Microglial Drivers of Alzheimer's Disease Pathology: An Evolution of Diverse Participating States.

Microglia, the resident immune-competent cells of the brain, become dysfunctional in Alzheimer's disease (AD), and their aberrant immune responses contribute to the accumulation of pathological proteins and neuronal injury. Genetic studies implicate microglia in the development of AD, prompting interest in developing immunomodulatory therapies to prevent or ameliorate disease. However, microglia take on diverse functional states in disease, playing both protective and detrimental roles in AD, which largely overlap and may shift over the disease course, complicating the identification of effective therapeutic targets. Extensive evidence gathered using transgenic mouse models supports an active role of microglia in pathology progression, though results vary and can be contradictory between different types of models and the degree of pathology at the time of study. Here, we review microglial immune signaling and responses that contribute to the accumulation and spread of pathological proteins or directly affect neuronal health. We additionally explore the use of induced pluripotent stem cell (iPSC)-derived models to study living human microglia and how they have contributed to our knowledge of AD and may begin to fill in the gaps left by mouse models. Ultimately, mouse and iPSC-derived models have their own limitations, and a comprehensive understanding of microglial dysfunction in AD will only be established by an integrated view across models and an appreciation for their complementary viewpoints and limitations.

Felodipine attenuates neuroinflammatory responses and tau hyperphosphorylation through JNK/P38 signaling in tau-overexpressing AD mice.

We previously demonstrated that felodipine, an L-type calcium channel blocker, inhibits LPS-mediated neuroinflammatory responses in BV2 microglial cells and wild-type mice. However, the effects of felodipine on tau pathology, a hallmark of Alzheimer's disease (AD), have not been explored yet. Therefore, in the present study, we determined whether felodipine affects neuroinflammation and tau hyperphosphorylation in 3-month-old P301S transgenic mice (PS19), an early phase AD mice model for tauopathy. Felodipine administration decreased tauopathy-mediated microglial activation and NLRP3 expression in PS19 mice but had no effect on tauopathy-associated astrogliosis. In addition, felodipine treatment significantly reduced tau hyperphosphorylation at S202/Thr205 and Thr212/Ser214 residues via inhibiting JNK/P38 signaling in PS19 mice. Collectively, our results suggest that felodipine significantly ameliorates tau hyper-phosphorylation and tauopathy-associated neuroinflammatory responses in AD mice model for tauopathy and could be a novel therapeutic agent for AD.

Real-time detection of Tau-381 protein using liquid crystal-based sensors for Alzheimer's disease diagnosis.

Tau is a protein found in the central nervous system (CNS) and is involved in stabilizing microtubules in axons. Given the link between Tau levels in the body and Alzheimer's disease (AD), there is a demand for straightforward and precise strategies to detect Tau in body fluids. In this study, we report liquid crystal (LC)-based sensors for the real-time detection of Tau protein, a well-known AD biomarker. The sensor uses a detection method based on the orientation change of the LC because of the competitive biomolecular interaction between Tau and Tau aptamers with the cationic polymer poly-L-lysine (PLL). Tau and its aptamers form stable complexes through electrostatic interactions. Owing to the consumption of the aptamer, the positively charged PLL fails to interact with the aptamer but binds to the negatively charged 1.2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) sodium salt (DOPG). The PLL and DOPG complex alters the orientation of the LC to ensure a planar anchoring of the 4-cyano-4'-pentylbiphenyl (5CB)/aqueous interface; this anchoring intensifies with increasing Tau concentration, thus enabling the observation of a bright optical image. Our LC-based sensor demonstrated a low detection limit of 2.77 pg/mL in phosphate buffered saline (PBS) and 10.86 pg/mL and 19.31 pg/mL in human serum and plasma, respectively. Moreover, it is anticipated to be suitable for point-of-care diagnosis of AD because it does not require specialized analytical equipment and only requires microliters of sample.

Can cerebrospinal fluid biomarkers tell us something about financial capacity in Alzheimer's disease patients? A preliminary study.

