Blood Pressure and Brain Injury in Older Adults: Findings from a Community-Based Autopsy Study

OBJECTIVES: To examine correlations between blood pressure (BP) and dementia-related pathological brain changes in a community-based autopsy sample.
DESIGN: Prospective cohort study.
SETTING: A large health maintenance organization in Seattle, Washington.
PARTICIPANTS: A cohort of 250 participants aged 65 and older and cognitively normal at time of enrollment in the Adult Changes in Thought (ACT) Study and who underwent autopsy.
MEASUREMENTS: BP and history of antihypertensive treatment were taken at enrollment. A linear regression model was used to examine the relationship between BP (systolic (SBP) and diastolic (DBP)) at enrollment and pathological changes in the cerebrum (cystic macroscopic infarcts, microinfarcts, neuritic plaques, neurofibrillary tangles, and cortical Lewy bodies).
RESULTS: The presence of more than 2 microinfarcts, but not any other pathological change, was independently associated with SBP in younger participants (65–80, n=137) but not in older participants (>80, n=91). The relative risk (RR) for more than two microinfarcts with each 10-mmHg increase in SBP was 1.15 (95% confidence interval (CI)=1.00–1.33) in the younger participants, adjusted for age at entry, sex, and time to death. This RR was particularly strong in younger participants not taking antihypertensive medications (RR=1.48, 95% CI=1.21, 1.81); significant associations were not observed in participants treated for hypertension. Findings for DBP were negative.
CONCLUSION: The association between high SBP and cerebrovascular damage in untreated older adults (65–80) suggests that adequate hypertension treatment may reduce dementia risk by minimizing microvascular injury to cerebrum.     

Immunophilin FKBP52 induces Tau-P301L filamentous assembly in vitro and modulates its activity in a model of tauopathy

The Tau protein is the major component of intracellular filaments observed in a number of neurodegenerative diseases known as tauopathies. The pathological mutant of Tau containing a proline-to-leucine mutation at position 301 (P301L) leads to severe human tauopathy. Here, we assess the impact of FK506-binding protein with a molecular mass of ∼52 kDa (FKBP52), an immunophilin protein that interacts with physiological Tau, on Tau-P301L activity. We identify a direct interaction of FKBP52 with Tau-P301L and its phosphorylated forms and demonstrate FKBP52’s ability to induce the formation of Tau-P301L oligomers. EM analysis shows that Tau-P301L oligomers, induced by FKBP52, can assemble into filaments. In the transgenic zebrafish expressing the human Tau-P301L mutant, FKBP52 knockdown is sufficient to redrive defective axonal outgrowth and branching related to Tau-P301L expression in spinal primary motoneurons. This result correlates with a significant reduction of pT181 pathological phosphorylated Tau and with recovery of the stereotypic escape response behavior. Collectively, FKBP52 appears to be an endogenous candidate that directly interacts with the pathogenic Tau-P301L and modulates its function in vitro and in vivo.Tau is a MAP mainly found in neurons (1, 2), which becomes hyperphosphorylated in several neurodegenerative diseases known as tauopathies and forms intraneuronal aggregates called neurofibrillary tangles (NFTs) (3–5). The accumulation of Tau aggregates is a multistep process that involves transient species, and growing evidence suggests that not only the NFTs but equally small oligomeric species contribute to Tau-mediated neurotoxicity (6–8). The pathological mutant of Tau containing a proline-to-leucine mutation at position 301 (P301L) is identified in frontotemporal dementia and Parkinsonism linked to chromosome 17 (FTDP-17) (9). Larvae of the zebrafish overexpressing the Tau-P301L mutant protein show defects in motoneuron development early on, and in this model, different Tau phosphoforms are associated with its pathological state (10).The FK506-binding protein with a molecular mass of ∼52 kDa (FKBP52) belongs to the immunophilin family and presents rotamase activity inhibited by FK506 binding (11). This enzymatic activity catalyzes the isomerization of peptidyl-prolyl bonds between cis and trans conformations, and therefore influences target protein folding and function (12, 13). FKBP52 contains additional functional domains, such as a tetratricopeptide repeat domain that serves as a binding site for molecular chaperone heat shock protein with a molecular mass of 90 kDa (14) and for which chaperone activity was observed (15).A novel role of FKBP52 has recently emerged because it binds directly to tubulin and induces tubulin depolymerization in vitro (16). Biochemical characterization of FKBP52 showed that it interacts with Tau, especially its hyperphosphorylated form, and demonstrated an antagonist effect of FKBP52 on Tau’s function in tubulin assembly (17). Here, we show that FKBP52 interacts with the pathological form of Tau-P301L and induces its oligomerization and assembly into filaments. Using a transgenic zebrafish model for Tau-P301L tauopathy (10), we show that FKBP52 knockdown attenuates pathological Tau activity to reestablish axonal outgrowth and branching in defective spinal primary motoneurons. This result confirms the functional implication of FKBP52 in modulating early pathological Tau activity, at least for axonal growth and motility. We propose that FKBP52 is an important regulator of Tau conformational change and assembly, and thus may be instrumental in a therapeutic approach to the disease.     

