Telomeres and telomerase biology in vertebrates: progress towards a non-human model for replicative senescence and ageing

Targeted therapies of curcumin focus on its therapeutic benefits in cancers and human health: Molecular signaling pathway-based approaches and future perspectives

The curry powder spices turmeric (Curcuma longa L.), which contains curcumin (diferuloylmethane), an orange-yellow chemical. Polyphenols are the most commonly used sources of curcumin. It combats oxidative stress and inflammation in diseases, such as hyperlipidemia, metabolic syndrome, arthritis, and depression. Most of these benefits are due to their anti-inflammatory and antioxidant properties. Curcumin consumption leads to decreased bioavailability, resulting in limited absorption, quick metabolism, and quick excretion, which hinders health improvement. Numerous factors can increase its bioavailability. Piperine enhances bioavailability when combined with curcumin in a complex. When combined with other enhancing agents, curcumin has a wide spectrum of health benefits. This review evaluates the therapeutic potential of curcumin with a specific emphasis on its approach based on molecular signaling pathways. This study investigated its influence on the progression of cancer, inflammation, and many health-related mechanisms, such as cell proliferation, apoptosis, and metastasis. Curcumin has a significant potential for the prevention and treatment of various diseases. Curcumin modulates several biochemical pathways and targets involved in cancer growth. Despite its limited tissue accumulation and bioavailability when administered orally, curcumin has proven useful. This review provides an in-depth analysis of curcumin's therapeutic applications, its molecular signaling pathway-based approach, and its potential for precision medicine in cancer and human health.

Senescence-Associated Secretory Phenotype as a Hinge Between Cardiovascular Diseases and Cancer

Overlapping risks for cancer and cardiovascular diseases (CVD), the two leading causes of mortality worldwide, suggest a shared biology between these diseases. The role of senescence in the development of cancer and CVD has been established. However, its role as the intersection between these diseases remains unclear. Senescence was originally characterized by an irreversible cell cycle arrest after a high number of divisions, namely replicative senescence (RS). However, it is becoming clear that senescence can also be instigated by cellular stress, so-called stress-induced premature senescence (SIPS). Telomere shortening is a hallmark of RS. The contribution of telomere DNA damage and subsequent DNA damage response/repair to SIPS has also been suggested. Although cellular senescence can mediate cell cycle arrest, senescent cells can also remain metabolically active and secrete cytokines, chemokines, growth factors, and reactive oxygen species (ROS), so-called senescence-associated secretory phenotype (SASP). The involvement of SASP in both cancer and CVD has been established. In patients with cancer or CVD, SASP is induced by various stressors including cancer treatments, pro-inflammatory cytokines, and ROS. Therefore, SASP can be the intersection between cancer and CVD. Importantly, the conventional concept of senescence as the mediator of cell cycle arrest has been challenged, as it was recently reported that chemotherapy-induced senescence can reprogram senescent cancer cells to acquire “stemness” (SAS: senescence-associated stemness). SAS allows senescent cancer cells to escape cell cycle arrest with strongly enhanced clonogenic growth capacity. SAS supports senescent cells to promote both cancer and CVD, particularly in highly stressful conditions such as cancer treatments, myocardial infarction, and heart failure. As therapeutic advances have increased overlapping risk factors for cancer and CVD, to further understand their interaction may provide better prevention, earlier detection, and safer treatment. Thus, it is critical to study the mechanisms by which these senescence pathways (SAS/SASP) are induced and regulated in both cancer and CVD.

Key miRNAs in Modulating Aging and Longevity: A Focus on Signaling Pathways and Cellular Targets

Aging is a multifactorial procedure accompanied by gradual deterioration of most biological procedures of cells. MicroRNAs (miRNAs) are a class of short non-coding RNAs that post-transcriptionally regulate the expression of mRNAs through sequence-specific binding, and contributing to many crucial aspects of cell biology. Several miRNAs are expressed differently in various organisms through aging. The function of miRNAs in modulating aging procedures has been disclosed recently with the detection of miRNAs that modulate longevity in the invertebrate model organisms, through the IIS pathway. In these model organisms, several miRNAs have been detected to both negatively and positively regulate lifespan via commonly aging pathways. miRNAs modulate age-related procedures and disorders in different mammalian tissues by measuring their tissue-specific expression in older and younger counterparts, including heart, skin, bone, brain, and muscle tissues. Moreover, several miRNAs have been contributed to modulating senescence in different human cells, and the roles of these miRNAs in modulating cellular senescence have allowed illustrating some mechanisms of aging. The review discusses the available data on miRNAs through the aging process and we highlight the roles of miRNAs as aging biomarkers and regulators of longevity in cellular senescence, tissue aging, and organism lifespan.

