Randy Strong

Rapamycin fed late in life extends lifespan in genetically heterogeneous mice

Inhibition of the TOR signalling pathway by genetic or pharmacological intervention extends lifespan in invertebrates, including yeast, nematodes and fruitflies; however, whether inhibition of mTOR signalling can extend lifespan in a mammalian species was unknown. Here we report that rapamycin, an inhibitor of the mTOR pathway, extends median and maximal lifespan of both male and female mice when fed beginning at 600 days of age. On the basis of age at 90% mortality, rapamycin led to an increase of 14% for females and 9% for males. The effect was seen at three independent test sites in genetically heterogeneous mice, chosen to avoid genotype-specific effects on disease susceptibility. Disease patterns of rapamycin-treated mice did not differ from those of control mice. In a separate study, rapamycin fed to mice beginning at 270 days of age also increased survival in both males and females, based on an interim analysis conducted near the median survival point. Rapamycin may extend lifespan by postponing death from cancer, by retarding mechanisms of ageing, or both. To our knowledge, these are the first results to demonstrate a role for mTOR signalling in the regulation of mammalian lifespan, as well as pharmacological extension of lifespan in both genders. These findings have implications for further development of interventions targeting mTOR for the treatment and prevention of age-related diseases.

Inhibition of mTOR by rapamycin abolishes cognitive deficits and reduces amyloid-β levels in a mouse model of alzheimer's disease

Background Reduced TOR signaling has been shown to significantly increase lifespan in a variety of organisms [1], [2], [3], [4]. It was recently demonstrated that long-term treatment with rapamycin, an inhibitor of the mTOR pathway[5], or ablation of the mTOR target p70S6K[6] extends lifespan in mice, possibly by delaying aging. Whether inhibition of the mTOR pathway would delay or prevent age-associated disease such as AD remained to be determined. Methodology/Principal Findings We used rapamycin administration and behavioral tools in a mouse model of AD as well as standard biochemical and immunohistochemical measures in brain tissue to provide answers for this question. Here we show that long-term inhibition of mTOR by rapamycin prevented AD-like cognitive deficits and lowered levels of Aβ42, a major toxic species in AD[7], in the PDAPP transgenic mouse model. These data indicate that inhibition of the mTOR pathway can reduce Aβ42 levels in vivo and block or delay AD in mice. As expected from the inhibition of mTOR, autophagy was increased in neurons of rapamycin-treated transgenic, but not in non-transgenic, PDAPP mice, suggesting that the reduction in Aβ and the improvement in cognitive function are due in part to increased autophagy, possibly as a response to high levels of Aβ. Conclusions/Significance Our data suggest that inhibition of mTOR by rapamycin, an intervention that extends lifespan in mice, can slow or block AD progression in a transgenic mouse model of the disease. Rapamycin, already used in clinical settings, may be a potentially effective therapeutic agent for the treatment of AD.

Rapamycin, But Not Resveratrol or Simvastatin, Extends Life Span of Genetically Heterogeneous Mice

Rapamycin was administered in food to genetically heterogeneous mice from the age of 9 months and produced significant increases in life span, including maximum life span, at each of three test sites. Median survival was extended by an average of 10% in males and 18% in females. Rapamycin attenuated age-associated decline in spontaneous activity in males but not in females. Causes of death were similar in control and rapamycin-treated mice. Resveratrol (at 300 and 1200 ppm food) and simvastatin (12 and 120 ppm) did not have significant effects on survival in male or female mice. Further evaluation of rapamycins effects on mice is likely to help delineate the role of the mammalian target of rapamycin complexes in the regulation of aging rate and age-dependent diseases and may help to guide a search for drugs that retard some or all of the diseases of aging.

