Apolipoprotein E4 Reduction with Antisense Oligonucleotides Decreases Neurodegeneration in a Tauopathy Model.

OBJECTIVE: Apolipoprotein E (ApoE) genotype is the strongest genetic risk factor for late-onset Alzheimer's disease, with the ε4 allele increasing risk in a dose-dependent fashion. In addition to ApoE4 playing a crucial role in amyloid-ß deposition, recent evidence suggests that it also plays an important role in tau pathology and tau-mediated neurodegeneration. It is not known, however, whether therapeutic reduction of ApoE4 would exert protective effects on tau-mediated neurodegeneration. METHODS: Herein, we used antisense oligonucleotides (ASOs) against human APOE to reduce ApoE4 levels in the P301S/ApoE4 mouse model of tauopathy. We treated P301S/ApoE4 mice with ApoE or control ASOs via intracerebroventricular injection at 6 and 7.5 months of age and performed brain pathological assessments at 9 months of age. RESULTS: Our results indicate that treatment with ApoE ASOs reduced ApoE4 protein levels by ~50%, significantly protected against tau pathology and associated neurodegeneration, decreased neuroinflammation, and preserved synaptic density. These data were also corroborated by a significant reduction in levels of neurofilament light chain (NfL) protein in plasma of ASO-treated mice. INTERPRETATION: We conclude that reducing ApoE4 levels should be explored further as a therapeutic approach for APOE4 carriers with tauopathy including Alzheimer's disease. ANN NEUROL 2021;89:952-966.

Lack of hepatic apoE does not influence early Aß deposition: observations from a new APOE knock-in model.

BACKGROUND: The apolipoprotein E (APOE) gene is the strongest genetic risk factor for late-onset Alzheimer disease (AD). ApoE is produced by both astrocytes and microglia in the brain, whereas hepatocytes produce the majority of apoE found in the periphery. Studies using APOE knock-in and transgenic mice have demonstrated a strong isoform-dependent effect of apoE on the accumulation of amyloid-ß (Aß) deposition in the brain in the form of both Aß-containing amyloid plaques and cerebral amyloid angiopathy. However, the specific contributions of different apoE pools to AD pathogenesis remain unknown. METHODS: We have begun to address these questions by generating new lines of APOE knock-in (APOE-KI) mice (ε2/ε2, ε3/ε3, and ε4/ε4) where the exons in the coding region of APOE are flanked by loxP sites, allowing for cell type-specific manipulation of gene expression. We assessed these mice both alone and after crossing them with mice with amyloid deposition in the brain. Using biochemical and histological methods. We also investigated how removal of APOE expression from hepatocytes affected cerebral amyloid deposition. RESULTS: As in other APOE knock-in mice, apoE protein was present predominantly in astrocytes in the brain under basal conditions and was also detected in reactive microglia surrounding amyloid plaques. Primary cultured astrocytes and microglia from the APOE-KI mice secreted apoE in lipoprotein particles of distinct size distribution upon native gel analysis with microglial particles being substantially smaller than the HDL-like particles secreted by astrocytes. Crossing of APP/PS1 transgenic mice to the different APOE-KI mice recapitulated the previously described isoform-specific effect (ε4 > ε3) on amyloid plaque and Aß accumulation. Deletion of APOE in hepatocytes did not alter brain apoE levels but did lead to a marked decrease in plasma apoE levels and changes in plasma lipid profile. Despite these changes in peripheral apoE and on plasma lipids, cerebral accumulation of amyloid plaques in APP/PS1 mice was not affected. CONCLUSIONS: Altogether, these new knock-in strains offer a novel and dynamic tool to study the role of APOE in AD pathogenesis in a spatially and temporally controlled manner.

In Search of an Identity for Amyloid Plaques.

In 1984, biochemists George Glenner and Caine Wong, in search of 'a unique amyloid fibril precursor protein in the serum' of Alzheimer disease (AD) patients, successfully isolated and sequenced the first 24 amino acids of a 'cerebrovascular amyloid fibril protein ß' that we now know as the amyloid-ß (Aß) peptide. This landmark paper laid the foundation for extensive research in the following decades that ultimately established the role of ß-amyloidosis as a player in the pathogenesis of AD.

Age-Dependent Effects of apoE Reduction Using Antisense Oligonucleotides in a Model of ß-amyloidosis.

