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Population aging is among the most important global transformations. Compared to European and North American countries, Chile is among the countries with the fastest growth of life expectancy at birth during recent decades. The aging of Chile's population is related to the improvement of living conditions, but also entails risks that tend to be associated with a rapid economic growth accompanied by large income inequalities and a chronic deficit of basic social benefits. The rapid demographic transition towards an aged population has unfolded in a context of poor development of public policies to tackle the opportunities and needs associated with an aging society. This article provides a brief overview of current Chilean public policy on aging, with a focus on healthy aging as defined by World Health Organization. The discussion addresses core challenges to successfully achieve healthy aging in Chile.

Reducing activity of the mTORC1/S6K1 pathway has been shown to extend lifespan in both vertebrate and invertebrate models. For instance, both pharmacological inhibition of mTORC1 with the drug rapamycin or S6K1 knockout extends lifespan in mice. Since studies with invertebrate models suggest that reducing translational activity can increase lifespan, we reasoned that the benefits of decreased mTORC1 or S6K1 activity might be due, at least in part, to a reduction of general translational activity. Here, we report that mice given a single dose of rapamycin have reduced translational activity, while mice receiving multiple injections of rapamycin over 4 weeks show no difference in translational activity compared with vehicle-injected controls. Furthermore, mice lacking S6K1 have no difference in global translational activity compared with wild-type littermates as measured by the percentage of ribosomes that are active in multiple tissues. Translational activity is reduced in S6K1-knockout mice following single injection of rapamycin, demonstrating that rapamycin’s effects on translation can occur independently of S6K1. Taken together, these data suggest that benefits of chronic rapamycin treatment or lack of S6K1 are dissociable from potential benefits of reduced translational activity, instead pointing to a model whereby changes in translation of specific subsets of mRNAs and/or translation-independent effects of reduced mTOR signaling underlie the longevity benefits.

In early 1951, the Israeli Knesset Library arranged to dedicate a series of the American Congressional Record to Senator Robert A. Taft, who “was unquestionably a major factor in the shaping of Pre...

Mutations in the LMNA gene, which encodes all A-type lamins, including lamin A and lamin C, cause a variety of tissue-specific degenerative diseases termed laminopathies. Little is known about the pathogenesis of these disorders. Previous studies have indicated that A-type lamins interact with the retinoblastoma protein (pRB). Here we probe the functional consequences of this association and further examine links between nuclear structure and cell cycle control. Since pRB is required for cell cycle arrest by p16(ink4a), we tested the responsiveness of multiple lamin A/C-depleted cell lines to overexpression of this CDK inhibitor and tumor suppressor. We find that the loss of A-type lamin expression results in marked destabilization of pRB. This reduction in pRB renders cells resistant to p16(ink4a)-mediated G(1) arrest. Reintroduction of lamin A, lamin C, or pRB restores p16(ink4a)-responsiveness to Lmna(-/-) cells. An array of lamin A mutants, representing a variety of pathologies as well as lamin A processing mutants, was introduced into Lmna(-/-) cells. Of these, a mutant associated with mandibuloacral dysplasia (MAD R527H), as well as two lamin A processing mutants, but not other disease-associated mutants, failed to restore p16(ink4a) responsiveness. Although our findings do not rule out links between altered pRB function and laminopathies, they fail to support such an assertion. These findings do link lamin A/C to the functional activation of a critical tumor suppressor pathway and further the possibility that somatic mutations in LMNA contribute to tumor progression.

