Oxidized extracellular DNA suppresses nitric oxide production by endothelial NO synthase (eNOS) in human endothelial cells (HUVEC)

The role of extracellular DNA (exDNA) in cellular processes

Nowadays, extracellular DNA or circulating cell-free DNA is considered to be a molecule with clinical applications (diagnosis, prognosis, monitoring of treatment responses, or patient follow-up) in diverse pathologies, especially in cancer. Nevertheless, because of its molecular characteristics, it can have many other functions. This review focuses on the participation of extracellular DNA (exDNA) in fundamental processes such as cell signaling, coagulation, immunity, evolution through horizontal transfer of genetic information, and adaptive response to inflammatory processes. A deeper understanding of its role in each of these processes will allow development of better tools to monitor and control pathologies, as well as helping to generate new therapeutic options, beyond the applicability of DNA in liquid biopsy.

Increased Transfection of the Easily Oxidizable GC-Rich DNA Fragments into the MCF7 Breast Cancer Cell

Objective

Easily oxidizable GC-rich DNA (GC-DNA) fragments accumulate in the cell-free DNA (cfDNA) of patients with various diseases. The human oxidized DNA penetrates the MCF7 breast cancer cells and significantly changes their physiology. It can be assumed that readily oxidizable GC-DNA fragments can penetrate the cancer cells and be expressed.

Methods

MCF7 cells were cultured in the presence of two types of GC-DNA probes: (1) vectors pBR322 and pEGFP and (2) plasmids carrying inserted human rDNA (pBR322-rDNA and pEGFP-rDNA). pEGFP and pEGFP-rDNA contained a CMV promoter and a fluorescent protein gene EGFP. ROS generation rate, accumulation of the DNA probes in MCF7, 8-oxodG content, expression of EGFP and NOX4, and localization of EGFP, NOX4, and 8-oxodG in MCF7 were explored. The applied methods were qPCR, fluorescent microscopy (FM), immunoassay, and flow cytometry (FCA).

Results

When GC-DNA is added to the cell culture medium, it interacts with the cell surface. At the site of GC-DNA contact with the cell, NOX4 is expressed, and ROS level increases. The ROS oxidize the GC-DNA. When using the plasmids pEGFP and pEGFP-rDNA, an increase in the amount of the DNA EGFP, RNA EGFP, and EGFP proteins was detected in the cells. These facts suggest that GC-DNA penetrates the cells and the EGFP gene is expressed. Insertions of the rDNA significantly increase the GC-DNA oxidation degree as well as the rate of plasmid transfection into the cells and the EGFP expression level. In the nucleus, the oxidized GC-rDNA fragments, but not the vectors, are localized within the nucleolus.

Conclusions

GC-rich cfDNA fragments that are prone to oxidation can easily penetrate the cancer cells and be expressed. The cfDNA should become a target for the antitumor therapy.

Agkistrodon acutus-purified protein C activator protects human umbilical vein endothelial cells against H2O2-induced apoptosis

CONTEXT

Recent studies show that the Agkistrodon acutus (Viperidae) (syn. Deinagkistrodon acutus) protein C activator (PCA) treats acute myocardial infarction and ischaemia-reperfusion animal models effectively, while the underlying mechanism remains unknown.

OBJECTIVE

To study the effect of PCA on the injury of human umbilical vein endothelial cells (HUVECs) induced by H₂O₂ and the underlying mechanism.

MATERIALS AND METHODS

Primary cultured HUVECs were pretreated with PCA (20, 40 and 80 μg/mL) for 1 h, then HUVEC apoptosis was induced by 300 μmol/mL H₂O₂. Apoptosis was analyzed by AnnexinV-FITC/PI, and reactive oxygen species (ROS) level was tested by flow cytometry. Colorimetric methods were used to detect the levels of NO and IL-1. In addition, real-time PCR and western blot analyses were used to detect the expression of eNOS and phospho-p38/MAPK.

RESULTS

Morphological changes were induced by H₂O₂ in HUVECs. The cell survival rate was increased by 43.9, 64.0 and 80.6% in each PCA pretreated group (20, 40 and 80 μg/mL) compared to the model group. In each PCA pretreated group, oxidative stress level was also decreased to 54.7, 42.7 and 25.1%. Moreover, the level of IL-1 was decreased to 83.3, 62.2 and 30.7%. The level of NO was increased by 155.9, 232.4 and 317.6%. Apoptosis rate was decreased to 59.0, 47.7 and 32.7%. Phospho-p38 expression was downregulated, but eNOS expression was upregulated.

DISCUSSION AND CONCLUSION

The results suggest that PCA can effectively protect the endothelial cells from injury induced by H₂O₂, which may be associated with antioxidation, upregulation of eNOS and downregulation of p38-MAPK.

Human circulating ribosomal DNA content significantly increases while circulating satellite III (1q12) content decreases under chronic occupational exposure to low-dose gamma- neutron and tritium beta-radiation

A single exposure to ionizing radiation (IR) results in an elevated cell-free DNA (cfDNA) content in the blood plasma. In this case, the cfDNA concentration can be a marker of the cell death in the organism. However, a chronic exposure to a low-dose IR enhances both the endonuclease activity and titer of antibodies to DNA in blood plasma, resulting in a decrease of the total concentration of circulating cfDNA in exposed people. In this case, the total cfDNA concentration should not be considered as a marker of the cell death in an exposed body. We assumed that a pool of the cfDNA circulating in the exposed people contains DNA fragments, which are resistant to a double-strand break formation in the environment of the elevated plasma endonuclease activity, and can be accumulated in the blood plasma. In order to test this hypothesis, we studied the content of GC-rich sequences (69%GC) of the transcribed region of human ribosomal repeat (rDNA), as well as the content of AT-rich repeat (63%AT) of satellite III (1q12) in the cfDNA samples obtained from 285 individuals. We have found that a chronic exposure to gamma-neutron radiation (N=88) and tritium β-radiation (N=88) evokes an increase of the rDNA content (RrDNA index) and a decrease of the satellite III content (RsatIII index) in the circulating cfDNA as compared with the cfDNA of non-exposed people (N=109). Such index that simultaneously displays both the increase of rDNA content and decrease of satellite III content in the cfDNA (RrDNA/RsatIII) can be recommended as a marker of chronic processes in the body that involve the elevated cell death rate and/or increased blood plasma endonuclease activity.

Multiple Ways of cfDNA Reception and Following ROS Production in Endothelial Cells

Oxidized cell-free DNA acts as a stress signal molecule and triggers an adaptive response in human cells. Various membrane DNA recognizing receptors are known as potential sensors for such DNA fragments. In order to clarify which of these sensors are able to interact with cfDNA fragments, circulating in human blood flow in heath and disease, we studied the influence of various cfDNA types on endothelial cells. We incubated these fragments at a physiologically optimal concentration with HUVEC cells for 3-24 h and detected the expression of either TLR9 or AIM2, RIG1 and STING receptors at mRNA and protein levels. We estimated that the activation of both TLR9 and other types of intracellular receptors initiates stress signaling in the endothelium independently. Signal transduction through these receptors activates NOX4 as the main source of ROS production in HUVECs.