight gain was significantly more increased (mean ± SEM; 2.9 ± 0.7 [n=8] vs. 5.2 ± 0.6g [n=11], p=0.02). With prominent endogenous albumin passage over the barrier, visualized as a DAB reaction product in electron microscopy after anti-albumin-HRP antibody incubation of 2%PFA fixated tissue slides, visible 2 wks after induction, a significant (p=0.036) increased ACR (36.0 ± 1.9 [n=8] vs. 57.7 ± 7.9 [n=11]) was found only at wk 4. During this period no significant change in BP (85 ± 2/114 ± 2 [n=8] vs. 90 ± 4/119 ± 4mmHg [n=10], diastolic/systolic) or in heart rate (712 ± 14 [n=8] vs. 747 ± 8beats/min [n=10]) was observed. Renal morphology revealed with comparable glomerular surface area (5342 ± 270 [n=3] vs. 5508 ± 250 μm2 [n=6]), significant increase of glomerular mesangial area (20.1 ± 0.9 [n=3]) vs. 38.4 ± 1.2% [n=6], p<0.01) and capillary surface area (16.6 ± 1.0 [n=3]) vs. 22.8 ± 0.7% [n=6], p=0.046). In conclusion, the data so far indicate that an intact glomerular EC-ESL is essential for glomerular integrity and prevention of albumin filtration is Key to preserving local quiescence of mesangial cells and podocytes. The conditional EC specific HAS2–KO mouse seems to be a valid model to assess the role of ESL in glomerular permeability barrier and vascular induced glomerular changes.