Beau M. Ances - US grants

DESCRIPTION (provided by applicant): Human immunodeficiency virus (HIV) infected patients are now living longer due to highly active antiretroviral therapy (HAART). More than 50% of all HIV infected patients will be > 50 years old by 2015. However, HAART has not decreased the prevalence of neurological disorders in HIV infected patients. Older HIV infected patients are at greater risk for developing neurological disorders and are a significant burden to caregivers. In addition, debate also exists concerning the overall efficacy of HAART as better brain penetrating regimens (neuroHAART) may control the virus in the brain but cause neurotoxicity. Current assessment of neurocognitive disorders due to HIV entails lengthy neuropsychological testing which may not be sensitive to early signs of neuronal dysfunction. It is imperative that an early presymptomatic biomarker is identified to test interventions that prevent HIV infected patients from developing neurocognitive impairment. One promising new approach is non-invasive neuroimaging of resting state brain functional connections. This technique has identified the default mode network- a series of brain areas involved in organizing memories and preparing for the future events. Our preliminary results demonstrate that HIV diminishes the integrity of brain functional connections within this network by 40%. HIV also amplifies the effects of aging as older infected patients have brain network connections equivalent to seronegative subjects who are 15-20 years older. We hypothesize that HIV-induced decreases in neuronal connectivity within the default mode network will precede neuropsychological testing differences. The proposal will: 1) measure the effects of HIV on brain functional connections; 2) investigate if HIV accelerates aging of brain networks; 3) evaluate the effects of neuroHAART on brain connections. These results will assist nurses and clinicians in deciding when to initiate HAART and help them evaluate the efficacy of tailored adjunctive neuroprotective therapies.

DESCRIPTION (provided by applicant): Adolescence is a period of physical, psychological, and social development. Many older adolescents (18-24 years old) engage in high-risk behaviors such as unprotected sex, multiple sex partners, and drug use. This has caused an increase in the prevalence of human immunodeficiency virus infected (HIV+) adolescents. In addition, many HIV+ adolescents continue to engage in high-risk behaviors leading to a further HIV spread. Current assessments of risky decision-making in adolescents involve self-administered surveys concerning sexual behaviors and drug use. It is imperative that early markers of risky behaviors are identified so that effective interventions are implemented to reduce adolescent HIV transmission. This proposal will utilize non-invasive neuroimaging, such as arterial spin labeling (ASL), to quantitatively measure cerebral blood flow (CBF) within risky decision-making networks. Preliminary ASL studies have demonstrated that HIV diminishes CBF by 60% within risky decision-making areas. We will also use computer based neurobehavioral tests that simulate real-life risky decision making situations. Correlations between neuroimaging and neurobehavioral methods could provide us unique insights into the mechanisms that fuel the adolescent HIV epidemic. The overall direct impact of our research will be: 1) an increase in our knowledge concerning the interaction between risky decision-making and HIV in adolescents 2) the development of early neuroimaging and neurobehavioral markers that assess the impact of HIV infection on risky decision- making networks. These results will assist nurses, clinicians, and public health practitioners in developing interventions that could save lives and reduce the spread of HIV in this vulnerable population. PUBLIC HEALTH RELEVANCE: An increase in the prevalence of HIV infected (HIV+) adolescents has occurred as many adolescents engage in high-risk behaviors such as unprotected sex, multiple sex partners, and drug use. This proposal will: 1) increase our knowledge concerning the interaction between risky decision-making and HIV in adolescents;2) develop early neuroimaging and neurobehavioral markers to assess the impact of HIV on risky behaviors. These results will assist practitioners in developing effective interventions to reduce adolescent HIV transmission.

