Cortical Aβ Deposition Research Articles

Tau, synapse loss and gliosis progress in an Alzheimer's mouse model after amyloid-β immunotherapy.

While preclinical studies assessing drugs for Alzheimer's disease (AD) are conducted in animal models that usually display only one neuropathological feature of AD, patients present with a complex combination of comorbidities and neuropathologies. Importantly, it is well-established that amyloid (Aβ) plaque and tau tangle accumulation interact in a phase-dependent manner, making it difficult to predict how targeting one might influence the other, as well as downstream degeneration. We developed a transgenic mouse model, APP/PS1xTau22, with progressive cortical Aβ deposition and hippocampal tau neurofibrillary inclusions to investigate how both neuropathologies act jointly to bring about neural degeneration, synapse loss, and glial phenotypes. We then assessed whether applying murine chimeric Aducanumab, an anti-amyloid immunotherapy, could impact the synergistic relationship between amyloid and tau. Drug treatment resulted in a ∼70% reduction in Aβ deposition in hippocampal and cortical areas and produced a robust peri-plaque microglial and astrocytic response. Removing amyloid from the brain did not reverse or slow tau pathology or alter synapse loss. Our findings suggest that, once the interaction between amyloid and tau is set in motion, reducing plaque burden by Aβ immunotherapy may stimulate glial responses, but is insufficient to curb degenerative phenotypes in this model.

Amyloid PET detects the deposition of brain Aβ earlier than CSF fluid biomarkers.

Understanding the relationship between amyloid beta (Aβ) positron emission tomography (PET) and Aβ cerebrospinal fluid (CSF) biomarkers will define their potential utility in Aβ treatment. Few population-based or neuropathologic comparisons have been reported. Participants 50+ years with Aβ PET and Aβ CSF biomarkers (phosphorylated tau [p-tau]181/Aβ42, n=505, and Aβ42/40, n=54) were included from the Mayo Clinic Study on Aging. From these participants, an autopsy subgroup was identified (n=47). The relationships of Aβ PET and Aβ CSF biomarkers were assessed cross-sectionally in all participants and longitudinally in autopsy data. Cross-sectionally, more participants were Aβ PET+ versus Aβ CSF- than Aβ PET- versus Aβ CSF+ with an incremental effect when using Aβ PET regions selected for early Aβ deposition. The sensitivity for the first detection of Thal phase≥1 in longitudinal data was higher for Aβ PET (89%) than p-tau181/Aβ42 (64%). Aβ PET can detect earlier cortical Aβ deposition than Aβ CSF biomarkers. Aβ PET+ versus Aβ CSF- findings are several-fold greater using regional Aβ PET analyses and in peri-threshold-standardized uptake value ratio participants. Amyloid beta (Aβ) positron emission tomography (PET) has greater sensitivity for Aβ deposition than Aβ cerebrospinal fluid (CSF) in early Aβ development. A population-based sample of participants (n=505) with PET and CSF tests was used. Cortical regions showing early Aβ on Aβ PET were also used in these analyses. Neuropathology was used to validate detection of Aβ by Aβ PET and Aβ CSF biomarkers.

Apolipoprotein B gene expression and regulation in relation to Alzheimer’s disease pathophysiology

Apolipoprotein B (APOB), a receptor-binding protein present in cholesterol-rich lipoproteins, has been implicated in Alzheimer's disease (AD). High levels of APOB-containing low-density lipoproteins (LDL) are linked to the pathogenesis of both early-onset familial and late-onset sporadic AD. Rare coding mutations in the APOB gene are associated with familial AD, suggesting a role for APOB-bound lipoproteins in the central nervous system. This research explores APOB gene regulation across the AD spectrum using four cohorts: BRAINEAC (elderly control brains), DBCBB (controls, AD brains), ROSMAP (controls, MCI, AD brains), and ADNI (control, MCI, AD clinical subjects). APOB protein levels, measured via mass spectrometry and ELISA, positively correlated with AD pathology indices and cognition, while APOB mRNA levels showed negative correlations. Brain APOB protein levels are also correlated with cortical Aβ levels. A common coding variant in the APOB gene locus affected its expression but didn't impact AD risk or brain cholesterol concentrations, except for 24-S-hydroxycholesterol. Polymorphisms in the CYP27A1 gene, notably rs4674344, were associated with APOB protein levels. A negative correlation was observed between brain APOB gene expression and AD biomarker levels. CSF APOB correlated with Tau pathology in presymptomatic subjects, while cortical APOB was strongly associated with cortical Aβ deposition in late-stage AD. The study discusses the potential link between blood-brain barrier dysfunction and AD symptoms in relation to APOB neurobiology. Overall, APOB's involvement in lipoprotein metabolism appears to influence AD pathology across different stages of the disease.

