Targeted cytoplasmic irradiation induces bystander responses

Area of Science:

• Radiobiology
• Cellular response to radiation
• Low-dose radiation effects

Background:

• Radiation-induced bystander responses challenge the dogma that direct DNA damage is the sole driver of cellular responses to radiation.
• Understanding these responses is crucial for assessing risks associated with low-dose radiation exposure.

Purpose of the Study:

• To investigate the mechanisms underlying radiation-induced bystander responses using targeted single-cell irradiation.
• To determine if direct DNA damage is necessary for initiating bystander signaling.
• To identify key molecular mediators involved in these responses.

Main Methods:

• Utilized a charged-particle microbeam to deliver single helium ions ((3)He(2+)) to individual radioresistant glioma cells.
• Examined bystander effects in cocultures of glioma cells and primary human fibroblasts.
• Assessed micronuclei yield as a marker of cellular damage and employed chemical scavengers (NO scavenger and filipin) to probe signaling pathways.

Main Results:

• Single-cell irradiation, even through the cytoplasm, induced significant bystander responses (36% increase in micronuclei in glioma, 78% in fibroblasts).
• Bystander effects were observed regardless of whether the nucleus or cytoplasm was targeted.
• Responses were abolished by nitric oxide (NO) scavenging and membrane raft disruption, implicating NO signaling.

Conclusions:

• Direct DNA damage is not required to initiate cell-signaling mechanisms following low-dose irradiation.
• The entire cell, not just the nucleus, functions as a sensor for radiation exposure.
• Nitric oxide plays a critical role in mediating radiation-induced bystander responses.