Vascular endothelial growth factor regulates expression of protective complement factor H in specialized capillary beds

Abstract

 

Purpose

 

Local VEGF production in microvascular beds is vital for endothelial cell function. Both the outer retina and renal glomerulus possess specialized epithelial cells that produce VEGF to maintain a fenestrated endothelium. In mice, ablation of retinal pigmented epithelial (RPE) cell VEGF causes rapid degeneration of the choriocapillaris and vision loss. Loss of glomerular VEGF leads to thrombotic microangiopathy (TMA) and haemolytic uremic syndrome (HUS). VEGF antagonists can cause glomerular TMA with HUS and may accelerate progression of dry AMD to geographic atrophy. Complement dysregulation is also a feature of atypical HUS and AMD, with genetic alterations in factor H (CFH) implicated in both diseases. Linking these observations, we show that VEGF regulates local CFH expression in both the outer retina and renal glomerulus.

 

Methods

 

Eyes from AMD patients and controls were analyzed for CFH and VEGF expression and for evidence of complement activation. CFH was also analyzed in human RPE and glomerular cells before and after VEGF treatment or antagonism. RPE cells were treated with VEGF and various inhibitors to study the mechanism of VEGF induced CFH up regulation. CFH expression and complement deposition was examined in RPE and podocyte-specific VEGF knockout mice.

 

Results

 

AMD patient eyes showed reduced CFH staining in the RPE and complement activation in the choriocapillaris. Loss or inhibition of epithelial derived VEGF led to local reduction in CFH expression and increased complement deposition in the retina and the glomerulus. This was mediated by reduced VEGFR2- PKC signaling that decreased activation of the CREB transcription factor.<br /> <br /> To further examine this relationship, RPE specific VEGF knockout mice are being crossed with complement C3 knockout mice to determine if phenotypic rescue of the choriocapillaris occurs. The AMD Y402H CFH polymorphism is being introduced into human RPE cells using CRISPR/Cas technology to allow further functional characterization.

 

Conclusions

 

The relationship between VEGF and CFH provides new insights into local mechanisms that protect the microvascular endothelium from complement-mediated injury and may provide an explanation for the off target effects of anti-VEGF agents. This work highlights biological similarities between the outer retina and glomerulus which could have implications for other diseases including diabetes.