Lifestyle impacts on the aging-associated expression of biomarkers of DNA damage and telomere dysfunction in human blood: Measuring the influence of lifestyle on aging

Cellular aging is characterised by telomere shortening, which can lead to uncapping of chromosome ends (telomere dysfunction) and that activation of DNA damage responses. There is some evidence the DNA damage accumulates during human aging and that lifestyle factors contribute to the accumulation of DNA damage. Recent studies have identified a set of serum markers that are induced by telomere dysfunction and DNA damage and these markers showed an increased expression in blood during human aging. Here, we investigated the influence of lifestyle factors (such as exercise, smoking, body mass) on the aging associated expression of serum markers of DNA damage (CRAMP, EF-1α, Stathmin, n-acetyl-glucosaminidase, and chitinase) in comparison to other described markers of cellular aging (p16INK4a upregulation and telomere shortening) in human peripheral blood. The study shows that lifestyle factors have an age-independent impact on the expression level of biomarkers of DNA damage. Smoking and increased body mass indices were associated with elevated levels of biomarkers of DNA damage independent of the age of the individuals. In contrast, exercise was associated with an age-independent reduction in the expression of biomarkers of DNA damage in human blood. The expression of biomarkers of DNA damage correlated positively with p16INK4a expression and negatively with telomere length in peripheral blood T-lymphocytes. Together, these data provide experimental evidence that both aging and lifestyle impact on the accumulation of DNA damage during human aging

Telomere Shortening Impairs Regeneration of the Olfactory Epithelium in Response to Injury but Not Under Homeostatic Conditions

Atrophy of the olfactory epithelium (OE) associated with impaired olfaction and dry nose represents one of the most common phenotypes of human aging. Impairment in regeneration of a functional olfactory epithelium can also occur in response to injury due to infection or nasal surgery. These complications occur more frequently in aged patients. Although age is the most unifying risk factor for atrophic changes and functional decline of the olfactory epithelium, little is known about molecular mechanisms that could influence maintenance and repair of the olfactory epithelium. Here, we analyzed the influence of telomere shortening (a basic mechanism of cellular aging) on homeostasis and regenerative reserve in response to chemical induced injury of the OE in late generation telomere knockout mice (G3 mTerc−/−) with short telomeres compared to wild type mice (mTerc+/+) with long telomeres. The study revealed no significant influence of telomere shortening on homeostatic maintenance of the OE during mouse aging. In contrast, the regenerative response to chemical induced injury of the OE was significantly impaired in G3 mTerc−/− mice compared to mTerc+/+ mice. Seven days after chemical induced damage, G3 mTerc−/− mice exhibited significantly enlarged areas of persisting atrophy compared to mTerc+/+ mice (p = 0.031). Telomere dysfunction was associated with impairments in cell proliferation in the regenerating epithelium. Deletion of the cell cycle inhibitor, Cdkn1a (p21) rescued defects in OE regeneration in telomere dysfunctional mice. Together, these data indicate that telomere shortening impairs the regenerative capacity of the OE by impairing cell cycle progression in a p21-dependent manner. These findings could be relevant for the impairment in OE function in elderly people

WNT signaling, in synergy with T/TBX6, controls Notch signaling by regulating Dll1 expression in the presomitic mesoderm of mouse embryos

Notch signaling in the presomitic mesoderm (psm) is critical for somite formation and patterning. Here, we show that WNT signals regulate transcription of the Notch ligand Dll1 in the tailbud and psm. LEF/TCF factors cooperate with TBX6 to activate transcription from the Dll1 promoter in vitro. Mutating either T or LEF/TCF sites in the Dll1 promoter abolishes reporter gene expression in vitro as well as in the tail bud and psm of transgenic embryos. Our results indicate that WNT activity, in synergy with TBX6, regulates Dll1 transcription and thereby controls Notch activity, somite formation, and patterning

Telomere shortening impairs regeneration of the olfactory epithelium in response to injury.

