Lifelong rapamycin administration ameliorates age-dependent cognitive deficits by reducing IL-1β and enhancing NMDA signaling

mTOR in aging, metabolism, and cancer

The target of rapamycin (TOR) is a highly conserved serine/threonine kinase that is part of two structurally and functionally distinct complexes, TORC1 and TORC2. In multicellular organisms, TOR regulates cell growth and metabolism in response to nutrients, growth factors and cellular energy. Deregulation of TOR signaling alters whole body metabolism and causes age-related disease. This review describes the most recent advances in TOR signaling with a particular focus on mammalian TOR (mTOR) in metabolic tissues vis-a-vis aging, obesity, type 2 diabetes, and cancer.

mTOR in aging, metabolism, and cancer

The target of rapamycin (TOR) is a highly conserved serine/threonine kinase that is part of two structurally and functionally distinct complexes, TORC1 and TORC2. In multicellular organisms, TOR regulates cell growth and metabolism in response to nutrients, growth factors and cellular energy. Deregulation of TOR signaling alters whole body metabolism and causes age-related disease. This review describes the most recent advances in TOR signaling with a particular focus on mammalian TOR (mTOR) in metabolic tissues vis-a-vis aging, obesity, type 2 diabetes, and cancer.

Translating advances from the basic biology of aging into clinical application

Recently, lifespan and healthspan have been extended in experimental animals using interventions that are potentially translatable into humans. A great deal of thought and work is needed beyond the usual steps in drug development to advance these findings into clinical application. Realistic pre-clinical and clinical trial paradigms need to be devised. Focusing on subjects with symptoms of age-related diseases or frailty or who are at imminent risk of developing these problems, measuring effects on short-term, clinically relevant outcomes, as opposed to long-term outcomes such as healthspan or lifespan, and developing biomarkers and outcome measures acceptable to regulatory agencies will be important. Research funding is a major roadblock, as is lack of investigators with combined expertise in the basic biology of aging, clinical geriatrics, and conducting investigational new drug clinical trials. Options are reviewed for developing a path from the bench to the bedside for interventions that target fundamental aging processes.

mTOR Inhibition: From Aging to Autism and Beyond

The mechanistic target of rapamycin (mTOR) is a highly conserved protein that regulates growth and proliferation in response to environmental and hormonal cues. Broadly speaking, organisms are constantly faced with the challenge of interpreting their environment and making a decision between "grow or do not grow." mTOR is a major component of the network that makes this decision at the cellular level and, to some extent, the tissue and organismal level as well. Although overly simplistic, this framework can be useful when considering the myriad functions ascribed to mTOR and the pleiotropic phenotypes associated with genetic or pharmacological modulation of mTOR signaling. In this review, I will consider mTOR function in this context and attempt to summarize and interpret the growing body of literature demonstrating interesting and varied effects of mTOR inhibitors. These include robust effects on a multitude of age-related parameters and pathologies, as well as several other processes not obviously linked to aging or age-related disease.

Insulin and IGF-1 signalling: longevity, protein homoeostasis and Alzheimer's disease

The quality control of protein homoeostasis deteriorates with aging, causing the accumulation of misfolded proteins and neurodegeneration. Thus, in AD (Alzheimer's disease), soluble oligomers, protofibrils and fibrils of the Aβ (amyloid β-peptide) and tau protein accumulate in specific brain regions. This is associated with the progressive destruction of synaptic circuits controlling memory and higher mental function. The primary signalling mechanisms that (i) become defective in AD to alter the normal proteostasis of Aβ and tau, and (ii) initiate a pathophysiological response to cause cognitive decline, are unclear. The IIS [insulin/IGF-1 (insulin-like growth factor 1)-like signalling] pathway is mechanistically linked to longevity, protein homoeostasis, learning and memory, and is emerging to be central to both (i) and (ii). This pathway is aberrantly overactivated in AD brain at the level of increased activation of the serine/threonine kinase Akt and the phosphorylation of its downstream targets, including mTOR (mammalian target of rapamycin). Feedback inhibition of normal insulin/IGF activation of the pathway also occurs in AD due to inactivation of IRS-1 (insulin receptor substrate 1) and decreased IRS-1/2 levels. Pathogenic forms of Aβ may induce aberrant sustained activation of the PI3K (phosphoinositide 3-kinase)/Akt signal in AD, also causing non-responsive insulin and IGF-1 receptor, and altered tau phosphorylation, conformation and function. Reducing IIS activity in animal models by decreasing IGF-1R levels or inhibiting mTOR activity alters Aβ and tau protein homoeostasis towards less toxic protein conformations, improves cognitive function and extends healthy lifespan. Thus normalizing IIS dysfunction may be therapeutically relevant in abrogating Aβ and tau proteotoxicity, synaptic dysfunction and cognitive decline in AD.

mTOR signalling: the molecular interface connecting metabolic stress, aging and cardiovascular diseases

