VEGF-B Is an Autocrine Gliotrophic Factor for Müller Cells under Pathologic Conditions.

Purpose Muller glia are important in retinal health and disease and are a major source of retinal VEGF-A. Of the different VEGF family members, the role of VEGF-A in retinal health and disease has been studied extensively. The potential contribution of other VEGF family members to retinal pathophysiology, however, remains poorly defined. This study aimed to understand the role of VEGF-B in Muller cell pathophysiology. Methods The expression of different VEGFs and their receptors in human MIO-M1 and mouse QMMuC-1 Muller cell lines and primary murine Muller cells was examined by RT-PCR, ELISA, and Western blot. The effect of recombinant VEGF-B or VEGF-B neutralization on Muller cell viability and survival under normal, hypoxic, and oxidative (4-hydroxynonenal [4-HNE]) conditions was evaluated by Alamar Blue, Yo-Pro uptake, and immunocytochemistry. The expression of glial fibrillary acidic protein, aquaporin-4, inward rectifying K+ channel subtype 4.1, glutamine synthetase, and transient receptor potential vanilloid 4 under different treatment conditions was examined by RT-PCR, immunocytochemistry, and Western blot. Transient receptor potential vanilloid 4 channel activity was assessed using a Fura-2-based calcium assay. Results VEGF-B was expressed in Muller cells at the highest levels compared with other members of the VEGF family. VEGF-B neutralization did not affect Muller cell viability or functionality under normal conditions, but enhanced hypoxia- or 4-HNE-induced Muller cell death and decreased inward rectifying K+ channel subtype 4.1 and aquaporin-4 expression. Recombinant VEGF-B restored Muller cell glutamine synthetase expression under hypoxic conditions and protected Muller cells from 4-HNE-induced damage by normalizing transient receptor potential vanilloid 4 channel expression and activity. Conclusions Autocrine production of VEGF-B protects Muller cells under pathologic conditions.