Ionizing radiation induces long-term senescence in endothelial cells through mitochondrial respiratory complex II dysfunction and superoxide generation

Abstract

Ionizing radiation causes oxidative stress, leading to acute and late cellular responses. We previously demonstrated that irradiation of non-proliferating endothelial cells, as observed in normal tissues, induces early apoptosis, which can be inhibited by pretreatment with Sphingosine-1-Phosphate. We now propose to better characterize the long-term radiation response of endothelial cells by studying the molecular pathways associated with senescence and its link with acute apoptosis. First, senescence was validated in irradiated quiescent microvascular HMVEC-L in a dose- and time-dependent manner by SA β-galactosidase staining, p16 and p21 expression, pro-inflammatory IL-8 secretion and DNA damage response activation. This premature aging was induced independently of Sphingosine 1-Phosphate treatment, supporting its non-connection with acute IR-induced apoptosis. Then, senescence under these conditions showed persistent activation of p53 pathway and mitochondrial dysfunctions, characterized by O2·- generation, inhibition of respiratory complex II activity and over-expression of SOD2 and GPX1 detoxification enzymes. Senescence was significantly inhibited by treatment with pifithrin-α, a p53 inhibitor, or by MnTBAP, a superoxide dismutase mimetic, validating those molecular actors in IR-induced endothelial cell aging. However, MnTBAP, but not pifithrin-α, was able to limit superoxide generation and to rescue the respiratory complex II activity. Furthermore, MnTBAP was not modulating p53 up-regulation, suggesting that IR-induced senescence in quiescent endothelial cells is provided by at least 2 different pathways dependent of the mitochondrial oxidative stress response and the p53 activation. Further characterization of the actors involved in the respiratory complex II dysfunction will open new pharmacological strategies to modulate late radiation toxicity.

Residual γH2AX foci induced by low dose x-ray radiation in bone marrow mesenchymal stem cells do not cause accelerated senescence in the progeny of irradiated cells

“…Indeed, we did not observe increased rates of γН2АХ foci at passages 3 and 5 after irradiation, implying that irradiated MSCs (at least at the doses used here) do not transmit the residual γH2AX foci through the cell divisions, as described by Vaurijoux et al [ 71 ]. At the same time the observed high rates of γН2АХ foci in the progeny (passages 8 and 11) of 1000 mGy-exposed cells is consistent with radiation-induced genome instability [ 72 , 73 ] or accelerated cellular senescence [ 74 , 75 ]. Genome instability and senescence are not necessarily linked.…”

Intimate Relations—Mitochondria and Ageing

“…In a separate study, quantitative mass spectrometry in mitochondria isolated from the brain of 5, 12 and 24 month old mice revealed changes in the expression of proteins involved in catabolic pathways and generation of metabolites, further highlighting that age-specific metabolic demands may influence the patterns of protein synthesis [ 25 ]. The induction of senescence (discussed more fully later) has also been linked to deterioration of mitochondrial OXPHOS [ 28 , 29 , 30 ].…”

Rosiglitazone Protects Endothelial Cells From Irradiation-Induced Mitochondrial Dysfunction

“…Experiments using ApoE −/− mice which harbor a polymerase gamma mutation (that makes them more prone to accumulate mtDNA mutations) revealed that elevated aortic mtDNA damage was associated with an increased atherosclerotic plaque size, thus providing direct causal evidence (Yu et al, 2013). Moreover, a range of studies have demonstrated the presence of changes in mitochondrial number, structure and function after exposure of different types of cells and tissues to high (5-20 Gy) doses of ionizing radiation, indicating induction of mitochondrial dysfunction (Pandey et al, 2006;Nugent et al, 2007;Dayal et al, 2009;Hu et al, 2017;Lafargue et al, 2017). However, findings specifically focusing on the effect of ionizing radiation exposure on endothelial mitochondria are scarce.…”