Hallmarks of lens aging and cataractogenesis

Lens homeostasis and transparency are dependent on the function and intercellular communication of its epithelia. While the lens epithelium is uniquely equipped with functional repair systems to withstand reactive oxygen species (ROS)-mediated oxidative insult, ROS are not necessarily detrimental to lens cells. Lens aging, and the onset of pathogenesis leading to cataract share an underlying theme; a progressive breakdown of oxidative stress repair systems driving a pro-oxidant shift in the intracellular environment, with cumulative ROS-induced damage to lens cell biomolecules leading to cellular dysfunction and pathology. Here we provide an overview of our current understanding of the sources and essential functions of lens ROS, antioxidative defenses, and changes in the major regulatory systems that serve to maintain the finely tuned balance of oxidative signaling vs. oxidative stress in lens cells. Age-related breakdown of these redox homeostasis systems in the lens leads to the onset of cataractogenesis. We propose eight candidate hallmarks that represent common denominators of aging and cataractogenesis in the mammalian lens: oxidative stress, altered cell signaling, loss of proteostasis, mitochondrial dysfunction, dysregulated ion homeostasis, cell senescence, genomic instability and intrinsic apoptotic cell death.

Characterization of tree shrew telomeres and telomerase

The use of tree shrews as experimental animals for biomedical research is a new practice. Several recent studies suggest that tree shrews are suitable for studying cancers, including breast cancer, glioblastoma, lung cancer, and hepatocellular carcinoma. However, the telomeres and the telomerase of tree shrews have not been studied to date. Here, we characterize telomeres and telomerase in tree shrews. The telomere length of tree shrews is approximately 23 kb, which is longer than that of primates and shorter than that of mice, and it is extended in breast tumor tissues according to Southern blot and flow-fluorescence in situ hybridization analyses. Tree shrew spleen, bone marrow, testis, ovary, and uterus show high telomerase activities, which are increased in breast tumor tissues by telomeric repeat amplification protocol assays. The telomere length becomes shorter, and telomerase activity decreases with age. The tree shrew TERT and TERC are more highly similar to primates than to rodents. These findings lay a solid foundation for using tree shrews to study aging and cancers.

Interphase Chromosomes in Replicative Senescence: Chromosome Positioning as a Senescence Biomarker and the Lack of Nuclear Motor-Driven Chromosome Repositioning in Senescent Cells

This study demonstrates, and confirms, that chromosome territory positioning is altered in primary senescent human dermal fibroblasts (HDFs). The chromosome territory positioning pattern is very similar to that found in HDFs made quiescent either by serum starvation or confluence; but not completely. A few chromosomes are found in different locations. One chromosome in particular stands out, chromosome 10, which is located in an intermediate location in young proliferating HDFs, but is found at the nuclear periphery in quiescent cells and in an opposing location of the nuclear interior in senescent HDFs. We have previously demonstrated that individual chromosome territories can be actively and rapidly relocated, with 15 min, after removal of serum from the culture media. These chromosome relocations require nuclear motor activity through the presence of nuclear myosin 1β (NM1β). We now also demonstrate rapid chromosome movement in HDFs after heat-shock at 42°C. Others have shown that heat shock genes are actively relocated using nuclear motor protein activity via actin or NM1β (Khanna et al., 2014; Pradhan et al., 2020). However, this current study reveals, that in senescent HDFs, chromosomes can no longer be relocated to expected nuclear locations upon these two types of stimuli. This coincides with a entirely different organisation and distribution of NM1β within senescent HDFs.

The Roles of mitochondrial dysfunction and Reactive Oxygen Species in Aging and Senescence

The aging process deteriorates organs' function at different levels, causing its progressive decline to resist stress, damage, and disease. In addition to alterations in metabolic control and gene expression, the rate of aging has been connected with the generation of high amounts of Reactive Oxygen Species (ROS). The essential perspective in free radical biology is that reactive oxygen species (ROS) and free radicals are toxic, mostly cause direct biological damage to targets, and are thus a major cause of oxidative stress. Different enzymatic and non-enzymatic compounds in the cells have roles in neutralizing this toxicity. Oxidative damage in aging is mostly high in particular molecular targets, such as mitochondrial DNA and aconitase, and oxidative stress in mitochondria can cause tissue aging across intrinsic apoptosis. Mitochondria's function and morphology are impaired through aging, following a decrease in the membrane potential by an increase in peroxide generation and size of the organelles. Telomeres may be the significant trigger of replicative senescence. Oxidative stress accelerates telomere loss, whereas antioxidants slow it down. Oxidative stress is a crucial modulator of telomere shortening, and that telomere-driven replicative senescence is mainly a stress response. The age-linked mitochondrial DNA mutation and protein dysfunction aggregate in some organs like the brain and skeletal muscle, thus contributing considerably to these post-mitotic tissues' aging. The aging process is mostly due to accumulated damage done by harmful species in some macromolecules such proteins, DNA, and lipids. The degradation of non-functional, oxidized proteins is a crucial part of the antioxidant defenses of cells, in which the clearance of these proteins occurs through autophagy in the cells, which is known as mitophagy for mitochondria.