Molecular interplay between mammalian target of rapamycin (mTOR), amyloid-β, and Tau: Effects on cognitive impairments

Accumulation of amyloid-β (Aβ) and Tau is an invariant feature of Alzheimer disease (AD). The upstream role of Aβ accumulation in the disease pathogenesis is widely accepted, and there is strong evidence showing that Aβ accumulation causes cognitive impairments. However, the molecular mechanisms linking Aβ to cognitive decline remain to be elucidated. Here we show that the buildup of Aβ increases the mammalian target of rapamycin (mTOR) signaling, whereas decreasing mTOR signaling reduces Aβ levels, thereby highlighting an interrelation between mTOR signaling and Aβ. The mTOR pathway plays a central role in controlling protein homeostasis and hence, neuronal functions; indeed mTOR signaling regulates different forms of learning and memory. Using an animal model of AD, we show that pharmacologically restoring mTOR signaling with rapamycin rescues cognitive deficits and ameliorates Aβ and Tau pathology by increasing autophagy. Indeed, we further show that autophagy induction is necessary for the rapamycin-mediated reduction in Aβ levels. The results presented here provide a molecular basis for the Aβ-induced cognitive deficits and, moreover, show that rapamycin, an FDA approved drug, improves learning and memory and reduces Aβ and Tau pathology.Accumulation of amyloid-beta (Abeta) and Tau is an invariant feature of Alzheimer disease (AD). The upstream role of Abeta accumulation in the disease pathogenesis is widely accepted, and there is strong evidence showing that Abeta accumulation causes cognitive impairments. However, the molecular mechanisms linking Abeta to cognitive decline remain to be elucidated. Here we show that the buildup of Abeta increases the mammalian target of rapamycin (mTOR) signaling, whereas decreasing mTOR signaling reduces Abeta levels, thereby highlighting an interrelation between mTOR signaling and Abeta. The mTOR pathway plays a central role in controlling protein homeostasis and hence, neuronal functions; indeed mTOR signaling regulates different forms of learning and memory. Using an animal model of AD, we show that pharmacologically restoring mTOR signaling with rapamycin rescues cognitive deficits and ameliorates Abeta and Tau pathology by increasing autophagy. Indeed, we further show that autophagy induction is necessary for the rapamycin-mediated reduction in Abeta levels. The results presented here provide a molecular basis for the Abeta-induced cognitive deficits and, moreover, show that rapamycin, an FDA approved drug, improves learning and memory and reduces Abeta and Tau pathology.

Rapamycin slows aging in mice

Rapamycin increases lifespan in mice, but whether this represents merely inhibition of lethal neoplastic diseases, or an overall slowing in multiple aspects of aging is currently unclear. We report here that many forms of age‐dependent change, including alterations in heart, liver, adrenal glands, endometrium, and tendon, as well as age‐dependent decline in spontaneous activity, occur more slowly in rapamycin‐treated mice, suggesting strongly that rapamycin retards multiple aspects of aging in mice, in addition to any beneficial effects it may have on neoplastic disease. We also note, however, that mice treated with rapamycin starting at 9 months of age have significantly higher incidence of testicular degeneration and cataracts; harmful effects of this kind will guide further studies on timing, dosage, and tissue‐specific actions of rapamycin relevant to the development of clinically useful inhibitors of TOR action.

Expression of heat shock protein 70 is altered by age and diet at the level of transcription

