Of flies, mice, and men: evolutionarily conserved tissue damage responses and aging

Studies in flies, mice, and human models have provided a conceptual framework for how paracrine interactions between damaged cells and the surrounding tissue control tissue repair. These studies have amassed evidence for an evolutionarily conserved secretory program that regulates tissue homeostasis. This program coordinates cell survival and proliferation during tissue regeneration and repair in young animals. By virtue of chronic engagement, however, it also contributes to the age-related decline of tissue homeostasis leading to degeneration, metabolic dysfunction, and cancer. Here, we review recent studies that shed light on the nature and regulation of this evolutionarily conserved secretory program.

An essential role for senescent cells in optimal wound healing through secretion of PDGF-AA

Cellular senescence suppresses cancer by halting the growth of premalignant cells, yet the accumulation of senescent cells is thought to drive age-related pathology through a senescence-associated secretory phenotype (SASP), the function of which is unclear. To understand the physiological role(s) of the complex senescent phenotype, we generated a mouse model in which senescent cells can be visualized and eliminated in living animals. We show that senescent fibroblasts and endothelial cells appear very early in response to a cutaneous wound, where they accelerate wound closure by inducing myofibroblast differentiation through the secretion of platelet-derived growth factor AA (PDGF-AA). In two mouse models, topical treatment of senescence-free wounds with recombinant PDGF-AA rescued the delayed wound closure and lack of myofibroblast differentiation. These findings define a beneficial role for the SASP in tissue repair and help to explain why the SASP evolved.

From tissue invasion to glucose metabolism: the many aspects of signal transducer and activator of transcription 3 pro-oncogenic activities

Abstract Background: The pro-oncogenic transcription factor STAT3 is constitutively active in tumours of many different origins, which often become addicted to its activity. STAT3 is believed to contribute to the initial survival of pre-cancerous cells as well as to hyper-proliferation and, later, metastasis.

MATERIALS AND METHODS

To evaluate the contribution of enhanced STAT3 activation in a controlled model system, we generated knock-in mice in which a mutant constitutively active Stat3C allele replaces the endogenous wild-type allele and analysed its contribution to breast tumorigenesis. Moreover, we generated Stat3C/C MEF cells and analysed their gene expression and metabolic profiles.

RESULTS

Constitutively active STAT3 could enhance the tumorigenic power of the rat Neu oncogene in MMTV-Neu transgenic mice and trigger the production of earlier onset and more invasive mammary tumours. Tumour-derived cell lines displayed higher migrating, invading and metastatic ability and showed disrupted distribution of cell-cell junction markers. These features were mediated by STAT3-dependent over-expression of the C-terminal tensin-like (Cten) focal adhesion protein. Moreover, STAT3C alone was able to induce aerobic glycolysis and down-regulate mitochondrial activity, both in primary fibroblasts and in STAT3-dependent tumour cell lines, acting via both HIF-1α-dependent and independent mechanisms.

CONCLUSIONS

STAT3 can induce a metabolic switch that predisposes cells to aberrant survival, enhanced proliferation and, finally, tumour transformation. Later, enhanced Cten expression contributes to tissue infiltration and metastasis. While not excluding the contribution of many other tumour-specific STAT3 target genes, our data provide a unifying explanation of several pro-oncogenic STAT3 activities.

Cellular senescence and the aging brain

Cellular senescence is a potent anti-cancer mechanism that arrests the proliferation of mitotically competent cells to prevent malignant transformation. Senescent cells accumulate with age in a variety of human and mouse tissues where they express a complex 'senescence-associated secretory phenotype' (SASP). The SASP includes many pro-inflammatory cytokines, chemokines, growth factors and proteases that have the potential to cause or exacerbate age-related pathology, both degenerative and hyperplastic. While cellular senescence in peripheral tissues has recently been linked to a number of age-related pathologies, its involvement in brain aging is just beginning to be explored. Recent data generated by several laboratories suggest that both aging and age-related neurodegenerative diseases are accompanied by an increase in SASP-expressing senescent cells of non-neuronal origin in the brain. Moreover, this increase correlates with neurodegeneration. Senescent cells in the brain could therefore constitute novel therapeutic targets for treating age-related neuropathologies.

PKM2, STAT3 and HIF-1α: The Warburg's vicious circle

The M2 isoform of pyruvate kinase, highly expressed in tumor cells, is known to engage a feed forward loop with the glycolysis master transcription factor HIF-1α. Gao and co-authors recently showed that dimeric PKM2 localizes to the nucleus in highly proliferating cancer cells, where it regulates in vivo growth by acting as a protein kinase and directly activating STAT3. STAT3 is therefore a novel player of the PKM2/HIF-1α feedback loop, since HIF-induced PKM2 activates STAT3 that in turn induces HIF-1α expression. These findings have profound implications for understanding the complex connections between gene regulation, metabolism, survival and proliferation in cancer.