Estimation of environmental, genetic and parental age at conception effects on telomere length in a wild mammal

Understanding individual variation in fitness-related traits requires separating the environmental and genetic determinants. Telomeres are protective caps at the ends of chromosomes that are thought to be a biomarker of senescence as their length predicts mortality risk and reflect the physiological consequences of environmental conditions. The relative contribution of genetic and environmental factors to individual variation in telomere length is, however, unclear, yet important for understanding its evolutionary dynamics. In particular, the evidence for transgenerational effects, in terms of parental age at conception, on telomere length is mixed. Here, we investigate the heritability of telomere length, using the 'animal model', and parental age at conception effects on offspring telomere length in a wild population of European badgers (Meles meles). Although we found no heritability of telomere length and low evolvability (<0.001), our power to detect heritability was low and a repeatability of 2% across individual lifetimes provides a low upper limit to ordinary narrow-sense heritability. However, year (32%) and cohort (3%) explained greater proportions of the phenotypic variance in telomere length, excluding qPCR plate and row variances. There was no support for cross-sectional or within-individual parental age at conception effects on offspring telomere length. Our results indicate a lack of transgenerational effects through parental age at conception and a low potential for evolutionary change in telomere length in this population. Instead, we provide evidence that individual variation in telomere length is largely driven by environmental variation in this wild mammal.

Evolution of telomere maintenance and tumour suppressor mechanisms across mammals

Mammalian species differ dramatically in telomere biology. Species larger than 5-10 kg repress somatic telomerase activity and have shorter telomeres, leading to replicative senescence. It has been proposed that evolution of replicative senescence in large-bodied species is an anti-tumour mechanism counteracting increased risk of cancer due to increased cell numbers. By contrast, small-bodied species express high telomerase activity and have longer telomeres. To counteract cancer risk due to longer lifespan, long-lived small-bodied species evolved additional telomere-independent tumour suppressor mechanisms. Here, we tested the connection between telomere biology and tumorigenesis by analysing the propensity of fibroblasts from 18 rodent species to form tumours. We found a negative correlation between species lifespan and anchorage-independent growth. Small-bodied species required inactivation of Rb and/or p53 and expression of oncogenic H-Ras to form tumours. Large-bodied species displayed a continuum of phenotypes requiring additional genetic 'hits' for malignant transformation. Based on these data we refine the model of the evolution of tumour suppressor mechanisms and telomeres. We propose that two different strategies evolved in small and large species because small-bodied species cannot tolerate small tumours that form prior to activation of the telomere barrier, and must instead use telomere-independent strategies that act earlier, at the hyperplasia stage.This article is part of the theme issue 'Understanding diversity in telomere dynamics'.

Biogerontology: research status, challenges and opportunities

Biogerontology is the study of the biological basis of ageing and age-related diseases. The phenomenon and the process of ageing are well understood in evolutionary and biological terms; and a conceptual framework has been established within which general principles of ageing and longevity can be formulated. The phenotype of ageing in terms of progressive loss of physical function and fitness is best seen during the period of survival after the evolution-determined essential lifespan (ELS) of a species. However, the ageing phenotype is highly heterogenous and individualistic at all levels from the whole body to the molecular one. Most significantly, the process and the progression of ageing are not determined by any specific gerontogenes. Ageing is the result of imperfect maintenance and repair systems that allow a progressive shrinkage of the homeodynamic space of an individual. The challenge is to develop and apply wholistic approaches to the complex trait of ageing for maintaining and/or improving health. One such approach is that of mild stress-induced physiological hormesis by physical, mental and nutritional hormetins. Biogerontological research offers numerous opportunities for developing evidence-based novel biomedical technologies for maintaining and improving health, for preventing the onset of age-related diseases, and for extending the health-span.

Development and validation of immortalized bovine mammary epithelial cell line as an in vitro model for the study of mammary gland functions

This study aimed to develop a bovine mammary epithelial (BME) cell line model, which provides a possibility to determine functional properties of the bovine mammary gland. The primary cell culture was derived from bovine mammary gland tissues and processed enzymatically to obtain cell colonies with epithelial-like morphology. The cultures of BME cells were purified and optimally cultured at 37 °C in DMEM/F12 medium supplemented with 10% fetal bovine serum. The BME cells were identified as epithelial cell line by the evaluating the expression of keratin-18 using immunofluorescence staining. A novel gene expression system strongly enhances the expression of telomerase, has been used to immortalize BME cell line termed hTBME cell line. Interestingly, telomerase remained active even after over 60 passages of hTBME cell line, required for immortalization of BME cells. In addition, the hTBME cell line was continuously subcultured with a spontaneous epithelial-like morphology, with a great proliferation activity, and without evidence of apoptotic and necrotic effects. Further characterization showed that hTBME cell line can be continuously propagated in culture with constant chromosomal features and without tumorigenic properties. Finally, established hTBME cell line was evaluated for mammary gland specific functions. Our results demonstrated that the hTBME cell line was able to retain functional-morphological structure, and functional differentiation by expression of beta (β)-casein as in the bovine mammary gland in vivo. Taken together, our findings suggest that the established hTBME cell line can serve as a valuable tool for the study of bovine mammary gland functions.

