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Jan Vijg

Publications and source records attributed to Jan Vijg.

At least 37 records · Page 2Linked to original sources
PubMed2005

Aging and genome maintenance.

Genomic instability in somatic cells has been implicated as a major stochastic mechanism of aging. Using a transgenic mouse model with chromosomally integrated lacZ mutational target genes, we found mutations to accumulate with age at an organ- and tissue-specific rate. Also the spectrum of age-accumulated mutations was found to differ greatly from organ to organ; while initially similar, mutation spectra of different tissues diverged significantly over the lifetime. To explain how genomic instability, which is inherently stochastic, can be a causal factor in aging, it is proposed that randomly induced mutations may adversely affect normal patterns of gene regulation, resulting in a mosaic of cells at various stages on a trajectory of degeneration, eventually resulting in cell death or neoplastic transformation. To directly address this question we demonstrate that it is now possible to analyze single cells, isolated from old and young tissues, for specific alterations in gene expression.

Aging↗
PubMed2004

Catalase transgenic mice: characterization and sensitivity to oxidative stress.

The role of catalase in the antioxidant defense system was studied using transgenic mice [Tg(CAT)] harboring a human genomic clone containing the entire human CAT gene. Catalase activity was 2-fold higher in the tissues of hemizygous [Tg(CAT)(+/o)] mice and 3- to 4-fold higher in the tissues of homozygous [Tg(CAT)(+/+)] mice compared to wild type mice. The human CAT transgene was expressed in a tissue-specific pattern that was similar to the endogenous catalase gene. The levels of other major antioxidant enzymes were not altered in the tissues of the transgenic mice. Hepatocytes and fibroblasts from the Tg(CAT)(+/+) mice were more resistant to hydrogen peroxide-induced cell death but were more sensitive to paraquat and TNFalpha toxicity. Fibroblasts from the Tg(CAT)(+/+) mice showed reduced growth rate in culture without treatment and reduced colony-forming capability after gamma-irradiation compared to fibroblasts from wild type mice. In addition, the Tg(CAT)(+/+) animals were more sensitive to gamma-irradiation.

Animals↗
PubMed2004

Transcripts of aging.

Recently, it has been demonstrated that similar alterations in gene expression profiles occur in cells from patients with Werner syndrome and from normally aged individuals. Changes involving the genes that are involved in RNA and DNA metabolism were particularly frequent - highlighting the importance of the smooth progression of replication and transcription for maintaining youthful vigor. In this article, we discuss the implications of this work for our understanding of the molecular basis of aging and the increasingly important role of microarrays for unraveling the functional pathways underlying the aging phenotype.

Aging↗
PubMed2004

Accelerating aging by mouse reverse genetics: a rational approach to understanding longevity.

Investigating the molecular basis of aging has been difficult, primarily owing to the pleiotropic and segmental nature of the aging phenotype. There are many often interacting symptoms of aging, some of which are obvious and appear to be common to every aged individual, whereas others affect only a subset of the elderly population. Although at first sight this would suggest multiple molecular mechanisms of aging, there now appears to be almost universal consensus that aging is ultimately the result of the accumulation of somatic damage in cellular macromolecules, with reactive oxygen species likely to be the main damage-inducing agent. What remains significant is unravelling how such damage can give rise to the large variety of aging symptoms and how these can be controlled. Although humans, with over a century of clinical observations, remain the obvious target of study, the mouse, with a relatively short lifespan, easy genetic accessibility and close relatedness to humans, is the tool par excellence to model aging-related phenotypes and test strategies of intervention. Here we present the argument that mouse models with engineered defects in genome maintenance systems are especially important because they often exhibit a premature appearance of aging symptoms. Confirming studies on human segmental progeroid syndromes, most of which are based on heritable mutations in genes involved in genome maintenance, the results thus far obtained with mouse models strongly suggest that lifespan and onset of aging are directly related to the quality of DNA metabolism. This may be in keeping with the recent discovery of a possible 'universal survival' pathway that improves antioxidant defence and genome maintenance and simultaneously extends lifespan in the mouse and several invertebrate species.

