Secretion of Down Syndrome Critical Region 1 Isoform 4 in Ischemic Retinal Ganglion Cells Displays Anti-Angiogenic Properties Via NFATc1-Dependent Pathway.

Down syndrome candidate region 1 (DSCR1) has two differentially regulated isoforms (DSCR1-1 and DSCR1-4) and is reported to play a role in a number of physiological processes, such as the inhibition of cardiac hypertrophy, attenuation of angiogenesis and carcinogenesis, and protection against neuronal death. However, the function of DSCR1 in the retina is still not clear. Therefore, we analyzed the expression and location of DSCR1 in the retina of neonatal mice with oxygen-induced retinopathy (OIR), and studied its effects on angiogenesis. The neonatal C57BL/6J mice were exposed to 75 % O2 for 5 days from postnatal day 7 (P7) to P12. At P12, the mice were returned to 21 % O2 at room air. The primary retinal ganglion cells (RGCs) were exposed to hypoxia (93 % N2, 5 % CO2, and 2 % O2) at 37 °C for 36 h. And then the mouse retinal microvascular endothelial cells (mRMECs) were treated with 25 ng/mL vascular endothelial growth factor (VEGF) or culture medium conditioned by hypoxic RGCs alone, hypoxic RGCs treated with DSCR1-4-siRNA (siDSCR1-4) or hypoxic RGCs treated with siDSCR1-4 and 200 ng/mL cyclosporin A (CsA), and then primed with VEGF (25 ng/mL). The expression of DSCR1-4 increased strongly at P16 after OIR. There was no change in messenger RNA (mRNA) expression of DSCR1-1 at P16 after OIR. The increased DSCR1 was mainly located in the RGCs of avascular retina. In addition, DSCR1-4 expression was increased in primary RGCs after hypoxia exposure. There was no change in mRNA expression of DSCR1-1 in primary RGCs after hypoxia exposure. Moreover, DSCR1-4 produced by hypoxic RGCs showed anti-angiogenic properties, with decreased cell proliferation, migration, tube formation, and inflammatory cytokines production. These properties were due to inhibited nuclear factor of activated T cell (NFATc) 1 dephosphorylation and translocation into nuclear in VEGF-treated mRMECs. Using siRNA-mediated knockdown of DSCR1-4 and NFATc1 inhibitor (Cs A) further demonstrated the inhibitory effect of DSCR1-4 on angiogenic properties in VEGF-induced mRMECs, and this effect was NFATc1-dependent. This report describes a novel effect of DSCR1-4 in the aspect of anti-angiogenesis, suggesting potential therapeutic strategies for proliferative retinopathies.