Impact of Charged Particle Exposure on Homologous DNA Double-Strand Break Repair in Human Blood-Derived Cells

Abstract

Ionizing radiation generates DNA double-strand breaks (DSB) which, unless faithfully repaired, can generate chromosomal rearrangements in hematopoietic stem and/or progenitor cells (HSPC), potentially priming the cells towards a leukemic phenotype. Using an enhanced green fluorescent protein (EGFP)-based reporter system, we recently identified differences in the removal of enzyme-mediated DSB in human HSPC versus mature peripheral blood lymphocytes (PBL), particularly regarding homologous DSB repair (HR). Assessment of chromosomal breaks via premature chromosome condensation or γH2AX foci indicated similar efficiency and kinetics of radiation-induced DSB formation and rejoining in PBL and HSPC. Prolonged persistence of chromosomal breaks was observed for higher LET charged particles which are known to induce more complex DNA damage compared to X-rays. Consistent with HR deficiency in HSPC observed in our previous study, we noticed here pronounced focal accumulation of 53BP1 after X-ray and carbon ion exposure (intermediate LET) in HSPC versus PBL. For higher LET, 53BP1 foci kinetics was similarly delayed in PBL and HSPC suggesting similar failure to repair complex DNA damage. Data obtained with plasmid reporter systems revealed a dose- and LET-dependent HR increase after X-ray, carbon ion and higher LET exposure, particularly in HR-proficient immortalized and primary lymphocytes, confirming preferential use of conservative HR in PBL for intermediate LET damage repair. HR measured adjacent to the leukemia-associated MLL breakpoint cluster sequence in reporter lines revealed dose dependency of potentially leukemogenic rearrangements underscoring the risk of leukemia-induction by radiation treatment.

γ-H2AX/53BP1/pKAP-1 foci and their linear tracks induced by in vitro exposure to radon and its progeny in human peripheral blood lymphocytes

“…We believed that the high yield of γ-H2AX foci induced by radon exposure, which is dependent on co-localization of γ-H2AX foci with 53BP1 or pKAP-1 foci, is the important reason for the significant increase of residual γ-H2AX foci level even at 12 h after termination of radon exposure. These results are consistent with the literature on that the yield of γ-H2AX foci induced by IR is significantly higher than those of 53BP1 foci and pKAP-1 foci1641. Notably, our finding on the sustained increase of γ-H2AX level induced by radon exposure is supported by other studies.…”

In vitro and in vivo assessment of direct effects of simulated solar and galactic cosmic radiation on human hematopoietic stem/progenitor cells

“…61‐64 In the case of ∼ 1‐2 high-LET iron ion traversals, nearly all of the energy deposited by their tracks and associated δ-ray penumbras involve more limited nuclear volumes and genomic regions located directly along the particle track 65,66 with much higher local ionization densities and resulting DSBs and clustered lesions. 67 HZE ion-induced DSBs have been shown to be more refractory and slower to repair than low LET IR-induced DSBs, with a greater proportion being preferentially repaired by Rad51-mediated homologous recombinational repair (HRR), 68,69 yielding much higher levels of simple and complex chromosomal rearrangements post irradiation. 70 Interestingly, two recent studies demonstrate that HSC have reduced DSB repair capacities compared with mature T-cells.…”

Initial radiation DNA damage observed in prematurely condensed chromosomes of G2-phase human lymphocytes and analytical model of ion tracks

“…As already shown, the quadratic term may result from two different effects. The most important effect is of a biological origin and can be connected with very efficient DNA repair mechanisms leading to CA which strongly depend on the local ionization density and thus on the radiation quality [5,6]. Additionally, quadratic coefficient may be associated with physical processes of ion track overlapping [7,8] and doubling of the locally absorbed dose.…”

“…Additionally, quadratic coefficient may be associated with physical processes of ion track overlapping [7,8] and doubling of the locally absorbed dose. Although, physics concerning interaction of ionizing radiation [9] and the processes of the DNA damage leading to chromosomal aberrations [5,10] are relatively well known, the allencompassing anticipation of the radiobiological outcomes is still missing. The physical models based on Monte Carlo simulations can correctly describe evolution of ion tracks formed in the irradiated tissue by starting with ionization and creation of fast delta electrons which transfer their energy in the next step to the atomic system and finally lead to production of chemically active radicals.…”