Prdx6 retards senescence and restores trabecular meshwork cell health by regulating reactive oxygen species

A progressive decline in antioxidant potential and accumulation of reactive oxygen species (ROS) are major causes of pathogenesis of several diseases, including glaucoma. Trabecular meshwork (TM) dysfunction resulting in higher intraocular pressure (IOP) is a hallmark of glaucoma, but its causes are unclear. Using human (h) TM cells derived from glaucomatous and normal subjects of different ages and cells facing oxidative-stress, we showed that specific loss of moonlighting antioxidant protein Peroxiredoxin (Prdx) 6 in aging or in glaucomatous TM cells caused ROS accumulation and pathobiological changes in TM cells. Prdx6 limits the levels of ROS, thus preventing overstimulation of genes and resultant deleterious effects. We found that Prdx6 levels declined in aging and were reduced dramatically in glaucomatous and aged TM cells. Biochemical assays revealed enhanced levels of ROS, and high expression/activation of TGFβs and its responsive extracellular matrix genes α-SM, fibronectin, TGase2 and Tsp1 in aged or glaucomatous cells. Furthermore, hTM cells displayed typical features of the combined effects of TGFβs and oxidative-stress-induced cellular changes, showing increased levels of lipid peroxidation, oxidative DNA damage, and senescence markers p16, p21 and SA-βgal activity, along with reduced levels of telomerase expression and activity. Exposure to oxidative-stress (H₂O₂) or knocking down of Prdx6 (with antisense) accelerated this process. Importantly, Prdx6 delivery to sick or aged TM cells reversed the process. We propose Prdx6 as a potential therapeutic target to guard the TM from oxidative-stress and age-dependent accumulation of ROS by balancing redox-homeostasis to prevent ocular disorders, like glaucoma.

No evidence for parental age effects on offspring leukocyte telomere length in free-living Soay sheep

In humans, the effect of paternal age at conception (PAC) on offspring leukocyte telomere length (LTL) is well established, with older fathers thought to pass on longer telomeres to their offspring in their sperm. Few studies have looked for PAC effects in other species, but it has been hypothesised that the effect will be exacerbated in polygamous species with higher levels of sperm competition and production. We test for maternal (MAC) and paternal age at conception effects on offspring LTL in Soay sheep, a primitive breed experiencing strong sperm competition. We use qPCR to measure relative telomere length in 389 blood samples (n = 318 individuals) collected from an unmanaged population of sheep on St Kilda, where individual age and parentage are known. We find no evidence that either MAC or PAC are associated with LTL in offspring across the age range, or when considering only young lambs (n = 164). This is the first study to test for parental age effects on offspring LTL in a wild mammal population, and the results contrast with the findings of numerous human studies that find a PAC effect, as well as predictions of a stronger PAC effect in polygamous species.

DNA Replication Origins and Fork Progression at Mammalian Telomeres

Telomeres are essential chromosomal regions that prevent critical shortening of linear chromosomes and genomic instability in eukaryotic cells. The bulk of telomeric DNA is replicated by semi-conservative DNA replication in the same way as the rest of the genome. However, recent findings revealed that replication of telomeric repeats is a potential cause of chromosomal instability, because DNA replication through telomeres is challenged by the repetitive telomeric sequences and specific structures that hamper the replication fork. In this review, we summarize current understanding of the mechanisms by which telomeres are faithfully and safely replicated in mammalian cells. Various telomere-associated proteins ensure efficient telomere replication at different steps, such as licensing of replication origins, passage of replication forks, proper fork restart after replication stress, and dissolution of post-replicative structures. In particular, shelterin proteins have central roles in the control of telomere replication. Through physical interactions, accessory proteins are recruited to maintain telomere integrity during DNA replication. Dormant replication origins and/or homology-directed repair may rescue inappropriate fork stalling or collapse that can cause defects in telomere structure and functions.

Sphere-Induced Rejuvenation of Swine and Human Müller Glia Is Primarily Caused by Telomere Elongation

Müller cells are the major supportive and protective glial cells in the retina with important functions in histogenesis and synaptogenesis during development, and in maintenance of mature neurons as they show to secrete various cytokines and manifest potentials of self-renewal and transdifferentiation into retinal neurons following injury in the vertebrate retinas. The swine retina has a visual streak structure similar to the human macular where cone photoreceptors are highly concentrated, thereby can serve as a better model for studying retinal diseases and for formulating cell-based therapeutics than the rodent retinas. Like most differentiated somatic mammalian cells, the isolated swine and human Müller glia become senescent over passages in culture, which restricts their potential application in basic and clinic researches. Here, we demonstrate that the senescence of swine and human Müller cells is caused by telomere attrition upon multiplications in vitro; and the senescent cells can be rejuvenated by sphere suspension culture. We also provide evidence that sphere-induced extension of telomeres in swine and human Müller glia is achieved by alternative lengthening of telomeres or/and by telomerase activation. Stem Cells 2017;35:1579-1591.

