Convergent adaptation of cellular machineries in the evolution of large body masses and long life spans.

In evolutionary terms, life on the planet has taken the form of independently living cells for the majority of time. In comparison, the mammalian radiation is a relatively recent event. The common mammalian ancestor was probably small and short-lived. The "recent" acquisition of an extended longevity and large body mass of some species of mammals present on the earth today suggests the possibility that similar cellular mechanisms have been influenced by the forces of natural selection to create a convergent evolution of longevity. Many cellular mechanisms are potentially relevant for extending longevity; in this assay, we review the literature focusing primarily on two cellular features: (1) the capacity for extensive cellular proliferation of differentiated cells, while maintaining genome stability; and (2) the capacity to detect DNA damage. We have observed that longevity and body mass are both positively linked to these cellular mechanisms and then used statistical tools to evaluate their relative importance. Our analysis suggest that the capacity for extensive cellular proliferation while maintaining sufficient genome stability, correlates to species body mass while the capacity to correctly identify the presence of DNA damage seems more an attribute of long-lived species. Finally, our data are in support of the idea that a slower development, allowing for better DNA damage detection and handling, should associate with longer life span.

A pro longevity role for cellular senescence.

Cellular senescence is a fundamental process that may play positive or detrimental roles for the organism. It is involved in tissue development and in tumor prevention although during aging is becoming a detrimental process contributing to the decline of tissue functions. In previous investigations, we have uncovered a better capacity to detect DNA damage in cells from long-lived mammals. Here, we report that cultured cells derived from long-lived species have a higher propensity to undergo senescence when challenged with DNA damage than cells derived from short-lived species. Using a panel of cells derived from six mammals, which range in lifespan from 3-4 years up to 120 years, we examined cell cycle response, induction of apoptosis and of cellular senescence. All species exhibited a cell cycle arrest while induction of apoptosis was variable. However, a significant positive correlation was found between the relative percent of cells, within a population which entered senescence following damage, and the lifespan of the species. We suggest that cellular senescence may have a positive role during development allowing it to contribute to the evolution of longevity.

DNA Damage Detection by 53BP1: Relationship to Species Longevity.

In order to examine potential differences in genomic stability, we have challenged fibroblasts derived from five different mammalian species of variable longevity with the genotoxic agents, etoposide and neocarzinostatin. We report that cells from longer-lived species exhibit more tumor protein p53 binding protein 1 (53BP1) foci for a given degree of DNA damage relative to shorter-lived species. The presence of a greater number of 53BP1 foci was associated with decreased DNA fragmentation and a lower percentage of cells exhibiting micronuclei. These data suggest that cells from longer-lived species have an enhanced DNA damage response. We propose that the number of 53BP1 foci that form in response to damage reflects the intrinsic capacity of cells to detect and respond to DNA harms.

E-cigarettes induce toxicological effects that can raise the cancer risk.

Electronic cigarettes (e-cigs) are devices designed to deliver nicotine in a vaping solution rather than smoke and without tobacco combustion. Perceived as a safer alternative to conventional cigarettes, e-cigs are aggressively marketed as lifestyle-choice consumables, thanks to few restrictions and a lack of regulatory guidelines. E-cigs have also gained popularity among never-smokers and teenagers, becoming an emergent public health issue. Despite the burgeoning worldwide consumption of e-cigs, their safety remains largely unproven and it is unknown whether these devices cause in vivo toxicological effects that could contribute to cancer. Here we demonstrate the co-mutagenic and cancer-initiating effects of e-cig vapour in a rat lung model. We found that e-cigs have a powerful booster effect on phase-I carcinogen-bioactivating enzymes, including activators of polycyclic aromatic hydrocarbons (PAHs), and increase oxygen free radical production and DNA oxidation to 8-hydroxy-2'-deoxyguanosine. Furthermore, we found that e-cigs damage DNA not only at chromosomal level in peripheral blood, such as strand breaks in leucocytes and micronuclei formation in reticulocytes, but also at gene level such as point mutations in urine. Our results demonstrate that exposure to e-cigs could endanger human health, particularly among younger more vulnerable consumers.

Genetic instability and aging under the scrutiny of comparative biology: a meta-analysis of spontaneous micronuclei frequency.

In gerontology, comparative biology of longevity offers a powerful observation point thus far underexploited. We use this approach to evaluate the role of genetic stability in longevity determination, extrapolating existing data from the literature. Screening eight pre-existing studies, we collected data from 47 mammalian species and analyzed the relationship of spontaneous micronucleated erythrocyte frequency to species maximum longevity and species adult body mass. Since in 26 of these species the spleen removes micronucleated erythrocytes from the peripheral circulation, we conducted further comparative analysis on the remaining 21 species. We demonstrate that spontaneous micronucleated erythrocyte frequency correlates primarily with body mass and not with maximum longevity. We suggest that other data on genetic stability could be collected from published works in different species and analyzed in a similar way to test further the role of genetic stability in aging.

DNA damage markers in dermal fibroblasts in vitro reflect chronological donor age.

The aging process is accompanied by an accumulation of cellular damage, which compromises the viability and function of cells and tissues. We aim to further explore the association between in vitro DNA damage markers and the chronological age of the donor, as well as long-lived family membership and presence of cardiovascular diseases. Therefore, numbers of 53BP1 foci, telomere-associated foci (TAF) and micronuclei were measured in cultured dermal fibroblasts obtained from three age groups of donors (mean age 22, 63 and 90 years). Fibroblasts were cultured without a stressor and with 0.6 µM rotenone for 3 days. We found that 53BP1 foci and TAF were more frequently present in fibroblasts of old donors compared to middle-aged and young donors. No association between micronuclei and donor age was found. Within the fibroblasts of the middle-aged donors we did not find associations between DNA damage markers and long-lived family membership or cardiovascular disease. Results were comparable when fibroblasts were stressed in vitro with rotenone. In conclusion, we found that DNA damage foci of cultured fibroblasts are significantly associated with the chronological age, but not biological age, of the donor.