The continuing increase in the prevalence of obesity and metabolic disorders such as type-II diabetes and an accelerating aging population globally will remain the major contributors to cardiovascular mortality and morbidity in the 21st century. It is well known that aging is highly associated with metabolic and cardiovascular diseases. Growing evidence also shows that obesity and metabolic diseases accelerate aging process. Studies in experimental animal models demonstrate similarity of metabolic and cardiovascular phenotypes in metabolic diseases and old age, e.g. insulin resistance, oxidative stress, chronic low grade inflammation, cardiac hypertrophy, cardiac fibrosis, and heart failure, as well as vascular dysfunctions. Despite intensive research, the molecular mechanisms linking metabolic stress, aging, and ultimately cardiovascular diseases are still elusive. Although the mammalian target of rapamycin (mTOR) signalling is a well known regulator of metabolism and lifespan in model organisms, its central role in linking metabolic stress, aging and cardiovascular diseases is recently emerging. In this article, we review the evidence supporting the role of mTOR signalling as a molecular interface connecting metabolic stress, aging and cardiovascular diseases. The therapeutic potentials of targeting mTOR signalling to protect against metabolic and age-associated cardiovascular diseases are discussed.

Mechanistic or mammalian target of rapamycin (mTOR) may determine robustness in young male mice at the cost of accelerated aging

Males, who are bigger and stronger than females, live shorter in most species from flies to mammals including humans. Cellular mass growth is driven in part by mTOR (Target of Rapamycin). When developmental growth is completed, then, instead of growth, mTOR drives aging, manifested by increased cellular functions, such as hyper-secretion by fibroblasts, thus altering homeostasis, leading to age-related diseases and death. We hypothesize that MTOR activity is elevated in male mice compared with females. Noteworthy, 6 months old males were 28 % heavier than females. Also levels of phosphorylated S6 (pS6) and phospho-AKT (p-AKT, Ser 473), markers of the mTOR activity, were higher in male organs tested. Levels of pS6 were highly variable among mice and correlated with body weight and p-AKT. With age, the difference between levels of pS6 between sexes tended to minimize, albeit males still had hyperactive mTOR. Unlike fasting, the intraperitoneal (i.p.) administration of rapamycin eliminated pS6 in all organs of all females measured by immunoblotting and immunohistochemistry without affecting p-AKT and blood insulin. Although i.p. rapamycin dramatically decreased levels of pS6 in males too, it was still detectable by immunoblotting upon longer exposure. Our study demonstrated that both tissue p-AKT and pS6 were higher in young male mice and were associated with increased body weight and insulin. These data can explain bigger body size and faster aging in males. Our data suggest higher efficacy of rapamycin compared to fasting. Higher sensitivity of females to rapamycin may explain more pronounced life extension by rapamycin observed in females compared to males in several studies.

Mitochondrial deficiency: a double-edged sword for aging and neurodegeneration

For decades, aging was considered the inevitable result of the accumulation of damaged macromolecules due to environmental factors and intrinsic processes. Our current knowledge clearly supports that aging is a complex biological process influenced by multiple evolutionary conserved molecular pathways. With the advanced age, loss of cellular homeostasis severely affects the structure and function of various tissues, especially those highly sensitive to stressful conditions like the central nervous system. In this regard, the age-related regression of neural circuits and the consequent poor neuronal plasticity have been associated with metabolic dysfunctions, in which the decline of mitochondrial activity significantly contributes. Interestingly, while mitochondrial lesions promote the onset of degenerative disorders, mild mitochondrial manipulations delay some of the age-related phenotypes and, more importantly, increase the lifespan of organisms ranging from invertebrates to mammals. Here, we survey the insulin/IGF-1 and the TOR signaling pathways and review how these two important longevity determinants regulate mitochondrial activity. Furthermore, we discuss the contribution of slight mitochondrial dysfunction in the engagement of pro-longevity processes and the opposite role of strong mitochondrial dysfunction in neurodegeneration.

Rapalogs in cancer prevention: anti-aging or anticancer?

Common cancer is an age-related disease. Slow aging is associated with reduced and delayed carcinogenesis. Calorie restriction (CR), the most studied anti-aging intervention, prevents cancer by slowing down the aging process. Evidence is emerging that CR decelerates aging by deactivating MTOR (Target of Rapamycin). Rapamycin and other rapalogs suppress cellular senescence, slow down aging and postpone age-related diseases including cancer. At the same time, rapalogs are approved for certain cancer treatments. Can cancer prevention be explained by direct targeting of cancer cells? Or does rapamycin prevent cancer indirectly through slowing down the aging process? Increasing evidence points to the latter scenario.

Management of anemia of inflammation in the elderly

Anemia of any degree is recognized as a significant independent contributor to morbidity, mortality, and frailty in elderly patients. Among the broad types of anemia in the elderly a peculiar role seems to be played by the anemia associated with chronic inflammation, which remains the most complex form of anemia to treat. The origin of this nonspecific inflammation in the elderly has not yet been clarified. It seems more plausible that the oxidative stress that accompanies ageing is the real cause of chronic inflammation of the elderly and that the same oxidative stress is actually a major cause of this anemia. The erythropoietic agents have the potential to play a therapeutic role in this patient population. Despite some promising results, rHuEPO does not have a specific indication for the treatment of anemia in the elderly. Moreover, concerns about their side effects have spurred the search for alternatives. Considering the etiopathogenetic mechanisms of anemia of inflammation in the elderly population, an integrated nutritional/dietetic approach with nutraceuticals that can manipulate oxidative stress and related inflammation may prevent the onset of this anemia and its negative impact on patients' performance and quality of life.

