Summary Reprogramming somatic cells to induced pluripotent stem cells (iPSCs), resets their identity back to an embryonic age, and thus presents a significant hurdle for modeling late-onset disorders. In this study, we describe a strategy for inducing aging-related features in human iPSC-derived lineages and apply it to the modeling of Parkinson’s disease (PD). Our approach involves expression of progerin, a truncated form of lamin A associated with premature aging. We found that expression of progerin in iPSC-derived fibroblasts and neurons induces multiple aging-related markers and characteristics, including dopamine-specific phenotypes such as neuromelanin accumulation. Induced aging in PD-iPSC-derived dopamine neurons revealed disease phenotypes that require both aging and genetic susceptibility, such as pronounced dendrite degeneration, progressive loss of tyrosine-hydroxylase (TH) expression and enlarged mitochondria or Lewy body-precursor inclusions. Thus, our study suggests that progerin-induced aging can be used to reveal late-onset age-related disease features in hiPSC-based disease models.

A major goal in aging research is to improve health during aging. In the case of mice, genetic manipulations that shorten or lengthen telomeres result, respectively, in decreased or increased longevity. Based on this, we have tested the effects of a telomerase gene therapy in adult (1 year of age) and old (2 years of age) mice. Treatment of 1- and 2-year old mice with an adeno associated virus (AAV) of wide tropism expressing mouse TERT had remarkable beneficial effects on health and fitness, including insulin sensitivity, osteoporosis, neuromuscular coordination and several molecular biomarkers of aging. Importantly, telomerase-treated mice did not develop more cancer than their control littermates, suggesting that the known tumorigenic activity of telomerase is severely decreased when expressed in adult or old organisms using AAV vectors. Finally, telomerase-treated mice, both at 1-year and at 2-year of age, had an increase in median lifespan of 24 and 13%, respectively. These beneficial effects were not observed with a catalytically inactive TERT, demonstrating that they require telomerase activity. Together, these results constitute a proof-of-principle of a role of TERT in delaying physiological aging and extending longevity in normal mice through a telomerase-based treatment, and demonstrate the feasibility of anti-aging gene therapy.

Identification of adult stem cells and their location (niches) is of great relevance for regenerative medicine.However, stem cell niches are still poorly defined in most adult tissues. Here, we show that the longest telomeres are a general feature of adult stem cell compartments. Using confocal telomere quantitative fluorescence in situ hybridization (telomapping), we find gradients of telomere length within tissues, with the longest telomeres mapping to the known stem cell compartments. In mouse hair follicles, we show that cells with the longest telomeres map to the known stem cell compartments, colocalize with stem cell markers, and behave as stem cells upon treatment with mitogenic stimuli. Using K15-EGFP reporter mice, which mark hair follicle stem cells, we show that GFP-positive cells have the longest telomeres. The stem cell compartments in small intestine, testis, cornea, and brain of the mouse are also enriched in cells with the longest telomeres. This constitutes the description of a novel general property of adult stem cell compartments. Finally, we make the novel finding that telomeres shorten with age in different mouse stem cell compartments, which parallels a decline in stem cell functionality, suggesting that telomere loss may contribute to stem cell dysfunction with age.[Keywords: Telomeres; stem cell niches; telomerase; mouse; aging] Supplemental material is available at http://www.genesdev.org.

A major limitation of studies of the relevance of telomere length to cancer and age-related diseases in human populations and to the development of telomere-based therapies has been the lack of suitable high-throughput (HT) assays to measure telomere length. We have developed an automated HT quantitative telomere FISH platform, HT quantitative FISH (Q-FISH), which allows the quantification of telomere length as well as percentage of short telomeres in large human sample sets. We show here that this technique provides the accuracy and sensitivity to uncover associations between telomere length and human disease.human disease ͉ quantitative FISH ͉ telomeres T elomeres are special structures at the ends of eukaryotic chromosomes that protect them from degradation and DNA repair activities (1). Telomerase is a reverse transcriptase that elongates telomeres in those cells where it is expressed, such as germ cells and stem cell populations (2, 3). Telomerase activity levels in adult tissues, however, are not sufficient to prevent telomere shortening associated to cell division, eventually leading to chromosomal instability and compromising tissue function (4-6). The notion that telomere shortening leads to loss of organismal viability is supported by premature aging phenotypes in late generation telomerase-deficient mice (5, 6) and by humans with decreased levels of telomerase and short telomeres, such as some cases of Dyskeratosis congenita and aplastic anemia (7,8). In contrast, cancer cells maintain their telomeres by up-regulating telomerase or by activating alternative telomere lengthening mechanisms (9, 10). Despite the relevance of telomere length to cancer and age-related diseases, on a few studies validated telomere length as a predictor for organismal fitness in human populations (11)(12)(13). Similarly, only a few telomere-based anticancer therapies have been developed to date by screening large compound libraries (14). These important drawbacks in telomere research have been due, at least in part, to the lack of fast and reliable high-throughput (HT) quantitative platforms to measure telomere length in large sample sets. Results Design and Validation of an HT Telomere Length QuantificationMethod. Quantitative fluorescence in situ hybridization (Q-FISH) of telomeres on metaphase spreads has been extensively used to obtain quantitative information on telomere length distributions (15-17). Also, the low detection limit of Q-FISH (Ͻ0.1 kb of telomere repeats) allows quantification of critically short telomeres (15-17), which is particularly relevant, because the frequency of critically short telomeres, rather than the mean telomere length, is determinant for telomere dysfunction (18,19). An important drawback of the conventional Q-FISH technique on metaphases has been, however, that it is extremely laborious and timeconsuming, thus precluding its application to human population studies and HT screenings. Here, we have developed an automated HT Q-FISH telomere-length analysis platform. Supporting information (S...

Telomere shortening to a critical length can trigger aging and shorter life spans in mice and humans by a mechanism that involves induction of a persistent DNA damage response at chromosome ends and loss of cellular viability. However, whether telomere length is a universal determinant of species longevity is not known. To determine whether telomere shortening can be a single parameter to predict species longevities, here we measured in parallel the telomere length of a wide variety of species (birds and mammals) with very different life spans and body sizes, including mouse (Mus musculus), goat (Capra hircus), Audouin’s gull (Larus audouinii), reindeer (Rangifer tarandus), griffon vulture (Gyps fulvus), bottlenose dolphin (Tursiops truncatus), American flamingo (Phoenicopterus ruber), and Sumatran elephant (Elephas maximus sumatranus). We found that the telomere shortening rate, but not the initial telomere length alone, is a powerful predictor of species life span. These results support the notion that critical telomere shortening and the consequent onset of telomeric DNA damage and cellular senescence are a general determinant of species life span.