Purpose: To analyze the cellular events involved in the construction of the organized vascular architecture and to characterize the tight junction in developing vessels of retina.
Methods: On post-natal days (P)4, P8, P12, P16, and P56, electron microscopy for retinal vessels and immunohistochemistry for CD31, ZO-1, glial fibrillary acidic protein, and α-smooth muscle actin were performed. ZO-1 expression was measured with progression of retinal vessel development in whole retina. Leakage was assessed by immunohistochemistry for CD31 on retinal vessels perfused with fluorescein conjugated dextran as well.
Results: The recruitment of pericytes and astrocytes to vascular tube of endothelial cells is closely associated with the formation of tight junction in developing retinal vessels. At P4, endothelial cells of retinal vessels behind the invading front directly contact to pericytes, but not to foot processes of astrocytes yet, where ZO-1 was already weakly immunoreactive along retinal endothelial cells. With the progression of retinal development, foot processes of astrocytes are gathered around retinal vessels and the maturation of tight junction in endothelial cells is clearly defined, which was temporally and spatially accordant to the expression of a tight junction protein, ZO-1. In addition tight junction could be formed with contact of pericytes to endothelial cells without the prominent ensheathment of astrocytic foot processes which was coincided with the appearance of a tight junction protein, ZO-1.
Conclusion: Our data suggests that the tight junction of endothelial cells in blood-retinal barrier could be developed by cellular interactions between pericytes, asctrocytes and endothelial cells. Moreover, ZO-1 as well as occluding or claudin might demonstrate the tightness of blood-retinal barrier in developing retina.