Alpha-Smooth Muscle Actin-Positive Perivascular Cells in Diabetic Retina and Choroid.

Soo Jin Kim,Sang A Kim,Yeong A Choi,Junyeop Lee,Do Young Park

doi:10.3390/ijms21062158

Abstract

Structural alterations of pericytes in microvessels are important features of diabetic retinopathy. Although capillary pericytes had been known not to have α-smooth muscle actin (αSMA), a recent study revealed that a specific fixation method enabled the visualization of αSMA along retinal capillaries. In this study, we applied snap-fixation in wild type and streptozotocin-induced diabetic mice to evaluate the differences in vascular smooth muscle cells of the retina and the choroid. Mice eyeballs were fixed in ice-cold methanol to prevent the depolymerization of filamentous actin. Snap-fixated retina showed αSMA expression in higher-order branches along the capillaries as well as the arterioles and venules, which were not detected by paraformaldehyde fixation. In contrast, most choriocapillaris, except those close to the arterioles, were not covered with αSMA-positive perivascular mural cells. Large choroidal vessels were covered with more αSMA-positive cells in the snap-fixated eyes. Diabetes induced less coverage of αSMA-positive perivascular mural cells overall, but they reached higher-order branches of the retinal capillaries, which was prominent in the aged mice. More αSMA-positive pericytes were observed in the choroid of diabetic mice, but the αSMA-positive expression reduced with aging. This study suggests the potential role of smooth muscle cells in the pathogenesis of age-related diabetic retinopathy and choroidopathy.

Highlights

Pericytes along the blood vessels are the specific mural cells embedded within the basement membrane of the vasculature and adjacent to endothelial cells
When the samples were fixed with PFA, no α-smooth muscle actin (αSMA)-positive cells were detected in the capillaries, as previously reported [6,21]; snap fixation revealed αSMA positive capillary perivascular cells in all three layers, residing along the capillary similar to capillary pericytes [4,22,23] rather than wrapping around like arterial vascular smooth muscle cells (VSMC)
Inhibition of F-actin depolymerization was favorable for αSMA detection in the retinal capillary

Summary

Introduction

Pericytes along the blood vessels are the specific mural cells embedded within the basement membrane of the vasculature and adjacent to endothelial cells. Perivascular mural cells, including pericytes and vascular smooth muscle cells (VSMC), maintain the structural and functional stability of blood vessels [1]. Compared with large-diameter vessels (e.g., arteries and veins), capillaries have the distinct characteristic that they are not covered by vascular smooth muscle cells [1]. Pericytes have been found to express alpha-smooth muscle actin (αSMA), a contractile filamentous component which is a major indicator of vascular smooth muscle cells [4,5]. Retinal capillaries are affected by vasoregulators, and the vascular tone of these capillaries is controlled; retinal capillaries lack vascular smooth muscle cells to generate the contractile function [6,7]. Recent studies detected the existence of capillary α-SMA by preventing filamentous actin depolymerization in the retina via the intravitreal injection of phalloidin and ice-cold methanol fixation (Snap fix) [8]

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Results

Conclusion