BACKGROUND: Although diagnostic markers in cerebrospinal fluid (CSF) have become a rapidly growing research field, they have not as yet been investigated in relation to capacities that are of interest to geriatric psychiatry and neuropsychology, such as financial capacity. The aim of this study was to assess whether CSF biomarkers can predict financial capacity in patients with a diagnosis of major neurocognitive disorder due to Alzheimer's disease (AD). METHODS: Participants were examined with a number of neuropsychological tests, with an emphasis on the Mini-Mental State Examination (MMSE), the Geriatric Depression Scale (GDS-15), and the Legal Capacity for Property Law Transactions Assessment Scale (LCPLTAS) and CSF tests. RESULTS: Amyloid ß peptide 1-42 (Aß42), total tau, and phosphorylated tau were not found to predict financial capacity performance in AD, but MMSE shows a strong positive correlation with LCPLTAS. CONCLUSIONS: These preliminary findings indicate that complex cognitive functions, such as financial capacity, may not be directly linked to CSF concentrations of the abovementioned biomarkers. Further studies with larger numbers of patients will be required to assess the reproducibility of these findings and to determine whether this approach can assist not only in diagnosis but also in neuropsychological assessment.

Ovariectomy exacerbates the disturbance of excitation- inhibition balance in the brain of APP/PS-1/tau mice.

Introduction: The prevalence of Alzheimer's disease (AD) is significantly gender-differentiated, with the number of female AD patients far exceeding that of males, accounting for two-thirds of the total prevalence. Although postmenopausal AD mice have been shown to have more prominent pathologic features and memory impairments than normal AD mice, the relevant molecular mechanisms leading to these outcomes have not been well elucidated. In the present study, we used the disturbance of excitation-inhibition balance in the postmenopausal brain as an entry point to explore the link between estrogen deficiency, disorders of the glutamatergic-GABAergic nervous system, and memory impairment. Methods: Wild-type (WT) mice and APP/PS1/tau (3 × Tg-AD) mice (10 months old) were randomly divided into four groups: WT+Sham group, WT+OVX group, 3 × Tg-AD+Sham group and 3 × Tg-AD+OVX group. Ovariectomy (OVX) was performed in the WT+OVX group and the 3 × Tg-AD+OVX group, and sham surgery was performed in the WT+Sham group and the 3 × Tg-AD+Sham group. The learning and memory ability and the anxiety and depression-like behavior changes of mice were evaluated by behavioral experiments, and the association between estrogen-estrogen receptors pathway and glutamatergic/GABAergic nervous system and female AD was evaluated by neurochemical experiments. Results: In WT and 3 × Tg-AD mice, OVX resulted in impaired learning and memory abilities and anxiety and depression-like behaviors; reduced estrogen levels and downregulated the expression of estrogen receptors; upregulated the expression of amyloid-ß, amyloid precursor protein, presenilin 1, and p-tau; upregulated the expression of Bcl-2-associated X protein and downregulated the expression of B-cell lymphoma-2, promoting cell apoptosis; reduced the number of neuronal dendrites and downregulated the expression of postsynaptic density protein-95; more importantly, OVX increased brain glutamate levels but downregulated the expression of N-methyl-D-aspartate receptor-2B, excitatory amino acid transporter 1, excitatory amino acid transporter 2, γ-aminobutyric acid receptor-A and γ-aminobutyric acid receptor-B. Conclusion: Our results suggested that OVX-induced estrogen-estrogen receptors pathway disruption caused learning and memory impairment and anxiety and depression-like behaviors, upregulated the expression of AD pathological markers, promoted apoptosis, destroyed neuronal structure, and most importantly, caused glutamatergic/GABAergic nervous system disorders.

Combining cerebrospinal fluid and PI-2620 tau-PET for biomarker-based stratification of Alzheimer's disease and 4R-tauopathies.