Because heat shock proteins have been shown to play a critical role in protecting cells from hyperthermia and other types of physiological stresses, it was of interest to determine what effect age and caloric restriction have on the ability of cells to regulate the expression of heat shock protein 70 (hsp70), the most prominent and most evolutionarily conserved of the heat shock proteins. Caloric restriction is the only experimental manipulation known to retard aging and increase survival of mammals. The ability of hepatocytes isolated from young/adult (4- to 7-month-old) and old (22- to 28-month-old) male Fischer F344 rats fed ad libitum or a caloric restriction diet (60% of the content of the ad libitum diet) to express hsp70 was determined after a mild heat shock (42.5 degrees C for 30 min). We found that the induction of hsp70 synthesis and mRNA levels by heat shock was 40 to 50% lower in hepatocytes isolated from old rats than in hepatocytes isolated from young rats. Using in situ hybridization, we found that essentially all hepatocytes from the young/adult and old rats expressed hsp70 in response to heat shock; therefore, the age-related decrease in the induction of hsp70 expression was not due to an age-related accumulation of cells that do not respond to heat shock. Measurements of hsp70 mRNA stability and hsp70 transcription demonstrated that the age-related decline in hsp70 expression arose from a decline in hsp70 transcription. Interestingly, the age-related decline in the induction of hsp70 expression was reversed by caloric restriction; e.g., the induction of hsp70 synthesis, mRNA levels, and nuclear transcription were significantly higher in hepatocytes isolated from old rats fed the caloric restricted diet than in hepatocytes isolated from old rats fed ad libitum. The levels of the heat shock transcription factor in nuclear extracts isolated from heat-shocked hepatocytes were measured in a gel shift assay. Binding of the heat shock transcription factor to the heat shock element decreased with age and was significantly higher in hepatocyte extracts isolated from old rats fed the caloric restriction diet than in those from old rats fed ad libitum. Thus, our study demonstrates that the ability of hepatocytes to respond to hyperthermia and express hsp70 decreases significantly with age and that this decrease occurs at the transcriptional level. In addition, caloric restriction, which retards aging, reversed the age-related decline in the induction of hsp70 transcription in hepatocytes.

Rapamycin-mediated lifespan increase in mice is dose and sex dependent and metabolically distinct from dietary restriction.

Rapamycin, an inhibitor of mTOR kinase, increased median lifespan of genetically heterogeneous mice by 23% (males) to 26% (females) when tested at a dose threefold higher than that used in our previous studies; maximal longevity was also increased in both sexes. Rapamycin increased lifespan more in females than in males at each dose evaluated, perhaps reflecting sexual dimorphism in blood levels of this drug. Some of the endocrine and metabolic changes seen in diet‐restricted mice are not seen in mice exposed to rapamycin, and the pattern of expression of hepatic genes involved in xenobiotic metabolism is also quite distinct in rapamycin‐treated and diet‐restricted mice, suggesting that these two interventions for extending mouse lifespan differ in many respects.

Inducing autophagy by rapamycin before, but not after, the formation of plaques and tangles ameliorates cognitive deficits.

Previous studies have shown that inducing autophagy ameliorates early cognitive deficits associated with the build-up of soluble amyloid-β (Aβ). However, the effects of inducing autophagy on plaques and tangles are yet to be determined. While soluble Aβ and tau represent toxic species in Alzheimers disease (AD) pathogenesis, there is well documented evidence that plaques and tangles also are detrimental to normal brain function. Thus, it is critical to assess the effects of inducing autophagy in an animal model with established plaques and tangles. Here we show that rapamycin, when given prophylactically to 2-month-old 3xTg-AD mice throughout their life, induces autophagy and significantly reduces plaques, tangles and cognitive deficits. In contrast, inducing autophagy in 15-month-old 3xTg-AD mice, which have established plaques and tangles, has no effects on AD-like pathology and cognitive deficits. In conclusion, we show that autophagy induction via rapamycin may represent a valid therapeutic strategy in AD when administered early in the disease progression.

Rapamycin Reverses Elevated mTORC1 Signaling in Lamin A/C–Deficient Mice, Rescues Cardiac and Skeletal Muscle Function, and Extends Survival