DESCRIPTION (provided by applicant): Human immunodeficiency virus (HIV) infected patients are now living longer due to potent antiretroviral therapy (ART). Despite the effectiveness of ART for systemic viral suppression, up to half of chronically HIV infected (HIV+) individuals will develop HIV associated neurocognitive disorders (HAND). Increasing efforts have focused on understanding the early pathophysiologic changes within the central nervous system (CNS) initiated during primary HIV infection (PHI, defined as the first year after HIV transmission). It remains unknown if early initiation of ART during PHI could reduce the future incidence of developing HAND. It is imperative that early biomarkers (including cerebrospinal fluid (CSF) and neuroimaging) are developed for understanding the mechanisms of crucial early events that may influence the trajectory of damage in the CNS. Previous studies of PHI have primarily been cross sectional and have focused on a limited number of PHI participants assessed by single modality. We propose a longitudinal study to assess the effects of PHI and early ART on brain structure which integrates structural neuroimaging analyses with blood and CSF measures of infection, inflammation and neurodenegeration, as well as clinical data including exposure to stimulant drugs of abuse to investigate possible mechanisms of brain injury beginning during PHI. Specifically, this study will employ structural neuroimaging methods (diffusion tensor imaging (DTI) and brain volumetrics) to study the CNS mechanisms that underlie the natural history of PHI in the CNS as well as the effects of starting ART in the early stages of infection. Based on our preliminary cross sectional analyses, we hypothesize that structural neuroimaging (DTI and brain volumetrics) will reveal progressive injury in the brain during early infection prior to ART which may be halted in subjects that initiate ART soon after seroconversion. Subjects using methamphetamine may have increased vulnerability to HIV-associated structural injury, tied to inflammation in the brain. This proposal will: (Aim 1) investigate the mechanisms of CNS injury in PHI prior to ART by temporally associating the emergence of abnormalities in structural imaging with laboratory biomarkers and neuropsychological performance. Additionally (Aim 2) we will explore the mechanisms of early ART effects in the CNS through assessment of white matter integrity and brain volumetrics over time in subjects both before and after starting ART. Our long term goal is to provide evidence for the appropriate timing of ART initiation and to evaluate the rationale of possible tailored adjunctive neuroprotective therapies to prevent HAND.

DESCRIPTION (provided by applicant): Management of older (¿ 50 years old) HIV-infected individuals is becoming increasingly complex as many develop multiple HIV-associated-non-AIDS-defining (HANA) comorbidities at an earlier onset. We will utilize frailty measurements and neuropsychological performance (NP) tests to determine if a combination of cognitive impairment and frailty identifies vulnerable older HIV-infected individuals (n=130). In addition, we will employ innovative brain imaging techniques [including arterial spin labeling magnetic resonance imaging (ASL-MRI) and positron emission tomography using Pittsburgh B compound (PET-PiB)] to quantitatively assess perfusion and amyloid deposition in older HIV-infected individuals. We will evaluate if frailty correlates with neuroimaging biomarkers (ASL and PET-PIB) of brain integrity in older HIV-infected patients. Finally, we will determine at three year follow-up if frail older HIV-infected individuals have greater rates of change from baseline in cognitive impairment (NP testing), amyloid deposition (PET-PiB), and perfusion (ASL-MRI) compared to pre-frail or non-frail older HIV-infected individuals. This proposal will place HIV associated changes in frailty and cognition into the mainstream of national brain aging research. We will develop biomarkers that will allow for early detection of changes in brain function at the pre-frail state. It is hoped that these biomarkers will assist in the early administration of tailoed effective interventions.

DESCRIPTION (provided by applicant): Human immunodeficiency virus (HIV) infected patients are now living longer due to potent antiretroviral therapy (ART). Despite the effectiveness of ART for systemic viral suppression, up to half of chronically HIV infected (HIV+) individuals will develop HIV associated neurocognitive disorders (HAND). Increasing efforts have focused on understanding the early pathophysiologic changes within the central nervous system (CNS) initiated during primary HIV infection (PHI, defined as the first year after HIV transmission). It remains unknown if early initiation of ART during PHI could reduce the future incidence of developing HAND. It is imperative that early biomarkers (including cerebrospinal fluid (CSF) and neuroimaging) are developed for understanding the mechanisms of crucial early events that may influence the trajectory of damage in the CNS. Previous studies of PHI have primarily been cross sectional and have focused on a limited number of PHI participants assessed by single modality. We propose a longitudinal study to assess the effects of PHI and early ART on brain structure which integrates structural neuroimaging analyses with blood and CSF measures of infection, inflammation and neurodenegeration, as well as clinical data including exposure to stimulant drugs of abuse to investigate possible mechanisms of brain injury beginning during PHI. Specifically, this study will employ structural neuroimaging methods (diffusion tensor imaging (DTI) and brain volumetrics) to study the CNS mechanisms that underlie the natural history of PHI in the CNS as well as the effects of starting ART in the early stages of infection. Based on our preliminary cross sectional analyses, we hypothesize that structural neuroimaging (DTI and brain volumetrics) will reveal progressive injury in the brain during early infection prior to ART which may be halted in subjects that initiate ART soon after seroconversion. Subjects using methamphetamine may have increased vulnerability to HIV-associated structural injury, tied to inflammation in the brain. This proposal will: (Aim 1) investigate the mechanisms of CNS injury in PHI prior to ART by temporally associating the emergence of abnormalities in structural imaging with laboratory biomarkers and neuropsychological performance. Additionally (Aim 2) we will explore the mechanisms of early ART effects in the CNS through assessment of white matter integrity and brain volumetrics over time in subjects both before and after starting ART. Our long term goal is to provide evidence for the appropriate timing of ART initiation and to evaluate the rationale of possible tailored adjunctive neuroprotective therapies to prevent HAND.

