Endothelial FAM3A positively regulates post-ischaemic angiogenesis

Abstract

Background 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. Methods 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. Findings 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 Ca 2+ levels. Increased intracellular Ca 2+ 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. Interpretation 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.

FAM3A – A mitochondrial route to the stimulation of angiogenesis?

“…Returning to the new publication by Xu et al, the localization of FAM3A in endothelial cells was first confirmed as being mitochondrial by immunostaining and subcellular fractionation [3]. Despite the fact that endothelial cells are usually primarily glycolytic, they contain mitochondria which have important functions in various aspects of cell physiology, from the regulation of Ca 2+ signalling dynamics, to the control of cell death pathways such as apoptosis [8].…”

“…Despite the fact that endothelial cells are usually primarily glycolytic, they contain mitochondria which have important functions in various aspects of cell physiology, from the regulation of Ca 2+ signalling dynamics, to the control of cell death pathways such as apoptosis [8]. When endothelial FAM3A expression was increased, this caused an increase in ATP production and secretion, which was then able to bind to and activate plasma membrane P2 receptors, causing an increase in cytosolic Ca 2+ levels [3]. This stimulated the transcription of VEGF-A, leading to an increase in endothelial angiogenesis [3].…”

“…When endothelial FAM3A expression was increased, this caused an increase in ATP production and secretion, which was then able to bind to and activate plasma membrane P2 receptors, causing an increase in cytosolic Ca 2+ levels [3]. This stimulated the transcription of VEGF-A, leading to an increase in endothelial angiogenesis [3]. An increase in the expression of FAM3A was found to promote endothelial tube formation, proliferation and migration, and also improved blood perfusion and capillary density in a mouse, hind limb ischaemia model [3].…”

“…An increase in the expression of FAM3A was found to promote endothelial tube formation, proliferation and migration, and also improved blood perfusion and capillary density in a mouse, hind limb ischaemia model [3]. Silencing of FAM3A had the opposite effect, decreasing mitochondrial respiration and ATP production and impairing angiogenesis [3]. Together, these data show that endothelial FAM3A positively regulates post-ischaemic angiogenesis [3].…”

“…Silencing of FAM3A had the opposite effect, decreasing mitochondrial respiration and ATP production and impairing angiogenesis [3]. Together, these data show that endothelial FAM3A positively regulates post-ischaemic angiogenesis [3]. Since it appears to work via an autocrine stimulation of endogenous VEGF release, it may overcome some of the problems seen with the stimulation of angiogenesis by the addition of exogenous VEGF.…”