Early neuropathological Alzheimer's changes in aged individuals are accompanied by decreased cerebrospinal fluid melatonin levels

Neuropathology is the most reliable criterion for diagnosing Alzheimer's disease (AD). A well-established system for staging the spread of neuropathological changes in AD is available. The clinical use of a biomarker that reflects the neuropathological change occurring in brain tissue has not yet been established. Melatonin is a product that plays not only a major role in the regulation of the circadian rhythms but may also exert neuroprotective effects in AD. Melatonin levels were determined in ventricular postmortem cerebrospinal fluid (CSF) of 121 subjects. Braak staging and a modified Braak staging for cortex (MBSC) were used to evaluate the severity of AD neuropathology. The present study revealed that not only the Braak stages of AD, but also the MBSC were negatively correlated with CSF melatonin levels. By using MBSC, we now demonstrate for the first time that CSF melatonin levels were significantly decreased in the aged individuals with early neuropathological changes in the temporal cortex, where the AD process starts. Those individuals that did not have any neurofibrillary tangle (NFT) or neuritic plaque (NP) in the temporal cortex, had much higher melatonin levels (287 +/- 68 and 280 +/- 64 pg/mL, respectively) than those individuals that had a few NFTs and NPs (82 +/- 4 and 39 +/- 8 pg/mL, respectively) in the temporal cortex. These results suggest that the decrease in CSF melatonin levels may be an early event in the development of AD possibly occurring even before the clinical symptoms.     

De novo designed protein inhibitors of amyloid aggregation and seeding

Neurodegenerative diseases are characterized by the pathologic accumulation of aggregated proteins. Known as amyloid, these fibrillar aggregates include proteins such as tau and amyloid-β (Aβ) in Alzheimer’s disease (AD) and alpha-synuclein (αSyn) in Parkinson’s disease (PD). The development and spread of amyloid fibrils within the brain correlates with disease onset and progression, and inhibiting amyloid formation is a possible route toward therapeutic development. Recent advances have enabled the determination of amyloid fibril structures to atomic-level resolution, improving the possibility of structure-based inhibitor design. In this work, we use these amyloid structures to design inhibitors that bind to the ends of fibrils, “capping” them so as to prevent further growth. Using de novo protein design, we develop a library of miniprotein inhibitors of 35 to 48 residues that target the amyloid structures of tau, Aβ, and αSyn. Biophysical characterization of top in silico designed inhibitors shows they form stable folds, have no sequence similarity to naturally occurring proteins, and specifically prevent the aggregation of their targeted amyloid-prone proteins in vitro. The inhibitors also prevent the seeded aggregation and toxicity of fibrils in cells. In vivo evaluation reveals their ability to reduce aggregation and rescue motor deficits in Caenorhabditis elegans models of PD and AD.

The aberrant aggregation of proteins into amyloid fibrils is a hallmark of many neurodegenerative diseases, including Alzheimer’s disease (AD) and Parkinson’s disease (PD) (1). In AD, amyloid-β (Aβ) and tau amyloid fibrils comprise the extracellular amyloid plaques and intracellular neurofibrillary tangles, respectively, characteristic of disease progression (2). Likewise, intracellular Lewy bodies found in the neurons of patients with PD and dementia with Lewy bodies (DLB) are primarily composed of αSyn fibrils (3). There are currently no therapies capable of significantly slowing or stopping the progression of any of these diseases, and inhibition of fibril formation has become a major target for therapeutic development (4, 5). Amyloid fibrils are composed of repeating layers of β-strand–rich protein monomers stacked upon each other, forming β-sheets. The β-sheets interdigitate to form a stable fibril core through interactions known as steric zippers (6). Antiamyloid therapies have typically focused on small molecules that prevent aggregation or dissociate preexisting aggregates and antibodies that promote fibril clearance (7–9). An alternative approach is the design of molecules that bind to the ends of the growing fibrils, capping their growth and preventing the further addition of more protein monomers. This approach has been successfully used to design peptide-based inhibitors of tau, Aβ, and αSyn aggregation (10–14). This design strategy considers the atomic structures of fibrils, employing rational and computational design techniques to derive a peptide sequence complementary to the growing fibril surface.Since the initial designs of structure-based capping inhibitor peptides, many advances have been made in both the determination of amyloid protein structure, as well as in methods of protein design. The first atomic-resolution structures of amyloid fibrils determined by X-ray crystallography were restricted to small peptide segments ∼6 to 11 amino acids in length (15). The recent advent of cryoelectron microscopy (cryo-EM), microelectron diffraction (MicroED), and solid-state NMR (ssNMR) spectroscopy have enabled the determination of amyloid protein structures that were previously unsolvable (16–18). These techniques have been used to solve an ever-growing list of structures of both recombinantly derived fibrils (19–21) as well as fibrils directly extracted from patient tissue (22–29). These structures have provided key insights into fibril architecture and polymorphism in relation to disease.Like the structural knowledge of amyloid fibrils, the toolbox of protein structure prediction and design has been rapidly expanding in recent years (30, 31). Significant advances in algorithms and computing power have facilitated the de novo design of proteins with a variety of properties and functions, ranging from stability, pH sensitivity, to even logic operations, with vast potential for use in therapeutics, diagnostics, etc (32–36). While the underlying design principles of de novo generated proteins are becoming well established, examples of their direct application into biological systems are still limited. In this work, we use de novo protein design to create 35 to 50 residue miniproteins that bind to the growing ends of tau, αSyn, and Aβ fibrils. We target recently determined full-length atomic structures of each amyloid protein in our designs to generate miniproteins capable of inhibiting aggregation, seeding, and toxicity both in vitro and in vivo.     

