Surface-bound basement membrane components accelerate amyloid-β peptide nucleation in air-free wells: an in vitro model of cerebral amyloid angiopathy

Current Management and Therapeutic Strategies for Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy (CAA) is characterized by accumulation of amyloid β (Aβ) in walls of leptomeningeal vessels and cortical capillaries in the brain. The loss of integrity of these vessels caused by cerebrovascular Aβ deposits results in fragile vessels and lobar intracerebral hemorrhages. CAA also manifests with progressive cognitive impairment or transient focal neurological symptoms. Although development of therapeutics for CAA is urgently needed, the pathogenesis of CAA remains to be fully elucidated. In this review, we summarize the epidemiology, pathology, clinical and radiological features, and perspectives for future research directions in CAA therapeutics. Recent advances in mass spectrometric methodology combined with vascular isolation techniques have aided understanding of the cerebrovascular proteome. In this paper, we describe several potential key CAA-associated molecules that have been identified by proteomic analyses (apolipoprotein E, clusterin, SRPX1 (sushi repeat-containing protein X-linked 1), TIMP3 (tissue inhibitor of metalloproteinases 3), and HTRA1 (HtrA serine peptidase 1)), and their pivotal roles in Aβ cytotoxicity, Aβ fibril formation, and vessel wall remodeling. Understanding the interactions between cerebrovascular Aβ deposits and molecules that accumulate with Aβ may lead to discovery of effective CAA therapeutics and to the identification of biomarkers for early diagnosis.

Enhanced accessibility and hydrophobicity of amyloidogenic intermediates of the β2-microglobulin D76N mutant revealed by high-pressure experiments

β2-Microglobulin (β2m) is the causative protein of dialysis-related amyloidosis. Its unfolding mainly proceeds along the pathway of N_C →U_C ⇄ U_T, whereas refolding follows the U_T → I_T (→N_T) →N_C pathway, in which N, I, and U are the native, intermediate, and unfolded states, respectively, with the Pro32 peptidyl-prolyl bond in cis or trans conformation as indicated by the subscript. It is noted that the I_T state is a putative amyloidogenic precursor state. Several aggregation-prone variants of β2m have been reported to date. One of these variants is D76N β2m, which is a naturally occurring amyloidogenic mutant. To elucidate the molecular mechanisms contributing to the enhanced amyloidogenicity of the mutant, we investigated the equilibrium and kinetic transitions of pressure-induced folding/unfolding equilibria in the wild type and D76N mutant by monitoring intrinsic tryptophan and 1-anilino-8-naphthalene sulfonate fluorescence. An analysis of kinetic data revealed that the different folding/unfolding behaviors of the wild type and D76N mutant were due to differences in the activation energy between the unfolded and the intermediate states as well as stability of the native state, leading to more rapid accumulation of I_T state for D76N in the refolding process. In addition, the I_T state was found to assume more hydrophobic nature. These changes induced the enhanced amyloidogenicity of the D76N mutant and the distinct pathogenic symptoms of patients. Our results suggest that the stabilization of the native state will be an effective approach for suppressing amyloid fibril formation of this mutant.

Understanding the Pathophysiology of Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy (CAA), one of the main types of cerebral small vessel disease, is a major cause of spontaneous intracerebral haemorrhage and an important contributor to cognitive decline in elderly patients. Despite the number of experimental in vitro studies and animal models, the pathophysiology of CAA is still largely unknown. Although several pathogenic mechanisms including an unbalance between production and clearance of amyloid beta (Aβ) protein as well as ‘the prion hypothesis’ have been invoked as possible disease triggers, they do not explain completely the disease pathogenesis. This incomplete disease knowledge limits the implementation of treatments able to prevent or halt the clinical progression. The continuous increase of CAA patients makes imperative the development of suitable experimental in vitro or animal models to identify disease biomarkers and new pharmacological treatments that could be administered in the early disease stages to prevent irreversible changes and disease progression.