Retinoblastoma (RB) tumor suppressor family pocket proteins induce cell cycle arrest by repressing transcription of E2F-regulated genes through both histone deacetylase (HDAC)-dependent and -independent mechanisms. In this study we have identified a stable complex that accounts for the recruitment of both repression activities to the pocket. One component of this complex is RBP1, a known pocket-binding protein that exhibits both HDAC-dependent and -independent repression functions. RB family proteins were shown to associate via the pocket with previously identified mSIN3-SAP30-HDAC complexes containing exclusively class I HDACs. Such enzymes do not interact directly with RB family proteins but rather utilize RBP1 to target the pocket. This mechanism was shown to account for the majority of RB-associated HDAC activity. We also show that in quiescent normal human cells this entire RBP1-mSIN3-SAP30-HDAC complex colocalizes with both RB family members and E2F4 in a limited number of discrete regions of the nucleus that in other studies have been shown to represent the initial origins of DNA replication following growth stimulation. These results suggest that RB family members, at least in part, drive exit from the cell cycle by recruitment of this HDAC complex via RBP1 to repress transcription from E2F-dependent promoters and possibly to alter chromatin structure at DNA origins.

A-type nuclear lamins, all encoded by the LMNA gene through alternative splicing, are targets for mutation in a wide range of rare diseases, including a dominant mutation that enhances production of lamin A splice variant progerin, causing Hutchinson-Gilford progeria syndrome (HGPS).1 Often ignored, however, is the complex and poorly understood connection between A-type lamins and cancer.2 Expression of the 2 main A-type lamins (Lamins A and C) vary in inconsistent patterns in a wide range of cancers. More recently, enhanced progerin expression has been associated with prostate cancer development, an intriguing finding, since this splice variant of lamin A occurs at low frequency in normal cells and has been associated with aging.1 A new study by Jung et al. reports a role for progerin in modulating p53 activity in renal cell carcinomas (RCCs), and, moreover, that progerin expression is controlled by the von Hippel-Lindau tumor suppressor (VHL).3 This is particularly interesting, since RCCs, like many cancers, are highly age-associated, and increasing influence of progerin with age could, at least in part, explain this phenomenon. Motivation for the study started with the puzzling observation that VHL inactivation is an early event in RCC tumor progression, inconsistent with its known role in promoting degradation of HIF-1α and thereby blocking the pro-angiogenic response to hypoxia.4 Putting together this observation with other clues, for instance that p53 declines functionally in RCCs generally without mutation, and that nuclear irregularities similar to those in HGPS (associated with progerin expression) are a common feature of RCCs, Jung et al. tested the hypothesis that VHL may regulate these pathways.3 Following these threads with extensive experimental studies, the authors found that RCCs lacking VHL have high progerin protein content in the absence of changes in LMNA mRNA levels, leading