Table 1.

The epigenetic regulation in radiation-induced normal tissue damage.

Epigenetic mechanisms	Irradiation organ	Epigenetic functions	Target genes/proteins	Damage effects	Reference
DNA methylation	Brain	Increased expression of DNMT1 and 3a	Increased expression of TET1 and TET3 proteins	Radiation-induced cognitive dysfunction	Acharya et al. [116]
	Thymus	Decreased expression of DNMT1, 3a, and 3b	Decrease in the levels of methyl-binding proteins MeCP2 and MBD2	Increased the risk of radiation-inducedleukemia and thymic lymphoma	Pogribny et al. [119]
	Human breast cancer cells (MDA-MB-231)	Decreased DNMT1 expression	Downregulation of RB1 expression	DNA damage and apoptosis	Antwih et al. [118]
	Brain	Decreased expression of DNMT1, 3a, and 3b	Decrease in the levels of methyl-binding protein MeCP2	Bystander effect in the spleen	Koturbash et al. [120]
Histone methylation	Intestine	Increased expression of histone H3 methylation	—	Radiation-induced intestinal damage	Herberg et al. [124]
Histone acetylation	Skin	Inhibition of HDAC activity	—	Radiation-induced skin damage and carcinogenesis	Zhang et al. [125]
Regulation of miRNAs	Hematopoietic system	Upregulation of miR-30a-3p, miR-30c-5p, etc.	—	Radiation-induced hematopoietic damage	Acharya et al. [129]
	Lung	Upregulation of miR-19a-3p, miR-144-5p, and miR-144-3p	—	Radiation-induced lung injury	Gao et al. [135]
	Spleen	Increased expression of miR-34a	Upregulation of gene p53	Radiation-induced spleen damage	Ghosh et al. [137]
	Hematopoietic and osteoblast cells	Increased expression of miR-30c	Suppression of gene REDD1	Radiation-induced hematopoietic and osteoblast cell damage	Li et al. [131]