CAA, defined by the deposition of amyloid in vessel walls of the central nervous system, compromises leptomeningeal and cortical vessels affecting medium and small size arteries and arterioles as well as capillary endothelium. The most common form of CAA is associated with amyloid-β (Aβ) deposition, particularly in elderly individuals and in patients with Alzheimer’s disease (AD) (Yamada, 2000). In these cases, Aβ, is originated by sequential processing of the amyloid precursor protein (APP) primarily generating peptides constituted by 40 and 42 amino acid residues-long peptides, Aβ40 and Aβ42, respectively. For reasons not completely understood, Aβ42 is one of the main components of parenchymal amyloid plaques while Aβ40 is the predominant species present in vascular deposits (Kalaria, 1992). The fibrillar and compact Aβ deposition in the brain vessel walls has been related to abnormalities in the vasculature, which can subsequently compromise the integrity of the blood brain barrier (BBB). Indeed, one of the most relevant pathological consequences of CAA is the development of intracerebral hemorrhages (ICH) usually affecting cortical and subcortical areas. Furthermore, recurrence is a common complication in CAA patients, which result in elevated mortality rates and disability (Greenberg et al., 2004). CAA translates also in other common clinical manifestations involving white matter changes associated with cortical microbleeds and progressive dementia (Greenberg et al., 2004). Unfortunately, definitive diagnosis of CAA can only be performed by brain necropsy, although clinical features allow the estimation of a diagnosis as probable or possible CAA according to the Boston criteria (Knudsen et al, 2001). The discovery of new biomarkers that underlie the CAA presence is a crucial challenge to avoid possible complications associated to treatments, such as cerebral bleedings related to antithrombotics or some adverse responses to vaccine-based therapy for AD dementia.
Representative Aβ immunohistochemistry of CAA grades following the criteria described by Vonsattel et al. in 1991 and modiﬁed by Greenberg and Vonsattel in 1997.
1) Role of Apolipoproteins in CAA: study of β-amyloid traffic across the blood brain barrier.
The impaired Aβ clearance and a deficient efflux across the blood–brain barrier (BBB) are key points involved in the accumulation of vascular Aβ and CAA. A prove of that is the presence of vascular amyloid and microhemorrhages when parenchymal Aβ is mobilized by immunization in AD (Uro-Coste et al., 2010). Therefore, Aβ transport routes seem to determine the final fate of this congophilic material.
Due to the evident involvement of certain Apolipoproteins, such us determined ApoE isoforms, in both AD (Schmechel et al., 1993) and CAA pathology (Greenberg et al., 1995), together with their ability to complex Aβ in vivo (Fagan et al., 2000), these lipid- carriers appear to be excellent candidates to mediate the Aβ traffic through the BBB. In the present project, we aim to deeply investigate the association of different variants of apolipoproteins and Aβ, regarding BBB-crossing efficiency and their ability to mobilize Aβ.
2) Involvement of proteolytic systems in the progression of CAA.
The mechanisms of vessel rupture triggering ICH because of Aβ deposition have not been yet elucidated. Neuropathological studies have demonstrated that Aβ deposits within brain vessel walls are related to abnormalities in the vasculature. In this regard, proteolytic systems might form part of the molecular pathway involved in the alteration of the BBB. Previous evidences of our group have shown that Matrix Metal·loproteinases (MMPs) are related to brain bleeding (Rosell et al., 2006; Alvarez-Sabín et al., 2004; Montaner et al., 2003). Thus, we aim to investigate the relationship between these family of proteins and the appearance of intracraneal hemorrages in CAA.
Our study includes the identification of both protein and genetic biomarkers for the diagnosis and prognosis of CAA-related hemorrhages. We are studying a cohort of probable CAA patients that have been recruited in Hospital Vall d’Hebron in collaboration with the Stroke Project of the Cerebrovascular Diseases Study Group (Spanish Society of Neurology) for more than 10 years.
We also are carrying out in vitro studies to understand the capacity of MMPs to digest different Aβ peptides producing truncated forms found in vivo.
Representative examples of CAA grade IV lesions. Human brain serial sections were stained with anti-βA and anti- MMP-2. Fibrinoid necrosis in some sections was detected through Mallory phosphotungstic acid staining. Cellular positive staining is indicated with green arrows for reactive astrocytes and pink arrows for histiocytes. Figure from Hernandez-Guillamon et al., Brain Pathol 2012.
3) Discovery of novel biomarkers related to vascular dysfunction in cerebral β-amyloidosis
Receptor-mediated transport across the BBB and drainage within interstitial fluid are important mechanisms for brain Aβ removal, which appear to be altered during aging and especially in cerebral β-amyloidosis (CAA and AD affected brains). We consider that the understanding of the mechanisms involved in the Aβ deposition in different structures of the cerebral vasculature would allow to design novel strategies to remove parenchymal amyloid for clinical purposes.
In the context of the project entitled “The Snowball: Interplay of amyloid and ischemia and their influence on blood-brain barrier, amyloid transportation systems and neurodegeneration in cerebral amyloid angiopathy” (funded by ISCIII under the program EU Joint Programme for Neurodegenerative Disease Research, H2020), we propose to identify new biomarkers and molecular pathways through the use of broad genomic and proteomic approaches using two different approaches; the APP23 transgenic mice line as an experimental model of cerebral β-amyloidosis, and human brain vessels from patients affected by CAA or AD.
- Mar Hernández Guillamon, PhD
- Sofía Fernández de Retana, PhD student
- Paula Marzazuela Fuentes, PhD student
- Montserrat Solé Piñol, Postdoctoral Researcher
- Prof. Jorge Ghiso and Dra. Agueda Rostagno. Pathology Dept. Langone Medical Center. NYU. New York, US.
- Dr. Fabien Gosselet. Blood-brain barrier laboratory, Artois University, France.
- Dra. Mary Cano. NanoUp Group. Institut Català de Nanociències i Nanotecnologia (ICN2), Barcelona.
- Dr. José Luis Sánchez-Quesada. Laboratorio de Bioquímica. Hospital de la Santa Creu i Sant Pau, Barcelona.
- Dra. Lydia Giménez-Llort. Departamento Psiquiatría de la Universidad Autónoma de Barcelona.
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