them to test and generate support for a model whereby the E3 ubiquitin ligase activity of VHL is required for progerin turnover.3 Excess progerin, in turn, binds to and sequesters p14/ARF, permitting p53 degradation through MDM2. Interestingly, this activity occurs independently of HIF-2α, another VHL regulated factor that can inhibit p53 function.5,6 Together, these findings connect VHL to the p53 pathway and ascribe to it additional tumor suppressor activities. Cellular production of normal lamin A involves the farnesylation of a cysteine residue in the C terminus of the protein.1 However, unlike other farnesylated proteins, such as Ras, the lamin A farnesylation event is transient, with proteolytic cleavage prior to the cysteine removing the modification in the mature protein. Progerin, however, lacks this cleavage site and remains permanently farnesylated, a feature that contributes to progeroid pathologies. Farnesyl transferase inhibitors, developed to inhibit Ras farnesylation, have been tested widely in cancer with limited success. The study by Jung et al. suggests that progerin may be another meaningful target of farnesyl transferase inhibitors in a subset of cancers.3 HGPS cells are reported to have both elevated DNA damage and an abnormal DNA damage response.1 However, the connection between progerin and p53 has not been made previously. This may be related to the nature of the cell being interrogated. For instance, primary fibroblasts engineered to express progerin have proliferation defects that can be suppressed through inhibition of p53 function by expression of HPV E6.7 Moreover, the progeroid phenotypes of a mouse HGPS model can be partially rescued by deletion of p53.8 The implication is that p53 remains at least partially active in these settings, even though progerin is expressed. One possibility is that the ability of progerin to interact with p14/ARF and suppress p53 depends on the immortalization status of the cells. Primary cells expressing progerin would maintain p53 inducibility, but not a subset of tumor cells, including RCCs. Consistently, Jung et al. identified a leukemia cell line where progerin expression was elevated, leading to inhibition of p53.3 However, they were also able to detect enhanced p53 expression in HGPS fibroblasts when progerin expression was reduced by siRNA, indicating that this regulatory pathway is at least partially intact. More studies will be needed to understand the complex interplay between progerin and p53 pathway components. Aging is the biggest risk factor for most forms of cancer, yet the molecular reasons underlying this phenomenon have yet to be ascertained. What changes in the aging organism enable cancer progression? While several possibilities, including dysregulated gene expression programs and enhanced inflammation, are likely factors, the study by Jung et al. raises a new possibility that progerin can interfere directly with normal events that mediate repair of DNA lesions.3 Further studies will be important to explore this intriguing possibility. (Fig. 1) Figure 1. Model for interactions between progerin and p53 pathway. This diagram, reproduced and enhanced from Jung et al.,3 demonstrates the proposed interactions between progerin and p53 in different settings. In normal cells (left), low progerin ...

