Identification of Endothelial-to-Mesenchymal Transition as a Potential Participant in Radiation Proctitis

Abstract

The endothelial-to-mesenchymal transition (EndoMT) is a crucial cellular process during heart development necessary to the formation of cardiac valves. This embryonic process reappears in several pathological situations, such as vascular injury or organ fibrosis of various etiologies, as a mediator of extracellular matrix-producing cells. Because radiation induces both vascular damage and fibrosis, we investigated whether radiation exposure induces EndoMT in primary human intestinal microvascular endothelial cells (HIMECs) and whether EndoMT contributes to radiation-induced rectal damage in humans and in a preclinical model of radiation proctitis in mice. Irradiated HIMECs show phenotypic hallmarks of radiation-induced endothelial cell activation in vitro. Moreover, HIMECs undergo changes in molecular expression pattern compatible with EndoMT, with up-regulation of mesenchymal markers and down-regulation of endothelial markers via transforming growth factor/Smad pathway activation. In vivo, EndoMT readily occurs in the human rectum after radiation therapy for rectal adenocarcinoma. Finally, EndoMT was observed in rectal mucosal and submucosal microvessels in a preclinical model of radiation proctitis in Tie2-green fluorescent protein reporter-expressing mice all along radiation proctitis development, also associated with transforming growth factor/Smad pathway activation. In conclusion, radiation-induced cell activation and tissue inflammation constitute a setting that fosters the phenotypic conversion of endothelial cells into mesenchymal cells. Therefore, EndoMT is identified as a potential participant in radiation-induced gut damage and may represent an interesting therapeutic target in cases of radiation-induced pelvic disease.

Quantitative MRI in murine radiation‐induced rectocolitis: comparison with histopathological inflammation score

“…In contrast, radiation‐induced models of inflammation have been shown to be controllable and reproducible . We have confirmed these findings in our study, as submucosal or transmural inflammation was observed in all animals in histopathology and MRI.…”

Matrix metalloproteinase 9 induces endothelial-mesenchymal transition via Notch activation in human kidney glomerular endothelial cells

“…EndoMT is involved in organ development and various types of fibrosis. For example, EndoMT contributes to cardiac fibrosis [ 10 – 12 ], pulmonary fibrosis [ 10 , 13 ], corneal fibrosis [ 14 ], radiation-induced pelvic disease [ 15 ] and inflammatory bowel disease-associated fibrosis [ 16 ]. EndoMT was also found in the early development of kidney interstitial fibrosis in the streptozocin (STZ)-induced diabetic nephropathy (DN) model [ 17 , 18 ].…”

HIF-1α Deletion in the Endothelium, but Not in the Epithelium, Protects From Radiation-Induced Enteritis

“…Primary human intestinal microvascular endothelial cells (HIMECs) were prepared as described. 21 , 22 HIMECs (passage 4) and human umbilical vein endothelial cells (HUVECs) (passage 3) were transfected as described previously. 23 Briefly, cells were seeded into 6-well plates for 48 hours to reach 50%–70% confluence and were transfected with siRNA (100 nM) using Dharmafect according to the manufacturer’s protocols (Dharmacon, Chicago, IL).…”