Inflammaging: disturbed interplay between autophagy and inflammasomes

Inflammaging refers to a low-grade pro-inflammatory phenotype which accompanies aging in mammals. The aging process is associated with a decline in autophagic capacity which impairs cellular housekeeping, leading to protein aggregation and accumulation of dysfunctional mitochondria which provoke reactive oxygen species (ROS) production and oxidative stress. Recent studies have clearly indicated that the ROS production induced by damaged mitochondria can stimulate intracellular danger-sensing multiprotein platforms called inflammasomes. Nod-like receptor 3 (NLRP3) can be activated by many danger signals, e.g. ROS, cathepsin B released from destabilized lysosomes and aggregated proteins, all of which evoke cellular stress and are involved in the aging process. NLRP3 activation is also enhanced in many age-related diseases, e.g. atherosclerosis, obesity and type 2 diabetes. NLRP3 activates inflammatory caspases, mostly caspase-1, which cleave the inactive precursors of IL-1β and IL-18 and stimulate their secretion. Consequently, these cytokines provoke inflammatory responses and accelerate the aging process by inhibiting autophagy. In conclusion, inhibition of autophagic capacity with aging generates the inflammaging condition via the activation of inflammasomes, in particular NLRP3. We will provide here a perspective on the current research of the ROS-dependent activation of inflammasomes triggered by the decline in autophagic cleansing of dysfunctional mitochondria.

Diet and aging

Nutrition has important long-term consequences for health that are not only limited to the individual but can be passed on to the next generation. It can contribute to the development and progression of chronic diseases thus effecting life span. Caloric restriction (CR) can extend the average and maximum life span and delay the onset of age-associated changes in many organisms. CR elicits coordinated and adaptive stress responses at the cellular and whole-organism level by modulating epigenetic mechanisms (e.g., DNA methylation, posttranslational histone modifications), signaling pathways that regulate cell growth and aging (e.g., TOR, AMPK, p53, and FOXO), and cell-to-cell signaling molecules (e.g., adiponectin). The overall effect of these adaptive stress responses is an increased resistance to subsequent stress, thus delaying age-related changes and promoting longevity. In human, CR could delay many diseases associated with aging including cancer, diabetes, atherosclerosis, cardiovascular disease, and neurodegenerative diseases. As an alternative to CR, several CR mimetics have been tested on animals and humans. At present, the most promising alternatives to the use of CR in humans seem to be exercise, alone or in combination with reduced calorie intake, and the use of plant-derived polyphenol resveratrol as a food supplement.

Prospective treatment of age-related diseases by slowing down aging

Atherosclerosis, hypertension, obesity, diabetic complications, cancer, benign prostate hyperplasia, Alzheimer and Parkinson diseases, age-related macular degeneration, osteoarthritis, osteoporosis, and seborrheic keratosis are strongly associated with aging, implying a common underlying process. Each disease is treated separately and, in most cases, symptomatically. Suppression of aging itself should delay or treat all age-related diseases, thus increasing healthy life span and maximal longevity. But, is it possible to slow down aging? Recent evidence indicates that the target of rapamycin signaling pathway is involved in cellular senescence and organismal aging. Preclinical and clinical studies demonstrated the therapeutic effects of rapamycin in diverse age-related diseases. One simple reason why a single drug is indicated for so many age-related diseases is that it inhibits the aging process.

The Role of Insulin and Insulin-Like Growth Factor-1/FoxO-Mediated Transcription for the Pathogenesis of Obesity-Associated Dementia

Epidemiological studies suggest that being obese in midlife is a risk factor for cognitive decline and dementia in later life. Hyperinsulinemia is one of the most frequent endocrine features in overweight people which results in insulin desensitization. Thus, chronically high insulin levels have been identified as risk factor for dementia. Accordingly, chronically high insulin levels might be harmful for brain function. Furthermore, insulin and IGF-1-induced signaling is reduced in the brains of patients suffering from Alzheimer's disease (AD). Interestingly, studies in rodents suggest that reduced insulin receptor (IR) and insulin-like growth factor-1 receptor (IGF-1R) signaling decrease AD pathology, that is, β-amyloid toxicity. Data obtained in C. elegans indicate that the beneficial effect mediated via reduced IR/IGF-1R signaling might partially be induced via the forkhead-box O transcription factors (FoxO). In the mammalian brain, there are FoxO1, FoxO3a, and FoxO6 expressed. Surprisingly, high-fat diet specifically reduces the expression of FoxO3a and FoxO6 suggesting that IR/IGF-1 → FoxO-mediated transcription is involved in the pathogenesis of obesity-associated cognitive impairment. Therefore, the function of FoxO1 and FoxO3a has been investigated in animal models of Alzheimer's disease in detail. The current paper focuses on the role of IR/IGF-1 signaling and IR/IGF-1 → FoxO-mediated transcription for the pathogenesis of obesity-associated dementia.