Linking white matter hyperintensities to regional cortical thinning, amyloid deposition, and synaptic density loss in Alzheimer's disease.

We investigated the association between white matter hyperintensities (WMH) and regional cortical thickness, amyloid and tau deposition, and synaptic density in the WMH-connected cortex using multimodal images. We included 107 participants (59 with Alzheimer's disease [AD]; 27 with mild cognitive impairment; 21 cognitively normal controls) with amyloid beta (Aβ) positivity on amyloid positron emission tomography (PET). The cortex connected to WMH was identified using probabilistic tractography. We found that WMH connected to the cortex with more severe regional degeneration as measured by cortical thickness, Aβ and tau deposition, and synaptic vesicle glycoprotein 2 A (SV2A) density using 18F-SynVesT-1 PET. In addition, higher ratios of Aβ in the deep WMH-connected versus WMH-unconnected cortex were significantly related to lower cognitive scores. Last, the cortical thickness of WMH-connected cortex reduced more than WMH-unconnected cortex over 12 months. Our results suggest that WMH may be associated with AD-intrinsic processes of degeneration, in addition to vascular mechanisms. We studied white matter hyperintensities (WMHs) and WMH-connected cortical changes. WMHs are associated with more severe regional cortical degeneration. Findings suggest WMHs may be associated with Alzheimer's disease-intrinsic processes of degeneration.

Remote Associations Between Tau and Cortical Amyloid-β Are Stage-Dependent.

Histopathologic studies of Alzheimer's disease (AD) suggest that extracellular amyloid-β (Aβ) plaques promote the spread of neurofibrillary tau tangles. However, these two proteinopathies initiate in spatially distinct brain regions, so how they interact during AD progression is unclear. In this study, we utilized Aβ and tau positron emission tomography (PET) scans from 572 older subjects (476 healthy controls (HC), 14 with mild cognitive impairment (MCI), 82 with mild AD), at varying stages of the disease, to investigate to what degree tau is associated with cortical Aβ deposition. Using multiple linear regression models and a pseudo-longitudinal ordering technique, we investigated remote tau-Aβ associations in four pathologic phases of AD progression based on tau spread: 1) no-tau, 2) pre-acceleration, 3) acceleration, and 4) post-acceleration. No significant tau-Aβ association was detected in the no-tau phase. In the pre-acceleration phase, the earliest stage of tau deposition, associations emerged between regional tau in medial temporal lobe (MTL) (i.e., entorhinal cortex, parahippocampal gyrus) and cortical Aβ in lateral temporal lobe regions. The strongest tau-Aβ associations were found in the acceleration phase, in which tau in MTL regions was strongly associated with cortical Aβ (i.e., temporal and frontal lobes regions). Strikingly, in the post-acceleration phase, including 96% of symptomatic subjects, tau-Aβ associations were no longer significant. The results indicate that associations between tau and Aβ are stage-dependent, which could have important implications for understanding the interplay between these two proteinopathies during the progressive stages of AD.

Human in vivo evidence of associations between herpes simplex virus and cerebral amyloid-beta load in normal aging

BackgroundMounting data suggests that herpes simplex virus type 1 (HSV-1) is involved in the pathogenesis of AD, possibly instigating amyloid-beta (Aβ) accumulation decades before the onset of clinical symptoms. However, human in vivo evidence linking HSV-1 infection to AD pathology is lacking in normal aging, which may contribute to the elucidation of the role of HSV-1 infection as a potential AD risk factor.MethodsTo shed light into this question, serum anti-HSV IgG levels were correlated with 18F-Florbetaben-PET binding to Aβ deposits and blood markers of neurodegeneration (pTau181 and neurofilament light chain) in cognitively normal older adults. Additionally, we investigated whether associations between anti-HSV IgG and AD markers were more evident in APOE4 carriers.ResultsWe showed that increased anti-HSV IgG levels are associated with higher Aβ load in fronto-temporal regions of cognitively normal older adults. Remarkably, these cortical regions exhibited abnormal patterns of resting state-functional connectivity (rs-FC) only in those individuals showing the highest levels of anti-HSV IgG. We further found that positive relationships between anti-HSV IgG levels and Aβ load, particularly in the anterior cingulate cortex, are moderated by the APOE4 genotype, the strongest genetic risk factor for AD. Importantly, anti-HSV IgG levels were unrelated to either subclinical cognitive deficits or to blood markers of neurodegeneration.ConclusionsAll together, these results suggest that HSV infection is selectively related to cortical Aβ deposition in normal aging, supporting the inclusion of cognitively normal older adults in prospective trials of antimicrobial therapy aimed at decreasing the AD risk in the aging population.