Environmental stress, ageing and glial cell senescence: a novel mechanistic link to Parkinson's disease?

Exposure to environmental toxins is associated with a variety of age-related diseases including cancer and neurodegeneration. For example, in Parkinson's disease (PD), chronic environmental exposure to certain toxins has been linked to the age-related development of neuropathology. Neuronal damage is believed to involve the induction of neuroinflammatory events as a consequence of glial cell activation. Cellular senescence is a potent anti-cancer mechanism that occurs in a number of proliferative cell types and causes the arrest of proliferation of cells at risk of malignant transformation following exposure to potentially oncogenic stimuli. With age, senescent cells accumulate and express a senescence-associated secretory phenotype (SASP; that is the robust secretion of many inflammatory cytokines, growth factors and proteases). Whereas cell senescence in peripheral tissues has been causally linked to a number of age-related pathologies, little is known about the induction of cellular senescence and the SASP in the brain. On the basis of recently reported findings, we propose that environmental stressors associated with PD may act in part by eliciting senescence and the SASP within non neuronal glial cells in the ageing brain, thus contributing to the characteristic decline in neuronal integrity that occurs in this disorder.

Senescent cells and their secretory phenotype as targets for cancer therapy

Cancer is a devastating disease that increases exponentially with age. Cancer arises from cells that proliferate in an unregulated manner, an attribute that is countered by cellular senescence. Cellular senescence is a potent tumor-suppressive process that halts the proliferation, essentially irreversibly, of cells at risk for malignant transformation. A number of anti-cancer drugs have emerged that induce tumor cells to undergo cellular senescence. However, although a senescence response can halt the proliferation of cancer cells, the presence of senescent cells in tissues has been associated with age-related diseases, including, ironically, late-life cancer. Thus, anti-cancer therapies that can induce senescence might also drive aging phenotypes and age-related pathology. The deleterious effects of senescent cells most likely derive from their senescence-associated secretory phenotype or SASP. The SASP entails the secretion of numerous inflammatory cytokines, growth factors and proteases that can render the tissue microenvironment favorable for tumor growth. Here, we discuss the beneficial and detrimental effects of inducing cellular senescence, and propose strategies for targeting senescent cells as a means to fight cancer.

Glucocorticoids suppress selected components of the senescence-associated secretory phenotype

Cellular senescence suppresses cancer by arresting the proliferation of cells at risk for malignant transformation. Recently, senescent cells were shown to secrete numerous cytokines, growth factors, and proteases that can alter the tissue microenvironment and may promote age-related pathology. To identify small molecules that suppress the senescence-associated secretory phenotype (SASP), we developed a screening protocol using normal human fibroblasts and a library of compounds that are approved for human use. Among the promising library constituents was the glucocorticoid corticosterone. Both corticosterone and the related glucocorticoid cortisol decreased the production and secretion of selected SASP components, including several pro-inflammatory cytokines. Importantly, the glucocorticoids suppressed the SASP without reverting the tumor suppressive growth arrest and were efficacious whether cells were induced to senesce by ionizing radiation or strong mitogenic signals delivered by oncogenic RAS or MAP kinase kinase 6 overexpression. Suppression of the prototypical SASP component IL-6 required the glucocorticoid receptor, which, in the presence of ligand, inhibited IL-1α signaling and NF-κB transactivation activity. Accordingly, co-treatments combining glucocorticoids with the glucocorticoid antagonist RU-486 or recombinant IL-1α efficiently reestablished NF-κB transcriptional activity and IL-6 secretion. Our findings demonstrate feasibility of screening for compounds that inhibit the effects of senescent cells. They further show that glucocorticoids inhibit selected components of the SASP and suggest that corticosterone and cortisol, two FDA-approved drugs, might exert their effects in part by suppressing senescence-associated inflammation.

Direct costs in diabetic and non diabetic people: the population-based Turin study, Italy

BACKGROUND AND AIMS

We compared direct costs of diabetic and non diabetic people covered by the Italian National Health System, focusing on the influence of age, sex, type of diabetes and treatment.

