Natalia Podlutskaya

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.

Chronic inhibition of mammalian target of rapamycin by rapamycin modulates cognitive and non-cognitive components of behavior throughout lifespan in mice

Aging is, by far, the greatest risk factor for most neurodegenerative diseases. In non-diseased conditions, normal aging can also be associated with declines in cognitive function that significantly affect quality of life in the elderly. It was recently shown that inhibition of Mammalian TOR (mTOR) activity in mice by chronic rapamycin treatment extends lifespan, possibly by delaying aging {Harrison, 2009 #4}{Miller, 2011 #168}. To explore the effect of chronic rapamycin treatment on normal brain aging we determined cognitive and non-cognitive components of behavior throughout lifespan in male and female C57BL/6 mice that were fed control- or rapamycin-supplemented chow. Our studies show that rapamycin enhances cognitive function in young adult mice and blocks age-associated cognitive decline in older animals. In addition, mice fed with rapamycin-supplemented chow showed decreased anxiety and depressive-like behavior at all ages tested. Levels of three major monoamines (norepinephrine, dopamine and 5-hydroxytryptamine) and their metabolites (3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindolacetic acid) were significantly augmented in midbrain of rapamycin-treated mice compared to controls. Our results suggest that chronic, partial inhibition of mTOR by oral rapamycin enhances learning and memory in young adults, maintains memory in old C57BL/6J mice, and has concomitant anxiolytic and antidepressant-like effects, possibly by stimulating major monoamine pathways in brain.

Environmental enrichment prevents astroglial pathological changes in the hippocampus of APP transgenic mice, model of Alzheimer's disease

Alzheimers disease (AD) is a neurodegenerative disease that affects neurons and glial cells and leads to dementia. Growing evidence shows that glial changes may precede neuronal alterations and behavioral impairment in the progression of the disease. The modulation of these changes could be addressed as a potential therapeutic strategy. Environmental enrichment has been classically associated to effects on neuronal morphology and function but less attention has been paid to the modulation of glia. We thus characterized astroglial changes in the hippocampus of adult PDAPP-J20 transgenic mice, a model of AD, exposed for 3 months to an enriched environment, from 5 to 8 months of age. Using confocal microscopy, three-dimensional reconstruction and Sholl analysis, we evaluated the morphology of two distinct populations of astrocytes: those associated to amyloid β plaques and those that were not. We found that plaque-associated astrocytes in PDAPP-J20 mice had an increased volume and process ramification than control astrocytes. Non-plaque-associated astrocytes showed a decrease in volume and an increase in the ramification of GFAP+ processes as compared with control astrocytes. Environmental enrichment prevented these alterations and promoted a cellular morphology similar to that found in control mice. Morphological changes in non-plaque-associated astrocytes were found also at 5 months of age, before amyloid β deposition in the hippocampus. These results suggest that glial alterations have an early onset in AD pathogenesis and that the exposure to an enriched environment is an appropriate strategy to reverse them. Cellular and molecular pathways involved in this regulation could constitute potential novel therapeutic targets.

The long lifespan of two bat species is correlated with resistance to protein oxidation and enhanced protein homeostasis

Altered structure, and hence function, of cellular macromolecules caused by oxidation can contribute to loss of physiological function with age. Here, we tested whether the lifespan of bats, which generally live far longer than predicted by their size, could be explained by reduced protein damage relative to short‐lived mice. We show significantly lower protein oxidation (carbonylation) in Mexican free‐tailed bats (Tadarida brasiliensis) relative to mice, and a trend for lower oxidation in samples from cave myotis bats (Myotis velifer) relative to mice. Both species of bat show in vivo and in vitro resistance to protein oxidation under conditions of acute oxidative stress. These bat species also show low levels of protein ubiquitination in total protein lysates along with reduced proteasome activity, suggesting diminished protein damage and removal in bats. Lastly, we show that bat‐derived protein fractions are resistant to urea‐induced protein unfolding relative to the level of unfolding detected in fractions from mice. Together, these data suggest that long lifespan in some bat species might be regulated by very efficient maintenance of protein homeostasis.—Salmon, A. B., Leonard, S., Masamsetti, V., Pierce, A., Podlutsky, A. J., Podlutskaya, N., Richardson, A., Austad, S. N., Chaudhuri, A. R. The long lifespan of two bat species is correlated with resistance to protein oxidation and enhanced protein homeostasis. FASEB J. 23, 2317–2326 (2009)

Over‐expression of heat shock factor 1 phenocopies the effect of chronic inhibition of TOR by rapamycin and is sufficient to ameliorate Alzheimer's‐like deficits in mice modeling the disease

Rapamycin, an inhibitor of target‐of‐rapamycin, extends lifespan in mice, possibly by delaying aging. We recently showed that rapamycin halts the progression of Alzheimers (AD)‐like deficits, reduces amyloid‐beta (Aβ) and induces autophagy in the human amyloid precursor protein (PDAPP) mouse model. To delineate the mechanisms by which chronic rapamycin delays AD we determined proteomic signatures in brains of control‐ and rapamycin‐treated PDAPP mice. Proteins with reported chaperone‐like activity were overrepresented among proteins up‐regulated in rapamycin‐fed PDAPP mice and the master regulator of the heat‐shock response, heat‐shock factor 1, was activated. This was accompanied by the up‐regulation of classical chaperones/heat shock proteins (HSPs) in brains of rapamycin‐fed PDAPP mice. The abundance of most HSP mRNAs except for alpha B‐crystallin, however, was unchanged, and the cap‐dependent translation inhibitor 4E‐BP was active, suggesting that increased expression of HSPs and proteins with chaperone activity may result from preferential translation of pre‐existing mRNAs as a consequence of inhibition of cap‐dependent translation. The effects of rapamycin on the reduction of Aβ, up‐regulation of chaperones, and amelioration of AD‐like cognitive deficits were recapitulated by transgenic over‐expression of heat‐shock factor 1 in PDAPP mice. These results suggest that, in addition to inducing autophagy, rapamycin preserves proteostasis by increasing chaperones. We propose that the failure of proteostasis associated with aging may be a key event enabling AD, and that chronic inhibition of target‐of‐rapamycin may delay AD by maintaining proteostasis in brain.