Specific Association of Worry and Amyloid‐β Deposition in Cognitive Unimpaired Older Adults

AbstractBackgroundAnxiety symptoms are common in cognitively unimpaired (CU) older adults prior to the onset of cognitive impairment. Evidence suggests that anxiety symptoms may be sequelae of amyloid‐beta (Aβ) deposition in early Alzheimer’s disease (AD) and/or anxiety may potentiate the pathophysiologic process. Despite this pivotal role, the specific components of anxiety associated with high brain Aβ in CU older adults are relatively unknown. It was previously reported that Aβ deposition is associated with a global anxiety score measured by State‐Trait Anxiety Inventory‐6 (STAI‐6) but not depression measured by Geriatric Depression Scale (GDS) total scores. Here, we examined the specific associations of individual anxiety symptoms with Aβ.MethodOlder adult participants were screened for the Anti‐Amyloid Treatment in Asymptomatic Alzheimer’s study (“A4 study”) and underwent assessments of anxiety (STAI‐6), depression (GDS), cognitive performance (MMSE and Preclinical Alzheimer Cognitive Composite /PACC), subjective cognition (Cognitive Function Instrument/CFI) and cortical Aβ deposition using Florbetapir PET standardized uptake value ratio (SUVR). Linear regression models estimated associations of STAI‐6 items, “calm,” “tense,” “upset,” “relax,” “content,” and “worry,” with Aβ deposition, adjusting for multiple potential confounders.ResultThe sample (n = 4486) were older adults ages 65 ‐ 85 (mean [SD] age, 71.29 [4.67] years, included 2647 women (59%) and 1323 (29.5%) who were classified as Aβ+. STAI‐6 total score ranged from 6 ‐ 24 (Mean 9.9 [3.1]). A significant positive association was found between the anxiety item measuring “worry”, and Aβ, adjusting for age, sex, education, marital status, depression (GDS), objective cognition (MMSE or PACC), and subjective cognition (CFI) [Table 1]. There were other significant (negative) associations between items measuring “calm” and “relax” and Aβ in similar regression models. Only the association of “worry” with Aβ remained significant after further adjustment for global anxiety measured by the total STAI‐6 score.ConclusionIn a large, well‐characterized sample of CU older adults, worry was significantly and most strongly associated with Aβ, independent of psychosocial factors, subjective and objective cognition and global anxiety. These findings suggest that self‐reported worry may have unique explanatory value in the clinical assessment of CU older adults at high risk of AD and cognitive impairment.

Risk architecture for altered hippocampal connectivity in normal aging differ between men and women

AbstractBackgroundFunctional MRI (fMRI) studies have associated impaired memory networks with increase in AD pathology. Recently, cross‐sectional analyses found b‐amyloid (Aβ) deposition associated with different patterns of hippocampal connectivity in a memory task based on sex and white matter hyperintensity volume (WMHV). However, cross‐sectional studies don’t provide insight into the driving mechanisms of network change. In this longitudinal study, we identify risk factors based on sex that are associated with memory network connectivity changes.MethodOur study included 54 cognitively normal older adults (N = 34 female, mean age 74.6 years) with MRI scans on average 2.43 (SD 0.82) years apart. T1w, T2‐FLAIR MRI, and PiB PET were collected to quantify cortical volume, WMHV and Aβ deposition, respectively. Task fMRI was collected while participants performed face‐name associative memory tasks. Left and right hippocampus seeds were used to estimate functional connectivity between hippocampus and voxels in the brain. Second‐level analyses were performed to determine regions of interest (ROI) with significant differences in sex by time interaction (p<0.001). The mean beta values were extracted from the significant ROIs for post‐hoc analysis where we performed multivariate linear regression analyses to find correlations with connectivity change (follow‐up minus baseline).ResultThree ROIs presented significant sex by time interactions: left‐right hippocampus, hippocampus‐anterior cingulate cortex (ACC), and hippocampus‐medial frontal gyrus. The change in left‐right hippocampus connectivity increased for women and decreased for men (Fig.1). For the other ROIs, connectivity increased for men and decreased for women (Fig.2). Left‐right hippocampal connectivity change had a significant sex‐WMHV interaction effect (p<0.01), where only women had a positive association between connectivity change and baseline WMHV. Hippocampus‐ACC connectivity change had a significant sex‐Aβ interaction (p<0.01), with greater baseline Aβ associated with increased connectivity change for men and decreased for women.ConclusionWe observed sex‐differences in risk architecture for altered hippocampal connectivity. In the presence of vascular pathology and Aβ, women appear to experience local hippocampal connectivity and decrease hippocampal‐frontal connectivity. Meanwhile, men experienced hippocampal‐frontal connectivity with increased Aβ burden. Characterizing these sex differences in memory network alterations can help guide the development of sex‐specific prevention and treatment strategies.

