Retinal capillary basement membrane (BM) thickening is closely associated with the development of vascular lesions in
diabetic retinopathy. Thickened capillary BM can compromise blood-retinal-barrier characteristics and contribute to
retinal vascular permeability, a significant clinical manifestation of
diabetic retinopathy. We have previously shown that high
glucose increases the expression and activity of
lysyl oxidase (LOX), a crosslinking
enzyme, in
retinal endothelial cells. Additionally, concomitant with overexpression of LOX, increased vascular permeability was observed in diabetic rat retinas. However, it is unknown whether decreasing LOX overexpression may have protective effects against development of
retinal vascular lesions in diabetes. To investigate whether reduced LOX level protects against diabetes-induced development of
retinal vascular lesions characteristic of
diabetic retinopathy, four groups of mice: wild type (WT) control mice,
streptozotocin (STZ)-induced diabetic mice, LOX +/- mice, and STZ-induced diabetic LOX +/- mice were used for this study. Diabetes was maintained for 16 weeks; at the end of the study, retinas were assessed for LOX
protein level by Western Blot (WB) analysis, and
retinal capillary networks were isolated using
retinal trypsin digestion and stained with
hematoxylin and
periodic acid Schiff to identify the number of acellular capillaries (AC) and pericyte loss (PL). In parallel, TUNEL assay was performed on
retinal trypsin digests (RTDs) to detect cells undergoing apoptosis in the
retinal capillary networks.
Retinal vascular permeability was analyzed following
FITC-dextran injection in
retinal whole mounts. A significant increase in LOX expression was detected in the diabetic retinas compared to those of the WT control retinas, and as expected, a significant decrease in LOX expression in the diabetic LOX +/- retinas was observed compared to those of the diabetic retinas. RTD images showed significantly increased AC and PL counts in the retinas of diabetic mice compared to those of the WT control mice. Importantly, the number of AC and PL was significantly decreased, as was
retinal vascular permeability in the retinas of the diabetic LOX +/- mice compared to those of the diabetic mice. Results suggest that decreasing diabetes-induced LOX overexpression may have protective effects against the development of vascular lesions characteristic of
diabetic retinopathy. Therefore, LOX overexpression may be a potential target in preventing
retinal vascular cell loss and excess permeability associated with
diabetic retinopathy.