Enhanced TGF-β Signaling Contributes to the Insulin-Induced Angiogenic Responses of Endothelial Cells

Abstract

SummaryAngiogenesis, the development of new blood vessels, is a key process in disease. We reported that insulin promotes translocation of transforming growth factor β (TGF-β) receptors to the plasma membrane of epithelial and fibroblast cells, thus enhancing TGF-β responsiveness. Since insulin promotes angiogenesis, we addressed whether increased autocrine TGF-β signaling participates in endothelial cell responses to insulin. We show that insulin enhances TGF-β responsiveness and autocrine TGF-β signaling in primary human endothelial cells, by inducing a rapid increase in cell surface TGF-β receptor levels. Autocrine TGF-β/Smad signaling contributed substantially to insulin-induced gene expression associated with angiogenesis, including TGF-β target genes encoding angiogenic mediators; was essential for endothelial cell migration; and participated in endothelial cell invasion and network formation. Blocking TGF-β signaling impaired insulin-induced microvessel outgrowth from neonatal aortic rings and modified insulin-stimulated blood vessel formation in zebrafish. We conclude that enhanced autocrine TGF-β signaling is integral to endothelial cell and angiogenic responses to insulin.

Integration of TGF-β-induced Smad signaling in the insulin-induced transcriptional response in endothelial cells

“…We previously reported that insulin increases TGF-β responsiveness and autocrine TGF-β /Smad signaling by promoting the transport of TGF-β receptors to the cell surface, and that this stimulation of TGF-β receptor transport results from insulin-induced Akt activation 14 . We also reported that the increased autocrine TGF-β response contributes to the insulin-induced angiogenic response 13 . To better appreciate the extent to which increased autocrine TGF-β contributes to insulin-induced changes in gene expression, we performed a genome-wide survey of changes in gene expression in response to insulin in human umbilical cord endothelial cells HUVECs, and assessed the contribution of TGF-β-induced Smad activation to the transcriptomic response.…”

“…Increased cell surface presentation of TGF-β receptors confers increased sensitivity to TGF-β, thus enhancing autocrine TGF-β signaling responses, raising the possibility that the insulin-induced increase in autocrine TGF-β signaling participates in gene expression and cellular responses to insulin. Indeed, we showed that elevated autocrine TGF-β signaling in response to insulin contributed to insulin-induced angiogenic responses in cell culture and ex vivo 13 . These findings invite questions regarding the extent to which TGF-β signaling participates and integrates in the response to insulin.…”

“…A number of insulin target genes have been identified and their mechanism of activation has been studied. On a larger scale, genome-wide studies provide better insight into the gene expression responses that are exerted in response to insulin, and these have been done in many different cells including hepatoma cells 4–6 , mouse fibroblasts 7,8 , osteoclasts precursors 9 , human skeletal muscle 10 , placenta 11 and endothelial cells 12,13 . Although many studies have looked into the effect of insulin in these cells, most large scale analyses did not take into account the participation or integration of other signaling pathways that may contribute to insulin-induced transcriptional responses.…”

“…We reported that Akt activation in response to insulin induces a rapid increase in cell surface TGF-β receptors in fibroblasts, epithelial cells, and endothelial cells, through mobilization of TGF-β receptors from an intracellular pool to the cell surface 13,14 . Increased cell surface presentation of TGF-β receptors confers increased sensitivity to TGF-β, thus enhancing autocrine TGF-β signaling responses, raising the possibility that the insulin-induced increase in autocrine TGF-β signaling participates in gene expression and cellular responses to insulin.…”

Angioregulatory microRNAs in Colorectal Cancer

“…A number of reports have demonstrated a significant role of SMAD signaling in angiogenesis [118,119]. TGF-β/SMAD mediated angiogenesis could be further enhanced by cooperation with insulin in EC [120]. PML could exert its antiangiogenic roles in IFN-α-dependent manner.…”