Molecular imaging of the association between serotonin degeneration and beta-amyloid deposition in mild cognitive impairment

BackgroundDegeneration of the serotonin system has been observed in Alzheimer’s disease (AD) and in mild cognitive impairment (MCI). In transgenic amyloid mouse models, serotonin degeneration is detected prior to widespread cortical beta-amyloid (Aβ) deposition, also suggesting that serotonin degeneration may be observed in preclinical AD. MethodsThe differences in the distribution of serotonin degeneration (reflected by the loss of the serotonin transporter, 5-HTT) relative to Aβ deposition was measured with positron emission tomography in a group of individuals with MCI and a group of healthy older adults. A multi-modal partial least squares (mmPLS) algorithm was applied to identify the spatial covariance pattern between 5-HTT availability and Aβ deposition. ResultsForty-five individuals with MCI and 35 healthy older adults were studied, 22 and 27 of whom were included in the analyses who were “amyloid positive” and “amyloid negative”, respectively. A pattern of lower cortical, subcortical and limbic 5-HTT availability and higher cortical Aβ deposition distinguished the MCI from the healthy older control participants. Greater expression of this pattern was correlated with greater deficits in memory and executive function in the MCI group, not in the control group. ConclusionA spatial covariance pattern of lower 5-HTT availability and Aβ deposition was observed to a greater extent in an MCI group relative to a control group and was associated with cognitive impairment in the MCI group. The results support the application of mmPLS to understand the neurochemical changes associated with Aβ deposition in the course of preclinical AD.

Neuroinflammation is independently associated with brain network dysfunction in Alzheimer’s disease

Brain network dysfunction is increasingly recognised in Alzheimer’s disease (AD). However, the causes of brain connectivity disruption are still poorly understood. Recently, neuroinflammation has been identified as an important factor in AD pathogenesis. Microglia participate in the construction and maintenance of healthy neuronal networks, but pro-inflammatory microglia can also damage these circuits. We hypothesised that microglial activation is independently associated with brain connectivity disruption in AD. We performed a cross-sectional multimodal imaging study and interrogated the relationship between imaging biomarkers of neuroinflammation, Aβ deposition, brain connectivity and cognition. 42 participants (12 Aβ-positive MCI, 14 Aβ-positive AD and 16 Aβ-negative healthy controls) were recruited. Participants had 11C-PBR28 and 18F-flutemetamol PET to quantify Aβ deposition and microglial activation, T1-weighted, diffusion tensor and resting-state functional MRI to assess structural network and functional network. 11C-PBR28 uptake, structural network integrity and functional network orgnisation were compared across diagnostic groups and the relationship between neuroinflammation and brain network was tested in 26 Aβ-positive patients. Increased 11C-PBR28 uptake, decreased FA, network small-worldness and local efficiency were observed in AD patients. Cortical 11C-PBR28 uptake correlated negatively with structural integrity (standardised β = −0.375, p = 0.037) and network local efficiency (standardised β = −0.468, p < 0.001), independent of cortical thickness and Aβ deposition, while Aβ was not. Network structural integrity, small-worldness and local efficiency, and cortical thickness were positively associated with cognition. Our findings suggest cortical neuroinflammation coincide with structural and functional network disruption independent of Aβ and cortical atrophy. These findings link the brain connectivity change and pathological process in Alzheimer’s disease, and suggest a pathway from neuroinflammation to systemic brain dysfunction.

Association of hippocampal subfield volumes with amyloid‐beta deposition in Alzheimer’s disease

AbstractBackgroundCharacteristic atrophy patterns of hippocampal subfield volumes and cortical amyloid‐beta (Aβ) deposition are two important neuroimaging biomarkers in Alzheimer’s disease (AD). We investigated the relationship between hippocampal subfield volumes and cortical Aβ deposition in AD.MethodFifty participants (11 cognitively unimpaired [CU], 10 with mild cognitive impairment [MCI], and 29 with AD) who underwent 18F‐florbetaben positron emission tomography, magnetic resonance imaging, and neuropsychological tests were enrolled. The hippocampal subfield volumes were obtained using an automated brain volumetry system with the Winterburn atlas and were compared among the diagnostic groups, and the correlations with the Aβ deposition and AD risk factors were determined.ResultPatients with MCI and AD showed decreased volume in the stratum radiatum/lacunosum/moleculare (SRLM) of the cornu ammonis (CA)1 and CA4‐dentate gyrus (DG) than the CU. Decreased SRLM and CA4‐DG volumes were associated with an increased Aβ deposition in the global cortex (R = ‐0.459, p = 0.001; R = ‐0.393, p = 0.005, respectively). The SRLM and CA4‐DG volumes aided in the distinction of AD from CU (areas under the receiver operating characteristic [AUROC] curve = 0.957 and 0.930 respectively, p &lt; 0.001), and Aβ+ from Aβ‐ individuals (AUROC curve = 0.763 and 0.763, respectively, p &lt; 0.001).ConclusionHippocampal subfield volumes demonstrated potential as imaging biomarkers in the diagnosis and detection of AD and Aβ deposition, respectively.

