Abstract
Purpose:
During the course of murine postnatal retinal maturation, many retinal ganglion cells (RGC) undergo programmed cell death. The immunoregulatory receptor, programmed cell death-1 (PD-1) is expressed in RGCs and contributes to RGC culling early in postnatal life. In contrast, absence of the PD-1 ligands, PD-L1 and PD-L2, in double ligand knockout mice, is associated with increased RGC numbers into adulthood. This observation supports an additional binding partner for PD-ligands in the retina. B7-1 is known to also bind PD-L1 in cells of lymphoid origin. In this study we tested whether B7-1 is expressed in the murine retina in the adult and early postnatal period.
Methods:
Expression of B7-1 protein in neonatal and adult retinas was examined by Western blot analysis and immunofluorescence staining of vertical retina sections. The following retinal cell markers were co-stained with B7-1 to determine colocalization and identify specific cell types-- Brn3a, protein kinase C (PKC) α, Goα,AP2α,calbindin D28K and glutamine synthetase. B7-1 gene expression was detected by RT-PCR and normalized using the housekeeping gene GAPDH.
Results:
RT-PCR results demonstrate that B7-1 gene expression is found throughout the neonatal and adult retina, peaking in the mature retina. Protein expression via Western blot analysis indicates that B7-1 gene expression undergoes translational regulation, wherein B7-1 expression is higher in neonatal retinas. B7-1 is expressed in the RGCs and bipolar interneurons of the mature mouse retina, but not in amacrine cells, horizontal cells, and Müller cells.
Conclusions:
B7-1 is expressed in RGCs and bipolar cells during murine postnatal retina maturation. Similar to that of PD-1 and PD-Ligands, B7-1 expression in the retina undergoes dynamic regulation during development, raising the possibility that B7-1 engagement through PD-ligand may play a role in RGC cell survival. These findings may lead to a greater understanding of the role of PD-1/PD-ligand in retinal development and health.
Keywords: 691 retina: proximal (bipolar, amacrine, and ganglion cells) •
698 retinal development •
615 neuroprotection