METHODS AND RESULTS

Diabetic people living in Turin were identified through the Regional Diabetes Registry and the files of hospital discharges and prescriptions. Data sources were linked to the administrative databases to assess health care services used by diabetic (n = 33,792) and non diabetic people(n = 863,123). Data were analyzed with the two-part model; the estimated direct costs per person/year were €3660.8 in diabetic people and €895.6 in non diabetic people, giving a cost ratio of 4.1. Diabetes accounted for 11.4% of total health care expenditure. The costs were attributed to hospitalizations (57.2%), drugs (25.6%), to outpatient care (11.9%), consumable goods (4.4%) and emergency care (0.9%). Estimated costs increased from € 2670.8 in diabetic people aged <45 years to € 3724.1 in those aged >74 years, the latter representing two third of the diabetic cohort; corresponding figures in non diabetic people were € 371.6 and € 2155.9. In all expenditure categories cost ratios of diabetic vs non diabetic people were higher in people aged <45 years, in type 1 diabetes and in insulin-treated type 2 diabetes.

CONCLUSION

Direct costs are 4-fold higher in diabetic than in non diabetic people, mainly due to care of the elderly and inpatient care. In developed countries, demographic changes will have a profound impact on costs for diabetes in next years.

Lamin B1 loss is a senescence-associated biomarker

Cellular senescence is a potent tumor-suppressive mechanism that arrests cell proliferation and has been linked to aging. However, studies of senescence have been impeded by the lack of simple, exclusive biomarkers of the senescent state. Senescent cells develop characteristic morphological changes, which include enlarged and often irregular nuclei and chromatin reorganization. Because alterations to the nuclear lamina can affect both nuclear morphology and gene expression, we examined the nuclear lamina of senescent cells. We show here than lamin B1 is lost from primary human and murine cell strains when they are induced to senesce by DNA damage, replicative exhaustion, or oncogene expression. Lamin B1 loss did not depend on the p38 mitogen-activated protein kinase, nuclear factor-κB, ataxia telangiectasia-mutated kinase, or reactive oxygen species signaling pathways, which are positive regulators of senescent phenotypes. However, activation of either the p53 or pRB tumor suppressor pathway was sufficient to induce lamin B1 loss. Lamin B1 declined at the mRNA level via a decrease in mRNA stability rather than by the caspase-mediated degradation seen during apoptosis. Last, lamin B1 protein and mRNA declined in mouse tissue after senescence was induced by irradiation. Our findings suggest that lamin B1 loss can serve as biomarker of senescence both in culture and in vivo.

STAT3 can serve as a hit in the process of malignant transformation of primary cells

The transcription factor signal transducer and activator of transcription 3 (STAT3) acts downstream of many pro-oncogenic signals, including cytokines, growth factors and oncogenes, and is accordingly constitutively active in a wide variety of tumors that often become addicted to it. Moreover, STAT3 is a key player in mediating inflammation-driven tumorigenesis, where its aberrant continuous activation is typically triggered by local or systemic production of the pro-inflammatory cytokine IL-6. We recently showed that mouse embryonic fibroblasts (MEFs) derived from STAT3C k/in mice, which express physiological levels of the constitutively active mutant STAT3C, display features of transformed cells such as increased proliferation, resistance to apoptosis and senescence, and aerobic glycolysis. Here, we show that pre-existing constitutively active STAT3 is sufficient to prime primary MEFs for malignant transformation upon spontaneous immortalization. Transformation is strictly STAT3-dependent and correlates with high resistance to apoptosis and enhanced expression of anti-apoptotic/pro-survival genes. Additionally, hypoxia inducible factor (HIF)-1α level is elevated by twofold and contributes to STAT3 oncogenic activity by supporting high rates of aerobic glycolysis. Thus, constitutively active STAT3, an accepted essential factor for tumor growth/progression, can also act as a first hit in multistep carcinogenesis; this ability to predispose cells to malignant transformation may be particularly relevant in the pro-oncogenic niche represented by chronically inflamed tissues.

[The use of municipality-level data on mortality in Italy: SENTIERI Project]

In Italy, complete municipality-level data on specific-cause mortality have been available at central level since 1980; Italy's National Institute of Statistics (Istat) collects data from all municipalities using two sources: i) the Office of Vital Statistics; and ii) the Civil Status Office. The Office of Vital Statistics records data on events such as births, deaths and migration for the population with official residence in the municipality, with the aim of describing the resident population's structure and composition. The Civil Status Office records data on the demographic dynamics (not only marital status but also causes of death); the data refer to the population living in the municipality, independently of official residence. Changes in the status of a municipality (e.g., the creation of a new municipality or the unification of diverse municipalities) are often not recorded simultaneously by these two offices, so that the data do not correspond.