Structural and metabolic brain correlates of excess Aβ accumulation at the earliest AD continuum

AbstractBackgroundThe discrepancy between the expected and actual level of cerebral amyloid (Aβ) deposition for any given level of soluble Alzheimer’s disease (AD) core biomarkers, has been proposed as a proxy measure of factors promoting fibrillar Aβ accumulation in the brain. However, the impact of these factors on brain structure and function in cognitively unimpaired (CU) individuals has not been reported. Here, we assessed the impact on brain structure and metabolism of the excess cortical Aβ deposition for a given level of CSF pTau/Aβ42 ratio, a marker of pathophysiological progression along the Alzheimer’s continuum. Furthermore, we analyzed whether this association is modulated by the APOE‐ε4 risk allele.MethodWe included 243 CU participants from the ALFA study (mean age=61.68 years) who underwent a lumbar puncture, magnetic resonance imaging (MRI), 18F‐Fluorodeoxyglucose (FDG) and 18F‐Flutemetamol positron emission tomography (PET) scans. CSF Aβ42 and pTau181 were measured with the Elecsys® immunoassay (Roche Diagnostics International Ltd). The centiloid pipeline was applied to Aβ PET and a general linear model (GLM) was implemented to regress out the effects of CSF pTau/Aβ42 ratio from centiloid values. These residualized centiloids (resCent) were used in subsequent GLMs to predict whole‐brain gray matter volume (GMv) as well as metabolism. Statistical significance threshold was set to p&lt;0.005, with a cluster extent correction of 100 voxels.ResultNegative associations between resCent and GMv were observed in the dorsolateral prefrontal cortex (Fig. 1a), while for FDG, positive associations were found in the inferior frontal and superior temporal gyrus, as well as the anterior cingulate and inferior temporal cortices (Fig. 1b). The associations for GMv were further modulated by the APOE‐ε4 risk allele in a dose‐dependent manner, indicating a lower GMv in ε4‐carriers, in the inferior and middle frontal gyrus, subgenual cingulate cortex and the insula (Fig. 2).ConclusionOur results suggest that, factors associated with excessive Aβ deposition are associated with structural and metabolic brain alterations already in the earliest stages of preclinical Alzheimer’s continuum. The associations for GMv were modulated by APOE‐ε4 indicating a higher structural vulnerability to these factors for carriers of the risk allele all along the preclinical stages of AD.

Cerebral microbleeds in dementia with Lewy bodies

IntroductionCerebral microbleeds (CMB) are associated with cognitive impairment and hypertensive or cerebral amyloid angiopathy. The pathophysiology and clinical significance of CMB in dementia with Lewy bodies (DLB) are not well understood. Our study aimed to investigate the prevalence of CMB in DLB and to estimate the magnitudes of their clinical associations. MethodsTwenty participants with DLB (mean age 74 ± 5 years) were included in this cross-sectional study. All participants underwent 3 T magnetic resonance imaging. CMB number and location were assessed on susceptibility-weighted imaging or quantitative susceptibility mapping. Amyloid-beta (Aβ) positron emission tomography (PET) scans were also performed. Between-group comparisons were estimated using risk ratios (RR) for categorical variables, and mean differences or median regression coefficients for continuous variables. ResultsCMB were present in 30% of the DLB participants, with a lobar predominance observed. DLB with CMB were more likely to be on antithrombotic therapy (100%), compared to those without CMB (43%; RR 2.33 [95% CI 1.27, 4.27]). Those with CMB were also more likely to report a history of hypertension (100%) compared to those without (70%; RR 1.75 [95% CI 1.11, 2.75]). DLB core clinical features, cognition and functional status did not differ between the two groups. There was no association found between the presence of CMB and cortical Aβ deposition on PET imaging. ConclusionCMB are not uncommon in DLB and may be associated with hypertensive small vessel disease. Further studies into the pathophysiology and clinical implications of CMB in DLB are needed.