INTRODUCTION: Recent advances in biomarker research have improved the diagnosis and monitoring of Alzheimer's disease (AD), but in vivo biomarker-based workflows to assess 4R-tauopathy (4RT) patients are currently missing. We suggest a novel biomarker-based algorithm to characterize AD and 4RTs. METHODS: We cross-sectionally assessed combinations of cerebrospinal fluid measures (CSF p-tau181 and t-tau) and 18F-PI-2620 tau-positron emission tomography (PET) in patients with AD (n = 64), clinically suspected 4RTs (progressive supranuclear palsy or corticobasal syndrome, n = 82) and healthy controls (n = 19). RESULTS: Elevated CSF p-tau181 and cortical 18F-PI-2620 binding was characteristic for AD while normal CSF p-tau181 with elevated subcortical 18F-PI-2620 binding was characteristic for 4RTs. 18F-PI-2620-assessed posterior cortical hypoperfusion could be used as an additional neuronal injury biomarker in AD. DISCUSSION: The specific combination of CSF markers and 18F-PI-2620 tau-PET in disease-specific regions facilitates the biomarker-guided stratification of AD and 4RTs. This has implications for biomarker-aided diagnostic workflows and the advancement in clinical trials. HIGHLIGHTS: Novel biomarker-based algorithm for differentiating AD and 4R-tauopathies. A combination of CSF p-tau181 and 18F-PI-2620 discriminates AD versus 4R tauopathies. Hypoperfusion serves as an additional neuronal injury biomarker in AD.

Phosphorylated Tau at T181 accumulates in the serum of hibernating Syrian hamsters and rapidly disappears after arousal.

The search for biomarkers for the early diagnosis of neurodegenerative diseases is a growing area. Numerous investigations are exploring minimally invasive and cost-effective biomarkers, with the detection of phosphorylated Tau (pTau) protein emerging as one of the most promising fields. pTau is the main component of the paired helical filaments found in the brains of Alzheimer's disease cases and serves as a precursor in the formation of neurofibrillary tangles (NFTs). Recent research has revealed that analysis of p-Tau181, p-Tau217 and p-Tau231 in blood may be an option for detecting the preclinical stage of Alzheimer's disease. In this study, we have analyzed the values of pTau 181 in the serum of Syrian hamsters during hibernation. Naturally, over the course of hibernation, these animals exhibit a reversible accumulation of pTau in the brain tissue, which rapidly disappears upon awakening. A biosensing system based on the interferometric optical detection method was used to measure the concentration of pTau181 protein in serum samples from Syrian hamsters. This method eliminates the matrix effect and amplifies the signal obtained by using silicon dioxide nanoparticles (SiO2 NPs) biofunctionalized with the αpTau181 antibody. Our results indicate a substantial increase in the serum concentration of pTau in threonine-181 during hibernation, which disappears completely 2-3 h after awakening. Investigating the mechanism by which pTau protein appears in the blood non-pathologically may enhance current diagnostic techniques. Furthermore, since this process is reversible, and no tangles are detected in the brains of hibernating hamsters, additional analysis may contribute to the discovery of improved biomarkers. Additionally, exploring drugs targeting pTau to prevent the formation of tangles or studying the outcomes of any pTau-targeted treatment could be valuable.

Chronic glial activation and behavioral alterations induced by acute/subacute pioglitazone treatment in a mouse model of traumatic brain injury.

Traumatic brain injury (TBI) is a disabling neurotraumatic condition and the leading cause of injury-related deaths and disability in the United States. Attenuation of neuroinflammation early after TBI is considered an important treatment target; however, while these inflammatory responses can induce secondary brain injury, they are also involved in the repair of the nervous system. Pioglitazone, which activates peroxisome proliferator-activated receptor gamma, has been shown to decrease inflammation acutely after TBI, but the long-term consequences of its use remain unknown. For this reason, the impacts of treatment with pioglitazone during the acute/subacute phase (30 min after injury and each subsequent 24 h for 5 days) after TBI were interrogated during the chronic phase (30- and 274-days post-injury (DPI)) in mice using the controlled cortical impact model of experimental TBI. Acute/subacute pioglitazone treatment after TBI results in long-term deleterious consequences, including disruption of tau homeostasis, chronic glial cell activation, neuronal pathology, and worsened injury severity particularly at 274 DPI, with male mice being more susceptible than female mice. Further, male pioglitazone-treated TBI mice exhibited increased dominant and offensive-like behavior while having a decreased non-social exploring behavior at 274 DPI. After TBI, both sexes exhibited glial activation at 30 DPI when treated with pioglitazone; however, while injury severity was increased in females it was not impacted in male mice. This work reveals that although pioglitazone has been shown to lead to attenuated TBI outcomes acutely, sex-based differences, timing and long-term consequences of treatment with glitazones must be considered and further studied prior to their clinical use for TBI therapy.

