Endothelial FAM3A positively regulates post-ischaemic angiogenesis

Angiogenesis improves reperfusion to the ischaemic tissue after vascular obstruction. The underlying molecular mechanisms of post-ischaemic angiogenesis are not clear. FAM3A belongs to the family with sequence similarity 3 (FAM3) genes, but its biological function in endothelial cells in regards to vascular diseases is not well understood.

Gain- and loss-of-function methods by adenovirus or associated-adenovirus (AAV) in different models were applied to investigate the effects of FAM3A on endothelial angiogenesis. Endothelial angiogenesis was analysed by tube formation, migration and proliferation in vitro, and the blood flow and capillary density in a hind limb ischaemic model in vivo.

Endothelial FAM3A expression is downregulated under hypoxic conditions. Overexpression of FAM3A promotes, but depletion of FAM3A suppresses, endothelial tube formation, proliferation and migration. Utilizing the mouse hind limb ischaemia model, we also observe that FAM3A overexpression can improve blood perfusion and increase capillary density, whereas FAM3A knockdown has the opposite effects. Mechanistically, mitochondrial FAM3A increases adenosine triphosphate (ATP) production and secretion; ATP binds to P2 receptors and then upregulates cytosolic free Ca²⁺ levels. Increased intracellular Ca²⁺ levels enhance phosphorylation of the transcriptional factor cAMP response element binding protein (CREB) and its recruitment to the VEGFA promoter, thus activating VEGFA transcription and the final endothelial angiogenesis.

In summary, our data demonstrate that FAM3A positively regulates angiogenesis through activation of VEGFA transcription, suggesting that FAM3A may constitute a novel molecular therapeutic target for ischaemic vascular disease.