Chronic vitamin D3 supplementation alleviates cognition impairment via inhibition of oxidative stress regulated by PI3K/AKT/Nrf2 in APP/PS1 transgenic mice

Oxidative stress plays essential role in the pathogenesis of Alzheimer's disease, and vitamin D3 (VD3) is a nutrient with neuroprotective and antioxidant activities. The present study aimed to confirm the neuroprotective effect and the ameliorative effect of cortical oxidative stress of VD3 in APP/PS1 transgenic mice. APP/PS1 mice were treated with VD3 for 20 weeks. After treatment, Morris Water Maze test was used to evaluate cognitive level. Western blotting was used to determine APP, p-tau, tau and PI3K/AKT/Nrf2 pathway-related protein expression levels. Immunohistochemical staining was performed to determine the levels of β amyloid peptide (Aβ) deposition. Enzyme linked immunosorbent assay was used to determine the 25(OH)D3 levels and oxidative stress status. Our results showed that treatment with VD3 ameliorated behavioral deficits of APP/PS1 mice. In addition, the administration of VD3 significantly increased the cortical 25(OH)D3 levels, while reducing the levels of cortical Aβ deposition and decreasing the expression levels of cortical APP, tau and p-tau in APP/PS1 mice. Moreover, VD3 protected the cortex against oxidative stress by enhancing the levels of superoxide dismutase, glutathione and total antioxidant capacity, and downregulating the malondialdehyde levels. Furthermore, VD3 clearly activated the PI3K/AKT/Nrf2 pathway, thereby elevating the expression levels of HO1 and NQO1. We concluded that VD3 improved cognitive function and cortical Alzheimer-like pathology of APP/PS1 mice, which may be related to the inhibition of oxidative stress via activation the PI3K/AKT/Nrf2 pathway.

A longitudinal investigation of Aβ, anxiety, depression, and mild cognitive impairment.

We investigated the longitudinal relationship between cortical amyloid deposition, anxiety, and depression and the risk of incident mild cognitive impairment (MCI). We followed 1440 community-dwelling, cognitively unimpaired individuals aged ≥ 50 years for a median of 5.5 years. Clinical anxiety and depression were assessed using Beck Anxiety and Depression Inventories (BAI, BDI-II). Cortical amyloid beta (Aβ) was measured by Pittsburgh compound B positron emission tomography (PiB-PET) and elevated deposition (PiB+) was defined as standardized uptake value ratio ≥ 1.48. We calculated Cox proportional hazards models with age as the time scale, adjusted for sex, education, and medical comorbidity. Cortical Aβ deposition (PiB+) independent of anxiety (BAI ≥ 10) or depression (BDI-II ≥ 13) increased the risk of MCI. There was a significant additive interaction between PiB+ and anxiety (joint effect hazard ratio 6.77; 95% confidence interval 3.58-12.79; P=.031) that is, being PiB+ and having anxiety further amplified the risk of MCI. Anxiety modified the association between PiB+ and incident MCI.

Amyloid-Associated Depression—or Not?

In the current issue of Biological Psychiatry, Mackin et al. ( 1 Mackin R.S. Insel P.S. Landau S. Bickford D. Morin R. Rhodes E. et al. Late-life depression is associated with reduced cortical amyloid burden: Findings from the Alzheimer’s Disease Neuroimaging Initiative Depression Project. Biol Psychiatry. 2021; 89: 757-765 Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar ) throw new light on the relationship between amyloid-β (Aβ) and depression in older individuals without dementia. But they may also compel us to throw some of our previous assumptions about this emerging field out the window. Early evidence for a link between late-life depression (LLD) and elevated Aβ pathogenesis came from postmortem studies of patients with dementia revealing an association between Aβ plaques and a history of major depression ( 2 Rapp M.A. Schnaider-Beeri M. Grossman H.T. Sano M. Perl D.P. Purohit D.P. et al. Increased hippocampal plaques and tangles in patients with Alzheimer disease with a lifetime history of major depression. Arch Gen Psychiatry. 2006; 63: 161-167 Crossref PubMed Scopus (294) Google Scholar ). The advent of positron emission tomography (PET) enabled the study of clinicopathologic associations in vivo and provided further support for Aβ pathogenesis as a possible mechanism underlying the connection between LLD and Alzheimer’s disease (AD). Elevated cortical Aβ deposition in older individuals with current or lifetime major depression has been observed in most PET studies ( 3 Kumar A. Kepe V. Barrio J.R. Siddarth P. Manoukian V. Elderkin-Thompson V. et al. Protein binding in patients with late-life depression. Arch Gen Psychiatry. 2011; 68: 1143-1150 Crossref PubMed Scopus (60) Google Scholar , 4 Wu K.Y. Hsiao I.T. Chen C.S. Chen C.H. Hsieh C.J. Wai Y.Y. et al. Increased brain amyloid deposition in patients with a lifetime history of major depression: Evidenced on 18F-florbetapir (AV-45/Amyvid) positron emission tomography. Eur J Nucl Med Mol Imaging. 2014; 41: 714-722 Crossref PubMed Scopus (76) Google Scholar ). Longitudinal cohort studies using PET imaging have also reported positive associations between Aβ pathology and subsyndromal depressive symptoms in cognitively normal older adults ( 5 Krell-Roesch J. Lowe V.J. Neureiter J. Pink A. Roberts R.O. Mielke M.M. et al. Depressive and anxiety symptoms and cortical amyloid deposition among cognitively normal elderly persons: The Mayo Clinic Study of Aging. Int Psychogeriatr. 2018; 30: 245-251 Crossref PubMed Scopus (34) Google Scholar , 6 Donovan N.J. Locascio J.J. Marshall G.A. Gatchel J. Hanseeuw B.J. Rentz D.M. et al. Longitudinal association of amyloid beta and anxious-depressive symptoms in cognitively normal older adults. Am J Psychiatry. 2018; 175: 530-537 Crossref PubMed Scopus (106) Google Scholar ). Of note, also in this issue of Biological Psychiatry, Xu et al. ( 7 Xu W. Feng W. Shen X.-N. Bi Y.-L. Ma Y.-H. Li J.-Q. et al. Amyloid pathologies modulate the associations of minimal depressive symptoms with cognitive impairments in older adults without dementia. Biol Psychiatry. 2021; 89: 766-775 Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar ) corroborate these findings in older adults without dementia and use causal mediation analyses to explore the mediation effects of AD pathologies on cognition. These authors thus provide important new evidence that the influence of minimal depressive symptoms on cognition is partially mediated by Aβ pathology and that the causal relationship between depression and Aβ might be bidirectional. SEE CORRESPONDING ARTICLE ON PAGE 757 SEE CORRESPONDING ARTICLE ON PAGE 757 Late-Life Depression Is Associated With Reduced Cortical Amyloid Burden: Findings From the Alzheimer’s Disease Neuroimaging Initiative Depression ProjectBiological PsychiatryVol. 89Issue 8PreviewWe evaluated the role of cortical amyloid deposition as a factor contributing to memory dysfunction and increased risk of dementia associated with late-life depression (LLD). Full-Text PDF

