Mesenchymal stromal cells having inactivated RB1 survive following low irradiation and accumulate damaged DNA: Hints for side effects following radiotherapy

Abstract

Following radiotherapy, bone sarcomas account for a significant percentage of recurring tumors. This risk is further increased in patients with hereditary retinoblastoma that undergo radiotherapy. We analyzed the effect of low and medium dose radiation on mesenchymal stromal cells (MSCs) with inactivated RB1 gene to gain insights on the molecular mechanisms that can induce second malignant neoplasm in cancer survivors.MSC cultures contain subpopulations of mesenchymal stem cells and committed progenitors that can differentiate into mesodermal derivatives: adipocytes, chondrocytes, and osteocytes. These stem cells and committed osteoblast precursors are the cell of origin in osteosarcoma, and RB1 gene mutations have a strong role in its pathogenesis. Following 40 and 2000 mGy X-ray exposure, MSCs with inactivated RB1 do not proliferate and accumulate high levels of unrepaired DNA as detected by persistence of gamma-H2AX foci. In samples with inactivated RB1 the radiation treatment did not increase apoptosis, necrosis or senescence versus untreated cells. Following radiation, CFU analysis showed a discrete number of cells with clonogenic capacity in cultures with silenced RB1.We extended our analysis to the other members of retinoblastoma gene family: RB2/P130 and P107. Also in the MSCs with silenced RB2/P130 and P107 we detected the presence of cells with unrepaired DNA following X-ray irradiation. Cells with unrepaired DNA may represent a reservoir of cells that may undergo neoplastic transformation. Our study suggests that, following radiotherapy, cancer patients with mutations of retinoblastoma genes may be under strict controls to evaluate onset of secondary neoplasms following radiotherapy.

Impact of lysosomal storage disorders on biology of mesenchymal stem cells: Evidences from in vitro silencing of glucocerebrosidase (GBA) and alpha‐galactosidase A (GLA) enzymes

“…ATM activity is finely regulated to avoid the activation of the DNA damage response in the absence of damage, as well as to allow rapid cessation of the signal once DNA damage sites have been recognized, regardless of whether they have been properly repaired. At the same time, gamma‐H2AX can remain bound to unrepaired DNA, as suggested by kinetics analysis of gamma‐H2AX clearance due to DNA‐damaging agents (Alessio et al, , ; Fu et al, ; Kao et al, ). Rodier and Campisi (2011) demonstrated evidence that persistent unrepaired DNA foci can trigger senescence by showing that persistent foci of damaged DNA, termed DNA‐SCARS , sustain damage‐induced senescence growth arrest.…”

Stress and stem cells: adult Muse cells tolerate extensive genotoxic stimuli better than mesenchymal stromal cells

“…Specific stress responses imply a correct DNA repair to completely recover performances of damaged cells [ 9 ]. Alternatively, cells harboring unrepairable damages may enter apoptosis or senescence [ 10 , 11 ].…”

γH2AX, 53BP1 and Rad51 protein foci changes in mesenchymal stem cells during prolonged X-ray irradiation

“…MSCs are considered to be relatively radioresistant in comparison to radiosensitive hematopoietic stem cells, mostly due to the activity of DNA DSBs repair pathways [ 27 ]. Therefore, MSCs can survive irradiation otherwise lethal to hematopoietic stem cells and can, in some cases, undergo neotransformation [ 28 ]. However, it is unknown how DNA DSBs are formed and repaired in these cells upon prolonged radiation exposures.…”