MRE11A: a novel negative regulator of human DNA mismatch repair.

BACKGROUND: DNA mismatch repair (MMR) is a highly conserved pathway that corrects DNA replication errors, the loss of which is attributed to the development of various types of cancers. Although well characterized, MMR factors remain to be identified. As a 3'-5' exonuclease and endonuclease, meiotic recombination 11 homolog A (MRE11A) is implicated in multiple DNA repair pathways. However, the role of MRE11A in MMR is unclear. METHODS: Initially, short-term and long-term survival assays were used to measure the cells' sensitivity to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Meanwhile, the level of apoptosis was also determined by flow cytometry after MNNG treatment. Western blotting and immunofluorescence assays were used to evaluate the DNA damage within one cell cycle after MNNG treatment. Next, a GFP-heteroduplex repair assay and microsatellite stability test were used to measure the MMR activities in cells. To investigate the mechanisms, western blotting, the GFP-heteroduplex repair assay, and chromatin immunoprecipitation were used. RESULTS: We show that knockdown of MRE11A increased the sensitivity of HeLa cells to MNNG treatment, as well as the MNNG-induced DNA damage and apoptosis, implying a potential role of MRE11 in MMR. Moreover, we found that MRE11A was largely recruited to chromatin and negatively regulated the DNA damage signals within the first cell cycle after MNNG treatment. We also showed that knockdown of MRE11A increased, while overexpressing MRE11A decreased, MMR activity in HeLa cells, suggesting that MRE11A negatively regulates MMR activity. Furthermore, we show that recruitment of MRE11A to chromatin requires MLH1 and that MRE11A competes with PMS2 for binding to MLH1. This decreases PMS2 levels in whole cells and on chromatin, and consequently comprises MMR activity. CONCLUSIONS: Our findings reveal that MRE11A is a negative regulator of human MMR.

Isofraxidin attenuates dextran sulfate sodium-induced ulcerative colitis through inhibiting pyroptosis by upregulating Nrf2 and reducing reactive oxidative species.

BACKGROUND: Ulcerative colitis (UC), a non-specific gastrointestinal disease, is commonly managed with aminosalicylic acids and immunosuppressive agents to control inflammation and relieve symptoms, despite frequent relapses. Isofraxidin is a coumarin compound extracted from traditional Chinese medicine, exhibiting anti-inflammatory and antioxidant properties; however, its alleviating effect on UC remains unclear. Therefore, we investigated the mechanism of isofraxidin in lipopolysaccharide (LPS)-induced cell inflammation in human intestinal epithelial cell (HIEC) and human colorectal adenocarcinoma cells (Caco-2), as well as in dextran sulfate sodium (DSS)-induced UC in mice. METHODS: We established colitis models in HIEC and Caco-2 cells and mice with LPS and DSS, respectively. Additionally, NLRP3 knockout mice and HIEC cells transfected with NLRP3 silencing gene and ML385 illustrated the role of isofraxidin in pyroptosis and oxidative stress. Data from cells and mice analyses were subjected to one-way analysis of variance or a paired t-test. RESULTS: Isofraxidin significantly alleviated LPS-induced cell inflammation and reduced lactic dehydrogenase release. Isofraxidin also reversed DSS- or LPS-induced pyroptosis in vivo and in vitro, increasing the expression of pyroptosis-related proteins. Moreover, isofraxidin alleviated oxidative stress induced by DSS or LPS, reducing reactive oxidative species (ROS), upregulation nuclear factor erythroid 2-related factor 2 (Nrf2), and promoting its entry into the nucleus. Mechanistically, ML385 reversed the inhibitory effect of isofraxidin on ROS and increased pyroptosis. CONCLUSION: Isofraxidin can inhibit pyroptosis through upregulating Nrf2, promoting its entry into the nucleus, and reducing ROS, thereby alleviating DSS-induced UC. Our results suggest isofraxidin as a promising therapeutic strategy for UC treatment.

Quercetin alleviates lipopolysaccharide­induced acute lung injury by inhibiting ferroptosis via the Sirt1/Nrf2/Gpx4 pathway.