Lifelong leukocyte telomere dynamics and survival in a free-living mammal

Telomeres play a fundamental role in the maintenance of genomic integrity at a cellular level, and average leukocyte telomere length (LTL) has been proposed as a biomarker of organismal aging. However, studies tracking LTL across the entire life course of individuals are lacking. Here, we examined lifelong patterns of variation in LTL among four birth cohorts of female Soay sheep (Ovis aries) that were longitudinally monitored and sampled from birth to death. Over the first 4 months of life, there was within‐individual loss of LTL, consistent with findings in the human and primate literature, but there was little evidence of consistent LTL loss associated with age after this point. Overall, we observed only weak evidence of individual consistency in LTL across years and over the entire lifespan: Within‐individual variation was considerable, and birth cohorts differed markedly in their telomere dynamics. Despite the high levels of LTL variation within the lifetimes of individuals, there remained significant associations between LTL and longevity. Detailed analysis of the longitudinal data set showed that this association was driven by improved survival of individuals with longer LTL over the first 2 years of life. There was no evidence that LTL predicted survival in later adulthood. Our data provide the first evidence from a mammal that LTL can predict mortality and lifespan under natural conditions, and also highlight the potentially dynamic nature of LTL within the lifetimes of individuals experiencing a complex and highly variable environment.

Spontaneous immortalization of mouse liver sinusoidal endothelial cells

The spontaneous immortalization of cells in vitro is a rare event requiring genomic instability, such as alterations in chromosomes and mutations in genes. In the present study, we report a spontaneously immortalized liver sinusoidal endothelial cell (LSEC) line generated from mouse liver. These immortalized LSECs showed typical LSEC characteristics with the structure of transcellular fenestrations, the expression of von Willebrand factor (VWF) and the ability to uptake DiI-acetylated-low density lipoprotein (DiI-Ac-LDL). However, these immortalized LSECs lost the ability to form capillary-like structures, and showed clonal and multilayer growth without contact inhibition. Moreover, their proliferation rate increased with the increase in the number of passages. In addition, these cells obained the expression of CD31 and desmin, and showed an upregulation of p53 protein expression; however, their karyotype was normal, and they could not form colonies in soft agar or tumors in SCID mice. In conclusion, in the present study, we successfully established a spontaneously immortalized LSEC line.

The size-life span trade-off decomposed: why large dogs die young

Large body size is one of the best predictors of long life span across species of mammals. In marked contrast, there is considerable evidence that, within species, larger individuals are actually shorter lived. This apparent cost of larger size is especially evident in the domestic dog, where artificial selection has led to breeds that vary in body size by almost two orders of magnitude and in average life expectancy by a factor of two. Survival costs of large size might be paid at different stages of the life cycle: a higher early mortality, an early onset of senescence, an elevated baseline mortality, or an increased rate of aging. After fitting different mortality hazard models to death data from 74 breeds of dogs, we describe the relationship between size and several mortality components. We did not find a clear correlation between body size and the onset of senescence. The baseline hazard is slightly higher in large dogs, but the driving force behind the trade-off between size and life span is apparently a strong positive relationship between size and aging rate. We conclude that large dogs die young mainly because they age quickly.

Association of telomere instability with senescence of porcine cells

Background

Telomeres are essential for the maintenance of genomic stability, and telomere dysfunction leads to cellular senescence, carcinogenesis, aging, and age-related diseases in humans. Pigs have become increasingly important large animal models for preclinical tests and study of human diseases, and also may provide xeno-transplantation sources. Thus far, Southern blot analysis has been used to estimate average telomere lengths in pigs. Telomere quantitative fluorescence in situ hybridization (Q-FISH), however, can reveal status of individual telomeres in fewer cells, in addition to quantifying relative telomere lengths, and has been commonly used for study of telomere function of mouse and human cells. We attempted to investigate telomere characteristics of porcine cells using telomere Q-FISH method.

Results

The average telomere lengths in porcine cells measured by Q-FISH correlated with those of quantitative real-time PCR method (qPCR) or telomere restriction fragments (TRFs) by Southern blot analysis. Unexpectedly, we found that porcine cells exhibited high incidence of telomere doublets revealed by Q-FISH method, coincided with increased frequency of cellular senescence. Also, telomeres shortened during subculture of various porcine primary cell types. Interestingly, the high frequency of porcine telomere doublets and telomere loss was associated with telomere dysfunction-induced foci (TIFs). The incidence of TIFs, telomere doublets and telomere loss increased with telomere shortening and cellular senescence during subculture.

Conclusion

Q-FISH method using telomere PNA probe is particularly useful for characterization of porcine telomeres. Porcine cells exhibit high frequency of telomere instability and are susceptible to telomere damage and replicative senescence.

