Single and fractionated ionizing radiation induce alterations in endothelial connexin expression and channel function

Radiotherapy is an effective treatment for most tumor types. However, emerging evidence indicates an increased risk for atherosclerosis after ionizing radiation exposure, initiated by endothelial cell dysfunction. Interestingly, endothelial cells express connexin (Cx) proteins that are reported to exert proatherogenic as well as atheroprotective effects. Furthermore, Cxs form channels, gap junctions and hemichannels, that are involved in bystander signaling that leads to indirect radiation effects in non-exposed cells. We here aimed to investigate the consequences of endothelial cell irradiation on Cx expression and channel function. Telomerase immortalized human Coronary Artery/Microvascular Endothelial cells were exposed to single and fractionated X-rays. Several biological endpoints were investigated at different time points after exposure: Cx gene and protein expression, gap junctional dye coupling and hemichannel function. We demonstrate that single and fractionated irradiation induce upregulation of proatherogenic Cx43 and downregulation of atheroprotective Cx40 gene and protein levels in a dose-dependent manner. Single and fractionated irradiation furthermore increased gap junctional communication and induced hemichannel opening. Our findings indicate alterations in Cx expression that are typically observed in endothelial cells covering atherosclerotic plaques. The observed radiation-induced increase in Cx channel function may promote bystander signaling thereby exacerbating endothelial cell damage and atherogenesis

Connexin43 Hemichannel Targeting With TAT-Gap19 Alleviates Radiation-Induced Endothelial Cell Damage

Background Emerging evidence indicates an excess risk of late occurring cardiovascular diseases, especially atherosclerosis, after thoracic cancer radiotherapy. Ionizing radiation (IR) induces cellular effects which may induce endothelial cell dysfunction, an early marker for atherosclerosis. In addition, intercellular communication through channels composed of transmembrane connexin proteins (Cxs), i.e. Gap junctions (direct cell-cell coupling) and hemichannels (paracrine release/uptake pathway) can modulate radiation-induced responses and therefore the atherosclerotic process. However, the role of endothelial hemichannel in IR-induced atherosclerosis has never been described before. Materials and Methods Telomerase-immortalized human Coronary Artery/Microvascular Endothelial cells (TICAE/TIME) were exposed to X-rays (0.1 and 5 Gy). Production of reactive oxygen species (ROS), DNA damage, cell death, inflammatory responses, and senescence were assessed with or without applying a Cx43 hemichannel blocker (TAT-Gap19). Results We report here that IR induces an increase in oxidative stress, cell death, inflammatory responses (IL-8, IL-1 beta, VCAM-1, MCP-1, and Endothelin-1) and premature cellular senescence in TICAE and TIME cells. These effects are significantly reduced in the presence of the Cx43 hemichannel-targeting peptide TAT-Gap19. Conclusion Our findings suggest that endothelial Cx43 hemichannels contribute to various IR-induced processes, such as ROS, cell death, inflammation, and senescence, resulting in an increase in endothelial cell damage, which could be protected by blocking these hemichannels. Thus, targeting Cx43 hemichannels may potentially exert radioprotective effects

Connexin43 hemichannel targeting with TAT-Gap19 alleviates radiation-induced endothelial cell damage

Background Emerging evidence indicates an excess risk of late occurring cardiovascular diseases, especially atherosclerosis, after thoracic cancer radiotherapy. Ionizing radiation (IR) induces cellular effects which may induce endothelial cell dysfunction, an early marker for atherosclerosis. In addition, intercellular communication through channels composed of transmembrane connexin proteins (Cxs), i.e. Gap junctions (direct cell-cell coupling) and hemichannels (paracrine release/uptake pathway) can modulate radiation-induced responses and therefore the atherosclerotic process. However, the role of endothelial hemichannel in IR-induced atherosclerosis has never been described before. Materials and Methods Telomerase-immortalized human Coronary Artery/Microvascular Endothelial cells (TICAE/TIME) were exposed to X-rays (0.1 and 5 Gy). Production of reactive oxygen species (ROS), DNA damage, cell death, inflammatory responses, and senescence were assessed with or without applying a Cx43 hemichannel blocker (TAT-Gap19). Results We report here that IR induces an increase in oxidative stress, cell death, inflammatory responses (IL-8, IL-1 beta, VCAM-1, MCP-1, and Endothelin-1) and premature cellular senescence in TICAE and TIME cells. These effects are significantly reduced in the presence of the Cx43 hemichannel-targeting peptide TAT-Gap19. Conclusion Our findings suggest that endothelial Cx43 hemichannels contribute to various IR-induced processes, such as ROS, cell death, inflammation, and senescence, resulting in an increase in endothelial cell damage, which could be protected by blocking these hemichannels. Thus, targeting Cx43 hemichannels may potentially exert radioprotective effects