? DESCRIPTION (provided by applicant): Management of older persons living with HIV (PLWH) (? 50 years old) is becoming increasingly more complex as a majority is greater than 50 years old. Attempts to improve the quality of life of older PLWH using adjunctive therapeutics to combination antiretroviral therapy (cART) have largely been unsuccessful. While the impact of physical activity on brain health (assessed by neuropsychological performance and neuroimaging) has been well studied in older healthy HIV uninfected (HIV-) individuals and neurodegenerative conditions, few studies have concentrated on older PLWH. Both clinically and pathophysiologically, HIV associated neurocognitive disorders (HAND) differs from other neurodegenerative disorders seen with aging (e.g. Alzheimer's disease (AD). A positive association relationship between exercise and cognition has been observed in PLWH, but physical activity has been primarily examined using self-report questionnaires that are subjective and not quantitative. To date, no study has focused on the direct effects of exercise on neuropsychological performance or neuroimaging in PLWH. The objective of this proposal is to conduct a prospective controlled intervention trial to determine if an increase in physical activity through a monitored aerobic and resistance exercise (EXS) program improves brain health in older PLWH. We will quantify physical function (physical activity using cardiorespiratory capacity and actigraphy) and brain function [neuropsychological performance testing and neuroimaging (cerebral blood flow (CBF) and brain volume)] in older physically inactive PLWH at baseline and 26 weeks after randomization to either an EXS or a social-interaction stretching (SIS) program. In addition, we will obtain serum markers of neurogenesis, glucose regulation, and systemic inflammation. Our specific aims include: Specific Aim 1. Examine the effects of exercise on cognitive function in older PLWH. Specific Aim 2. Examine the effects of exercise on brain structural/functional measures in older PLWH. Secondary endpoints of this proposal will identify implementation factors needed to scale up an EXS program in older PLWH to HIV clinics at multiple institutions. Key barriers and facilitators will b analyzed from qualitative data obtained from questionnaires, focus groups, and in-depth interviews of shareholders. A direct impact of these expected outcomes will be the adoption of a more physically active lifestyle by older PLWH and improved EXS guidelines and programs for older PLWH.

? DESCRIPTION (provided by applicant): The major technological and analytical advances in human brain imaging achieved as part of the Human Connectome Projects (HCP) enable examination of structural and functional brain connectivity at unprecedented levels of spatial and temporal resolution. This information is proving invaluable for enhancing our understanding of normative variation in young adult brain connectivity. It is now timely to use the tools and analytical approaches developed by the HCP to understand how structural and functional wiring of the brain changes during the aging process. Using state-of-the art HCP imaging approaches will allow investigators to push our currently limited understanding of normative brain aging to new levels. We propose an effort involving a consortium of five sites (Massachusetts General Hospital, University of California at Los Angeles, University of Minnesota, Washington University in St. Louis, and Oxford University), with extensive complementary expertise in human brain imaging and aging and including many investigators associated with the original adult and pilot lifespan HCP efforts. This synergistic integration of advances from the MGH and WU-MINN-OXFORD HCPs with cutting-edge expertise in aging provides an unprecedented opportunity to advance our understanding of the normative changes in human brain connectivity with aging. Aim 1 will be to optimize existing HCP Lifespan Pilot project protocols to respect practical constraints in studying adults over a wide age range, including the very old (80+ years). Aim 2 will be to collect high quality neuroimaging, behavioral, and other datasets on 1200 individuals in the age range of 36 - 100+ years, using matched protocols across sites. This will enable robust cross-sectional analyses of age-related changes in network properties including metrics of connectivity, network integrity, response properties during tasks, and behavior. Aim 3 will be to collect and analyze longitudinal data on a subset of 300 individuals in three understudied and scientifically interesting groups: ages 36-44 (when late maturational and early aging processes may co-occur); ages 45-59 (perimenopausal, when rapid hormonal changes can affect cognition and the brain); and ages 80 - 100+ (the `very old', whose brains may reflect a `healthy survivor' state). The information gained relating to these important periods will enhance our understanding of how important phenomena such as hormonal changes affect the brain and will provide insights into factors that enable cognitively intact function into advanced aging. Aim 4 will capitalize on our success in sharing data in the Human Connectome Project (HCP), and will use these established tools, platforms, and procedures to make this data publicly available through the Connectome Coordination Facility.