Apolipoprotein E and clusterin inhibit the early phase of amyloid-β aggregation in an in vitro model of cerebral amyloid angiopathy

Sporadic cerebral amyloid angiopathy (CAA) is characterized by cerebrovascular amyloid-β (Aβ) deposition, which leads to lobar hemorrhage and dementia. Biological molecules affecting the development of CAA have not been fully characterized. In this study, we performed proteome analysis of biopsied leptomeningeal and cortical vessels obtained from 6 CAA patients and 5 non-CAA patients who underwent surgery for large lobar hemorrhages. We found that 6 proteins, including Aβ, apolipoprotein E (apoE), clusterin (CLU), albumin, complement C4 and vitronectin were significantly upregulated in the vessels of CAA patients as compared to non-CAA patients. ApoE and CLU were found in all CAA patients. We next examined the effects of apoE and CLU on the early phase of Aβ aggregation, using a simple yet powerful in vitro model of CAA, which recapitulates the intramural periarterial drainage pathway model. We found that physiological concentrations of apoE and CLU delayed the initiation time of amyloid growth kinetics in a concentration-dependent manner. These data indicate that apoE and CLU may act as extracellular chaperones to inhibit Aβ amyloid deposition in CAA.

Increased Aβ pathology in aged Tg2576 mice born to mothers fed a high fat diet

Maternal obesity is associated with increased risk of developing diabetes, obesity and premature death in adult offspring. Mid-life diabetes, hypertension and hypercholesterolaemia are risk factors for the development of sporadic Alzheimer’s disease (AD). A key pathogenic feature of AD is the accumulation of β-amyloid (Aβ) in the brain. The purpose of this study was to investigate the effect of high fat diet feeding during early life on Aβ pathology in the Tg2576 mouse model of AD. Female mice were fed a standard (C) or high fat (HF) diet before mating and during gestation and lactation. At weaning, male offspring were fed a C diet. Significantly higher levels of guanidine-soluble Aβ and plaque loads were observed in the hippocampi of 11-month old Tg2576 mice born to mothers fed a HF diet. Changes in the extracellular matrix led to increased retention of Aβ within the parenchyma. These data support a role for maternal and gestational health on the health of the aged brain and pathologies associated with AD and may provide a novel target for both the prevention and treatment of AD.

Effects of a reduced disulfide bond on aggregation properties of the human IgG1 CH3 domain

Recombinant human monoclonal antibodies have become important protein-based therapeutics for the treatment of various diseases. An IgG1 molecule, which is now mainly used for antibody preparation, consists of a total of 12 immunoglobulin domains. Each domain has one disulfide bond. The CH3 domain is the C-terminal domain of the heavy chain of IgG1. The disulfide bonds of some of the CH3 domains are known to be reduced in recombinant human monoclonal antibodies. The lack of intramolecular disulfide bonds may decrease the stability and increase the aggregation propensity of an antibody molecule. To investigate the effects of a reduced disulfide bond in the CH3 domain on conformational stability and aggregation propensity, we performed several physicochemical measurements including circular dichroism, differential scanning calorimetry (DSC), and 2D NMR. DSC measurements showed that both the stability and reversibility of the reduced form were lower than those of the oxidized form. In addition, detailed analyses of the thermal denaturation data revealed that, although a dominant fraction of the reduced form retained a stable dimeric structure, some fractions assumed a less-specifically associated oligomeric state between monomers. The results of the present study revealed the characteristic aggregation properties of antibody molecules.

Misfolding of amyloidogenic proteins and their interactions with membranes

In this paper, we discuss amyloidogenic proteins, their misfolding, resulting structures, and interactions with membranes, which lead to membrane damage and subsequent cell death. Many of these proteins are implicated in serious illnesses such as Alzheimer’s disease and Parkinson’s disease. Misfolding of amyloidogenic proteins leads to the formation of polymorphic oligomers and fibrils. Oligomeric aggregates are widely thought to be the toxic species, however, fibrils also play a role in membrane damage. We focus on the structure of these aggregates and their interactions with model membranes. Study of interactions of amlyoidogenic proteins with model and natural membranes has shown the importance of the lipid bilayer in protein misfolding and aggregation and has led to the development of several models for membrane permeabilization by the resulting amyloid aggregates. We discuss several of these models: formation of structured pores by misfolded amyloidogenic proteins, extraction of lipids, interactions with receptors in biological membranes, and membrane destabilization by amyloid aggregates perhaps analogous to that caused by antimicrobial peptides.