A STAT3-mediated metabolic switch is involved in tumour transformation and STAT3 addiction

The pro-oncogenic transcription factor STAT3 is constitutively activated in a wide variety of tumours that often become addicted to its activity, but no unifying view of a core function determining this widespread STAT3-dependence has yet emerged. We show here that constitutively active STAT3 acts as a master regulator of cell metabolism, inducing aerobic glycolysis and down-regulating mitochondrial activity both in primary fibroblasts and in STAT3-dependent tumour cell lines. As a result, cells are protected from apoptosis and senescence while becoming highly sensitive to glucose deprivation. We show that enhanced glycolysis is dependent on HIF-1α up-regulation, while reduced mitochondrial activity is HIF-1α-independent and likely caused by STAT3-mediated down-regulation of mitochondrial proteins. The induction of aerobic glycolysis is an important component of STAT3 pro-oncogenic activities, since inhibition of STAT3 tyrosine phosphorylation in the tumour cell lines down-regulates glycolysis prior to leading to growth arrest and cell death, both in vitro and in vivo. We propose that this novel, central metabolic role is at the core of the addiction for STAT3 shown by so many biologically different tumours.

Factors affecting in-hospital heat-related mortality: a multi-city case-crossover analysis

BACKGROUND

Several studies have identified strong effects of high temperatures on mortality at population level; however, individual vulnerability factors associated with heat-related in-hospital mortality are largely unknown. The objective of the study was to evaluate heat-related in-hospital mortality using a multi-city case-crossover analysis.

METHODS

We studied residents of four Italian cities, aged 65+ years, who died during 1997-2004. For 94,944 individuals who died in hospital and were hospitalised two or more days before death, demographics, chronic conditions, primary diagnoses of last event and hospital wards were considered. A city-specific case-crossover analysis was performed to evaluate the association between apparent temperature and mortality. Pooled odds ratios (OR) of dying on a day with a temperature of 30 degrees C compared to a day with a temperature of 20 degrees C were estimated with a random-effects meta-analysis.

RESULTS

We estimated an overall OR of 1.32 (95% confidence interval: 1.25, 1.39). Age, marital status and hospital ward were important risk indicators. Patients in general medicine were at higher risk than those in high and intensive care units. A history of psychiatric disorders and cerebrovascular diseases gave a higher vulnerability. Mortality was greater among patients hospitalised for heart failure, stroke and chronic pulmonary diseases.

CONCLUSIONS

In-hospital mortality is strongly associated with high temperatures. A comfortable temperature in hospitals and increased attention to vulnerable patients during heatwaves, especially in general medicine, are necessary preventive measures.

Airport and city-centre temperatures in the evaluation of the association between heat and mortality

A variety of ambient exposure indicators have been used to evaluate the impact of high temperature on mortality and in the identification of susceptible population sub-groups, but no study has evaluated how airport and city centre temperatures differ in their association with mortality during summer. This study considers the differences in temperatures measured at the airport and in the city centre of three Italian cities (Milan, Rome and Turin) and investigates the impact of these measures on daily mortality. The case-crossover design was applied to evaluate the association between daily mean apparent temperature (MAT) and daily total mortality. The analysis was conducted for the entire population and for subgroups defined by demographic characteristics, socioeconomic status and chronic comorbidity (based on hospitalisation during the preceding 2 years). The percentage risk of dying, with 95% confidence intervals (95% CI), on a day with MAT at the 95th percentile with respect to the 25th percentile of the June-September daily distribution was estimated. Airport and city-centre temperature distributions, which vary among cities and between stations, have a heterogeneous impact on mortality. Milan was the city with the greatest differences in mean MAT between airport and city stations, and the overall risk of dying was greater when airport MAT (+47% increase, 95%CI 38-57) was considered in comparison to city MAT (+37% increase, 95%CI 30-45). In Rome and Turin, the results were very similar for both apparent temperature measures. In all cities, the elderly, women and subjects with previous psychiatric conditions, depression, heart and circulation disorders and cerebrovascular disease were at higher risk of dying during hot days, and the degree of effect modification was similar using airport or city-centre MAT. Studies on the impact of meteorological variables on mortality, or other health indicators, need to account for the possible differences between airport and city centre meteorological variables in order to give more accurate estimates of health effects.

[Carpal tunnel syndrome (CTS) in the Piedmont Region: regional incidence and prevalence of CTS based on hospital records of patients who underwent surgery]

BACKGROUND

Carpal tunnel syndrome (CTS) is the most frequent entrapment neuropathy of the upper extremities. Despite CTS being a priority for public health, only a few studies have investigated the prevalence and incidence in the general population. In Italy, administrative data are available only for CTS cases which were judged work-related by the Workers Compensation Board. These data indicate a steady increase in CTS over the last decade. Hospital admission archives (SDO) also contain information on CTS patients who underwent surgery.

