The genomic DNA and its precursor nucleotides are always in danger of oxidation by reactive oxygen species (ROS) which are produced during the oxygen respiration and other normal metabolisms. Various oxidized bases and nucleotides are formed in DNA or nucleotide pools by ROS, and such oxidative lesions in nucleic acids cause mutations or cell death if they are not repaired or eliminated. Mutations induce cancers, and cell death is related to various neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease (AD).
Our aim is to understand mechanisms protecting our genomes from damage caused by reactive oxygen species. We are investigating mutagenesis in proliferative cells and carcinogenesis, and also cell death in postmitotic cells and neurodegeneration.
8-Oxoguanine (8-oxoG) causes mutagenesis and carcinogenesis in mammals, which are prevented by MTH1 (8-oxo-dGTPase), OGG1 (8-oxoG DNA glycosylase) and MUTYH (adenine DNA glycosylase). MTH1 and OGG1 prevent cell death by suppressing 8-oxoG accumulation in DNA, while MUTYH triggers cell death by excising adenine opposite 8-oxoG in DNA. MUTYH induces neuronal dysfunction and microglial activation in nerve tissues under oxidative stress, thus enhancing neurodegeneration.
We investigated age-related alterations in behavior, 8-oxoG levels, and neurogenesis in the brains of Mth1/Ogg1-double knockout (TO-DKO), Ogg1-knockout, and human MTH1-transgenic (hMTH1-Tg) mice. Spontaneous locomotor activity was significantly decreased in wild-type mice with age, and females consistently exhibited higher locomotor activity than males. This decrease was significantly suppressed in female but not male TO-DKO mice and markedly enhanced in female hMTH1-Tg mice. Long-term memory retrieval was impaired in middle-aged female TO-DKO mice. 8-oxoG accumulation significantly increased in nuclear DNA, particularly in the dentate gyrus (DG), subventricular zone (SVZ) and major island of Calleja (ICjM) in middle-aged female TO-DKO mice. In middle-aged female TO-DKO mice, neurogenesis was severely impaired in SVZ and DG, accompanied by ICjM and DG atrophy. Conversely, expression of hMTH1 efficiently suppressed 8-oxoG accumulation in both SVZ and DG with hypertrophy of ICjM. These findings indicate that newborn neurons from SVZ maintain ICjM in the adult brain, and increased accumulation of 8-oxoG in nuclear DNA of neural progenitors in females is caused by 8-oxo-dGTP incorporation during proliferation, causing depletion of neural progenitors, altered behavior, and cognitive function changes with age.
Insulin production and insulin signaling are impaired in Alzheimer disease (AD) brains, and thus impaired glucose metabolism and mitochondrial dysfunction increase oxidative damage and enhance neurodegeneration. Human TFAM expression in AD mouse brain effectively suppresses the mitochondrial dysfunction, thereby suppressing AD pathogenesis. Gene expression profiling in AD cortex demonstrates a link between amyloidosis and neuroinflammation.
8-oxoG is highly accumulated in AD)brains during the pathogenic process. MTH1 hydrolyzes 8-oxo-dGTP to 8-oxo-dGMP, thereby avoiding 8-oxo-dG incorporation into DNA. 8-OxoG DNA glycosylase-1 (OGG1) excises 8-oxoG paired with cytosine in DNA, thereby minimizing 8-oxoG accumulation in DNA. Levels of MTH1 and OGG1 are significantly reduced in the brains of sporadic AD cases. To understand how 8-oxoG accumulation in the genome is involved in AD pathogenesis, we established an AD mouse model with knockout of Mth1 and Ogg1 genes in a 3xTg-AD background. MTH1 and OGG1 deficiency increased 8-oxoG accumulation in nuclear and, to a lesser extent, mitochondrial genomes, causing microglial activation and neuronal loss with impaired cognitive function at 4-5 months of age. Furthermore, minocycline, which inhibits microglial activation and reduces neuroinflammation, markedly decreased the nuclear accumulation of 8-oxoG in microglia, and inhibited microgliosis and neuronal loss. Gene expression profiling revealed that MTH1 and OGG1 efficiently suppress progression of AD by inducing various protective genes against AD pathogenesis initiated by Ass/Tau accumulation in 3xTg-AD brain. Our findings indicate that efficient suppression of 8-oxoG accumulation in brain genomes is a new approach for prevention and treatment of AD.