Testing the Oxidative Stress Hypothesis of Aging in Primate Fibroblasts: Is There a Correlation Between Species Longevity and Cellular ROS Production?

The present study was conducted to test predictions of the oxidative stress theory of aging assessing reactive oxygen species production and oxidative stress resistance in cultured fibroblasts from 13 primate species ranging in body size from 0.25 to 120 kg and in longevity from 20 to 90 years. We assessed both basal and stress-induced reactive oxygen species production in fibroblasts from five great apes (human, chimpanzee, bonobo, gorilla, and orangutan), four Old World monkeys (baboon, rhesus and crested black macaques, and patas monkey), three New World monkeys (common marmoset, red-bellied tamarin, and woolly monkey), and one lemur (ring-tailed lemur). Measurements of cellular MitoSox fluorescence, an indicator of mitochondrial superoxide (O2(·-)) generation, showed an inverse correlation between longevity and steady state or metabolic stress-induced mitochondrial O2(·-) production, but this correlation was lost when the effects of body mass were removed, and the data were analyzed using phylogenetically independent contrasts. Fibroblasts from longer-lived primate species also exhibited superior resistance to H(2)O(2)-induced apoptotic cell death than cells from shorter-living primates. After correction for body mass and lack of phylogenetic independence, this correlation, although still discernible, fell short of significance by regression analysis. Thus, increased longevity in this sample of primates is not causally associated with low cellular reactive oxygen species generation, but further studies are warranted to test the association between increased cellular resistance to oxidative stressor and primate longevity.

Decreased in vitro mitochondrial function is associated with enhanced brain metabolism, blood flow, and memory in Surf1-deficient mice

Recent studies have challenged the prevailing view that reduced mitochondrial function and increased oxidative stress are correlated with reduced longevity. Mice carrying a homozygous knockout (KO) of the Surf1 gene showed a significant decrease in mitochondrial electron transport chain Complex IV activity, yet displayed increased lifespan and reduced brain damage after excitotoxic insults. In the present study, we examined brain metabolism, brain hemodynamics, and memory of Surf1 KO mice using in vitro measures of mitochondrial function, in vivo neuroimaging, and behavioral testing. We show that decreased respiration and increased generation of hydrogen peroxide in isolated Surf1 KO brain mitochondria are associated with increased brain glucose metabolism, cerebral blood flow, and lactate levels, and with enhanced memory in Surf1 KO mice. These metabolic and functional changes in Surf1 KO brains were accompanied by higher levels of hypoxia-inducible factor 1 alpha, and by increases in the activated form of cyclic AMP response element-binding factor, which is integral to memory formation. These findings suggest that Surf1 deficiency-induced metabolic alterations may have positive effects on brain function. Exploring the relationship between mitochondrial activity, oxidative stress, and brain function will enhance our understanding of cognitive aging and of age-related neurologic disorders.

mTOR regulates chaperone networks and cognitive outcomes in mice modeling Alzheimer's disease

Background:Alzheimer’s disease (AD) is anage-dependent neurodegenerative condition that has in common with other neurodegenerations the accumulation and aggregation of misfolded proteins, which in the case of AD is represented by a wide range of aggregates ofamyloid-ß (Aß) peptides. The target of rapamycin (TOR) pathway is a majorsignaling hub that integrates nutrient/growth factor availability with cell metabolism. Reduced activity of the TOR pathway extends invertebrate lifespan, and, in mice, pharmacologic reduction of TOR signaling during adulthood extends life and strongly inhibits mTOR function in brain. We recently showed that systemic, longterm inhibition of mTOR by rapamycin lowers Aß levels and preserves learning and memory in transgenic mice modeling AD.Methods: To determine the mechanisms by which inhibition of mTOR modulates histopathological and cognitive outcomes in AD we performed proteomic and gene expression studies in brain tissues of control orrapamycin-treated PDAPP transgenic mice. Results: A large proportion of protein supregulated in rapamycin-treated transgenic brains weremembers of the chaperone family of proteins, of which many are induced by cellular stress. Heat shock proteins and chaperones promote proteostasis by assisting in the proper folding of proteins or in their targeting for degradation. The master transcriptional regulator of heat shock proteins is heat shock factor 1 (HSF1), which is negatively regulated by TOR. HSF1 is required for lifespan extension and conversely, its overexpression is sufficient to extend longevity in Celegans. Consistent with the observed up regulation of heat shock proteins in rapamycin-treated transgenic brains, we found that phosphorylation of HSF1 at Ser326, which is associated with increased transcriptional activity, was significantly elevated in rapamycin-treated brain tissues. In contrast, phosphorylation of HSF1 at Ser330, which inhibits transcriptional activity, was unchanged by rapamycin treatment. Examination of brain sections byimmunohistochemistry revealed that activated HSF1 was preferentially increased and was Tran located to the nucleus of granular cells in hippocampal dentate gyrus. Conclusions:Maintenance of proteostasis may be sufficient to prevent Aß accumulation and improve cognitive outcomes in mice modeling AD. We will report on the requirement for enhanced proteostasis for the reduction in Aß levels and the preservation of cognitive function in PDAPP transgenic animals producing high levels of amyloid.