Fibroblast growth factor receptor 3 effects on proliferation and telomerase activity in sheep growth plate chondrocytes

BACKGROUND

Fibroblast growth factor receptor 3 (FGFR3) inhibits growth-plate chondrocyte proliferation and limits bone elongation. Gain-of-function FGFR3 mutations cause dwarfism, reduced telomerase activity and shorter telomeres in growth plate chondroyctes suggesting that FGFR3 reduces proliferative capacity, inhibits telomerase, and enhances senescence. Thyroid hormone (T3) plays a role in cellular maturation of growth plate chondrocytes and a known target of T3 is FGFR3. The present study addressed whether reduced FGFR3 expression enhanced telomerase activity, mRNA expression of telomerase reverse transcriptase (TERT) and RNA component of telomerase (TR), and chondrocyte proliferation, and whether the stimulation of FGFR3 by T3 evoked the opposite response.

RESULTS

Sheep growth-plate proliferative zone chondrocytes were cultured and transfected with siRNA to reduce FGFR3 expression; FGFR3 siRNA reduced chondrocyte FGFR3 mRNA and protein resulting in greater proliferation and increased TERT mRNA expression and telomerase activity (p < 0.05). Chondrocytes treated with T3 significantly enhanced FGFR3 mRNA and protein expression and reduced telomerase activity (p < 0.05); TERT and TR were not significantly reduced. The action of T3 at the growth plate may be partially mediated through the FGFR3 pathway.

CONCLUSIONS

The results suggest that FGFR3 inhibits chondrocyte proliferation by down-regulating TERT expression and reducing telomerase activity indicating an important role for telomerase in sustaining chondrocyte proliferative capacity during bone elongation.

An evolutionary review of human telomere biology: the thrifty telomere hypothesis and notes on potential adaptive paternal effects

Telomeres, repetitive DNA sequences found at the ends of linear chromosomes, play a role in regulating cellular proliferation, and shorten with increasing age in proliferating human tissues. The rate of age-related shortening of telomeres is highest early in life and decreases with age. Shortened telomeres are thought to limit the proliferation of cells and are associated with increased morbidity and mortality. Although natural selection is widely assumed to operate against long telomeres because they entail increased cancer risk, the evidence for this is mixed. Instead, here it is proposed that telomere length is primarily limited by energetic constraints. Cell proliferation is energetically expensive, so shorter telomeres should lead to a thrifty phenotype. Shorter telomeres are proposed to restrain adaptive immunity as an energy saving mechanism. Such a limited immune system, however, might also result in chronic infections, inflammatory stress, premature aging, and death--a more "disposable soma." With an increased reproductive lifespan, the fitness costs of premature aging are higher and longer telomeres will be favored by selection. Telomeres exhibit a paternal effect whereby the offspring of older fathers have longer telomeres due to increased telomere lengths of sperm with age. This paternal effect is proposed to be an adaptive signal of the expected age of male reproduction in the environment offspring are born into. The offspring of lineages of older fathers will tend to have longer, and thereby less thrifty, telomeres, better preparing them for an environment with higher expected ages at reproduction.

Telomere length and ApoE polymorphism in mild cognitive impairment, degenerative and vascular dementia

BACKGROUND

Clarifying the aetiology of dementia is of crucial importance in the management of patients as well as for research purposes but it is not always possible clinically. Therefore the identification of biological markers should complement clinical approaches. Telomere shortening is emerging as an important mechanism in vascular aging and the pathogenesis of hypertension and atherosclerosis. Thus, telomere length could be a potential candidate to accurately separate vascular from degenerative cognitive impairment.

OBJECTIVES

To evaluate the usefulness of telomere length alone or combined with ApoE polymorphism in diagnosing mild cognitive impairment (MCI) and in differentiating Alzheimer's disease (AD) from vascular (VaD) and mixed dementia (MD).

METHODS

Telomere length in peripheral blood lymphocytes was performed by flow cytometry in 439 patients (mean age, 85.1 years): 204 cognitively normal, 187 demented patients: 80 AD, 86 MD, and 21 with VaD; and 48 patients with MCI. Simple and multiple ordered logistic regressions were used to predict the risk of dementia from telomere length, ApoE polymorphism and age.

RESULTS

ApoEε4 was statistically associated with patients with dementia (p<0.001) compared to cognitively normal or MCI patients; but not with the aetiologies of dementia (AD, VaD and MD) (p=0.385). No significant differences in telomere length were found among patients with different aetiologies or severities of dementia. In the global model, the combination of telomere length and ApoE polymorphism did not confer a significantly higher dementia risk (OR=0.95, 95% CI=0.69-1.32; p=0.784) than APOEε4 alone (OR=2.12, 95% CI=1.15-3.9; p=0.016).

CONCLUSION

This longitudinal study in very old patients provided no evidence suggesting that telomere length alone could be used to distinguish between the different types of dementia or MCI, nor combined with the ApoE polymorphism.

