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

Müller 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 Müller cell pathophysiology. The expression of different VEGFs and their receptors in human MIO-M1 and mouse QMMuC-1 Müller cell lines and primary murine Müller cells was examined by RT-PCR, ELISA, and Western blot. The effect of recombinant VEGF-B or VEGF-B neutralization on Müller 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. VEGF-B was expressed in Müller cells at the highest levels compared with other members of the VEGF family. VEGF-B neutralization did not affect Müller cell viability or functionality under normal conditions, but enhanced hypoxia- or 4-HNE-induced Müller cell death and decreased inward rectifying K+ channel subtype 4.1 and aquaporin-4 expression. Recombinant VEGF-B restored Müller cell glutamine synthetase expression under hypoxic conditions and protected Müller cells from 4-HNE-induced damage by normalizing transient receptor potential vanilloid 4 channel expression and activity. Autocrine production of VEGF-B protects Müller cells under pathologic conditions.