Hoozemans, Jeroen J.M.

AbstractBackgroundRecent studies highlight distinct patterns of cortical atrophy between amnestic (typical) and non‐amnestic (atypical, with subtypes: behavioural, dysexecutive, logopenic and visuospatial) clinical phenotypes of Alzheimer’s disease (AD). The current study aimed to assess regional MRI patterns of cortical atrophy across AD phenotypes, and their association with amyloid‐beta (Aß), phosphorylated tau (pTau), axonal degeneration (NfL) and microvascular deterioration (COLIV).MethodPostmortem In‐situ 3DT1 3T‐MRI data was collected for 33 AD (17 typical, 16 atypical) and 16 control brain donors. Images were segmented and AAL3 atlas regional volumes were obtained using QyScore®. At subsequent autopsy, eight brain regions were selected, immunostained for Aß (4G8), pTau (AT8), Neurofilament‐light (NFL), and Collagen‐IV (COLIV), and quantified using qupath. Group comparisons and volume‐pathology associations were analyzed using linear models and partial correlations with covariates age, sex, postmortem delay, and intracranial volume.ResultsCompared to controls, AD phenotype groups showed overall lower cortical volume, while only minor volume differences were observed between AD phenotype groups, observed primarily in limbic regions (Figure 1). Across pathological markers, AD phenotype groups showed consistently higher immunoreactivity than controls, while atypical AD showed consistently higher immunoreactivity than typical AD (Figure 2). Moreover, different patterns of pathology could be observed between atypical subtypes (e.g. distinctly higher pTau load in the occipital gyrus of the visuospatial subtype). In typical AD, global volume loss was associated with lower Aß and higher pTau, NFL and COLIV immunoreactivity, while in atypical AD, global volume loss was primarily associated with higher NFL immunoreactivity (Figure 3a). Regionally, AD phenotype differences in atrophy‐pathology association were most pronounced in the (para)hippocampal regions. This distinction was mainly characterized by negative associations for NFL and COLIV, which was only observed in typical AD (Figure 3b‐c).ConclusionAtrophy patterns between AD phenotypes showed only minor differences, potentially attributable to the on average later disease stage of the study cohort. The higher immunoreactivity for pathological markers found in atypical AD might suggest a more severe disease burden. (Para)hippocampal volume decline was associated with axonal and microvascular deterioration in typical AD, but not in the higher pathologically burdened atypical AD group, suggesting a differential susceptibility between AD phenotypes.

AbstractBackgroundRecent studies highlight distinct patterns of cortical atrophy between amnestic (typical) and non‐amnestic (atypical, with subtypes: behavioural, dysexecutive, logopenic and visuospatial) clinical phenotypes of Alzheimer’s disease (AD). The current study aimed to assess regional MRI patterns of cortical atrophy across AD phenotypes, and their association with amyloid‐beta (Aβ), phosphorylated tau (pTau), axonal degeneration (NfL) and microvascular deterioration (COLIV).MethodPostmortem In‐situ 3DT1 3T‐MRI data was collected for 33 AD (17 typical, 16 atypical) and 16 control brain donors. Images were segmented and AAL3 atlas regional volumes were obtained using QyScore®. At subsequent autopsy, eight brain regions were selected, immunostained for Aβ (4G8), pTau (AT8), Neurofilament‐light (NFL), and Collagen‐IV (COLIV), and quantified using qupath. Group comparisons and volume‐pathology associations were analyzed using linear models and partial correlations with covariates age, sex, postmortem delay, and intracranial volume.ResultsCompared to controls, AD phenotype groups showed overall lower cortical volume, while only minor volume differences were observed between AD phenotype groups, observed primarily in limbic regions (Fig. 1). Across pathological markers, AD phenotype groups showed consistently higher immunoreactivity than controls, while atypical AD showed consistently higher immunoreactivity than typical AD (Fig. 2). Moreover, different patterns of pathology could be observed between atypical subtypes (e.g. distinctly higher pTau load in the occipital gyrus of the visuospatial subtype). In typical AD, global volume loss was associated with lower Aβ and higher pTau, NFL and COLIV immunoreactivity, while in atypical AD, global volume loss was primarily associated with higher NFL immunoreactivity (Fig. 3a). Regionally, AD phenotype differences in atrophy‐pathology association were most pronounced in the (para) hippocampal regions. This distinction was mainly characterized by negative associations for NFL and COLIV, which was only observed in typical AD (Fig. 3b‐c).ConclusionAtrophy patterns between AD phenotypes showed only minor differences, potentially attributable to the on average later disease stage of the study cohort. The higher immunoreactivity for pathological markers found in atypical AD might suggest a more severe disease burden. (Para) hippocampal volume decline was associated with axonal and microvascular deterioration in typical AD, but not in the higher pathologically burdened atypical AD group, suggesting a differential susceptibility between AD phenotypes.

