B cell-derived exosomal miR-34a-5p mediates radiation-induced bystander effect through ferroptosis.

Objectives: The radiation-induced bystander effect (RIBE) is a destructive reaction that occurs in non-irradiated cells. Exosomes, as an important intercellular information carrier, are considered potential mediators of RIBE, but their role in B cells remains unclear. Methods: B cell line IM-9 cells were irradiated to obtain exosomes for small RNA sequencing, and cell assays were used to assess the key miRNA's role in non-irradiated B cell ferroptosis. Results: Exosomes isolated from irradiated and non-irradiated B cells were well characterized, displaying typical cup-shaped morphology (50-150 nm) and expressing exosomal markers ALIX and TSG101. miR-34a-5p was identified to be a key miRNA in regulating ferroptosis, and significantly upregulated in irradiated B cell derived exosomes (IR-exo). IR-exo remarkedly promoted ferroptosis of non-irradiated IM-9 cells, as evident by enhanced lactate dehydrogenase activity and lipid peroxidation, and reduced SLC7A11, GPX4 and FTH1 expression. However, miR-34a-5p silencing in IR-exo reversed IR-exo-induced ferroptosis in non-irradiated B cells. Moreover, CDKN1A inhibition partially counteracted the suppressive effect of miR-34a-5p knockdown on non-irradiated B cell ferroptosis. Conclusions: Our findings suggest that irradiated exosomal miR-34a-5p promotes non-irradiated B cell ferroptosis through CDKN1A, uncovering a novel mechanism for RIBE and offering a new therapeutic target for radioprotection.