The DNA damage checkpoint protein ATM promotes hepatocellular apoptosis and fibrosis in a mouse model of non-alcoholic fatty liver disease

Steatoapoptosis is a hallmark of non-alcoholic fatty liver disease (NAFLD) and is an important factor in liver disease progression. We hypothesized that increased reactive oxygen species resulting from excess dietary fat contribute to liver disease by causing DNA damage and apoptotic cell death, and tested this by investigating the effects of feeding mice high fat or standard diets for 8 weeks. High fat diet feeding resulted in increased hepatic H2O2, superoxide production, and expression of oxidative stress response genes, confirming that the high fat diet induced hepatic oxidative stress. High fat diet feeding also increased hepatic steatosis, hepatitis and DNA damage as exemplified by an increase in the percentage of 8-hydroxyguanosine (8-OHG) positive hepatocytes in high fat diet fed mice. Consistent with reports that the DNA damage checkpoint kinase Ataxia Telangiectasia Mutated (ATM) is activated by oxidative stress, ATM phosphorylation was induced in the livers of wild type mice following high fat diet feeding. We therefore examined the effects of high fat diet feeding in Atm-deficient mice. The prevalence of apoptosis and expression of the pro-apoptotic factor PUMA were significantly reduced in Atm-deficient mice fed the high fat diet when compared with wild type controls. Furthermore, high fat diet fed Atm−/− mice had significantly less hepatic fibrosis than Atm+/+ or Atm+/− mice fed the same diet. Together, these data demonstrate a prominent role for the ATM pathway in the response to hepatic fat accumulation and link ATM activation to fatty liver-induced steatoapoptosis and fibrosis, key features of NAFLD progression

The Non-Homologous End Joining Protein PAXX Acts to Restrict HSV-1 Infection.

Herpes simplex virus 1 (HSV-1) has extensive interactions with the host DNA damage response (DDR) machinery that can be either detrimental or beneficial to the virus. Proteins in the homologous recombination pathway are known to be required for efficient replication of the viral genome, while different members of the classical non-homologous end-joining (c-NHEJ) pathway have opposing effects on HSV-1 infection. Here, we have investigated the role of the recently-discovered c-NHEJ component, PAXX (Paralogue of XRCC4 and XLF), which we found to be excluded from the nucleus during HSV-1 infection. We have established that cells lacking PAXX have an intact innate immune response to HSV-1 but show a defect in viral genome replication efficiency. Counterintuitively, PAXX-/- cells were able to produce greater numbers of infectious virions, indicating that PAXX acts to restrict HSV-1 infection in a manner that is different from other c-NHEJ factors

Mitochondrial complex I activity in microglia sustains neuroinflammation

Sustained smouldering, or low-grade activation, of myeloid cells is a common hallmark of several chronic neurological diseases, including multiple sclerosis1. Distinct metabolic and mitochondrial features guide the activation and the diverse functional states of myeloid cells2. However, how these metabolic features act to perpetuate inflammation of the central nervous system is unclear. Here, using a multiomics approach, we identify a molecular signature that sustains the activation of microglia through mitochondrial complex I activity driving reverse electron transport and the production of reactive oxygen species. Mechanistically, blocking complex I in pro-inflammatory microglia protects the central nervous system against neurotoxic damage and improves functional outcomes in an animal disease model in vivo. Complex I activity in microglia is a potential therapeutic target to foster neuroprotection in chronic inflammatory disorders of the central nervous system3

Mammalian BTBD12 (SLX4) Protects against Genomic Instability during Mammalian Spermatogenesis

The mammalian ortholog of yeast Slx4, BTBD12, is an ATM substrate that functions as a scaffold for various DNA repair activities. Mutations of human BTBD12 have been reported in a new sub-type of Fanconi anemia patients. Recent studies have implicated the fly and worm orthologs, MUS312 and HIM-18, in the regulation of meiotic crossovers arising from double-strand break (DSB) initiating events and also in genome stability prior to meiosis. Using a Btbd12 mutant mouse, we analyzed the role of BTBD12 in mammalian gametogenesis. BTBD12 localizes to pre-meiotic spermatogonia and to meiotic spermatocytes in wildtype males. Btbd12 mutant mice have less than 15% normal spermatozoa and are subfertile. Loss of BTBD12 during embryogenesis results in impaired primordial germ cell proliferation and increased apoptosis, which reduces the spermatogonial pool in the early postnatal testis. During prophase I, DSBs initiate normally in Btbd12 mutant animals. However, DSB repair is delayed or impeded, resulting in persistent γH2AX and RAD51, and the choice of repair pathway may be altered, resulting in elevated MLH1/MLH3 focus numbers at pachynema. The result is an increase in apoptosis through prophase I and beyond. Unlike yeast Slx4, therefore, BTBD12 appears to function in meiotic prophase I, possibly during the recombination events that lead to the production of crossovers. In line with its expected regulation by ATM kinase, BTBD12 protein is reduced in the testis of Atm−/− males, and Btbd12 mutant mice exhibit increased genomic instability in the form of elevated blood cell micronucleus formation similar to that seen in Atm−/− males. Taken together, these data indicate that BTBD12 functions throughout gametogenesis to maintain genome stability, possibly by co-ordinating repair processes and/or by linking DNA repair events to the cell cycle via ATM

Mitochondrial complex I activity in microglia sustains neuroinflammation.