Imidacloprid unique and repeated treatment produces cholinergic transmission disruption and apoptotic cell death in SN56 cells.

Imidacloprid (IMI), the most widely used worldwide neonicotinoid biocide, produces cognitive disorders after repeated and single treatment. However, little was studied about the possible mechanisms that produce this effect. Cholinergic neurotransmission regulates cognitive function. Most cholinergic neuronal bodies are present in the basal forebrain (BF), regulating memory and learning process, and their dysfunction or loss produces cognition decline. BF SN56 cholinergic wild-type or acetylcholinesterase (AChE), ß-amyloid-precursor-protein (ßAPP), Tau, glycogen-synthase-kinase-3-beta (GSK3ß), beta-site-amyloid-precursor-protein-cleaving enzyme 1 (BACE1), and/or nuclear-factor-erythroid-2-related-factor-2 (NRF2) silenced cells were treated for 1 and 14 days with IMI (1 µM-800 µM) with or without recombinant heat-shock-protein-70 (rHSP70), recombinant proteasome 20S (rP20S) and with or without N-acetyl-cysteine (NAC) to determine the possible mechanisms that mediate this effect. IMI treatment for 1 and 14 days altered cholinergic transmission through AChE inhibition, and triggered cell death partially through oxidative stress generation, AChE-S overexpression, HSP70 downregulation, P20S inhibition, and Aß and Tau peptides accumulation. IMI produced oxidative stress through reactive oxygen species production and antioxidant NRF2 pathway downregulation, and induced Aß and Tau accumulation through BACE1, GSK3ß, HSP70, and P20S dysfunction. These results may assist in determining the mechanisms that produce cognitive dysfunction observed following IMI exposure and provide new therapeutic tools.

Molecular Modeling Insights on the Pharmaceuticals and Hypotheses of Alzheimer's Disease.

Alzheimer's disease (AD) stands as the predominant contributor to dementia cases. The ongoing developments in our understanding of its pathogenesis have sparked the interest of researchers, driving them to explore innovative treatment approaches. Existing therapies incorporating cholinesterase inhibitors and/or NMDA antagonists have shown limited improvement in alleviating symptoms. This, in turn, highlights the urgency for the pursuit of more effective therapeutic options. Given the annual rise in the number of individuals affected by dementia, it is imperative to allocate resources and efforts towards the exploration of novel therapeutic options. This review aims to provide a comprehensive overview of the AD-related hypotheses, along with the computational approaches employed in research within each hypothesis. In this comprehensive review, the authors shed light on using various computational tools, including diverse case studies, in the pursuit of finding efficacious treatments for AD. The development of more sophisticated diagnostic techniques is crucial, enabling early detection and intervention in the battle against this challenging condition. The potential treatments investigated in this analysis are poised to assume ever more significant functions in both preventing and treating AD, ultimately enhancing the management of the condition and the overall well-being of individuals affected by AD.

Dissecting the immune response of CD4+ T cells in Alzheimer's disease.

The formation of amyloid-ß (Aß) plaques is a neuropathological hallmark of Alzheimer's disease (AD), however, these pathological aggregates can also be found in the brains of cognitively unimpaired elderly population. In that context, individual variations in the Aß-specific immune response could be key factors that determine the level of Aß-induced neuroinflammation and thus the propensity to develop AD. CD4+ T cells are the cornerstone of the immune response that coordinate the effector functions of both adaptive and innate immunity. However, despite intensive research efforts, the precise role of these cells during AD pathogenesis is still not fully elucidated. Both pathogenic and beneficial effects have been observed in various animal models of AD, as well as in humans with AD. Although this functional duality of CD4+ T cells in AD can be simply attributed to the vast phenotype heterogeneity of this cell lineage, disease stage-specific effect have also been proposed. Therefore, in this review, we summarized the current understanding of the role of CD4+ T cells in the pathophysiology of AD, from the aspect of their antigen specificity, activation, and phenotype characteristics. Such knowledge is of practical importance as it paves the way for immunomodulation as a therapeutic option for AD treatment, given that currently available therapies have not yielded satisfactory results.

