Retinal Microvasculature Smooth Muscle and Pericytes: Analysis of Protein Expression and Vessel Heterogeneity
Abstract
The retina is one of the most active metabolic tissues in the human body that necessitates a substantial continuous blood supply. The retinal circulation which supplies the inner two-thirds of the retina is derived from the central retinal artery, while the outer one-third of the retina obtains nutrients via the choroidal circulation. Disturbance in the retinal blood supply contributes to numerous ocular diseases. Besides, it is believed that the loss of the ability to alter the vascular tone during fluctuations in intramural pressure is the earliest feature of many retinal diseases such as glaucoma, diabetic retinopathy and macular degeneration. A comprehensive understanding of the myogenic mechanisms involved in regulating the blood flow in retinal microvasculature and how retinal diseases affect it could aid in the development and identification of new diagnostic strategies and therapeutic targets for retinal diseases. In the current study, confocal immunolabeling of whole-mount preparations was performed to investigate the expression of αSMA, NG2, calponin, caldesmon and SM22 as well as CaV1.2 and CaV3.1 in rat retina. In addition, analysis of the images concerning the level of expression, vessel diameter and arrangement of α-smooth muscle actin (αSMA) fibres. we illustrated that 1st, 2nd and 3rd order arterioles had the most highly organized αSMA fibres and the most profound expression of myogenic proteins (αSMA, calponin, SM22, CaV1.2 and CaV3.1) suggesting that these vascular smooth muscle cells (VSMCs) may contribute most to the regulation of blood flow in the retina. Pre-capillary, capillary and venular pericytes, on the other hand, displayed little αSMA, no calponin and little or no SM22, CaV1.2 and CaV3.1, suggesting their contractile capacity is likely to be very limited. Finally, the data analysis of the T-type channel (CaV3.1) suggests that it becomes more important in regulating tone in smaller retinal vessels and indicates the possible undiscovered role of this channel in the myogenic activity.