Inosine triphosphate pyrophosphatase (ITPA) hydrolyzes inosine triphosphate (ITP), which is a product of oxidized deamination of ATP, and other deaminated purine nucleotides to the corresponding nucleoside monophosphates. In humans, ITPA deficiency causes severe encephalopathy with epileptic seizure, microcephaly, and developmental retardation. In this study, we established neural stem cell-specific Itpa-conditional KO mice (Itpa-cKO mice) to clarify the effects of ITPA deficiency on the neural system. The Itpa-cKO mice showed growth retardation and died within 3 weeks of birth. We did not observe any microcephaly in the Itpa-cKO mice, although the female Itpa-cKO mice did show adrenal hypoplasia. The Itpa-cKO mice showed limb-clasping upon tail suspension and spontaneous and/or audiogenic seizure. Whole-cell patch-clamp recordings from entorhinal cortex neurons in brain slices revealed a depolarized resting membrane potential, increased firing, and frequent spontaneous miniature excitatory postsynaptic current and miniature inhibitory postsynaptic current in the Itpa-cKO mice compared with ITPA-proficient controls. Accumulated ITP or its metabolites, such as cyclic inosine monophosphates, or RNA containing inosines may cause membrane depolarization and hyperexcitability in neurons and induce the phenotype of ITPA-deficient mice, including seizure.
1. Anene-Nzelu CG, Li PY, Luu TDA, Ng SL, Tiang Z, Pan B, Tan WLW, Ackers-Johnson M, Chen CK, Lim YP, Qin RWM, Chua WW, Yi LX, Foo RS, Nakabeppu Y. 8-Oxoguanine DNA Glycosylase (OGG1) Deficiency Exacerbates Doxorubicin-Induced Cardiac Dysfunction. Oxid Med Cell Longev 2022: 9180267, 2022.
2. Mizuno, Y., Abolhassani, N., Mazzei, G., Sakumi, K., Saito, T., Saido, T.C., Ninomiya, T., Iwaki, T., Yamasaki, R., Kira, J.-i., and Nakabeppu, Y. MUTYH Actively Contributes to Microglial Activation and Impaired Neurogenesis in the Pathogenesis of Alzheimer's Disease. Oxid Med Cell Longev 2021, 8635088, 2021.
3. Mizuno, Y., Abolhassani, N., Mazzei, G., Saito, T., Saido, T.C., Yamasaki, R., Kira, J.I., and Nakabeppu, Y. Deficiency of MTH1 and/or OGG1 increases the accumulation of 8-oxoguanine in the brain of the App(NL-G-F/NL-G-F) knock-in mouse model of Alzheimer's disease, accompanied by accelerated microgliosis and reduced anxiety-like behavior. Neurosci Res 177: 118-134, 2021.
4. Mazzei, G., Ikegami, R., Abolhassani, N., Haruyama, N., Sakumi, K., Saito, T., Saido, T.C., and Nakabeppu, Y. A high-fat diet exacerbates the Alzheimer's disease pathology in the hippocampus of the App(NL-F/NL-F) knock-in mouse model. Aging Cell 20: e13429, 2021.
5. Nakamura, T., Okabe, K., Hirayama, S., Chirifu, M., Ikemizu, S., Morioka, H., Nakabeppu, Y., and Yamagata, Y. Structure of the mammalian adenine DNA glycosylase MUTYH: insights into the base excision repair pathway and cancer. Nucleic Acids Res 49: 7154-7163, 2021.
