Mitochondrial maintenance under oxidative stress depends on mitochondrially localised α-OGG1.

Accumulation of 8-oxoguanine (8-oxoG) in mitochondrial DNA and mitochondrial dysfunction have been observed in cells deficient for the DNA glycosylase OGG1 when exposed to oxidative stress. In human cells, up to eight mRNAs for OGG1 can be generated by alternative splicing and it is still unclear which of them codes for the protein that ensures the repair of 8-oxoG in mitochondria. Here, we show that the α-OGG1 isoform, considered up to now to be exclusively nuclear, has a functional mitochondrial-targeting sequence and is imported into mitochondria. We analyse the sub-mitochondrial localisation of α-OGG1 with unprecedented resolution and show that this DNA glycosylase is associated with DNA in mitochondrial nucleoids. We show that the presence of α-OGG1 inside mitochondria and its enzymatic activity are required to preserve the mitochondrial network in cells exposed to oxidative stress. Altogether, these results unveil a new role of α-OGG1 in the mitochondria and indicate that the same isoform ensures the repair of 8-oxoG in both nuclear and mitochondrial genomes. The activity of α-OGG1 in mitochondria is sufficient for the recovery of organelle function after oxidative stress.

Procedures for Flow Cytometry-Based Sorting of Unfixed Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infected Cells and Other Infectious Agents.

In response to the recent COVID-19 pandemic, many laboratories are involved in research supporting SARS-CoV-2 vaccine development and clinical trials. Flow cytometry laboratories will be responsible for a large part of this effort by sorting unfixed antigen-specific lymphocytes. Therefore, it is critical and timely that we have an understanding of risk assessment and established procedures of infectious cell sorting. Here we present procedures covering the biosafety aspects of sorting unfixed SARS-CoV-2-infected cells and other infectious agents of similar risk level. These procedures follow the ISAC Biosafety Committee guidelines and were recently approved by the National Institutes of Health Institutional Biosafety Committee for sorting SARS-CoV-2-infected cells. © 2020 International Society for Advancement of Cytometry.

Novel Impactor and Microsphere-Based Assay Used to Measure Containment of Aerosols Generated in a Flow Cytometer Cell Sorter.

Today's state-of-the-art cell sorting flow cytometers are equipped with aerosol containment systems designed to evacuate aerosols from the sort chamber during a sort. This biosafety device is especially important when the sort operator is sorting infectious or potentially infections samples. Hence, it is critical to evaluate the performance for this system in normal operation and in "failure" mode to determine the efficacy of containment. In the past decade, the most popular published method for evaluating containment has been the Glo-Germ bead procedure. These highly fluorescent and multisize particles can easily be detected on a microscope slide and enumerated using a fluorescent microscope. Collecting particles on this slide is accomplished using an Aerotech impactor. This sampler collects potentially escaping aerosols from the sort chamber before enumerating any particles. Although the Glo-Germ procedure has been adopted by many labs, there are several drawbacks with the procedure that have limited its adoption by cell sorter laboratories: The Aerotech impactor is a reusable device that requires rigorous cleaning between measurements. The surface area of the collection slide is large and difficult to scan on a fluorescence microscope. These beads produce a wide variation in sizes resulting in inconsistency in flow rates. Here, we describe a novel and replacement method utilizing a Cyclex-d impactor and Dragon Green beads. This method was compared for sensitivity of detection of escaped aerosols with a published method for aerosol detection which utilizes a UV-APS aerodynamic particle sizer and a UV-excitable dye. One of the advantages of the Cyclex-d system is the narrow-defined field of collection as compared to the standard Glo-Germ bead procedure, this means a smaller sampling area is used in the Cyclex-d impactor as compared to the AeroTech impactor. In addition, the sensitivity of detection was found to be better using the Cyclex-d collection device as compared to the standard Glo-Germ bead procedure. © 2018 International Society for Advancement of Cytometry.

Inflammatory cells dynamics control neovascularization and tissue healing after localized radiation induced injury in mice.

