Suppressing STAT3 activity protects the endothelial barrier from VEGF-mediated vascular permeability

Vascular permeability can be triggered by inflammation or ischemia in the heart, brain, or lung, where it promotes edema, exacerbates disease progression, and impairs tissue recovery. Vascular endothelial growth factor (VEGF) is a potent inducer of vascular permeability, and VEGF plays an integral role in regulating vascular barrier function in physiological conditions and a variety of pathologies, such as cancer, ischemic stroke, cardiovascular disease, retinal conditions, and COVID-19-associated pulmonary edema and sepsis that often leads to acute lung injury, including acute respiratory distress syndrome. However, after initially stimulating permeability, VEGF subsequently mediates angiogenesis to repair damaged tissue following pathological injury. Consequently, understanding the molecular mechanisms of VEGF-induced vascular permeability will facilitate the development of promising therapies that achieve the delicate balance of inhibiting vascular permeability while preserving tissue repair mediated by VEGF signaling. Here, we demonstrate that VEGF signals through signal transducer and activator of transcription 3 (STAT3) to promote vascular permeability. Specifically, we show that STAT3 ablation reduces vascular permeability using endothelial cell-specific STAT3 knockout mice as well as VEGF-inducible zebrafish crossed with CRISPR-Cas9 generated genomic STAT3 knockout zebrafish. Importantly, STAT3 deficiency does not impair vascular development and function in these animals. Wildtype C57BL/6 mice treated with JAK2 inhibitor, AG490, exhibit decreased vascular permeability when measured in vivo by Miles permeability assay, confirming the role of JAK2 in VEGF-induced vascular permeability. Using human endothelial cells, we describe a novel mechanism of STAT3-dependent transcriptional regulation of intercellular adhesion molecule 1 (ICAM-1), an endothelial transmembrane protein involved in the regulation of vascular permeability. FDA-approved anti-microbial drug, pyrimethamine (PYR), has been identified as an inhibitor of STAT3 function at concentrations known to be safely achieved in humans. We report that PYR substantially reduces VEGF-induced vascular permeability in mice. We confirm that pharmacologically targeting STAT3 increases vascular barrier integrity in human endothelium using two additional STAT3 inhibitor compounds, including atovaquone, an FDA-approved anti-parasitic drug shown to inhibit STAT3-dependent transcription. Taken together, our findings suggest that the VEGF, VEGFR-2, JAK2, and STAT3 signaling cascade regulates vascular barrier integrity and compounds known to inhibit STAT3-dependent activity reduce VEGF-induced vascular permeability in vertebrate models.