Microtubule-binding drugs offset tau sequestration by stabilizing microtubules and reversing fast axonal transport deficits in a tauopathy model

We tested the hypothesis that microtubule (MT)-binding drugs could be therapeutically beneficial in tauopathies by functionally substituting for the MT-binding protein tau, which is sequestered into inclusions of human tauopathies and transgenic mouse models thereof. Transgenic mice were treated for 12 weeks with weekly i.p. injections of 10 or 25 mg/m(2) paclitaxel (Paxceed). Both doses restored fast axonal transport in spinal axons, wherein MT numbers and stable (detyrosinated) tubulins were increased, compared with sham treatment, and only Paxceed ameliorated motor impairments in tau transgenic mice. Thus, MT-stabilizing drugs could have therapeutic potential for treating neurodegenerative tauopathies by offsetting losses of tau function that result from the sequestration of this MT-stabilizing protein into filamentous inclusions.     

Propagation of aggregated p53: Cross-reaction and coaggregation vs. seeding

Destabilized mutant p53s coaggregate with WT p53, p63, and p73 in cancer cell lines. We found that stoichiometric amounts of aggregation-prone mutants induced only small amounts of WT p53 to coaggregate, and preformed aggregates did not significantly seed the aggregation of bulk protein. Similarly, p53 mutants trapped only small amounts of p63 and p73 into their p53 aggregates. Tetrameric full-length protein aggregated at similar rates and kinetics to isolated core domains, but there was some induced aggregation of WT by mutants in hetero-tetramers. p53 aggregation thus differs from the usual formation of amyloid fibril or prion aggregates where tiny amounts of preformed aggregate rapidly seed further aggregation. The proposed aggregation mechanism of p53 of rate-determining sequential unfolding and combination of two molecules accounts for the difference. A molecule of fast-unfolding mutant preferentially reacts with another molecule of mutant and only occasionally traps a slower unfolding WT molecule. The mutant population rapidly self-aggregates before much WT protein is depleted. Subsequently, WT protein self-aggregates at its normal rate. However, the continual production of mutant p53 in a cancer cell would gradually trap more and more WT and other proteins, accounting for the observations of coaggregates in vivo. The mechanism corresponds more to trapping by cross-reaction and coaggregation rather than classical seeding and growth.The mechanism of aggregation of p53 (1) is different from that of the classical nucleation—growth of formation of amyloid fibrils (2–5). The classical mechanisms involve relatively slow nucleation events followed by rapid growth. The fibrils or their fragments act as seeds to accelerate greatly the polymerization of molecules from solution. However, the initiation of aggregation of p53 is relatively rapid, there appears to be little seeding from already polymerized molecules (6, 7), and stirring does not significantly speed up aggregation (1). An extensive Φ-value analysis of the aggregation of core domains of p53 suggests that the initial events involve the sequential unfolding of two molecules, involving a combination of first-order and second-order kinetics (1). Full-length p53, however, has a tetramerization domain, which gives a mixture of dimers and tetramers at normally encountered concentrations of protein. At 37 °C, tetrameric p53 dissociates into dimers with a dissociation constant of 50 nM, and the dimers to monomers with a dissociation constant of 0.55 nM, with half lives of 20 and 50 min, respectively, for dissociation (8). Tetramerization of p53 may complicate the aggregation kinetics. The possibilities of intramolecular core-domain interactions could, for example, change the kinetic mechanism and accelerate the initial aggregation events by proximity effects of core domains in tetramers. Further, WT protein may form mixed hybrids with a destabilized, oncogenic mutant and facilitate seeding of the aggregation of WT domains, which may be a cause of negative dominance (9–11). Aggregation-prone mutant p53 is also proposed to coaggregate with and inactivate p63 and p73 via residues 251–257 (strand S9) in the core domain acting as an aggregation nucleus (9). p53 does not form heterotetramers with p63 or p73 (12) but binds via core domain interactions (13–15).Here, we first probed the consequences of tetramerization on the aggregation of full-length p53 and its mutants. Then, we examined the effects of mutant p53 seeding the aggregation of WT p53 and family members p63 and p73. We found that the kinetics of aggregation of full-length p53 is very similar to that of isolated core domains, and therefore the mechanistic data on monomers can be transferred to oligomers. We verified that coprecipitation of mutant p53 with p63 and p73 can be replicated in vitro, as well with WT p53, but that it occurs by a process of coaggregation and trapping by cross-reaction rather than seeding.     