6. MTH1 and OGG1 maintain a low level of 8-oxoguanine in Alzheimer's brain, and prevent the progression of Alzheimer's pathogenesis. Oka S, Leon J, Sakumi K, Abolhassani N, Sheng Z, Tsuchimoto D, LaFerla FM, Nakabeppu Y. Sci Rep 11:5819, 2021.
7. Neural stem cell-specific ITPA deficiency causes neural depolarization and epilepsy. Koga Y, Tsuchimoto D, Hayashi Y, Abolhassani N, Yoneshima Y, Sakumi K, Nakanishi H, Toyokuni S, Nakabeppu Y. JCI Insight 5:e140229, 2020.
8. 8-Oxoguanine accumulation in aged female brain impairs neurogenesis in the dentate gyrus and major island of Calleja, causing sexually dimorphic phenotypes. Haruyama, N., Sakumi, K., Katogi, A., Tsuchimoto, D., De Luca, G., Bignami, M., and Nakabeppu, Y. Prog Neurobiol 180:101613, 2019.
9. Origins of Brain Insulin and Its Function. In Diabetes Mellitus, A rist factor for Alzheimmer's disease. Nakabeppu, Y. (Nakabeppu, Y., and Ninomiya, T., eds), Springer, Advances in Experimental Medicine and Biology 1128: 1-11,2019.
10. Molecular Pathophysiology of Insulin Depletion, Mitochondrial Dysfunction, and Oxidative Stress in Alzheimer's Disease Brain. In Diabetes Mellitus, A risk factor for Alzheimer's disease. Nakabeppu, Y. (Nakabeppu, Y., and Ninomiya, T., eds), Springer, Advances in Experimental Medicine and Biology 1128: 27-44, 2019.
11. MTH1 as a nucleotide pool sanitizing enzyme: Friend or foe? Nakabeppu, Y., Ohta, E., and Abolhassani, N. Free Radic Biol Med 107: 151-158, 2017.
12. Neurodegeneration Caused by Accumulation of an Oxidized Base Lesion, 8-oxoguanine, in Nuclear and Mitochondrial DNA: From Animal Models to Human Diseases. In The Base Excision Repair Pathway – Molecular Mechanisms and Role in Disease Development and Therapeutic Design. Nakabeppu, Y. (Wilson III, D. M., ed), World Scientific, 523-556, 2017.
13. Comparative profiling of cortical gene expression in Alzheimer's disease patients and mouse models demonstrates a link between amyloidosis and neuroinflammation. Castillo, E., Leon, J., Mazzei, G., Abolhassani, N., Haruyama, N., Saito, T., Saido, T., Hokama, M., Iwaki, T., Ohara, T., Ninomiya, T., Kiyohara, Y., Sakumi, K., LaFerla, F. M., and Nakabeppu, Y. Sci Rep 7: 17762, 2017.
14. 2-Oxoadenosine induces cytotoxicity through intracellular accumulation of 2-oxo-ATP and depletion of ATP but not via the p38 MAPK pathway. Asada, S., Ohta, E., Akimoto, Y., Abolhassani, N., Tsuchimoto, D., and Nakabeppu, Y. Sci Rep 7: 6528, 2017.
15. Molecular pathophysiology of impaired glucose metabolism, mitochondrial dysfunction, and oxidative DNA damage in Alzheimer's disease brain. Abolhassani, N., Leon, J., Sheng, Z., Oka, S., Hamasaki, H., Iwaki, T., and Nakabeppu, Y. Mech Ageing Dev 161: 95-104, 2017.
16. Deoxyinosine triphosphate induces MLH1/PMS2- and p53-dependent cell growth arrest and DNA instability in mammalian cells. Yoneshima, Y., Abolhassani, N., Iyama, T., Sakumi, K., Shiomi, N., Mori, M., Shiomi, T., Noda, T., Tsuchimoto, D., and Nakabeppu, Y. Sci Rep 6: 32849, 2016.
