ALK1 heterozygosity delays development of late normal tissue damage in the irradiated mouse kidney.

Background And Purpose: Activin receptor-like kinase 1 (ALK1) is a transforming growth factor β (TGF-β) receptor, which is mainly expressed in endothelial cells regulating proliferation and migration in vitro and angiogenesis in vivo. Endothelial cells also express the co-receptor endoglin, which modulates ALK1 effects on endothelial cells. Our previous studies showed that mice with reduced endoglin levels develop less irradiation-induced vascular damage and fibrosis, caused by an impaired inflammatory response. This study was aimed at investigating the role of ALK1 in late radiation toxicity.

Material And Methods: Kidneys of ALK(+/+) and ALK1(+/-) mice were irradiated with 14 Gy. Mice were sacrificed at 10, 20, and 30 weeks after irradiation and gene expression and protein levels were analyzed.

Results: Compared to wild type littermates, ALK1(+/-) mice developed less inflammation and fibrosis at 20 weeks after irradiation, but displayed an increase in pro-inflammatory and pro-fibrotic gene expression at 30 weeks. In addition, ALK1(+/-) mice showed superior vascular integrity at 10 and 20 weeks after irradiation which deteriorated at 30 weeks coinciding with changes in the VEGF pathway.

Conclusions: ALK1(+/-) mice develop a delayed normal tissue response by modulating the inflammatory response and growth factor expression after irradiation.