Abstract Aims Although the neuroanatomical distribution of tau and amyloid‐β is well studied in Alzheimer's disease (AD) (non)‐amnestic clinical variants, that of neuroinflammation remains unexplored. We investigate the neuroanatomical distribution of activated myeloid cells, astrocytes, and complement alongside amyloid‐β and phosphorylated tau in a clinically well‐defined prospectively collected AD cohort. Methods Clinical variants were diagnosed antemortem, and brain tissue was collected post‐mortem. Typical AD ( n = 10), behavioural/dysexecutive AD ( n = 6), posterior cortical atrophy (PCA) AD ( n = 3), and controls ( n = 10) were neuropathologically assessed for AD neuropathology, concurrent pathology including Lewy body disease, limbic‐predominant age‐related TDP‐43 encephalopathy neuropathologic change (LATE‐NC), and vascular pathology. For quantitative assessment, we analysed the corticolimbic distribution of phosphorylated tau, amyloid‐β, CD68, MHC‐II, C4b, and glial fibrillary acidic protein (GFAP) using digital pathology. Results Phosphorylated tau was distinctly distributed in each variant. In all variants, amyloid‐β was neocortical‐dominant, with a notable increase in the middle frontal cortex of behavioural/dysexecutive AD. Typical AD and PCA AD had no concurrent Lewy body disease, whereas three out of six cases with behavioural/dysexecutive AD did. LATE‐NC stage >0 was observed in three AD cases, two typical AD (stage 1/3), and one behavioural/dysexecutive AD (stage 2/3). Vascular pathology was present in each variant. In typical AD, CD68 and MHC‐II were hippocampal‐dominant. In behavioural/dysexecutive AD, C4b was elevated in the middle frontal and inferior parietal cortex. In PCA AD, MHC‐II was increased in the fusiform gyrus, and GFAP in parietal cortices. Correlations between AD neuropathology and neuroinflammation were distinct within variants. Conclusions Our data suggests that different involvement of neuroinflammation may add to clinical heterogeneity in AD, which has implications for neuroinflammation‐based biomarkers and future therapeutics.

AbstractBackgroundOther than the typical (memory‐dominant) variant, Alzheimer’s disease (AD) can present as posterior cortical atrophy (PCA) and behavioral/dysexecutive AD. Tangle distribution differs amongst clinical variants. Neuroinflammation is important in AD pathogenesis and may contribute to Aβ and p‐tau distribution. The relationship between pathological hallmarks, neuroinflammation and, APOE genotype in (a)typical AD is still largely unknown.MethodI will discuss our most recent studies on neuroinflammation in (a)typical AD from cohorts derived from the Netherlands Brain Bank and the Mayo Clinic. Atypicality is investigated from both a neuropathological perspective(N=19) and a clinical perspective (N=30, unpublished data). Additionally, the association ofAPOE ε4 with specific Aβ deposits (i.e., the ‘coarse‐grained plaque’ and the classic cored plaque) and their underlying neuroinflammatory response is investigated (N=60, unpublished data).ResultIn neuropathologically‐defined atypical AD, microglia, and complement show an atypical distribution across regions, resembling that of p‐tau. Clinical atypical AD variants show in addition to a distinct distribution for p‐tau and Aβ, a distinct distribution for activated microglia (CD68, MHC‐II), complement (C4b), and astrocytes (GFAP) (p<.05) (Fig. 1). Furthermore, when investigating Aβ in detail, we observed an atypical plaque, defined as the ‘coarse‐grained plaque’. This APOE ε4+ plaque is associated with increased neuroinflammation and p‐tau burden (ρ(58)=0.5 and 0.6;p<.05) in contrast to the classic cored plaque.ConclusionOur data supports that not all types of Aβ deposits are associated to p‐tau damage. Neuroinflammation, a process that is differently activated within AD variants, may be the link between Aβ aggregation and subsequent neurodegeneration and contribute to clinical variability.