R-loops trigger the release of cytoplasmic ssDNAs leading to chronic inflammation upon DNA damage

How DNA damage leads to chronic inflammation and tissue degeneration with aging remains to be fully resolved. Here, we show that DNA damage leads to cellular senescence, fibrosis, loss-of-tissue architecture, and chronic pancreatitis in mice with an inborn defect in the excision repair cross complementation group 1 (Ercc1) gene. We find that DNA damage-driven R-loops causally contribute to the active release and buildup of single-stranded DNAs (ssDNAs) in the cytoplasm of cells triggering a viral-like immune response in progeroid and naturally aged pancreata. To reduce the proinflammatory load, we developed an extracellular vesicle (EV)-based strategy to deliver recombinant S1 or ribonuclease H nucleases in inflamed Ercc1(−/−) pancreatic cells. Treatment of Ercc1(−/−) animals with the EV-delivered nuclease cargo eliminates DNA damage-induced R-loops and cytoplasmic ssDNAs alleviating chronic inflammation. Thus, DNA damage-driven ssDNAs causally contribute to tissue degeneration, Ercc1(−/−) paving the way for novel rationalized intervention strategies against age-related chronic inflammation

Tissue-infiltrating macrophages mediate an exosome-based metabolic reprogramming upon DNA damage

DNA damage and metabolic disorders are intimately linked with premature disease onset but the underlying mechanisms remain poorly understood. Here, we show that persistent DNA damage accumulation in tissue-infiltrating macrophages carrying an ERCC1-XPF DNA repair defect (Er1(F/-)) triggers Golgi dispersal, dilation of endoplasmic reticulum, autophagy and exosome biogenesis leading to the secretion of extracellular vesicles (EVs) in vivo and ex vivo. Macrophage-derived EVs accumulate in Er1(F/-) animal sera and are secreted in macrophage media after DNA damage. The Er1(F/-) EV cargo is taken up by recipient cells leading to an increase in insulin-independent glucose transporter levels, enhanced cellular glucose uptake, higher cellular oxygen consumption rate and greater tolerance to glucose challenge in mice. We find that high glucose in EV-targeted cells triggers pro-inflammatory stimuli via mTOR activation. This, in turn, establishes chronic inflammation and tissue pathology in mice with important ramifications for DNA repair-deficient, progeroid syndromes and aging

Ablation of CNTN2+Pyramidal Neurons During Development Results in Defects in Neocortical Size and Axonal Tract Formation

Corticothalamic axons express Contactin-2 (CNTN2/TAG-1), a neuronal recognition molecule of the immunoglobulin superfamily involved in neurogenesis, neurite outgrowth, and fasciculation. TAG-1, which is expressed transiently by cortical pyramidal neurons during embryonic development, has been shown to be fundamental for axonal recognition, cellular migration, and neuronal proliferation in the developing cortex. Although Tag-1(-/-) mice do not exhibit any obvious defects in the corticofugal system, the role of TAG-1+ neurons during the development of the cortex remains elusive. We have generated a mouse model expressing EGFP under the Tag-1 promoter and encompassing the coding sequence of Diptheria Toxin subunit A (DTA) under quiescence with no effect on the expression of endogenous Tag-1. We show that while the line recapitulates the expression pattern of the molecule, it highlights an extended expression in the forebrain, including multiple axonal tracts and neuronal populations, both spatially and temporally. Crossing these mice to the Emx1-Cre strain, we ablated the vast majority of TAG-1+ cortical neurons. Among the observed defects were a significantly smaller cortex, a reduction of corticothalamic axons as well as callosal and commissural defects. Such defects are common in neurodevelopmental disorders, thus this mouse could serve as a useful model to study physiological and pathophysiological cortical development

XPF interacts with TOP2B for R-loop processing and DNA looping on actively transcribed genes

Co-transcriptional RNA-DNA hybrids can not only cause DNA damage threatening genome integrity but also regulate gene activity in a mechanism that remains unclear. Here, we show that the nucleotide excision repair factor XPF interacts with the insulator binding protein CTCF and the cohesin subunits SMC1A and SMC3, leading to R-loop-dependent DNA looping upon transcription activation. To facilitate R-loop processing, XPF interacts and recruits with TOP2B on active gene promoters, leading to double-strand break accumulation and the activation of a DNA damage response. Abrogation of TOP2B leads to the diminished recruitment of XPF, CTCF, and the cohesin subunits to promoters of actively transcribed genes and R-loops and the concurrent impairment of CTCF-mediated DNA looping. Together, our findings disclose an essential role for XPF with TOP2B and the CTCF/cohesin complex in R-loop processing for transcription activation with important ramifications for DNA repair-deficient syndromes associated with transcription-associated DNA damage

Tissue-infiltrating macrophages mediate an exosome-based metabolic reprogramming upon DNA damage

DNA damage and metabolic disorders are intimately linked with premature disease onset but the underlying mechanisms remain poorly understood. Here, we show that persistent DNA damage accumulation in tissue-infiltrating macrophages carrying an ERCC1-XPF DNA repair defect (Er1(F/-)) triggers Golgi dispersal, dilation of endoplasmic reticulum, autophagy and exosome biogenesis leading to the secretion of extracellular vesicles (EVs) in vivo and ex vivo. Macrophage-derived EVs accumulate in Er1(F/-) animal sera and are secreted in macrophage media after DNA damage. The Er1(F/-) EV cargo is taken up by recipient cells leading to an increase in insulin-independent glucose transporter levels, enhanced cellular glucose uptake, higher cellular oxygen consumption rate and greater tolerance to glucose challenge in mice. We find that high glucose in EV-targeted cells triggers pro-inflammatory stimuli via mTOR activation. This, in turn, establishes chronic inflammation and tissue pathology in mice with important ramifications for DNA repair-deficient, progeroid syndromes and aging

Tissue-infiltrating macrophages mediate an exosome-based metabolic reprogramming upon DNA damage

DNA damage and metabolic disorders are intimately linked with premature disease onset but the underlying mechanisms remain poorly understood. Here, we show that persistent DNA damage accumulation in tissue-infiltrating macrophages carrying an ERCC1-XPF DNA repair defect (Er1(F/-)) triggers Golgi dispersal, dilation of endoplasmic reticulum, autophagy and exosome biogenesis leading to the secretion of extracellular vesicles (EVs) in vivo and ex vivo. Macrophage-derived EVs accumulate in Er1(F/-) animal sera and are secreted in macrophage media after DNA damage. The Er1(F/-) EV cargo is taken up by recipient cells leading to an increase in insulin-independent glucose transporter levels, enhanced cellular glucose uptake, higher cellular oxygen consumption rate and greater tolerance to glucose challenge in mice. We find that high glucose in EV-targeted cells triggers pro-inflammatory stimuli via mTOR activation. This, in turn, establishes chronic inflammation and tissue pathology in mice with important ramifications for DNA repair-deficient, progeroid syndromes and aging