Reprogramming murine telomerase rapidly inhibits the growth of mouse cancer cells in vitro and in vivo

Telomerase plays a critical role in cancer, prompting the pursuit of various telomerase-based therapeutic strategies. One such strategy, telomerase interference, exploits the high telomerase activity in cancer cells and reprograms telomerase to encode "toxic" telomeres. To date, telomerase interference has been tested in human cancer cells xenografted into mice, an approach that does not recapitulate spontaneous malignancy and offers few insights about host toxicities, because human telomerase is targeted in a mouse host. To address these limitations, we designed and validated two new gene constructs specifically targeting mouse telomerase: mutant template mouse telomerase RNA (MT-mTer) and small interfering RNA against wild-type mouse telomerase RNA (α-mTer-siRNA). Using lentiviral delivery in mouse prostate cancer cells, we achieved α-mTer-siRNA-mediated knockdown of wild-type mTer (80% depletion) and concurrent overexpression of MT-mTer (50-fold). We showed that the two constructs effectively synergize to reprogram murine telomerase to add mutant instead of wild-type telomeric repeats, resulting in rapid telomeric uncapping (5-fold increase in DNA damage foci). This, in turn, led to rapid and significant apoptosis (>90% of cells) and growth inhibition in vitro (90% reduction in viable cell mass) and in vivo (75% reduction in tumor allograft wet weight). In summary, we have shown that mouse cancer cells are vulnerable to direct telomerase interference using novel murine telomerase-targeting constructs; this approach can now be used to study the true therapeutic potential of telomerase interference in mouse spontaneous cancer models.

Genetic variation exists for telomeric array organization within and among the genomes of normal, immortalized, and transformed chicken systems

This study investigated telomeric array organization of diverse chicken genotypes utilizing in vivo and in vitro cells having phenotypes with different proliferation potencies. Our experimental objective was to characterize the extent and nature of array variation present to explore the hypothesis that mega-telomeres are a universal and fixed feature of chicken genotypes. Four different genotypes were studied including normal (UCD 001, USDA-ADOL Line 0), immortalized (DF-1), and transformed (DT40) cells. Both cytogenetic and molecular approaches were utilized to develop an integrated view of telomeric array organization. It was determined that significant variation exists within and among chicken genotypes for chromosome-specific telomeric array organization and total genomic-telomeric sequence content. Although there was variation for mega-telomere number and distribution, two mega-telomere loci were in common among chicken genetic lines (GGA 9 and GGA W). The DF-1 cell line was discovered to maintain a complex derivative karyotype involving chromosome fusions in the homozygous and heterozygous condition. Also, the DF-1 cell line was found to contain the greatest amount of telomeric sequence per genome (17%) as compared to UCD 001 (5%) and DT40 (1.2%). The chicken is an excellent model for studying unique and universal features of vertebrate telomere biology, and characterization of the telomere length variation among genotypes will be useful in the exploration of mechanisms controlling telomere length maintenance in different cell types having unique phenotypes.

Spontaneously immortalized mouse mesothelial cells display characteristics of malignant transformation

OBJECTIVES

Mesotheliomas occur in occult serous cavities after chronic exposure of mesothelial cells to asbestos fibres. Molecular events that contribute to the development of this cancer are therefore not readily accessible for study. We have used in vitro culture systems to study and compare induced and spontaneous transformation events in primary mouse mesothelial cells.

MATERIALS AND METHODS

Mouse mesothelial cells were cultivated until small populations of proliferating cells emerged from senescing cultures. Spontaneously transformed cultures of cells were characterized and compared to malignantly transformed cells.

RESULTS

Human mesothelial cells had a finite lifespan of 10-15 population doublings when cultured in vitro; mouse mesothelial cells typically exhibit this same pattern. Here, we show that mouse mesothelial cells can be cultured for extended periods and that these cells can transform spontaneously. Lines of spontaneously transformed cells generated in this study are immortal and growth factor-independent. They display the salient characteristic features of transformation, including increased proliferation rate, lack of contact inhibition, aneuploidy and ability to grow in anchorage-independent conditions. A subset of these cell lines developed into tumours in syngeneic mice. Comparative gene expression analysis demonstrated that spontaneously transformed cell lines were more closely related to neoplastic cells than to primary cells.

CONCLUSION

These findings have implications for interpretation of in vitro transformation studies, demonstrating broad similarity between spontaneous and induced genetic changes.

Distinct tumor suppressor mechanisms evolve in rodent species that differ in size and lifespan

Large, long-lived species experience more lifetime cell divisions and hence a greater risk of spontaneous tumor formation than smaller, short-lived species. Large, long-lived species are thus expected to evolve more elaborate tumor suppressor systems. In previous work, we showed that telomerase activity coevolves with body mass, but not lifespan, in rodents: telomerase activity is repressed in the somatic tissues of large rodent species but remains active in small ones. Without telomerase activity, the telomeres of replicating cells become progressively shorter until, at some critical length, cells stop dividing. Our findings therefore suggested that repression of telomerase activity mitigates the increased risk of cancer in larger-bodied species but not necessarily longer-lived ones. These findings imply that other tumor suppressor mechanisms must mitigate increased cancer risk in long-lived species. Here, we examined the proliferation of fibroblasts from 15 rodent species with diverse body sizes and lifespans. We show that, consistent with repressed telomerase activity, fibroblasts from large rodents undergo replicative senescence accompanied by telomere shortening and overexpression of p16(Ink4a) and p21(Cip1/Waf1) cycline-dependent kinase inhibitors. Interestingly, small rodents with different lifespans show a striking difference: cells from small shorter-lived species display continuous rapid proliferation, whereas cells from small long-lived species display continuous slow proliferation. We hypothesize that cells of small long-lived rodents, lacking replicative senescence, have evolved alternative tumor-suppressor mechanisms that prevent inappropriate cell division in vivo and slow cell growth in vitro. Thus, large-bodied species and small but long-lived species have evolved distinct tumor suppressor mechanisms.