Pathways to personalized medicine-Embracing heterogeneity for progress in clinical therapeutics research in Alzheimer's disease.

Biological and clinical heterogeneity is a major challenge in research for developing new treatments for Alzheimer's disease (AD). AD may be defined by its amyloid beta and tau pathologies, but we recognize that mixed pathologies are common, and that diverse genetics, central nervous system (CNS) and systemic pathophysiological processes, and environmental/experiential factors contribute to AD's diverse clinical and neuropathological features. All these factors are rational targets for therapeutic development; indeed, there are hundreds of candidate pharmacological, dietary, neurostimulation, and lifestyle interventions that show benefits in homogeneous laboratory models. Conventional clinical trial designs accommodate heterogeneity poorly, and this may be one reason that progress in translating candidate interventions has been so difficult. We review the challenges of AD's heterogeneity for the clinical trials enterprise. We then discuss how advances in repeatable biomarkers and digital phenotyping enable novel "single-case" and adaptive trial designs to accelerate therapeutics development, moving us closer to personalized research and medicine for AD. HIGHLIGHTS: Alzheimer's disease is diverse in its clinical features, course, risks, and biology. Typical randomized controlled trials are exclusive and necessarily large to attain arm comparability with broad outcomes. Repeated blood biomarkers and digital tracking can improve outcome measure precision and sensitivity. This enables the use of novel "single-case" and adaptive trial designs for inclusivity, rigor, and efficiency.

Endocrine Dyscrasia in the Etiology and Therapy of Alzheimer's Disease.

The increase in the incidence of dementia over the last century correlates strongly with the increases in post-reproductive lifespan during this time. As post-reproductive lifespan continues to increase it is likely that the incidence of dementia will also increase unless therapies are developed to prevent, slow or cure dementia. A growing body of evidence implicates age-related endocrine dyscrasia and the length of time that the brain is subjected to this endocrine dyscrasia, as a key causal event leading to the cognitive decline associated with aging and Alzheimer's disease (AD), the major form of dementia in our society. In particular, the elevations in circulating gonadotropins, resulting from the loss of gonadal sex hormone production with menopause and andropause, appear central to the development of AD neuropathology and cognitive decline. This is supported by numerous cell biology, preclinical animal, and epidemiological studies, as well as human clinical studies where suppression of circulating luteinizing hormone and/or follicle-stimulating hormone with either gonadotropin-releasing hormone analogues, or via physiological hormone replacement therapy, has been demonstrated to halt or significantly slow cognitive decline in those with AD. This review provides an overview of past and present studies demonstrating the importance of hypothalamic-pituitary-gonadal hormone balance for normal cognitive functioning, and how targeting age-related endocrine dyscrasia with hormone rebalancing strategies provides an alternative treatment route for those with AD.

Emerging microglial biology highlights potential therapeutic targets for Alzheimer's disease.

Alzheimer's disease is a chronic degenerative disease of the central nervous system, which primarily affects elderly people and accounts for 70-80 % of dementia cases. The current prevailing amyloid cascade hypothesis suggests that Alzheimer's disease begins with the deposition of amyloid ß (Aß) in the brain. Major therapeutic strategies target Aß production, aggregation, and clearance, although many clinical trials have shown that these therapeutic strategies are not sufficient to completely improve cognitive deficits in AD patients. Recent genome-wide association studies have identified that multiple important regulators are the most significant genetic risk factors for Alzheimer's disease, especially in the innate immune pathways. These genetic risk factors suggest a critical role for microglia, highlighting their therapeutic potential in treating neurodegenerative diseases. In this review, we discuss how these recently documented AD risk genes affect microglial function and AD pathology and how they can be further targeted to regulate microglial states and slow AD progression, especially the highly anticipated APOE and TREM2 targets. We focused on recent findings that modulation of innate and adaptive neuroimmune microenvironment crosstalk reverses cognitive deficits in AD patients. We also considered novel strategies for microglia in AD patients.