Local overexposure to ionizing radiation leads to chronic inflammation, vascular damage and cachexia. Here we investigate the kinetics of inflammatory cells from day (D)1 to D180 after mouse hindlimb irradiation and analyze the role of monocyte (Mo) subsets in tissue revascularization. At D1, we find that Mo and T cells are mobilized from spleen and bone marrow to the blood. New vessel formation during early phase, as demonstrated by ~1.4- and 2-fold increased angiographic score and capillary density, respectively, correlates with an increase of circulating T cells, and Mohi and type 1-like macrophages in irradiated muscle. At D90 vascular rarefaction and cachexia are observed, associated with decreased numbers of circulating Molo and Type 2-like macrophages in irradiated tissue. Moreover, CCR2- and CX3CR1-deficency negatively influences neovascularization. However adoptive transfer of Mohi enhances vessel growth. Our data demonstrate the radiation-induced dynamic inflammatory waves and the major role of inflammatory cells in neovascularization.

Species-targeted sorting and cultivation of commensal bacteria from the gut microbiome using flow cytometry under anaerobic conditions.

BACKGROUND: There is a growing interest in using gut commensal bacteria as "next generation" probiotics. However, this approach is still hampered by the fact that there are few or no strains available for specific species that are difficult to cultivate. Our objective was to adapt flow cytometry and cell sorting to be able to detect, separate, isolate, and cultivate new strains of commensal species from fecal material. We focused on the extremely oxygen sensitive (EOS) species Faecalibacterium prausnitzii and the under-represented, health-associated keystone species Christensenella minuta as proof-of-concept. RESULTS: A BD Influx® cell sorter was equipped with a glovebox that covered the sorting area. This box was flushed with nitrogen to deplete oxygen in the enclosure. Anaerobic conditions were maintained during the whole process, resulting in only minor viability loss during sorting and culture of unstained F. prausnitzii strains ATCC 27766, ATCC 27768, and DSM 17677. We then generated polyclonal antibodies against target species by immunizing rabbits with heat-inactivated bacteria. Two polyclonal antibodies were directed against F. prausnitzii type strains that belong to different phylogroups, whereas one was directed against C. minuta strain DSM 22607. The specificity of the antibodies was demonstrated by sorting and sequencing the stained bacterial fractions from fecal material. In addition, staining solutions including LIVE/DEAD™ BacLight™ Bacterial Viability staining and polyclonal antibodies did not severely impact bacterial viability while allowing discrimination between groups of strains. Finally, we combined these staining strategies as well as additional criteria based on bacterial shape for C. minuta and were able to detect, isolate, and cultivate new F. prausnitzii and C. minuta strains from healthy volunteer's fecal samples. CONCLUSIONS: Targeted cell-sorting under anaerobic conditions is a promising tool for the study of fecal microbiota. It gives the opportunity to quickly analyze microbial populations, and can be used to sort EOS and/or under-represented strains of interest using specific antibodies, thus opening new avenues for culture experiments. Video abstract.

Modulation of astrocyte reactivity improves functional deficits in mouse models of Alzheimer's disease.

Astrocyte reactivity and neuroinflammation are hallmarks of CNS pathological conditions such as Alzheimer's disease. However, the specific role of reactive astrocytes is still debated. This controversy may stem from the fact that most strategies used to modulate astrocyte reactivity and explore its contribution to disease outcomes have only limited specificity. Moreover, reactive astrocytes are now emerging as heterogeneous cells and all types of astrocyte reactivity may not be controlled efficiently by such strategies.Here, we used cell type-specific approaches in vivo and identified the JAK2-STAT3 pathway, as necessary and sufficient for the induction and maintenance of astrocyte reactivity. Modulation of this cascade by viral gene transfer in mouse astrocytes efficiently controlled several morphological and molecular features of reactivity. Inhibition of this pathway in mouse models of Alzheimer's disease improved three key pathological hallmarks by reducing amyloid deposition, improving spatial learning and restoring synaptic deficits.In conclusion, the JAK2-STAT3 cascade operates as a master regulator of astrocyte reactivity in vivo. Its inhibition offers new therapeutic opportunities for Alzheimer's disease.

TNFSF10/TRAIL regulates human T4 effector memory lymphocyte radiosensitivity and predicts radiation-induced acute and subacute dermatitis.