Rapamycin treatment of a mouse model for a human laminopathy improves cardiac and muscle function, suggesting a therapy for human patients. Rapping Down mTORC1 Aids Ailing Muscles Rapamycin—a bacterial product discovered in soil samples from the eponymous Rapa Nui, or Easter Island—is a markedly versatile drug. Clinically, it is used to prevent organ transplant rejection, treat cancer, and improve angioplasty outcomes; it also increases life span in organisms ranging from yeast to mice. Now, Ramos and colleagues show its potential for treating muscle disease caused by mutations in LMNA. LMNA encodes A-type lamins, intermediate filament proteins that form the nuclear lamina, a layer just under the nuclear membrane. Different LMNA mutations cause distinct diseases, but reduced A-type lamin function is generally linked to skeletal muscle dystrophy and dilated cardiomyopathy, in which the heart is enlarged and weakened. Mice that lack Lmna likewise develop these conditions, dying young of heart problems. Ramos et al. speculated that signaling pathways involved in muscle remodeling, such as that for the kinase mTOR—the mammalian target of rapamycin—might be dysregulated in Lmna−/− mice, contributing to their problems. mTOR complex 1 (mTORC1) senses information about energy, nutrients, and stress; in response, it regulates cellular processes such as protein synthesis and autophagy (in which cellular components are degraded to reallocate nutrients). The authors found that mTORC1 signaling was hyperactivated in skeletal and heart muscle in Lmna−/− mice. Furthermore, the mTORC1 inhibitor rapamycin decreased mTORC1 signaling, improved skeletal and cardiac muscle function, and increased the life span of these mice. Lmna−/− mice also exhibited defective autophagy, which could be improved by rapamycin. In addition, previous work showed abnormal aggregation of desmin, which normally forms filaments that are important for muscle structure, in these mice. Rapamycin decreased these aggregates. This study indicates that hyperactive mTORC1 signaling helps to create the phenotypes of Lmna−/− mice. There are no effective treatments for the related conditions in humans; this work—and related findings reported by Choi et al. in this issue—indicate that rapamycin-related compounds might serve such a role. Mutations in LMNA, the gene that encodes A-type lamins, cause multiple diseases including dystrophies of the skeletal muscle and fat, dilated cardiomyopathy, and progeria-like syndromes (collectively termed laminopathies). Reduced A-type lamin function, however, is most commonly associated with skeletal muscle dystrophy and dilated cardiomyopathy rather than lipodystrophy or progeria. The mechanisms underlying these diseases are only beginning to be unraveled. We report that mice deficient in Lmna, which corresponds to the human gene LMNA, have enhanced mTORC1 (mammalian target of rapamycin complex 1) signaling specifically in tissues linked to pathology, namely, cardiac and skeletal muscle. Pharmacologic reversal of elevated mTORC1 signaling by rapamycin improves cardiac and skeletal muscle function and enhances survival in mice lacking A-type lamins. At the cellular level, rapamycin decreases the number of myocytes with abnormal desmin accumulation and decreases the amount of desmin in both muscle and cardiac tissue of Lmna−/− mice. In addition, inhibition of mTORC1 signaling with rapamycin improves defective autophagic-mediated degradation in Lmna−/− mice. Together, these findings point to aberrant mTORC1 signaling as a mechanistic component of laminopathies associated with reduced A-type lamin function and offer a potential therapeutic approach, namely, the use of rapamycin-related mTORC1 inhibitors.

Nordihydroguaiaretic acid and aspirin increase lifespan of genetically heterogeneous male mice

The National Institute on Agings Interventions Testing Program was established to evaluate agents that are purported to increase lifespan and delay the appearance of age‐related disease in genetically heterogeneous mice. Up to five compounds are added to the study each year and each compound is tested at three test sites (The Jackson Laboratory, University of Michigan, and University of Texas Health Science Center at San Antonio). Mice in the first cohort were exposed to one of four agents: aspirin, nitroflurbiprofen, 4‐OH‐α‐phenyl‐N‐tert‐butyl nitrone, or nordihydroguaiaretic acid (NDGA). Sample size was sufficient to detect a 10% difference in lifespan in either sex, with 80% power, using data from two of the three sites. Pooling data from all three sites, a log‐rank test showed that both NDGA (p = 0.0006) and aspirin (p = 0.01) led to increased lifespan of male mice. Comparison of the proportion of live mice at the age of 90% mortality was used as a surrogate for measurement of maximum lifespan; neither NDGA (p = 0.12) nor aspirin (p = 0.16) had a significant effect in this test. Measures of blood levels of NDGA or aspirin and its salicylic acid metabolite suggest that the observed lack of effects of NDGA or aspirin on lifespan in females could be related to gender differences in drug disposition or metabolism. Further studies are warranted to find whether NDGA or aspirin, over a range of doses, might prove to postpone death and various age‐related outcomes reproducibly in mice.