Cell-free DNA (cfDNA) is a circulating DNA of nuclear and mitochondrial origin mainly derived from dying cells. Recent studies have shown that cfDNA is a stress signaling DAMP (damage-associated molecular pattern) molecule. We report here that the expression profiles of cfDNA-induced factors NRF2 and NF-κB are distinct depending on the target cell's type and the GC-content and oxidation rate of the cfDNA. Stem cells (MSC) have shown higher expression of NRF2 without inflammation in response to cfDNA. In contrast, inflammatory response launched by NF-κB was dominant in differentiated cells HUVEC, MCF7, and fibroblasts, with a possibility of transition to massive apoptosis. In each cell type examined, the response for oxidized cfDNA was more acute with higher peak intensity and faster resolution than that for nonoxidized cfDNA. GC-rich nonoxidized cfDNA evoked a weaker and prolonged response with proinflammatory component (NF-κB) as predominant. The exploration of apoptosis rates after adding cfDNA showed that cfDNA with moderately increased GC-content and lightly oxidized DNA promoted cell survival in a hormetic manner. Novel potential therapeutic approaches are proposed, which depend on the current cfDNA content: either preconditioning with low doses of cfDNA before a planned adverse impact or eliminating (binding, etc.) cfDNA when its content has already become high.

Rhythmic electrical stimulation of the snail foot leads to sensitization of the defensive reflex. This sensitization has dynamics similar to those of posttetanic potentiation of the amplitude of the acetylcholine-evoked influx current of defensive behavior command neurons in the common snail. It is likely that an increase in the cholinosensitivity of the somatic membrane of defensive behavior command neurons in the common snail may be involved in the mechanism of sensitization of the animal's defensive response. Methiothepin, an antagonist of serotonin receptors, prevented the posttetanic potentiation of the acetylcholine-evoked influx current as well as behavioral sensitization. Serotonin, like methiothepin, also impaired posttetanic potentiation of the acetylcholine-evoked influx current. It is suggested that methiothepin-sensitive serotonin receptors are involved in the postsynaptic mechanism of behavioral sensitization.

In pathology or under damaging conditions, the properties of cell-free DNA (cfDNA) change. An example of such change is GC enrichment, which drastically alters the biological properties of cfDNA. GC-rich cfDNA is a factor of stress signaling, whereas genomic cfDNA is biologically inactive. GC-rich cfDNA stimulates TLR9-MyD88-NF-κB signaling cascade, leading to an increase in proinflammatory cytokine levels in the organism. In addition, GC-rich DNA is prone to oxidation and oxidized cfDNA can stimulate secondary oxidative stress. This article is a review of works dedicated to the investigation of a low-dose ionizing radiation effect, a bystander effect, and the role of cfDNA in both of these processes.

IntroductionMesenchymal stem cells (MSCs) are applied as the therapeutic agents, e.g., in the tumor radiation therapy.Purpose of the StudyTo evaluate the human adipose MSC early response to low-dose ionizing radiation (LDIR).Materials and MethodsWe investigated different LDIR (3, 10, and 50 cGy) effects on reactive oxygen species production, DNA oxidation (marker 8-oxodG), and DNA breaks (marker ɣ H2AX) in the two lines of human adipose MSC. Using reverse transcriptase–polymerase chain reaction, fluorescence-activated cell sorting, and fluorescence microscopy, we determined expression of genes involved in the oxidative stress development (NOX4), antioxidative response (NRF2), antiapoptotic and proapoptotic response (BCL2, BCL2A1, BCL2L1, BIRC2, BIRC3, and BAX1), in the development of the nuclear DNA damage response (DDR) (BRCA1, BRCA2, ATM, and P53). Cell cycle changes were investigated by genes transcription changes (CCND1, CDKN2A, and CDKN1A) and using proliferation markers KI-67 and proliferating cell nuclear antigen (PCNA).ResultsFifteen to 120 min after exposure to LDIR in MSCs, transient oxidative stress and apoptosis of the most damaged cells against the background of the cell cycle arrest were induced. Simultaneously, DDR and an antiapoptotic response were found in other cells of the population. The 10-cGy dose causes the strongest and fastest DDR following cell nuclei DNA damage. The 3-cGy dose induces a less noticeable and prolonged response. The maximal low range dose, 50 cGy, causes a damaging effect on the MSCs.ConclusionTransient oxidative stress and the death of a small fraction of the damaged cells are essential components of the MSC population response to LDIR along with the development of DDR and antiapoptotic response. A scheme describing the early MSC response to LDIR is proposed.