Aging, Premature↗
PubMed2003

Attenuation of leukocyte-endothelium interaction by antioxidant enzymes.

This report assessed the effect of overexpressing Cu,Zn superoxide dismutase (SOD) and/or catalase on the interaction of mononuclear cells (MNCs) and endothelial cells (ECs). ECs were obtained from the aorta of wild-type mice and transgenic mice overexpressing Cu,ZnSOD and/or catalase. MNCs were obtained from wild-type mice. Treatment of wild-type ECs with CuSO4-oxidized low-density lipoprotein (oxLDL) significantly elevated the expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) and increased the adherence of MNCs. Overexpression of Cu,ZnSOD and/or catalase in ECs attenuated the adherence of MNCs and the expression of cell adhesion molecules induced by oxLDL. For example, ECs overexpressing Cu,ZnSOD and/or catalase showed significantly less expression of VCAM-1 and ICAM-1 and less number of adherent MNCs than wild-type ECs. Moreover, ECs overexpressing Cu,ZnSOD and catalase in combination showed significantly less expression of VCAM-1 and ICAM-1 and less number of adherent MNCs than those overexpressing either Cu,ZnSOD or catalase alone. These results suggest that combinational overexpression of Cu,ZnSOD and catalase can reduce the expression of cell adhesion molecules and inhibit the adherence of leukocyte to ECs more efficiently than overexpression of Cu,ZnSOD or catalase alone.

Animals↗
PubMed2003

Aging and genome maintenance: lessons from the mouse?

Recent progress in the science of aging is driven largely by the use of model systems, ranging from yeast and nematodes to mice. These models have revealed conservation in genetic pathways that balance energy production and its damaging by-products with pathways that preserve somatic maintenance. Maintaining genome integrity has emerged as a major factor in longevity and cell viability. Here we discuss the use of mouse models with defects in genome maintenance for understanding the molecular basis of aging in humans.

Aging↗
PubMed2003

A strategy for the ubiquitous overexpression of human catalase and CuZn superoxide dismutase genes in transgenic mice.

In the present study, we generated transgenic mice that overexpress catalase or CuZn superoxide dismutase (CuZnSOD) in all tissues using large genomic DNA fragments. An 80 kb human genomic DNA, containing the 33 kb human CAT gene as well as the 41 kb of 5' and the 6 kb of 3' flanking regions, was obtained by screening a human P1 library and was used to produce transgenic mice Tg(CAT). Transgenic mice Tg(SOD1) were produced by a similar strategy using a 64 kb human genomic DNA containing the 10 kb human SOD1 gene and the 27 kb of both 5' and 3' flanking regions. Catalase mRNA levels were 2-6- fold higher and catalase activity levels were 2-4- fold higher in the various tissues of the hemizygous Tg(CAT) mice compared with wild type mice. The mRNA levels for CuZnSOD were 2-12- fold higher and the CuZnSOD activity levels were 2-5- fold higher in the hemizygous Tg(SOD1) mice compared with wild type mice. In summary, our study demonstrates that a strategy of using large genomic DNA containing either the entire human CAT or SOD1 gene with large flanking regions gives ubiquitous increased expression of CuZnSOD and catalase. In addition, the expression of catalase closely reflects the tissue specific pattern found in the endogenous gene. These transgenic mice will be useful in studying the role of oxidative stress/damage in aging and age-related pathologies.

5' Flanking Region↗
PubMed2003

Functional genomics of ageing.

Ageing is the most complex phenotype currently known, since it becomes manifest in all organs and tissues, affects an organism's entire physiology, impacts function at all levels and increases susceptibility to all major chronic diseases. Insight into the molecular and cellular targets of the ageing process would offer the unprecedented opportunity to postpone and prevent some, if not all, of its deteriorative aspects by preventive and therapeutic means. Thus far, our understanding of the causes of ageing is limited. To an important extent this is due to our inability, in the past, to study ageing systems. Instead, ample information has been gathered about individual cellular components at various ages, but this has not allowed a clear understanding of the integrated genomic circuits that control mechanisms of ageing, survival and stress responses. With the emergence of functional genomics, we finally have the opportunity to study ageing in a comprehensive manner, as a function of the dynamic network of genes that determines the physiology of an individual organism over time.