Sensitivity of T4 effector-memory (T4EM) lymphocytes to radiation-induced apoptosis shows heritability compatible with a Mendelian mode of transmission. Using gene expression studies and flow cytometry, we show a higher TNF-Related Apoptosis Inducing Ligand (TRAIL/TNFSF10)mRNA level and a higher level of membrane bound TRAIL (mTRAIL) on radiosensitive compared to radioresistant T4EM lymphocytes. Functionally, we show that mTRAIL mediates a pro-apoptotic autocrine signaling after irradiation of T4EM lymphocytes linking mTRAIL expression to T4EM radiosensitivity. Using single marker and multimarker Family-Based Association Testing, we identified 3 SNPs in the TRAIL gene that are significantly associated with T4EM lymphocytes radiosensitivity. Among these 3 SNPs, two are also associated with acute and subacute dermatitis after radiotherapy in breast cancer indicating that T4EM lymphocytes radiosensitivity may be used to predict response to radiotherapy. Altogether, these results show that mTRAIL level regulates the response of T4EM lymphocytes to ionizing radiation and suggest that TRAIL/TNFSF10 genetic variants hold promise as markers of individual radiosensitivity.

Assessment of human multi-potent hematopoietic stem/progenitor cell potential using a single in vitro screening system.

Hematopoietic stem cells are responsible for the generation of the entire blood system through life. This characteristic relies on their ability to self renew and on their multi-potentiality. Thus quantification of the number of hematopoietic stem cells in a given cell population requires to show both properties in the studied cell populations. Although xenografts models that support human hematopoietic stem cells have been described, such in vivo experimental systems remain restrictive for high throughput screening purposes for example. In this work we developed a conditional tetracycline inducible system controlling the expression of the human NOTCH ligand Delta-like 1 in the murine stromal MS5 cells. We cultured hematopoietic immature cells enriched in progenitor/stem cells in contact with MS5 cells that conditionally express Delta-like 1, in conditions designed to generate multipotential lineage differentiation. We show that upon induction or repression of DL1 expression during co-culture, human immature CD34(+)CD38(-/low)(CD45RA(-)CD90(+)) cells can express their B, T, NK, granulo/monocytic and erythroid potentials in a single well, and at the single cell level. We also document the interference of low NOTCH activation with human B and myelo/erythroid lymphoid differentiation. This system represents a novel tool to precisely quantify human hematopoietic immature cells with both lymphoid and myeloid potentials.

Cellular and molecular effect of MEHP Involving LXRα in human fetal testis and ovary.

BACKGROUND: Phthalates have been shown to have reprotoxic effects in rodents and human during fetal life. Previous studies indicate that some members of the nuclear receptor (NR) superfamilly potentially mediate phthalate effects. This study aimed to assess if expression of these nuclear receptors are modulated in the response to MEHP exposure on the human fetal gonads in vitro. METHODOLOGY/PRINCIPAL FINDINGS: Testes and ovaries from 7 to 12 gestational weeks human fetuses were exposed to 10(-4)M MEHP for 72 h in vitro. Transcriptional level of NRs and of downstream genes was then investigated using TLDA (TaqMan Low Density Array) and qPCR approaches. To determine whether somatic or germ cells of the testis are involved in the response to MEHP exposure, we developed a highly efficient cytometric germ cell sorting approach. In vitro exposure of fetal testes and ovaries to MEHP up-regulated the expression of LXRα, SREBP members and of downstream genes involved in the lipid and cholesterol synthesis in the whole gonad. In sorted testicular cells, this effect is only observable in somatic cells but not in the gonocytes. Moreover, the germ cell loss induced by MEHP exposure, that we previously described, is restricted to the male gonad as oogonia density is not affected in vitro. CONCLUSIONS/SIGNIFICANCE: We evidenced for the first time that phthalate increases the levels of mRNA for LXRα, and SREBP members potentially deregulating lipids/cholesterol synthesis in human fetal gonads. Interestingly, this novel effect is observable in both male and female whereas the germ cell apoptosis is restricted to the male gonad. Furthermore, we presented here a novel and potentially very useful flow cytometric cell sorting method to analyse molecular changes in germ cells versus somatic cells.