Acknowledgements: We thank P. Chinnery, F. Dazzi, D. Franciotta, G. Griffiths, G. Pluchino, R. Peruzzotti-Jametti, J. Smith, A. Tolkovsky, J. Van den Ameele, R. Magliozzi, R. Milazzo, S. Spadini and A. Biffi for their insights throughout this study; A. Tolkovsky, M. Whitehead and D. Wallace for providing the microglial BV2 cells, neuronal SH-SY5Y cells and the Nd6 mice, respectively; H. Bridges for her technical assistance with the set-up and analysis of the ex vivo metabolic flux experiments; D. Trajkovski, V. Pappa, R. Chowdhury, C. S. Yu, A. Speed and O. Hruba for their technical assistance; R. Grenfell for his technical assistance with the CyTOF acquisition; T. Adejumo (Fluidigm) for his contribution towards the development of the CyTOF antibody panel, processing of data and analysis; the members of the Cambridge NIHR BRC Cell Phenotyping Hub for their cell sorting support; the staff at the CRUK Genomics Core Facility for processing the scRNA-seq samples and for their technical support; and S.-A. Thomas, M. Rice, J. Glide and all of the technicians of the Anne McLaren Building in Cambridge for their help throughout the study. This research was supported by Fondazione Italiana Sclerosi Multipla FISM and Italian Multiple Sclerosis Association AISM Senior research fellowship financed or co-financed with the ‘5 per mille’ public funding 2017/B/5 (to L.P.-J.); Wellcome Trust Clinical Research Career Development Fellowship G105713 (to L.P.-J.); Isaac Newton Trust Research Grant RG 97440 (to S.P. and L.P.-J.); Fondazione Italiana Sclerosi Multipla FISM and Italian Multiple Sclerosis Association AISM 2018/R/14 (to S.P. and L.P.-J.); National MS Society Research Grant RFA-2203-39318 (to L.P.-J.) and Grant RG 1802-30200 (to S.P. and L.P.-J.); Evelyn Trust (to S.P.); Bascule Charitable Trust (to S.P.); NIHR Cambridge BRC (to S.P.); Wings for Life RG 82921 (to S.P. and L.P.-J.), Medical Research Council UK (MC_UU_00028/4), Wellcome Trust Investigator award (220257/Z/20/Z) (to M.P.M.); Henry Wellcome Fellowship 215888/Z/19/Z (to A.E.V.); National MS Society Post-doctoral fellowship FG-2008-36954 and a Catalyst Award from the UK MS Society H160 (to C.M.W. and S.P.); US National Institute of General and Medical Sciences RM1GM131968 (to A.D.); US National Heart, Lung and Blood Institute R01HL146442, R01HL149714, R01HL148151, R01HL161004 and R21HL150032 (to A.D.); European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) Postdoctoral Research Fellowship Exchange Program G104956 (to A.M.N.); and Erasmus+ student internship (to A.M.R.v.d.B. and L.R.). Research in the G.B. laboratory is supported by the UK Dementia Research Institute, which receives contributions from UK DRI, the UK MRC, the Alzheimer’s Society and Alzheimer’s Research UK. Research at TINS is supported by PNRR-III-C9-2022-I8. L.P. and I.M. were funded by the Wellcome Trust (203151/Z/16/Z) and the UKRI Medical Research Council (MC_PC_17230).Sustained smouldering, or low-grade activation, of myeloid cells is a common hallmark of several chronic neurological diseases, including multiple sclerosis1. Distinct metabolic and mitochondrial features guide the activation and the diverse functional states of myeloid cells2. However, how these metabolic features act to perpetuate inflammation of the central nervous system is unclear. Here, using a multiomics approach, we identify a molecular signature that sustains the activation of microglia through mitochondrial complex I activity driving reverse electron transport and the production of reactive oxygen species. Mechanistically, blocking complex I in pro-inflammatory microglia protects the central nervous system against neurotoxic damage and improves functional outcomes in an animal disease model in vivo. Complex I activity in microglia is a potential therapeutic target to foster neuroprotection in chronic inflammatory disorders of the central nervous system3.This research was supported by Fondazione Italiana Sclerosi Multipla FIMS and Italian Multiple Sclerosis Association AISM Senior research fellowship financed or co-financed with the ‘5 per mille’ public funding 2017/B/5 (to L.P.-J.); Wellcome Trust Clinical Research Career Development Fellowship G105713 (to L.P.-J.); Isaac Newton Trust Research Grant RG 97440 (to S.P. and L.P.-J.); Fondazione Italiana Sclerosi Multipla FIMS and Italian Multiple Sclerosis Association AISM 2018/R/14 (to S.P. and L.P.-J.); National MS Society Research Grant RFA-2203-39318 (to L.P.-J.) and Grant RG 1802-30200 (to S.P. and L.P.-J.); Evelyn Trust (to S.P.); Bascule Charitable Trust (to S.P.); NIHR Cambridge BRC (to S.P.); Wings for Life RG 82921 (to S.P. and L.P.-J.), Medical Research Council UK (MC_UU_00028/4), Wellcome Trust Investigator award (220257/Z/20/Z) (to M.P.M.); Henry Wellcome Fellowship 215888/Z/19/Z (to A.E.V.); National MS Society Post-doctoral fellowship FG-2008-36954 (to C.M.W.); US National Institute of General and Medical Sciences RM1GM131968 (to A.D.); US National Heart, Lung and Blood Institute R01HL146442, R01HL149714, R01HL148151, R01HL161004 and R21HL150032 (to A.D.); European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) Postdoctoral Research Fellowship Exchange Program G104956 (to A.M.N.); and Erasmus+ student internship (to A.M.R.v.d.B. and L.R.). Research in the G.B. laboratory is supported by the UK Dementia Research Institute, which receives contributions from UK DRI, the UK MRC, the Alzheimer’s Society and Alzheimer’s Research UK. Research at TINS is supported by PNRR-III-C9-2022-I8. L.P. and I.M. were funded by the Wellcome Trust (203151/Z/16/Z) and the UKRI Medical Research Council (MC_PC_17230)