Hydration water mobility is enhanced around tau amyloid fibers

The paired helical filaments (PHF) formed by the intrinsically disordered human protein tau are one of the pathological hallmarks of Alzheimer disease. PHF are fibers of amyloid nature that are composed of a rigid core and an unstructured fuzzy coat. The mechanisms of fiber formation, in particular the role that hydration water might play, remain poorly understood. We combined protein deuteration, neutron scattering, and all-atom molecular dynamics simulations to study the dynamics of hydration water at the surface of fibers formed by the full-length human protein htau40. In comparison with monomeric tau, hydration water on the surface of tau fibers is more mobile, as evidenced by an increased fraction of translationally diffusing water molecules, a higher diffusion coefficient, and increased mean-squared displacements in neutron scattering experiments. Fibers formed by the hexapeptide ³⁰⁶VQIVYK³¹¹ were taken as a model for the tau fiber core and studied by molecular dynamics simulations, revealing that hydration water dynamics around the core domain is significantly reduced after fiber formation. Thus, an increase in water dynamics around the fuzzy coat is proposed to be at the origin of the experimentally observed increase in hydration water dynamics around the entire tau fiber. The observed increase in hydration water dynamics is suggested to promote fiber formation through entropic effects. Detection of the enhanced hydration water mobility around tau fibers is conjectured to potentially contribute to the early diagnosis of Alzheimer patients by diffusion MRI.Amyloid fibers are the most stable forms of ordered protein aggregates. They have attracted much attention because of their implication in so-called conformational diseases, which include a variety of neurodegenerative disorders (1). Consequently, means of hindering or reversing fiber formation are actively researched (2). Pathological fibers are often formed by intrinsically disordered proteins (IDPs) that lack a well-defined 3D structure in their native state and are best described by an ensemble of different conformations (3). The human protein tau is an IDP that normally regulates microtubule stability in neurons. When tau aggregates, it forms paired helical filaments (PHF) that are one of the two histological hallmarks of Alzheimer disease (AD) (4, 5). As yet, and despite considerable effort over the past 30 y, the understanding of tau fibrillation in AD and other taupathies remains largely incomplete (6). The longest human tau isoform, htau40, is composed of 441 amino acid residues and is organized into several domains (see Fig. 1), including the repeat domains R1−R4 (residues 244–369) that constitute, together with the P1 and P2 domains, the microtubule binding regions (7). Essential for the nucleation of tau fibers is the presence of hexapeptides (²⁷⁵VQIINK²⁸⁰ and ³⁰⁶VQIVYK³¹¹) in R2 and R3 (8) that have a high propensity to form β-structures. Although precise structures of tau PHF remain unknown (6), they can be divided into two structurally different regions (see Fig. 1): (i) a rigid β-rich core (denoted as the fiber core domain), which is essentially composed of the four repeat domains, and (ii) the remainder, the so-called fuzzy coat, which is highly flexible (9–11).Open in a separate windowFig. 1.Schematic representation of the tau isoform htau40 in its monomeric (Top) and fibrillated (Bottom) forms. The microtubule binding domain is roughly composed of the four repeat domains R1−R4 (residues 244–369) and the proline-rich domains P1 and P2. R1−R4 constitute the core domain, which forms cross-β structures as well as steric zippers in the fiber, whereas the rest of the protein is referred to as the fuzzy coat domain, which remains disordered in the fiber form. The amyloidogenic hexapeptide ³⁰⁶VQIVYK³¹¹ can be used as a model for the fiber core.Water is known to play key roles in protein folding, stability, and activity (12). It mediates protein−protein and protein−DNA recognition, is involved in allostery, partakes in enzymatic reactions and proton and electron transfer, and more generally plasticizes biological macromolecules by providing their surface with an extensive and highly dynamic network of hydrogen bonds. Compared with folded proteins, tau has been shown to have a stronger coupling with its hydration water (13). However, very little is known about the role water plays in protein aggregation in general and in tau fibrillation in particular. A recent study on two different amyloid systems concluded that water plays a key role in fiber growth and polymorphism, inter alia through entropic effects (14). A study by Chong and Ham (15) highlighted the role of water in protein aggregation propensity by revealing a tight relation between the hydration free energy of a protein and its propensity to aggregate.Among the experimental methodologies available to study protein hydration water, neutron scattering (NS) stands out owing to its pronounced sensitivity to motions of hydrogen atoms. Indeed, hydrogen atoms incoherently scatter neutrons about two orders of magnitude more strongly than all other atoms present in a biological sample, including deuterium atoms. Consequently, NS has been widely used to study bulk and confined water at room temperature (16), hydration water of peptides (17), proteins (18–21), and water inside cells (22). More specifically, NS probes atomic motions on the nanosecond to picosecond timescales and on the angstrom length scales (23), thus ensuring the time and space resolution necessary for investigating water dynamics with atomistic detail. Elastic incoherent NS (EINS) reflects the global dynamics averaged over all atoms but does not provide any information on the nature of the observed motions. Quasi-elastic NS (QENS), however, allows the quantification of energy exchanges between the sample and the neutron beam and provides quantitative information about the nature of motions observed. Because of a pronounced isotope effect, the replacement of hydrogen by deuterium atoms effectively masks the labeled part of a sample in incoherent NS experiments. Perdeuteration of proteins (i.e., deuteration of the entire protein) hydrated in H₂O thus puts the focus on hydration water dynamics by minimizing the protein contribution to the NS signal. All-atom molecular dynamics (MD) simulation is a useful complement to NS because both methods probe atomic motions on the same time and length scales. Whereas incoherent NS provides an accurate measure of the average dynamics of hydrogen atoms throughout the sample, MD simulations provide atomic-scale insight into motions occurring within particular space and time windows of interest (24).Here we experimentally and computationally address the effect of tau fiber formation on the dynamics of its surrounding hydration water. We produced perdeuterated htau40 as well as a perdeuterated heparin analog, and measured by NS the dynamical properties of hydration water on the surface of tau monomers and of tau fibers whose formation was triggered by the heparin analog. Both elastic and quasi-elastic NS indicate an increased mobility of hydration water on tau fibers compared with tau monomers. MD simulations provide circumstantial evidence suggesting that it is the increase in water dynamics around the disordered fuzzy coat and not around the fiber core that is at the origin of the experimentally observed increase in tau hydration water dynamics after fibrillation. We conjecture that the observed gain in water dynamics reflects an increase in water entropy that is favorable to the fiber formation.     