SUMMARY/ABSTRACT This proposal will study falls in older adults with preclinical Alzheimer?s disease (AD). Conversion to symptomatic AD is not an immediate process; rather, it develops slowly over a series of preclinical stages. Although symptomatic AD is characterized by progressive cognitive problems, growing evidence suggests that functional mobility abnormalities and an increase in falls may precede cognitive impairment. Falls are a leading cause of morbidity and mortality in the older adult population. Older AD patients have more than twice the risk of falls compared to the general population. Measures of everyday function are currently not included in the evaluation of cognitively normal individuals with preclinical AD. Within a well-characterized cohort of older, cognitively normal individuals (>65 years old) who are followed by the Knight Alzheimer?s Disease Research Center, we will perform longitudinal in-home assessments to quantitatively evaluate falls and functional mobility. We hypothesize that brain neuropathology (e.g., the presence of amyloid and/or tau proteins, evidence of neurodegeneration) lead to changes in functional connectivity of brain networks. These brain network changes affect both central nervous system markers (e.g., cognitive performance) and peripheral nervous system markers (e.g., balance, strength, vision, and sensation). We suggest that a synergistic interaction between central and peripheral changes leads to altered functional mobility, resulting in an increase in falls. Our findings will advance the field of AD by identifying novel ?real-world? biomarkers in preclinical stages of AD. Assessment of falls and gait instability in the home setting could potentially serve as an inexpensive and non-invasive screening tool to identify individuals at greatest risk for conversion to symptomatic AD. This may have important implications for the timing of interventions in secondary prevention trials in AD.

ABSTRACT/PROJECT SUMMARY This proposal systematically characterizes brain efficiency and recruitment in virologically suppressed persons living with HIV (PLWH) and demographically similar HIV uninfected (HIV-) controls. This proposal collects advanced functional neuroimaging that provide critical information about cerebral blood flow (CBF) and brain connectivity (functional connectivity strength; FCS); quantitative measures of immune dysfunction in the blood and cerebrospinal fluid (CSF) (immune activation and immune exhaustion); and neuropsychological performance testing. This overall goal of this proposal is to delineate the interplay between dysfunction in frontal networks and recruitment of compensatory networks that underlie the neuropsychiatric symptoms seen in PLWH. This proposal investigates fundamental questions through two aims. Aim 1 determines the neuroimaging signatures of brain efficiency and recruitment in virologically suppressed PLWH. We hypothesize that PLWH will have increased recruitment of compensatory networks to offset reduced engagement in frontal networks. Among PLWH, we hypothesize that worse neuropsychological performance will be associated with reduced brain efficiency, despite recruitment of compensatory networks . We hypothesize that the presence of immune dysfunction (immune activation and exhaustion) among PLWH will be associated with reduced brain efficiency despite recruitment of compensatory networks. Aim 2 determines the effects of brain efficiency and recruitment on aging in virologically suppressed PLWH. We hypothesize that younger PLWH (< 50 years old) will have a profile of brain efficiency and recruitment that is similar to older HIV- individuals (> 50 years old). Compared to younger PLWH (< 50 years old) older PLWH (? 50 years old) will have reduced brain efficiency despite recruitment of compensatory networks. We hypothesize that this relationship may be mediated by immune dysfunction. Results of this study will provide powerful insight into the pathophysiology of disease and will reveal arenas for future possible interventions in PLWH who have impaired neuropsychological performance.