A-type lamins, generated from the LMNA gene by differential splicing, are type V intermediate filament proteins that polymerize to form part of the nuclear lamina, and are of considerable medical interest because missense mutations in LMNA give rise to a wide range of dystrophic and progeroid syndromes. Among these are dilated cardiomyopathy and two forms of muscular dystrophy (limb-girdle and Emery-Dreifuss), which are modeled in lmna (-/-) mice and mice engineered to express human disease mutations. Our recent study demonstrates that cardiac and skeletal muscle pathology in lmna (-/-) mice can be attributed to elevated MTORC1 signaling leading to impairment of autophagic flux. An accompanying paper from another laboratory shows similar impairments in mice engineered to express the LMNA H222P associated with dilated cardiomyopathy in humans and also in left ventricular tissue from human subjects. MTORC1 inhibition with rapalogs restores autophagic flux and improves cardiac function in both mouse models, and extends survival in the lmna (-/-) mice. These findings elaborate a potential treatment option for dilated cardiomyopathy and muscular dystrophy associated with LMNA mutation and supplement growing evidence linking impaired autophagy to human disease.

The question of whether aging can be modeled in cell culture has been highly debated among specialists in the field ever since the seminal publication that primary fibroblasts undergo a finite numb...

Budding yeast is a preeminent model organism in studies of cellular aging pathways that are conserved in eukaryotes, including humans. There are two primary ways to query the lifespan of this organism.1 If one asks how many times a cell can divide, the answer will be its replicative life span (RLS). If, on the other hand, one asks how long a cell can stay alive without dividing, the answer will be its chronological life span (CLS). Budding yeast is a facultative aerobe with exceptional genetic tractability. Hence, many environmental and genetic factors are known to affect replicative and chronological lifespan. Since the context of the RLS and CLS assays is different, with dividing vs. non-dividing cells, it is not immediately obvious whether these factors should be overlapping. The results to date are ambiguous. Some well-studied interventions like dietary restriction as well as reduced TOR and protein kinase A signaling, extend both replicative and chronological lifespan.1 However, in a quantitative comparison of gene deletions that extend lifespan in both assays, no significant overlap was observed.2 Further complicating the issue is the differences in methodology regarding chronological aging. When performed in synthetic-defined complete (SDC) media, it was recently shown that acidification of the medium during the growth phase accelerates mortality.3 Lifespan is extended by buffering the culture medium to pH 6.0 or performing the experiment in rich YEPD medium, which is more refractory to acidification. Interestingly, a recent report indicates that media acidification may be a limiting component to long-term survival of non-proliferative mammalian cells as well.4 To what extent acidification accelerates normal CLS aging mechanisms and whether it relates at all to replicative aging remain unknown. Instead of focusing on the factors that are shared, or not, between CLS and RLS pathways, a different way to probe the relationship between CLS and RLS is to examine how one aging process affects the other. More than a decade ago, it was reported that the longer cells age chronologically, the fewer times they can divide when nutrients are restored.5 A new study by Murakami et al.6 found that chronologically aged cells had a reduced replicative lifespan, confirming the earlier report.5 In addition to replicating the initial study, in which the CLS portion of the assay was performed in YEPD, this study compared three CLS conditions: YEPD, SDC and buffered SDC, finding that replicative lifespan is dramatically shortened in the SDC conditions associated with acidification. These findings indicate that conditions associated with acidification and rapid chronological aging impact the replicative lifespan of the cells, suggesting that the consequences of acidification are related to those of slower aging in YPD and possibly replicative aging as well. Murakami et al. went further. The CLS to RLS transition is essentially a transition from a non-dividing state, to a dividing one. Hence, querying parameters associated with cell cycle progression ought to be pertinent for the CLS to RLS transition. Indeed, Murakami et al. found that cells with the greatest replicative potential after quiescence were smaller and arrested properly in the G1 phase of the cell cycle, before DNA replication. These results further support the significance of G1 control mechanisms in aging.7,8 Why would cells that are chronologically aged have a reduced replicative lifespan? All cells in a quiescent population would be exposed to damage, either due to acidification or other causes. However, the authors note that once the population reenters a proliferative state, this damage may stay with the mother cells. This would “free up” the daughters, maximizing the fitness of the population as a whole. This model is appealing and far-reaching. Cycles of quiescent and proliferative states are the norm not only for single-celled organisms in the wild, but also for cells in animal tissues. Many questions remain. For example, what is the mechanistic basis for the interventions (e.g., buffering acidification) that extend CLS, which then also extend RLS? Which aspect of G1 control is causally related to the CLS→RLS transition? Finally, while Murakami et al. examined how CLS influences RLS, the reverse relationship is also worth examining. Do replicatively older mothers have a reduced CLS and, if so, why? While standard CLS methods cannot address this issue, a plate-based CLS assay is theoretically amenable.9 Whatever the answers to the above questions might be, yeast aging with its chronological and replicative flavors will continue to drive progress in the field (Fig. 1). Figure 1. Schematic of the relationship between the non-dividing state of chronological aging (shown in yellow), and the dividing state during which cells age replicatively (shown in blue). Conditions such as acid stress, which accelerate chronological ...