Proteolysis of tau by granzyme A in tauopathies generates fragments that are aggregation prone.

Tauopathies, including Alzheimer's disease, Corticobasal Degeneration and Progressive Supranuclear Palsy, are characterised by the aggregation of tau into insoluble neurofibrillary tangles in the brain. Tau is subject to a range of post-translational modifications, including proteolysis, that can promote its aggregation. Neuroinflammation is a hallmark of tauopathies and evidence is growing for a role of CD8+ T cells in disease pathogenesis. CD8+ T cells release granzyme proteases but what role these proteases play in neuronal dysfunction is currently lacking. Here, we identified that granzyme A (GzmA) is present in brain tissue and proteolytically cleaves tau. Mass spectrometric analysis of tau fragments produced on digestion of tau with GzmA identified three cleavage sites at R194-S195, R209-S210 and K240-S241. Mutation of the critical Arg or Lys residues at the cleavage sites in tau or chemical inhibition of GzmA blocked the proteolysis of tau by GzmA. Development of a semi-targeted mass spectrometry approach identified peptides in tauopathy brain tissue corresponding to proteolysis by GzmA at R209-S210 and K240-S241 in tau. When expressed in cells the GzmA-cleaved C-terminal fragments of tau were highly phosphorylated and aggregated upon incubation of the cells with tauopathy brain seed. The C-terminal fragment tau195-441 was able to transfer between cells and promote aggregation of tau in acceptor cells, indicating the propensity for such tau fragments to propagate between cells. Collectively, these results raise the possibility that GzmA, released from infiltrating cytotoxic CD8+ T cells, proteolytically cleaves tau into fragments that may contribute to its pathological properties in tauopathies.

Plasma NfL, GFAP, amyloid, and p-tau species as Prognostic biomarkers in Parkinson's disease.

INTRODUCTION: The prognostic role of plasma neurofilament light chain (NfL), phospho-tau, beta-amyloid, and GFAP is still debated in Parkinson's disease (PD). METHODS: Plasma p-tau181, p-tau231, Aß1-40, Aß1-42, GFAP, and NfL were measured by SIMOA in 136 PD with 2.9 + 1.7 years of follow-up and 76 controls. Differences in plasma levels between controls and PD and their correlation with clinical severity and progression rates were evaluated using linear regression analyses. RESULTS: Patients exhibited similar distribution of plasma biomarkers but higher P-tau181, P-tau231 and lower Aß1-42 compared with controls. NfL and GFAP correlated with baseline motor and non-motor severity measures. At follow-up, NfL emerged as the best predictor of progression with marginal effect of GFAP and p-tau181 adjusting for age, sex, disease duration, and baseline motor severity. CONCLUSION: The present findings confirmed plasma NfL as best predictor of progression in PD, with a marginal role of p-tau181 and GFAP.

Updates in Alzheimer's disease: from basic research to diagnosis and therapies.

Alzheimer's disease (AD) is the most common neurodegenerative disorder, characterized pathologically by extracellular deposition of ß-amyloid (Aß) into senile plaques and intracellular accumulation of hyperphosphorylated tau (pTau) as neurofibrillary tangles. Clinically, AD patients show memory deterioration with varying cognitive dysfunctions. The exact molecular mechanisms underlying AD are still not fully understood, and there are no efficient drugs to stop or reverse the disease progression. In this review, we first provide an update on how the risk factors, including APOE variants, infections and inflammation, contribute to AD; how Aß and tau become abnormally accumulated and how this accumulation plays a role in AD neurodegeneration. Then we summarize the commonly used experimental models, diagnostic and prediction strategies, and advances in periphery biomarkers from high-risk populations for AD. Finally, we introduce current status of development of disease-modifying drugs, including the newly officially approved Aß vaccines, as well as novel and promising strategies to target the abnormal pTau. Together, this paper was aimed to update AD research progress from fundamental mechanisms to the clinical diagnosis and therapies.

Calcineurin inhibition prevents synaptic plasticity deficit induced by brain-derived tau oligomers.