Aging↗
PubMed2003

Reduction of pressor response to vasoconstrictor agents by overexpression of catalase in mice.

BACKGROUND: Hydrogen peroxide (H(2)O(2)) has been shown to induce vascular smooth muscle cell contraction in vitro. In this study, the effect of endogenously produced H(2)O(2) on blood pressure (BP) was examined using a transgenic mouse model (hCatTg(+/0)) in which catalase is overexpressed. METHODS: The hCatTg(+/0) and wild-type mice received a bolus injection of norepinephrine (NE; 1 microg/g) or angiotensin II (Ang II; 0.5 microg/g), or an osmotic minipump infusion of NE (2.5 microg/g/day) or Ang II (0.5 microg/g/day) for 7 days. Systolic BP (SBP) was measured using a tail-cuff apparatus. H(2)O(2) release from mouse aortas was measured using an H(2)O(2) assay kit. RESULTS: The hCatTg(+/0) and wild-type mice showed similar basal levels of systolic BP (SBP) and H(2)O(2) release from the aorta. A bolus injection of NE or Ang II increased SBP 31 +/- 5 and 37 +/- 6 mm Hg, respectively, in wild-type mice. In contrast, same doses of NE and Ang II increased SBP only 15 +/- 3 and 17 +/- 4 mm Hg, respectively, in hCatTg(+/0) mice. Osmotic minipump infusion of NE or Ang II increased SBP by approximately 30 mm Hg in wild-type mice, but only by about 10 mm Hg in hCatTg(+/0) mice. The addition of NE or Ang II to the incubation media significantly increased H(2)O(2) release from the aortic segment of wild-type mice but did not alter H(2)O(2) release from the aortic segment of hCatTg(+/0) mice. CONCLUSION: Overexpression of catalase diminishes the pressor response to NE and Ang II by reducing H(2)O(2) production in the arterial wall.

Angiotensin II↗
PubMed2003

Oxygen accelerates the accumulation of mutations during the senescence and immortalization of murine cells in culture.

Oxidative damage is a causal factor in aging and cancer, but it is still not clear how DNA damage, the cellular responses to such damage and its conversion to mutations by misrepair or misreplication contribute to these processes. Using transgenic mice carrying a lacZ mutation reporter, we have previously shown that mutations increase with age in most organs and tissues in vivo. It has also been previously shown that mouse cells respond to oxidative stress, typical of standard culture conditions, by undergoing cellular senescence. To understand better the consequences of oxidative stress, we cultured mouse embryo fibroblasts (MEFs) from lacZ mice under physiological oxygen tension (3%) or the high oxygen tension (20%) associated with standard culture, and determined the frequency and spectrum of mutations. Upon primary culture, the mutation frequency was found to increase approximately three-fold relative to the embryo. The majority of mutations were genome rearrangements. Subsequent culture in 20% oxygen resulted in senescence, followed by spontaneous immortalization. Immortalization was accompanied by an additional three-fold increase in mutations, most of which were G:C to T:A transversions, a signature mutation of oxidative DNA damage. In 3% oxygen, by contrast, MEFs did not senesce and the mutation frequency and spectrum remained similar to primary cultures. These findings demonstrate for the first time the impact of oxidative stress on the genomic integrity of murine cells during senescence and immortalization.

Animals↗
PubMed2003

Combined oral benzo[a]pyrene and inhalatory ozone exposure have no effect on lung tumor development in DNA repair-deficient Xpa mice.