We studied cholinergic component of visceral sensory input to defensive behavior command neurons in edible snail. Nicotinic receptor antagonist tubocurarine and muscarinic receptor antagonist atropine reversibly decreased the amplitude of the total excitatory postsynaptic potential induced by electrostimulation of the peripheral region in the mechanosensory receptor field of command neurons on the surface of internal organs. Our results indicate that acetylcholine is involved in sensory signal transduction from the visceral sac to command neurons of snail parietal ganglia. The subsynaptic membrane of visceral synaptic input contains nicotinic and muscarinic receptors.

The concept of hormesis describes a phenomenon of adaptive response to low-dose ionizing radiation (LDIR). Similarly, the concept of mitohormesis states that the adaptive program in mitochondria is activated in response to minor stress effects. The mechanisms of hormesis effects are not clear, but it is assumed that they can be mediated by reactive oxygen species. Here, we studied effects of LDIR on mitochondria in mesenchymal stem cells. We have found that X-ray radiation at a dose of 10 cGy as well as oxidized fragments of cell-free DNA (cfDNA) at a concentration of 50 ng/mL resulted in an increased expression of a large number of genes regulating the function of the mitochondrial respiratory chain complexes in human mesenchymal stem cells (MSC). Several genes remained upregulated within hours after the exposure. Both X-ray radiation and oxidized cfDNA resulted in upregulation of FIS1 and MFN1 genes, which regulated fusion and fission of mitochondria, within 3–24 h after the exposure. Three hours after the exposure, the number of copies of mitochondrial DNA in cells had increased. These findings support the hypothesis that assumes oxidized cell-free DNA as a mediator of MSC response to low doses of radiation.

Exocytosis inhibitor Exo 1, dynamin inhibitory peptide (inhibitor of endocytosis), and colchicine disturb short-term potentiation of cholinosensitivity of defensive behavior command neurons in edible snail induced by rhythmic electrical orthodromic stimulation. We hypothesize that the short-term potentiation of cholinosensitivity in the extra-synaptic membrane develops due to incorporation of extra cholinoceptors into neuron plasmalemma as a result of enhanced recycling of the internalized cholinoceptors with participation of microtubules.

Фрагменты внеклеточной ДНК (вкДНК) из погибших клеток, как мы показали ранее, могут являться фактором стресс-сигнализации при действии малых доз радиации, и антиапоптотический ответ в мезенхимных стволовых клетках (МСК) при действии малых доз радиации может развиваться посредством участия внеклеточного медиатора передачи сигнала между клетками -фрагментов окисленной вкДНК. Однако не исследованы сигнальные каскады, обеспечивающие эти эффекты. Цель. Изучить влияние малых доз радиации и окисленных фрагментов вкДНК на активацию в МСК генов сигнальных каскадов, регулирующих ответ клеток на повреждение ДНК. Материалы и методы. Мы исследовали влияние малых доз радиации (10 сГр) и фрагментов окисленной вкДНК (в концентрации 50 нг/мл) на активацию в МСК генов сигнальных каскадов, регулирующих ответ клеток на повреждение ДНК. Результаты. Показано, что в МСК при действии малых доз радиации через 15-40 мин активируется транскрипционная активность проапоптотических генов, возрастает уровень апоптоза и в результате гибели части клеток популяции в среде культивирования МСК образуются фрагменты окисленной внеклеточной ДНК. Через 3-72 ч уровень экспрессии генов ING2, HUWE1, TP53, BBC3, NOXA, P53AIP1, BAX, BAK1, MMP7, ENDOG снижается в 1,5-3 раза (p<0,01), что сопровождается повышением уровня экспрессии антиапоптотических генов BCL2, BCL2A1 (Bfl-1/A1), BCL2L1 (BCL-X), BIRC2 (c-IAP1) в 2-4 раза (p<0,001) и, как следствие, снижением уровня апоптоза. Поскольку наблюдается одинаковая регуляция экспрессии генов МСК в ответ на облучение и при действии окисленных фрагментов вкДНК, одним из факторов стресс-сигнализации при действии малых доз радиации могут являться фрагменты вкДНК погибших клеток. Заключение. Показано, что малые дозы радиации и окисленная вкДНК активируют сигнальный путь, регулирующий ответ на повреждение ДНК, что приводит к антиапоптотическому ответу в МСК. Ключевые слова: внеклеточная ДНК, малые дозы ионизирующего излучения, апоптоз.