The role of polymerase η in protecting against genome instability and telomere defects caused by the generation of environmentally relevant DNA lesions

Telomeres, the protective caps at chromosome ends, shorten with age in most human cell types, but may be shortened prematurely by DNA damaging agents. Defective telomeres contribute to aging-related diseases and may give rise to genomic alterations implicated in carcinogenesis. Translesion DNA synthesis is a critical cellular mechanism that ensures progression of DNA replication forks, most notably, in the face of bulky DNA lesions. Numerous environmental exposures generate bulky lesions, such as ultraviolet (UV) light and hexavalent chromium (Cr(VI)). Translesion synthesis polymerase η’s (polη) role in protecting against UV-induced lesions in the genome has been extensively documented, but its role at telomeres is unknown. Additionally, UV-induced lesions have been shown to form at telomeres. Chronic inhalation of Cr(VI) induces respiratory diseases associated with aging and telomere dysfunction, including pulmonary fibrosis and cancers, and our previous work established that Cr(VI) causes telomere damage. However, the mechanism(s) by which environmental genotoxicants promote telomere loss and defects is unknown. We investigated roles for polη in preserving telomeres following acute physical UVC exposure and chronic chemical Cr(VI) exposure. Similar to its role in protecting against UV-induced DNA damage, we report that polη protects against cytotoxicity and DNA replication stress caused by Cr(VI). Our study supports a novel role for translesion DNA synthesis in preserving telomeres after UVC and Cr(VI) exposure and genotoxic stress. We uncover a mechanism by which environmental genotoxicants alter telomere integrity, and a fundamental cellular pathway that preserves telomere function in the face of genotoxic replication stress. Telomere alterations and dysfunction have been shown to impact human health. This research is significant and relevant to public health because knowledge gained will be useful for designing intervention therapies that preserve telomeres in human populations following exposure to environmental genotoxicants. The hope is that preventative measures will inhibit or delay diseases and pathologies related to telomere defects

Spontaneous DNA damage to the nuclear genome promotes senescence, T redox imbalance and aging

Accumulation of senescent cells over time contributes to aging and age-related diseases. However, what drives senescence in vivo is not clear. Here we used a genetic approach to determine if spontaneous nuclear DNA damage is sufficient to initiate senescence in mammals. Ercc1-/Δ mice with reduced expression of ERCC1-XPF endonuclease have impaired capacity to repair the nuclear genome. Ercc1-/Δ mice accumulated spontaneous, oxidative DNA damage more rapidly than wild-type (WT) mice. As a consequence, senescent cells accumulated more rapidly in Ercc1-/Δ mice compared to repair-competent animals. However, the levels of DNA damage and senescent cells in Ercc1-/Δ mice never exceeded that observed in old WT mice. Surprisingly, levels of reactive oxygen species (ROS) were increased in tissues of Ercc1-/Δ mice to an extent identical to naturally-aged WT mice. Increased enzymatic production of ROS and decreased antioxidants contributed to the elevation in oxidative stress in both Ercc1-/Δ and aged WT mice. Chronic treatment of Ercc1-/Δ mice with the mitochondrial-targeted radical scavenger XJB-5–131 attenuated oxidative DNA damage, senescence and age-related pathology. Our findings indicate that nuclear genotoxic stress arises, at least in part, due to mitochondrial-derived ROS, and this spontaneous DNA damage is sufficient to drive increased levels of ROS, cellular senescence, and the consequent age-related physiological decline

Spontaneous DNA damage to the nuclear genome promotes senescence,redox imbalance and aging

Accumulation of senescent cells over time contributes to aging and age-related diseases. However, what drives senescence in vivo is not clear. Here we used a genetic approach to determine if spontaneous nuclear DNA damage is sufficient to initiate senescence in mammals. Ercc1-/Δ mice with reduced expression of ERCC1-XPF endonuclease have impaired capacity to repair the nuclear genome. Ercc1-/Δ mice accumulated spontaneous, oxidative DNA damage more rapidly than wild-type (WT) mice. As a consequence, senescent cells accumulated more rapidly in Ercc1-/Δ mice compared to repair-competent animals. However, the levels of DNA damage and senescent cells in Ercc1-/Δ mice never exceeded that observed in old WT mice. Surprisingly, levels of reactive oxygen species (ROS) were increased in tissues of Ercc1-/Δ mice to an extent identical to naturally-aged WT mice. Increased enzymatic production of ROS and decreased antioxidants contributed to the elevation in oxidative stress in both Ercc1-/Δ and aged WT mice. Chronic treatment of Ercc1-/Δ mice with the mitochondrial-targeted radical scavenger XJB-5–131 attenuated oxidative DNA damage, senescence and age-related pathology. Our findings indicate that nuclear genotoxic stress arises, at least in part, due to mitochondrial-derived ROS, and this spontaneous DNA damage is sufficient to drive increased levels of ROS, cellular senescence, and the consequent age-related physiological decline

Functional Genomics of Chlorine-induced Acute Lung Injury in Mice

Acute lung injury can be induced indirectly (e.g., sepsis) or directly (e.g., chlorine inhalation). Because treatment is still limited to supportive measures, mortality remains high (∼74,500 deaths/yr). In the past, accidental (railroad derailments) and intentional (Iraq terrorism) chlorine exposures have led to deaths and hospitalizations from acute lung injury. To better understand the molecular events controlling chlorine-induced acute lung injury, we have developed a functional genomics approach using inbred mice strains. Various mouse strains were exposed to chlorine (45 ppm × 24 h) and survival was monitored. The most divergent strains varied by more than threefold in mean survival time, supporting the likelihood of an underlying genetic basis of susceptibility. These divergent strains are excellent models for additional genetic analysis to identify critical candidate genes controlling chlorine-induced acute lung injury. Gene-targeted mice then could be used to test the functional significance of susceptibility candidate genes, which could be valuable in revealing novel insights into the biology of acute lung injury

Spontaneous DNA damage to the nuclear genome promotes senescence, redox imbalance and aging

Accumulation of senescent cells over time contributes to aging and age-related diseases. However, what drives senescence in vivo is not clear. Here we used a genetic approach to determine if spontaneous nuclear DNA damage is sufficient to initiate senescence in mammals. Ercc1(-/Delta) mice with reduced expression of ERCC1-XPF endonuclease have impaired capacity to repair the nuclear genome. Ercc1(-/Delta) mice accumulated spontaneous, oxidative DNA damage more rapidly than wild-type (WT) mice. As a consequence, senescent cells accumulated more rapidly in Ercc1(-/Delta) mice compared to repair-competent animals. However, the levels of DNA damage and senescent cells in Ercc1(-/Delta) mice never exceeded that observed in old WT mice. Surprisingly, levels of reactive oxygen species (ROS) were increased in tissues of Ercc1(-/Delta) mice to an extent identical to naturally-aged WT mice. Increased enzymatic production of ROS and decreased antioxidants contributed to the elevation in oxidative stress in both Ercc1(-/Delta) and aged WT mice. Chronic treatment of Ercc1(-/Delta) mice with the mitochondrial-targeted radical scavenger XJB-5-131 attenuated oxidative DNA damage, senescence and age-related pathology. Our findings indicate that nuclear genotoxic stress arises, at least in part, due to mitochondrial-derived ROS, and this spontaneous DNA damage is sufficient to drive increased levels of ROS, cellular senescence, and the consequent age-related physiological decline