OBJECTIVES

To determine: 1) the incidence and prevalence of first CTS, based on hospital records of patients who underwent surgery in the Piedmont Region; 2) to describe the geographical and temporal variation.

METHODS

Crude and standardized incidence rates of CTS were computed for the period 2002-2003; geographical variation was assessed using bayesan estimators to detect spatial clusters. Crude and standardized prevalence rates of first hospitalization were calculated for every two-year period between 1996 and 2003.

RESULTS AND CONCLUSIONS

The crude incidence rate was 227.2 (C.I.95% 221.9-232.7) per 100,000 women and 54.4 (C.I. 95% 51.9-57.1) per 100,000 men. The prevalence of first hospitalization was very high and varied widely by geographic area. Two possible explanations for such wide variation between areas include differences in exposure to risk factors for CTS and in the diagnostic criteria used. The increasing prevalence over time was only partly explained by an increase in work-related cases. The development of standardized diagnostic criteria would improve understanding of the effect of workplace exposures on CTS. The number of new cases per year in Piedmont was estimated at 1,500, much higher than the compensation claims related to CTS. Health education campaigns addressed to general practitioners on compensation law could improve reporting to the workers' compensation board.

[Workplace injuries and professional mobility correlated with health problems. The potential and limitations of the ISTAT Labour Force survey--July 1999]

BACKGROUND

Knowledge on the occupational and social factors that influence the relationship between illness, absence from work and occupational mobility is at present insufficient.

OBJECTIVES

To map out, by social class and occupational group, the impact of health problems on work and the distribution of accidents and morbidity associated with occupation.

METHODS

Using data from the National Survey of the Italian Labour Force (ISTAT, 1999), covering a sample of 200,384 subjects, prevalence odds ratios of morbidity, work injuries and change of occupation due to health problems were calculated by social class and occupation, adjusting for age and residence.

RESULTS

The working class showed a higher risk, due to health problems, of a reduction in time worked (OR = 3.70 in men and OR = 4.10 in women), of choosing to work part-time (OR = 2.04 in men and OR = 2.27 in women), or of withdrawing from the workforce (for artisans, skilled manual workers, farmers and agricultural labourers OR = 1.63 in men and OR = 1.47 in women). This class was also at a greater disadvantage not only with respect to accident rates (OR = 1.85 in men and OR = 1.88 in women), but also with respect to the time needed for post-trauma rehabilitation and return to work (for absences of one week to one month: OR = 1.67 and 1.83 for men and women, respectively; for absences of more than one month: OR = 1.29 and OR = 1.69). Moreover, the working class, when compared to other social classes, had a higher rate of suffering from illness, physical impairment or other physical and psychological problems caused or aggravated by working activity (25% in men and 32% in women).

CONCLUSIONS

The ISTAT National Survey provides an estimate of minor accidents with prognoses of less than three days, including those not reported to the National Institute for Insurance against Occupational Accidents and Diseases (INAIL). This allows a preliminary exploration of the relationship between health problems and occupational mobility; however, it seems necessary to collect more detailed information in order to more exhaustively explore the mechanisms which generate the inequalities observed.

[Healthy life expectancy in the occupied segment of the Turin population]

BACKGROUND

The indicators of healthy life expectancy measure differences in health among various population subgroups more sensitively than do indicators of mortality.

OBJECTIVES

The aim of the study was to analyze some of the above indicators to evaluate the differences among occupational categories in Turin.

METHODS

Mortality tables by occupation were calculated on Turin residents, aged 18-64 years in 1991, using the Turin Longitudinal Study which combines personal, census, and health information for the residents of the city. Longitudinal assessments of health expectancy were obtained by means of record-linkage with the Cancer Registry, the Diabetes Registry, and hospital discharge records. In addition, prevalence estimates of good health, disability, and chronic illness, obtained from ISTAT (Central Statistics Institute) investigations in 1999-2000 were combined with mortality data using Sullivan's algorithm.

RESULTS

Among men there was a systematic disadvantage in almost all indicators of health expectancy for some manual occupations, while jobs requiring more qualifications were more advantaged. The health profile for women was more controversial, with an overall disadvantage among women who were professional consultants, although this group showed substantial variability: the legal professions had the lowest life and health expectancies, with approximately 3 years of life less than the health professions, which were among the most advantaged.

DISCUSSION

The various indicators gave results which were at times conflicting, especially because the information obtained from the available sources had major limitations. The development of indicators needs to aim for greater homogeneity between mortality and health data to ensure maximum comparability.