Neuropsychological test performances and normal aging

This study was designed to assess the relevance of normal aging to performance in a variety of neuropsychological tests, in a wide range of age groups. The battery included tests of several cognitive abilities of varying complexity (attention, orientation, memory, self-regulation, categorial ability and so on). The results showed that some tests (Orientation, Attention, Digit Span, Naming, Block Design, Self-regulation, Calculation, Weigl) are not significantly affected by aging while in others performance clearly declines with age. However, the age at onset of the decline is far from uniform. In some tests (Logical Memory, delayed recall section of Supraspan Test, Hooper Test, Finger Tapping Test) it is manifest in early middle age while in others (Faces Recognition, Set Test, Reproduction of Geometric Designs) it does not appear until much later in life.     

Heritable variation in telomere length predicts mortality in Soay sheep

Telomere length (TL) is considered an important biomarker of whole-organism health and aging. Across humans and other vertebrates, short telomeres are associated with increased subsequent mortality risk, but the processes responsible for this correlation remain uncertain. A key unanswered question is whether TL–mortality associations arise due to positive effects of genes or early-life environment on both an individual’s average lifetime TL and their longevity, or due to more immediate effects of environmental stressors on within-individual TL loss and increased mortality risk. Addressing this question requires longitudinal TL and life history data across the entire lifetimes of many individuals, which are difficult to obtain for long-lived species like humans. Using longitudinal data and samples collected over nearly two decades, as part of a long-term study of wild Soay sheep, we dissected an observed positive association between TL and subsequent survival using multivariate quantitative genetic models. We found no evidence that telomere attrition was associated with increased mortality risk, suggesting that TL is not an important marker of biological aging or exposure to environmental stress in our study system. Instead, we find that among-individual differences in average TL are associated with increased lifespan. Our analyses suggest that this correlation between an individual’s average TL and lifespan has a genetic basis. This demonstrates that TL has the potential to evolve under natural conditions, and suggests an important role of genetics underlying the widespread observation that short telomeres predict mortality.