There is considerable concern about an enhanced risk of lung tumor development upon exposure of humans to polycyclic aromatic hydrocarbons (PAHs), like benzo[a] pyrene (B[a]P), in combination with induced lung cell proliferation by toxic agents like ozone. We studied this issue in wild-type (WT) C57BL/6 mice, the cancer prone nucleotide excision repair-deficient Xeroderma pigmentosum complementation group A mice (Xpa-/-) and the even more sensitive Xpa-/-/p53+/- mice. The mice were treated with B[a]P through the diet at a dose of 75 p.p.m., in combination with intermittent ozone exposures (0.8 p.p.m.). First, a dose-range finding study with WT and Xpa-/- mice was conducted to determine the optimal ozone concentration giving high cell proliferation and low toxic side effects. We show by BrdU incorporation that cell proliferation in the lung was induced by ozone, with an optimal concentration of 0.8 p.p.m., which was subsequently used in the (sub)chronic studies. In the subchronic study, in which lacZ mutant frequency and BPDE-DNA adduct formation were measured, the mice were treated for 13 weeks with B[a]P and/or ozone, whereas in the chronic study this treatment protocol was followed by a 6 month period on control feed and filtered air. As expected, oral B[a]P exposure appeared to be highly carcinogenic to Xpa-/- and Xpa-/-/p53+/- mice and to a lesser extent to WT mice. A high incidence of forestomach tumors and some tumors of the esophagus were found. In the lung, a clear genotoxic effect of B[a]P was found as shown by the presence of BPDE-DNA adducts. However, these DNA adducts in combination with induction of cell proliferation did not result in increased lacZ mutations, nor in lung tumor formation not even in the highly sensitive Xpa-/- and Xpa-/-/p53+/- mice. The implication of these findings for tumor risk assessment will be discussed.

Administration, Inhalation↗
PubMed2002

Large genome rearrangements as a primary cause of aging.

In his introductory chapter of the Mutation Research special issue on 'Genetic Instability and Aging', the late Bernard Strehler provided some historical perspectives on the long-standing hypothesis that aging is primarily caused by changes in the genome of somatic cells (Strehler, 1995, Mutat. Res. 338 (1995) 3). Based on his own findings of a loss of ribosomal RNA gene copies in postmitotic tissues of dogs as well as humans during aging, his main conclusion was that deletional mutations are more likely than point mutations to be a main causal factor in aging. To directly assess the levels of different types of spontaneous mutations in organs and tissues during aging, we have used a mouse model harboring a chromosomally integrated cluster of lacZ-containing plasmids that can be recovered and analyzed in Escherichia coli. Our results indicate the accumulation of mutations in some but not all organs of the mouse with significant differences in mutational spectra. In addition to point mutations, genome rearrangements involving up to 66 Mb of genomic DNA appeared to be a major component of the mutational spectra. Physical characterization of the breakpoints of such rearrangements indicated their possible origin by erroneous, non-homologous DNA double-strand break repair. Based on their increased occurrence during aging in some tissues and their often very large size, we have designed a model for an aging tissue in terms of a cellular mosaic with a gradual increase in genome rearrangements that leads to functional senescence, neoplastic transformation or death of individual cells by disrupting nuclear architecture and patterns of gene regulation.

Aging↗
PubMed2002

Clonally expanded mtDNA point mutations are abundant in individual cells of human tissues.

Using single-cell sequence analysis, we discovered that a high proportion of cells in tissues as diverse as buccal epithelium and heart muscle contain high proportions of clonal mutant mtDNA expanded from single initial mutant mtDNA molecules. We demonstrate that intracellular clonal expansion of somatic point mutations is a common event in normal human tissues. This finding implies efficient homogenization of mitochondrial genomes within individual cells. Significant qualitative differences observed between the spectra of clonally expanded mutations in proliferating epithelial cells and postmitotic cardiomyocytes suggest, however, that either the processes generating these mutations or mechanisms driving them to homoplasmy are likely to be fundamentally different between the two tissues. Furthermore, the ability of somatic mtDNA mutations to expand (required for their phenotypic expression), as well as their apparently high incidence, reinforces the possibility that these mutations may be involved actively in various physiological processes such as aging and degenerative disease. The abundance of clonally expanded point mutations in individual cells of normal tissues also suggests that the recently discovered accumulation of mtDNA mutations in tumors may be explained by processes that are similar or identical to those operating in the normal tissue.

Adult↗
PubMed2002

On key lesions and all that: a tribute to Paul Lohman.