Compelling evidence suggests that cognitive decline in Alzheimer's disease is associated with the accumulation and aggregation of tau protein, with the most toxic aggregates being in the form of oligomers. This underscores the necessity for direct isolation and analysis of brain-derived tau oligomers from patients with Alzheimer's disease, potentially offering novel perspectives into tau toxicity. Alzheimer's brain-derived tau oligomers are potent inhibitors of synaptic plasticity; however, the involved mechanism is still not fully understood. We previously reported a significantly reduced incidence of Alzheimer's disease in ageing humans chronically treated with a Food and Drug Administration-approved calcineurin inhibitor, FK506 (tacrolimus), used as an immunosuppressant after solid organ transplant. Using a combination of electrophysiological and RNA-sequencing techniques, we provide here evidence that FK506 has the potential to block the acute toxic effect of brain-derived tau oligomers on synaptic plasticity, as well as to restore the levels of some key synaptic mRNAs. These results further support FK506 as a promising novel therapeutic strategy for the treatment of Alzheimer's disease.

Association of quantitative histopathology measurements with antemortem medial temporal lobe cortical thickness in the Alzheimer's disease continuum.

The medial temporal lobe (MTL) is a hotspot for neuropathology, and measurements of MTL atrophy are often used as a biomarker for cognitive decline associated with neurodegenerative disease. Due to the aggregation of multiple proteinopathies in this region, the specific relationship of MTL atrophy to distinct neuropathologies is not well understood. Here, we develop two quantitative algorithms using deep learning to measure phosphorylated tau (p-tau) and TDP-43 (pTDP-43) pathology, which are both known to accumulate in the MTL and are associated with MTL neurodegeneration. We focus on these pathologies in the context of Alzheimer's disease (AD) and limbic predominant age-related TDP-43 encephalopathy (LATE) and apply our deep learning algorithms to distinct histology sections, on which MTL subregions were digitally annotated. We demonstrate that both quantitative pathology measures show high agreement with expert visual ratings of pathology and discriminate well between pathology stages. In 140 cases with antemortem MR imaging, we compare the association of semi-quantitative and quantitative postmortem measures of these pathologies in the hippocampus with in vivo structural measures of the MTL and its subregions. We find widespread associations of p-tau pathology with MTL subregional structural measures, whereas pTDP-43 pathology had more limited associations with the hippocampus and entorhinal cortex. Quantitative measurements of p-tau pathology resulted in a significantly better model of antemortem structural measures than semi-quantitative ratings and showed strong associations with cortical thickness and volume. By providing a more granular measure of pathology, the quantitative p-tau measures also showed a significant negative association with structure in a severe AD subgroup where semi-quantitative ratings displayed a ceiling effect. Our findings demonstrate the advantages of using quantitative neuropathology to understand the relationship of pathology to structure, particularly for p-tau, and motivate the use of quantitative pathology measurements in future studies.

Heterogeneity of factors associated with cognitive decline and cortical atrophy in early- versus late-onset Alzheimer's disease.

The objectives of this study were to investigate the variable factors associated with cognitive function and cortical atrophy and estimated variable importance of those factors in affecting cognitive function and cortical atrophy in patients with EOAD and LOAD. Patients with EOAD (n = 40), LOAD (n = 34), and healthy volunteers with normal cognition were included (n = 65). All of them performed 3T MRI, [18F]THK5351 PET (THK), [18F]flutemetamol PET (FLUTE), and detailed neuropsychological tests. To investigate factors associated with neuropsychological test results and cortical thickness in each group, we conducted multivariable linear regression models, including amyloid, tau, cerebral small vessel disease markers on MRI, and vascular risk factors. Then, we estimated variable importance in associating cognitive functions and cortical thickness, using relative importance analysis. In patients with EOAD, global THK retention was the most important contributor to the model variances for most neuropsychological tests, except for memory. However, in patients with LOAD, multiple contributors beyond tau were important in explaining variance of neuropsychological tests. In analyses with mean cortical thickness, global THK retention was the main contributor in patients with EOAD, while in LOAD patients, multiple factors contributed equally to mean cortical thickness. Therefore, EOAD and LOAD may have different pathomechanistic courses.