Telomeres are repetitive sequences of noncoding DNA found at the terminal ends of linear chromosomes, and they play an important role in maintaining DNA stability and integrity (1–3). Telomeres shorten during cell replication and in response to oxidative stress (4, 5), and cellular senescence and apoptosis is triggered once telomeres reach a critically short threshold (2). The important role of telomeres in cellular senescence has led to telomere shortening being considered as one of nine “hallmarks of aging,” and average telomere length (TL) as an important biomarker of whole-organism health and biological aging (6). In humans, relatively short leukocyte telomeres have been linked to a range of age-related diseases such as diabetes, cancer, and cardiovascular disease (7–9) and increased subsequent mortality risk (10–12). A recent metaanalysis suggests this pattern may generalize beyond humans: Across studies from 20 nonmodel vertebrate species (predominantly birds), there was an overall positive association between TL and subsequent survival (13). Although evidence for a causal role for telomeres in whole-organism aging and longevity remains weak (14), these findings highlight the potential significance of TL as a biomarker of human and animal health (15, 16) and for our understanding of life history evolution (17, 18).Studies in humans and other vertebrates have found evidence for consistent differences in TL among individuals over multiple measurements (19, 20). Such repeatable among-individual differences in any trait may result from the trait being under genetic influence, from long-term effects of the early-life environment, and/or environmental conditions that persist across the lifetime. There is good evidence that variation in average TL in blood cells has a genetic basis in humans and other vertebrates, although estimates of the heritability (the proportion of variation attributed to additive genetic effects) of TL are variable (21, 22). Recent studies of wild vertebrates have also revealed considerable variation in adult TL among birth cohorts, suggesting persistent impacts of early-life environment (23, 24). At the same time, there is growing evidence that TL is highly dynamic across an individual’s lifetime, and metaanalyses of human and nonhuman animal studies show that experience of diverse forms of environmental stress are predictive of shorter TL (25–27). Indeed, some studies using longitudinal TL data have found that telomere shortening over successive measurements rather than TL per se is predictive of mortality (28–30). Thus, the emerging picture from studies in humans and other vertebrates is that shorter TL generally predicts increased risk of subsequent mortality, and that variation in TL is under the influence of both genetics and environmental stressors.The observation that shorter TL measurements predict increased mortality risk could be underpinned by two nonmutually exclusive processes operating across the lifetimes of individuals. Firstly, individuals may differ in their average TL across life, and individuals with shorter TL may be shorter lived. This pattern is referred to as the “selective disappearance” of individuals with shorter telomeres, and it implies that TL reflects constitutive differences among individuals (for example, due to genetics or differences in early-life environment) which shape their longevity (31, 32). Secondly, individuals may differ in their pattern of TL change over time, and individuals showing the greatest telomere loss across successive measurements are more likely to die subsequently. This pattern is consistent with the idea that within-individual telomere dynamics reflect recent and cumulative experiences of environmental stress and physiological deterioration that also predict mortality. Neither pattern necessarily implies a causal role for telomeres in driving the mortality risk of an organism, because associations between TL and survival could result from both traits being correlated with underlying, unmeasured variables which causally impact survival (14, 18). Nevertheless, unraveling the contribution of genetics, early-life environment, and more immediate telomere shortening to the observed association between TL and survival is essential for our understanding of TL as a biomarker of health and aging (19).To our knowledge, no study to date has assessed the relative importance of the different processes underlying the relationship between TL and mortality risk across the entire lifespan. To do so demands repeated measurements from across life to characterize among- and within-individual variation in TL, a population pedigree or genomic information to separate genetic and environmental sources of variation, and detailed information on individual health and fitness outcomes over the lifetime. Here, we use a multivariate mixed-effects modeling approach to analyze extensive, longitudinal data from a long-term study of wild Soay sheep living on St Kilda, Scotland, to distinguish between possible models of why shorter TL predicts increased mortality risk. We find that the observed positive association between TL and mortality in this system is underpinned by selective disappearance of individuals with shorter average TL. Importantly, our results suggest this is largely driven by genetically based differences in both TL and longevity.     

Small molecules disaggregate alpha-synuclein and prevent seeding from patient brain-derived fibrils

The amyloid aggregation of alpha-synuclein within the brain is associated with the pathogenesis of Parkinson’s disease (PD) and other related synucleinopathies, including multiple system atrophy (MSA). Alpha-synuclein aggregates are a major therapeutic target for treatment of these diseases. We identify two small molecules capable of disassembling preformed alpha-synuclein fibrils. The compounds, termed CNS-11 and CNS-11g, disaggregate recombinant alpha-synuclein fibrils in vitro, prevent the intracellular seeded aggregation of alpha-synuclein fibrils, and mitigate alpha-synuclein fibril cytotoxicity in neuronal cells. Furthermore, we demonstrate that both compounds disassemble fibrils extracted from MSA patient brains and prevent their intracellular seeding. They also reduce in vivo alpha-synuclein aggregates in C. elegans. Both compounds also penetrate brain tissue in mice. A molecular dynamics–based computational model suggests the compounds may exert their disaggregating effects on the N terminus of the fibril core. These compounds appear to be promising therapeutic leads for targeting alpha-synuclein for the treatment of synucleinopathies.