ABSTRACT/PROJECT SUMMARY In this proposal we explore the transition from preclinical to symptomatic Alzheimer disease (AD) by incorporating the novel tau imaging tracer ([18F]-AV-1451) within the biomarker-rich protocol of the Dominantly Inherited Alzheimer Network (DIAN). We leverage the existing infrastructure of DIAN and a collaboration with Avid Radiopharmaceuticals to initiate tau positron emission tomography (PET) imaging in this unique cohort. DIAN provides fundamental support to the hypothesis that AD consists of a preclinical stage in which accumulation of beta-amyloid (A?) plaques and tau neurofibrillary tangle (NFT) gradually lead to neuronal dysfunction and cognitive impairment. However, key gaps remain in our understanding of the temporal and spatial interactions that occur between A? and tau during the transition from preclinical to clinical symptoms. This proposal answers these fundamental questions through three aims. Aim 1 studies the temporal dynamics of tau deposition (using AV-1451) in relation to estimated years to symptom onset (EYO) and existing biomarkers in DIAN (including cerebrospinal fluid, neuroimaging, and cognitive performance). Aim 2 studies the spatial (both local and distributed) changes of tau deposition (using AV-1451). Aim 3 studies the relationship between in vivo tau deposition (using AV-1451) and neuropathology. Unique to autosomal dominant AD (ADAD), the young age of the DIAN participants eliminates overlap with potential age-related neuropathology or tauopathy (PART). Our overall hypothesis is that conversion from cognitively normal to symptomatic AD can be accurately predicted by neuroimaging biomarkers, in particular by AV-1451 PET. Results from this proposal are fundamental for our understanding of PET tau as not only a diagnostic indicator of disease but also a therapeutic marker to evaluate the clinical efficacy of future interventions in ADAD.

ABSTRACT FOR OVERVIEW The Aging Adult Brain Connectome (AABC) leverages the existing infrastructure developed by the Human Connectome Project for Aging (HCP-A) by obtaining longitudinal follow-up data (neuroimaging, cognitive testing, and blood) using a standardized protocol from a well characterized cohort of over 1,000 healthy individuals to generate within-participant brain trajectories for up to 10 years. At initial recruitment, individuals enrolled in the HCP-A were generally physically and cognitively healthy but over time some will develop preclinical AD or early cognitive changes due to AD or ADRD. The AABC is comprised of four Projects: Project 1 examine the effects of stress and allostatic load, including inflammation, during the early adult period. Project 2 examines the effects of lifestyle behaviors on the trajectory of cognitive and brain changes during the mid adult period. Project 3 examine the effects of menopause transition/vasomotor symptoms during the mid adult period. Project 4 exam- ine the clinical and neural indicators of resiliency and resistance to AD and ADRD in the later decades of adult- hood. The AABC also consists of 4 Cores: The Administration Core (AC) will provide essential core and site leadership to carry out the scientific mission of the AABC. The diversity recruitment and retention unit (DRRU) will be located within this core and will ensure that the AABC continues to recruit and retain an adequate distri- bution of races that is currently seen in the US. The Integrated Data Acquisition Core (IDAC) provides expertise and personnel from each site to acquire high quality neuroimaging, deep phenotyping of non-imaging data, and biosamples from each site.The Informatics, Data Analysis, and Statistics Core (IDASC) will house project imag- ing data using the IntraDB database, will perform quality control of raw and analyzed data, will develop and run cross-sectional and longitudinal pipelines to produce multi-modal imaging data phenotypes for each project, will provide dimension-reduced summaries, will impute missing data; and will develop and run statistical models for each project. The IDASC will also be responsible for data sharing with the general public. The Genetics and Multi-omics Specimens Core (GMSC) will provide genetic information on participants evaluated through the AABC who have been characterized using a uniform protocol. Multi-omic data and AD biomarker data will be generated by the GMSC.

Project 1 Abstract An overarching theme of the Alzheimer's Disease Biomarkers-Down syndrome (ABC-DS) program is to characterize Alzheimer disease (AD) in Down syndrome (DS) and to determine if it has a pathological progression comparable to late onset AD (LOAD) and thus can inform translational research focused on prevention and treatment for all people with AD. People with DS are at extremely high risk of AD in middle age due, at least in large measure, to lifelong overexpression of the gene coding for APP, located on Chr. 21. A hypothesized model has been proposed for LOAD consisting of early amyloid (A) deposition followed by tau (T) deposition and then neurodegeneration (N) (AT(N)). Inflammation and cerebrovascular disease (CVD) are more common in adults with DS and may modify the AT(N) framework. Project 1 utilizes outcomes collected by ABC- DS Cores to follow the conversion of adults with DS from when they are clinically unaffected by AD to progression of incident MCI-DS and subsequent dementia. This project will determine if the AT(N) framework is descriptive of AD progression in adults with DS and, if different, in what way. A second priority is to determine if AD risk and progression is modified by certain risk factors. Aim 1 examines the AT(N) framework with regard to the development of symptomatic cognitive decline (MCI-DS/Dementia). We hypothesize that early changes in amyloid (A) are followed by changes in neurofibrillary pathology (T) and then changes in neurodegeneration (N). We predict the overall sequence of events that leads to symptomatic cognitive decline in DS is similar to AD in other at risk AD populations but quantitative differences will be present in the time span over which these events occur. Aim 2 examines the contribution of selected factors that modify the risk or progression to cognitive decline (MCI-DS/dementia) and in the AT(N) framework to lead to individual variability in DS. We hypothesize that inflammatory changes and cerebrovascular disease (CVD) modify the risk of amyloid and tau deposition. Furthermore, we hypothesize that sex and commonly co-occurring medical conditions (e.g. seizures, hyperlipidemia, obesity, and sleep apnea) may contribute to the heterogeneity in the age at onset of MCI-DS and/or the rate of progression from MCI-DS to dementia. Aim 3 examines select factors that contribute to within- population variability in AD vulnerability in collaboration with Projects 2 and 3. Results from this Project could contribute to efforts to discover effective intervention(s) within this high risk population and for AD more broadly.

