Aim: Metabolic rewiring of the quiescent vasculature is responsible for endothelial growth. This study set out to investigate the importance of the SLC-family transporter SLC7A11, in the control of endothelial cell identity and proliferation in the developing retina vasculature.

Methods and results: To investigate active translation alterations in proliferating and quiescent endothelial cells we employed RiboTag sequencing studies. Interestingly 5 Solute carrier Transporters were significantly enriched in the proliferating endothelium, including the cystine transporter SLC7A11. Results were validated by immunohistochemistry in proliferating cultured human endothelial cells, as well as in the proliferative vascular front of the retinal postnatal endothelium. Transported cystine from the SLC7A11, is rapidly reduced to cysteine and can flux to acetyl-CoA through the enzyme cystathionine gamma lyase (CSE). Indeed 13C metabolic flux analysis showed that the SLC7A11^high proliferative endothelium, utilized cystine carbons to support more than 30% of the endothelial acetyl-CoA pool. Subsequent 13C proteomic analysis linked the cystine derived acetyl-moiety to the acetylation of histone 3 (H3). Combined Actseq and ATACseq methods in endothelial cells with either preserved cysteinolytic capacity or genetically modified to exhibit cysteinostasis (i.e.inducible CSE knock out) showed that the cysteine carbon is responsible for maintaining the chromatin accessible to the transcriptional factor Erg1. RNAseq analysis and transcriptional factor footprinting confirmed that CSE preserves endothelial cell fate commitment, proliferation and identity. Functionally, in vitro and ex vivo models of angiogenesis showed that cysteine catabolism is essential for endothelial proliferation. Simultaneously, in vivo, depletion of CSE and induction of endothelial cysteinostasis reduced the proliferative capacity of the vascular front and induced endothelial expression of mesenchymal markers e.g. collagen V.

Conclusions: Cystine import through the SLC7A11 transporter and subsequent metabolic rewiring to acetyl-CoA through the CSE enzyme, regulate endothelial cell transcription and proliferative capacity by preserving the endothelial chromatin architecture.