17. PKCeta deficiency improves lipid metabolism and atherosclerosis in apolipoprotein E-deficient mice. Torisu, K., Zhang, X., Nonaka, M., Kaji, T., Tsuchimoto, D., Kajitani, K., Sakumi, K., Torisu, T., Chida, K., Sueishi, K., Kubo, M., Hata, J., Kitazono, T., Kiyohara, Y., and Nakabeppu, Y. Genes Cells 21: 1030-1048, 2016.
18. Deficiency of base excision repair enzyme NEIL3 drives increased predisposition to autoimmunity. Massaad, M. J., Zhou, J., Tsuchimoto, D., Chou, J., Jabara, H., Janssen, E., Glauzy, S., Olson, B. G., Morbach, H., Ohsumi, T. K., Schmitz, K., Kyriacos, M., Kane, J., Torisu, K., Nakabeppu, Y., Notarangelo, L. D., Chouery, E., Megarbane, A., Kang, P. B., Al-Idrissi, E., Aldhekri, H., Meffre, E., Mizui, M., Tsokos, G. C., Manis, J. P., Al-Herz, W., Wallace, S. S., and Geha, R. S. J Clin Invest 126: 4219-4236, 2016.
19. 8-Oxoguanine accumulation in mitochondrial DNA causes mitochondrial dysfunction and impairs neuritogenesis in cultured adult mouse cortical neurons under oxidative conditions. Leon, J., Sakumi, K., Castillo, E., Sheng, Z., Oka, S., and Nakabeppu, Y. Sci Rep 6: 22086, 2016.
20. Galectin-1 deficiency improves axonal swelling of motor neurones in SOD1(G93A) transgenic mice. Kobayakawa, Y., Sakumi, K., Kajitani, K., Kadoya, T., Horie, H., Kira, J., and Nakabeppu, Y. Neuropathol Appl Neurobiol 41: 227-244, 2015.
21. Altered Expression of Diabetes-Related Genes in Alzheimer's Disease Brains: The Hisayama Study. Hokama M, Oka S, Leon J, Ninomiya T, Honda H, Sasaki K, Iwaki T, Ohara T, Sasaki T, LaFerla FM, Kiyohara Y, Nakabeppu Y. Cereb Cortex 24: 2476-2488. 2014.
23. Fosb gene products contribute to excitotoxic microglial activation by regulating the expression of complement C5a receptors in microglia. Nomaru H, Sakumi K, Katogi A, Ohnishi YN, Kajitani K, Tsuchimoto D, Nestler EJ, Nakabeppu Y. Glia 62: 1284-1298, 2014.
24. fosB-Null Mice Display Impaired Adult Hippocampal Neurogenesis and Spontaneous Epilepsy with Depressive Behavior. Yutsudo N, Kamada T, Kajitani K, Nomaru H, Katogi A, Ohnishi YH, Ohnishi YN, Takase K, Sakumi K, Shigeto H, Nakabeppu Y. Neuropsychopharmacology 38: 895-906, 2013.
25. 8-Oxoguanine causes neurodegeneration during MUTYH-mediated DNA base excision repair. Sheng Z, Oka S, Tsuchimoto D, Abolhassani N, Nomaru H, Sakumi K, Yamada H, Nakabeppu Y. J Clin Invest 122: 4344-4361. 2012.
26. MutT homolog-1 attenuates oxidative DNA damage and delays photoreceptor cell death in inherited retinal degeneration. Murakami Y, Ikeda Y, Yoshida N, Notomi S, Hisatomi T, Oka S, De Luca G, Yonemitsu Y, Bignami M, Nakabeppu Y, Ishibashi T. Am J Pathol 181: 1378-1386, 2012.
27. FosB is essential for the enhancement of stress tolerance and antagonizes locomotor sensitization by ΔFosB. Ohnishi YN, Ohnishi YH, Hokama M, Nomaru H, Yamazaki K, Tominaga Y, Sakumi K, Nestler EJ, Nakabeppu Y. Biol Psychiatry 70: 487-495, 2011.