Induction of amyloid-\u03b2 deposits from serially transmitted, histologically silent, A\u03b2 seeds issued from human brains

In humans, iatrogenic transmission of cerebral amyloid-β (Aβ)-amyloidosis is suspected following inoculation of pituitary-derived hormones or dural grafts presumably contaminated with Aβ proteins as well as after cerebral surgeries. Experimentally, intracerebral inoculation of brain homogenate extracts containing misfolded Aβ can seed Aβ deposition in transgenic mouse models of amyloidosis or in non-human primates. The transmission of cerebral Aβ is governed by the host and by the inoculated samples. It is critical to better characterize the propensities of different hosts to develop Aβ deposition after contamination by an Aβ-positive sample as well as to better assess which biological samples can transmit this lesion. Aβ precursor protein (huAPPwt) mice express humanized non-mutated forms of Aβ precursor protein and do not spontaneously develop Aβ or amyloid deposits. We found that inoculation of Aβ-positive brain extracts from Alzheimer patients in these mice leads to a sparse Aβ deposition close to the alveus 18 months post-inoculation. However, it does not induce cortical or hippocampal Aβ deposition. Secondary inoculation of apparently amyloid deposit-free hippocampal extracts from these huAPPwt mice to APPswe/PS1dE9 mouse models of amyloidosis enhanced Aβ deposition in the alveus 9 months post-inoculation. This suggests that Aβ seeds issued from human brain samples can persist in furtive forms in brain tissues while maintaining their ability to foster Aβ deposition in receptive hosts that overexpress endogenous Aβ. This work emphasizes the need for high-level preventive measures, especially in the context of neurosurgery, to prevent the risk of iatrogenic transmission of Aβ lesions from samples with sparse amyloid markers.

Plasma Glial Fibrillary Acidic Protein Levels Differ Along the Spectra of Amyloid Burden and Clinical Disease Stage.