Often described as the counterpart of the mammalian lysosome, the yeast vacuole is the destination for cellular constituents targeted for degradation by autophagic processes. However, the vacuole serves other roles, for instance, as a regulator of cellular ion homeostasis and a storage reservoir for nutrients, metal ions and other metabolites.1 The vacuole is also dynamically regulated, both in number and size in response to environmental conditions, including those linked to replicative lifespan.1 For instance, nutrient restriction, which extends lifespan or the number of daughters that one mother can produce, causes yeast cells to undergo vacuolar fusion events, leading to one large vacuole in place of the 4–5 that normally exist under nutrient-replete conditions. In contrast, osmotic stress leads to enhanced fission and the production of several small vacuolar fragments. In a recent report, Gebre et al. examine the relationship between vacuolar fusion and longevity, finding that overexpression of Osh6, an oxysterol-binding protein that mediates membrane sterol deposition, enhances longevity.2 Several yeast genes are required for vacuolar fusion, and in their absence, yeast vacuoles appear as a multitude of vesicles. Among these are ERG6, which is required for ergosterol synthesis,3 and NYV1, which encodes a vacuolar SNARE complex component.4 Both of these genes are also required for lifespan extension by calorie restriction.5 Also required are the set of OSH genes; in the absence of all seven, vacuoles are fragmented.6 Gebre et al. tested whether overexpression of any OSH gene rescued defects of other fragmentation mutants, finding that elevated Osh6 levels restored fusion in a nyv1Δ background.2 Overexpression of Osh6 did not rescue the erg6Δ, presumably because these genes act in the same pathway involving sterol synthesis and vacuolar membrane deposition. They then showed that OSH6 overexpression led to extension of replicative lifespan. These findings point to Osh6 as having a specific role in modulating vacuolar membrane sterol content and a potential relationship between this function and longevity. Another piece of evidence that vacuolar fusion may be important for longevity in yeast comes from the observation that vacuolar membranes become disordered in replicatively old cells.2,5 Thus, enhanced fusion driven by Osh6 overexpression may help maintain vacuoles in a normal state later in the lifespan of a yeast cell. It remains unclear, however, why this matters, particularly since young yeast cells can proliferate normally with fragmented vacuoles. One possibility comes back to the starvation response, in which autophagy becomes important for survival, as fusion events promote mixing of autophagic cargoes with vacuolar enzymes. Genome-wide transcriptional studies suggest that old cells attempt to initiate a starvation response. If vacuolar fusion is important for autophagic flux under these conditions, then defects in this process may compromise continued yeast viability and proliferation. A related view would be that vacuolar fragmentation may be an indicator of altered lipid composition in vacuolar membranes resulting from age-related elevation of autophagosome-fusion events.5 Reduced TOR signaling enhances lifespan in a wide range of organisms including yeast.7 Recent studies show that the TORC1 complex localizes to the vacuolar membrane and mediates vacuole fragmentation.8,9 Gebre et al. speculate that elevated Osh6 levels may inhibit TORC1 function at the vacuolar membrane, tipping the balance toward fusion.2 Consistently, Osh6 overexpression failed to further enhance the long lifespan of a tor1Δ strain, suggesting that the two genetic interventions may be leading to lifespan extension through similar mechanisms. One final possibility that cannot be ruled out is that Osh6 overexpression may affect lifespan in part through vacuole-independent mechanisms, since Gebre found unexpectedly that expression of sterol synthesis genes was reduced under these conditions. Of course, many of these possible pathways are non-exclusive, and Osh6 overexpression may affect replicative aging through multiple mechanisms. Many yeast aging genes have been identified, and it is paramount that the field begins to understand why altered expression of these genes affects longevity. The study by Gebre et al. points to a role for the vacuole in longevity control and possibly link this organelle to calorie restriction and TOR signaling.2 A critical next step will be to determine how altered vacuolar dynamics impact aging.

In Saccharomyces cerevisiae, methylation of the principal membrane sterol at C-24 produces the C-28 methyl group specific to ergosterol and represents one of the few structural differences between ergosterol and cholesterol. C-28 in S. cerevisiae has been suggested to be essential for the sparking function (W. J. Pinto and W. R. Nes, J. Biol. Chem. 258:4472-4476, 1983), a cell cycle event that may be required to enter G1 (C. Dahl, H.-P. Biemann, and J. Dahl, Proc. Natl. Acad. Sci. USA 84:4012-4016, 1987). The sterol biosynthetic pathway in S. cerevisiae was genetically altered to assess the functional role of the C-28 methyl group of ergosterol. ERG6, the putative structural gene for S-adenosylmethionine: delta 24-methyltransferase, which catalyzes C-24 methylation, was cloned, and haploid strains containing erg6 null alleles (erg6 delta 1 and erg6 delta ::LEU2) were generated. Although erg6 delta cells are unable to methylate ergosterol precursors at C-24, they exhibit normal vegatative growth, suggesting that C-28 sterols are not essential in S. cerevisiae. However, erg6 delta cells exhibit pleiotropic phenotypes that include defective conjugation, hypersensitivity to cycloheximide, resistance to nystatin, a severely diminished capacity for genetic transformation, and defective tryptophan uptake. These phenotypes reflect the role of ergosterol as a regulator of membrane permeability and fluidity. Genetic mapping experiments revealed that ERG6 is located on chromosome XIII, tightly linked to sec59.