ABSTRACT/PROJECT SUMMARY This proposal employs novel methods to identify key determinants and consequences of concurrent HIV infection and regular cannabis use. We will acquire extensive phenotype data from peripheral and brain markers of immune activation, brain structure, and neuropsychological performance (NP) in persons living with HIV (PLWH) receiving combination anti-retroviral therapy (cART) (80 regular cannabis users and 80 non-users) and HIV uninfected (HIV-) controls (80 regular cannabis users and 80 non-users). Our overall hypothesis is that cannabis use leads to increases in inflammation in the peripheral and brain compartments. We also hypothesize that phenotypic signatures due to regular cannabis use and HIV will be delineated through NP and brain volumetrics. In Aim 1 we hypothesize that regular cannabis use will increase both peripheral and brain immune indices in PLWH on cART. In Aim 2 we hypothesize that regular cannabis use will lead to a worsening of NP and reductions in brain volumetrics in both PLWH on cART and HIV- controls. This proposal will provide key insights into the effects of regular cannabis and HIV on peripheral and brain markers of immune function and NP in PLWH and HIV- controls. These insights are critical for cure strategies and ongoing HIV treatment initiatives.

Project 3: Project Summary/Abstract The gut microbiome (GM) is comprised of thousands of microbial taxa, with a vast repertoire of functional pathways that interact with the host environment. Dysbiosis of the GM is associated with numerous disease states within and beyond the gastrointestinal tract. GM dysbiosis has also been implicated in Alzheimer disease (AD), with recent data demonstrating AD patients have distinct GM taxonomic composition from those of healthy controls. Further, these taxa correlate with presence of AD biomarkers in the cerebrospinal fluid (CSF), as well as dysregulation of a key inflammatory pathway. However, knowledge about changes in the GM prior to symptomatic AD onset is limited. The rationale behind our proposal is that changes in the GM that occur prior to symptomatic AD are critical for understanding AD pathogenesis. This proposal pursues three aims: 1) Characterize gut bacterial content and organ permeability in adults at different stages of AD, 2) Identify longitudinal changes in bacterial content and organ permeability in cognitively normal individuals without or with preclinical AD, and symptomatic AD, and 3) Associate bacterial content and organ permeability with other modalities of AD biomarkers obtained from other Projects and Cores of this PPG. Aim 1 will test the hypothesis that cognitively normal individuals with preclinical AD (e.g., amyloid positive) already exhibit altered GM composition and increased gut permeability. To address this hypothesis, we will leverage our unique set of stool samples from healthy individuals without preclinical AD (n=400), cognitively normal with preclinical AD (n=150), and symptomatic AD (n=50) individuals from ACS and other Knight ADRC- affiliated studies. By combining metagenomic sequencing, metatranscriptomic profiling, and detection of fecal and serum markers of permeability and inflammation, we will determine distinct compositional and functional features of preclinical and symptomatic AD. Based on these characterizations, Aim2 will test the hypothesis that these features correlate with AD progression, with symptomatic AD individuals displaying the greatest shifts over time. Aim 3 will connect our findings with other biomarkers identified in the PPG, with the hypothesis that changes in GM and organ permeability will correlate with longitudinal changes in CSF tau and p-tau, PET tau uptake, CSF and plasma inflammatory markers, and physical activity. This proposal is innovative and significant because our multidisciplinary team will identify early biomarkers that precede the onset of symptomatic AD. Our work will impact and advance AD research by characterizing GM dysbiosis during AD pathogenesis as well as establish a foundation for cost-effective, noninvasive measures to diagnose AD.