Mitochondrial complex I activity in microglia sustains neuroinflammation.

Sustained smouldering, or low-grade activation, of myeloid cells is a common hallmark of several chronic neurological diseases, including multiple sclerosis1. Distinct metabolic and mitochondrial features guide the activation and the diverse functional states of myeloid cells2. However, how these metabolic features act to perpetuate inflammation of the central nervous system is unclear. Here, using a multiomics approach, we identify a molecular signature that sustains the activation of microglia through mitochondrial complex I activity driving reverse electron transport and the production of reactive oxygen species. Mechanistically, blocking complex I in pro-inflammatory microglia protects the central nervous system against neurotoxic damage and improves functional outcomes in an animal disease model in vivo. Complex I activity in microglia is a potential therapeutic target to foster neuroprotection in chronic inflammatory disorders of the central nervous system3.This research was supported by Fondazione Italiana Sclerosi Multipla FIMS and Italian Multiple Sclerosis Association AISM Senior research fellowship financed or co-financed with the ‘5 per mille’ public funding 2017/B/5 (to L.P.-J.); Wellcome Trust Clinical Research Career Development Fellowship G105713 (to L.P.-J.); Isaac Newton Trust Research Grant RG 97440 (to S.P. and L.P.-J.); Fondazione Italiana Sclerosi Multipla FIMS and Italian Multiple Sclerosis Association AISM 2018/R/14 (to S.P. and L.P.-J.); National MS Society Research Grant RFA-2203-39318 (to L.P.-J.) and Grant RG 1802-30200 (to S.P. and L.P.-J.); Evelyn Trust (to S.P.); Bascule Charitable Trust (to S.P.); NIHR Cambridge BRC (to S.P.); Wings for Life RG 82921 (to S.P. and L.P.-J.), Medical Research Council UK (MC_UU_00028/4), Wellcome Trust Investigator award (220257/Z/20/Z) (to M.P.M.); Henry Wellcome Fellowship 215888/Z/19/Z (to A.E.V.); National MS Society Post-doctoral fellowship FG-2008-36954 (to C.M.W.); US National Institute of General and Medical Sciences RM1GM131968 (to A.D.); US National Heart, Lung and Blood Institute R01HL146442, R01HL149714, R01HL148151, R01HL161004 and R21HL150032 (to A.D.); European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) Postdoctoral Research Fellowship Exchange Program G104956 (to A.M.N.); and Erasmus+ student internship (to A.M.R.v.d.B. and L.R.). Research in the G.B. laboratory is supported by the UK Dementia Research Institute, which receives contributions from UK DRI, the UK MRC, the Alzheimer’s Society and Alzheimer’s Research UK. Research at TINS is supported by PNRR-III-C9-2022-I8. L.P. and I.M. were funded by the Wellcome Trust (203151/Z/16/Z) and the UKRI Medical Research Council (MC_PC_17230)