Measuring plasma glial fibrillary acidic protein (GFAP) alongside cortical amyloid-β (Aβ) may shed light on astrocytic changes in aging and Alzheimer's disease (AD). To examine associations between plasma GFAP and cortical Aβ deposition in older adults across the typical aging-to-AD dementia spectrum. We studied two independent samples from UCSF (Cohort 1, N = 50; Cohort 2, N = 37) covering the spectra of clinical severity (CDR Sum of Boxes; CDR-SB) and Aβ-PET burden. Aβ-PET was completed with either florbetapir or Pittsburgh Compound B and standardized uptake value ratios were converted to the Centiloid (CL) scale for analyses. All participants with CDR-SB > 0 were Aβ-PET positive, while clinically normal participants (CDR-SB = 0) were a mix of Aβ-PET positive and negative. Regression analyses evaluated main effect and interaction associations between plasma GFAP, Aβ-PET, and clinical severity. In both cohorts, plasma GFAP increased linearly with Aβ-PET CLs in clinically normal older adults. In Cohort 2, which included participants with more severe clinical dysfunction and Aβ-PET burden, the association between Aβ and GFAP became curvilinear (inverted U-shape; quadratic model R2 change = 0.165, p = 0.009), and Aβ-PET interacted with CDR-SB (R2 change = 0.164, p = 0.007): older adults with intermediate functional impairment (CDR-SB = 0.5-4.0) showed a weak (negative) association between Aβ-PET CLs and plasma GFAP, while older adults with dementia (CDR-SB > 4.0) showed a strong, negative association of higher Aβ-PET CLs with lower plasma GFAP. The relationship between astrocytic integrity and cortical Aβ may be highly dynamic, with linear, positive associations early in disease that diverge in more severe disease stages.

Association of Cortical and Subcortical β-Amyloid With Standardized Measures of Depressive and Anxiety Symptoms in Adults Without Dementia.

The purpose of this study was to test the hypothesis that subcortical β-amyloid (Aβ) deposition was associated with elevated scores on standardized measures of depressive and anxiety symptoms when compared with cortical (Aβ) deposition in persons without dementia. The authors performed a cross-sectional study, derived from the population-based Mayo Clinic Study of Aging, comprising participants aged ≥70 years (N=1,022; 55% males; 28% apolipoprotein E [APOE] ε4 carriers; without cognitive impairment, N=842; mild cognitive impairment; N=180). To assess Aβ deposition in cortical and subcortical (the amygdala, striatum, and thalamus) regions, participants underwent Pittsburgh Compound B positron emission tomography (PiB-PET) and completed the Beck Depression Inventory-II (BDI-II) and the Beck Anxiety Inventory (BAI). The investigators ran linear regression models to examine the association between PiB-PET standardized uptake value ratios (SUVRs) in the neocortex and subcortical regions and depressive and anxiety symptoms (BDI-II and BAI total scores). Models were adjusted for age, sex, education level, and APOE ε4 carrier status and stratified by cognitive status (without cognitive impairment, mild cognitive impairment). Cortical PiB-PET SUVRs were associated with depressive symptoms (β=0.57 [SE=0.13], p<0.001) and anxiety symptoms (β=0.34 [SE=0.13], p=0.011). PiB-PET SUVRs in the amygdala were associated only with depressive symptoms (β=0.80 [SE=0.26], p=0.002). PiB-PET SUVRs in the striatum and thalamus were associated with depressive symptoms (striatum: β=0.69 [SE=0.18], p<0.001; thalamus: β=0.61 [SE=0.24], p=0.011) and anxiety symptoms (striatum: β=0.56 [SE=0.18], p=0.002; thalamus: β=0.65 [SE=0.24], p=0.008). In the mild cognitive impairment subsample, Aβ deposition, regardless of neuroanatomic location, was associated with depressive symptoms but not anxiety symptoms. Elevated amyloid deposition in cortical and subcortical brain regions was associated with higher depressive and anxiety symptoms, although these findings did not significantly differ by cortical versus subcortical Aβ deposition. This cross-sectional observation needs to be confirmed by a longitudinal study.

Sleep Disturbance Forecasts β-Amyloid Accumulation across Subsequent Years

Experimental sleep-wake disruption in rodents and humans causally modulates β-amyloid (Aβ) dynamics (e.g., [1-3]). This leads to the hypothesis that, beyond cross-sectional associations, impaired sleep structure and physiology could represent prospective biomarkers of the speed with which Aβ accumulates over time. Here, we test the hypothesis that initial baseline measures of non-rapid eye movement (NREM) sleep slow-wave activity (SWA) and sleep quality (efficiency) provide future forecasting sensitivity to the rate of Aβ accumulation over subsequent years. A cohort of clinically normal older adults was assessed using objective sleep polysomnography in combination with longitudinal tracking of Aβ accumulation with [11C]PiB positron emission tomography (PET) imaging. Both the proportion of NREM SWA below 1Hz and the measure of sleep efficiency predicted the speed (slope) of subsequent Aβ deposition over time, and these associations remained robust when taking into account additional cofactors of interest (e.g., age, sex, sleep apnea). Moreover, these measures were specific, such that no other macro- and microphysiological architecture metrics of sleep demonstrated such sensitivity. Our data support the proposal that objective sleep markers could be part of a set of biomarkers that statistically forecast the longitudinal trajectory of cortical Aβ deposition in the human brain. Sleep may therefore represent a potentially affordable, scalable, repeatable, and non-invasive tool for quantifying of Aβ pathological progression, prior to cognitive symptoms of Alzheimer's disease (AD).