Effect of diabetes and hyaluronidase on the retinal endothelial glycocalyx in mice

Abstract

We sought to investigate the effects of diabetes and hyaluronidase on the thickness of the endothelial glycocalyx layer in the mouse retina. In our study, the retinal circulation of diabetic Ins2(Akita) mice and their nondiabetic littermates were observed via intravital microscopy. The endothelial glycocalyx thickness was determined from the infusion of two fluorescently labeled plasma markers, one of which was a high molecular weight rhodamine dextran (MW=155,000) excluded from the glycocalyx, and the other a more permeable low molecular weight sodium fluorescein (MW=376). In nondiabetic C57BL/6 mice, the glycocalyx thickness also was evaluated prior to and following infusion of hyaluronidase, an enzyme that can degrade hyaluronic acid on the endothelial surface. A leakage index was used to evaluate the influence of hyaluronidase on the transport of the fluorescent tracers from the plasma into the surrounding tissue, and plasma samples were obtained to measure levels of circulating hyaluronic acid. Both diabetes and hyaluronidase infusion significantly reduced the thickness of the glycocalyx in retinal arterioles (but not in venules), and hyaluronidase increased retinal microvascular leakage of both fluorescent tracers into the surrounding tissue. However, only hyaluronidase infusion (not diabetes) increased circulating plasma levels of hyaluronic acid. In summary, our findings demonstrate that diabetes and hyaluronidase reduce the thickness of the retinal endothelial glycocalyx, in which hyaluronic acid may play a significant role in barrier function.

The Pathological Relevance of Increased Endothelial Glycocalyx Permeability

“…DR is characterized by microaneurysms, leukocyte-endothelial adhesion, hemorrhage, capillary occlusion, neovascularization, and increased permeability. 51 Diabetic rats have a significantly thinner retinal endothelial glycocalyx compared with control rats (28.3 versus 60.2 nmol/L, P < 0.01), measured using transmission electron microscopy. 52 In addition, in the Akita mouse model of type 1 diabetes, anesthetized diabetic mice have a significantly thinner glycocalyx in retinal arterioles.…”

Roles of Endovascular Calyx Related Enzymes in Endothelial Dysfunction and Diabetic Vascular Complications

“…In hyperglycemic and/or inflammatory environments, hyaluronidase expression is upregulated, cutting the glycocalyx and producing hyaluronic acid fragments. Previous studies found that hyaluronic acid and hyaluronidase activity are increased in the serum of diabetics patients (Nieuwdorp et al, 2006a) and mice (Ikegami-Kawai et al, 2003;Leskova et al, 2019). Increased plasma hyaluronic acid and hyaluronidase activity were detected in both human Type 1 (Nieuwdorp et al, 2006a) and Type 2 (Broekhuizen et al, 2010) diabetes.…”

The Glycocalyx and Its Role in Vascular Physiology and Vascular Related Diseases

“…Leskova et al . 106 investigated the effects of diabetes and HYAL1 on the thickness of the GCX in the mouse retina. The retinal circulation of diabetic Ins2 (Akita) mice and their nondiabetic littermates were observed via intravital microscopy.…”