The apolipoprotein E (APOE) gene is the strongest genetic risk factor for late-onset Alzheimer disease. Previous studies suggest that reduction of apoE levels through genetic manipulation can reduce Aß pathology. However, it is not clear how reduction of apoE levels after birth would affect amyloid deposition. We utilize an antisense oligonucleotide (ASO) to reduce apoE expression in the brains of APP/PS1-21 mice homozygous for the APOE-ε4 or APOE-ε3 allele. ASO treatment starting after birth led to a significant decrease in Aß pathology when assessed at 4 months. Interestingly, ASO treatment starting at the onset of amyloid deposition led to an increase in Aß plaque size and a reduction in plaque-associated neuritic dystrophy with no change in overall plaque load. These results suggest that lowering apoE levels prior to plaque deposition can strongly affect the initiation of Aß pathology while lowering apoE after Aß seeding modulates plaque size and toxicity.

A Critical Role of Ser26 Hydrogen Bonding in Aß42 Assembly and Toxicity.

Amyloid ß-protein (Aß) assembly is a seminal process in Alzheimer's disease. Elucidating the mechanistic features of this process is thought to be vital for the design and targeting of therapeutic agents. Computational studies of the most pathologic form of Aß, the 42-residue Aß42 peptide, have suggested that hydrogen bonding involving Ser26 may be particularly important in organizing a monomer folding nucleus and in subsequent peptide assembly. To study this question, we experimentally determined structure-activity relationships among Aß42 peptides in which Ser26 was replaced with Gly, Ala, α-aminobutryic acid (Abu), or Cys. We observed that aliphatic substitutions (Ala and Abu) produced substantially increased rates of formation of ß-sheet, hydrophobic surface, and fibrils, and higher levels of cellular toxicity. Replacement of the Ser hydroxyl group with a sulfhydryl moiety (Cys) did not have these effects. Instead, this peptide behaved like native Aß42, even though the hydropathy of Cys was similar to that of Abu and very different from that of Ser. We conclude that H bonding of Ser26 is the factor most important in its contribution to Aß42 conformation, assembly, and subsequent toxicity.

Apolipoprotein E and Alzheimer's disease: the influence of apolipoprotein E on amyloid-ß and other amyloidogenic proteins.

Alzheimer's disease (AD) is one of the fastest-growing causes of death and disability in persons 65 years of age or older, affecting more than 5 million Americans alone. Clinical manifestations of AD include progressive decline in memory, executive function, language, and other cognitive domains. Research efforts within the last three decades have identified APOE as the most significant genetic risk factor for late-onset AD, which accounts for >99% of cases. The apoE protein is hypothesized to affect AD pathogenesis through a variety of mechanisms, from its effects on the blood-brain barrier, the innate immune system, and synaptic function to the accumulation of amyloid-ß (Aß). Here, we discuss the role of apoE on the biophysical properties and metabolism of the Aß peptide, the principal component of amyloid plaques and cerebral amyloid angiopathy (CAA). CAA is characterized by the deposition of amyloid proteins (including Aß) in the leptomeningeal medium and small arteries, which is found in most AD cases but sometimes occurs as an independent entity. Accumulation of these pathologies in the brain is one of the pathological hallmarks of AD. Beyond Aß, we will extend the discussion to the potential role of apoE on other amyloidogenic proteins found in AD, and also a number of diverse neurodegenerative diseases.

Osteolipoma of the knee.

A case of a right knee intra-articular osteolipoma in a 64-year-old man is reported. The patient presented for evaluation of a 1-year history of nontraumatic, mechanically-exacerbated, medial-sided right knee pain. Radiographs demonstrated a partially calcified 3.0 cm mass anterior to the distal medial femur at the suprapatellar fossa. Magnetic resonance imaging examination confirmed a 4.0 × 3.6 cm well-circumscribed mass deep to the medial patellofemoral ligament, with predominantly fat characteristics on T1-weighted and T2-weighted sequences. The mass had irregular ossification superiorly with surrounding heterogeneous enhancement. Histologic examination of an excisional biopsy showed the lesion to be an osteolipoma. Osteolipoma is a rare histologic variant of lipoma with osseous metaplasia, but should be considered in the differential of a fat-containing neoplasm with ossification.