Acute lung injury (ALI) causes high morbidity and mortality rates in critically ill patients, and there are currently no effective therapeutic drugs. Ferroptosis is a newly discovered mode of regulated cell death that contributes to the progression of ALI. Quercetin possesses anti­inflammatory and antioxidant properties. However, whether quercetin can protect against lipopolysaccharide (LPS)­induced ALI by inhibiting ferroptosis and its underlying mechanisms remains unclear. The present study evaluated the protective effects of quercetin and underlying molecular mechanisms in LPS­induced ALI by establishing an ALI mouse model and an alveolar epithelial cell injury model via treatment of the mice or alveolar epithelial cells with LPS. Mouse lung injury was assessed by evaluating the histological lung injury score, bronchoalveolar lavage fluid cell count and inflammatory cytokine levels; alveolar epithelial cell injury was assessed by Cell counting kit­8, lactate dehydrogenase and EDU assays; and ferroptosis was assessed by detecting the changes in the levels of malondialdehyde, glutathione, iron, glutathione peroxidase 4 (Gpx4) and 4­hydroxynonenal in vivo and vitro. The present study indicated that quercetin effectively ameliorated LPS­induced ALI in the mouse model by reducing histopathological changes, proinflammatory cytokine release and reactive oxygen species generation and inhibiting ferroptosis. Quercetin significantly decreased ferroptosis and improved the proliferative ability of LPS­treated alveolar epithelial cells. Additionally, it was demonstrated that quercetin markedly enhanced the alveolar epithelial barrier, as evidenced by the upregulation of tight junction protein expression both in vivo and in vitro. Mechanistically, quercetin effectively activated the sirtuin 1 (Sirt1)/nuclear factor erythroid 2­related factor 2 (Nrf2)/Gpx4 signaling pathway, and targeted in vivo inhibition or in vitro knockdown of Sirt1 significantly reduced the anti­ferroptotic functions of quercetin. In conclusion, the results demonstrated that quercetin exerts its therapeutic effects against LPS­induced ALI by inhibiting ferroptosis via the activation of the Sirt1/Nrf2/Gpx4 signaling pathway.

Downregulations of CD36 and Calpain-1, Inflammation, and Atherosclerosis by Simvastatin in Apolipoprotein E Knockout Mice.

BACKGROUND: In the previous in vitro study, we found that simvastatin decreased the protein expression of CD36, the scavenger receptor, and calpain-1, the Ca2+-sensitive cysteine protease, in oxidized low-density lipoprotein (oxLDL)-treated macrophages. In this in vivo study, we investigated whether simvastatin downregulates the expression of CD36 and calpain-1 and inhibits the inflammation and atherosclerosis in apolipoprotein E knockout (ApoE KO) mice. METHODS: Twenty male 6-week-old ApoE KO mice were divided into 2 groups: the ApoE KO group and the ApoE KO + simvastatin (ApoE KO + Sim) group. Atherosclerotic lesions were evaluated and the expressions of CD68, CD36, and calpain-1 in aorta were examined. RESULTS: Simvastatin inhibited the atherosclerotic lesion in ApoE KO mice. In addition, simvastatin reduced the contents of oxLDL, thiobarbituric acid reactive substances, interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in serum, decreased the mRNA and protein expressions of CD36 and reduced the mRNA expression of TNF-α and IL-6 in the aortas. Furthermore, simvastatin reduced the calpain activity and the protein expression of calpain-1 in the aorta. CONCLUSION: The results suggested that the attenuation of atherosclerotic lesions in ApoE KO mice by simvastatin might be associated with the downregulations of CD36 and calpain-1 and with inflammation.

Transfusion-associated graft-versus-host-disease: case report and review of literature.

Transfusion-associated graft-versus-host disease (GVHD) is a rare condition that can occur after receipt of any cellular blood component with viable lymphocytes. Pathogenesis depends on immunocompetent donor T lymphocytes and a host immune system unable to clear donor cells before they proliferate, engraft, and attack host cells. Unlike bone marrow transplantation-associated GVHD, transfusion-associated disease destroys marrow stem cells early in the course of the disease, resulting in pancytopenia contributing to a fulminant clinical course and nearly 100% mortality. Transfusion-associated disease may be diagnosed late or completely missed; thus, true incidence rates are uncertain. We report our experience with an oncology patient who developed transfusion-associated GVHD. This report also reviews the literature to discuss established GVHD risk factors as well as provide recommendations for standardized reporting to better understand incidence rates and possible risk factors. This information would allow individual physicians and blood bank associations to make more informed decisions on the use of irradiated blood products.

[Chronic myeloid leukemia onset with marked thrombocythemia].

This study was aimed to investigate the clinical, pathological and biological features of a special case of chronic myeloid leukemia (CML) with marked thrombocythemic onset. The morphological changes of cells were analyzed by using bone marrow smear and biopsy; Ph chromosome, a specific marker of CML, was assayed by conventional chromosomal analysis and fluorescence in situ hybridization, bcr/abl fusion gene was detected by reverse transcription-polymerase chain reaction. The results indicated that CML mimicked essential thrombocythemia (ET) at presentation was relatively rare and might be misdiagnosed as ET, bone marrow smear and biopsy revealed, marked thrombocytosis and moderate leukocytosis; RT-PCR, FISH and conventional chromosomal analysis demonstrated the existence of Ph chromosome and bcr/abl fusion gene. This special CML could progress into accelerated phase or blast crisis. The megakaryocytes in Ph+ ET were smaller than normal ones and had typically hypolobulated round nuclei. Patients diagnosed as Ph+ ET might progress into CML and showed a high tendency to myelofibrosis and blastic transformation. It is concluded that the value of routine cytogenetical and molecular biological analysis in diagnosis for potential CML cases, which mimicked ET as in this presentation, is very distinctive, and the importance is magnified by the recent availability of imatinib, a specific inhibitor of the bcr/abl tyrosine kinase produced by the Philadelphia chromosome. Every case of "ET" should be tested for the Philadelphia chromosome and bcr/abl transcript.