Parkinson’s disease (PD), multiple system atrophy (MSA), and dementia with Lewy bodies (DLB) are neurodegenerative disorders characterized by abnormal accumulation of the protein alpha-synuclein (1). Known as synucleinopathies, these diseases are hallmarked by the fibrillar aggregation of alpha-synuclein in either neurons or glial cells (2). Alpha-synuclein aggregation is potentially causative of disease progression as variants in alpha-synuclein that promote aggregation are associated with early-age disease onset and familial forms of PD and DLB (3). In PD, alpha-synuclein aggregation occurs primarily in dopaminergic neurons, while in MSA, aggregation is primarily in oligodendrocytes (4, 5). Natively, alpha-synuclein functions as a vesicle transport protein and more recently found to be involved in P-body and mRNA stability (6, 7). Alpha-synuclein is an intrinsically disordered protein, which has made the determination of an atomic structure of its soluble form challenging. It has been shown that soluble alpha-synuclein adopts a helical form when bound to cell membranes, while its aggregated form adopts the cross-beta structure typical of other amyloid fibrils (8–10). Multiple structures of fibrillar alpha-synuclein have been determined both of recombinant (11–16) and brain-derived fibrils (17, 18).In addition to primary aggregation, one mechanism by which alpha-synuclein pathology spreads throughout the brain is the prion-like seeding of alpha-synuclein aggregates (19). Alpha-synuclein fibrils can seed the aggregation of soluble native protein, and Lewy body pathology is observed to spread through connected brain regions (19). Aggregation of alpha-synuclein, both primary and seeded, has become a main therapeutic target for synucleinopathies. Antibodies that sequester alpha-synuclein aggregates are currently under development, as well as small molecules that bind monomer and prevent primary aggregation (20). We recently identified several rationally designed peptides and small proteins capable of binding to the growing ends of alpha-synuclein fibrils and preventing fibril elongation and seeding (21, 22). In this current study, we present small molecules capable of disaggregating preformed alpha-synuclein fibrils. We demonstrate the efficacy of these molecules with in vitro studies, cell culture models, and in vivo models using both recombinant and patient brain-derived alpha-synuclein fibrils. We also present a structure-based model to describe their possible mechanism of fibril disaggregation.     

Mutant presenilin 1 expression in excitatory neurons impairs enrichment-mediated phenotypes of adult hippocampal progenitor cells

Inheritance of mutant presenilin 1 genes (PSEN1) encoding presenilin 1 (PS1)variants causes autosomal dominant forms of familial Alzheimer’s disease (FAD). We previously reported that ubiquitous expression of FAD-linked PS1 variants in mice impairs environmental enrichment (EE)-induced proliferation and neuronal commitment of adult hippocampal neural progenitor cells (AHNPCs). Notably, the self-renewal and differentiation properties of cultured AHNPCs expressing either human PS1 wild-type or PS1 variants were identical, suggesting that accessory cells within the hippocampal niche expressing PS1 variants may modulate AHNPC phenotypes in vivo. We now report that nontransgenic mouse AHNPCs transduced with retroviruses harboring cDNAs that encode either human PS1 wild-type or FAD-linked PS1 variants show no differences in EE-mediated proliferation and neuronal differentiation. Moreover, conditional inactivation of a mutant PS1 transgene in type-1 primary progenitor cells failed to rescue impairments of EE-induced proliferation, survival, or neurogenesis. In contrast, conditional inactivation of the mutant PS1 transgene in excitatory neurons of the mouse forebrain largely rescued the deficits in EE-induced proliferation and survival of AHNPCs, but not their differentiation into mature neuronal phenotypes. These results persuasively argue for a noncell autonomous effect of FAD-linked PS1 mutants on EE-mediated adult hippocampal neurogenesis.     

Glycemia and Levels of Cerebrospinal Fluid Amyloid and Tau in Patients Attending a Memory Clinic

OBJECTIVES: To determine the association between markers of glycemia and cerebrospinal fluid (CSF) amyloid β 1–42 (Aβ42) and tau levels in patients attending a memory clinic. DESIGN: Cross‐sectional study. SETTING: Memory clinic. PARTICIPANTS: Two hundred forty‐five consecutive patients attending a memory clinic. Clinical diagnoses were subjective cognitive complaints (n=91), mild cognitive impairment (n=62), Alzheimer's disease (n=58), and other dementia (n=34). Twenty‐one patients had diabetes mellitus. MEASUREMENTS: Glycosylated hemoglobin (HbA1c); fasting blood glucose levels; and CSF levels of Aβ42, total tau, and p‐tau 181. RESULTS: In regression analyses across the whole study sample adjusted for age, sex, and diagnostic group, there was no relationship between HbA1c or fasting glucose and CSF tau, p‐tau 182, or Aβ42 levels. Stratification for diabetes mellitus did not change the results. CONCLUSION: These observations do not support the hypothesis that the association between dysglycemia and impaired cognitive functioning is mediated through aberrant amyloid or tau metabolism.     

