Murray, Melissa E.

AbstractBackgroundThe coarse‐grained plaque is a biochemically and morphologically distinct amyloid‐β (Aβ) deposit that was discovered in clinically‐defined atypical Alzheimer’s disease (AD). Unlike other Aβ deposits, this plaque is not observed in cognitively normal people. This study investigates the hypothesis that the coarse‐grained plaque is distinctly associated with AD neuropathologic change and glial activation within the context of AD subtypes.MethodSixty AD cases from the FLorida Autopsied Multi‐Ethnic (FLAME) cohort were assessed. We included 20 hippocampal sparing (HpSp) AD, 20 typical AD, and 20 limbic predominant AD. Immunohistochemistry was performed on the middle frontal, inferior temporal, and inferior parietal cortex for AD neuropathology (Aβ [6F/3D], phospho‐tau [AT8], tau [GT38]) and glial activation (CD68 [KP1] and GFAP). Digital pathology was used to quantify burden. Thioflavin‐S tangle counts were performed at time of neuropathologic diagnosis. Distinct deposit types, including classic cored plaques, coarse‐grained plaques, cerebral amyloid angiopathy (CAA)‐Type 1, and CAA‐Type 2, were semi‐quantitatively scored on Aβ (Fig. 1). Correlations between demographic, clinical, and neuropathologic characteristics were assessed using Spearman rho analysis and reported if p<0.05. An independent cohort of ∼100 HpSp AD cases will be assessed to validate initial findings.ResultIn the frontal cortex of HpSp AD, higher scores of classic cored plaques correlated with older age at onset and death, non‐APOE ε4 carriership, and less CAA‐Type 1 and Type 2 (Fig. 2). On the contrary, the severity of coarse‐grained plaques correlated with a younger age at onset and death, APOE ε4 carriership, higher scores for CAA‐Type 1, CAA‐Type 2, and increased burden of Aβ, GFAP, and CD68. Classic cored plaques correlated negatively with phospho‐tau and tau, whereas coarse‐grained plaques correlated positively with phospho‐tau, tau, and tangles. The two deposit types were negatively correlated with each other. Correlations were weaker but showed similar trends in other AD subtypes (Fig. 2) and regions.ConclusionWithin HpSp AD, classic cored and coarse‐grained plaques show distinct correlations with glial activation, (phospho‐)tau, and tangles. These results suggest opposite directions of association for these deposits on AD neuropathologic change that may impact clinical symptoms. These findings are relevant to therapies targeting overall Aβ pathology.

AbstractBackgroundAlzheimer’s disease (AD) is neuropathologically characterized by amyloid‐β (Aβ) plaques and tau neurofibrillary tangles often quantified by Thal phase and Braak stage, respectively. Aβ also frequently deposits in the cerebrovasculature with severity categorized by a cerebral amyloid angiopathy (CAA) score. These and related measures often show high variability within AD suggesting distinct underlying mechanisms, the identification of which may reveal important biological insights into AD pathophysiology. We hypothesize that, within the AD brain, neuropathology and levels of core AD‐related proteins are influenced by variations in DNA methylation (DNAm). To test this, we performed epigenome‐wide association studies (EWAS) using DNAm clusters from the temporal cortex (TCX) and cerebellum (CER) with AD‐related neuropathologic measures (Braak, Thal, and CAA) and brain biochemical levels of five proteins (apoE, Aβ40, Aβ42, tau, and p‐tau).MethodsDNAm from neuropathologically‐confirmed AD cases available through the Mayo Clinic brain bank was measured by reduced representation bisulfite sequencing (RRBS) from 471 brain samples, 200 of which had both TCX and CER measures. Neuropathology was scored by an experienced neuropathologist. TCX levels of five AD‐related proteins from three tissue fractions (buffer‐, detergent‐, and in‐soluble) were measured by ELISA (Liu 2020). CpG methylation (CpGm) was binned by a 15‐state chromatin model (Kundaje 2015) and averaged. Averaged CpGm clusters were tested for their association with each endophenotype through multi‐variable linear regression. The influence of CpGm clusters on expression levels of nearby genes was also investigated through multi‐variable regression.ResultsOur innovative binning method demonstrated expected and biologically relevant CpGm patterns. We identified multiple epigenome‐wide significant CpGm clusters unique to each AD‐related endophenotype and brain region. Comparisons between the TCX and CER further revealed brain region‐specific enrichment of distinct CpGm clusters. Significant CpGm clusters were further characterized by their influence on gene expression.ConclusionsAlthough all neuropathologic and biochemical endophenotypes tested are core to AD pathophysiology, our results suggest each has a distinct epigenetic architecture underlying their variability in the AD brain. By discovering brain region‐specific DNAm changes that contribute to each neuropathologic or biochemical outcome, we can identify core components of complex mechanisms that individually and jointly contribute to AD.

AbstractBackgroundNeuropathologically, Alzheimer’s disease (AD) is characterized by the presence of senile plaques composed of beta‐amyloid (Aβ) and neurofibrillary tangles made of hyperphosphorylated tau. Aβ and p‐tau have been shown to impact endoplasmic reticulum homeostasis, DNA damage response and autophagic functions. Intriguingly, alterations in these systems have also been connected to dysfunctions in UFMylation, a ubiquitin‐like posttranslational modification. Analogous to ubiquitin, UFM1, is conjugated to substrates via a catalytic cascade involving UFM1‐specific set of E1 (UBA5), E2 (UFC1), and a complex that consists of E3 ligase (UFL1), DDRGK1 and CDK5RAP3. UFMylation is reversible, and this is mediated by UFSP2. The UFMylation pathway is essential for brain development as complete loss of function of any of its components result in severe neurodevelopmental disorders. However, alterations in UFMylation and their role in and significance for age‐related AD remains unknown.MethodWe performed Western blot and Meso Scale Discovery based ELISA to measure the protein level of UFM1, UFSP2, tau, p‐tau and other UFMylation pathway components in human post‐mortem brain. Analyses were performed with RIPA‐ and 2% SDS‐soluble fraction from frontal cortex. To validate our finding in human tissues, we knocked out UFM1 and UFSP2 in ReN cells, a neural progenitor cell model that has already been used to study AD and that can be terminally differentiated in neurons.ResultWe found a significant reduction of RIPA UFSP2, but an increase of RIPA and SDS UFM1 in AD compared to controls. Strikingly, RIPA UFSP2 had a strong negative correlation with both RIPA and SDS UFM1. Furthermore. UFM1 was significantly increased in UFSP2‐KO neurons compared to WT, mirroring the negative correlation between UFM1 and UFSP2 observed in human brain. In addition, RIPA and SDS UFM1 had a strong positive correlation with p‐tau, indicating that dysfunctional UFMylation might play an important role for disease pathogenesis.ConclusionReduction of RIPA soluble UFSP2 in human AD frontal cortex might result in the abnormal accumulation of UFM1 and this might further facilitate the AD pathogenesis. Because of its role for several central AD‐relevant pathways, the UFMylation pathway might be a potential therapeutic target for AD.