**8. Epigenetics**

Much research has been carried out into the role of sex hormones in determining lifespan [84], and one hypothesis is that sex hormones appear to influence the immune system. It is well known that estrogens, androgens and progesterone affect cells of the innate and adaptive immune system differently during the reproductive phase of life [85]. It is widely recognized that estrogens inhibit natural killer cell cytotoxicity and reduce neutrophil chemotaxis and consequently inflammation [86, 87]. Moreover, macrophages treated in vitro with oestradiol display a reduced production of pro-inflammatory cytokines, such as IL-1β, IL-6 and TNF-α [88]. Estrogens and androgens are responsible for a reduced immature number of T-lymphocytes and thymus involution after puberty [89] and can also influence the adaptive immunity in an opposing way, contributing to an improved humoral response in women but also favoring the appearance of autoreactive clones and the susceptibility to autoimmune

The sudden loss of ovarian estrogen and progesterone production that characterizes menopause induces pathophysiological changes in different organs and systems [91], bone density, breast cellular composition, cardiovascular health, mood/cognitive function and sexual wellbeing. Menopause reflects the inevitable final hallmark of a woman's fertile lifespan and of the above-described beneficial effects of estrogens on immune responses. Rapid reduction of estrogen levels results in an increased susceptibility and mortality toward a series of infectious diseases caused in old women losing of their immunological privilege toward infection

It is noteworthy that women will soon spend half of their life in postmenopause, if the current

The ageing process is dynamic and characterized by a continuous remodeling, and it appears evident that the main actors are DNA repair, apoptosis, immune response, oxidative stress and inflammation that these mechanisms are necessary to interact in an efficient way. But life expectancy at birth has been increasing in western societies thanks to the continuous improvement of medical assistance with respect to age-related diseases, especially CVD and

Among lifestyle factors, having a major impact on the whole organism oxidative stress response, there are impaired nutrition, reduced physical activity, alcohol consumption and cigarette smoking, which are major contributors to the failure of systemic homeostasis, especially if persisting for a long part of the individual's life. For these reasons the effects of physical activity and diet in oxidative stress response in humans have been suggested that both are

In support of this hypothesis, it has been reported that dietary restricted mice, which live much longer and show a very delayed aging phenotype [93, 94]. Thus, dietary restriction can trigger a molecular genetic response which postpones ageing and age-related phenotypes. Specifically, reduced glucose metabolisms result in an increase in ROS accumulation

trend of increasing human life expectancy should persist.

able to tip the balance of oxidative burden/antioxidant response.

**7. Lifestyle and physical activity**

cancer, environmental factors and lifestyle.

diseases [90].

14 Senescence - Physiology or Pathology

[85, 92].

In the field of longevity, more recent studies have shown that an important role is also played by epigenetics. In fact, studies in various models have revealed that genetic differences and somatic modulations underlie longevity, but also non-genetic factors play an important role. These considerations have pointed out the importance of epigenetic mechanisms in modulating longevity pathways.

Epigenome, the intermediate layer of genomic information between the genome and transcriptome, is another molecular level that could provide additional insight in the processes of ageing. Epigenetic regulation of transcription is mediated by histone modification, DNA methylation and microRNAs.

Chromatin and epigenetic factors influenced gene expression dynamically by regulating access of transcriptional machinery to DNA. It is clear that, with age, there is a general loss of histones coupled with local and global chromatin remodeling, an imbalance of activating and repressive histone modifications and transcriptional change in all ageing models.

Additionally, particularly in mammalian systems, there is a global and local change in DNA methylation, site-specific loss and gain in heterochromatin and significant nuclear reorganization

Methylation patterns of genes involved in, for example, development and morphogenesis, DNA binding and regulation of transcription [108, 109], seem to change with age; a progressive linear increase in methylation with age at the ELOVL2 gene was found in a cohort of 501 long-lived individuals [110].

The epigenomic field recently became more accessible for the screening of large study populations; however, larger studies, new methodologies and the consistent use of different study designs to follow up results might help to unravel the genomic component of healthy ageing and longevity.

It was proposed that a mathematical model, on the basis of the methylation levels of 353 CpG units, formulated a mathematical model, the so-called epigenetic clock, which was able to predict the chronological age of a subject starting from the methylation level of several cells and tissues of his body [111]. This model also indicates that methylation represents one of the most accurate biomarkers of age and it was able to predict all-cause mortality also after adjusting for traditional risk factors [112]. Finally, when it was used to estimate the biological age of several tissues from supercentenarians, it has been demonstrated that the brain and muscle represent the youngest tissues of these exceptional individuals [113].

However, even if the relationship between methylation process and ageing is still not clear, this discovery has some wide potential applications, ranging from detailed monitoring of changes occurring with age to forensic purposes. It therefore appears clear that future advances in this field could help the understanding of the complex physiology of ageing, lifespan and age-associated diseases.

Starting from the observations, epigenetic modifications affect not only the ageing process but also its quality [114]. Epigenome-wide association studies identified hundreds of sites spread along the entire genome in which methylation levels change between the oldest old and younger subjects.

Although serum microRNAs play roles in the diagnosis of various diseases, little is known about circulating miRNAs in the ageing process. Human serum from healthy individuals contains abundant quantities and species of circulating miRNAs, and they can be readily detected with almost all routine RNA analysis techniques, including qRT-PCR. Zhang et al. evaluated miRNA expression profiles in the sera of healthy individuals at different steps of the ageing process, and they found a different miRNA regulation in the ageing process. In particular, they found that miRNAs changed significantly in the ageing process: miR-29b, miR-106b, miR-130b, miR-142-5p and miR-340 decreased, and miR-92a, miR-222 and miR-375 increased [115].

Evidence provided suggested also that TLR signaling transduction is impaired in cells from aged animals, as suggested by lack of response to the stimulation of lipopolysaccharide (LPS), and the increased pro-inflammatory cytokine release observed in macrophages of aged mice even if no conclusive results can be obtained on the TLR baseline expression level in animal model during ageing [116]. In particular, a trio of miRNA, such as miR-155, miR-21 and miR-146a, has proven to be key TLR signaling modulators, and, importantly, these miRNAs are codified by endotoxin-responsive genes [117].
