Endothelial surface layer degradation by chronic hyaluronidase infusion induces proteinuria in apolipoprotein E-deficient mice

Abstract

Objective: Functional studies show that disruption of endothelial surface layer (ESL) is accompanied by enhanced sensitivity of the vasculature towards atherogenic stimuli. However, relevance of ESL disruption as causal mechanism for vascular dysfunction remains to be demonstrated. We examined if loss of ESL through enzymatic degradation would affect vascular barrier properties in an atherogenic model.

Methods: Eight week old male apolipoprotein E deficient mice on Western-type diet for 10 weeks received continuous active or heat-inactivated hyaluronidase (10 U/hr, i.v.) through an osmotic minipump during 4 weeks. Blood chemistry and anatomic changes in both macrovasculature and kidneys were examined.

Results: Infusion with active hyaluronidase resulted in decreased ESL (0.32±0.22 mL) and plasma volume (1.03±0.18 mL) compared to inactivated hyaluronidase (0.52±0.29 mL and 1.28±0.08 mL, p<0.05 respectively).Active hyaluronidase increased proteinuria compared to inactive hyaluronidase (0.27±0.02 vs. 0.15±0.01 µg/µg protein/creatinin, p<0.05) without changes in glomerular morphology or development of tubulo-interstitial inflammation. Atherosclerotic lesions in the aortic branches showed increased matrix production (collagen, 32±5 vs. 18±3%; glycosaminoglycans, 11±5 vs. 0.1±0.01%, active vs. inactive hyaluronidase, p<0.05).

Conclusion: ESL degradation in apoE deficient mice contributes to reduced increased urinary protein excretion without significant changes in renal morphology. Second, the induction of compositional changes in atherogenic plaques by hyaluronidase point towards increased plaque vulnerability. These findings support further efforts to evaluate whether ESL restoration is a valuable target to prevent (micro) vascular disease progression.

Figure 1. Photomicrographs of Sirius red-stained lesions within two major vessels branching from the aortic arch with a difference in onset of atherogenic development.

The (A, B, C) innominate- (early start) and (D, E, F) left subclavian artery (later start) from apoE^−/− mice on (A, D) a Western-type atherogenic diet alone, or in combination with (B, E) inactive- or (C, F) active hyaluronidase infusion, (inset F) Higher magnification of Sirius red-stained lesion within the left subclavian artery from apoE^−/− mice on a combined Western-type atherogenic diet and active hyaluronidase infusion. Arrow head indicates absence of long stretches of the intimal layer underneath a plaque. Bar = 0.2 mm, bar inset = 50 µm.

Figure 2. Atherogenic progression in the innominate- (white bars) and left subclavian (black bars) artery from apoE^−/− mice on a combined Western-type atherogenic diet with inactive- or active hyaluronidase infusion.

(A) Distribution and level of advanced plaque areas, given µm² ×10.000. Distribution and percentage of (B) collagen or (C) glycosaminoglycan within each plaque area. Distribution of individual macrophage areas within each plaque area (D), given in µm².

Figure 3. Renal morphology of periodic acid Schiff’s stained (PAS) glomeruli of apoE^−/− mice on a combined Western-type atherogenic diet with (A) inactive- or (B)active hyaluronidase infusion.

Bar = 50 µm.

Figure 4. Renal protein leakage of apoE^−/− mice on normal chow (NC) or on a Western-type atherogenic diet (HFC) for 10 weeks or in combination with active- or inactive hyaluronidase infusion, given as protein/creatinin excretion ratio (µg/µg).

Values are means ± SD from end-point urine samples. Difference in protein/creatinin ratio was assessed by means of two-sample t-test (2-way). *P<0.05 of apoE^−/− on HFC and inactive hyaluronidase vs. apoE^−/− on NC; **P<0.05 of apoE^−/− on HFC and active hyaluronidase vs. apoE^−/− on NC or apoE^−/− on HFC and inactive hyaluronidase.