<p>(A, B) Representative photographs of hematoxylin and eosin-stained sagital sections of the nasal cavity, seven days after intranasal injection of Triton-X in 6 month old (A) G3 <i>mTerc^−/−</i> and (B-E) <i>mTerc^+/+</i> mice. Dotted line in A and B marks incompletely regenerated epithelium of 0–2 cell layer thickness, double line marks incompletely regenerated epithelium of 3–4 cell layer thickness, dot/bar line marks completely regenerated epithelium of 5–6 cell layer thickness. Representative high-power photographs of G3 <i>mTerc^−/−</i> mice showing (C) incompletely regenerated epithelium with 0–2 cell layer thickness (dotted line), (D) 3–4 cell layer thickness (double linier) (E) completely regenerated olfactory epithelium (E). (F, G) The histograms show the percentage of the olfactory epithelium with incomplete regeneration in <i>mTerc^+/+</i> and G3 <i>mTerc^−/−</i> mice at seven days after Triton-X induced injury: (F) percentage of incompletely regenerated epithelium of 0–2 cell layer thickness, (G) percentage of incompletely regenerated epithelium of 0–4 cell layer thickness.</p

Morphological Analysis of the olfactory epithelium at day 2 after Triton-X application.

<p>(A,B) Representative photographs of hematoxylin and eosin-stained sagittal sections of the OE, two days after intranasal injection of Triton-X in 6 month old (A) G3 <i>mTerc^−/−</i> and (B) <i>mTerc^+/+</i> mice. There are no significant differences between the two cohorts, both showing strong damage to 80–90% of the OE. The histograms show the percentage of the chemically damaged olfactory epithelium in <i>mTerc^+/+</i> and G3 <i>mTerc^−/−</i> mice at two days after Triton-X induced injury: (C) percentage of damaged epithelium of 0–4 cell layer thickness (P = 0.7887), (D) percentage of completely damaged epithelium of 0–2 cell layer thickness (P = 0.8208).</p

Telomere shortening does not affect homeostasis of the olfactory epithelium in aging mice.

<p>(A, B): Representative photographs of hematoxylin and eosin-stained longitudinal sections of the OE from 2–3 month old (A) <i>mTerc^+/+</i> and (B) G3 <i>mTerc^−/−</i> mice, and 10–12 month old (C) <i>mTerc^+/+</i> and (D) G3 <i>mTerc^−/−</i> mice. (E-J) Immunohistological analysis of longitudinal sections of the OE 10–12 month old (E, G, I) <i>mTerc^+/+</i> and (F, H, J) G3 <i>mTerc^−/−</i> mice: (E, F) Olfactory marker protein (OMP), (G, H) GAP43 and (I, J) proliferating cell nuclear antigen (PCNA). White arrows point to PCNA positive cells (G, H). (K) Histogram showing percentage of PCNA-positive cells in the OE of 10–12 month old <i>mTerc^+/+</i> and G3 <i>mTerc^−/−</i> mice (n = 10 mice per group, P = 0.4580).</p

Limited proliferation potential of the OE in telomere deficient mice.

<p>(A,B) Representative photographs of BrdU-stained longitudinal sections of the olfactory epithelium, 7 days after Triton-X treatment in (A) <i>mTerc^+/+</i> and (B) G3 <i>mTerc^−/−</i> mice. (C) Histogram showing BrdU positive cells in the OE of G3 <i>mTerc^+/+</i> and <i>mTerc^+/+</i> mice. Note that there is no significant difference of the ratio of BrdU positive cells v.s. negative cells between <i>mTerc^+/+</i> and G3 <i>mTerc^−/−</i> mice in injured olfactory epithelium of one cell layer thickness (P = 0.216) but there was a significant reduction of BrdU positive cells in G3 <i>mTerc^−/−</i> compared to <i>mTerc^+/+</i> mice in injured olfactory epithelium of three cell layer thickness (P = 0.008) and 5–6 cell layer thickness (P = 0.0293), n = 5 mice per group. (D) The histogram shows the percentage of the olfactory epithelium with incomplete regeneration (0–2 cell layer thickness) in 6–8 month mice of the indicated genotypes at 7 days after Triton-X induced injury. Note that <i>p21</i> deletion rescues regenerative defects in G3 <i>mTerc^−/−</i> mice. The cohorts in this experiment show an overall higher rate of tissue damage compared to the previous experiment depicted in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0027801#pone-0027801-g003" target="_blank">Figures 3</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0027801#pone-0027801-g004" target="_blank">4</a>.</p

Shortened telomeres in the olfactory epithelium of G3 <i>mTerc^−/−</i> mice.

<p>(A, B): Distribution of the mean telomere fluorescence intensity (TFI) of cells of the olfactory epithelium in 6–8 month old <i>mTerc^+/+</i> mice (A) and of G3 <i>mTerc^−/−</i> mice (B) (n = 4 mice per group). The dotted line shows the mean TFI of olfactory epithelial cells in mice of the two cohorts. Note that the olfactory epithelium of G3 <i>mTerc^−/−</i> have shorter telomeres than <i>mTerc^+/+</i> mice (P = 0.0207).</p