28. NUDT16 is a (deoxy)inosine diphosphatase, and its deficiency induces accumulation of single-strand breaks in nuclear DNA and growth arrest. Iyama T, Abolhassani N, Tsuchimoto D, Nonaka M, Nakabeppu Y. Nucleic Acids Res 38: 4834-43, 2010.
29. NUDT16 and ITPA play a dual protective role in maintaining chromosome stability and cell growth by eliminating dIDP/IDP and dITP/ITP from nucleotide pools in mammals. Abolhassani N, Iyama T, Tsuchimoto D, Sakumi K, Ohno M, Behmanesh M, Nakabeppu Y. Nucleic Acids Res 38: 2891-903, 2010.
30. ITPase-deficient mice show growth retardation and die before weaning. Behmanesh M, Sakumi K, Abolhassani N, Toyokuni S, Oka S, Ohnishi YN, Tsuchimoto D, Nakabeppu Y. Cell Death Differ 16: 1315-4322, 2009.
31. Oxidation of mitochondrial deoxynucleotide pools by exposure to sodium nitroprusside induces cell death. Ichikawa J, Tsuchimoto D, Oka S, Ohno M, Furuichi M, Sakumi K, Nakabeppu Y. DNA Repair 7: 418-30, 2008.
32. A genome-wide distribution of 8-oxoguanine correlates with the preferred regions for recombination and single nucleotide polymorphism in the human genome. Ohno M, Miura T, Furuichi M, Tominaga Y, Tsuchimoto D, Sakumi K, Nakabeppu Y. Genome Res 16: 567-75, 2006.
33. MTH1, an oxidized purine nucleoside triphosphatase, protects the dopamine neurons from oxidative damage in nucleic acids caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Yamaguchi H, Kajitani K, Dan Y, Furuichi M, Ohno M, Sakumi K, Kang D, Nakabeppu Y. Cell Death Differ 13: 551-63, 2006.
34. MTH1, an oxidized purine nucleoside triphosphatase, suppresses the accumulation of oxidative damage of nucleic acids in the hippocampal microglia during kainate-induced excitotoxicity. Kajitani K, Yamaguchi H, Dan Y, Furuichi M, Kang D, Nakabeppu Y. J Neurosci 26: 1688-1698, 2006.
35. Up-regulation of hMUTYH, a DNA repair enzyme, in the mitochondria of substantia nigra in Parkinson's disease. Arai T, Fukae J, Hatano T, Kubo S, Ohtsubo T, Nakabeppu Y, Mori H, Mizuno Y, Hattori N. Acta Neuropathol 112: 139-45, 2006.
36. Growth retardation and dyslymphopoiesis accompanied by G2/M arrest in APEX2-null mice. Ide Y, Tsuchimoto D, Tominaga Y, Nakashima M, Watanabe T, Sakumi K, Ohno M, Nakabeppu Y. Blood 104: 4097-4103, 2004.
37. An oxidized purine nucleoside triphosphatase, MTH1, suppresses cell death caused by oxidative stress. Yoshimura D, Sakumi K, Ohno M, Sakai Y, Furuichi M, Iwai S, Nakabeppu Y. J Biol Chem 278: 37965-37973, 2003.
38. A molecular basis for the selective recognition of 2-hydroxy-dATP and 8-oxo-dGTP by human MTH1. Sakai Y, Furuichi M, Takahashi M, Mishima M, Iwai S, Shirakawa M, Nakabeppu Y. J Biol Chem 277:8579-8587, 2002.
39. Impairment of mitochondrial DNA repair enzymes against accumulation of 8-oxo-guanine in the spinal motor neurons of amyotrophic lateral sclerosis. Kikuchi H, Furuta A, Nishioka K, Suzuki SO, Nakabeppu Y, Iwaki T. Acta Neuropathol 103: 408-14, 2002.
40. Expression of 8-oxoguanine DNA glycosylase is reduced and associated with neurofibrillary tangles in Alzheimer's disease brain. Iida T, Furuta A, Nishioka K, Nakabeppu Y, Iwaki T. Acta Neuropathologica 103: 20-25, 2002.