Biology subjects

Behrendt, R.

Publications and source records attributed to Behrendt, R..

5 recordsLinked to original sources

bioRxiv2022

Clearance of genome-damaged cells from the hematopoietic system via p53 without contribution by the cGAS/STING axis

Cell-intrinsic response patterns control risks arising from genome-damage, preventing malignant transformation. The DNA sensor cyclic-GMP-AMP synthase (cGAS) has emerged as a new principle detecting genome damage, as it can be triggered by aberrant self-DNA. Stimulator of interferon genes (STING)-activation downstream of cGAS can drive cells into senescence or cell death and induces antiproliferative type I interferon (IFN) and pro-apoptotic tumor necrosis factor responses. Herein, we investigated how DNA damage-driven activation of cGAS/STING signaling impacts on hematopoiesis. Defective ribonucleotide excision repair (RER) in the hematopoietic system caused chromosomal instability as well as robust activation of the cGAS/STING/IFN axis, and compromised hematopoietic stem cell function, resulting in cytopenia and ultimately leukemia. Whereas loss of p53 largely rescued RER-deficient hematopoiesis at the cost of further accelerated leukemogenesis, the additional inactivation of cGAS, STING or type I IFN signaling had no detectable effect on blood cell generation and leukemia development. Moreover, cGAS-deficient hematopoiesis showed unaltered responses to spontaneous or acute DNA damage. Our data demonstrate that the cGAS/STING pathway is dispensable for the hematopoietic system coping with chronic or acute DNA damage and does not protect against leukemic transformation in the absence of RER.

cell biology↗

bioRxiv2022

Validation of an RNase H2 activity assay suitable for clinical screening

As the key enzyme mediating ribonucleotide excision repair, RNase H2 is essential for the removal of single ribonucleotides from DNA in order to prevent genome damage. Loss of RNase H2 activity directly contributes to the pathogenesis of autoinflammatory and autoimmune diseases and might further play a role in ageing and neurodegeneration. Moreover, RNase H2 activity is a potential diagnostic and prognostic marker in several types of cancer. Until today, no method for quantification of RNase H2 activity has been validated for the clinical setting. Herein, validation and benchmarks of a FRET-based whole-cell lysate RNase H2 activity assay are presented, including standard conditions and procedures to calculate standardized RNase H2 activity. Spanning a wide working range, the assay is applicable to various human cell or tissue samples with overall methodological assay variability from 8.6% to 16%. The assay readily detected reduced RNase H2 activity in lymphocytes of a patient with systemic sclerosis carrying a RNASEH2C variant. Implementation of larger control groups will help to assess the diagnostic and prognostic value of clinical screening for RNase H2 activity in the future.

immunology↗

bioRxiv2022

cGAS/STING-DEPENDENT SENSING OF ENDOGENOUS RNA

Defects in nucleic acid metabolizing enzymes lead to spontaneous but selective activation of either cGAS/STING or RIG-like receptor (RLR) signaling, causing a pathogenic type I interferon response and inflammatory diseases. In these pathophysiological conditions, cGAS-driven IFN production is linked to spontaneous DNA damage. Physiological, or tonic, IFN signaling on the other hand is essential to functionally prime nucleic acid sensing pathways. Here we show that low-level chronic DNA damage in mice lacking the Aicardi-Goutieres syndrome gene SAMHD1 reduced tumor-free survival when crossed to a p53-deficient, but not to DNA mismatch repair-deficient background. Increased DNA damage did not result in higher levels of type I interferon. Instead, we found that the chronic interferon response in SAMHD1-deficient mice was driven by the MDA5/MAVS pathway but required functional priming through the cGAS/STING pathway. Our work positions cGAS/STING upstream of tonic IFN signaling and highlights an important role of the pathway in physiological and pathophysiological innate immune priming. SummaryLoss of the dNTPase and DNA repair enzyme SAMHD1 is associated with cancer and causes systemic autoimmunity. We show transformation-promoting spontaneous DNA damage and MDA5-driven but cGAS/STING-dependent chronic type I interferon production in SAMHD1-deficient mice.

immunology↗

bioRxiv2022

Nuclear envelope disruption triggers hallmarks of aging in lung alveolar macrophages

Aging is characterized by gradual immune dysfunction and increased risk for many diseases, including respiratory infections. Genomic instability is thought to play a central role in the aging process but the mechanisms that damage nuclear DNA in aging are insufficiently defined. Cells that migrate or reside within confined environments experience forces applied to their nucleus, leading to transient nuclear envelope (NE) ruptures. NE ruptures are associated with DNA damage, and Lamin A/C is required to limit these events. Here, we show that Lamin A/C protects lung alveolar macrophages from NE rupture and hallmarks of aging. Lamin A/C ablation in immune cells results in a selective depletion of lung alveolar macrophages (AM) and a heightened susceptibility to influenza infection. Lamin A/C-deficient AM that persist display constitutive nuclear envelope rupture marks, DNA damage and p53-dependent senescence. In wild-type mice, we found that AM migrate within constricted spaces in vivo, at heights that induce NE rupture and DNA damage. AM from aged wild-type mice and from Lamin A/C-deficient mice share an upregulated lysosomal signature with CD63 expression, and we find that CD63 is required to clear damaged DNA in macrophages. We propose that induction of genomic instability by NE disruption represents a mechanism of aging in alveolar macrophages.

immunology↗

bioRxiv2020

Filaggrin deficient mice have a lower threshold for cutaneous allergen sensitization but do not develop spontaneous skin inflammation or atopy

Defects of filaggrin (FLG) compromise epidermal barrier function and represent an important known genetic risk factor for atopic dermatitis (AD), but also for systemic atopy, including allergic sensitization and asthma. The flaky tail mouse model, widely used to address mechanisms of atopy induction by barrier-defective skin, harbors two mutations that affect the skin barrier, the mutation Flgft, resulting in near-complete loss of FLG expression, and the matted mutation inactivating transmembrane protein 79 (Tmem79). Upon separation of the two mutant loci, which are closely linked on chromosome 3, mice defective only for Tmem79 featured pronounced dermatitis and systemic atopy. Upon extensive backcross to BALB/c, also Flgft/ft mice (assumed to be wild type for Tmem79), developed AD-like dermatitis and reproduced the human atopic march, with high IgE levels and spontaneous asthma, suggesting a key role for functional Flg in protection from atopy also in mice. In contrast, BALB/c mice congenic for a targeted Flg knock out mutation did not develop skin inflammation or atopy. To resolve this discrepancy, we generated Flg-deficient mice on a pure BALB/c background by inactivating the Flg gene in BALB/c embryos. These animals feature an ichthyosis phenotype, but do not develop spontaneous dermatitis or systemic atopy. We sequenced the genome of the atopic Flgft BALB/c congenics and discovered that they were unexpectedly homozygous for the atopy-causing Tmem79matted mutation. In summary, we show that Flg-deficiency does not cause atopy in mice. This finding is in line with lack of atopic disease in a fraction of Ichthyosis vulgaris patients carrying two FLG null alleles. However, absence of FLG may promote and modulate dermatitis caused by other genetic barrier defects, as skin inflammation in Tmem79ma/maFlgft/ft BALB/c congenics is qualitatively different compared to Tmem79ma/ma mice.

immunology↗