Telomere length in early life predicts lifespan

The attrition of telomeres, the ends of eukaryote chromosomes, is thought to play an important role in cell deterioration with advancing age. The observed variation in telomere length among individuals of the same age is therefore thought to be related to variation in potential longevity. Studies of this relationship are hampered by the time scale over which individuals need to be followed, particularly in long-lived species where lifespan variation is greatest. So far, data are based either on simple comparisons of telomere length among different age classes or on individuals whose telomere length is measured at most twice and whose subsequent survival is monitored for only a short proportion of the typical lifespan. Both approaches are subject to bias. Key studies, in which telomere length is tracked from early in life, and actual lifespan recorded, have been lacking. We measured telomere length in zebra finches (n = 99) from the nestling stage and at various points thereafter, and recorded their natural lifespan (which varied from less than 1 to almost 9 y). We found telomere length at 25 d to be a very strong predictor of realized lifespan (P < 0.001); those individuals living longest had relatively long telomeres at all points at which they were measured. Reproduction increased adult telomere loss, but this effect appeared transient and did not influence survival. Our results provide the strongest evidence available of the relationship between telomere length and lifespan and emphasize the importance of understanding factors that determine early life telomere length.     

REGIONAL CEREBRAL BLOOD FLOW MEASUREMENTS IN THE DIAGNOSIS OF DEMENTIA

The Xenon-133 regional cerebral blood flow technique (rCBF) was used to assess cortical perfusion in a group of 15 elderly patients (mean age = 79.1, SD = 8.7) with a probable diagnosis of Dementia of the Alzheimer type (DAT). Nine had mild DAT and six were in the moderate stages of DAT. These patients were compared with 15 age and sex matched normal elderly controls (mean age = 75.1, SD = 5.6). RCBF was measured in each patient and control at rest with eyes closed. The DAT patients had significantly lower mean global CBF than normal controls (t = -4.63, p< 0,0001). In addition, a further 15 normal elderly subjects aged 60 to 92 were assessed and combined with the original 15 to allow calculation of a normal range of rCBF for elderly individuals. Seventy-three per cent of the DAT patients fell below the lower limit of the normal range (39.3 - 59.3 ISI units). These results show the possible usefulness of rCBF as an aid in the diagnosis of early DAT.     

Inhibition of glycogen synthase kinase-3 by lithium correlates with reduced tauopathy and degeneration in vivo

Neurofibrillary tangles composed of hyperphosphorylated, aggregated tau are a common pathological feature of tauopathies, including Alzheimer's disease. Abnormal phosphorylation of tau by kinases or phosphatases has been proposed as a pathogenic mechanism in tangle formation. To investigate whether kinase inhibition can reduce tauopathy and the degeneration associated with it in vivo, transgenic mice overexpressing mutant human tau were treated with the glycogen synthase kinase-3 (GSK-3) inhibitor lithium chloride. Treatment resulted in significant inhibition of GSK-3 activity. Lithium administration also resulted in significantly lower levels of phosphorylation at several epitopes of tau known to be hyperphosphorylated in Alzheimer's disease and significantly reduced levels of aggregated, insoluble tau. Administration of a second GSK-3 inhibitor also correlated with reduced insoluble tau levels, supporting the idea that lithium exerts its effect through GSK-3 inhibition. Levels of aggregated tau correlated strongly with degree of axonal degeneration, and lithium-chloride-treated mice showed less degeneration if administration was started during early stages of tangle development. These results support the idea that kinases are involved in tauopathy progression and that kinase inhibitors may be effective therapeutically.     

Muscle power of the ankle flexors predicts functional performance in community-dwelling older women

OBJECTIVES: To test the hypothesis that peak power of the ankle flexors is related to physical functioning in older women with functional limitations. DESIGN: A cross-sectional study. SETTING: University-based human physiology laboratory. PARTICIPANTS: Thirty-four older women (75.4 +/- 5.1 years, 67.8 +/- 11.3 kg, body mass index 27.4 +/- 4.5) with self-reported functional limitations. MEASUREMENTS: Plantarflexion (PF) and dorsiflexion (DF) peak power and isometric strength with physical performance (stair climb time, repeated chair rise time, maximal and habitual gait velocity) were determined. An isokinetic dynamometer was used to measure isometric strength, isokinetic peak torque and power of PF and DF at five angular velocities (30 degrees, 60 degrees, 90 degrees, 120 degrees, and 180 degrees.sec-1), and isometric strength. RESULTS: Peak torque for both PF and DF declined with increasing velocity of movement (PF: P <.0001; DF: P <.0001), whereas peak power increased with increasing velocity up to 120 degrees.sec-1. The strongest univariate associations were found between chair rise time and DF peak power (r = 0.50; P <.002), stair climb time and DF peak power (r = 0.49; P <.003), habitual gait velocity and PF isometric strength (r = 0.53; P <.001), and maximal gait and PF isometric strength (r = 0.47; P <.005). Multivariate regression analysis revealed that DF and PF peak power along with the physical functioning and general health scores from the Medical Outcomes Study Short Form were independent predictors of chair and stair climb performance. CONCLUSION: These data suggest that ankle muscle power together with self-reported measures of health and physical functioning are essential components of functional mobility in older women with functional limitations.