This paper is a tribute to Paul Lohman at the occasion of his retirement from the position of Professor in the Medical Faculty at the Leiden University in The Netherlands and as Director of its Department of Radiation Genetics and Chemical Mutagenesis. Paul's contributions to the science of genetic toxicology are discussed in the context of more recent insights as to how mammalian cells process DNA damage, and how this may lead to cancer and, possibly, aging. Starting with his work on the characterization of UV-induced DNA repair in cultured cells from xeroderma pigmentosum patients and the development of methodology for monitoring the removal of UV-induced lesions in human cells, the concept of the key lesion is introduced. Among the myriad of DNA lesions that can be induced in DNA as a consequence of exposure to a range of natural or synthetic mutagens, key lesions are the ones responsible for subsequent adverse effects, for example, because they give rise to mutation. The development of methods using immunofluorescence microscopy to detect and identify such key lesions and quantitate them at the single cell level, is one of the highlights of Paul's career. Based on the perceived need to evaluate mutational end points in vivo in relation to specific lesions identified by his immunofluorescence methods, Paul subsequently made crucial contributions to the development of the first transgenic mouse model to measure mutations in chromosomally integrated reporter genes. In parallel to his experimental work, Paul greatly contributed to genetic toxicology at the theoretical level by his work on the development and evaluation of methods for assessment or prediction of risks of exposure to environmental mutagens. Finally, Paul has served the discipline of genetic toxicology in a more administrative role in various ways, both locally as one of the founders of the Medical Genetics Center South-West Netherlands and internationally by playing a prominent role in organizations such as ICPEMC. Here, his numerous contributions to the journal Mutation Research, both as author on many papers and as Executive Managing Editor should not go unmentioned.

Genetics↗
PubMed2002

Age-related mutation accumulation at a lacZ reporter locus in normal and tumor tissues of Trp53-deficient mice.

Increased genomic instability has been found associated with cancer and aging. The p53 tumor suppressor protein is a major determinant of genomic instability as a regulator of cell cycle control and apoptosis in response to DNA damage. To investigate the rate of age-related mutation accumulation in the absence of p53, we crossed Trp53 null mice with transgenic mice harboring a lacZ mutational target gene. In the hybrid animals, lacZ mutation frequencies at early age (i.e. at about 2 months) were found to be the same as in the control lacZ animals. However, up until about 6 months, when the Trp53-knockout mice usually die from cancer, mutations were found to accumulate with age in the spleen, and to a lesser extent in the liver, at a more rapid rate than in the control Trp53(+/+) or Trp53(+/-), lacZ hybrid mice. Treatment of 2-3-month-old Trp53(-/-), lacZ hybrid mice with the powerful mutagen ethyl nitrosourea (ENU) resulted in a higher number of mutations induced in the liver but not in the spleen, as compared to the Trp53(+/+), lacZ mice. These results suggest that p53 is not an important determinant of gene mutation induction, either spontaneously during development or after treatment with a mutagen. The accelerated age-related accumulation of mutations in normal spleen and liver could be explained by the defect in apoptosis, which would prevent severely damaged cells from being eliminated.

Aging↗
PubMed2002

Mutational fingerprints of aging.

Using a lacZ plasmid transgenic mouse model, spectra of spontaneous point mutations were determined in brain, heart, liver, spleen and small intestine in young and old mice. While similar at a young age, the mutation spectra among these organs were significantly different in old age. In brain and heart G:C-->A:T transitions at CpG sites were the predominant mutation, suggesting that oxidative damage is not a major mutagenic event in these tissues. Other base changes, especially those affecting A:T base pairs, positively correlated with increasing proliferative activity of the different tissues. A relatively high percentage of base changes at A:T base pairs and compound mutants were found in both spleen and spontaneous lymphoma, suggesting a possible role of the hypermutation process in splenocytes in carcinogenesis. The similar mutant spectra observed at a young age may reflect a common mutation mechanism for all tissues that could be driven by the rapid cell division that takes place during development. However, the spectra of the young tissues did not resemble that of the most proliferative aged tissue, implying that replicative history per se is not the underlying causal factor of age-related organ-specific differences in mutation spectra. Rather, differences in organ function, possibly in association with replicative history, may explain the divergence in mutation spectra during aging.

Aging↗