Coevolution of telomerase activity and body mass in mammals: from mice to beavers

Telomerase is repressed in the majority of human somatic tissues. As a result human somatic cells undergo replicative senescence, which plays an important role in suppressing tumorigenesis, and at the same time contributes to the process of aging. Repression of somatic telomerase activity is not a universal phenomenon among mammals. Mice, for example, express telomerase in somatic tissues, and mouse cells are immortal when cultured at physiological oxygen concentration. What is the status of telomerase in other animals, beyond human and laboratory mouse, and why do some species evolve repression of telomerase activity while others do not? Here we discuss the data on telomere biology in various mammalian species, and a recent study of telomerase activity in a large collection of wild rodent species, which showed that telomerase activity coevolves with body mass, but not lifespan. Large rodents repress telomerase activity, while small rodents maintain high levels of telomerase activity in somatic cells. We discuss a model that large body mass presents an increased cancer risk, which drives the evolution of telomerase suppression and replicative senescence.

Assessing ageing of individual T lymphocytes: mission impossible?

Effector T lymphocytes are the progeny of a limited number of antigen-specific precursor cells and it has been estimated that clonotypic human T cells may expand million fold on their way reaching high cell numbers that are sufficient for immune protection. Moreover, memory T cell responses are characterized by repetitive expansion of antigen-specific T cell clonotypes, and limitations in the proliferative capacity could lead to immune senescence. Because telomeres progressively shorten as a function of cell division, telomere length is a powerful indicator of the replicative in vivo history of human T lymphocytes. In this review, we summarize observations made over the last decade on telomere length dynamics of well-defined T cell populations derived from healthy donors and patients with infectious disease or cancer. We focus on T cell differentiation, T cell ageing, and natural and vaccine induced immune responses. We also discuss the scientific evidence for in vivo replicative senescence of antigen-specific T cells, and evaluate the available methods for measuring telomere lengths and telomerase activity, and their potential and limitations to increase our understanding of T cell physiology.

Characteristics of primary and immortalized fibroblast cells derived from the miniature and domestic pigs

Background

The pig, Sus scrofa domestica includes both the miniature and commercial domestic breed. These animals have influenced the human life and economies and have been studied throughout history. Although the miniature breeds are more recent and have increasingly been used in a variety of biomedical studies, their cell lines have rarely been established. Therefore, we sought to establish primary and immortal cell lines derived from both the miniature and domestic pig to better enable insight into possible in vivo growth differences.

Results

The in vitro lifespan of primary domestic pig fibroblast (PF) and miniature pig fibroblast (MPF) cells using a standard 3T3 protocol was determined. Both of the primary PF and MPF cells were shown to have a two-step replicative senescence barrier. Primary MPF cells exhibited a relatively shorter lifespan and slower proliferation rate compared to those of primary PF cells. Beyond senescence barriers, lifespan-extended PF and MPF cells were eventually established and indicated spontaneous cellular immortalization. In contrast to the immortalized PF cells, immortal MPF cells showed a transformed phenotype and possessed more frequent chromosomal abnormalities and loss of p53 regulatory function. The lifespan of primary MPF and PF cells was extended by inactivation of the p53 function using transduction by SV40LT without any detectable senescent phenotype.

Conclusion

These results suggest that p53 signaling might be a major determinant for the replicative senescence in the MPF cells that have the shorter lifespan and slower growth rate compared to PF cells in vitro.

Endothelial senescence after high-cholesterol, high-fat diet challenge in baboons

Increasing evidence indicates that replicative senescence and premature endothelial senescence could contribute to endothelial dysfunction. This study aims at testing the hypothesis that a high-fat diet may lead to premature vascular endothelial senescence in a nonhuman primate model. We isolated endothelial cells from left and right femoral arteries in 10 baboons before and after a 7-wk high-fat dietary treatment. We compared the morphological alterations, replicative capacities, and senescence-associated β-galactosidase activities (SA-β-gal) at these two time points. We found that high-fat diet increased the prevalence of endothelial senescence. Endothelial replicative capacities declined dramatically, and SA-β-gal activities increased significantly in postdietary challenge. There was no change in telomeric length using quantitative flow fluorescence in situ hybridization analysis, suggesting that some stressors lead to cell senescence independent of telomere dysfunction. Our findings that high-fat diet causes endothelial damage through the premature senescence suggest a novel mechanism for the diet-induced endothelial dysfunction.